Wireless telephone distribution system with time and space diversity transmission

Wireless telephone distribution system with transmission with diversity in time and space.

Field of the Invention

The present invention relates to wireless communication systems in both directions. In particular, the present invention relates to wireless telephone systems with antennas of diversity in space and signal transmission with diversity in time, to reduce the fade of the signal and measure the position of the subscriber.

Background of the invention

Wireless radio communication is subject to the adverse effects of signal fading, in which the signal level in the receiver temporarily loses intensity for a variety of reasons, such as because of variable reflections in multiple paths, which they cause the cancellation of signals, loss in the transmission variable over time, due to atmospheric conditions and the movement of a mobile receiver, which introduces obstructions in the signal path, and the like. The fading of the signal causes a faulty reception, discomfort or, in extreme cases, a loss of the call connection.

The use of various forms of signal diversity to reduce fading is known. For example, as indicated in US Pat. with No. 5,280,472, signal diversity mitigates the detrimental effects of fading. There are three main types of diversity: diversity in time, diversity in frequency and diversity in space.

The diversity in time is obtained through the use of repetition, interleaving or error correction coding, which is a form of repetition. Error detection techniques, in combination with automatic retransmission, provide a form of time diversity.

In frequency diversity, signal energy widens across a wide bandwidth to combat fading. Frequency modulation (FM) is a form of frequency diversity. Another form of frequency diversity is multiple code division multiple access (CDMA), also known as spread spectrum. Due to its intrinsic nature as a broadband signal, CDMA is less susceptible to fading, compared to a narrowband modulation signal. Because fading occurs, in general, only in a part of the radio spectrum at any given time, a spread spectrum signal is inherently resistant to the adverse effects of fading.

Diversity in space is provided by transmitting or receiving the same signal by more than one antenna, geographically separated. The diversity in space provides alternative signal paths for protection against any of the paths being subject to fading at any time. The diversity in space also creates a certain diversity in time, since the receiver receives the same signal, separated by small propagation delays. The difference in propagation delays requires that the receiver be able to discriminate between the incoming signals. One solution is the use of multiple receivers, one for each signal that arrives. For example, it is known from US Pat. No. 5,280,472 the deliberate introduction of relatively small delays compared to an information symbol, in a multi-antenna CDMA system with diversity in space, in order to create artificial signals with multi-path time diversity, greater than a chip delay, up to a few chips. CDMA systems are able to discriminate between different identical signals that reach the receiver with different propagation delays greater than a chip delay. Such receptors are known as Rake receptors. However, prior art systems require multiple CDMA receivers, a CDMA receiver for each independent received CDMA signal. It is desirable to provide a system for receiving CDMA signals with time diversity that does not require multiple CDMA receivers.

The measurement or determination of the position of mobile units is well known. In some systems, fixed antennas measure the mobile position. In other systems, the mobile unit determines its position from multiple received signals. If the system is two-way, the communication link allows exchange of position data to both the mobile subscriber and the fixed system. Several known systems use satellites or multiple antennas to provide information about the position of a mobile subscriber. For example, multiple directional reception antennas can be used to triangulate the position of a mobile transmitter. In such systems, stationary receivers determine the position of the mobile subscriber; in other systems, the mobile subscriber determines its position from the received signals. For example, the Global Positioning System (GPS) is a multi-satellite system that provides signals that allow a mobile subscriber station to determine its position in latitude and longitude. However, both satellite systems and GPS receivers to receive signals from satellites tend to be expensive.

The combination of a GPS receiver and a cell phone is shown in US Pat. No. 5,223,844. Such a combination provides useful services such as a security alarm service to deter theft of a car, in which the triggering of the alarm also alerts the security service about the position of the car. In general, it is desirable to provide a system that combines a telephone or data service with position measurement, at a reasonable cost.

It is desirable to provide a signal system with time diversity that uses time division multiple access (TDMA), in various combinations with antennas with space diversity and CDMA, to provide a variety of systems that resist the fade, reduce receiver cost and provide a position measurement for mobile subscribers.

Summary of the invention

The present invention is incorporated as a wireless communication system in which time diversity and diversity in space are used to reduce fading and simplify receiver design. The present invention is further incorporated as a wireless communication system in which time division signals are multiplexed by code division (spread spectrum) on antennas of diversity in space, to provide a wireless communication system with the ability to determine the position of the subscriber using the same communication signals that are used for primary wireless communication.

Specifically, a data packet that, for example, can carry telephony voice traffic, is transmitted in three different instants from three different antennas. The receiver thus receives the same data packet at three different times, from three different antennas. The receiver uses the best data packet or a combination of data packets to reduce the effects of fading.

In addition, the receiver uses the absolute time and relative extrapolated arrival of the three data packets to determine their position with respect to the three transmission antennas. First, the absolute distance to one of the antennas is determined by the time required for a round trip message. Next, the relative time of arrival of the data packets, with reference to a universal time, from the other two antennas, indicates the relative distances compared to the first antenna. Because the three transmitting antennas are in known fixed positions, the receiver calculates its own position as the intersection of three constant distance curves (in the case of two dimensions, circles or, in the three-dimensional case, the intersection of three spheres). Alternatively, the mobile subscriber station provides raw delay measurement data, back to a fixed station or location service center, which calculates the position of the mobile subscriber.

More particularly, the present invention is incorporated as a system that uses CDMA to modulate a TDMA signal that is transmitted from three antennas with diversity in space. In a first embodiment, TDMA signals are used to transmit multiple repetitions of the same data packet from a transfer station, with three antennas with diversity in space. In a second embodiment, the TDMA signals are used to transmit multiple repetitions of the same data packet from three transfer stations, each transfer station including one of three antennas with space diversity. The data packets may either be identical or they may carry substantially the same information, but modulated with different spreading codes or different segments of the same spreading code.

Brief description of the figures

Figure 1 is a system diagram of a wireless telephony distribution system that includes a first embodiment of a transfer station according to the present invention.

Figure 2 is a block diagram of a first embodiment of a wireless telephone distribution system according to the present invention.

Figure 3 is a system diagram of a first embodiment of a wireless telephone distribution system according to the present invention.

Figure 4 is a system diagram of a wireless telephone distribution system that includes a second embodiment of a transfer station in accordance with the present invention.

Figure 5 is a system diagram of a second embodiment of a wireless telephone distribution system according to the present invention.

Figure 6 is a block diagram of a second embodiment of a wireless telephone distribution system according to the present invention.

