Improved method for estimating tdoa and fdoa in a wireless location system

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DESCRIPTION

Improved procedure for estimating TDOA and FDOA in a Wireless Location System

The present invention relates to methods and apparatus used in locating wireless transmitters, such as those used in analog or digital cellular systems, personal communication systems (PCS), enhanced specialized mobile radios (ESMR), and other types of communication systems. wireless.

A pioneering work in relation to Wireless Location Systems is described in US Patent No. 5,327,144, dated July 5, 1994, "Cellular Telephone Location System", which discloses a system for locating cell phones using Novel techniques of difference in time of arrival (TDOA). Additional improvements to the system disclosed in patent 5,327,144 are disclosed in United States Patent No. 5,608,410, dated March 4, 1997, "System for Locating a Source of Bursty Transmissions." In particular, United States Patent No. 5,608,410 discloses a system for locating the transmitter in which a maximum probability estimation algorithm is used to generate a matrix of values ​​of the difference in arrival time and the difference in arrival frequency. All data in the matrix is ​​examined to determine the absolute peak and fine interpolation is performed to better resolve possible estimates. TruePosition has continued to develop significant improvements to the original inventive concepts and has developed techniques to further improve the accuracy of wireless location systems while significantly reducing the cost of these systems. Patents relating to such enhancements include: US Patent No. 6,091,362, July 18, 2000, "Bandwidth Synthesis for Wireless Location System"; US Patent No. 6,097,336, August 1, 2000, "Method for Improving the Accuracy of a Wireless Location System"; US Patent No. 6,115,599, September 5, 2000, "Directed Retry Method for Use in a Wireless Location System"; US Patent No. 6,172,644 B1, January 9, 2001, "Emergency Location Method for a Wireless Location System"; and US Patent No. 6,184,829 B1, February 6, 2001, "Calibration for Wireless Location System."

Over the past few years, the cellular industry has increased the number of over-the-air interface protocols available for use with wireless phones, increased the number of frequency bands in which wireless or mobile phones can operate, and expanded the number of expressions that refer to or are related to mobile phones to include "personal communication services", "wireless" and others. Over-the-air interface protocols now include AMPS, N-AMPS, TDMA, CDMA, GSM, TACS, ESMR, GPRS, EDGE, and others. Changes in terminology and the increase in the number of over-the-air interfaces do not change the basic principles and inventions discovered and improved by the inventors. However, adapting to current industry terminology, the inventors now call the system described herein a Wireless Location System.

The inventors have conducted extensive experiments with Wireless Location System technology to demonstrate both the feasibility and value of the technology. For example, several experiments have been conducted over several months in 1995 and 1996 in the cities of Philadelphia and Baltimore to verify the system's ability to mitigate multipath in large urban settings. Then in 1996 the inventors built a system in Houston to test the effectiveness of the technology in this area and its ability to interface directly with E9-1-1 systems. Then, in 1997, the system was tested over a 906-square-kilometer (350-square-mile) area in New Jersey and used to locate actual 9-1-1 calls from real people in trouble. Since that time, system trials have expanded to include 125 cell sites covering an area of ​​more than 5,180 square kilometers (2,000 square miles). During all of these trials, the techniques set forth and disclosed herein were tested for effectiveness and further developed and the system has been shown to overcome the limitations of other approaches that have been proposed for locating wireless phones. In fact, since December 1998, no other Wireless Location System has been installed anywhere else in the world that is capable of locating actual 9-1-1 callers. The Wireless Location System innovation disclosed herein has been recognized by the wireless industry through an extensive amount of media coverage given to the system's capabilities, as well as through awards. For example, the prestigious Wireless Appy Award awarded to the system by the Cellular Telephone Industry Association in October 1977 and the Christopher Columbus Fellowship Foundation and Discover Magazine found the Wireless Location System one of the 4 most important innovations of 1998 out of 4,000 nominations submitted. .

The value and importance of the Wireless Location System has been recognized by the wireless communications industry. In June 1996, the Federal Communications Commission issued requirements for the communications industry's deployment of location systems for use in locating 9-1-1 wireless callers, with the October 2001 deadline. Locating wireless callers to E9-1-1 will reduce response time, save lives, and save enormous costs due to reduced resource use in emergency response. Furthermore, numerous reports and studies have concluded that various wireless applications, such as location-sensitive billing, fleet management, and others, will have great commercial value in the years to come.

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Background on wireless communication systems

There are many different types of over-the-air interface protocols used for wireless communication systems. These protocols are used in different frequency bands, both in the United States and internationally. The frequency band does not impact the effectiveness of the Wireless Location System for locating wireless phones.

All over-the-air interface protocols use two types of "channels." The first type includes control channels that are used to transmit information about the wireless telephone or transmitter, to initiate or end calls, or to transfer data in bursts. For example, some types of short message services transfer data over the control channel. At different over-the-air interfaces, the control channels are known for different technology, but the use of the control channels at each over-the-air interface is similar. Control channels generally have identifying information about the telephone or wireless transmitter contained in the transmission. The control channels also include various data transfer protocols that are not voice specific, these include General Packet Radio Service (GPRS), Enhanced Data Rate for Evolution of GSM (EDGE) and Enhanced GPRS (EGPRS) .

The second type includes voice channels that are typically used to transmit voice communications over the air interface. These channels are used only after a call has been established using the control channels. Voice channels will typically use dedicated resources within the wireless communication system while control channels will use shared resources. This distinction will generally make the use of the control channels for wireless location purposes more cost effective than the use of voice channels, although there are some applications for which regular location over the voice channel is desired. Voice channels generally do not have identifying information about the phone or wireless transmitter in the transmission. Some of the differences in over-the-air interface protocols are explained below.

AMPS - It is the original air interface protocol used for cellular communications in the United States. In the AMPS system, separate dedicated channels are assigned for use by the control channels (RCC). According to the TIA / EIA IS-553A standard, each control channel block must start on a 333 or 334 cellular channel, but the block can be of variable length. In the United States, by convention, the AMPS control channel block is 21 channels wide, but it is also known to use a 26-channel block. A reverse voice channel (RVC) can occupy any channel that is not assigned to a control channel. The control channel modulation is FSK (frequency shift keying), while the voice channels are modulated accusing FM (frequency modulation).

N-AMPS - This over-the-air interface is an expansion of the AMPS over-the-air interface protocol and is defined in the EIA / TIA IS-88 standard. The control channels are substantially the same as for the AMPS; however, the voice channels are different. The voice channels occupy less than 10 kHz of bandwidth, compared to the 30 kHz used by AMPS and the modulation is FM.

TDMA - This interface is also known as D-AMPS and is defined in the EIA / TIA IS-136 standard. This air interface is characterized by the use of separation in both frequency and time. The control channels are known as Digital Control Channels (DCCH) and are transmitted in bursts in time slots assigned for use by the DCCH. Unlike AMPS, DCCH can be assigned anywhere in the frequency band, although there are generally some frequency assignments that are more attractive than others based on the use of probability blocks. The voice channels are known as Digital Traffic Channels (DTC). DCCHs and DTCs can occupy the same frequency assignment, but not the same time slot assignment in a given frequency assignment. DCCHs and DTCs use the same modulation scheme, known as π / 4 DQPSK (Differential Quadrature Phase Shift Keying). In the cellular band, a provider can use both the AMPS and TDMA protocols, as long as the frequency assignments for each protocol are kept separate. A provider can also add digital channels to support high-speed data transfer protocols such as GPRS and EDGE.

CDMA - This over-the-air interface is defined by the EIA / TIA IS-95A standard. This over-the-air interface is characterized by the use of both frequency and code separation. However, because adjacent cell sites can use the same frequency sets, CDMA is also characterized by very careful power control. This careful power control leads to a situation known to those skilled in the art as the near-far problem, which makes it difficult for wireless location to function properly for most approaches. The control channels are known as Access Channels and the voice channels are known as Traffic Channels. Access and Traffic Channels may share the same frequency band, but are separated by code. The Access and Traffic Channels use the same modulation scheme, known as OQPSK. CDMA can support high-speed data transfer protocols through code aggregation.

GSM - This over-the-air interface is defined by the international standard for Global System for Mobile Communications. Like TDMA, GSM is characterized by the use of separation in both frequency and time. The channel bandwidth is 200 kHz, which is wider than the 30 kHz used for TDMA. Channels

ES 2 386 669 T3 control are known as Independent Dedicated Control Channels (SDCCH) and are transmitted in bursts in time slots assigned for use by the SDCCH. The SDCCH can be assigned anywhere in the frequency band. The voice channels are known as Traffic Channels (TCH). The SDCCH and TCH can occupy the same frequency assignments, but not the same time slot assignment in a given frequency assignment. SDCCH and TCH use the same modulation scheme, known as GMSK. GSM can also support higher data transfer protocols such as GPRS and EGPRS.

As used herein, reference to any of the over-the-air interfaces should refer to all of the over-the-air interfaces, unless otherwise specified. Additionally, a reference to control channels or voice channels should refer to all types of control or voice channels, whatever the preferred terminology for a particular over-the-air interface. Finally, there are many types of air interfaces used throughout the world and there is no intention to exclude any air interface from the inventive concepts described within the present specification. Indeed, those skilled in the art will recognize that other interfaces used elsewhere are derivative or similar in class to those described above.

Summary of the invention

As is well known to those skilled in the wireless location art, the measured TDOA values ​​can be used to determine the geographic location of a wireless transmitter. Similarly, measured FDOA values ​​can be used to determine the speed of a wireless transmitter. The present invention is particularly directed to improved methods for the determination of such TDOA and / or FDOA values. The invention can be used to limit the frequencies and time period examined for the presence of the signal to be located, which can result in improvements in terms of better signal detection, lower false signal detection and faster and more efficient use of processing resources to locate a call.

For example, in an example implementation, a procedure used in locating a mobile transmitter includes providing a set of cross-correlation values, in which each cross-correlation value is associated with a corresponding TDOA and / or FDOA estimate and is produced by cross-correlating a reference signal with a cooperating signal. The reference signal comprises a copy of a signal transmitted by the mobile transmitter as received at a first antenna and the cooperating signal comprises a copy of the same signal as received at a second antenna. The procedure further includes determining a most likely range of TDOA and / or FDOA estimates and then identifying an ultimate cross-correlation value within the subset of cross-correlation values ​​that correspond to the most likely range of TDOA and / or estimates. or FDOA. The TDOA and / or FDOA value that corresponds to the optimal cross-correlation value is then used in calculating the location of the mobile transmitter.

The invention relates to a method according to claim 1 and to a system according to claim 17.

Other features and advantages of the invention will be disclosed below.

Brief description of the drawings

Figures 1 and 1A schematically represent a Wireless Location System according to the present invention.

Figure 2 schematically represents a Signal Collection System (SCS) 10 in accordance with the present invention.

Figure 2A schematically represents a receiver module 10-2 employed by the Signal Collection System.

Figures 2B and 2C schematically represent alternative ways of coupling the receiver module (s) 10-2 to the antennas 10-1.

Figure 2C-1 is a flow diagram of a process employed by the Wireless Location System when using narrow band receiver modules.

Figure 2D schematically represents a DSP 10-3 module used in the Signal Collection System according to the present invention.

Figure 2E is a flow diagram of the operation of the DSP module (s) 10-3 and Figure 2E-1 is a flow diagram of the process used by the DSP modules for the detection of active channels.

Figure 2F schematically represents a 10-5 Control and Communications Module in accordance with the present invention.

Figures 2G-2J depict aspects of currently preferred SCS calibration procedures.

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Figure 2G is a schematic illustration of the baseline and error values ​​used to explain an external calibration procedure in accordance with the present invention. Figure 2H is a flow chart of an internal calibration procedure. Figure 2I is an example transfer function of an AMPS control channel and Figure 2J represents an example combined signal.

Figures 2K and 2L are flow charts of two procedures for monitoring the performance of the Wireless Location System in accordance with the present invention.

Figure 3 schematically represents a TDOA Location Processor 12 in accordance with the present invention.

Figure 3A depicts the structure of an example network map maintained by TLP controllers in accordance with the present invention.

Figures 4 and 4A schematically represent different aspects of an Application Processor 14 in accordance with the present invention.

Figure 5 is a flow chart of a central station-based location processing procedure in accordance with the present invention.

Figure 6 is a flow chart of a station-based location processing procedure in accordance with the present invention.

Figure 7 is a flow chart of a procedure for determining, for each transmission for which location is desired, whether to employ central or station based processing.

Figure 8 is a flow chart of a dynamic process used to select cooperating antennas and SCSs 10 used in location processing.

Figure 9 is a diagram referenced below in explaining a procedure for selecting a candidate list of SCSs and antennas using a predetermined set of criteria.

Figure 10 is a flow chart of an improved procedure for TDOA and / or FDOA estimation in accordance with the present invention.

Detailed description of preferred embodiments

An objective of the present invention is to produce better TDOA and FDOA estimates for use in determining the location of mobile or cordless phones and other mobile transmitters by using a combination of system topology, geographic topology, and RF propagation information. to create a set of assumptions about a signal received by one of the receivers in the network of signal collection sites. Having received the signal at one location, the time interval for any other location can be estimated from the distance between the two locations. The Doppler shift of the signal at a single site allows some velocity information to be collected and thus any other site can be allowed to limit the frequencies sought. Since a much smaller search window is produced by using these assumptions, the number of "false positives" is reduced and the signal correlation threshold can be lowered, allowing the contribution of signals with a signal-to-signal ratio. Lower noise (SNR) to TDOA, AOA (angle of arrival) or hybrid TDOA / AOA location calculations. (The term "false positives" means a false or incorrect identification of a signal received at a cooperating site as being the same as the signal received at the reference antenna site.)

The following is a description of a WLS of the type in which the present invention can be used. The description is intended to provide the interested reader with a comprehensive understanding of a presently preferred environment in which the present invention can be used. It should be noted, however, that, except to the extent that it may be expressly limited, the claims of the present application are in no way limited to the details of the illustrative WLS described herein. Indeed, for example, the present inventors consider their invention as applicable to wireless location systems characterized as TDOA systems, AOA systems and TDOA / AOA hybrid systems. The illustrative WLS description of the presently preferred embodiments of the inventive method for estimating TDOA and FDOA will now be developed.

WLS overview

A Wireless Location System, or WLS, can be configured to function as a passive layer of a wireless communication system, such as a cellular system, PCS, or ESMR, although the concepts are not limited to just those types of communication systems. Wireless communication systems are generally not suitable for wireless locating devices, because the transmitter designs

Wireless ES 2 386 669 T3 and cell sites do not include the functionality necessary to achieve precise location. Precise location in this application is defined as the precision of 9.29 to 37.2 square meters (100 to 400 feet RMS (root mean square)). This differs from the location accuracy that can be achieved by existing cell sites, which is generally limited to the radius of the cell site. In general, cell sites are not designed or programmed to cooperate with each other to determine the location of a wireless transmitter. Additionally, wireless transmitters such as cell phones and PCS are designed to be low cost and therefore generally do not have a built-in location capability. A WLS can be designed to be a low cost addition to a wireless communication system that involves minimal changes to cell sites and no changes at all to standard wireless transmitters. The system can be considered passive because it does not contain transmitters and therefore does not cause interference to the wireless communication system.

As shown in Figure 1, the Wireless Location System has four main classes of subsystems: Signal Collection Systems (SCS) 10, TDOA Location Processors (TLP) 12, Application Processors (AP) 14 and the Network Operations Console (NOC) 16. Each SCS is responsible for the reception of the RF signals transmitted by the wireless transmitters on both the control channels and the voice channels. In general, each SCS is preferably installed in a cell site of a wireless provider and therefore works in parallel with the base station. Each TLP 12 is responsible for managing a network of SCS 10 and for providing a centralized store of digital signal processing (DSP) resources that can be used in location calculations. The SCS 10 and TLP 12 work together to determine the location of the wireless transmitters, as will be explained more fully below. Digital signal processing is the preferred way to process radio signals because DSPs are relatively inexpensive, provide consistent performance, and are easily reprogrammable to handle many different tasks. Both the SCS 10 and TLP 12 contain a significant amount of DSP resources and the software in these systems can work dynamically to determine where to perform a particular processing function based on trade-offs between processing time, communications time, time in wait and cost. Each TLP 12 exists centrally primarily to reduce the overall cost of implementing the Wireless Location System, although the techniques discussed herein are not limited to the preferred architecture shown. That is, the DSP resources can be located within the Wireless Location System with no change in the basic concepts or the disclosed functionality.

The APs 14 are responsible for the management of all resources in the Wireless Location System, including all the SCS 10 and the TLPs 12. Each AP 14 also contains a specialized database containing "triggers" for the Wireless Location System. . To conserve resources, the Wireless Location System can be programmed to locate only certain predetermined types of transmissions. When a transmission of a predetermined type occurs, then the Wireless Location System is activated to begin location processing. Otherwise, the Wireless Location System can be programmed to ignore the transmission. Each AP 14 also contains application interfaces that allow a variety of applications to securely access the Wireless Location System. These applications can, for example, access real-time or non-real-time location records, create or delete certain types of triggers, or have the Wireless Location System take other options. Each AP 14 is also capable of certain post-processing functions that allow the AP 14 to combine a number of location records to generate extended reports or analyzes useful for applications such as traffic monitoring or RF optimization.

The NOC 16 is a network management system that provides Wireless Location System operators with easy access to Wireless Location System programming parameters. For example, in some cities, the Wireless Location System may contain many hundreds even thousands of SCS 10. The NOC is the most effective way to manage a large Wireless Location System, using graphical user interface capabilities. The NOC will also receive real-time alerts if certain functions within the Wireless Location System are not working properly. These real-time alerts can be used by the operator to quickly take corrective action and prevent location service degradation. Experience with Wireless Location System testing indicates that the ability of the system to maintain good location accuracy over time is directly related to the ability of the operator to keep the system operating within its predetermined parameters.

Readers of US Patents 5,327,144 and 5,608,410 and the present specification will observe similarities between these respective systems. Indeed, the system disclosed herein builds significantly on and also significantly improves on the system disclosed in those previous patents. For example, the SCS 10 has been extended and improved upon from the Antenna Placement System described in 5,608,410. The SCS 10 now has the ability to support many more antennas at a single cell site and can additionally support the use of extended antennas as described below. This allows the SCS to work with the now commonly used sectorized cell sites. The SCS 10 can also transfer data from multiple antennas to a cell-site to the TLP 12 instead of always combining the data from multiple antennas before transferring it. Additionally, the SCS 10 can support multiple over-the-air interface protocols thus allowing the SCS 10 to function even when a wireless provider changes.

ES 2 386 669 T3 continuously configuring your system.

The TLP 12 is similar to the central emplacement system unveiled in 5,608,410, but it has been extended and improved as well. For example, the TLP 12 has been made scalable so that the amount of DSP resources required by each TLP 12 can be appropriately scaled to fit the number of locations per second required by the Wireless Location System clients. To support scaling for different capabilities of the Wireless Location System, a networking scheme has been added to the TLP 12 so that multiple TLPs 12 can cooperate to share the RF data across the boundaries of the Wireless Location System network. Wireless Communications. Additionally, the TLP 12 has been given control means to determine the SCS 10 and, more importantly, the antennas of each of the SCS 10, from which the TLP 12 is to receive data to process a specific location. Previously, the Antenna Site Systems will automatically send data to the Central Site System, whether or not it has been required by the Central Site System. Additionally, the SCS 10 and TLP 12 combined have been designed with additional means to eliminate multipath from received transmissions.

The Central Site System Database Subsystem has been extended and developed within AP 14. The AP 14 can support a greater variety of applications than previously disclosed in 5,608,410, including the ability to post-process large volumes of location records of multiple wireless transmitters. This post-processed data can produce, for example, highly efficient maps for use by wireless providers to improve and optimize the RF design of communication systems. This can be achieved, for example, by plotting the locations of all callers in an area and the strength of the received signal at a number of cell sites. The provider can then determine if each cell site is, in fact, serving the exact coverage area desired by the provider. The AP 14 can now store location records anonymously, that is, with the MIN and / or other identity information removed from the location record, so that the location record can be used for RF optimization or traffic monitoring. without raising concerns about the privacy of an individual user.

As shown in Figure 1A, a currently preferred implementation of the Wireless Location System includes a plurality of SCS regions each comprising multiple SCS 10. For example "SCS Region 1" includes SCS 10A and 10B (and preferably others, not shown) that are located at respective cell sites and share antennas with base stations at those cell sites. Extraction and insertion units 11A and 11B are used to interface fractional T1 / E1 lines to full T1 / E1 lines, which in turn are connected to a 13A Digital Access and Control System (DACS). DACS 13A and another DACS 13B are used as more specifically described below for communications between SCS 10A, 10B, etc. and multiple TLP 12A, 12B, etc. As shown, TLPs are typically co-located and interconnected via an Ethernet network (backbone) and a second redundant Ethernet network. Multiple AP 14A and 14B, multiple 16A and 16B NOCs and a terminal server 15 are also coupled to Ethernet networks. Routers 19A and 19B are used to couple a Wireless Location System to one or more other Location System (s) Wireless (s).

Signal collection systems 10

In general, cell sites will have one of the following antenna configurations: (i) an omni-directional site with 1 or 2 receiving antennas or (ii) a sectorized site with 1, 2 or 3 sectors and with 1 or 2 receiving antennas used in each sector. As the number of cell sites has increased in the United States and internationally, sectorized cell sites have become the predominant configuration. However, there is also an increasing number of microcells and picocells, which can be omnidirectional. Therefore, the SCS 10 has been designed to be configurable for any of these typical cell sites and has been provided with mechanisms to employ any number of antennas at a cell site.

The basic architectural elements of the SCS 10 remain the same as in the Antenna Placement System described in 5,608,410, but several enhancements have been made to increase the flexibility of the SCS 10 and to reduce the costs of commercial deployment of the system. The currently most preferred embodiment of SCS 10 is described herein. The SCS 10, a view of which is shown in Figure 2, includes 10-2A through 10-2C digital receiver modules; DSP modules 10-3A to 10-3C; a serial bus 10-4, a communication and control module 10-5; a GPS module 10-6 and a clock distribution module 10-7. The SCS 10 has the following external connections: power supply, fractional T1 / E1 communications, RF connections to antennas, and GPS antenna connection for time generation (or clock distribution) module 10-7. The architecture and packaging of the SCS 10 allows it to be physically located together with the cell sites (which is the most common installation site), located in other types of towers (such as FM, AM, two-way emergency communications, television, etc. ) or located in other building structures (such as roofs, silos, etc.).

