Methods and Apparatuses For Using Assistance Data Relating to Satellite Position Systems

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DESCRIPTION

Procedure and apparatus for using assistive data in connection with satellite positioning systems.

Field of the invention

The present invention relates to receivers that can determine position information from satellites and in particular, it relates to receivers that can be applied to satellite positioning systems (SPS) such as the US global positioning system (GPS).

Related requests

The present application refers to and hereby claims the benefit of the filing dates of two provisional applications by the same inventor, Leonid Sheynblat. The first provisional application is entitled "Methods and Apparatus for Using Assistance data Relating to Satellite Position Systems", serial no. 60 / 190,600, filed March 20, 2000. The second provisional application is entitled "Method and Apparatus for Using Satellite Status Information in Satellite Positioning Systems", Serial No. 60 / 228,258, filed August 25, 2000.

Background of the invention

GPS receivers typically determine their position by calculating the arrival times of signals transmitted simultaneously from a plurality of GPS satellites (or NAVSTAR). These satellites transmit, as part of their message, both satellite positioning data and clock synchronism data, the so-called "ephemeris" data. The process of searching for and acquiring GPS signals, reading the ephemeris data for multiple satellites, and calculating the location of the receiver from this data is time consuming, often several minutes. In many cases, this long processing time is unacceptable and also severely limits battery life in miniaturized portable applications.

GPS reception systems have two main functions. The first is the calculation of the pseudo-ranges to the various GPS satellites, and the second is the calculation of the position of the receiver using these pseudo-ranges and satellite ephemeris and timing data. Pseudo-ranges are simply the arrival times of satellite signals measured by a local clock. This definition of pseudorange is sometimes also called a code phase. Satellite timing and ephemeris data is extracted from the GPS signal once it is acquired and tracked. As noted above, collecting this information typically takes a relatively long time (30 seconds to several minutes) and must be done with a good received signal level in order to achieve low error rates.

Most GPS receivers use correlation procedures to calculate pseudo-ranges. These correlation procedures are performed in real time, often with hardware correlators. GPS signals contain repetitive, high-rate signals called pseudo-random sequences (PN). The codes available for civil applications are called C / A (coarse acquisition) codes, and have a reverse binary phase transmission rate, or "hashing" rate, of 1.023 MHz and a repetition period of 1023 code elements. for a code period of 1 millisecond. The code sequences belong to a family known as Gold codes, and each GPS satellite emits a signal with a unique Gold code.

For a signal received from a given GPS satellite, after a baseband downconversion process, a correlation receiver multiplies the received signal by a stored replica of the appropriate Gold code included in its local memory, and then integrates, or filters pass low, the product in order to get an indication of the presence of the signal. This process is called a "correlation" operation. By sequentially adjusting the relative timing of this stored replica to the received signal, and observing the correlation output, the receiver can determine the time delay between the received signal and a local clock. The initial determination of the presence of such an output is called "acquisition." Once the acquisition occurs, the process enters the "tracking" phase in which the local reference timing is adjusted small amounts in order to maintain a high correlation output. The correlation output during the tracking phase can be viewed as the GPS signal with the pseudo-random code removed, or, in common terminology, "de-spread." This signal is narrow band, with a bandwidth consistent with a 50 bits per second binary phase shift modulated (BPSK) data signal that is superimposed on the GPS waveform.

The correlation acquisition process is time consuming, especially if the received signals are weak. To improve acquisition time, most GPS receivers use multiple correlators (typically up to 36), allowing parallel search for correlation peaks.

Conventional GPS receiving equipment is typically designed to receive GPS signals in open spaces since satellite signals are line of sight and therefore can be blocked by metal and other materials. Enhanced GPS receivers provide signal sensitivity that enables tracking of GPS satellite signals indoors, or in the presence of weak multipath signals or signals that are pure reflections. The ability to acquire weak GPS signals of this type, however, typically causes other problems. For example, simultaneous tracking of strong and weak signals can cause the receiver to pick up a signal

ES 2 345 708 T3 cross-correlated which is not an authentic signal. Instead of finding a weak true peak, a stronger cross-correlated peak can be acquired. Keeping track of a weak satellite signal does not guarantee that it is a direct signal. This weak signal can be a reflected signal or a combination of direct and indirect signals. The combined signals are called multipath signals. The path of the reflected signal is typically longer than the path of the direct signal. This difference in path length causes the reflected signal time of arrival measurement to be normally delayed or the corresponding code phase measurement to contain a positive offset. In general, the magnitude of the deviation is proportional to the relative delay between the reflected and direct paths. The possible absence of a direct signal component makes existing multipath mitigation techniques (such as a narrow correlator or a strobe correlator) obsolete.