Figure 7 is a timing diagram of a time division multiplex signal that modulates a code division multiplex signal according to the present invention.

Figures 8 and 9 are a block diagram of a first embodiment of a transfer station according to the present invention.

Figure 10A is a time slot allocation diagram of a wireless telephone distribution system according to the present invention, illustrating time division multiplexing and code division multiplexing for 6 simultaneous calls.

Figure 10B is a time slot allocation diagram of a wireless telephony distribution system in accordance with the present invention, illustrating time division multiplexing and code division multiplexing for 12 simultaneous calls.

Figures 11A and 11B are a time slot allocation diagram of a wireless telephony distribution system according to the present invention, illustrating time division multiplexing and code division multiplexing for 24 simultaneous calls.

Figure 12 is a block diagram of a second embodiment of a transfer station according to the present invention.

Figure 13 is a block diagram of a subscriber station in accordance with the present invention.

Figure 14 is a block diagram of a centralized and integrated transfer station in accordance with the present invention.

Figure 15 is a block diagram of an implementation of transfer station antennas.

Figure 16 is a block diagram of an implementation of distributed antennas of the present invention using coaxial cable or fiber optic cable.

Figure 17 is a timing diagram of a time division multiplex signal that modulates a code division multiplex signal in accordance with the present invention.

Figure 18 is a system diagram illustrating an implementation of distributed antennas of the present invention.

Figure 19 is a block diagram illustrating a system according to the present invention where the location center is external to the communication system.

Figure 20 is an illustration of a system according to the present invention for determining the position of a mobile subscriber station.

Figure 21 is a system according to the present invention illustrating a method for determining the position of a mobile subscriber station.

Figure 22 is a synchronism diagram illustrating a method for determining the distance from a subscriber station and a transmission transfer station.

Fig. 23 is a synchronism diagram illustrating a method for determining the relative distances from a subscriber station to two transmission transfer stations.

Detailed description

SYSTEM DESCRIPTION - FIRST REALIZATION; Figures 1, 2, 3, 8, 9

In a first embodiment of the invention shown in Figure 1, a mobile user having an antenna 10 is connected to a CDMA transfer station 14. The CDMA transfer station 14 additionally includes an antenna T , 16, an antenna A, 11, an antenna B, 12 and an antenna C, 13. Antennas A, B and C can be mounted either in independent structures, as shown, or in a single mast. The only physical requirement is that the space between the antennas must be sufficient for a diversity in space without correlation. Although a quarter wavelength separation may be sufficient, at least ten wavelengths are preferable. At 1 GHz, 10 wavelengths are approximately 9.14 m (30 feet), while at 5 GHz, 10 wavelengths are approximately 1.83 m (6 feet).

The mobile subscriber antenna 10 (which is also referred to herein as the antenna of the user terminal, or the antenna of the subscriber station or simply the antenna U) is coupled by a two-way radio link, or both ways, to the A, B and C antennas. The CDMA transfer station 14 is additionally connected by means of a bidirectional radio link through the antenna T, by appropriate switching, to the public switched telephone network.

During operation, the direct channel telephony voice traffic that is received in data packets by the antenna T, is transmitted by the antenna A during the time slot 1, is repeated by the antenna B during the time slot B , and is further repeated by antenna C during time slot 3. All three repeated data packets are received sequentially by antenna 10. In the opposite direction, the data packets representing telephony voice traffic, transmitted from the antenna 10, are received substantially simultaneously by the antennas A, B and C. The CDMA transfer station 14 further retransmits , data packets received in the reverse direction through the T antenna, back to the telephone network.

Figure 2 is a diagram of an overview of a system according to the present invention that includes the different interconnections between the support network, that is, between the public switched network 20 and the switching center and the central processor 22 , and CDMA transfer stations 26, 28, 30, 32, 34, 36 and 38.

The user located in the CDMA subscriber station 42 is connected, through the antenna 10, with the CDMA transfer station 38, through the antennas A, B and C. The antenna T, 39, located in the CDMA transfer station 38 carries wireless TDMA telephony voice traffic to the antenna 25 located in the base station 24. Each of the other CDMA transfer stations is connected to the switching center 22 by a variety of means of communication. interconnection. The connection means W between the TDMA base station 24 and the CDMA transfer station 36 are wireless means having a TDMA channel structure with six TDMA slots. The WE wireless TDMA distribution interconnect may be a commercially available wireless local loop system, such as the Ultraphone® digital radio telephone system, provided by Interdigital Communications Corporation. The TDMA time slot structure is carried through the transfer station to become the time slot structure for the CDMA signal structured in slots, at the output. The WE connection means are the same as the W connection, with the exception that there are four W modules that work in parallel to provide basic connectivity for 24 voice channels. The connection means F uses a fiber optic cable that is connected between the switching center 22 and the CDMA transfer station 32, without passing through a wireless base station. Because the connection means F (fiber optic cable) incorporates a modem with a TDM / TDMA channel structure similar to W and WE, they easily act as an interface with the transfer station. The FT (fiber optic cable carrying standard T1 multiplexing) connection between the switching center 22 and the CDMA transfer station 30 is a fiber optic cable that uses a standard T1 multiplexer as channel combination means. Therefore, the transfer station that handles the WE connection means can be easily adapted to operate with the FT connection means. The connections C (coaxial cable) with the CDMA transfer station 25, and CT with the CDMA transfer station 28 (coaxial cable carrying the standard multiplexing of T1) are cable means that function as F and FT, respectively. The connection means L to the CDMA transfer station 36 is a conditioned line that carries a data stream of up to 100 kb / s, which has the same structure as the wireless TDMA connection means W. LE connection means (not shown) use 4 lines conditioned to operate in the same way as WE connection means. The PG connection means to the CDMA transfer station 34 is a torque gain capability that has been arranged as an input interface to a transfer station.

The use of a combination of aerial and fiber optic / cable means for connection to the transfer stations, and a common exit air interface, between the transfer stations and the CDMA user terminals, results in a rapid response and flexible and an economical solution. In addition, normal telephone lines conditioned to handle 64 kb / s to 100 kb / s can also be used to replace the TDMA wireless input to the transfer station. It is also very cost effective to connect the input side of the transfer station to the output of a torque gain module. Because the air interface remains the same for all these interconnection means, this extended concept becomes a very cost-effective transition and solution vehicle.