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Timing generation

The Wireless Location System relies on accurate timing of all SCS 10 contained within a network. Several different timing generation systems have been described in previous disclosures, however the currently most preferred embodiment is based on an improved GPS 10-6 receiver. The enhanced GPS receiver differs from most traditional GPS receivers in that the receiver contains algorithms that eliminate some of the instabilities in the timing of GPS signals and ensure that any two SCS 10s contained within the network can receive time pulses that are within approximately ten nanoseconds of each other. These improved GPS receivers are now commercially available and further reduce some of the errors related to time reference that were observed in previous implementations of wireless location systems. While these improved GPS receivers can produce a very accurate time reference, the receiver output can still have unacceptable phase noise. Therefore, the receiver output is fed into a phase locked loop circuit controlled by a phase low noise crystal oscillator that can now produce 10 MHz and one pulse per second (PPS) reference signals within less than 0.01 degrees RMS of phase noise and with a pulse output to any SCS 10 on a Wireless Location System network within ten nanoseconds of any other pulse to another SCS 10. This combination of improved GPS receiver, crystal oscillator and phase locked loop is now the most preferred method of producing stable frequency and time reference signals with low phase noise.

The SCS 10 is designed to support multiple frequency bands and multiple providers with equipment located at the same cell site. This can take place by using multiple internal receivers in a single SCS chassis or by using multiple chassis each with separate receivers. In the case where multiple SCS chassis are placed in the same cell site, the SCS 10 can share a single time generation / clock distribution circuit 10-7 and therefore reduce the overall cost of the system. The 10 MHz and one PPS of output signals from the timing generation circuit are amplified and temporarily stored internally in the SCS 10 and then made available via external connectors. Therefore a second SCS can receive its times from a first SCS using the memorized output and external connectors. These signals can also be made available to base station equipment co-located at the cell site. This could be useful for the base station, for example, in improving the frequency reuse pattern of a wireless communication system.

Receiver Module 10-2 (Wideband Realization)

When a wireless transmitter performs the transmission, the Wireless Location System has to receive the transmission at multiple SCS 10 located at multiple geographically dispersed cell sites. Therefore, each SCS 10 has the ability to receive a transmission on any RF channel from which the transmission may originate. Additionally, since the SCS 10 is capable of supporting multiple over-the-air interface protocols, the SCS 10 also supports multiple types of RF channels. This is in contrast to more common base station receivers, which typically receive only one type of channel and are typically capable of receiving only on selected RF channels at each cell site. For example, a typical TDMA base station receiver will only support 30 kHz wide channels and each receiver is programmed to receive signals from only one channel whose frequency does not change often (ie there is a relatively fixed frequency plan). Therefore, very few TDMA base station receivers will receive a transmission on any given frequency. As another example, even though some GSM base station receivers are capable of frequency hopping, receivers at multiple base stations are generally not capable of simultaneously tuning to a single frequency in order to perform location processing. In fact, receivers in GSM base stations are programmed for frequency hopping to avoid the use of an RF channel that is being used by another transmitter so that interference is minimized.

The SCS 10-2 receiver module is preferably a dual wideband digital receiver that can receive the full frequency band and all RF channels from an over-the-air interface. For cellular systems in the United States, this receiver module is either 15 MHz wide or 25 MHz wide so that all channels from a single provider or all channels from both providers can be received. This receiver module has many of the features of the receiver previously described in Patent Number 5,608,410, and Figure 2A is a block diagram of the presently preferred embodiment. Each receiver module contains a 10-2-1 RF tuner section, a 10-2-2 control and data interface section, and a 10-2-3 analog-to-digital conversion section. The 10-2-1 RF Tuner section includes two completely independent digital receivers (including Tuner # 1 and Tuner # 2) that convert the analog RF input from an external connector into a digitized data stream. Unlike most base station receivers, the SCS receiver module does not perform diversity mixing or switching. Rather, the digitized signal from each independent receiver is made available to location processing. The present inventors have determined that there is an advantage in location processing especially multipath mitigation processing in the process independently of the signals from each antenna rather than combining in the receiver module.

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The receiver module 10-2 performs, or connects to elements that perform, the following functions: automatic gain control (to support both strong signals near and weak signals far away), band-pass filtering to remove potential interference signals from outside the RF band of interest, synthesis of frequencies necessary for mixing with RF signals to create an IF signal that can be sampled, mixing and analog-to-digital conversion (ADC) for sampling RF signals and outputting a digitized data stream having appropriate bandwidth and bit resolution. The frequency synthesizer locks the synthesized frequency to the 10 MHz reference signal from the 10-7 time generation / clock distribution module (Figure 2). All circuits used in the receiver module maintain the low phase noise characteristics of the time reference signal. The receiver module preferably has a spurious free dynamic range of at least 80 dB.

The 10-2 receiver module also contains circuitry for generating test frequencies and calibration signals, as well as test ports where measurements can be made by technicians during installation or repairs. Various calibration processes are described in more detail below. Internally generated test frequencies and test ports provide an easy procedure for engineers and technicians to quickly test the receiver module and diagnose any suspected problems. This is especially useful during the manufacturing process.

One of the advantages of the Wireless Location System described herein is that no new antennas are required at cell sites. The Wireless Location System can use existing antennas already installed in most cell sites, including both omnidirectional and sectorized antennas. This feature can result in significant savings in the installation and maintenance costs of the Wireless Location System over other approaches that have been described in the prior art. SCS 10-2 digital receivers can be connected to existing antennas in two ways, as shown in Figures 2B and 2C respectively. In Figure 2B, SCS receivers 10-2 are connected to the RF splitter or splitter at the existing cell site. In this way, the SCS 10 uses the low noise preamplifier, band pass filter and RF multi-connector or splitter at the cell site. This type of connection typically limits the SCS 10 to support a single provider's frequency band. For example, a cellular provider at site A will typically use the band pass filter to block signals from the provider's customers at site B and vice versa.

In Figure 2C, the existing RF path at the cell site has been discontinued and a new RF amplifier, band pass filter and splitter has been added as part of the Wireless Location System. The new band-pass filter will pass multiple contiguous frequency bands, such as both the cellular providers at site A and site B, thus allowing the Wireless Location System to locate wireless transmitters using both cellular systems but using the antennas of a single cell site. In this configuration, the Wireless Location System uses RF components adjusted at each cell deferral so that the frequency and phase responses are identical. This is unlike existing RF components, which can be from different manufacturers or use different model numbers at various cell sites. Adapting the response characteristics of the RF components reduces a possible source of error for location processing, even though the Wireless Location System has the ability to compensate for these sources of error. Finally, the new pre-amplifier installed with the Wireless Location System will have a very low noise figure to improve the sensitivity of the SCS 10 in a cell site. The overall noise figure of the SCS 10-2 digital receivers is dominated by the noise figures of the low noise amplifiers. Because the Wireless Location System can use weak signals in location processing, while the base station typically cannot process weak signals, the Wireless Location System can benefit significantly from a high-quality, very low-noise amplifier.

To enhance the Wireless Location System's ability to accurately determine TDOA for wireless transmission, the phase response versus frequency of the RF components of the cell site is determined at installation time and updated at other times. certain times and is then stored in a table in the Wireless Location System. This can be important because, for example, bandpass filters and / or multi-connectors made by some manufacturers have a non-linear, bouncy frequency-phase response near the bandpass limit. If the bandpass limit is very close or coincides with the reverse or voice control channels, then the Wireless Location System makes incorrect measurements of the phase characteristics of the transmitted signal if the Wireless Location System does not correct the measurements. using stored characteristics. This becomes even more important if a supplier has installed multiple connectors and / or band pass filters from more than one manufacturer, since the characteristics at each site may be different. In addition to phase versus frequency response measurements, other environmental factors can cause changes in the RF path prior to the ADC. These factors require occasional and sometimes periodic calibration on the SCS 10.

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Alternate Narrowband Realization of Receiver Module 10-2

In addition to or as an alternative to the wideband receiver module, the SCS 10 also supports a narrowband embodiment of the receiver module 10-2. Unlike the wideband receiver module that can simultaneously receive all the RF channels in use by a wireless communication system, the narrowband receiver can only receive one or a few RF channels at a time. For example, the SCS 10 supports a 60 kHz narrow band receiver for use in AMPS / TDMA systems, covering two contiguous 30 kHz channels. This receiver is still a digital receiver as described for the wideband module, however frequency synthesis and mixing circuits are used to dynamically adjust the receiver module to various RF channels on demand. This dynamic tuning can typically take place in a millisecond or less, and the receiver can dwell on a specific RF channel for as long as it takes to receive and digitize the RF data for location processing.

The purpose of the narrow band receiver is to reduce the costs of implementing a Wireless Location System due to the costs incurred with the wide band receivers. Naturally, there is a loss in performance, but the availability of these multiple receivers allows wireless providers to have more cost / performance options. Additional inventive functions and enhancements have been added to the Wireless Location System to support this new type of narrow band receiver. When using the wideband receiver, all RF channels are received continuously on all SCS 10 and, subsequent to transmission, the Wireless Location System can use DSPs 10-3 (Figure 2) to dynamically select any RF channel of digital memory. With the narrowband receiver, the Wireless Location System must ensure a priori that narrowband receivers at multiple cell sites are simultaneously tuned to the same RF channel so that all receivers can simultaneously receive, digitize and store the same RF channel. wireless transmission. For this reason, the narrow-band receiver is generally used only for locating transmissions on the voice channel, which can be known a priori that a transmission is to be carried out. Since transmissions on the control channel can take place asynchronously at any time, the narrowband receiver may not be set to the correct channel to receive the transmission.

When narrowband receivers are used to locate transmissions on the AMPS voice channel, the Wireless Location System has the ability to temporarily change the modulation characteristics of the AMPS wireless transmitter to aid in location processing. This may be necessary because the AMPS voice channels are only FM modulated with the addition of a low-level supervisory tone known as SAT. As is known in the art, a Cramer-Rao lower limit of AMPS FM modulation is significantly worse than the Manchester encoded FSK modulation used by AMPS reverse channels and "target and burst" transmissions on the voice channel. Additionally, wireless AMP transmitters may be transmitting with significantly reduced power if there is no modulation input signal (ie no one is speaking). To improve location estimation by improving modulation characteristics without relying on the existence or amplitude of the input modulation signal, the Wireless Location System can make an AMPS wireless transmitter transmit a "target and burst" message. at a point in time when narrowband receivers in multiple SCS 10 are tuned to the RF channel where the message will be sent. This is further described below.

The Wireless Location System performs the following steps when using the narrowband receiver module (see the flow chart in Figure 2C-1):

a first wireless transmitter is connected a priori to transmission on a particular RF channel;

the Wireless Location System is activated to estimate the location of the first wireless transmitter (activation can take place both internally and externally through a command / response interface);

The Wireless Location System determines the cell site, sector, RF channel, time slot, long code mask, and encryption key (all information elements may not be required for all over-the-air interface protocols) currently on use by the first wireless transmitter;

The Wireless Location System tunes an appropriate first narrowband receiver and appropriate first SCS 10 to the RF channel and timeslot at the designated sector and cell site, where "appropriate" typically means both available and located together. or in close proximity;

the first SCS 10 receives a time slot of RF data, typically ranging from a few microseconds to tens of milliseconds, from the first narrow band receiver and evaluates the transmission power, SNR and modulation characteristics;

if the transmission power or SNR is below a predetermined threshold, the Wireless Location System waits a predetermined duration of time and then returns to the previous third stage (in which the Wireless Location System determines the cell site, sector, etc.);

if the transmission is a transmission on the AMPS voice channel and the modulation is below the threshold,

ES 2 386 669 T3 then the Wireless Location System instructs the wireless communication system to send a command to the first wireless transmitter to produce a "target and burst" on the first wireless transmitter;

the Wireless Location System requests the wireless communication system to prevent handover of the wireless transmitter to another RF channel for a predetermined period of time;

The Wireless Location System receives a response from the wireless communication system indicating the period of time during which the first wireless transmitter will be prevented from being handed over and, if requested, the period of time during which the wireless communication system will send a message. command the first wireless transmitter to produce a "target and burst";

the Wireless Location System determines the list of antennas to be used in location processing (the antenna selection process is described below);

The Wireless Location System determines the earliest Wireless Location System timestamp at which narrowband receivers connected to selected antennas are available to simultaneously begin collecting RF data from the RF channel currently in use by the first wireless transmitter;

Based on the earliest Wireless Location System timestamp and time periods in the response of the wireless communication system, the Wireless Location System commands narrowband receivers to connect to antennas that will be used in processing. from the location to tune in to the cell site, RF sector and channel currently in use by the first wireless transmitter and to receive RF data for a predetermined dwell period (based on signal bandwidth, SNR, and integration requirements);

RF data received by narrowband receivers is written to dual port memory; location processing begins on received RF data, as described in patents 5,327,14 4 and 5,608,410 and in the sections below;

the Wireless Location System again determines the cell site, sector, RF channel, time slot, long code mask and encryption key currently in use by the first wireless transmitter;

if the cell site, sector, RF channel, time slot, long code mask, and encryption key currently in use by the first wireless transmitter has changed between queries (i.e. before and after collecting the RF data) the Wireless Location System completes the location process, produces an alert message that the location processing failed because the wireless transmitter changed the state of the transmission during the period of time in which the RF data was being received and reactivates this entire process;

the location processing with the received RF data is completed according to the steps described below.

Determining the information elements including cell site, sector, RF channel, time slot, long code mask, and encryption keys (all information elements may not be required for all interface protocols by air) are typically obtained by the Wireless Location System through a command / response interface between the Wireless Location System and the wireless communication system.

Using the narrow band receiver in the manner described above is known as random tuning because the receivers can be routed to any RF channel on demand in the system. An advantage of random tuning is that locations are processed only for those wireless transmitters for which the Wireless Location System is activated. A disadvantage of random tuning is that there are several synchronization factors, including the interface between the wireless communication system and the Wireless Location System and latency times in planning the production of the system's necessary receivers, can limit the throughput of the total location. For example, in a TDMA system, a random tuning used through the Wireless Location System will typically limit location processing to about 2.5 locations per second per cell-site sector.

Therefore, the narrow band receiver also supports another mode, known as automatic sequence tuning, which can perform location processing with higher throughput. For example, in a TDMA system, using similar assumptions about dwell time and settling time equal to operation on the narrowband receiver described above, sequential tuning can achieve location processing performance of approximately 41 locations. per second per cell-site sector, meaning that all 395 RF TDMA channels can be processed in approximately 9 seconds. This increased rate can be achieved by taking advantage of for example the two contiguous RF channels that can be received simultaneously, processing the location of the three TDMA time slots on one RF channel eliminating the need for synchronization with the wireless communication system. When the Wireless Location System is using narrowband receivers for sequential tuning, the Wireless Location System has no knowledge of the identity of the wireless transmitter because the Wireless Location System does not wait for an activation nor does the Wireless Location System query wireless communication system for identity information

ES 2 386 669 T3 prior to receiving the transmission. In this procedure, the Wireless Location System sequentially advances through each cell site, RF channel, and time slot, performs location processing, and reports a location record identifying a timestamp, cell site, channel. RF, time slot and location. Following the location log report, the Wireless Location System and the wireless communication system match the location logs to the data from the wireless communication system indicating which wireless transmitters were in use at the time and which cell sites, channels RF and time slots were used for each wireless transmitter. The Wireless Location System can then retain the location records for the wireless transmitters of interest and discard those location records for the remaining wireless transmitters.

10-3 digital signal processor module

The SCS 10-2 digital receiver modules output a stream of digitized RF data having a specified bandwidth and bit resolution. For example, a 15 MHz embodiment of the wideband receiver can output a data stream containing 60 million samples per second, at a resolution of 14 bits per sample. This RF data stream will contain all the RF channels that are used by the wireless communication system. The 10-3 DSP modules receive the digitized data stream and can extract any individual RF channel through digital mixing and filtering. DSPs can also reduce the on-demand bit resolution of the Wireless Location System, as necessary to reduce bandwidth requirements between SCS 10 and TLP 12. The Wireless Location System can dynamically select the bit resolution with which to send the digitized baseband RF data, based on the processing requirements for each location. DSPs are used for these functions to reduce systematic errors that can occur from mixing and filtering with analog components. The use of the DSPs allows a perfect adaptation in the processing between any two SCS 10.

A block diagram of the 10-3 DSP module is shown in Figure 2D and the operation of the DSP module is depicted in the flow diagram of Figure 2E. As shown in Figure 2D, the DSP module 10-3 comprises the following elements: a pair of DSP elements 10-3-1A and 10-3-1B, collectively referred to as a "first" DSP; 10-3-2 series to parallel converters; 10-3-3 dual port memory elements; a second DSP 10-3-4; a parallel-to-series converter; a FIFO buffer; a 10-3-5 DSP (which includes the RAM) for detection, another 10-3-6 DSP for demodulation and another 100-3-7 DSP for normalization and control and a 10-3-8 address generator. In a currently preferred embodiment, the DSP module 10-3 receives the broadband digitized data stream (Figure 2E, step S1) and uses the first DSP (10-3-1A and 10-3-1B) to extract blocks of channels (step S2). For example, a first DSP programmed to function as a digital pull receiver can pull four blocks of channels, with each block including at least 1.25 MHz of bandwidth. This bandwidth can include 42 AMPS or TDMA channels, 6 GSM channels, or one CDMA channel. The DSP does not require that the blocks be contiguous, since the DSP can independently digitally tune to any set of RF channels within the bandwidth of the wideband digitized data stream. The DSP may also perform broadband or narrowband energy detection on all or any of the channels in the block, and report the per channel power levels to the TLP (step S3). For example, every 10 ms, the DSP can perform broadband energy detection and create an RF spectral map for all channels and all receivers (see step S9). Because this spectral map can be sent from SCS 10 to TLP 12 every 10 ms over the communications link connecting SCS 10 and TLP 12, there could be significant data overhead. Therefore, the DSP reduces data overhead by sending the data in a finite number of levels. Typically, for example, 84 dB of dynamic range might require 14 bits. In the compacting process implemented by the DSP, the data is reduced, for example, to only four bits by selecting 16 important RF spectral levels to send to the TLP 12. The choice of the number of levels and therefore the number of bits, as well as the representation of the levels, can be adjusted automatically by the Wireless Location System. These adjustments are made to maximize the information value of the RF spectral messages sent to the TLP 12 as well as to optimize the use of the available bandwidth on the communication link between the SCS 10 and the TLP 12.

After conversion, each block of RF channels (each at least 1.25 MHz) is passed through the 10-3-2 serial to parallel converter and then stored in the 10-3-3 dual port digital memory. (step S4). Digital memory is circular memory, which means that the DSP module begins writing data to the first memory address and then continues sequentially until the last memory address is reached. When the last memory address is reached, the DSP returns to the first memory address and continues sequentially writing data to memory. Each DSP module typically contains enough memory to store several seconds of data for each block of RF channels to support latency and queue times in the paging process.

In the DSP module, the memory address where the digitized and converted RF data is written to memory is the timestamp used throughout the Wireless Location System and referenced by the location process in the TDOA determination. . To ensure that the timestamps are aligned at each SCS 10 in the Wireless Location System, the address generator 10-3-8 receives the signal of one pulse per second from the time generation / clock distribution module 10-7. (Figure 2). Periodically, the

ES 2 386 669 T3 address generator in all SCS 10 in a Wireless Location System will simultaneously reset themselves to known addresses. This enables location processing to reduce or eliminate accumulated time errors in the recording of timestamps for each digitized data item.

The 10-3-8 address generator controls both writing and reading from the 10-3-3 dual port digital memory. The writing takes place continuously since the ADC is continuously sampling and digitizing the RF signals and the first DSP (10-3-1A and 10-3-1B) is continuously performing the digital extraction reception function. However, reading occurs in bursts when the Wireless Location System requests data to perform location demodulation and processing. The Wireless Location System can even perform location processing recursively in a single transmission and therefore requires access to data multiple times. To service the many requirements of the Wireless Location System, the address generator allows dual port digital memory to be read at a faster rate than writing takes place. Typically, reading can be done eight times faster than writing.

The DSP 10-3 uses the second DSP 10-3-4 to read the data from the 10-3-3 digital memory and then performs a second digital extraction receiver function to extract baseband data from the blocks of memory. RF channels (step S5). For example, the second DSP can extract any 30 kHz AMPS or simple TDMA channel from any block of RF channels that have been digitized and stored in memory. In the same way, the second DSP can extract any single GSM channel. The second DSP is not required to extract a CDMA channel, since the channel bandwidth occupies the full bandwidth of the stored RF data. The combination of the first DSP 10-3-1A, 10-3-1B and the second DSP 10-3-4 allows the DSP module to select, store and retrieve any single RF channel in a wireless communication system. A DSP module will typically store four blocks of channels. In a dual-mode AMPS / TDMA system, a single DSP module can continuously and simultaneously monitor up to 42 analog reverse control channels, up to 84 digital control channels, and also be tasked with monitoring and locating any voice channel transmission. A single SCS chassis will typically support up to three 10-2 receiver modules (Figure 2), to cover the three sectors of two antennas each and up to nine DSP modules (three DSP modules per receiver allowing a bandwidth of 15 Full MHz is simultaneously stored in digital memory). As such, the SCS 10 is a highly modular system that can be easily scaled to accommodate any type of cell site configuration and processing load.

The DSP module 10-3 also performs other functions, including automatic detection of active channels used in each sector (step S6), demodulation (step S7), and station-based location processing (step S8). The Wireless Location System maintains an active map of RF channel usage in a wireless communication system (step S9), allowing the Wireless Location System to manage receiver and processing resources and quickly start processing when it has had. place a particular broadcast of interest. The active map comprises a table maintained within the Wireless Location System that lists for each antenna connected to an SCS 10 the primary channels assigned to that SCS 10 and the protocols used on those channels. A primary channel is an RF control channel assigned to a base station located in conjunction with or close to that of the base station that it uses for communications with the wireless transmitters. For example, in a typical cellular system with sectorized cell sites, there will be an RF control channel frequency assigned for use in each sector. Those control channel frequencies would typically be assigned as primary channels for a co-located SCS 10.

The same SCS 10 can also be assigned to monitor RF control channels or other nearby base stations as primary channels, even if other SCS 10 also have the same primary channels assigned. In this way, the Wireless Location System implements a system demodulation redundancy that ensures that any given wireless transmission has an infinitesimal probability of being lost. When this redundancy feature is used in demodulation, the Wireless Location System will receive, detect and demodulate the same wireless transmission two or more times on more than one SCS 10. The Wireless Location System includes means to detect when this multiple demodulation has taken place and to activate location processing only once. This function conserves the processing and communication resources of the Wireless Location System and is further described below. This ability for a simple SCS 10 to detect and demodulate wireless transmissions taking place at non-localized cell sites in conjunction with the SCS 10 enables Wireless Location System operators to more efficiently deploy Wireless Location System networks. For example, the Wireless Location System can be designed so that the Wireless Location System uses much less SCS 10 than the base stations that the wireless communication system has.