The GPS navigation message is the information transmitted to a GPS receiver from a GPS satellite. It is in the form of the 50-bit-per-second data stream that is modulated into GPS signals.

The data message is included in a data frame that is 1500 bits long. It has five subframes each containing GPS system time. Each subframe consists of 10 words of 30 bits each. Subframes 1 through 3 repeat every 30 seconds. There are twenty-five pages of data that appear in sequence in the fourth and fifth subframes; one every 30 seconds. Therefore, each of these twenty-five pages repeats every 750 seconds.

Subframes 4 and 5 contain two types of health data for GPS satellites: (a) each of the 32 pages containing almanac data relative to clock / ephemeris provides a working health 8-bit satellite operation relative to the satellite whose almanac data they carry, and (b) the 25^to Subframe page 4 and 5 together contain six-bit health data for up to 32 satellites. Additional satellite health data is provided in subframe 1.

Typically, a GPS receiver will receive information regarding the status (eg, "good working") of a satellite and then process the GPS signals by not acquiring and not tracking malfunctioning satellites while acquiring and tracking signals. GPS from well-functioning satellites. As an alternative, separate GPS receivers can be designed to acquire and track malfunctioning satellites but avoid using their signals in the location calculation after having read the health data from the ephemeris message from a satellite signal. malfunction (see related provisional patent application "Method and Apparatus for Using Satellite Status Information in Satellite Positioning Systems", Serial No. 60 / 228,258, filed August 25, 2000.

Satellite positioning systems have used various types of assistive data to improve the performance of an SPS receiver. For example, an SPS receiver can receive Doppler estimates from an external source (eg, a radio transmission to the SPS receiver). Another type of assistance data can be satellite identification in view of the estimated or known location of the SPS receiver. In the past, the identification of these satellites has not included any indication as to whether the satellites may have poor geometry relative to the estimated location of the SPS receiver or relative to each other. Also, in the past, satellite identification in view of an SPS receiver has not included an indication of bad geometry with satellite good performance data.

Document EP0874248 describes the geolocation of cell phones through the use of the GPS system.

Summary of the invention

According to the invention there is provided the method of any of claims 1, 2 or 3. According to the invention there is provided the apparatus of any of claims 8, 9 or 10.

Procedures and apparatus are described for determining an ordered set of SPS satellites in view of a mobile SPS receiver. One method includes determining an array of SPS satellites in view of a position (e.g., a representative position) in a cell of a cellular communication system and then transmitting the array of SPS satellites from a cellular transmission site located within from or near the cell so that an SPS receiver located within the cell of the cellular communication system can receive the array of SPS satellites.

The ordering of SPS satellites in the ordered set can be done according to different procedures, such as minimizing a dilution of geometric precision (GDOP); minimizing a dilution of position precision (PDOP), minimizing a dilution of horizontal precision (HDOP), providing a position solution that uses SPS satellites that have a desired geometry relative to each other, providing a position solution that uses SPS satellites that have a desired geometry relative to the mobile SPS receiver; sorting based on a probability of acquisition of the SPS satellite signal; sorting based on a measurement quality estimate from the ordered set of SPS satellites; sorting performed by providing an optimal geometric trilateration solution, and sorting based on user-defined selection criteria. In addition, the ranking may include satellite health information.

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An apparatus for creating an array of SPS satellites is described including; a server to determine an ordered set of SPS satellites in view of a cell of a cellular communication system at a given time and a transmitter, coupled to the server, to transmit the ordered set of SPS satellites from a cellular transmission site located within from or near the cell. Thus, a mobile SPS receiver located within the cell can receive the array of SPS satellites.