In the system diagram of Figure 3, the telephony voice traffic through the public switched network 20 is coupled to a TDMA base station 24 having an antenna 25 for the transmission and reception of TDMA signals. A plurality of CDMA transfer stations 44, 46, 48, 50 and 52 provide a wireless telephone service for a plurality of subscribers 45 and 47. Each CDMA transfer station includes a T antenna to receive and transmit TDMA signals, as well as an independent A antenna, B antenna and C antenna, to communicate with mobile subscribers 45 and 47. By way of example, the station TDMA 24 base can have a range of a radius of 56.32 km (35 miles), which covers numerous CDMA transfer stations. Each CDMA transfer station can usually have a range of 8.05 km (5 miles) and be separated 4.83 km (3 miles) from each other to provide cellular coverage of the entire area. The CDMA transfer station 46 will service the subscriber 45, while the CDMA transfer station 50 will service the subscriber 47. As each subscriber moves through the system, a different CDMA transfer station will be assigned to service that subscriber.

An alternative embodiment takes advantage of the rich connectivity described above to more widely distribute the three antennas that are used to provide diversity in transmission space. The wider distribution allows compensation not only for multipath fading, but also for fading due to blocking. For example, if the CDMA user (antenna 10 in Figure 1) is placed behind a building or hill, the signal from the three space diversity antennas, in a single transmission station, will fade.

However, if the energy in each time slot was transmitted from different transfer stations, as in Figure 4, there would be a high probability that the user terminal would be blocked with respect to the three transfer stations at the time Therefore, it is possible to randomize the effects of fading due to blocking and that are more similar to multipath fading. Randomization is achieved by having the central controller assign the different time slots individually during the call establishment procedure. When implemented using W or WE connection means, there is little impact on the capacity between the base stations and the transfer stations, but this would increase the number of TDMA receivers. However, there is also an improvement in diversity in the link from the base station to the transfer station. In general terms, the impact on the other connection means with fixed cable installation is even smaller. An important advantage of using multiple transfer stations as sources of transmission diversity is that this allows the user CDMA receiver to evaluate the signal quality from each transfer station and request a transfer during individual time slots to as better links are found, providing an extremely reliable and smooth transition as the user passes through an area.

SYSTEM DESCRIPTION - SECOND EMBODIMENT; Figures 4, 5, 6, 12

Figure 4 illustrates a wireless telephone distribution system with improved diversity in space. As before, a mobile user antenna 10 is coupled to an antenna A during time slot 1, an antenna B during time slot 2 and an antenna C during time slot 3. However, each of the A, B and C antennas are mounted in respective independent CDMA transfer stations 54, 56 and 58. In particular, an antenna A, 60 is provided at the CDMA transfer station 54, an antenna B, 68 is provided at the CDMA transfer station 56 and an antenna C, 64 is provided at the transfer station of CDMA 58. Each of the respective transfer stations 54, 56 and 58 are coupled, through respective antennas 62, 70 and 66, to the TDMA wireless digital telephone system. The signals received by the subscriber station antenna 10, from the antennas A, B and C, are similar to those received in the configuration of Figure 4. However, due to the separation of the antennas A, B and C, in the independent CDMA transfer stations 54, 56, 58 the signal diversity is greatly improved, both in transmission and reception.

The system configuration of Figure 6 is similar to that of Figure 2, with the exception that each CDMA transfer station has either an antenna B, or antenna B or antenna C. For example, the CDMA transfer station A, 108, has an independent antenna A, 109. The CDMA transfer station 106 has an antenna B, 107. Similarly, the CDMA transfer station 104 has an antenna C, 105. Thus, the antenna 10 of the CDMA subscriber station 112 receives signals from each of the CDMA transfer stations 108, 106 and 104. The received signals are multiplexed by time division, in the sense that Only one of the antennas, A, B or C, is transmitting to antenna 10 at any one time. During transmission, however, the A, B and C antennas provide multiple signals multiplexed by code division to other users.

In the present embodiment, each transfer station has only one type of antenna: either antenna A, or antenna B or antenna C. Figure 5 illustrates a system arrangement that covers a service area. . As before, the public switched network 72 is connected to a TDMA base station 74 that has a transmission antenna 75 that covers an area with a radius of approximately 56.32 km (35 miles). Throughout the service area, the CDMA transfer stations are separated from each other in one direction 84, and are placed in another direction 86 to cover the service area. For illustration purposes, regular placement has been shown. In practice, CDMA transfer stations are positioned such that they provide coverage whereby a plurality of subscribers 88, 90 are always within the range of an antenna A, B and C. For example, CDMA transfer stations 76 and 82 are of antenna type A, while CDMA transfer station 80 is a type C antenna and CDMA transfer station 78 is a type B antenna. in this mode, the subscriber 88 receives signals from the CDMA transfer stations 76, 78 and 80, while the subscriber 90 can receive signals from the CDMA transfer station 82, 78 and 80.

A time slot structure for use in the present invention is shown in Figure 7. Six time slots are used. Time slots 1 and 2 are used for reception, followed by time slot 3, where the subscriber station transmits, followed by time slot 4, which is also used for reception. During time slots 5 and 6, the CDMA receiver scans the transmission from the other transfer stations.

CALL ESTABLISHMENT

When a circuit is to be established or transferred, the base station assigns a frequency, base station and transfer station pair, a slot and a PN sequence. This then transmits to the transfer station all of these assignments and identifies which subscriber will use the circuit. During call establishment, the transfer station passes the slot and PN sequence assignments to the desired transfer station. See, for example, Figure 17, in which the TDMA time slots 1 to 8 are associated with users A to F, respectively. In a given time slot, for example, time slot 2, the message for user B contains synchronization information 1701, common control data 1702 for extensive system functions, private control data 1704 and dedicated user traffic 1705 for user B. Dedicated user traffic 1705 is used during call establishment to transmit signaling information and initialization data.

DIRECT JOURNEY

Compression and decompression of the signals, plus the bits added for direct error correction (FEC) are performed at the base station. In the direct direction (towards the subscriber station), the base station transmits continuously, but the information contained in each slot is directed to a particular subscriber station.