In the Wireless Location System, the primary channels are entered and maintained in the table using two procedures: direct programming and automatic detection. Direct programming involves entering the primary channel data into the table using one of the Wireless Location System user interfaces, such as the Network Operations Console 16 (Figure 1) or by receiving the data from channel assignment from the Wireless Location System to the wireless communication system interface. Alternatively, the DSP 10-3 module also runs a background process known as discovery

ES 2 386 669 T3 automatic wherein the DSP uses a scheduled or spare processing capacity to detect transmissions on several possible RF channels and then attempts to demodulate those transmissions using probable protocols. The DSP module can then confirm that the directly programmed primary channels are correct and can also quickly detect changes made to the channels at the base station and send an alert to the operator of the Wireless Location System.

The DSP module performs the following stages in automatic detection (see Figure 2E-1):

for each possible voice and / or control channel that can be used in the coverage area of ​​the SCS 10, metric counters are set (step S7-1);

at the beginning of a detection period, all metric counters are reset to zero (step S7-2); each time a transmission takes place on a specified RF channel, and the received power level is above a particular preset threshold, the metric counter for that channel is incremented (step S7-3);

Each time a transmission takes place on a specified RF channel and the received power level is above a second particular preset threshold, the DSP module attempts to demodulate a certain part of the transmission using a first preferred protocol (step S7-4 );

if the demodulation is successful, a second metric counter is incremented for that channel (step S7-5); if the demodulation is unsuccessful, the DSP module tries to demodulate a part of the transmission using a second preferred protocol (step S7-6);

if demodulation is successful, a third metric counter for that channel is incremented (step S7-7);

At the end of a detection period, the Wireless Location System reads all the metric counters (step S7-8) and the Wireless Location System automatically assigns primary channels based on the metric counters (step S7-9).

The Wireless Location System operator can review the metric counters and automatic assignment of primary channels and modulation protocols and override any adjustments that have been made automatically. Also, if more than two protocols preferred by the wireless provider can be used, then the DSP 10-3 module can be downloaded with software to detect the additional protocols. The SCS 10 architecture, based on 10-2 broadband receivers, 10-3 DSP modules, and downloadable software enables the Wireless Location System to support multiple demodulation protocols in a single system. There is a significant cost advantage in supporting multiple protocols within a single system, since only a single SCS 10 is required at a cell site. This is unlike many base station architectures, which may require different transceiver modules for different modulation protocols. For example, while the SCS 10 could simultaneously support AMPS, TDMA, and CDMA on the same SCS 10, there is no base station currently available that can support this functionality.

The ability to detect and demodulate multiple protocols also includes the ability to independently detect the use of authentication in messages transmitted over certain over-the-air interface protocols. The use of authentication fields in wireless transmitters became prevalent in the last few years as a means of reducing the occurrence of fraud in wireless communication systems. However, not all wireless transmitters have implemented authentication. When authentication is used, the protocol generally inserts an additional field in the transmitted message. Frequently this field is inserted between the identity of the wireless transmitter and the dialed digits in the transmitted message. When a wireless transmission is demodulated, the Wireless Location System determines the number of fields in the transmitted message, as well as the type of message (ie record, source, paged response, etc.). The Wireless Location System demodulates all fields if it appears that extra fields are present, in consideration of the type of message transmitted, then the Wireless Location System checks all fields for a trigger condition. For example, if the digits marked "911" appear in the proper place in a field and the field is located in both its proper place without authentication and in its proper place with authentication, then the Wireless Location System is activated normally. In this example, the digits "911" would be required to appear in sequence as "911" or "* 911", with no other digits before or after both sequences. This functionality reduces or eliminates false activation due to the "911" digits appearing as part of an authentication field.

Support for multiple demodulation protocols is important for the Wireless Location System to function successfully because location processing must be activated quickly when a wireless caller has dialed "911". The Wireless Location System can activate location processing using two procedures: The Wireless Location System independently demodulates control channel transmissions and will activate location processing using any number of criteria such as dialed digits or the Wireless Location System may receive activations from an external source such as the provider's wireless communication system. The present inventors have discovered that independent demodulation by the SCS 10 results in a faster wake-up time, when measured from the moment the wireless user presses the "SEND" or "TALK" button (or similar) on a wireless transmitter.

ES 2 386 669 T3

Control and communications module 10-5

The 10-5 communication and control module, shown in Figure 2F, includes 10-5-1 data buffers, a 10-5-2 controller, a 10-5-3 memory, a 10-5-4 CPU and a T1 / E1 10-5-5 communications chip. The module has many of the features previously described in Patent Number 5,608,410. Various improvements have been added in the present embodiment. For example, the SCS 10 now includes an automatic remote reset capability, even if the CPU in the communication and control module ceases to run its programmed software. This capability can reduce the operating costs of the Wireless Location System because technicians are not required to travel to the cell site to replenish an SCS 10 if it ceases to function normally. The automatic remote reset circuitry operates by monitoring the communication interface between the SCS 10 and the TLP 12 for a particular sequence of bits. This sequence of bits is a sequence that does not occur during normal communications between the SCS 10 and the TLP 12. This sequence, for example, may consist of an all-ones pattern. The reset circuit operates independently of the CPU so that even if the CPU has placed itself in a locked or other non-operational state, the circuit can still achieve the SCS 10 reset and return the CPU to an operational state. .

This module now has the ability to record and report a wide variety of statistics and variables used in monitoring or diagnosing the performance of the SCS 10. For example, the SCS 10 can monitor the percentage capacity usage of any DSP or other processor in SCS 10, as well as the communication interface between SCS 10 and TLP 12. These values ​​are regularly reported to AP 14 and NOC 16 and are used to determine when additional processing and communications resources are required in the system. For example, alarm thresholds can be set in the NOC to indicate to an operator if any resource is consistently exceeding a preset threshold. The SCS 10 can also monitor the number of times the transmissions have been successfully demodulated, as well as the number of failures. This is useful to allow operators to determine if the signal thresholds for demodulation have been optimally set.

This module, as well as the other modules, can also self-notify its identity to the TLP 12. As described below, many SCS 10 can be connected to a single TLP 12. Typically, the communications between the SCS 10 and the TLP 12 are they share with the communications between the base stations and the MSCs. It is often difficult to quickly determine exactly which SCS 10 has been assigned to particular circuits. Therefore, the SCS 10 contain a hard-coded identity, which is recorded at the time of installation. This identity can be read and verified by the TLP 12 to positively determine which SCS 10 has assigned a provider for each of several different communication circuits.

Communications from the SCS to the TLC support a variety of messages, including: commands and responses, software download, status and speed, parameter download, diagnostics, spectrum data, phase data, primary channel demodulation, and RF data. The communications protocol is designed to optimize the performance of the Wireless Location System by minimizing protocol overhead and the protocol includes a message priority scheme. Each type of message is assigned a priority and the SCS 10 and tLp 12 will queue the messages by priority so that a higher priority message is sent before a lower priority message is sent. For example, demodulation messages are generally set to a high priority because the Wireless Location System must activate location processing on certain types of calls (eg, E9-1-1) without delay. Although higher priority messages are queued before lower priority messages, the protocol generally does not pre-empt a message already in transit. That is, a message in the process of being sent through the communications interface from SCS 10 to TLP 12 will be fully completed, but then the next message to be sent will be the highest priority message with the previous timestamp. . To minimize latency for high priority messages, long messages, such as RF data, are sent in segments. For example, the RF data for a full 100 millisecond AMPS transmission can be separated into 10 millisecond segments. In this way, a high priority message can be queued between segments of the RF data.

Performance monitoring and calibration

The architecture of the SCS 10 relies heavily on digital technologies including the digital receiver and digital signal processors. Once the RF signals have been digitized, the times, frequency, and phase differences can be carefully controlled in various processes. Most importantly, any time, frequency and phase differences can be perfectly adjusted between the various receivers and various SCS 10 used in the Wireless Location System. However, prior to ADC, RF signals pass through a number of RF components, including antennas, cables, low-noise amplifiers, filters, duplexers, multi-connectors, and RF splitters. Each of these RF components has important characteristics for the Wireless Location System, including delay and phase response to frequency. When the analog RF components are perfectly matched between the pairs of SCS 10, such as between the SCS 10A and the SCS 10B in Figure 2G, then the effects of these characteristics are automatically eliminated in the location processing. But when the characteristics of the components are not adjusted, then the location processing may inadvertently include instrumental errors resulting from the mismatch. Additionally, many of these RF components can

ES 2 386 669 T3 experience instability with power, time, temperature or other factors that can add instrumental errors to the determination of the location. Therefore, various inventive techniques have been developed to calibrate the RF components in the Wireless Location System and to monitor the performance of the Wireless Location System on a regular basis. After calibration, the Wireless Location System stores the values ​​of these delay and phase responses with respect to frequency (i.e. the RF channel number) in a table in the Wireless Location System for use in correcting these. instrumental errors. Figures 2G-2J are referenced below in explanation of these calibration procedures.

External calibration procedure

With reference to Figure 2G, the time stability of the Wireless Location System is measured along baselines, in which each baseline is composed of two SCS, 10A and 10B, and an imaginary line (A - B) drawn between them. In a TDOA / FDOA type of Wireless Location System, the locations of the wireless transmitters are calculated by measuring the differences in the times each SCS 10 records the arrival of the signal from a wireless transmitter. Therefore, it is important that the differences in the times measured by the SCS 10 along any baseline are primarily attributed to the transmission time of the signal from the wireless transmitter and minimally attributed to variations in the components of the signal. RF and analog of the SCS 10 themselves. To meet the accuracy goals of the Wireless Location System, the timing stability for any pair of SCS 10 is kept much less than 100 nanoseconds RMS (root mean square). Thus, the Wireless Location System components will contribute less than 100 feet of instrumentation error in estimating the location of a wireless transmitter. Part of this error is assigned to the ambiguity of the signal used to calibrate the system. This ambiguity can be determined from the well-known Cramer-Rao lower limit equation. In the case of an AMPS reverse control channel, this error is approximately 40 nanoseconds RMS. The remainder of the recorded error is assigned to the Wireless Location System components, primarily the RF and analog components in the SCS 10.

In the external calibration procedure, the Wireless Location System uses a network of calibration transmitters whose signal characteristics match those of the target wireless transmitters. These calibration transmitters can be ordinary cordless phones that emit periodic registration signals and / or paging response signals. Each usable SCS to SCS baseline is preferably periodically calibrated using a calibration transmitter that has a relatively clear and unobstructed path for both SCS 10 associated with the baseline. The calibration signal is processed identically to a signal from a target wireless transmitter. Since the TDOA values ​​are known a priori, any errors in the calculations are due to systematic errors in the Wireless Location System. These systematic errors can then be eliminated in subsequent location calculations for the target transmitters.

Figure 2G illustrates the external calibration procedure to minimize timing errors. As shown, a first SCS 10A at point "A" and a second SCS 10B at point "B" have an associated baseline AB. A calibration signal emitted at a time T0 by a calibration transmitter at point "C" will theoretically reach the first SCS 10A at a time T0 + Tac. Tac is the measure of the amount of time required for the calibration signal to travel from the antenna in the calibration transmitter to the dual port digital memory in a digital receiver. In the same way, the same calibration signal will reach a second SCS 10B in a theoretical time T0 + Tbc. Typically, however, the calibration signal will not reach the digital memory in the digital signal processing components of the respective SCS 10 at exactly the correct times. Rather, there will be errors e1 and e2 in the amount of time (Tac, Tbc) it takes for the calibration signal to propagate from the calibration transmitter to the SCS 10, respectively, so that the exact times of arrival will actually be T0. + Tac + e1 and T0 + Tbc + e2. Such errors will be due to some degree to delays in the propagation of the signal through the air, that is, from the antenna of the calibration transmitters to the antennas of the SCS; however, the errors will be mainly due to time-varying characteristics in the front-end components of the SCS. The errors e1 and e2 cannot be determined per se because the system does not know the exact moment (T0) at which the calibration signal was transmitted. The system can, however, determine the error in the difference in the time of arrival of the calibration signal at the respective SCS 10 in any pair of SCS 10. This TDOA error value is defined as the difference between the measured TDOA value and the theoretical TDOA value τΰ, where τ0 is the theoretical difference between the theoretical delay values ​​Tac and Tbc. The theoretical TDOA values ​​for each pair of SCS 10 and each calibration transmitter are known because the positions of the SCS 10 and the calibration transmitter and the speed at which the calibration signal propagates are known. The measured TDOA baseline (TDOAa-b) can be represented as TDOAa-b = + e, where e = e1 - e2. In a similar way, a calibration signal from a second calibration transmitter at point "D" will have associated errors e3 and e4. The final value of e to subtract from the TDOA measurements for a target transmitter will be a function (eg, weighted average) of the e-values ​​derived for one or more calibration transmitters. Therefore, a given TDOA measurement (TDOAmeasured) for a pair of SCS 10 at points "X" and "Y" and a wireless transmitter at an unknown location will be corrected as follows:

TDOAx-Y = TDOAmeasure - e

ES 2 386 669 T3 e = k1 e1 + k2 e2 + ... kN eN in which k1, k2, etc., are weighting factors and e1, e2, etc., are the errors determined by subtracting the TDOA values measured from the theoretical values ​​for each calibration transmitter. In this example, the error value e 1 may be the error value associated with the calibration transmitter at point "C" in the drawing. The weighting factors are determined by the Wireless Location System operator and entered into the configuration tables for each baseline. The operator will take into consideration the distance from each calibration transmitter to the SCS 10 at points "X" and "Y", the empirically determined line of sight for each calibration transmitter to the SCS 10 at points "X" and " Y ", and the contribution that each SCS" X "and" Y "would have to an estimate of the location of a wireless transmitter that could be located in the proximity of each calibration transmitter. In general, the calibration transmitters that are closer to the SCS 10 at the “X” and “Y” points will be weighted higher than the calibration transmitters that are further apart and the calibration transmitters with a better line of sight to SCS 10 at points “X” and “Y” will be weighted higher than calibration transmitters with poorer line of sight.

Each error component e1, e2, etc., and therefore the resulting error component e, can vary widely, and out of order, over time because some of the error components are due to multipath reflection from the transmitter. calibration at each SCS 10. Multipath reflection is highly dependent on path and therefore varies from measurement to measurement and path to path. It is not an objective of this procedure to determine the multipath reflection for these calibration runs, but rather to determine the part of the errors that can be attributed to the components of the SCS 10. Typically, therefore, the error values ​​e1 and e3 they will have a common component since they relate to the same first SCS 10A. In the same way, the error values ​​e2 and e4 will also have a common component since they relate to the second SCS 10B. It is known that while multipath components can vary wildly, error components vary slowly and typically vary sinusoidally. Therefore, in the external calibration procedure, the error values ​​e are filtered using a weighted, time-based filter that decreases the weight of the disorderly varying multipath components while keeping the error components that change relatively slowly. attributed to SCS 10. One such example filter used in the external calibration procedure is the Kalman filter.

The period between calibration transmissions is varied depending on the error drift rates determined for the SCS components. The drift rate period should be much longer than the calibration interval period. The Wireless Location System monitors the drift rate period to continually determine the rate of change and can periodically adjust the calibration interval, if necessary. Typically, the calibration rate for the Wireless Location System such as one according to the present invention is between 10 and 30 minutes. This corresponds well to the typical time period for a registration rate in a wireless communication system. If the Wireless Location System determined that the calibration interval should be set to a calibration faster than the record rate of the wireless communication system, then the AP 14 (Figure 1) would automatically force the calibration transmitters to transmit via a pager. to the transmitter within the prescribed interval. Each calibration transmitter can be individually driven and therefore the calibration interval associated with each calibration transmitter may be different.

Since the calibration transmitters used in the external calibration procedure are standard telephones, the Wireless Location System must have a mechanism to distinguish those telephones from other wireless transmitters that are being located for various application purposes. The Wireless Location System maintains a list of the identities of the calibration transmitters, typically at the TLP 12 and at the AP 14. In a cellular system, the identity of the calibration transmitter can be the Mobile Identity Number, or MIN. When the calibration transmitter makes a transmission, the transmitter is received at each SCS 10 and demodulated by the appropriate SCS 10. The Wireless Location System compares the identity of the transmission with the previously stored task assignment list of identities of all calibration transmitters. If the Wireless Location System determines that the transmission was a calibration transmission, then the Wireless Location System initiates external calibration processing.

Internal calibration procedure

In addition to the external calibration procedure, it is an objective of the present invention to calibrate all channels of a wideband digital receiver used in the SCS 10 of the Wireless Location System. The external calibration procedure will typically calibrate only a single channel of the multiple channels used in the wideband digital receiver. This is because fixed calibration transmitters will typically scan on the highest power control channel, which will typically be the same control channel each time. The transfer function of a wideband digital receiver, along with the other associated components, does not remain perfectly constant, however, and will vary with time and temperature. Therefore, even though the external calibration procedure can successfully calibrate a single channel, there is no assurance that the remaining channels will also be calibrated.

ES 2 386 669 T3

The internal calibration procedure, represented in the flow chart of Figure 2H, is particularly suited for the calibration of a first individual receiver system (i.e., SCS 10) that is characterized by a transfer function that varies with time and the frequency, in which the transfer function defines how the amplitude and phase of a signal received by the receiving system will be altered, and the receiving system is used in a location system to determine the location of a wireless transmitter by, in part, determining a difference in time of arrival of the signal transmitted by a wireless transmitter and received by the receiving system to be calibrated and other receiving system and in which the precision of the location estimate depends, in part, on the precision of the TDOa measurements made by the system. An example of an AMPS RCC transfer function is depicted in Figure 2I, which depicts how the phase of the transfer function varies through the 21 control channels spanning 630 kHz.

With reference to Figure 2H, the internal calibration procedure includes the steps of temporarily and electronically disconnecting the antenna used by a receiving system from the receiving system (step S-20); injecting an internally generated broadband signal with known and stable signal characteristics into the first receiver system (step S-21); using the generated broadband signal to obtain an estimate of how the transfer function varies across the bandwidth of the first receiver system (step S22) and using the estimate to mitigate the effects of the variation of the first transfer function with the time and frequency measurements made by the first receiver system (step S-23). An example of a broadband signal used for internal calibration is a combined signal, which is composed of multiple individual elements, of equal amplitude frequency and known spacing, such as 5 kHz. An example of such a signal is shown in Figure 2I.

The antenna should be temporarily disconnected during the internal calibration process to prevent external signals from entering the wideband receiver and to ensure that the receiver is only receiving the stable wideband signal. The antenna is electronically disconnected for only a few milliseconds to minimize the possibility of also losing too many signals from a wireless transmitter. Additionally, internal calibration is typically performed immediately after external calibration to minimize the possibility of any component in the SCS 10 drifting during the interval between external and internal calibration. The antenna is disconnected from the wideband receiver using two electronically controlled RF relays (not shown). An RF switch cannot provide perfect isolation between input and output even when in the "off" position, but can provide up to 70 dB of isolation. Two relays can be used in series to increase the amount of isolation and to further ensure that no signal leaks from the wideband receiver antenna during calibration. Similarly, when the internal calibration function is not being used, the internal calibration signal is disconnected and the RF relays are also disconnected to prevent any leakage of the internal calibration signals within the wideband receiver when the receiver is in use. collecting signals from wireless transmitters.

The external calibration procedure provides a single channel absolute calibration and the internal calibration procedure then calibrates all other channels relative to the channel that has been absolute calibrated. The combined signal is particularly suitable as a stable broadband signal because it can be easily generated using a stored replica of the signal and a digital-to-analog converter.

External calibration using a broadband calibration signal

The external calibration procedure described below can be used in connection with an SCS receiver system 10 characterized by a variable transfer function of time and frequency, preferably including the antennas, filters, amplifiers, duplexers, multi-connectors, splitters, and wiring associated with the SCS receiver system. The method includes the step of transmitting a known, stable broadband calibration signal from an external transmitter. The wideband calibration signal is then used to estimate the transfer function across the prescribed bandwidth of the SCS receiver system. Transfer function estimation is subsequently used to mitigate the effects of transfer function variation in subsequent TDOA / FDOA measurements. The external transmission is preferably of short duration and low power to avoid interference with the wireless communication system that houses the Wireless Location System.

In the preferred method, the receiving system of the SCS is synchronized with the external transmitter. Such synchronization can be done using GPS time units. Furthermore, the receiving system can be programmed to receive and process the full bandwidth of the calibration signal only at the time the calibration signal is being sent. The receiving system does not perform calibration processing at any time other than during synchronization with external calibration transmissions. In addition, a wireless communication link is used between the receiving system and the external calibration transmitter to exchange commands and responses. The external transmitter can use a directional antenna to direct the broadband signal only to the antennas of the SCS receiver system. Such a directional antenna can be a Yagi antenna (ie linear longitudinal radiation matrix). The calibration procedure preferably includes performing external transmission only when the directional antenna is directed at the antennas of the receiving system and the risk of multipath reflection is low.

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Station drift calibration

Another aspect of the present invention relates to the calibration procedure for correcting station drift in an SCS receiver system. "Station drift" is defined as the finite delay between when an RF signal from a wireless transmitter reaches the antenna and when the same signal reaches the broadband receiver. The inventive method includes the step of measuring the length of the cable from the antennas to the filters and determining the corresponding delays associated with the length of the cable. In addition, the method includes injecting a known signal into the RF filter, duplexer, multi-connector, or splitter and measuring the delay response and phase response versus frequency from the input of each broadband receiver device. The delay and phase values ​​are combined and then used to correct subsequent location measurements. When used with the GPS-based timing generation described above, the method preferably includes correcting the lengths of the GPS cable. Furthermore, an externally generated reference signal is preferably used to monitor changes in seasonal drift that may arise due to weather and aging. Finally, the station drift per RF channel and for each receiving system in the Wireless Location System is preferably stored in table form in the Wireless Location System for use in correcting post location processing.