The server further includes a processor; and an information source coupled to the processor. The information source contains sets of SPS satellites in view of cells in the cellular service area and the processor determines the ordered set of SPS satellites for the cell within the cellular service area. The server can be a GPS reference server, a cellular switching center, a location server, a cellular transmission site, a base station controller, or a mobile SPS receiver.

A method is described to obtain an ordered set of SPS satellites, in view of a mobile SPS receiver that includes receiving an ordered set of SPS satellites through a cellular transmission from a cellular transmission site, by means of a mobile SPS receiver configured to receive both SPS signals and signals transmitted from the cellular transmission site. Thus, by allowing the mobile SPS receiver to search for the SPS satellites in an order of the ordered set of SPS satellites obtained from the transmission. The mobile SPS receiver can modify the search for SPS satellites before or after the acquisition of the SPS satellites based on SPS satellite good performance data.

Further described is an apparatus for receiving an array of SPS satellites including a mobile SPS receiver for receiving SPS signals; and a receiver configured to receive signals transmitted from a cellular transmission site; so that an array of SPS satellites can be transmitted through the cellular transmission site to the receiver and the mobile SPS receiver can search for the SPS satellites in an order of the array of SPS satellites.

In addition, procedures and apparatus are described that allow bidirectional communication with a mobile SPS receiver. One method includes receiving a transmission from a mobile SPS receiver within a cell of a cellular service area, the mobile SPS receiver being configured to transmit and receive cellular signals; determining an ordered set of SPS satellites in view of the mobile SPS receiver, at a given time, based in part on the received transmission; and transmitting the array of SPS satellites from a cellular transmission site; so that the mobile SPS receiver can receive the ordered set of SPS satellites.

Furthermore, an apparatus is described to facilitate bidirectional communication with a mobile SPS receiver that includes a receiver for receiving a transmission, from a mobile SPS receiver, originating within a cell of a cellular service area, the SPS receiver being configured mobile to transmit and receive cellular signals; a transmitter for transmitting the cellular signals from a cellular transmission site; and a server for determining an array of SPS satellites in view of the mobile SPS receiver, such that the array of SPS satellites is transmitted by the transmitter and received by the mobile SPS receiver.

The server further includes a processor, and an information source coupled to the processor. The information source contains sets of SPS satellites in view of cells of the cellular service area and the processor determines the ordered set of SPS satellites for the cell within the cellular service areas. The server can be a GPS reference server, a cellular switching center, a location server, a cellular transmission site, a base station controller, or a mobile SPS receiver.

A method is also described to facilitate the acquisition of an ordered set of SPS satellites in view of a mobile SPS receiver, through bidirectional communication by means of a mobile SPS receiver, which includes transmitting from a cell in a cellular service area. to a cellular transmission site that receives transmissions from the cell, via a mobile SPS receiver configured to receive SPS signals and to transmit and receive cellular signals. The mobile SPS receiver receives an ordered set of SPS satellites from the cellular transmission site. The ordered set of satellites are those that are in view of the mobile SPS receiver at a given moment; so that the mobile SPS receiver can search the SPS satellites according to an order of the ordered set of SPS satellites obtained from the transmission received from the cellular transmission site. The satellite health data can be included in the transmission and the mobile SPS receiver can modify the search for SPS satellites before or after the acquisition of the SPS satellites based in part on the satellite health data. In addition, the mobile SPS receiver can modify the ordered set after receipt.

An apparatus is also described to facilitate the acquisition of an ordered set of SPS satellites in view of a mobile SPS receiver, through bidirectional communication by means of a mobile SPS receiver, including a mobile SPS receiver to receive SPS signals; a receiver configured to receive signals transmitted from a cellular transmission site; and a transmitter for transmitting cellular signals to a cellular transmission site; so that when the transmitter, located within a cell of a cellular service area, establishes communication with the cellular transmission site, an ordered set of SPS satellites can be transmitted through the cellular transmission site to the receiver and the mobile SPS receiver. You can search for SPS satellites in an order of the ordered set of SPS satellites.

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Also described is a method for receiving an ordered set of SPS satellites, the ordered set being determined by a mobile SPS receiver.

Another disclosed technique uses a history of stored GPS satellite signal quality information for a location to determine an ordered set of SP satellites.

Another described technique uses mobile SPS receiver information to determine an ordered set of SPS satellites.