By way of example, the base station can transmit the information during slot 1, at a fa frequency. The transfer station receives the information by demodulating the signal at the fa frequency during slot 1, and regenerating the information only at the symbol or bit level. The transfer station does not perform any decoding (ie error correction, compression and decompression). The design of the transfer station is simplified, therefore, thanks to the acceptance of the signal already encoded from the TDMA base station. After regeneration at the symbol level, the received TDMA signal is combined with the assigned PN sequence and is retransmitted from the base station as a CDMA signal at the frequency fp, without any intentional delay, to the antenna A. The transfer station additionally stores the information received from the base station in a memory buffer. At the end of the transmission of the antenna A, the information bits stored in the memory buffer are modulated on a continuation of the PN signal and broadcast, through an appropriate transmitter, to the antenna B. Thus, the identical information signal using the same PN sequence, but increased by a fixed number of chips, is transmitted on the antenna B. The relative position, or phase of the PN sequence with respect to the transmitted information , is different. At the conclusion of the first repetition, the information contained in the time slot buffer is extracted by reading a third time to provide a third repetition of the information, modulated by a continuation of the PN sequence, even with a different phase, through an appropriate transmitter, to antenna C.

SUBSCRIBER STATION PROCESSING

The subscriber station, using the correct CDMA code, receives during each of the three slots that contain an information signal repetition, such that it receives three identical repetitions of the data packet from three antennas located in different positions . The subscriber station then compares the three repetitions and selects the one with the best quality, which may be based on the speed or proportion of bit errors, phase distortion, signal-to-noise ratio, etc. In this way, the diversity of transmission in space is achieved. Only a single antenna is needed at the subscriber station. The subscriber station demodulates and decodes the signal, and performs error correction, decompression, etc. A maximum probability combiner can be used to combine the power from the three time slots. Ideally, the energy of the received data packets is maximally combined before making a firm decision.

During the third time slot T3, the subscriber station transmits back to the transfer station using a PN sequence similar to the one it received. The PN sequence can be the one that was deducted from the reception (after regeneration) or it can be generated locally based on the original code received during the call establishment. Because the subscriber station does not transmit during the same period of time it is receiving, no diplexer or slot filter is necessary. A simple T / R (transmission / reception) switch is used to switch the antenna between transmission and reception. Only a single receiver is needed at the subscriber station to achieve a diversity of three branches. The three chains required by a Rake receiver are not necessary in the present invention.

On the other hand, the benefits of triple redundancy in space and time, with a certain frequency protection provided by the expanded spectrum, are not obtained adversely affecting capacity. The diversity of three branches typically achieves a reduction for deep fading of at least 10 dB (a factor of 10x). Although the three transmitted repetitions of the same information signal increase the interference level by a factor of 3 (approximately 5 dB), because the fades are 10 dB less, the transmitter power levels can be reduced by a factor of 10 (10 dB). In this way, the total amount of interference is reduced by a factor of 10/3 or 5 dB. Because the transfer station to a subscriber link is operated in a self-interference mode, this means that three times more simultaneous subscriber circuits can be used, than if diversity were not used.

RETURN PATH

In the reverse direction (from the subscriber station to the transfer station), three receivers are connected respectively to three antennas located in the transfer station, to provide a space diversity of three conventional branches. The same analysis in relation to the interference and the number of available circuits is applied to the transmission in the reverse direction as well as in the direct sense, except that the information is transmitted only once and is received simultaneously by the three antennas. from the base station.

In addition to increasing the number of subscribers per unit of frequency, the present invention is cost effective. First, the subscriber station only needs a single receiver r. Second, you don't need a diplexer. Third, the transfer station does not need to decode or re-encode any signal. The number of subscribers for each transmitter is the same, although, because the diversity in space in the reverse direction is used, the number of subscribers per receiver is increased. Conversely, the subscriber station noise may be allowed to be louder if full use of the increase in the number of subscribers is not fully utilized.

The signal received by the transfer station from the subscriber station is retransmitted (again with regeneration at the symbol or bit level, but without decoding) from the transfer station, back to the base station, without a delay intentional during the same slot. Provided that the slot is within the same TDMA frame or, at least, with a duration of one frame of the slot used from the base station to the transfer station, no additional delay is incurred for the use of this system.

TRANSFER STATION - FIRST REALIZATION; figures 8, 9, 15

The CDMA transfer station has a TDMA input on the T antenna. The output side of the transfer station on the A, B and C antennas uses a CDMA structure to reach a large number of subscribers in areas with a relatively dense population. The CDMA has several attributes that make it desirable for this application. The broadband signal is inherently robust in a multipath environment and has the ability to overcome interference, intentional or otherwise. The possibility that selective fading causes the entire spectrum to be suppressed is reduced as the transmitted spectrum increases. A higher chip speed, or an increased TW product, reduces the amount of fading margin that is required to achieve a specified level of performance.

The spread spectrum signals have intrinsic multi-path protection for fading protection. However, statistical models do not take into account, in general, the duration or frequency with which fading occurs. The specific geometry at each location, or how the geometry is changing relative to the receiver, determines the actual fading parameters. For small cells, with low antennas, the difference in path lengths for strong signals is very likely to be small. The result of this is a flat fading. That is, the spectrum over ten or fifteen megahertz will fade at the same time. Therefore, it is not possible to use the intrinsic multi-path protection features of spread spectrum signals to protect against flat fading, unless at least 25 or 30 MHz is available. In addition, there is often no path multiple of importance that has a sufficient delay to take advantage of an additional Rake receiver. Even so, the use of multiple paths, real or artificial, requires additional receivers / correlators in the CDMA user terminal. Therefore, in order to maintain reliable operation using only CDMA, the addition of a margin of at least 15 dB to the power allocation of the link is required, in particular to take into account the situation in which a mobile user stops in one of the nulls or a fixed user the location geometry changes slightly.

The present invention utilizes the other important feature of spread spectrum systems, the ability to overcome interference, as a technique to combat difficult multi-path situations. The capacity of a CDMA system is limited by the amount of interference that is being received by the desired receiver. Provided that the TW product is large enough to raise the desired signal out of interference, it does not matter what the speed of the transmitted data really is. Therefore, with the present invention, the speed of the transmitted information is reduced to allow the transmitted signal to be repeated three times from three different antennas, whereby a triple transmission diversity is obtained that allows to reduce the range of Power transmitted at least 10 dB for a high performance link. Therefore, even if additional interference is introduced into the links, the CDMA processing gain easily exceeds the adverse impact. That is, the gain from triple diversity greatly exceeds, in a high quality system, the loss due to added interference.