Performance monitoring

The Wireless Location System uses procedures similar to calibration for performance monitoring on a regular and developed basis. These procedures are depicted in the flow charts of Figures 2K and 2L. Two performance monitoring procedures are used: landlines and conducting supervised point trials. The landline procedure comprises the following steps (see Figure 2K):

standard wireless transmitters are permanently placed at various points within the coverage area of ​​the Wireless Location System (these are hereinafter referred to as landlines) (step S-30);

the points where landlines have been placed are measured so that their location is accurately known within a predetermined distance, for example 3.05 meters (ten feet) (step S-31); the measured locations are stored in a table in the AP 14 (step S-32);

landlines are allowed to register with the wireless communication system, at a rate and intervals set by the wireless communication system for all wireless transmitters in the system (step S-33) on each registration transmission by a landline phone , the Wireless Location System locates the landline using normal location processing (as with calibration transmitters, the Wireless Location System can identify a transmission as coming from a landline telephone by storing the identities in a table) (step S-34);

the Wireless Location System calculates an error between the calculated location determined by the location processing and the stored location determined by the measurements (step S-35);

the location, the error value and other measured parameters are stored together with the timestamp in a database in the AP 14 (step S-36);

the AP 14 monitors the instantaneous error and other measured parameters (collectively referred to as an extended location record) and additionally calculates various statistical values ​​of the errors and other measured parameters (step S-37) and if any of the errors or other values ​​exceed a predetermined threshold or historical statistical value, either instantaneously or after statistical filtering on a prescribed number of location estimates, the AP 14 signals an alarm to the operator of the Wireless Location System (step S-38).

The extended location log includes a large number of measured parameters useful for analyzing the instantaneous and historical performance of the Wireless Location System. These parameters include: the RF channel used by the wireless transmitter, the antenna ports used by the Wireless Location System to demodulate the wireless transmission, the antenna ports from which the Wireless Location System requested RF data, the peak, mean and variance in the transmission power during the interval used for location processing, the SCS 10 and the antenna port chosen for reference in location processing, the correlation value of the cross-spectrum correlation between each SCS 10 and antenna used in the location processing and the SCS 10 and reference antenna, the delay value for each baseline, the multipath mitigation parameters, and the residual values remaining after multipath mitigation calculations. Any of these measured parameters can be monitored by the Wireless Location System in order to determine the performance of the Wireless Location System. An example of the type of monitoring performed by the Wireless Location System may be the variance between the instantaneous value of the correlation at a baseline and the historical range of the correlation value. Another may be the variance between the instantaneous value of the received power in a particular antenna and the historical range of the received powers. Any other statistical value can be calculated and this list is not exhaustive.

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The number of landlines placed within the coverage area of ​​the Wireless Location System can be determined based on the density of cell sites, the difficulty of the terrain, and the historical ease with which wireless communications systems have operated in the area. area. Typically the ratio is approximately one landline phone for every six cell sites. However in some areas a one-to-one relationship may be required. Landlines provide a continuous means to monitor the performance of the Wireless Location System, as well as to monitor any changes to the frequency plan that the provider may make. Many times, changes in the frequency plan will cause a variation in the performance of the Wireless Location System and monitoring the performance of landlines provides an immediate indication to the operator of the Wireless Location System.

Conducting supervised point trials is very similar to monitoring landlines. Landline telephones can typically only be located indoors where power is accessible (ie telephones must be continuously powered to be effective). In order to have a more complete measurement of the performance of the location, the conduction of tests of external test points is also carried out. With reference to Figure 2L, as with landlines, prescribed test points are measured throughout the coverage area of ​​the Wireless Location System within 3.05 meters (ten feet) (step S-40). Each test point is assigned a code, in which the code consists of either a "*" or a "#", followed by a sequence of numbers (step S-41). For example, "* 1001" to "* 1099" can be a sequence of 99 codes used for test points. These codes should be sequences, which when marked, have no meaning to the wireless communication system (ie the codes do not produce a feature or other translation takes place in the MSC, except for an intercept message). The AP 14 stores the code for each test point along with the measured location (step S-42). After these initial stages, any wireless transmitter that dials any of the codes will be activated and located using normal location processing (steps S-43 and S-44). The Wireless Location System automatically calculates an error between the calculated location determined by the location processing and the stored location determined by measurements, and the location and error value are stored together with the timestamp in a database in the AP 14 (stages S-45 and S-46). The AP 14 monitors the instantaneous error as well as various statistical error values. If the error values ​​exceed a predetermined threshold or historical statistical value, either instantly or after performing statistical filtering through a prescribed number of location estimates, the AP 14 sends an alarm signal to the operator of the Wireless Location System. (step S-47).

TDOA Location Processor (TLP)

The TLP 12, depicted in Figures 1, 1A, and 3, is a centralized digital signal processing system that manages many aspects of the Wireless Location System, especially SCS 10, and provides control over all location processing. Because location processing is DSP intensive, one of the main advantages of TLP 12 is that DSP resources can be shared between location processing initiated by transmissions on any of the SCS 10 in a Location System. Wireless That is, the additional cost of the DSPs in the SCS 10 is reduced by having the resources available centrally. As shown in Figure 3, there are three main components of the TLP 12: DSP modules 12-1, T1 / E1 communication modules 12-2, and a controller module 12-3.

The T1 / E1 12-2 communication modules provide the communication interface to the SCS 10 (T1 and E1 are standard communication speeds available worldwide). Each SCS 10 communicates with a TLP 12 using one or more DS0s (which are typically 56 kbps or 64 kbps). Each SCS 10 is typically connected to a fractional T1 or E1 circuit, using, for example, an extraction and insertion unit or a bank of channels at the cell site. Frequently, this circuit is shared with the base station, which communicates with the MSC. At a central site, the DS0 assigned to the base station is separated from the DS0 assigned to the SCS 10. This is typically done external to the TLP 12 using a digital access and control system (DACS) 13A that not only separates the DS0s but also it also prepares the DS0s of multiple SCS 10s in complete T1 or E1 circuits. These circuits are then connected from DACS 13A to DACS 13B and then to the T1 / E1 communications module in TLP 12. Each T1 / E1 communications module contains enough digital memory to temporarily store data packets to and from each SCS 10 that communicates. with the module. A single TLP chassis can support one or more T1 / E1 communication modules.

DSP 12-1 modules provide a common pool resource for location processing. A single module can typically contain two to eight digital signal processors, each of which is equally available for location processing. Two types of location processing are supported: central-based and station-based, which are described in more detail below. The TLP 12-3 controller handles DSP 12-1 modules for optimal performance. Each DSP module contains enough digital memory to store all the data necessary for location processing. A DSP will not be involved until all the data necessary to begin location processing has been moved from each of the SCS 10 involved into the digital memory of the DSP module. Only then is a DSP assigned the specific task of locating a specific wireless transmitter. Using that technique, DSPs, which are an expensive resource, are never kept waiting, a single TLP chassis can support one or more DSP modules.

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Controller module 12-3 provides real-time management of all location processing within the Wireless Location System. The AP 14 is the top-level management entity within the Wireless Location System, however its database architecture is not fast enough to perform real-time decision making when transmission takes place. The controller module 12-3 receives messages from the SCS 10, including: status, spectral energy on various channels for various antennas, demodulated messages, and diagnostics. This allows the controller to continuously determine events that occur in the Wireless Location System, as well as to send orders to take certain actions. When a controller module receives demodulated messages from SCS 10, the controller module decides whether location processing is required for a particular wireless transmission. Controller module 12-3 also determines which SCS 10 and antennas to use in location processing, including whether to use central-based or station-based location processing.

The controller module instructs the SCS 10 to return the necessary data and sequentially instructs the communication modules and DSP modules to perform their necessary roles in location processing. These stages are described in more detail below.

The 12-3 controller module maintains a table known as the Signal of Interest Table (SOIT). This table contains all the criteria that can be used to trigger location processing on a particular wireless transmission. Criteria may include, for example, Mobile Identity Number, Mobile Station ID, Electronic Serial Number, dialed digits, system ID, RF channel number, cell site number, or sector number , type of transmission and other types of data elements. Some of the trigger items may have higher or lower priority levels associated with them for use in determining the order of processing. Triggers of the highest priority location will always be processed before the lowest priority location triggers. However, a lower priority trigger that has already started location processing completes processing before it is assigned to a higher priority task. The master Task Assignment List for the Wireless Location System is kept in the AP 14 and copies the Task Assignment List is automatically downloaded to the Table of Signals of Interest in each TLP 12 in the Wireless Location System. The complete Signals of Interest Table is downloaded to a TLP 12 when the TLP 12 is first reset or started. After these two events, only the changes are downloaded from AP 14 to each TLP 12 to conserve communication bandwidth. The TLP 12 to AP 14 communications protocol preferably contains sufficient redundancy and error checking to prevent incorrect data ever being entered into the Signals of Interest Table. When the AP 14 and TLP 12 periodically have a spare processing capacity available, the AP 14 reconfirms the entries in the Sign of Interest Table to ensure that all entries in the Table of Signals of Interest in the Wireless Location System they are in complete synchronization.

Each TLP chassis has a maximum capacity associated with the chassis. For example, a single TLP chassis may only have enough capacity to support between 48 and 60 SCS 10. When a wireless communication system is larger than the capacity of the single TLP chassis, multiple TLP chassis are connected together using Ethernet networking. Controller module 12-3 is responsible for communications and networking between TLPs and communicates with controller modules in other TLP chassis and with Application Processors 14 over the Ethernet network. Communications between TLPs are required when location processing requires the use of SCS 10 that are connected to different TLP chassis. Location processing for each wireless transmission is assigned to a single DSP module in a single TLP chassis. Controller modules 12-3 in TLP chassis select the DSP module on which to perform location processing and then route all RF data used in location processing to that DSP module. If RF data is required from the SCS 10s connected to more than one TLP 12, then the controller modules in all the required TLP chassis communicate to move the RF data from all the required SCS 10s to their respective connected TLPs 12 and then to the DSP module and TLP chassis assigned to the location processing. The controller module supports two totally independent Ethernet networks for redundancy. A break or failure in any of the networks causes the affected TLPs 12 to immediately shift all communications to the other network.

Controller modules 12-3 maintain a complete network map of the Wireless Location System, including the SCS 10 associated with each TLP chassis. The network map is a table stored in the controller module that contains a list of candidate SCS / antennas that can be used in location processing and various parameters associated with each of the SCS / antennas. The structure of an example network map is depicted in Figure 3A. There is a separate entry in the table for each antenna connected to an SCS 10. When wireless transmission occurs in an area that is covered by an SCS 10 communicating with more than one TLP chassis, the controller modules in the TLP chassis involved determine what TLP chassis will be the “master” TLP chassis for the purpose of managing location processing. Typically, the TLP chassis associated with the SCS 10 that is assigned the primary channel for wireless transmission is the one assigned as the master. However, other TLP chassis can be assigned instead if that TLP temporarily does not have DSP resources available for location processing or if most of the SCS 10 involved in location processing are connected to other TLP chassis and the controller module are minimizing communications between TLPs. This decision-making process is totally dynamic, but

ES 2 386 669 T3 is aided by tables in TLP 12 that predetermine the preferred TLP chassis for each primary channel assignment. Tables are created by the Wireless Location System operator and programmed using the Network Operations Console.

The networking described in this document works both for TLP chassis associated with the same wireless provider, as well as for chassis that overlap or at the edge of a coverage area between two wireless providers. Thus it is possible that a TLP 12 belonging to a first wireless provider is networked and therefore receives RF data from a TLP 12 (and the SCS 10 associated with that TLP 12) belonging to a second wireless provider. This networking is particularly valuable in rural areas, where Wireless Location System performance can be improved by deploying SCS 10 in cell sites of multiple wireless providers. Since in many cases wireless providers do not co-locate cell sites, this feature allows the Wireless Location System to access more geographically diverse antennas than might be available if the Wireless Location System used only single cell sites. wireless provider. As described below, the proper selection and use of antennas for location processing can improve the performance of the Wireless Location System.

The controller module 12-3 passes many messages, including location registers, to the AP 14, many of which are described below. Typically, however, demodulated data is not passed from TLP 12 to AP 14. If, however, the TLP 12 receives demodulated data from a particular wireless transmitter and the TLP 12 identifies the wireless transmitter as being a registered customer of a second wireless provider in a different coverage area, the TLP 12 may pass the demodulated data to the first (in service) AP 14A. This will allow the first AP 14A to communicate with the second AP 14B associated with the second wireless provider and determine if the particular wireless transmission has been registered with any type of location services. If so, the second AP 14B may instruct the first AP 14A to locate the identity of the particular wireless transmission within the Table of Signals of Interest so that the particular wireless transmitter is located whenever the particular wireless transmitter is in the area. coverage of the first Wireless Location System associated with the first AP 14A. When the first Wireless Location System has detected that the particular wireless transmitter has not registered for a period of time that exceeds a predetermined threshold, the first AP 14A may instruct the second AP 14B that the identity of the particular wireless transmitter be removed. of the Table of Signals of Interest for the reason that it is no longer present in the coverage area associated with the first AP 14A.

Diagnostic port

The TLP 12 supports a diagnostic port that is highly useful in the operation and diagnosis of problems within the Wireless Location System. This diagnostic port can be accessed both locally on a TLP 12 and remotely through the Ethernet network that connects the TLP 12 to APs. The diagnostic port allows the operator to write to a file all RF and demodulation data received from the SCS 10, as well as the intermediate and final results of all location processing. This data is erased from the TLP 12 after location estimate processing and thus the diagnostic port provides the means to save the data for further post-processing and analysis. The inventors' experience in operating large-scale wireless location systems is that a small number of location estimates can occasionally have very large errors, and these large errors can dominate the overall performance statistics of the Wireless Location System at a time. throughout any measurement period. Therefore, it is important to provide the operator with a set of tools that allow the Wireless Location System to detect and trace the cause of very large errors in order to diagnose and mitigate these errors. The diagnostic port can be set to obtain the above information for all location estimates, for location estimates of particular wireless transmitters or at particular test points, or for location estimates that satisfy a certain criterion. For example, for landlines or test conduction of measured points, the diagnostic port determines the error in the real-time location estimate and then writes the information described above only for those location estimates whose error exceeds a predetermined threshold. The diagnostic port determines the error in real time by storing the measured latitude, longitude coordinates of each landline and test conduction point in a table and then a radial error calculation is performed between a location estimate for the corresponding test point.

Redundancy

The TLP 12 implement redundancy using various inventive techniques, allowing the Wireless Location System to support an M plus N redundancy procedure. M plus N redundancy means that N redundant (or spare) TLP chassis are used to provide a full redundant reservation to M TLP chassis online. For example, M can be ten and N can be two.

First, the controller modules in different TLP chassis continually exchange status and “heartbeat” messages at predetermined time intervals with each other and with each AP 14 assigned to monitor the TLP chassis. Therefore, each controller module has continuously and completely the state of each of the others.

ES 2 386 669 T3 controller modules in the Wireless Location System. Controller modules in different TLP chassis periodically select a controller module in a TLP 12 to be the master controller for a group of TLP chassis. The master controller may decide to place a first TLP chassis in an offline state if the first TLP 12A reports a failure or degradation condition in its status message or if the first TLP 12A fails to report any status or heartbeat messages within your allotted and predetermined time. If the master controller places a first TLP 12A in an offline state, the master controller can assign a second TLP 12B to perform redundant switchover and take over the tasks of the first TLP 12A offline. The configuration that has been loaded into the first TLP 12A is automatically sent to the second TLP 12B; This configuration can be downloaded either from the master controller or from an AP 14 connected to the TLPs 12. The master controller can be a controller module of any one of the TLP 12 that is not in an offline state, however there is a preference that the master controller be a controller module in a backup TLP 12. When the master controller is a controller module in a standby TLP 12, the time required to detect a failing first TLP 12A, place the first TLP 12A in an offline state, and then perform redundant switching.

Second, all T1 or E1 communications between the SCS 10 and each of the T1 / E1 communications modules 12-2 are preferably routed through a highly reliable DACS that is dedicated to redundancy control. The DACS 13B connects to each prepared T1 / E1 circuit containing DS0 of the SCS 10 and also connects to each T1 / E1 communication module 12-2 of each TLP 12. Each controller module in each TLP 12 contains a DACS 13B map that describes the DACS connection list and port assignments. This DACS 13B connects to the Ethernet network described above and can be controlled by any of the 12-3 controller modules in any of the 12 TLPs. When the second TLP 12 is placed in an offline state by the master controller, the master controller sends commands to DACS 13B to switch the T1 / E1 ready circuit communicating with the first TLP 12A to a second TLP 12B that has been in. a state of reserve. At the same time, the AP 14 downloads the complete configuration file that has been in use for the second (and now offline) TLP 12B to the third (and now online) TLP 12C. The time from first detection of a first TLP chassis in failure to complete changeover and assumption of processing responsibilities by a third TLP chassis is typically less than a few seconds. In many cases, no RF data is lost by the SCS 10 associated with the first failing TLP chassis and location processing can continue without interruption. At the time of a TLP failure when a first TLP 12A has been placed in an offline state, the NOC 16 creates an alert to notify the Wireless Location System operator that the event has occurred.

Third, each TLP chassis contains redundant power supplies, fans, and other components. A TLP chassis can also support multiple DSP modules, so the failure of a single DSP module or even a single DSP in a DSP module reduces the overall amount of available processing resources but does not cause the failure of the TLP chassis. In all other cases described in this paragraph, the failing component of the TLP 12 can be replaced without placing the entire TLP chassis in an offline state. For example, if a single power supply fails, the redundant power supply has enough capacity to support only the chassis load. The failing power supply contains the necessary circuitry to remove itself from the load on the chassis and not cause additional degradation to the chassis. Similarly, a failed DSP module can also remove itself from the live parts of the chassis, so that it does not cause a failure of the motherboard or other modules. This allows the rest of the chassis, including a second DSP module, to continue to function normally. Naturally, the overall throughput of the chassis is reduced but a total failure is avoided.

Application Processor (AP) 14

The AP 14 is a centralized database system, comprising a number of software processes that manage the complete Wireless Location System, provide interfaces to external users and applications, store location records and configurations, and support various functionalities related to location. app. The AP 14 uses a commercial hardware platform that is sized to accommodate the performance of the Wireless Location System. The AP also uses a commercial relational database system (RDBMS), which has been significantly customized to provide the functionality described herein. While the SCS 10 and the TLP 12 preferably work together in a pure real-time mode to determine location and create location records, the AP 14 can operate in both a real-time mode to store and send location records as well as in a non-real-time mode to post-process location records and provide access and reports over time. The ability to store, retrieve, and post-process location records for various types of application systems and analysis has proven to be a powerful advantage of the present invention. The main collection of software processes is known as the ApCore, shown in Figure 4 and includes the following functions:

The AP Performance Watchdog (ApPerfGuard) is a dedicated software process that is responsible for starting, stopping, and monitoring most other ApCore processes as well as ApCore's communications with the NOC 16. Upon receiving an update command from the configuration from the NOC, the ApPerfGuard updates the database and notifies all other processes of the change. The ApPerfGuard starts and stops the appropriate processes when the NOC instructs the ApCore to enter specific run states and monitors

ES 2 386 669 T3 constantly all other software processes scheduled to run to restart them if they have exited or stopped and restart any process that is not already responding properly. ApPerfGuard is assigned one of the highest processing priorities so that this process cannot be blocked by other "escaped" processes. The ApPerfGuard also has dedicated memory that is not accessible by other software processes to prevent any possible corruption from other software processes.

The AP Dispatcher (ApMnDsptch) is a software process that receives location records from TLPs 12 and forwards the location records to other processes. This process contains a separate thread for each physical TLP 12 configured in the system and each thread receives location records from that TLP 12. For system reliability, the ApCore maintains a list containing the last location register sequence number received from each TLP 12 and sends this sequence number to TLP 12 after the initial connection. Subsequently, the AP 14 and the TLP 12 maintain a protocol whereby the TLP 12 sends each location record with a unique identifier. ApMnDsptch sends location records to multiple processes, including Ap911, ApDbSend, ApDbRecvLoc, and ApDbFileRecv.

The AP Task Assignment Process (ApDbSend) controls the Task Assignment List within the Wireless Location System. The Task Assignment List is the master list of all activation criteria that determine which wireless transmitters will be located, which applications created the criteria, and which applications can receive location record information. The ApDbSend process contains a separate thread for each TLP 12, through which the ApDbSend synchronizes the Task Assignment List with the Table of Signals of Interest in each TLP 12. The ApDbSend does not send application information to the Table of Signals of Interest, only the activation criteria. Therefore the TLP 12 does not know why a wireless transmitter should be located. The Task Assignment List allows wireless transmitters to be located based on Mobile Identity Number (MIN), Mobile Station Identifier (MSID), Electronic Serial Number (ESN) and other identity numbers, dialed sequences of characters and / or digits, Local System ID (SID), cell site and sector of origin, RF channel of origin or type of message. The Task Assignment List allows multiple applications to receive location records from the same wireless transmitter. Thus, a single location record from a wireless transmitter that has dialed "911" can be sent, for example, to a PSAP 911, a fleet management application, a traffic management application, and a traffic management application. RF optimization.

The Task Assignment List also contains a variety of markers and fields for each trigger criteria, some of which are described elsewhere in this specification. A marker, for example, specifies the maximum time limit before the Wireless Location System must provide a rough or final estimate of the wireless transmitter. Another marker allows location processing to be disabled for a particular trigger criteria such as the identity of the wireless transmitter. Another field contains the authentication required to make changes to the criteria for a particular activation; authentication allows the operator of the Wireless Location System to specify which applications are authorized to add, delete or make changes to any activation criteria and associated fields or markers. Another field contains the Location Grade of Service associated with the activation criteria; the Grade of Service indicates to the Wireless Location System the desired level of precision and priority level for the location processing associated with a particular activation criteria. For example, some applications may be satisfied with a rough location estimate (perhaps for a reduced location processing fee), while other applications may be satisfied with low priority processing that does not guarantee completion for any given transmission. (and that can be bypassed by high priority processing tasks). The Wireless Location System includes means to support the use of wildcards for the activation criteria in the Task Assignment List. For example an activation criterion can be entered as "MIN = 215555 ****". This will cause the Wireless Location System to activate location processing for any wireless transmitter whose MIN begins with the six digits 215555 and ends with any four digits. Wildcard characters can be placed in any position in a trigger criteria. This feature can save the number of memory locations required in the Task Assignment List and the Signals of Interest Table by grouping related wireless transmitter blocks together.

The ApDbSend also supports dynamic task assignment. For example, the MIN, ESN, MSID or other identity of any wireless transmitter that has dialed “911” will automatically be placed on the Task Assignment List by ApDbSend for one hour. Therefore, any additional transmissions from the wireless transmitter that dialed “911” are also located in cases of additional emergency. For example, if a PSAP calls back a wireless transmitter that has dialed “911” in the last hour, the Wireless Location System will activate on the response message to paging the wireless transmitter and can make this wireless transmitter available to the PSAP. new location record. This dynamic task assignment can be set for any time interval after a start event and for any type of trigger criteria. The ApDbSend process is also a server for task assignment requests received from other applications. These applications, such as a fleet management, can send task assignment requests through a direct connection, for example. These applications can either place or remove trigger criteria. The ApDbSend performs an authentication process with each application to verify that the application has been authorized to place or remove activation criteria and each application can only change the activation criteria

ES 2 386 669 T3 related to that application.