Another disclosed technique includes determining an ordered set of SPS satellites in view of a mobile SPS receiver at a given time; and transmitting the array of SPS satellites to a cellular transmission site; so that a server can receive the ordered set of SPS satellites in view of the mobile SPS receiver.

Brief description of the drawings

Figure 1A shows a set of satellites in view of a satellite positioning system (SPS) receiver.

Figure 1B shows a top-down view of the satellites shown in Figure 1A relative to the SPS receiver.

Figure 1C illustrates a cellular communication system having a plurality of cells each served by a cell site, and each of which is coupled to a cellular switching center.

Figure 1D illustrates an example of a combined SPS receiver and communication system in accordance with one embodiment of the present invention.

Figure 2 shows an embodiment of a cell-based information source that provides an association between priority order sets at given times relative to cellular service areas and / or cellular cell sites, in accordance with the teachings of the present invention.

FIG. 3 is a flow chart illustrating a procedure for determining a priority order of satellites in view in accordance with the teachings of the present invention.

Detailed description

The description describes, in one example, the determination of an ordered set of SPS satellites that are in sight of an SPS receiver. The order of the ordered set of satellites is based on the approximate location of the SPS receiver, which is determined from the identification or knowledge of a cellular transmission site in cellular communication with a communication system of the SPS receiver. Knowledge of the cellular transmission site may be implicit in the case where the data identifying the SPS satellites in view of the SPS receiver is provided by a reference SPS receiver located in geographic proximity to the cellular transmission site communicating with the SPS receiver. In one example, the order of the ordered set of satellites is also based on the locations of the satellites relative to the approximate location of the SPS receiver.

Figure 1A shows a set of SPS satellites that are within sight of an SPS receiver 100. The SPS receiver also includes a communication system such as a two-way cellular telephone or two-way (or one-way) paging device. Examples of such communication systems that are coupled to SPS receivers are described in co-pending US Patent Application No. 08 / 842,559, filed April 15, 1997. See also PCT publication WO 98/25157.

Figure 1B shows a top-down view of the satellites shown in Figure 1A relative to the SPS receiver 100. Satellites 102, 104, 106, 108, 110, and 112 are shown at locations at a particular time of day. It should be noted that because the satellites change position over time, some of the SPS satellites shown in Figure 1A may not be visible to the SPS receiver 100 at different times. Furthermore, the SPS receiver 100 is normally mobile. Thus, the satellites in view of the SPS receiver 100 may change as the SPS receiver 100 moves to different locations. Also, in other examples, the SPS signal source may become blocked (eg hidden behind a building) or greatly dimmed. This blocking or dimming can be taken into account when selecting an ordered list of satellites, which is described below.

Figure 1C shows an example of a cell-based communication system 10 that includes a plurality of cell sites, each designed to serve a particular geographic location or area. Examples of cell-based communication systems of this type are well known in the art. See, for example, US Patent 5,519,760 which describes a cellular network system. Cell-based communication system 10 includes two cells 12 and 14 both defined to be within a cellular service area 11. In addition, system 10 includes cells 18 and 20. It will be appreciated that a plurality of other cells with corresponding cell sites and / or cell service areas may also be included in system 10 and coupled to one or more cell switching centers, such as cell switching center 24 and cell switching center 24b.

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Within each cell, such as cell 12, there is a wireless cell-site or cell-site such as cell-site 13 that includes an antenna 13a designed to communicate via wireless communication medium with a communication receiver that may be a combined GPS receiver and mobile communication system such as receiver 16 shown in FIG. 1C. An example of such a combined system is shown in Figure 1D and may include both a GPS antenna 377 and a communication system antenna 379. It will be appreciated that alternative examples may employ a single antenna or more than two antennas.

Each cell site is coupled to a cell switching center. In Figure 1C, cell sites 13, 15, and 19 are coupled to switch hub 24 via connections 13b, 15b, and 19b respectively and cell site 21 is coupled to a different switch hub 24b via connection 21 b. These connections are typically wired connections between the respective cell-site and the cellular switching centers 24 and 24b. Each cell-site includes an antenna and a transmitter and receiver for communicating with communication systems served by the cell-site. It will be appreciated that a communication system within a cell, such as receptor 22 shown in cell 4, may in fact communicate with cell site 19 in cell 18 due to blockage (or other reasons why site 21 cannot communicate with the receiver 22).