A block diagram of the transfer station according to the first embodiment of the present invention for the direct channel is shown in Figure 8. The TDMA T antenna, 916, is coupled, via a transfer receive switch 918, to a TDMA 800 receiver. The output of the TDMA 800 receiver is connected to an 802 demultiplexer, the output of which is stored in registers of 806 buffer of time slots. A time multiplexer 808 accesses the contents of the buffer slots 806 of time slots and provides data packets that are supplied as output to various CDMA encoders 810 intended for transmission over the antenna A. The output of the multiplexer Time 808 also provides data packets that are supplied as output to a plurality of CDMA encoders 812 intended for transmission over the C antenna. Similarly, time multiplexer 808 provides data packets that are supplied as output to a plurality of CDMA encoders 814 provided for transmission over antenna B. Each of the plurality of CDMA encoders 810, 812 and 814 is provides for the respective CDMA transmitters 816, 824 and 826. Each of the CDMA transmitters is coupled to a respective antenna 822, 824 and 826 in order to provide respective antenna A, antenna B and antenna C transmissions.

The coordination of the synchronism regulation and control of the TDMA 800 receiver, as well as the buffer slots 806 of time slots, the time multiplexer 808 and each of the plurality of CDMA encoders, is controlled by a synchronization and control device 804. The synchronization and control apparatus 804 also provides a position identification (ID) representing the particular transfer station to the plurality of CDMA encoders 810, 812 and 814, for inclusion in the signals transmitted on the antennas A, B and C.

The transfer station of Figure 8 also includes a CDMA receiver and a TDMA transmitter 900, which is shown in greater detail in the block diagram of Figure 9. The TDMA transmitter is connected to the antenna 916 through the 918 transmission and reception switch, while CDMA receivers are connected through respective diplexers to antenna A, antenna B and antenna C, as shown in greater detail in Figure 15.

Figure 9 is a block diagram of a transfer station illustrating the structure of the handling signals in the reverse channel. Antennas A, B and C, which are indicated respectively as 822, 824 and 826, are connected to the CDMA receiver A, 902, the CDMA receiver B, 904 and the respective CDMA receiver C, 906. The output of the respective CDMA receivers A, B and C is supplied to a maximum probability combiner 908, the output of which is provided to a buffer memory buffer and a time slot multiplexer 910. The memory buffering registers of the time slot multiplexer 910 provide data packets to a TDMA transmitter 914 that is coupled, through the transmit and receive switch 918, to the antenna 916. The TDMA receiver and CDMA transmitter 828 corresponding to the block diagram of Figure 8, is coupled with the other terminal of the transmit and receive switch

918.

Figure 15 illustrates the antenna configuration of a transfer station that allows antenna A, antenna B and antenna C to be shared between TDMA and CDMA transmission and reception signals. A modulator 1502 is connected, through a time multiplexer 1503, to diplexers 1510, 1514 and 1518, respectively connected to antenna A, 1512, antenna B, 1516 and antenna C, 1520. The other inputs of the diplexers 1510, 1514 and 1518 are connected, respectively, to the outputs of the demodulators 1504, 1506 and 1508.

In the operation illustrated in Figure 8, a TDMA signal received on the antenna 916 is demultiplexed and placed in the buffer slots 806 of time slots. A data packet intended for a given subscriber is selected by time multiplexer 808 during time slot 1 to encode a CDMA signal by one of a plurality of encoders 810 for transmission over antenna A. The same data packet is again selected by time multiplexer 808 to encode a CDMA signal by one of a plurality of encoders 812 during time slot 2, for transmission over antenna B. Finally, that same packet of data is subsequently selected by time multiplexer 808 to encode a CDMA signal by one of a plurality of encoders 814 for transmission, during time slot 4, by antenna C.

In the reverse direction, and referring to Figure 9, the transmission of CDMA from the subscriber station, during time slot 3, is received substantially simultaneously by the antennas 822, 824 and 826. Each of the receivers CDMA 902, 904 and 906 receive the same data packet. A maximum probability combiner 904 combines the power from the three time slots before making a firm decision. In general terms, the signal that is more intense and free of errors will be selected. After selection, the data packet is kept in a buffer memory buffer and time slot multiplexer 910, awaiting placement in its appropriate time slot for transmission, by the TDMA transmitter 914, by the antenna 916.

TRANSFER STATION - SECOND REALIZATION; figure 12

A transfer station according to the second embodiment of the present invention is shown in Figure 12. In essence, this transfer station is similar to the transfer station of Figures 8 and 9, with the exception that only one CDMA, A, B or C antenna is provided. In particular, in Figure 12, the antenna 1200 is connected, via a transmission and reception switch 1202, to a TDMA receiver 1204. The output of the TDMA receiver 1204 is demultiplexed at 1206 and placed in the buffer slots 1208 of time slots. A data packet placed in the time slot buffer 1208 is multiplexed in time by a demultiplexer 1210 to one of a plurality of CDMA encoders 1212. The encoded CDMA signal is amplified in the coupled CDMA transmitter 1214 , through a diplexer 1218, to antenna A, 1228.

The A 1228 antenna also works to receive CDMA signals. To this end, a CDMA receiver 1226 is connected to antenna A, 1228, through a diplexer 1218 to provide packets of data received to the combiner and buffer slots 1224 of time slots. A time multiplexer 1222 takes the data packets contained in the buffer slots 1224 of time slots and composes a time multiplexed signal for a TDMA transmitter 1220, which is connected, through a transmit and receive switch 1202, to antenna 1200. The operation of the transfer station is controlled by a synchronization and control apparatus 1216 which also includes a unique position identification (ID) for this particular transfer station, and call establishment control parameters.

During operation, the transfer station receives TDMA signals through the T 1200 antenna, which are demodulated in the TDMA receiver 1204 and demultiplexed in the demultiplexer 1206 for placement in the buffer slots 1208 of time slots. The data packets contained in the buffer slots 1208 of time slots are transmitted by the antenna A during the time slot 1. For this purpose, the time multiplexer 1210, the CDMA encoders 1212 and the CDMA transmitter 1214 retrieve the respective data packets from the buffer slots 1208 of time slots and encode the appropriate data packet into a signal. CDMA encoded on antenna A. On the return path, the CDMA 1226 receiver receives signals simultaneously through the A, B and C antennas during all time slots. The received data packets are demodulated by respective PN codes and placed in some 1224 time slot combiner buffer records, such that each time slot is assigned to a different user. After this, the data packets are temporarily multiplexed in the multiplexer 1222 for transmission by the TDMA transmitter 1220, through the transmission and reception switch 1202, by the antenna 1200.