The AP 911 (Ap911) process manages each interface between the Wireless Location System and the elements of the E9-1-1 network, such as tandem switches, selective routers, ALI databases and / or the PSAPs. The Ap911 process contains a separate wire for each connection to an E9-1-1 network element and can support more than one wire for each network element. The Ap911 process can operate simultaneously in many modes based on user settings and as described herein. Processing the E9-1-1 location registers on time is one of the highest processing priorities on the AP 14 and therefore the Ap911 runs entirely in random access memory (RAM) to avoid lag. associated with first storing and then retrieving a location record from any type of disk. When the ApMnDsptch sends a location record to Ap911, the Ap911 immediately performs a routing determination and sends the location record through the appropriate interface to network element E9-1-1. A separate process, running in parallel, records the location records within the aP 14 database.

The AP 14, through the Ap911 process and other processes, supports two modes of providing location records to applications, including the E9-1-1: the "push" and "pull" modes. Applications that require push mode receive a location record as soon as it is available on the AP 14. This mode is especially effective for the E9-1-1 which has a very critical time need for location records, as E9-1-1 networks must route wireless 9-1-1 calls to the correct PSAP in a few seconds after the wireless caller has dialed “911”. Applications requesting pull mode do not automatically receive location records, but instead must send a query to the AP 14 regarding a particular wireless transmitter to receive the latest, or any other location record, on the wireless transmitter. . The query from the application can specify the last location record, a series of location records, or all location records that satisfy a specific time or other criteria, such as the type of transmission. An example of the use of pull mode in the case of a “911” call is that the E9-1-1 network first receives the voice part of the “911” call and then they query the AP 14 to receive the location record. associated with that call.

When the Ap911 process is connected to many elements of the E9-1-1 network, the Ap911 must determine which element of the E9-1-1 network to push the locate record to (assuming “push” mode is selected) . The AP 14 makes this determination using a dynamic routing table. The dynamic routing table is used to divide a geographic region into cells. Each cell, or entry, in the dynamic routing table contains the routing instructions for that cell. It is well known that a minute of latitude is 1.03 kilometers (6083 feet), which is approximately 111 meters (365 feet) per thousandth of a degree. Additionally, each minute of longitude is the cosine (latitude) times 1.83 kilometers (6083 feet), which for the Philadelphia area is approximately 1.42 kilometers (4659 feet) or approximately 85.3 meters (380 feet) per thousandth. degree. A table of size of one thousand per thousand or one million cells, can thus contain a routing table for an area that is approximately 111 km (69 miles) by 85.3 km (53 miles) that is larger than the area Philadelphia in this example and each cell could contain a geographic area of ​​112 m (365 ft) by 85.3 m (280 ft). The number of bits allocated to each entry in the table should only be sufficient to support the maximum number of routing possibilities. For example, if the total number of routing possibilities is sixteen or less, then the memory for the dynamic routing table is one million times four bits, or half a megabyte. Using this scheme, an area the size of Pennsylvania could be contained in a table of approximately twenty megabytes or less, with extensive routing possibilities available. Given the relatively inexpensive cost of memory, this inventive dynamic routing table provides the AP 14 with a means to quickly push location records for "911" calls only to the appropriate E9-1-1 network element.

The AP 14 allows each entry in the dynamic router to be populated using manual or automatic means. Using automated means, for example, an electronic mapping application can create a polygon definition of the coverage area of ​​a specific E9-1-1 network element, such as a PSAP. The definition of the polygon is then translated into a list of latitude and longitude points contained within the polygon. The cell of the dynamic routing table corresponding to each latitude point, longitude, is then given the routing instruction for that element of the E9-1-1 network that is responsible for that geographic polygon.

When the Ap911 process receives a "911" location record for a specific wireless transmitter, the Ap911 converts the latitude, longitude, to the address of a specific cell in the dynamic routing table. The Ap911 then consults the cell to determine the routing instructions, which can be the push or pull mode and the identity of the E9-1-1 network element responsible for serving the geographic area in which the call "911 ”. If push mode has been selected, then the Ap911 automatically pushes the locate record to the E9-1-1 network element. If pull mode has been selected, then the Ap911 places the location record in a circular table of "911" location records and waits for a query.

The dynamic routing means described above involves the use of a geographically defined database that can be applied to other applications besides 911 and therefore supported by other processes besides Ap911. For example the AP 14 can automatically determine the billing zone from which a wireless call was placed for a Location Sensitive Billing application. In addition, the

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AP 14 can automatically send an alert when a particular wireless transmitter has entered or left a prescribed geographic area defined by an application. The use of particular geographic databases, dynamic routing actions, any other location-triggered actions are defined in the fields and markers associated with each trigger criteria. The Wireless Location System includes means to easily manage these geographically defined databases using an electronic map that can create polygons encompassing a prescribed geographic area. The Wireless Location System extracts from the electronic map a table of latitude and longitude points contained within the polygon. Each application can use its own set of polygons and can define a set of actions to be taken when a location record for an activated wireless transmission is contained within each polygon in the set.

The AP database reception process (ApDbRecvLoc) receives all location records from the ApMnDsptch through shared memory and places the location records into the AP location database. The ApDbRecvLoc starts ten threads and each one retrieves location records from shared memory, validates each record before inserting the records into the database, and inserts the records into the correct location records partition in the database. To preserve integrity, location records with any type of error are not written to the location records database but are instead placed in an error file that can be reviewed by the operator of the Wireless Location System. and then manually enter it into the database after resolution of the error. If the location database has failed or has been placed in an offline state, the location records are written to a flat file from where they can be further processed by the ApDbFileRecv.

The AP file receiving process (ApDbFileRecv) reads flat files containing location records and inserts the records into the location database. Flat files are a security mechanism used by the AP 14 to fully reserve the integrity of the AP 14 in all cases except a complete failure of the hard drives. There are several different types of flat files read by ApDbFileRecv, including Database Crash, Synchronization, Overflow, and Bug Fix. Drop Database flat files are written by the ApDbRecvLoc process if the location database is temporarily inaccessible; This file allows the AP 14 to ensure that location records are preserved during the occurrence of this type of problem. Synchronization flat files are written by the ApLocSync process (described below) when location records are transferred between pairs of redundant AP systems. The Overflow flat files are written by the ApMnDsptch when the location records are arriving at the AP 14 at a faster rate than the ApDbRecvLoc can process and insert the records into the location database. This can happen during periods of very high peak velocity. Overflow files prevent any logs from being lost during peak periods. The Bug Fix flat files contain the location records that had errors but have already been corrected and can now be inserted into the location database.

Because the AP 14 has a centralized role in the Wireless Location System, the architecture of the AP 14 has been designed to be completely redundant. A redundant AP 14 system includes fully redundant hardware platforms, fully redundant RDBMS, redundant disk drives, and redundant networks to each other, TLPs 12, NOCs 16, and external applications. The software architecture of the AP 14 is also designed to support fault tolerant redundancy. The following examples illustrate the functionality supported by redundant APs. Each TLP 12 sends location records to both the primary and redundant APs 14 when both APs are in an online state. Only the primary AP 14 will process incoming task assignment requests and only the primary AP 14 will accept configuration change requests from the NOC 16. The primary AP 14 then synchronizes with the redundant AP 14 under careful control. Both the primary and redundant APs will accept basic start and stop commands from the NOC. Both APs constantly monitor their own application health and system parameters and monitor the corresponding parameters of the other AP 14 and decide which AP 14 will be primary and which will be redundant based on a composite score. This composite score is determined by compiling the errors reported by multiple processes into a shared memory area and monitoring swap space and disk space. There are several processes dedicated to supporting redundancy.

The AP Location Synchronization Process (ApLocSync) runs on each AP 14 and detects the need to synchronize the location records between the APs and then creates the “synchronization records” that list the location records that need to be transferred. from one AP 14 to another AP 14. Location records are then transferred between APs using a direct connection. ApLocSync compares the location record partitions and location record sequence numbers stored in each location database. Typically, if both the primary and redundant APs 14 are functioning properly, synchronization is not needed because both APs are receiving location records simultaneously from the TLPs 12. However, if an AP 14 fails or is placed in an offline mode, then synchronization will be required later. The ApLocSync is notified when the ApMnDsptch connects to a TLP 12 so that it can determine whether or not synchronization is required.

The AP Task Assignment Synchronization Process (ApTaskSync) runs on each AP 14 and synchronizes the task assignment information between the primary AP 14 and the redundant AP 14. The ApTaskSync on the primary AP 14 receives the task assignment information from the ApDbSend and then sends the task information

ES 2 386 669 T3 assignment of tasks to ApTaskSync process on redundant AP 14. If the primary AP 14 had failed before the ApTaskSync had completed task replication, then the ApTaskSync will perform a full synchronization of the task assignment database when the failed AP 14 is brought back to an online state. .

The AP configuration synchronization process (ApConfigSync) runs on each AP 14 and synchronizes the configuration information between the primary AP 14 and the redundant AP 14. The ApConfigSync uses the RDBMS replication facility. The configuration information includes all the information needed by the SCS 10, TLP 12 and AP 14 for proper operation of the Wireless Location System in a wireless provider network.

In addition to the core functions described above, the AP 14 also supports a large number of processes, functions, and interfaces useful in the operation of the Wireless Location System, as well as useful for various applications that desire location information. While the processes, functions and interfaces described in this document belong in this section to AP 14, the implementation of many of these processes, functions and interfaces extends throughout the entire Wireless Location System and therefore its inventive value. it should not be read as being limited to AP 14 only.

Roaming

The AP 14 supports "roaming" between wireless location systems located in different cities or operated by different wireless providers. If a first wireless transmitter has subscribed to an application in a first Wireless Location System and therefore has an entry in the Task Assignment List in the first AP 14 in the first Wireless Location System, then the first wireless transmitter You can also subscribe to roaming. Each AP 14 and TLP 12 in each Wireless Location System contains a table in which a list of valid "local" subscriber identities is maintained. The list is typically a range and for example, for normal cell phones, the range can be determined by the NPA / NXX codes (or interchange area code) associated with the MIN or MSID of the cell phones. When a wireless transmitter meeting the "local" criteria makes a transmission, a TLP 12 receives demodulated data from one or more SCS 10 and checks the Trigger Information in the Signals of Interest Table. If any trigger criteria are satisfied, the location process begins on that transmission; otherwise, the transmission is not processed by the Wireless Location System.

When a first wireless transmitter that does not meet the "local" criteria transmits in a second Wireless Location System, the second TLP 12 in the second Wireless Location System checks the Table of Signals of Interest for an activation. One of three actions can occur: (i) if the transmission satisfies an existing criterion in the Table of Signals of Interest, the transmitter is located and the location record is sent from the second AP 14 in the second Wireless Location System to the first AP 14 in the first Wireless Location System; (ii) if the first wireless transmitter has a "roaming" entry in the Signals of Interest Table that indicates that the first wireless transmitter has "registered" with the second location system but has no trigger criteria, then the transmission it is not processed by the second Wireless Location System and the expiration timestamp is set as described below; (iii) if the first wireless transmitter does not have a "roaming" entry and therefore has not been "registered", then the demodulated data is passed from the TLP 12 to the second AP 14.

In the third case above, the second AP 14 uses the identity of the first wireless transmitter to identify the first AP 14 in the first Wireless Location System as the "local" Wireless Location System of the first wireless transmitter. The second AP 14 in the second Wireless Location System sends a query to the first AP 14 in the first Wireless Location System to determine if the first wireless transmitter has subscribed to any location application and therefore has any activation criteria in the Task Assignment List from the first AP 14. If a trigger is present on the first AP 14, the trigger criteria, along with any associated fields or markers, are sent from the first AP 14 to the second AP 14 and entered into the Task Assignment List and Signal Table. of Interest as a “itinerant” entry with the activation criteria. If the first AP 14 responds to the second AP 14 indicating that the first wireless transmitter has no activation criteria, then the second AP 14 “registers” the first wireless transmitter in the Task Assignment List and Signals of Interest Table as an “itinerant” without activation criteria. Therefore, both the current and future transmission from the first wireless transmitter can be positively identified by the TLP 12 in the second Wireless Location System as they have been registered without activation criteria and the second AP 14 is not required to make additional queries. to the first AP 14.

When the second AP 14 registers the first wireless transmitter with a roaming entry in the Assignment List of Tasks and the Table of Signals of Interest with or without trigger criteria, the roaming entry is assigned an expiration timestamp. The expiration timestamp is set to the current time plus a first predetermined interval. Each time the first wireless transmitter makes a transmission, the roaming entry timeout stamp in the Task Assignment List in the Signals of Interest Table is set to the current time of the most recent transmission in the first predetermined interval. . If he

ES 2 386 669 T3 first wireless transmitter does not make additional transmissions prior to the expiration of the timestamp of its roaming entry, then the roaming entry is automatically deleted. If, after deletion, the first wireless transmitter makes another transmission, then the registration process takes place again.

The first AP 14 and the second AP 14 maintain communications over a wide area network. The network can be based on TCP / IP or a protocol similar to the latest version of IS-41. Each AP 14 in communication with other APs in other wireless location systems maintains a table that provides the identity of each AP 14 and the Wireless Location System corresponding to each range of valid identities of wireless transmitters.

Multi-pass locating records

Certain applications may require a very fast estimate of the general location of a wireless transmitter, followed by a more accurate estimate of the location that can be sent later. This can be valuable, for example for E9-1-1 systems that handle wireless calls and must make a call routing decision very quickly, but may wait a little longer for a more exact location to be displayed on the terminal. E9-1-1 call taking electronic map. The Wireless Location System supports these applications with an inventive multi-pass location processing mode, described below. The AP 14 supports this mode with multi-pass location records. For certain entries, the Task Assignment List on AP 14 contains a marker indicating the maximum time limit before a particular application should receive a rough estimate of the location and a second maximum time limit in which an application individual should receive a final location estimate. For these certain applications, the AP 14 includes a marker in the location record that indicates the status of the location estimate contained in the record, which may, for example, be set to a first-pass estimate (i.e., approximate) or final step estimate. The Wireless Location System will generally determine the best location estimate within the time limit established by the application, that is, the Wireless Location System will process the maximum amount of RF data that can be supported within the time limit. Since any particular wireless transmission can trigger a location registration for one or more applications, the Wireless Location System supports multiple modes simultaneously. For example, a wireless transmitter with a particular MIN may dial "911". This can trigger a two-step location record for the E9-1-1 application, but a single-step location record for a fleet management application that is monitoring that particular MIN. This can be extended to any number of applications.

Modulation manifold and triggers

In wireless communication systems in dense urban or suburban areas, frequencies or channels can be reused multiple times within relatively short distances. Since the Wireless Location System is capable of independently detecting and demodulating wireless transmissions without the aid of the wireless communication system, a single wireless transmission can frequently be detected and successfully demodulated in multiple SCS 10 within the Wireless Location System. This can happen both intentionally and unintentionally. An unintended circumstance is caused by close frequency reuse, such as a particular wireless transmission that can be received above a predetermined threshold by more than one SCS 10, when each SCS 10 believes that it is monitoring only transmissions that happen only within of the cell-site located in conjunction with the SCS 10. An intentional event is produced by programming more than one SCS 10 to detect and demodulate transmissions that occur at a particular cell site on a particular frequency. As described above, this is generally used with adjacent or neighboring SCS 10 to provide system demodulation redundancy to further increase the probability that any particular wireless transmission will be detected and demodulated successfully.

Any type of event could potentially lead to multiple activations within the Wireless Location System, causing location processing to start multiple times for the same transmission. This results in an excess and inefficient use of processing and communication resources. Therefore, the Wireless Location System includes means for detecting when the same transmission has been detected and demodulated more than once and for selecting the best demodulating SCS 10 as the starting point for the location process. When the Wireless Location System successfully detects and demodulates the same transmission multiple times on multiple SCS / antennas, the Wireless Location System uses the following criteria to select the SCS / demodulation antenna to use to continue the process of determining whether to activate and possibly start the location processing (again, these criteria can be weighed in determining the final decision): (i) a jointly located SCS / antenna at the cell-site to which a particular frequency has been assigned is preferred over another SCS / antenna, but this preference can be adapted if there is no operational and online SCS / antenna jointly located at the cell site to which the particular frequency has been assigned, (ii) SCS / antennas with higher average SNR are preferred over those with lower average SNR and (iii) SCS / antennas with lower transmission demodulation bit errors are preferred over those with higher transmission errors. bits. The weighting applied

ES 2 386 669 T3 each of these preferences can be adjusted by the operator of the Wireless Location System to suit the particular design of each system.

Interface with the wireless communication system

The Wireless Location System contains means for communicating via an interface with the wireless communication system, such as a mobile switching center (MSC) or mobile positioning controller (MPC). That interface can be based, for example, on a standard secure protocol such as the latest version of the IS-41 or TCP / IP protocols. The formats, fields, and authentication aspects of these protocols are well known. The Wireless Location System supports a variety of command / response and informational messages through this interface which is designed to aid in the successful detection, demodulation and activation of wireless transmissions, as well as providing a means to pass location records to the wireless communication system. In particular, this interface provides means for the Wireless Location System to obtain information on which wireless transmitters have been assigned to particular voice channel parameters and particular cell sites. Example messages supported by the Wireless Location System over this interface to the wireless communication system include the following:

Inquiries on MIN / MDN / MSID / IMSI / TMSI Mappings - Certain types of wireless transmitters will transmit your identity in a familiar way that can be dialed over the telephone network. Other types of wireless transmitters transmit an identity that cannot be dialed, but which is translated into a number that can be dialed using a table within the wireless communication system. The transmitted identity is permanent in most cases, but it can also be temporary. Location application users connected to AP 14 typically prefer to place triggers on the Task Assignment List using identities that can be dialed. The identities that can be dialed are typically known as Mobile Directory Numbers (MDN).

The other types of identities for which translation may be required include Mobile Identity Number (MIN), Mobile Subscriber Identity (MSID), International Mobile Subscriber Identity (IMSI), and Temporary Mobile Subscriber Identity (TMSI). If the wireless communication system has enabled the use of encryption for any of these data fields of the messages transmitted by the wireless transmitters, the Wireless Location System may also query the encryption information along with the identity information. The Wireless Location System includes means for querying the wireless communication system for alternate identities for a trigger identity that has been placed on the Task Assignment List by a location application or for querying the wireless communication system for alternate identities to an identity that has been demodulated by an SCS 10. Other events can also trigger this type of query. For this type of inquiry, typically the Wireless Location System initiates the command and the wireless communication system responds.

Inquiry / Command Change on Voice RF Channel Assignment - Many wireless transmissions on voice channels do not contain identity information. Therefore, when the Wireless Location System is activated to perform location processing on a transmission on the voice channel, the Wireless Location System queries the wireless Communications system for the voice channel assignment information. current for the particular transmitter for which the Wireless Location System has been activated. For an AMPS transmission, for example, the Wireless Location System preferably requests the cell site, sector, and RF channel number currently in use by the wireless transmitter. For a TDMA transmission, for example, the Wireless Location System preferably queries the cell site, sector, RF channel number and timeslot currently in use by the wireless transmitter. Other pieces of information that may be required include the long code mask and encryption keys. In general, the Wireless Location System will initiate the command and the wireless communication system will respond. However, the Wireless Location System will also accept an activation order from the wireless communication system that contains the information detailed in this document.

The time setting in this command / response message is very critical since handovers on the voice channel can happen quite frequently in wireless communication systems. That is, the Wireless Location System will locate any wireless transmitter that is transmitting on a particular channel therefore the Wireless Location System and the wireless communication system must together ensure that the identity of the wireless transmitter and the channel assignment information voice are in perfect sync. The Wireless Location System uses various means to achieve this goal. The Wireless Location System can, for example, query the voice channel mapping information for a particular wireless transmitter, receive the necessary RF data, then query again the voice channel mapping information for the same wireless transmitter already then verify that the status of the wireless transmitter has not changed during the time that the RF data has been collected by the Wireless Location System. Location processing is not required to complete before the second query, since it is only important to verify that the correct RF data has been received. The Wireless Location System can also, for example as part of the first

ES 2 386 669 T3 query command to the wireless communication system to prevent a handover from taking place for the particular wireless transmitter during the period of time that the Wireless Location System is receiving the RF data. Then, after collecting the RF data, the Wireless Location System will again query the voice channel assignment information for the same wireless transmitter, it will instruct the wireless communication system to allow handovers again for said wireless transmitter and then verify that the status of the wireless transmitter has not changed during the time that the RF data was being collected by the Wireless Location System.

For various reasons, both the Wireless Location System and the wireless communication system may prefer that the wireless transmitter be assigned to another voice RF channel prior to performing location processing. Therefore, as part of the command / response sequence, The wireless communications system may instruct the Wireless Location System to temporarily suspend location processing until the wireless communications system has completed a handover sequence with the wireless transmitter and the wireless communications system has notified the Location System. Wireless that RF data can be received and the voice RF channel on which the data can be received. Alternatively, the Wireless Location System may determine that the particular voice RF channel a particular wireless transmitter is currently using is not suitable for obtaining an acceptable location estimate and request that the wireless communication system command the wireless transmitter for handover. Alternatively, the Wireless Location System may request that the wireless communication system instruct the wireless transmitter to handover to a series of voice RF channels in sequence to perform a series of location estimates, whereby the Wireless Location System can improve the accuracy of the location estimate through a series of handovers; this procedure is further described below.

The Wireless Location System can also use this set of command / response messages to query the wireless communication system for the identity of a wireless transmitter that has been using a particular voice channel (and time slot, etc.) in a particular cell location at a particular time. This allows the Wireless Location System to first perform location processing on transmissions without knowing the identities and then determine the identity of the wireless transmitters making the transmissions and add this information to the location register. This particular inventive feature allows the use of automatic sequential location of transmissions on the voice channel.

Trigger Reception - The Wireless Location System can receive triggers from the wireless communication system to perform location processing on a voice channel transmission without knowing the identity of the wireless transmitter. This set of messages bypasses the Task Assignment List and does not use the trigger mechanisms within the Wireless Location System. In contrast, the wireless communication system only determines which wireless transmissions to locate and then sends a command to the Wireless Location System to collect RF data from a particular voice channel at a particular cell site and perform the processing of the location. The Wireless Location System responds with a confirmation containing a timestamp of when the RF data was collected. The Wireless Location System also responds with a location record in an appropriate format when location processing has been completed. Based on the time of the order to the Wireless Location System and the response with the RF data collection timestamp, the wireless communication system determines if the status of the wireless transmitter subsequently changed to the order and if there is a good probability successful in collecting RF data.