In a typical example, the mobile GPS receiver 16 includes a cell-based communication system, which is integrated with the GPS receiver, such that both the GPS receiver and the communication system are included in the same housing. When this combined system is used for cellular telephone communications, transmissions occur between receiver 16 and cell site 13. Transmissions from receiver 16 to cell site 13 then propagate through connection 13b to cell switching center 24 and then either to another cell phone in a cell served by cell switching center 24, or through from a connection 30 (usually wired) to another telephone via the terrestrial network / system 28. It will be appreciated that the term "wired" includes fiber optic connections and other non-wireless connections such as copper cabling, and the like. Transmissions from the other phone, which is communicating with receiver 16, are carried from cell switching center 24 via connection 13b and cell site 13 back to receiver 16 in the conventional manner.

Remote data processing system 26 (which may be referred to as GPS server or location server in some embodiments) is included in system 10 and is used when, in some examples, a mobile GPS receiver is used within a particular cell to determine the position of the receiver using GPS signals received by the GPS receiver. The GPS server 26 can be coupled to the network / landline phone system 28 through connection 27 and can also optionally be coupled to cellular switching center 24 through connection 25 and also optionally coupled to center 24b through connection 25b . It will be appreciated that connections 25 and 27 are normally wired connections although they may be wireless. Also shown as an optional component of system 10 is a query terminal 29 which may consist of another computer system, which is coupled via network 28 to the GPS server. This inquiry terminal 29 can send a request for the position of a particular GPS receiver in one of the cells to the GPS server 26 which then initiates a conversation with a particular GPS receiver through the cellular switching center in order to determine the position. of the GPS receiver and report that position back to the inquiry terminal 29.

It should be noted that a cell-based communication system is a communication system, which has more than one transmitter, each of which serves a different geographical area, which is predefined at any instant in time. Cell sites can also move, rather than being stationary land sites; for example, cell sites in the Iridium and Globalstar systems are low Earth orbit satellites. Typically, each transmitter is a wireless transmitter, serving a cell, having a geographic radius of less than 20 miles, although the area covered depends on the particular cellular system. There are numerous types of cellular communication systems, such as cellular phones, PCS (personal communication system), SMR (specialized mobile radio), one-way and two-way paging systems, RAM, ARDIS, and wireless packet data systems. Typically the different predefined geographic areas are called cells and a plurality of cells are grouped together to form a cellular service area such as the cellular service area 11 shown in Figure 1C and this plurality of cells are coupled to one or more centers of cellular switching that provide connections to networks and / or terrestrial telephone systems. Service areas are often used for billing purposes. Therefore, it can happen that cells in more than one service area are connected to a switching center. For example, in Figure 1C, cells 1 and 2 are in service area 11, and cell 3 is in service area 18, although all three are connected to switching center 24. Alternatively it sometimes happens that cells within a service area are connected to different switching centers, especially in densely populated areas. In general, a service area is defined as a set of cells that are geographically very close to each other. Another class of cellular systems that fits the above description is satellite-based, in which cellular base stations are satellites that normally orbit the Earth. In these systems, cell sectors and service areas move as a function of time. Examples of such systems include Iridium, Globalstar, Orbcomm, and Odyssey.

Figure 1D shows a generalized combined GPS and communication transceiver system. System 375 includes a GPS receiver 376 having a GPS antenna 377 and a communication transceiver 378 having a communication antenna 379. GPS receiver 376 is coupled to communication transceiver 378 through connection 380 shown in FIG. 1D. In normal operation, the communication system transceiver 378 receives approximate Doppler information through the antenna 379 and provides this approximate Doppler information.

ES 2 345 708 T3 on the link 380 to the GPS receiver 376 that performs the pseudo-range determination by receiving the GPS signals from the GPS satellites through the GPS antenna 377. Various embodiments for the combined 375 system are known in the art and have been described in copending applications referred to above.