The transfer station is the conversion point for establishing a correspondence relationship of the TDM / TDMA signal with a CDMA signal. The CDMA signal, when properly designed, has superior behavior against multipath interference. The input side of the transfer station is part of a structured distribution network. This is basically a tandem relay point located in the network, that is, the address for the final CDMA user also includes the address of the intermediate point (the transfer station). Because, in the general case, the final CDMA user can move and access the network through another transfer point, it will be necessary to provide the ability to enter the address of the transfer station regardless of the address of CDMA users. For fixed subscribers such as the TDMA subscriber station 40 of Figure 2, this will not be a problem, except for a reinforcement routing or for protection against fading.

The preferred input network includes a certain number of base stations, transfer stations and TDMA user stations, as shown in Figure 2. Any time slot at any frequency can be assigned to any TDMA user transfer or station. . In order to reduce the cost of the transfer station, it has been proposed that, once a CDMA user has been connected through a specific transfer station, any additional CDMA users assigned to the transfer station, also will be assigned to a time slot on the same frequency as the first user. By properly managing these assignments, the number of TDMA radio elements can be significantly reduced. The base station 24 or the switching center and the central processor 22 will manage the radio resources and allocate the frequencies, the time slots and the PN codes, thereby ensuring efficient use of the spectrum and radios. The frequency, time slot and PN code are all assigned during the initial call establishment procedure.

Local transmissions on the output side of the transfer station are CDMA, but each subscriber is assigned a specific time slot of a time division signal. Therefore, the individual information rate is increased by the number of time slots. However, the total data rate for all subscribers remains the same and the total power transmitted for all signals remains the same; It is only redistributed. Because the individual time slots are disconnected or deactivated unless there is activity, the transmitted power is reduced by approximately 3 dB for voice traffic. Because the same information is transmitted three times, the average transmitted power is increased by 5 dB. Therefore, the total power transmitted from each transfer station is increased by 5 dB, when transmitted three times, but is also reduced by 10 dB, due to the improvement of diversity, with the result of a global reduction 5 dB in average power. Overall, the interference introduced in other cells is reduced by 5 dB.

The base station (24 in Figure 2) or the switching center and the central processor (22 in Figure 2) will also manage the handover procedure. There will have to be at least four time slots to get diversity on the CDMA side and there will still be a time slot for the CDMA receiver to scan other transfer stations. Four time slots only provide double diversity. With five time slots, it is possible to achieve the desired level of triple diversity. Of course, by adding additional receivers in the CDMA user terminal, it will be possible to perform a parallel scan for better synchronization signals. However, adding another receiver to all CDMA user terminals would be an expensive solution. Therefore, with three time slots there is only a double diversity, and there is no transfer. With four time slots, there is a triple diversity for fixed CDMA subscribers and a double diversity for mobile CDMA subscribers. With five time slots, there is triple diversity for both fixed and mobile CDMA users. With six or more time slots, there is an opportunity to add flexibility to the channel structure. Figure 7 shows the structure of CDMA user terminal slots for six time slots.

The triple antenna structure located in the transfer station is used in the return link when simultaneously listening to a single burst from each active subscriber, within its assigned time slot, in the three antennas, which is also achieved A diversity in triple space. The global synchronism structures for direct and reverse CDMA links in the transfer station are shown in Figure 10A. For illustrative purposes, six time slots have been shown, but, as previously described, it is possible to implement any number of time slots, three or more, so that the upper reasonable limit is in the environment of 32.

The transmission order of the three active time slots can be distributed over the total number of time slots, and even more than three time slots can be used. With triple diversity, the power transmitted from the CDMA user terminals can be reduced by at least 5 dB, probably more, but 5 dB is subject to maintaining correspondence with direct link performance. In any case, the transmitted power is controlled and maintained at the minimum level to maintain a high quality link. It is also possible, at higher frequencies, to achieve a certain independence of the antennas even in a relatively small area or radius. Therefore, a similar approach to diversity in space and transmission time, which is used in the direct link, can also be applied to the reverse link. Double diversity must lead to a significant improvement in most situations.

Each transfer station continuously transmits a spread spectrum channel for synchronization and control purposes. The synchronization and control channel identifies the particular transfer station and manages the user terminals on condition that they have been assigned to the transfer station. A large part of the time, the synchronization and control channel does not carry any user traffic. The synchronization and control channel can be a narrowband channel that can be easily captured and monitored. The information support portion of the control signal has a previously assigned time slot and includes system and signaling messages for all users assigned to the particular area covered by that transfer station. The processing gain is sufficient to allow a transfer station to include several CDMA signals provided with time slots, to be transmitted in parallel, thereby allowing the geometric array of antennas to be shared. Also, only a single synchronization and control channel is required for multiple CDMA modules equipped with slots that are integrated in a single position.

SUBSCRIBER STATION; figure 13

A block diagram of the subscriber station according to the present invention is shown in Figure 13. An antenna 1300 is coupled to a CDMA receiver 1304 through a transmit and receive switch 1302. The output of the CDMA receiver 1304 provides data packets to data buffer records 1306, 1308 and 1310. A combiner 1314 selects and combines the data stored in the intermediate storage registers 1306, 1308 and 1310, in order to provide an output to a digital to analog converter 1316, which also includes means for decompressing the compressed signal in order to Provide an audio output. An analog audio input is provided to an analog-to-digital converter 1322, which also provides means to compress the audio signal. The output of the analog-to-digital converter 1322 is a digital form of audio samples assembled in the form of data packets in a memory buffer 1320. A CDMA transmitter 1318 encodes the contents of the memory buffer 1320 and provides a coded CDMA signal, through the transmit and receive switch 1302 to the antenna 1300. The CDMA subscriber station is synchronized by a synchronization and synchronization controller 1312, which also measures the signal delay for a position measurement, as described hereinafter.

In the direct sense, the CDMA receiver 1304 receives three identical data packets and places one of the data packets, during the time slot T1, in the intermediate storage register 1306, a second of the data packets, during the time slot T2, in the buffer buffer 1308, and a third of the data packets, received during time slot T4, in the buffer buffer 1310. The combiner 1314 selects one or more of the contents of the memory buffer records to be combined or selected as the best data received, for conversion into an analog audio output of the digital to analog converter output 1316. Using three data packets with diversity in time and space, the present system is less susceptible to fading, and, because the same receiver is used to demodulate the three samples, no complex signal intensity balancing procedure is necessary. .

In the reverse direction, the analog audio input to the analog-to-digital converter 1322, which also includes a digital compression algorithm, provides a data packet for the intermediate storage register 1320. During the time slot T3, the transmitter of CDMA 1318 encodes the contents of intermediate storage register 1320 for transmission as a CDMA signal over antenna 1300.