Perform Transmission - The Wireless Location System can command the wireless communication system to force a particular wireless transmitter to perform a transmission at a particular time or within a prescribed time interval. The wireless communication system responds with a confirmation of a time or time interval in which to wait for the transmission. The types of transmissions that the Wireless Location System can force include, for example, audit responses and paging responses. Using this set of messages, the Wireless Location System can also command the wireless communication system to force the wireless transmitter to transmit using a higher power level setting. In many cases, wireless transmitters will try to use the lowest power level settings when transmitting to preserve battery life. To improve the accuracy of the location estimate, the Wireless Location System may prefer that the wireless transmitter use a higher power level setting. The wireless communication system responds to the Wireless Location System with a confirmation that the highest power level setting will be used and a time or time interval in which to wait for transmission.

Delay the response of the wireless communication system to mobile access - Some over-the-air interface protocols, such as CDMA, use a mechanism in which the wireless transmitter initiates transmissions on a channel, such as an Access Channel, for example, at a lower setting or a very low power level setting and then enters a sequence of stages in which (i) the wireless transmitter performs an access transmission; (ii) the wireless transmitter waits for a response from the communication system

ES 2 386 669 T3 wireless; (iii) if no response is received by the wireless transmitter from the wireless communication system within a predetermined time, the wireless transmitter increases its power level setting by a predetermined amount, and then returns to step (i) ; (iv) if the response is received by the wireless transmitter from the wireless communication system within a predetermined time, the wireless transmitter then enters a normal message exchange. This mechanism is useful to ensure that the wireless transmitter uses only the lowest useful power level setting for transmission and does not waste additional power or battery life. It is possible, however, that the lowest power level setting at which the wireless transmitter can successfully communicate with the wireless communication system is not sufficient to obtain an acceptable location estimate. Therefore, the Wireless Location System may instruct the wireless communication system to delay its response to these transmissions by a predetermined amount or time. The delay action will cause the wireless transmitter to repeat the sequence of steps (i) to (iii) one or more times than normal with the result that one or more access transmissions will be at a power level higher than normal. . The higher power level may preferably allow the Wireless Location System to determine a more accurate location estimate. The Wireless Location System can command this type of delay action for both a particular wireless transmitter, as well as for a particular type of wireless transmissions (for example, for all “911” calls), for wireless transmitters within a specified range. from the base station the transmitter is trying to communicate to or for all wireless transmitters in a particular area.

Send confirmation to wireless transmitter - The Wireless Location System does not include means within it to notify the wireless transmitter of an action because the Wireless Location System is unable to transmit; As described above the Wireless Location System can only receive transmissions. Therefore, if the Wireless Location System wishes to send, for example, a confirmation tone upon completion of a certain action, the Wireless Location System instructs the wireless communication system to transmit a particular message. The message may include, for example, an audible confirmation tone, spoken message or synthesized message to the wireless transmitter or a text message sent via a short message service or pager. The Wireless Location System receives confirmation from the wireless communication system that the message has been accepted and sent to the wireless transmitter. This set of command / response messages is important to enable the Wireless Location System to support certain end-user application functions such as Location Processing Prohibition.

Notify Location Logs - The Wireless Location System automatically reports location logs to the wireless communications system for those wireless transmitters assigned to notify the wireless communications system, as well as for those transmissions for which the wireless communications system initiated triggers. The Wireless Location System also notifies of any historical location records consulted by the wireless communication system and that the wireless communication system is authorized to receive.

Monitoring of the internal interfaces of the wireless communication system, status table

In addition to the above interface between the Wireless Location System and the wireless communication system, the Wireless Location System also includes means for monitoring the existing interfaces within the wireless communication system in order to intercept messages important to the Wireless Location System for the identification of wireless transmitters and the RF channels in use by these transmitters. These interfaces may include, for example, the "a-interface" and "the a-bis interface" used in wireless communication systems employing the GSM over-the-air interface protocol. These interfaces are well known and published in various standards. By monitoring bidirectional messages on these interfaces between base stations (BTS), base station controllers (BSC) and mobile switching centers (MSC) and other points, the Wireless Location System can obtain the same information about the assignment. from wireless transmitters to specific channels that the wireless communication system knows itself about. The Wireless Location System includes means to monitor these interfaces at various points. For example, the SCS 10 may monitor a BTS-to-BSC interface. Alternatively, a TLP 12 or AP 14 may also monitor a BSC in which a number of BTS-to-BSC interfaces have been concentrated. The internal interfaces to the wireless communication system are not encrypted and the layered protocols are known to those of skill in the art. The advantage for the Wireless Location System in monitoring these interfaces is that the Wireless Location System may not be required to independently detect and demodulate the control channel messages from the wireless transmitters. Furthermore, the Wireless Location System can obtain all the necessary voice channel assignment information from these interfaces.

Using these means for a transmission on the control channel, the SCS 10 receives the transmissions as described above and records the RF data from the control channel in memory without performing detection and demodulation. Separately, the Wireless Location System monitors messages that occur through prescribed interfaces within the wireless communication system and triggers the Wireless Location System when the Wireless Location System discovers a message that

ES 2 386 669 T3 contains a trigger event. Initiated by the activation event, the Wireless Location System determines the approximate time in which the wireless transmission occurred and instructs the first SCS 10 and a second SCS 10B each to search its memory for the beginning of the transmission. This first chosen SCS 10A is an SCS that is either located in conjunction with the base station to which the wireless transmitter has communicated or is an SCS that is adjacent to the base station to which the wireless transmitter has communicated. That is, the first SCS 10A is an SCS to which the control channel had been assigned as a primary channel. If the first SCS 10A successfully determines and reports the start of transmission, then location processing proceeds normally, using the means described below. If the first SCS 10A cannot successfully determine the start of transmission, then the second SCS 10B notifies the start of transmission and the location processing proceeds normally.

The Wireless Location System uses these means for transmissions on the voice channel. For all triggers contained in the Task Assignment List, the Wireless Location System monitors the prescribed interfaces for messages pertaining to those triggers. Messages of interest include, for example, voice channel assignment messages, handover messages, frequency hopping messages, power up / power down messages, directed retry messages, completion messages, and other action messages. and similar status. The Wireless Location System continuously maintains a copy of the status and status of these wireless transmitters and a Status Table on the AP 14. Each time the Wireless Location System detects a message that belongs to one of the entries in the Task Assignment List, the Wireless Location System updates its own Status Table. Subsequently, the Wireless Location System can be activated to perform location processing, such as in a regular time interval, and access the Status Table to accurately determine each cell site, sector, RF channel and time slot that is currently being used by the wireless transmitter. The example contained herein describes the means by which the Wireless Location System interfaces with a GSM-based wireless communication system. The Wireless Location System also supports similar functions with systems based on other over-the-air interfaces.

For certain over-the-air interfaces, such as CDMA, the Wireless Location System also maintains certain identity information obtained from the Access bursts on the control channel in the Status Table; this information is later used to decode the masks used by the voice channels. For example, the CDMA over-the-air interface protocol uses an electronic serial number (ESN) of a wireless transmitter to, in part, determine the long code mask used in encoding voice channel transmissions. The Wireless Location System keeps your information in the Status Table for Task Assignment List entries because many wireless transmitters can transmit the information only once; for example, many CDMA mobiles will only transmit their ESN during the first Access burst after the wireless transmitter becomes active in a geographic area. This ability to independently determine the long code mask is very useful in cases where an interface between the Wireless Location System and the wireless communication system is not operational and / or the Wireless Location System is not capable of monitoring. one of the internal interfaces of the wireless communication system. The Wireless Location System operator can optionally set the Wireless Location System to maintain identity information for all wireless transmitters. In addition to the above reasons, the Wireless Location System can provide voice channel tracking for all wireless transmitters that trigger location processing by calling "911". As described above, the Wireless Location System uses dynamic task assignment to provide a location of a wireless transmitter for a prescribed time after dialing "911", for example. By maintaining identity information for all wireless transmitters in the Status Table, the Wireless Location System is able to provide voice channel tracking for all transmitters in the event of a prescribed trigger event and not only those with previous entries in the Task Assignment List.

Application interface

Using the AP 14, the Wireless Location System supports a variety of standards-based end-user interfaces and provider location applications using secure protocols such as TCP / IP, X.25, SS-7, and IS-41. Each interface between the AP 14 and an external application is a secure and authenticated connection that allows the AP 14 to positively verify the identity of the application connecting to the AP 14. This is necessary because each connected application is granted only limited access to the location records in a real-time and / or historical mode. In addition, the AP 14 supports additional command / response, real-time, and post-processing functions that are described in more detail below. Access to these additional features also requires authentication. The AP 14 maintains a list of users and the authentication means associated with each user. No application can access location records or functions for which the application does not have the appropriate authentication or access rights. In addition, the AP 14 supports a complete record of all actions taken by each application in the event that problems arise or further investigation of the actions is required. For each command or function listed below, the AP 14 preferably supports a protocol in which each action or the result of each is confirmed, as appropriate.

ES 2 386 669 T3

Edit Task Assignment List - This command allows external applications to add, delete or edit entries in the Task Assignment List, including any fields or bookmarks associated with each entry. This command can be supported in a single entry mode, or in a batch entry mode in which a list of entries is included in a single command. The latter is useful, for example, in a mass application such as location-sensitive billing where large volumes of wireless transmitters are supported by the external application and it is desired to minimize protocol overhead. This command can add or delete applications for a particular entry in the Task Assignment List, however, this command cannot completely delete an entry if the entry also contains other applications not associated or authorized by the application sending the order.

Set location interval - The Wireless Location System can be set to process location at any interval for a particular wireless transmitter, both on the control and voice channels. For example, certain applications may require the location of a wireless transmitter every few seconds when the transmitter is busy on a voice channel. When the wireless transmitter makes an initial transmission, the Wireless Location System is initially activated using a standard entry in the Task Assignment List. If one of the fields or markers in this entry specifies the location update at a set interval, then the Wireless Location System creates a dynamic task in the Task Assignment List that is triggered by a timer instead of an identity. or other criteria conveyed. Each time the timer expires, which can range from one second to several hours, the Wireless Location System will automatically activate to locate the wireless transmitter. The Wireless Location System uses its interface with the wireless communication system to query the status of the wireless transmitter, including voice call parameters as described above. If the wireless transmitter is busy on a voice channel, then the Wireless Location System performs location processing. If the wireless transmitter is not engaged in any of the existing transmissions, the Wireless Location System will instruct the wireless communication system to make the wireless transmitter transmit immediately. When the dynamic task is set, the Wireless Location System also sets an expiration time in which the dynamic task ends.

End User Add / Delete - This command can be executed by an end user of a wireless transmitter to place the identity of the wireless transmitter on the Task Assignment List with location processing allowed, to remove the identity of the wireless transmitter from the Task Assignment List and thereby remove the identity as a trigger or to place the identity of the wireless transmitter on the Task Assignment List with location processing disabled. When location processing has been disabled by the end user, known as Prohibited Location Processing then no location processing will be performed for the wireless transmitter. The Wireless Location System operator may optionally select one of several actions by the Wireless Location System in response to a Prohibited Location Processing command by the end user: (i) the disable action can be superimposed on all other triggers on the Task Assignment List, including the trigger due to an emergency call such as "911", (ii) the disable action can be superimposed on any another trigger in the Task Assignment List, except a trigger due to an emergency call such as “911”, (iii) the disable action can be overridden by other triggers selected in the Task Assignment List. In the former case, the end user is given complete control over the privacy of transmissions by the wireless transmitter since no location processing will be performed on that transmitter for any reason. In the second case, the end user can still receive the benefits of localization during an emergency, but not at other times. In an example of the third case, an employer who is the actual owner of a particular wireless transmitter may override an end-user action by an employee who is using the wireless transmitter as part of their job but may not wish to be. located. The Wireless Location System can query the wireless communication system, as described above, to obtain the mapping of the identity contained in the wireless transmission to other identities.

Additions and deletions by the end user are made by marking sequences of characters and figures and pressing the "SEND" button or equivalent on the wireless transmitter. These sequences can be optionally chosen and can be known to the operator of the Wireless Location System. For example, a string might be "* 55 SEND" to disable location processing. Other sequences are also possible. When the end user can dial in this prescribed sequence, the wireless transmitter will transmit the sequence through one of the prescribed control channels of the wireless communication system. Since the Wireless Location System independently detects and demodulates all transmissions on the reverse control channel, the Wireless Location System can independently interpret the prescribed dial sequence and perform appropriate feature updates in the Task Assignment List. , as described above. When the Wireless Location System has completed updating the Task Assignment List, the Wireless Location System instructs the wireless communication system to send a confirmation to the end user. As described above, this takes the form of an audible tone, recorded or synthesized voice, or a text message. This command is executed through the interface between the Wireless Location System and the monitoring system.

ES 2 386 669 T3 wireless communications.

Command to transmit - This command allows applications external to the Wireless Location System to send a command to the wireless communication system to cause a particular wireless transmitter, or group of wireless transmitters, to transmit. This command may contain a marker or field that the wireless transmitter (s) must transmit immediately or at a prescribed time. This command includes the effort to locate the wireless transmitter (s) on demand, since the transmissions will be detected, demodulated and activated, causing location processing and the generation of a location record. This is useful in eliminating or reducing any delay in determining the location such as waiting until the next registration time period by the wireless transmitter or waiting for an independent transmission to occur.

Consultation and updating of external database - The Wireless Location System includes means to access an external database, consult said external database using the identity of the wireless transmitter or other parameters contained in the transmission or the activation criteria and to mix the data obtained from the external database with the data generated by the Wireless Location System to create a new improved location record.

The enhanced location record can then be sent to the requesting applications. The external database may contain, for example, data elements such as customer information, medical information, paid characteristics, application-related information, customer account information, contact information, or prescribed sets of actions to be taken following a location activation event. The Wireless Location System can also cause updates to the external database, for example, to increase or decrease a billing account associated with the provision of location services or to update the external database with the last associated location record. with the particular wireless transmitter. The Wireless Location System contains means to perform the actions described herein in more than one external database. The list and sequence of external databases to be accessed and the subsequent actions to be taken are contained in one of the fields contained in the activation criteria in the Task Assignment List.

Random Anonymous Location Processing - The Wireless Location System includes means for performing large scale random anonymous location processing. This feature is valuable for certain types of applications that require the collection of a large volume of data on a population of wireless transmitters without regard to the specific identities of individual transmitters. Applications of this type include: RF optimization, which allows wireless providers to measure the performance of the wireless communication system by simultaneously determining the location and other parameters of the transmission; Traffic Management, which allows affected government and commercial agencies to monitor the flow of traffic on various highways using statistically significant samples of wireless transmitters traveling in vehicles and Local Traffic Estimation, which allows commercial companies to estimate the flow of traffic around a particular area which can help determine the viability of a particular business.

Applications requesting random anonymous location processing optionally receive location records from two sources: (i) a copy of location records generated by other applications and (ii) location records that may have been randomly triggered by the System. of Wireless Location without regard to any specific criteria. All location records generated from any source are sent with all identity and activation criteria information removed from the location records; however, the requesting application (s) can determine whether the record was generated from a totally random process or is a copy of another trigger criteria. Random location records are generated by a low priority task within the Wireless Location System that performs location processing on randomly selected transmissions as long as processing and communications resources are available and otherwise unused in an instant. of particular time. The requesting application (s) may specify whether the random location processing is performed over the entire coverage area of ​​the Wireless Location System, over specific geographic areas such as along prescribed highways or through specific cell site coverage areas. . Therefore, the requesting application or applications can direct the resources of the Wireless Location System to that area of ​​greatest interest for each application. Depending on the randomness desired by the application or applications, the Wireless Location System can adjust the preferences to randomly select certain types of transmissions such as log messages, source messages, pager response messages or transmissions on the radio channel. voice.

Anonymous geographic group tracking - The Wireless Location System includes means to trigger location processing repetitively for anonymous groups of wireless transmitters within a prescribed geographic area. For example, a particular location application may wish to monitor the path of travel of a wireless transmitter over a prescribed period of time, but without the Wireless Location System revealing the particular identity of the wireless transmitter. The time period can be many hours, days, or weeks. Using the means, Wireless Location System: select

ES 2 386 669 T3 randomly a wireless transmitter that initiates a transmission in the geographic area of ​​interest for the application; performs location processing in the transmission of interest; irreversibly translates and encodes the identity of the wireless transmitter into a new encoded identifier; creates a location record using only the new encoded identifier as a means of identification; sends the location record to the requesting location application (s); and creates a dynamic task in the Task Assignment List for the wireless transmitter, in which the dynamic task has an associated expiration period. Subsequently, when the prescribed wireless transmitter initiates transmission, the Wireless Location System must activate using the dynamic task, perform location processing on the transmission of interest, irreversibly produce and encode the identity of the wireless transmitter in the new identifier. encoded using the same means as before so that the encoded identifier is the same, creating a location record using the encoded identifier and submitting the location record to the requesting location application (s). The means described in this document can be combined with other functions of the Wireless Location System that to carry out this type of supervision uses the transmissions on either the control or voice channel. Additionally, the means described herein fully preserve the private identity of the wireless transmitter, and furthermore allow other kinds of applications to monitor the travel paths of wireless transmitters. These kinds of applications can be of great value in determining highway planning and design, alternate route planning, or construction of commercial and retail spaces.

Grouping, Classifying and Labeling of Location Records - The Wireless Location System includes means for post-processing the location records for certain requesting applications to group, classify or label the location records. For each interface supported by the Wireless Location System, the Wireless Location System stores a profile of the types of data for which the application is both authorized and requester and the types of filters or post-processing actions desired by the application. Many applications, such as the examples contained herein, do not require individual location records or specific identities of individual transmitters. For example, an RF optimization application deduces more value from a large set of location record data for a particular cell site or channel than it would deduce from any individual location record. As another example, a traffic monitoring application requires only transmitter location records that are on prescribed roads or highways and additionally requires that these records be grouped by road or highway section and by direction of travel. Other applications may request that the Wireless Location System send location records that have been formatted to improve display appearance by, for example, adjusting the transmitter location estimate so that the transmitter location appears on an electronic map. directly on a road segment drawn the place of adjacent to the portfolio segment. Therefore, the Wireless Location System preferably "sticks" the location estimate to the nearest drawn road segment.

The Wireless Location System can filter and report location records to an application for wireless transmitter communication only at a particular cell site, sector, terrestrial channel, or group of RF channels. Before sending the record to the requesting application, the Wireless Location System first verifies that the appropriate fields in the record satisfy the requirements. Records that do not meet the requirements are not submitted and records that meet the requirements are submitted. Some filters are geographic and must be calculated by the Wireless Location System. For example, the Wireless Location System may process a location record to determine the nearest wallet segment and the direction of travel of the wireless transmitter in the wallet segment. The Wireless Location System can then send to the application only records that are determined to be in a particular portfolio segment and can further enhance the location record by adding a field containing the determined portfolio segment. To determine the closest portfolio segment, a database of portfolio segments of interest is provided to the Wireless Location System by the requesting application. This database is stored in a table in which each road segment is stored with a latitude and longitude coordinate that defines the end points of each segment. Each road segment can be modeled as a straight or curved line and can be modeled to support one or two directions of travel. Next, for each location record determined by the Wireless Location System, the Wireless Location System compares the latitude and longitude in the location record with each road segment stored in the database and determines the shortest distance to starting from a rendered line connecting the two end points of the segment with the latitude and longitude of the location record. The shortest distance is a calculated imaginary line orthogonal to the line connecting the two end points of the stored road segment. When the nearest road segment has been determined, the Wireless Location System can further determine the direction of movement on the road segment by comparing the direction of travel of the wireless transmitter reported by the location processing with the orientation of the road segment. The direction that produces the smallest error with respect to the orientation of the road segments is then reported by the Wireless Location System.

ES 2 386 669 T3

Network Operations Console (NOC) 16

The NOC 16 is a network management system that allows Wireless Location System operators to easily access the Wireless Location System programming parameters. For example, in some cities, the Wireless Location System may contain many hundreds and even thousands of SCS 10. The NOC is the most effective way to manage a large Wireless Location System, using graphical user interface capabilities. The NOC will also receive real-time alerts if certain functions within the Wireless Location System are not working properly. These real-time alarms can be used by the operator to quickly take corrective action and prevent degradation of location service. Experience with testing the Wireless Location System shows that the ability of the system to maintain good location accuracy over time is directly related to the ability of the operator to keep the system operating within its predetermined parameters.

Location processing

The Wireless Location System is capable of performing location processing using two different procedures known as central-based processing and station-based processing. Both techniques are first disclosed in Patent Number 5,327,144 and are further improved in the present specification. Location processing depends in part on the ability to accurately determine certain phase characteristics of the signal as received at multiple antennas and multiple SCS 10. Therefore, it is a goal of the Wireless Location System to identify and eliminate sources of phase error that impede the location processing ability to determine the phase characteristics of the received signal. One source of phase error is within the wireless transmitter itself, specifically the oscillator (typically a crystal oscillator) and the phase lock loops that allow the phone to tune to specific channels for transmission. Low cost crystal oscillators will generally have higher phase noise. Some over-the-air interface specifications, such as IS-136 and IS-95A, have specifications that cover the phase noise with which a cordless phone can transmit. Other over-the-air interface specifications, such as IS-553A, do not specify phase noise in detail. It is therefore a motive of the present invention to automatically reduce and / or eliminate the phase noise of the wireless transmitter as a source of the phase error in the location processing, in part by automatically selecting the use of an in-line processing. central-to-central or station-based processing. The automatic selection also considers the efficiency with which the communication link between the SCS 10 and the TLP 12 is used and the availability of DSP resources in each of the SCS 10 and TLP 12.

When central-based processing is used, the TDOA and FDOA determination and multipath processing are performed in the TLP 12 in conjunction with the position and velocity determination. This procedure is preferred when the wireless transmitter has phase noise that is above a predetermined threshold. In these cases, central-based processing is more effective in reducing or eliminating phase noise from the wireless transmitter as a source of phase error because the TDOA estimation is performed using a digital representation of the actual RF transmission from two antennas, which can be on the same SCS 10 or on different SCS 10. In this procedure, those skilled in the art will recognize that transmitter phase noise is common mode noise in TDOA processing and is therefore automatically canceled in the TDOA determination process. This procedure works best, for example, with many low-cost AMPS cell phones that have high phase noise. The basic stages in central-based processing include the stages listed below and represented in the flow chart in Figure 6:

a wireless transmitter initiates a transmission on either a control channel or a voice channel (step S50);

the transmission is received on multiple antennas and multiple SCS 10 in the Wireless Location System (step S51);

the transmission is converted to a digital format in the receiver connected to each SCS / antenna (step S52); the digital data is stored in a memory of the receivers in each SCS 10 (step S53);

the transmission is demodulated (step S54);

the Wireless Location System determines whether to start location processing for transmission (step S55);

if activated, the TLP 12 requests a copy of the digital data from the memory of the receivers in multiple SCS 10 (step S56);

digital data is sent from multiple SCS 10 to a selected TLP 12 (step S57);

the TLP 12 performs the TDOA, FDOA and multipath mitigation on the digital data from pairs of antennas (step S58);

the TLP 12 performs the position and speed determination using the TDOA data and then creates a location record and sends the location record to the AP 14 (step S59).