For the locations of the satellites 102-112 and the SPS receiver 100 shown in FIG. 1A, a priority acquisition order of the satellites 102-112 is determined. This order represents an optimized order for acquiring SPS signals from the SPS satellites based on, for example, the geometry of the satellites in relation to the position of the SPS receiver 100. In one embodiment of the present invention, the satellites 102-112 are listed in the order that provides a desirable geometry between the satellites 102-112 and the SPS receiver 100. For example, the elevation and angle of the satellites 102-112 relative to the SPS receiver 100 may be factors in determining priority order. In yet another example, the best priority order / selection results in the lowest GDOP (Geometric Precision Dilution) and / or PDOP (Position Precision Dilution) and / or HDOP (Horizontal Precision Dilution). Typically, a location server responsible for generating messages chooses the satellites according to a "top n" procedure. In an example of such a procedure, the satellites chosen are those that best optimize the geometry between their locations and the location of the 100 SPS receiver. For example, in a top 4 configuration, the SPS satellites in Figure 1A would be chosen to fill the ordered list of satellites, and would be ordered as follows (from highest priority to lowest priority): 108, 104, 112 and 102. The best n satellite selection procedure provides the information related to the satellite acquisition strategy to be followed by the 100 SPS receiver. In one example, the SPS receiver 100 may choose to stop the satellite acquisition process after the best n satellites have been acquired. Therefore, it is not necessary to prioritize all satellites in view. In fact, less desirable satellites may not be used to resolve the location of the 100 SPS receiver. In another example the location server may provide assistance for a subset of satellites in view of the SPS receiver, such as a set of the best n's. The order is usually chosen to first try to acquire the SPS satellites that are not too close to the horizon and that provide an optimal geometric triangulation solution. The first requirement generally means that SPS signals will be more easily received from non-near-horizon satellites and the last requirement means that the position solution (from pseudo-ranges to higher-order satellites in the order) will have better accuracy (lower error ) than a position solution that could use the lowest order satellites in the order. The order may reflect the expected quality of the measurements (for example, the first satellites in the order are expected to provide higher quality measurements than the rest of the satellites in the order).

It should be appreciated that the acquisition of satellites is a stage in the location determination process. It is also appreciated that if elevation and azimuth data are provided to an SPS receiver, it could use such data to further optimize its satellite acquisition strategy. It is further appreciated that different criteria of geometry or relative location can be used to prioritize the order of satellite acquisition, such as good satellite operation.

The assistance for the proper functioning of the satellite protects against approximate measurements of the satellite. In highly obstructed signal environments, GPS satellite signals are very often received with a very high dynamic range. Receiving GPS signals with signal strengths that differ by more than about 17 dB can cause a GPS receiver to acquire a cross-correlated signal rather than a relatively weaker true signal. A procedure that can be used to detect and possibly correct or eliminate a cross-correlated measurement is described in co-pending US Patent Application Serial No. 09 / 241,334, filed February 1, 1999.

However, for a GPS receiver to detect the presence of cross-correlated signals, all signals from both good and bad satellites must be acquired. A problem would arise if a strong "bad" satellite signal were cross-correlated with a weak "good" satellite signal. Without knowing the presence of a “malfunction” signal, a GPS receiver may not be able to detect a cross-correlation state.

In one example, GPS reference receivers that provide reference data for location servers (also called position determination entity (PDE) in CDMA cell phone systems and service mobile location center (SMLC) in cell phone systems). GSM cell phone) acquire and track all satellites in sight; those of good operation and those of malfunction. In addition, all GPS technologies (such as a GPS receiver) integrated with or connected to wireless devices (such as a cell phone or a two-way paging device) also acquire and track all satellites in sight: the good ones. malfunctions and malfunctions. In a Wireless Assisted GPS (WAG) mode (for example, see the examples described in co-pending U.S. Patent Application No. 08 / 842,559, filed April 15, 1997) the server (s) Location servers can provide “healthy” status information to mobiles communicating with a wireless network served by the location server (s). This health information may accompany any other support information provided by the location server (s). In general, assistive information enables rapid acquisition of GPS signals in highly restrictive signal environments. To achieve such performance improvements, the assistive information may specify the satellites to be searched, the estimated time of arrival of these signals, and the expected frequency (Doppler) of the signals. This assistive information can be provided to improve a three-dimensional search for a satellite signal.