The simplification of the CDMA user terminal is a first-order consideration in the present system. The main simplification is the ability to temporarily share the receiver and, in particular, the correlator as it performs its different functions. The ability to transmit and receive at different times also simplifies the implementation of the small portable user terminal. The single receiver sequentially receives the three signals with diversity in space, within the three different time slots, and then moves to different codes to search for improved signals from other transfer stations. That same receiver is also used for the purpose of capture and monitoring. Because the user terminal does not receive during the slot in which it is transmitting, there is no need for a diplexer or a slot filter. Only a simple on / off switch is used. Because only a single PN code is necessary at a given time, the PN code generation procedure is also greatly simplified. Baseband processing can be carried out in a common processor of relatively low speed.

In the time slots in which the user terminal is not receiving or transmitting, the receiver is free to search the synchronization and control channels from other transfer stations. When the user terminal identifies a synchronization and control channel that is better than the one assigned to it, the user terminal sends a message to the network controller telling the controller that it has identified a potential candidate for handover. The network controller uses this input, along with other information, to make the transfer decision. The network controller sends the handover message to the affected entities. The identities of the codes to be searched by the user terminal are provided by the central network controller through the transfer station, where they are placed in the control channel.

TIME SLOT STRUCTURE; Figures 10A, 10B, 11A, 11B, 17

Figure 10A shows the assignment of time slots to multiplex 6 simultaneous calls. Time slot assignments for transmission, 1002, and for reception, 1004 are illustrated. The entry in each box contains the activity during the corresponding time slot. During time slot 1, antenna A transmits T1 to user 1, antenna B transmits T6 to user 6 and antenna C transmits T4 to user 4. At the same time, antennas A, B and C receive R5 from user 5. During the next time slot 2, antenna A transmits T2 to user 2, antenna B transmits T1 to user 1 and antenna C transmits T5 to user 5. At the same time, antennas A, B and C receive R6 from the user 6. Continuing through the diagram in Figure 10A, during time slot 3, antenna A transmits T3 to user 3, antenna B transmits T2 to user 2 and antenna C transmits T6 to user 6. At the same time, antennas A, B and C receive R1 from user 1.

Note that, during time slot 3, none of the antennas A, B or C is transmitting to user 1. Instead, user 1 is transmitting and the transfer station is receiving by the three antennas from the user 1. However, during the time slot 4 the third transmission is made to the user 1. That is, during time slot 4, antenna A transmits T4 to user 4, antenna B transmits T3 to user 3 and antenna C transmits T1 to user 1. Time slots 5 and 6 are not used directly for data transfer to or from the user 1. The time slot assignments shown in Figures 10A, 10B, 11A and 11B are consistent with Figure 7, where user 1 is receiving during time slots 1, 2 and 4, and transmits during the slot of time 3. The pattern can be observed in the slot assignments in Figure 10A, by looking for the times at which T1 is transmitted. The transmission of T1 appears in time slots 1, 2 and 4, respectively on the A, B and C antennas. No transmission to T1 appears during T3, but the reference to reception time slots 1004 indicates that R1 is received from user 1, during time slot 3. Because, in any given time slot, there are three transmissions and one reception simultaneously, at least 4 addressable CDMA PN spreading code sequences are required.

Therefore, time division multiplexing is used in the sense that successive time slots carry data directed to different users. Code division multiplexing is used in the sense that, during each time slot multiplexed in time, multiple PN code sequences allow simultaneous communication with multiple users. The result is a signal multiplexed by time division and multiplexed by code division.

Figure 10B shows the allocation of time slots for multiplexing 12 simultaneous calls. Time slot assignments for transmission, 1006, and for reception, 1008 are illustrated. During time slot 1, antenna A transmits T1 to user 1 and T7 to user 7, antenna B transmits T6 to user 6 and T12 to user 12, and antenna C transmits T4 to user 4 and T10 to user 10. At the same time, antennas A, B and C receive R5 from user 5 and R11 from user 11.

The allocation of time slots for multiplexing 24 simultaneous calls has been shown in Figures 11A and 11B. Figure 11A shows the transmission from the transfer station (direct direction), while Figure 11B shows the transmission to the transfer station (reverse direction). Time slot assignments for transmission, 1102, 1104, 1106, and for reception, 1108 are illustrated. As an example, during time slot 5, antenna A transmits T5, T11, T17 and T23 (i.e., T5 to user 5, T11 to user 11, etc.). Antenna B transmits T4, T10, T16 and T22. The antenna C transmits T2, T8, T14 and T20. At the same time (during time slot 5), antennas A, B and C receive R3, R9, R15 and R21 (i.e., R3 from user 3, R9 from user 9, R15 from user) 15 and R21 from user 21).

For Figure 10A, a single CDMA encoder is required for each antenna to handle 6 simultaneous calls. In Figure 10B, two CDMA encoders are required for each antenna to handle 12 simultaneous calls. Similarly, in Figure 11A, four CDMA encoders are required for each antenna. Thus, for example, if 180 PN code sequences are available, then 180/6, or 30, CDMA encoders are required for each antenna in order to handle 180 simultaneous calls. If, for this greater number of required accesses, the number of time slots is increased, the number of encoders will decrease proportionally.

ALTERNATIVE SYSTEM CONFIGURATIONS; figures 14, 16

A further improvement extends the distance between the diversity antennas of the transfer station by using broadband cables that are 304.8 meters (one thousand feet) or more. The transfer station sends the spread spectrum signal in final radiofrequency, through the cable to the antenna. The antenna at the end of the cable contains a radio frequency amplifier. An implementation that distributes signals over the cable has the same improvement against blocking described for the transmission diversity approach across multiple transfer stations.

However, instead of using a separate cable for each antenna, a preferred embodiment shares a single cable and uses frequency multiplexing to assign a different cable carrier frequency to each antenna. In this way, the desired signal is transmitted only from the antenna closest to the user, which reduces interference. As a further improvement, a cable distribution system integrates different elements into a personal and local communications system network. The basic building block is the CDMA module structured in six time slots, which serially excites three antennas to obtain a diversity in space and triple transmission time. For simplicity, the design of the transfer station that handles the incoming TDMA signal also has a structure of six basic time slots. The modular structuring of six time slots can be easily deployed to accommodate multiples of 12, 18, 24 and 30 or 32. Figure 14 shows the implementation for several different combinations. The preferred embodiment uses a wireless input, such as W or WE, as the input to the transfer station; however, a cable distribution system works equally well with cable signals, such as input.