The Wireless Location System uses a variable number of bits to represent transmission when sending digital data from SCS 10 to TLP 12. As explained above, the SCS receiver digitizes wireless transmissions with a high resolution or high number of bits per digital sample to achieve a sufficient dynamic range. This is especially required when using digital receivers from

ES 2 386 669 T3 broadband, which may be simultaneously receiving signals close to SCS 10A and far from SCS 10B. For example, up to 14 bits may be required to represent a dynamic range of 84 dB. Location processing does not always require that high resolution per digital sample, however. Frequently, locations of sufficient precision can be achieved by the Wireless Location System using fewer bits per digital sample. Therefore, to minimize the implementation costs of the Wireless Location System by conserving bandwidth in the communication links between each SCS 10 and TLP 12, the Wireless Location System determines the smallest number of bits required to represent transmission digitally as long as a desired level of precision is still maintained. This determination is based, for example, on the particular air interface protocol used by the wireless transmitter, the SNR of the transmission, the degree to which the transmission has been disturbed by fading and / or multipath, and the current state of the queues. processing and communication in each SCS 10. The number of bits sent from SCS 10 to TLP 12 is reduced in two ways: the number of bits per sample is minimized and the shortest length or the fewest possible segments of the transmission is used for location processing. The TLP 12 can use this minimal RF data to perform location processing and then compare the result to the desired level of precision. This comparison is made based on a calculation of the confidence interval. If the location estimate does not fall within the desired precision limits, the TLP 12 will recursively request additional data from the selected SCS 10. The additional data may include an additional number of bits per digital sample and / or may include more segments of the transmission. This process of requesting additional data can continue recursively until the TLP 12 has achieved the prescribed location accuracy.

There are additional details to the basic stages described above. These details are described in previous Patent Numbers 5,327,144 and 5,608,410 elsewhere in this specification. An improvement to the processes described in previous patents is the selection of a single reference antenna / SCS that is used for each baseline in location processing. In prior techniques, baselines were determined using pairs of antenna sites around a ring. In the present Wireless Location System, the only reference antenna / SCS used is generally the one with the highest SNR signal, although other criteria may also be used as described below. The use of a high SNR reference assists in central-based location processing when the other SCS / antennas used in location processing are very weak, such as at or below the noise floor (i.e. a ratio signal to zero or negative noise). When using station-based location processing, the reference signal is a remodulated signal, which is intentionally created to have a high signal-to-noise ratio, further aiding location processing for very weak signals in other SCSs. / antennas. The actual selection of the reference antenna / SCS is described below.

The Wireless Location System mitigates multipath first by recursively estimating the components of the received multipath in addition to the direct path component and then subtracting these components from the received signal. Therefore the Wireless Location System models the received signal and compares the model with the actual received signal and tries to minimize the difference between the two using a weighted least squares difference. For each signal x (t) transmitted from a wireless transmitter, the signal y (t) received at each SCS / antenna is a complex combination of signals:

y (t) = Σ x (t - tn) an e^{jw (t}'^tn), for all n = 0 to N;

where x (t) is the signal as transmitted by the wireless transmitter;

an and tn are the complex amplitude and delays of the multipath components;

N is the total number of multipath components in the received signal and a0 and t0 are constants for the most direct path component.

The operator of the Wireless Location System empirically determines a set of constraints for each component of the multipath that applies to the specific environment in which each Wireless Location System is operating. The purpose of these restrictions is to limit the amount of processing time that the Wireless Location System uses in optimizing the results for each multipath mitigation calculation. For example, the Wireless Location System can be set to determine only four multipath components: the first component can be assumed to have a time delay in the interval aunt to tib; the second component can be assumed to have a time delay in the range T2a to T2b; the third component can be assumed to have a time delay in the interval t₃aat₃b; and similar for the fourth component; however the fourth component is a single value that effectively represents a complex combination of many tens of individual (and somewhat fuzzy) multipath components whose time delay exceeds the range of the third component. For ease of processing, the Wireless Location System transforms the pre-frequency domain equation and then solves the individual components so that the weighted least squares difference is minimized.

When using station-based processing, TDOA and FDOA determination and multipath mitigation are performed at SCS 10, while position and velocity determination is typically performed at TLP 12. The main advantage of station-based processing , as described in Patent Number 5,327,144, is the reduction in the amount of data that is sent on the communications link between each SCS 10 and TLP 12. Without

However, there may be other advantages as well. A new objective of the present invention is to increase the effective signal processing gain during TDOA processing. As noted above, central-based processing has the advantage of eliminating or reducing the phase error caused by phase noise in the wireless transmitter. However, no previous disclosure has addressed how to eliminate or reduce the same phase noise error when using station-based processing. The present invention reduces phase error and increases effective signal processing gain using the steps listed below and shown in Figure 6:

a wireless transmitter initiates a transmission on either a control channel or a voice channel (step S60);

the transmission is received on multiple antennas and on multiple SCS 10 in the Wireless Location System (step S61);

the transmission is converted to a digital format in the receiver connected to each antenna (step S62); the digital data is stored in a memory in the SCS 10 (step S63);

the transmission is demodulated (step S64);

the Wireless Location System determines whether to start location processing for transmission (step S65);

if activated, a first SCS 10A demodulates the transmission and determines an appropriate phase correction interval (step S66);

For each said phase correction interval, the first SCS 10A calculates an appropriate phase correction and an amplitude correction and encodes this phase correction parameter and amplitude correction parameter together with the demodulated data (step S67);

the demodulated data and the amplitude correction and phase correction parameters are sent from the first SCS 10A to the TLP 12 (step S68);

the TLP 12 determines the SCS 10 and receiver antennas to be used in the location processing (step S69);

the TLP 12 sends the demodulated data and the phase correction and amplitude correction parameters to every second SCS 10B to be used in the location processing (step S70);

the first SCS 10 and every second SCS 10B create a first remodulated signal based on the demodulated data and phase correction and amplitude correction parameters (step S71);

the first SCS 10A and every second SCS 10B perform TDOA, FDOA and multipath mitigation using the digital data stored in memory in each SCS 10 and the first remodulated signal (step S72);

TDOA, FDOA and multipath mitigation data is sent from the first SCS 10A and every second SCS 10B to the TLP 12 (step S73);

the TLP 12 performs the position and speed determination using the TDOA data (step S74) and the TLP 12 creates a location record and sends the location record to the AP 14 (step S75).

The advantages of determining phase correction and amplitude correction parameters are most obvious in locating CDMA wireless transmitters based on IS-95A. As is well known, reverse transmissions from the IS-95A transmitter are sent using non-coherent modulation. Most CDMA base stations only integrate over a single bit slot due to non-coherent modulation. For the CDMA Access Channel, with a bit rate of 4800 bits per second, there are 256 chips sent per bit, allowing an integration gain of 24 dB. Using the technique described above, the TDOA processing in each SCS 10 can integrate, for example, over a full 160 millisecond burst (196,608 chips) to produce an integration gain of 53 dB. This additional processing gain enables the present invention to detect and locate CDMA transmissions using multiple SCS 10, even if base stations located in conjunction with SCS 10 cannot detect the same CDMA transmission.

For a particular transmission, if both the phase correction parameters and the amplitude correction parameters are calculated to be zero, or are not required, then these parameters are not sent to conserve the number of bits transmitted on the communications link. between each SCS 10 and TLP 12. In another embodiment of the invention, the Wireless Location System uses a fixed phase correction interval for a particular transmission or for all transmissions of a particular air interface protocol or for all transmissions made by a particular type of wireless transmitter. . This can, for example, be based on empirical data collected over some period of time by the Wireless Location System that shows reasonable consistency in phase noise exhibited by various classes of transmitters. In these cases, the SCS 10 can spare the processing step of determining the appropriate phase correction interval.

Those skilled in the art will recognize that there are many ways to measure the phase noise of a wireless transmitter. In one embodiment, a remodulated, noiseless, pure copy of the signal received at the first SCS 10A can be generated by the DSPs in the SCS, then the received signal can be compared against the pure signal at each phase correction interval and phase difference can be directly measured. In this embodiment, the phase correction parameter will be calculated as the negative of the phase difference across the phase correction interval. The number of bits required to represent the phase correction parameter will vary with the magnitude of the phase correction parameter and the number of bits may vary for each phase correction interval. It has been observed that some transmissions, for example, show higher phase noise initially in the transmission and less phase noise towards the middle and later in the transmission.

ES 2 386 669 T3

Station-based processing is most useful for wireless transmitters that have relatively low phase noise. Although not necessarily required by their respective over-the-air interface standards, wireless phones using the TDMA, CDMA, or GSM protocols typically show lower phase noise. As the phase noise of a wireless transmitter increases, the length of the phase correction interval may decrease and / or the number of bits required to represent the phase correction parameters increases. Station-based processing is not effective when the number of bits required to represent the demodulated data plus the amplitude and phase correction parameters exceeds by a certain proportion the number of bits required to perform central-based processing. It is therefore an object of the present invention to automatically determine for each transmission for which a location is desired whether to process the location using central-based processing or station-based processing. The steps in making this determination are listed below and shown in Figure 7:

a wireless transmitter initiates transmission either on a control channel or on a voice channel (step S80);

the transmission is received in a first SCS 10A (step S81);

the transmission is converted to a digital format in the receiver connected to each antenna (step S82);

the Wireless Location System determines whether to start location processing for transmission (step S83);

if activated, a first SCS 10A demodulates the transmission and estimates an appropriate phase correction interval and the number of bits required to encode the phase correction and amplitude correction parameters (step S84);

the first SCS 10A then estimates the number of bits required for central-based processing;

Based on the number of bits required for each respective procedure, the SCS 10 or the TLP 12 determines whether to use central-based processing or station-based processing to perform location processing for this transmission (Step S85) .

In another embodiment of the invention, the Wireless Location System may always use central-based processing or station-based processing for all transmissions of a particular air interface protocol or for all transmissions made by a particular class of transmitter. wireless. This can, for example, be based on empirical data collected over some period of time by the Wireless Location System that shows reasonable consistency in phase noise exhibited by various classes of transmitters. In these cases, the SCS 10 and / or the TLP 12 can skip the processing step of determining the appropriate processing procedure.

A further improvement of the present invention, used for both central-based and station-based processing, is the use of threshold criteria to include baselines in the final determination of the location and speed of the wireless transmitter. For each baseline, the Wireless Location System calculates a number of parameters including: the SCS / antenna port used with the reference SCS / antenna in the baseline calculation, the peak, average and variance in transmit power as received on the SCS / antenna port used in the baseline and on the interval used for the location processing, the correlation value of the cross-spectrum correlation between the SCS / antenna used in the baseline and the SCS / reference antenna, the delay value for the baseline, the multipath mitigation parameters, residual values ​​remaining after multipath mitigation calculations, the contribution of the SCS / antenna to the weighted GDOP in the final locating solution, and a baseline fit quality measure if included in the final location solution. Each baseline is included in the final location solution if each meets or exceeds the threshold criteria for each of the parameters described herein. A baseline can be excluded from the location solution if it fails to satisfy one or more of the threshold criteria. Therefore, it is often possible that the number of SCS / antennas actually used in the final location solution is less than the total number considered.

Previous Patent Numbers 5,327,144 and 5,608,410 disclose a procedure by which location processing minimizes the value of the least squares difference (LSD) of the following equation:

LSD = [Q12 (Delay_T12 - Delay_O12)² + Q13 (Delay_Tn - Delay_On)² + ... + Qxy (Delay_Txy Delay_Oxy)²]

In the present implementation, this equation has been rearranged as follows to make the location processing code more efficient:

LSD = Σ (TDOAüí - ti + tü)² w²; for all i = 1 to N-1 where N = number of SCS / antennas used in location processing;

TDOA0i = the TDOA for the i-th location from the reference location 0;

ti = the theoretical line of sight propagation time from the wireless transmitter to the i-th site, t0 = the theoretical line of sight propagation time from the transmitter to the reference and

ES 2 386 669 T3 w, = the weighting factor, or quality, applied to the i-th baseline.

In the present implementation, the Wireless Location System also uses another alternative form of the equation that can assist in determining location solutions when the reference signal is not very strong or when there is likely to be a deviation in the solution of location using the previous evacuation form:

LSD '= Σ (TDOAüí - ti)² Wi² - b² Σ w²; for all i = 0 to N-1 where N = number of SCS / antennas used in location processing;

TDOAüí = the TDOA for the i-th location from the reference location 0;

ti = the propagation time in the theoretical line of sight from the wireless transmitter to the i-th site, b = a deviation that is calculated separately for each theoretical point that minimizes the LSD 'at that theoretical point and

Wi = the weighting factor, or quality, applied to the ith baseline.

The LSD 'form of the equation offers an easier means of eliminating a bias in the location solutions at the reference site by making Wo equal the maximum value of the other weights or by basing Wo on the relative signal strength at the reference site. Note that if Wo is much greater than other weights, then b is approximately equal to to. In general, the weights or quality factors are based on criteria similar to those explained above for the threshold criteria in the inclusion of baselines. That is, the results of the criteria calculations are used for weights and when the criteria fall below the threshold the weight is then set to zero and is effectively not included in the determination of the final location solution.

Antenna Selection Process for Location Processing

Previous inventions and disclosures, such as those listed above, have described techniques in which a first, a second, or possibly a third antenna site, cell site, or base station is required to determine location. Patent Number 5,608,410 further discloses a Dynamic Selection Subsystem (DSS) that is responsible for determining which data frames and from which antenna site locations will be used to calculate the location of a responding transmitter. In the DSS, if the data frames are received from more than a threshold number of sites, the DSS determines which are the candidates for hold or exclude and then dynamically organizes the data frames for location processing. DSS prefers to use more than a minimal number of antenna sites so that the solution is overdetermined. Additionally, DSS ensures that all transmissions used in location processing are received from the same transmitter and from the same transmission.

The preferred embodiments of the previous inventions have several limitations, however. First, either only one antenna is used per antenna site (or cell site) or the data from two or four diversity antennas was first combined at the antenna site (or cell site) prior to transmission to the site. central. Additionally, all antenna sites that received the transmission send data frames to the central site, even if the DSS later discarded the data frames. As a result, some communications bandwidth may have been wasted sending data that was not used.

The present inventors have determined that while a minimum of two or three sites are required to determine the location, the actual selection of antennas and SCS 10 for use in location processing can have a significant effect on the results of the location processing. The localization. Furthermore, it is advantageous to include the means to use more than one antenna in each SCS 10 in the location processing. The reason for using data from multiple antennas at a cell-site independently in location processing is that the received signal at each antenna is uniquely affected by multipath, fading, and other disturbances. It is well known in the art that when two antennas are separated by a distance of more than one wavelength, then each antenna will receive the signal in a separate path. Therefore, there is often additional and unique information to be obtained on the location of the wireless transmitter through the use of multiple antennas and the ability of the Wireless Location System to mitigate multipath is consequently improved.

It is therefore an object of the present invention to provide an improved method for using the signals received from more than one antenna in an SCS 10 in location processing. It is a further objective to provide a method to improve the dynamic process used to select the cooperating antennas and SCS 10 used in location processing. The first objective is achieved by providing means within the SCS 10 to select and use any segment of data collected from any number of antennas in an SCS in location processing. As described above, each antenna at a cell site is connected to an internal receiver of the SCS 10. Each receiver converts the signals

ES 2 386 669 T3 received from the antenna in a digital form and then temporarily stores the digitized signals in a memory in the receiver. The TLP 12 has been provided with means to instruct any SCS 10 to retrieve data segments from any receiver's buffer and to provide the data for use in location processing. The second objective is achieved by providing means within the Wireless Location System to monitor a large number of antennas for reception of the transmission that the Wireless Location System wishes to locate, and then selecting a smaller set of antennas for use in processing the location based on a predetermined set of parameters. An example of this selection process is represented by the flow chart in Figure 8:

a wireless transmitter initiates a transmission either on a control channel or on a voice channel (step S90) the transmission is received on multiple antennas and on multiple SCS 10 in the Wireless Location System (step S91);

the transmission is converted to a digital format in the receiver connected to each antenna (step S92); the digital data is stored in a memory in each SCS 10 (step S93);

the transmission is demodulated in at least one SCS 10A and the channel number in which the transmission occurred and the cell site and sector serving the wireless transmitter are determined (step S94);

Based on the cell site and serving sector, an SCS 10A is designated as the 'primary' SCS 10 for processing that transmission (step S95);

the primary SCS 10A determines a timestamp associated with the demodulated data (step S96);

the Wireless Location System determines whether to start processing for transmission (step S97);

if location processing is activated, the Wireless Location System determines a list of SCS 10 and candidate antennas to use in location processing (step S98);

each candidate SCS / antenna measures and reports various parameters at the channel number of the transmission and at the time of the timestamp determined by the primary SCS 10A (step S99);

The Wireless Location System instructs the candidate SCS / antennas to use specified criteria and selects a reference SCS / antenna and a processing list of SCS / antennas to be used in the location processing (step S100) and the Location System Wireless proceeds with location processing as described above, using data from the SCS / antenna processing list (step S101).

Selecting the primary SCS / antenna

The process for choosing the 'primary' SCS / antenna is critical, as the candidate list for SCS 10 and antennas 10-1 is determined in part based on the designation of the primary SCS / antenna. When a wireless transmitter transmits on a particular RF channel, the transmission can often spread many kilometers (miles) before the signal attenuates below the level at which it can be demodulated. Therefore, there are often many SCS / antennas capable of signal demodulation. This is especially the case in urban and suburban areas where the frequency reuse pattern of many wireless communication systems can be quite dense. For example, due to the high utilization rate of wireless and the dense separation of cell sites, the present inventors have tested wireless communication systems in which the same RF control channel and digital color code were used in cell sites. cells about 1.6 kilometers (one mile) apart. Because the Wireless Location System independently demodulates these transmissions, the Wireless Location System can frequently demodulate the same transmission on two, three or more separate SCS / antennas. The Wireless Location System detects that the same transmission has been demodulated multiple times on multiple SCS / antennas when the Wireless Location System receives multiple frames of demodulated data sent from different SCS / antennas, each with a number of bit errors below a predetermined bit error threshold and with the demodulated data coinciding within an acceptable limit of bit errors and all happening within a predetermined time interval.

When the Wireless Location System detects demodulated data from multiple SCS / antennas, it examines the following parameters to determine which SCS / antenna will be designated the primary SCS: Average SNR over the transmission interval used for location processing, the variance in SNR over the same interval, correlation of the start of received transmission against a pure precursor (i.e. for AMPS, stippling and Barker code) , the number of bit errors in the demodulated data and the magnitude and rate of change of the SNR from just before transmission set-up to transmission set-up as well as other similar parameters. The average SNR is typically determined on each SCS / antenna either over the entire duration of the transmission to be used for location processing or over a shorter interval. Average SNR over a shorter interval can be determined by performing a correlation with the dotting sequence and / or the Barker code and / or the sync word, depending on the particular over-the-air interface protocol and over a short interval. of time before, during and after the timestamp reported by each 10 sCs. The time interval can typically be +/- 200 microseconds centered on the timestamp, for example. The Wireless Location System will generally order the SCS / antennas using the following criteria, each of which may be weighted (multiplied by an appropriate factor) when combining the criteria to determine the final decision: SCS / antennas with the number

ES 2 386 669 T3 lower bit errors are preferred to SCS / antennas with a higher number of bit errors, average SNR for a given SCS / antenna must be greater than a predetermined threshold to be designated as primary; SCS / antennas with a higher average SNR are preferred over those with a lower SNR; SCS / antennas with a lower SNR variance are preferred to those with a higher SNR variance and SCS / antennas with a faster rate of SNR change at transmission establishment are preferred to those with a higher SNR rate. lower change. The weighting applied to each of these criteria can be adjusted by the operator of the Wireless Location System to adapt to the particular design of each system.

The candidate list of SCS 10 and antennas 10-1 are selected using a predetermined set of criteria based on, for example, knowledge of cell site types, antenna types at cell sites, antenna geometry and weighting factor that weights certain antennas more than other antennas. The weighting factor takes into account the knowledge of the terrain in which the Wireless Location System is operating, previous empirical data on the contribution that each antenna has had to good estimates of the location and other factors that may be specific for each installation of WLS different. In one embodiment, for example, the Wireless Location System may select the candidate list to include all SCS 10 up to a maximum number of sites (maximum_number_of_locations) that is closer to a predefined maximum radius from the primary site (maximum_radius_from_primary). For example, in an urban or suburban environment, where there may be a large number of cell sites, the maximum number of sites may be limited to nineteen. Nineteen sites would include the primary, the first six-site ring surrounding the primary (assuming a classic hexagonal distribution of cell sites), and the next twelve-site ring surrounding this first ring. This is depicted in Figure 9. In another embodiment, in a suburban or rural environment, the maximum_radius_from_primary can be set to 64.4 kilometers (40 miles) to ensure that the widest possible set of candidate SCS / antennas is available. The Wireless Location System is provided with means for limiting the total number of candidate SCS 10 to a maximum number (maximum_number_candidates), although each candidate SCS may be allowed to choose the best port from among its available antennas. This limits the maximum time spent by the Wireless Location System processing a particular location. The maximum_number_candidates can be set to thirty-two, for example, which means that in a typical three-sector diversity wireless communications system, up to 32 * 6 = 192 antennas in total could be considered for location processing for a particular transmission. To limit the time spent processing a particular location, the Wireless Location System is provided with means to limit the number of antennas used in location processing to the number_maximum_ antennas_processed. The max_number_anthenas_processed is generally less than max_number_candidates and is typically set to sixteen.

While the Wireless Location System is provided with the ability to dynamically determine the candidate list of SCS 10 and antennas based on a predetermined set of criteria described above, the Wireless Location System can also store a fixed candidate list in a table. Therefore, for each cell site and sector in the wireless communication system, the Wireless Location System has a separate table that defines the candidate list of SCS 10 and antennas 10-1 to use whenever a wireless transmitter initiates a transmission. at that cell and sector site. Rather than dynamically choosing candidate SCS / antennas each time a location request is triggered, the Wireless Location System reads the candidate list directly from the table when location processing starts.