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When satellite signals are acquired, pseudoranges, Dopplers, and other satellite signal measurements are analyzed for cross-correlation states. To perform this analysis, measurements must be made for all satellites in view: the good ones and the bad ones. In this example, the satellite health information is used to detect a cross-correlation state and then the cross-correlated and / or "malfunction" satellites are analyzed to determine whether they should be included in the location calculation process or corrected. . When the support information is provided only for well-functioning satellites (the good-functioning of the satellite is implied in the satellite list) and the current and valid satellite-good-status information is not available for the rover GPS receiver , the mobile will try to acquire only well-functioning satellites. In this case, the mobile would not be aware of a possible presence of a "strong" malfunctioning satellite that is potentially cross-correlated with relatively weaker malfunctioning satellites and therefore would not be tested. The use of undetected cross-correlated signals can lead to large position errors thus affecting the quality of location service.

The order by priority can be changed based on the satellite health information.

Alternatively, the health information can be received directly from the satellites and this health information can be used in the same manner described herein as the health information that is received from a transmitter at a cell site.

Success information can be transmitted from a cell site by broadcasting this information to all satellites in view of a cell phone base station ("cell site"). Alternatively, it can be provided to a cell phone upon request (on demand) for a phone location; the health information can be transmitted from the cell phone base station to the cell phone which then provides the health information to a GPS receiver that is coupled to the cell phone. In case the information is transmitted on demand, a GPS server can determine the appropriate information (for example, good working order) based on a cell site that is in cellular radio / wireless communication with the phone and this cell site determines an approximate location that is used to determine satellites in view of that location and then transmission occurs from the updated good working information for these satellites (in one case) to the cell phone which in turn provides the information to the mobile GPS receiver for use in processing SPS signal on the GPS receiver. Otherwise, the GPS server may retain the updated health information and use it to process the pseudo-ranges (eg correlation measurements) received from the mobile GPS receiver to determine the position of the mobile GPS receiver. In both cases, the pseudo-ranges (eg correlation measurements specifying code phases) and the estimated Doppler are determined even for known malfunctioning GPS satellites so that cross-correlations can be detected as described herein. For example, a GPS receiver may receive updated health information from a cell site but still acquire GPS signals from a GPS satellite that was indicated as malfunctioning in the transmitted updated health information. Co-pending U.S. application serial number 08 / 842,559, filed April 15, 1997, describes a procedure for identifying a cell site that is in wireless communication with a cell phone and which then determines attendance data. satellite for satellites in view based on an approximate location derived from the identification of this cell site. This method can be used with the present invention when the satellite assist data in this case is either good satellite performance (for example based on the satellite almanac) or good updated satellite performance (for example more current than information of the existing satellite almanac message regarding the proper functioning of the satellite).

In another example, an SPS receiver can, based on stored or acquired information, autonomously determine the optimal satellite order and provide the ordered list to a location server responsible for generating messages (and which can then provide the ordered list to other SPS receivers and / or assistive data in the order as provided by the SPS receiver).

In one embodiment, a location server can, based on information provided from a mobile SPS receiver or stored information (eg, a GPS signal quality history), determine an ordered list of satellites that would reflect the probability of signal acquisition. satisfactory (for example, satellites near the horizon would have a lower probability of acquiring a successful signal).

Figure 2 shows an example of a cell-based information source that in one example is maintained on an SPS server such as a global positioning system (GPS) server. Alternatively, the information source can be maintained at a cellular switching center, a base station controller, or each cell site. Typically, the information source is routinely maintained and updated on the SPS server that is coupled to the cellular switching center. The information source can hold data in various formats, and it is appreciated that the format 200 shown in FIG. 2 illustrates only one example of such formats.

Typically, each set of priority information at a particular time, such as the time priority set A1, will include a corresponding location or identification for a cell site or service area. For example, for priority order sets A1 and A2 there is a corresponding identification of cellular service area A as well as latitude and longitude for a representative location in this service area. It is appreciated that normally this latitude and longitude is an “average” location that is generally

ES 2 345 708 T3 is centrally located within the geographic region of the cellular service area. However, other possible approaches may be used particularly when the cellular service area includes unused land.

As shown in the exemplary cell-based information source of FIG. 2, the cell-based information source includes a column 202 that specifies the cellular service area and a column 204 that specifies a cell site number or identification. Note that for cellular service area A the location or cell site identification is not specified, and therefore the approximate location is based on a representative location in the cellular service area, and therefore orders A1 and A2 by priority to acquire SPS satellites are based on this location depending on the particular time, such as ti and t times₂. Column 206 includes a specification of the latitude and longitude for the particular representative location in the service area. Column 208 includes a latitude and longitude specification for the location of a particular cell site within the cellular service area that can be used as a representative location for a mobile SPS receiver receiving priority order. Column 210 includes the priority orders of satellites in view at times ti and t2 for the appropriate representative location. In an alternative embodiment, the ordered list (and the corresponding cell-based information) can be determined in real time, near real time, continuously or on demand.

Figure 3 is a flow chart illustrating an example of a method for determining a priority order of SPS satellites in view in accordance with the teachings of the present invention. In step 302, an approximate location of an SPS receiver is determined from a cell-based information source. The SPS receiver is in wireless radio / cellular communication with at least one wireless cell site, and the identity of this cell site is determined. The approximate location is based on at least one of a representative location in a cellular service area that includes this cell or a representative location of the wireless cell site in the cellular service area and again represents the approximate location of the SPS receiver to which serves the wireless cell-site. A cell-based information source (see for example Figure 2) can be used to query or determine the approximate location based on the identification of the wireless cell site that is in communication with a cellular communication system that is coupled to the SPS receiver. Alternatively, the cell-based information source can be used to query or determine the appropriate priority order directly from the identification of the wireless cell site that is in communication with the SPS receiver. In step 304, a priority order based on the approximate location of the SPS receiver (or the identification of the wireless cell site that communicates with the SPS receiver through a cellular communication system that is coupled with the SPS receiver) is Determines for satellites in sight of the approximate location. In one example, satellites are prioritized based on their location relative to the approximate location of the SPS receiver. In another example, satellites are prioritized based on their location relative to each other and relative to their approximate location. It is appreciated that some criteria other than geometry can be used to prioritize order. In step 306, the priority order is transmitted from the wireless cell-site to the SPS receiver and then the SPS receiver searches for and acquires SPS signals from the SPS satellites in the designated order in order of priority sent to the SPS receiver.

A more detailed discussion of cellular communication systems and their use with SPS receivers is disclosed in US Patent Application Number 08 / 842,559, now US Patent Number 6208290, filed April 15, 1997, entitled "An Improved GPS Receiver Utilizing a Communication Link ”by Norman F. Krasner.

The priority order of SPS satellites provided by the location server or derived from the SPS receiver can be used to improve the time to acquire satellites, the time required to determine the location information, and can reduce the bandwidth requirements to provide data. from the location server to the SPS receiver.

In this discussion, examples have been described with reference to the application in the US global positioning system (GPS) system, which is an example of an SPS system. It should be clear, however, that these procedures are equally applicable to other satellite positioning systems, such as the Russian Glonass system. Thus, the term "GPS" used herein includes such alternative satellite positioning systems, including the Russian Glonass system. Likewise, the term "GPS signals" includes signals from alternative satellite positioning systems.

Furthermore, although the examples are described with reference to GPS satellites, it will be appreciated that the teachings are equally applicable to positioning systems using pseudolites or a combination of satellites and pseudolites. Pseudoliths are terrestrial transmitters that emit a PN code (similar to a GPS signal) modulated into an L-band (or other frequency) carrier signal, generally synchronized with a GPS time. Each transmitter can be assigned a unique PN code to allow identification by a rover. Pseudolites are useful in situations where GPS signals from an orbiting satellite may not be available, such as tunnels, mines, buildings, urban canyons, or other closed areas. "Satellite" as used herein is intended to include pseudoliths or equivalents of pseudoliths, and the term GPS signals, as used herein, is intended to include GPS-like signals from pseudoliths or equivalents of pseudolites.

In the detailed description above, the apparatus and method of the present invention have been described with reference to specific exemplary embodiments. However, it will be apparent that various modifications and changes can be made without departing from the broader scope of the present invention. The present specification and the figures should therefore be considered illustrative rather than restrictive.