In general, a large number of candidate SCS 10 are chosen to provide the Wireless Location System with sufficient opportunity and capacity to measure and mitigate multipath. In any given transmission, any one or more particular antennas on one or more SCS 10 can receive signals that are affected to varying degrees by multipath. Therefore, it is advantageous to provide this means within the Wireless Location System to dynamically select a set of antennas that can receive less multipath than other antennas. The Wireless Location System uses various techniques to mitigate as much multipath as possible of the received signal; however it is often prudent to choose a set of antennas that contain the least amount of multipath.

Choice of reference and cooperating SCS / antennas

In choosing the set of SCS / antennas to use in location processing, the Wireless Location System sorts the candidate SCS / antennas using various criteria, including for example: Average SNR in the transmission interval used for location processing, the variance in the SNR in the same interval, correlation of the beginning of the received transmission against a pure precursor (i.e. for AMPS, stippling and Barker code) and / or demodulated data from the primary SCS / antenna, the transmission establishment time in relation to the establishment reported in the SCS / antenna in which the transmission was demodulated and the magnitude and rate of change of the SNR just before the establishment of the transmission to the establishment of the transmission as well as other parameters Similar. The average SNR is typically determined at each SCS and for each antenna in the candidate list both over the entire duration of the transmission to be used for location processing and over a shorter interval. The average SNR over the shorter interval can be determined by correlating with the stippling sequence and / or code.

ES 2 386 669 T3

Barker and / or sync word, depending on the particular over-the-air interface protocol and for a shorter interval of time before, during, and after the timestamp reported by the primary SCS 10. The time interval can typically be +/- 200 microseconds centered on the timestamp, for example. The Wireless Location System will generally order the SCS / antennas using the following criteria, each of which may be weighted when combining the criteria to determine the final decision: the average SNR for a given SCS / antenna must be greater than a threshold default to be designated as the primary; SCS / antennas with a higher average SNR are preferred over those with a lower SNR; SCS / antennas with an establishment closer to the establishment notified by the SCS / demodulation antenna are preferred to those with a more distant establishment in time; SCS / antennas with a faster SNR rate of change are preferred over those with a slower rate of change; SCS / antennas with lower incremental weighted GDOP are preferred over those with higher incremental weighted GDOP, where the weight is based on the estimated path loss from the primary SCS. The weighting applied to each of these preferences can be adjusted by the operator of the Wireless Location System to suit the particular design of each system. The number of different SCS 10 used in location processing is maximized up to a predetermined limit; the number of antennas used in each SCS 10 is limited to a predetermined limit and the total number of SCS / antennas used is limited to a maximum_number_antennas_processed. The SCS / antenna with the highest rating using the processes described above is designated as the reference SCS / antenna for location processing.

Selection of the best port within an SCS 10

Often times, the SCS / antennas on the candidate list or on the list to use for location processing will include only one or two antennas in a particular SCS. In these cases, the Wireless Location System may allow the SCS 10 to choose the "best port" from all or some of the antennas on a particular SCS. For example, if the Wireless Location System chooses to use only one antenna on a first SCS 10, then the first SCS 10 can select the best antenna port from the six typical antenna ports that connect to that SCS 10 or it can choose the best antenna port of the two antenna ports or just one sector of the cell site. The best antenna port is chosen using the same process and comparing the same parameters as described above for choosing the set of SCS / antennas to use in the location processing, except that all the antennas being considered for the best port are all on the same SCS 10. In the antenna comparison for the best port, the SCS 10 can also optionally divide the received signal into segments and then measure the SNR separately on each segment of the received signal. The SCS 10 can then optionally choose the best antenna port with the highest SNR by: (i) using the antenna port with the most segments with the highest SNR, (ii) averaging the SNR across all the segments and using the antenna port with the highest average SNR or (iii) using the antenna port with the highest SNR of any segment.

Collision detection and recovery

Because the Wireless Location System will use data from many SCS / antenna ports in locating and processing, there is a chance that the signal received at one or more SCS / antenna ports will contain energy that is contiguous channel interference from another wireless transmitter (ie a partial or total collision has occurred between two separate wireless transmissions). There is also a reasonable probability that the contiguous channel interference has a much higher SNR than the signal from the target wireless transmitter and if not detected by the Wireless Location System, the contiguous channel interference can result in an incorrect choice of channel. best antenna port on an SCS 10, SCS / reference antenna, SCS / candidate antennas, or SCS / antenna to use in location processing. Adjacent channel interference can also produce poor TDOA and FDOA results, leading to a poor or poor location estimate. The probability of collision increases with the density of cell sites in the host wireless communication system, especially in dense suburban or rural environments where frequencies are often reused and wireless usage by subscribers is high.

Therefore, the Wireless Location System includes means for detecting and recovering from the types of collisions described above. For example, in the process of selecting a better port, the reference SCS / antenna or candidate SCS / antenna, the Wireless Location System determines the average SNR of the received signal and the variance of the SNR during the transmission interval. ; When the variance of the SNR is above a predetermined threshold, the Wireless Location System assigns a probability that a collision has occurred. If the signal received at an SCS / antenna has increased or decreased its SNR by a single notch, and by an amount greater than a predetermined threshold, the Wireless Location System assigns a probability that a collision has occurred. Additionally, if the average SNR of the signal received at a remote SCS is greater than the average SNR that would be predicted by a propagation model, given the cell site where the wireless transmitter started its transmission and the transmission power levels Known antennas and antenna patterns of the transmitting and receiving antennas, the Wireless Location System assigns a probability that a collision has occurred. If the probability that a collision has occurred is above the predetermined threshold, then the Wireless Location System performs the additional processing described below to check whether and to what extent a collision may have disturbed the signal received at an SCS / antenna. . The advantage of assigning probabilities is to reduce or eliminate the extra processing for

ES 2 386 669 T3 most of the transmissions for which the collisions have not happened. It should be noted that the threshold levels, assigned probabilities, and other details of the collision detection and recovery processes described herein are configurable, that is, selected based on the application, environment, system variables, etc. particular, which would affect your selection.

For transmissions received at an SCS / antenna for which the probability of a collision is above a predetermined threshold and prior to use of the RF data from a particular antenna port in a determination of the reference SCS / antenna, determination of the For better port or location processing, the Wireless Location System preferably verifies that the RF data from each antenna port is coming from the correct wireless transmitter. This is determined, for example, by demodulating segments of the received signal to verify, for example, that the MIN, MSID or other identification information is correct or that the dialed digits or other characteristics of the message match those received by the SCS. / antenna that initially demodulated the transmission. The Wireless Location System can also correlate a short message of the signal received at an antenna port with the signal received at the primary SCS 10 to verify that the correlation result is above a predetermined threshold. If the Wireless Location System detects that the variance in SNR over the entire duration of the transmission is above the predetermined threshold, The Wireless Location System can divide the transmission into segments and test each segment as described herein to determine if the energy in that segment is primarily derived from the signal of the wireless transmitter for which location processing has been selected. or from an interfering transmitter.

The Wireless Location System may choose to use the RF data from a particular SCS / antenna in location processing even if the Wireless Location System has detected that a partial collision has occurred at that SCS / antenna. In these cases, the SCS 10 uses the means described above to identify that part of the received transmission that represents a signal from the wireless transmitter for which location processing has been selected and that part of the received transmission that contains interference from contiguous channel. The Wireless Location System may instruct the SCS 10 to send or use only selected segments of the received transmission that do not contain contiguous channel interference. When determining the TDOA and FDOA for a baseline using only selected segments from a SCS / antenna, the Wireless Location System uses only the corresponding elements of the transmission as received at the reference SCS / antenna. The Wireless Location System can continue to use all segments for baselines where no collisions were detected. In many cases, the Wireless Location System is capable of completing location processing and achieving an acceptable location error using only part of the transmission. This inventive ability to select an appropriate subset of the received transmission and perform location processing in a segment-by-segment mode enables the Wireless Location System to complete location processing successfully in cases where it could have failed using previous techniques. .

Multi-step location processing

Certain applications may require a very quick estimate of the general location of the wireless transmitter, followed by a more accurate estimate of the location that can be sent later. This can be valuable, for example for E9-1-1 systems that can handle wireless calls and must make a call routing decision very quickly, but may wait a little longer for a more exact location to show up on the terminal. E9-1-1 electronic call taking map. The Wireless Location System supports these applications with a multi-step location processing mode.

In many cases, location accuracy is improved by using longer segments of the stream and increasing the processing gain over longer integration intervals. Longer segments of the transmission require longer processing periods in the SCS 10 and TLP 12, as well as longer periods of time for the transmission of the RF data through the communications interface from the SCS 10 to the TLP 12 . Therefore, the Wireless Location System includes means for identifying those transmissions that require a quick but rough estimate of the location followed by more comprehensive location processing that produces a better location estimate. The Sign of Interest Table includes a marker for each Sign of Interest that requires a multistep localization approach. This marker specifies the maximum amount of time allowed by the requesting location application for the first estimate to be sent as well as the maximum amount of time allowed by the requesting location application for the final location estimate to be sent. The Wireless Location System performs a rough location estimate by selecting a subset of the transmission on which to perform location processing. The Wireless Location System can choose, for example, the segment that was identified in the primary SCS / antenna with the highest average SNR. After a rough location estimate has been determined, using the procedures described above, but with only a subset of the transmission, the TLP 12 sends the location estimate to the AP 14, which then sends the rough estimate to the application. Applicant with a marker indicating that the estimate is only approximate. The Wireless Location System then performs its standard location processing using all the procedures mentioned above and sends this

ES 2 386 669 T3 location estimate with a marker indicating the final state of this location estimate. The Wireless Location System may perform coarse location estimation and final location estimate sequentially on the same DSP in a TLP 12 or it may perform location processing in parallel on different DSPs. Parallel processing may be necessary to meet the maximum time requirements of requesting location applications. The Wireless Location System supports different maximum time requirements of different location applications for the same wireless transmission.

Very short baseline TDOA

The Wireless Location System is designed to operate in urban, suburban and rural areas. In rural areas, when there are not enough cell sites available for a single wireless provider, the Wireless Location System can be deployed with SCS 10 located at the cell sites of other wireless providers or on other types of towers, including radio stations. AM or FM, search, and two-way wireless towers. In these cases, instead of sharing the existing antennas of the wireless provider, the Wireless Location System may require the installation of antennas, filters and appropriate low noise amplifiers to adapt to the frequency band of the wireless transmitters of interest to be located. . For example, an AM radio station tower may require the addition of 800 MHz antennas to locate transmitters in the cellular band. There may be cases, however, where additional towers of any kind are not available at reasonable cost and the Wireless Location System needs to be deployed in only a few towers of the wireless provider. In these cases, the Wireless Location System supports an antenna mode known as very short baseline TDOA. This antenna mode becomes active when additional antennas are installed in a single cell-site tower, whereby the antennas are placed less than one wavelength apart. This may require the addition of only one antenna per cell-site sector so that the Wireless Location System uses an existing receiving antenna in a sector and an additional antenna that has been positioned close to the existing receiving antenna. Typically, the two antennas in the sector are oriented so that the primary axes, or direction line, of the principal axes are parallel and the spacing between the two antenna elements is precisely known. In addition, the two RF paths from the antenna elements to the receivers are calibrated in the SCS 10.

In normal mode, the Wireless Location System determines the TDOA and FDOA for pairs of antennas that are separated by many wavelengths. For a TDOA on a baseline using antennas from two different cell sites, the antenna pairs are separated by thousands of wavelengths. For a TDOA on a baseline using antennas at the same cell site, the antenna pairs are separated by tens of wavelengths. In either case, the TDOA determination effectively results in a hyperbolic line that bisects the baseline and passes through the location of the wireless transmitter. When the antennas are separated into multiple wavelengths, the received signal has taken independent paths from the wireless transmitter to each antenna, including experimenting with different multipaths and Doppler shifts. However, when two antennas are closer than one wavelength, the two received signals have taken essentially the same path and experienced the same fading, multipath, and Doppler shift. Therefore, the TDOA and FDOA processing of the Wireless Location System typically produces a Doppler shift of zero (or near zero) hertz and a time difference on the order of zero to one nanosecond. Such a short time difference equivalent to an unambiguous phase difference between the signals received at the two antennas on a very short baseline. For example, at 834 MHz, the wavelength of a transmission on the aMpS reverse control channel is approximately 0.36 meters (1.18 feet). A time difference of 0.1 nanoseconds is equivalent to a received phase difference of approximately 30 degrees. In this case, the TDOA measurement produces a hyperbola that is essentially a straight line, although it passes through the location of the wireless transmitter and in a direction that is rotated 30 degrees from the direction of the parallel lines formed by the two antennas on the very short baseline. When the results of this very short baseline TDOA at a single cell site is combined with a TDOA measurement at a baseline between two cell sites, the Wireless Location System can determine a location estimate using only two cell sites. cells.

Improved procedures for TDOA and / or FDOA estimation

Wireless Location Systems based totally or in part on TDOA generally perform a cross correlation on pairs of received signals. A mobile phone or other mobile transmitter performs the transmission, which is then received at multiple antennas in the system. The locating system can then dynamically choose one of the antennas as the "primary" antenna and use the remaining antennas as "cooperating" antennas. The signal received at the primary antenna is then known as the reference signal and the signals received at the cooperating antennas are known as cooperating signals. Cross-correlation, in both the time and frequency domain, is performed to accurately determine the TDOA and / or FDOA of the primary and cooperating signals.

As mentioned, the WLS performs the cross-correlation of each cooperating signal with the reference signal, using either one of the mathematically equivalent sets of processes, both a time-domain cross-correlation process and a spectrum process. crossed in the frequency domain.

ES 2 386 669 T3

Both the time-domain cross-correlation process and the frequency-domain cross-spectrum process are referred to as cross-correlation and thus any reference in this document to cross-correlation should be understood to refer to both the correlation process. time domain crossover process as well as frequency domain crossover process or any other mathematically equivalent process. These mathematically equivalent processes to cross correlation include the use of Kalman filters, Coincident Filters, or other adapted filters. Pattern recognition techniques can also be used on the cooperating signal in the time and / or frequency domains to estimate the goodness of fit to the reference signal. For purposes of processing efficiency, a cross-spectrum process is typically used. The WLS separately cross-correlates each received cooperating signal with the reference signal, producing a separate TDOA result for each pair of signals. An imaginary line drawn from the primary antenna to each cooperating antenna is known as a baseline and therefore each TDOA result is associated with a more specific line. The TDOA results, or baselines, are then combined together with an a priori knowledge of the locations of the receiving antennas to produce an estimate of the location of the mobile transmitter.

Cross-correlation processes produce an array of values. The array can be both one-dimensional and two-dimensional. A one-dimensional array contains values ​​that represent the magnitude of the cross-correlation over a range of possible TDOA time values. For example, an array may contain cells that move in time by 5 microseconds each. Each cell contains the cross-correlation result when that time value is checked against a possible TDOA estimate. In the matrix, one cross-correlation result will be more optimal than the other results, and the TDOA estimate for that baseline is set equal to the time value associated with the cell that contains the optimal cross-correlation result. Super-resolution techniques used in a WLS can result in time values ​​that are interpolated between two time values. A two-dimensional matrix contains values ​​that represent the magnitude of the cross-correlation over a range of both possible TDOA time values ​​and possible FDOA frequency values. A non-zero FDOA value can be the result of a Doppler shift if the moving transmitter (or a reflective surface) is moving. Each search of the cross-correlation matrix to find the optimal value will then simultaneously result in finding a TDOA value and a FDOA.

Because the WLS generally does not know either the location of the mobile transmitter or whether the transmitter is moving (and thereby producing a Doppler shift) before starting processing, cross-correlation results are searched over a wide range. possible TDOA and FDOA values ​​to find optimal values. The presence of interfering transmitters, multipath, and other noise sources can produce false results — that is, there may be other values ​​in the cross-correlation result matrix that are close to the optimal value or perhaps even greater than the optimal value. These values ​​can lead to a misleading or incorrect interpretation of the results or a false identification of the optimal value and therefore an incorrect associated TDOA and / or FDOA value. There is, therefore, a great advantage to a procedure that can reduce the likelihood of false results occurring.

The present invention, which may be referred to as restricted TDOA / FDOA, limits the search for TDOA or FDOA to ranges of values ​​that represent the most likely range of values ​​to the exclusion of all other possible values. The present invention is of particular value for low SNR signals, in which the probability of a false result due to noise increases significantly relative to the probability of finding the true optimal result. Mobile transmitters based on CDMA or another spread spectrum over-the-air interface protocol are examples of protocols that frequently use low SNR signals.

An example of restricted TDOA involves limiting the search for the optimal value of the cross-correlation magnitude to an interval or search interval that is not greater than the distance in time between the first antenna associated with the reference signal and the second. antenna associated with the cooperating signal. In this example, if the first and second antennas are at different cell sites 8 kilometers (5 miles) apart, then they are about 26.8 microseconds apart in time (assuming radio waves travel at the speed of 0 , 3 meters per nanosecond (0.984 feet per nanosecond). By convention, a TDOA value of 0 microseconds is defined to be at the point exactly midway between the first and second antennas, therefore the interval of time values ​​between the first and second antennas is from +13.4 microseconds to -13.4 microseconds. Because there can be errors associated with knowing precisely the exact time each receiver was connected to each antenna, the range of time values ​​sought may be slightly extended by a predetermined error value. If an error value of 100 nanoseconds is used in this example, then the desired time range can be from +13.5 microseconds to -13.5 microseconds.

This example can be extended by using additional information about the mobile transmitter to further limit the range of time values ​​sought. If the mobile transmitter is known to be closer to the reference site than to the cooperating site, then the range of time values ​​sought can be limited only to positive values: +13.5 microseconds to 0 microseconds. If the mobile transmitter is known to be within a particular distance from the reference cell site, determined by either the time of an idea-and-lap delay measurement or a relative power measurement, then the range of time values searched can be further limited. Each limitation of the range sought

ES 2 386 669 T3 increases the probability of correctly finding the optimal result and decreases the probability of incorrectly selecting a false result.

When considering mobile transmitters such as mobile phones, the matrix of correlation values ​​is normally two-dimensional because the phones are frequently on the move. A moving mobile transmitter will produce a different Doppler shift for each baseline, or each pair of cooperating reference signals for which the cross-correlation is performed. The probability of wrong mode selection of a false result increases in a two-dimensional matrix because the FDOA and TDOA have to be determined simultaneously. An error in identifying the Doppler shift (FDOA) correctly can lead to incorrectly identifying the TDOA as well. The ability to correctly identify Doppler shifts decreases with low SNR signals such as those generated by CDMA or other spread spectrum air interface protocols. Therefore, the disclosed invention also includes a mechanism for limiting the search for FDOA values ​​to a predefined range.

In one example, if the mobile transmitter is known to be said, then the FDOA search range can be limited to 0 Hertz, or from 0 Hertz to +/- a predefined error value. If the clocks used in the receivers on the first and second antennas have a relative drift rate of less than 1 Hz, then the FDOA search interval can be limited to +1 Hz to -1 Hz. The mobile transmitter can be known to be fixed. if it is located in a parked car or in a box in a warehouse. The transmitter is also assumed to be fixed if one or more baselines with strong received signals result in zero or very low Doppler shift. That knowledge can be used in processing the correlation for other baselines where the received signals may be weaker and processing the correlation independently may have more difficulty in determining the FDOA correctly.

The disclosed invention is particularly advantageous if both TDOA and FDOA can be restricted when looking for correlation results.

By further limiting searches based on threshold conditions, four possible restriction cases occur:

1. full Doppler search, full time search;

2. restricted Doppler search, full time search;

3. full Doppler search, narrowly restricted time search;

Four. Doppler search restricted, time search narrowly restricted.

These cases are appropriate under very specific circumstances.

For the first case, full Doppler search with a full time search, the wireless device can be either moving or stationary and can be anywhere in the signal collection range of the system receiver.

In the second case, restricted Doppler search and full time search, the wireless device is assumed to be almost fixed based on the signal initially received by the primary site. The wireless device can be anywhere in the signal pickup range of the system receiver.

In the third case, full Doppler search and narrowly restricted time search, the wireless device is assumed to be moving, but is very close to the cooperating site. Both of these assumptions are derived from the signal received by the primary site.

Furthermore, in the fourth case, restricted Doppler search, narrowly restricted time search, the wireless device is assumed to be fixed or moving very slowly and very close to the cooperating site. Both of these assumptions are derived from the signal received by the primary site.

Referring now to Figure 10, the presently preferred implementation of the invention can be summarized as follows: First, a set of cross-correlation values ​​is provided. As explained above, each cross-correlation value is associated with a corresponding TDOA and / or FDOA estimate and is produced by cross-correlating a reference signal with a cooperating signal. Next, a range of most likely TDOA and / or FDOA estimates is determined, and then the optimal cross-correlation value is identified within the subset of cross-correlation values ​​that correspond to the most likely range of TDOA and / or FDOA estimates. Finally, the TDOA and / or FDOA value that corresponds to the optimal cross-correlation value is used in calculating the location of the mobile transmitter.

Conclution

The true scope of the present invention is not limited to the preferred embodiments currently disclosed herein. For example, the foregoing disclosure of a currently preferred embodiment of the Wireless Location System uses explanatory terms, such as Signal Collection System (SCS), TDOA Location Processor (TLP), Application Processor (AP), and the like, which do not I know

ES 2 386 669 T3 should be construed as limiting the scope of protection of the following claims or otherwise implying that the inventive aspects of the system are limited to the particular disclosed methods and apparatus. Furthermore, as will be understood by those skilled in the art, many of the inventive aspects disclosed herein can be applied in location systems that are not based on TDOA techniques. For example, the processes by which the Wireless Location System determines TDOA and FDOA values ​​can be applied to non-TDOA systems. Similarly, the invention is not limited to systems employing SCS constructed as described above and systems employing APs that satisfy all the particularities described above. SCS, TLP and Ap are, in essence, programmable data collection and processing devices that could take a variety of forms without departing from the inventive concepts disclosed herein. Given the rapidly decreasing costs of signal processing functions and other processing functions, it is easily possible, for example, to transfer the processing of a particular function from one of the functional elements (such as the TLP) described herein to other functional elements (such as the SCS or AP) without changing the inventive operation of the system. In many cases, the place of implementation (ie the functional element) described herein is merely a designer's preference and not a strict requirement. Accordingly, except as may be expressly limited, the scope of protection of the following claims is not intended to be limited to the specific embodiments described above.