In a cable-based personal communication system, the transfer stations are transferred back to the central controller, which reduces the cost of the transfer station, because it does not have to be made more robust or fed remotely. This also reduces the number of spare parts required and the cost of maintaining the units, because they are all in one place and easily accessible. Transfer stations can also be reallocated dynamically as the traffic load changes during the day or week, so the total number of transfer stations required is significantly reduced. The bandwidth of the distribution network is increased, but developments in the cable and fiber optic distribution system have an increasing bandwidth for a decreasing cost, to accommodate the increase in bandwidth at a reasonable cost. The advantage of having several interconnection options to select means that the choice of interconnection becomes an economic choice determined by the cost factors associated with each installation. Each network is expected to include many, or all, of the interconnection options.

The arrangement of the system in which the transfer stations are moved back to the same position as the central controller, is shown in the lower part of Figure 14. A general broadband distribution system is used by cable or optical fiber in both directions 1402 to link the centrally located transfer stations with the antennas located at a distance. Considerable flexibility is available when configuring the broadband spectrum in signal formats, to link the centrally located transfer stations with each transfer station antenna. However, for simplicity, it is preferable to retain the TDMA protocol with its air interface protocol with triple space / time diversity, structured CDMA in time slots, and a frequency translation signal as a common air interface for each antenna.

Each antenna is assigned an independent center frequency in the broadband distribution cable 1402. Due to the ability to share TDMA and CDMA, many users can be serviced by the same antenna using the same cable frequency. The transfer station antenna located in the N position includes a transceiver, which is tuned to the assigned cable frequency. The central controller transmits and receives data packets in the final TDMA / CDMA waveform representing the telephone traffic at each assigned frequency of the broadband distribution cable 1402. Thus, as shown in Figure 16, each remote position includes a remote transceiver (transmitter, receiver, local oscillator, diplexer and antenna) at location 1602. The unit located remotely is a relatively simple receiver, frequency translator and low power transmitter, for both direct and reverse senses. A low power transmitter amplifier is suitable because the cells are small and triple diversity (three antennas and three time slots) is being used to link the subscriber station with the system. The transmission side of the central controller provides individual information flows together with the associated signaling and control information, at interface A 'of Figure 14, which is presented in assignable time slots, in the form of packets.

The signaling information includes the identification number (s) of the called parties, code, service profile and authentication code, etc. The control information includes routing information (i.e., which base station, transfer station, antenna designation), power levels, activation or deactivation traffic, handover messages, etc. A large amount of this information is transmitted before the user information (telephony voice traffic) begins to pass through the circuit, although a significant amount of information is also passed during the time that the telephony voice traffic is actually found in the circuit. A separate control channel is required even after the connection with the user has been completed. The base station function translates this information into the protocol that is required to act as an interface with the TDMA air interface and provides a TDMA radio spectrum on the W interface. The transfer station converts the TDMA protocol into an air interface protocol with triple space / time diversity, CDMA and structured in time slots, and transmits this signal firstly through antenna A, then through the antenna B and, finally, by antenna C (figure 14).

The combined base station and transfer station (BT) module 1404, centrally located, combines the function of the base station and that of the transfer station and converts the signal that appears in A 'into the triple interface air interface of CDMA structured in time slots. A combined BT module can be achieved by direct combination of independent equipment, or the modules developed for the combined use of the base station and the transfer station can be integrated. The CDMA signal branches to the output of the transfer station or to the output of the BT module, as shown in Figures 15 and 16. In the case of transfer stations that are connected to the respective antennas by three different cables, the output is simply switched at the appropriate time. When a single cable is used to reach all the antennas, the output of the transfer station is jumped in frequency at the appropriate time, by changing the frequency of the synthesizer to the assigned frequency of the antenna. The BT module is agile in frequency in a similar way.

It is important to note that user information is reproduced or copied in each of the three time slots, but that the PN code continues to run and is different during each time slot. Therefore, the repetition is not the same as in the case of imitation of multiple paths or of multiple emulated paths. The PN generator simply continues running without storing or resetting the sequence. Operating the PN code continuously is simpler to implement, compared to starting a PN sequence again.

In the following exposition it has been assumed that the time slots follow one immediately after the other; This is not, however, necessary on condition that the receiver has a priori knowledge of the sequence of jumps. In the preferred embodiment, the BT transmits in two contiguous time slots and then listens for the response signal from the user terminal. During the user transmission time slot, the user terminal instructs the BT module not to send the third diversity time slot if the first two time slots have provided adequate performance and a position measurement is not necessary. The use of double diversity only reduces interference for other users and leaves the user's receiver free to perform other functions.

An alternative approach is the use of a direct error correction code of 1/3 that widens along the three slots. The use of such coding provides improved performance if the error statistics during each of the time slots are practically the same. If a time slot worsens significantly, and can be identified as bad, it may be better to ignore the bad time slot and request an antenna transfer to replace that time slot, in case the poor performance continues. Because the statistics of channels with real diversity are expected to result in uneven time slot statistics, the preferred alternative is not to use an error correction code directly in the three time slots. Even if only error detection codes and error correction codes are included within each time slot, it is possible to use error correction codes directly over multiple time slots.

Each antenna, assuming there is data to transmit, transmits during each of the time slots. Because the data is transmitted three times, there will be three CDMA signals that are transmitted in each time slot, for each module assigned to that antenna. If there are 4 modules assigned to the antenna, so that 4 modules support 24 users at any given time, there will be 12 CDMA signals emanating from the antenna in each time slot (see Figures 11A, 11B). If the utilization factor is approximately 50%, then only six CDMA signals will actually be transmitted and, if the third time slot is not required from 20% to 25% of the time, they will only be transmitted from 4 to 5 CDMA signals at any given time. The same antennas are used for the receiving side, or reverse link (from the user to the transfer station).

As indicated above, the CDMA user terminal transmits only during a time slot, and the transfer station simultaneously receives that transmission over those same three antennas, which results in a diversity in triple space in the receiver. The three reception signals arrive at the transfer station, or BT module, either by independent wires, or at different frequencies, as shown in Figures 15 and 16, and processed or treated separately. These treated signals are added together using maximum probability combiners. The S / I from each antenna path is measured and stored in memory over a range of at least ten time slots. The registration of signal statistics is used by the maximum probability combination procedure. The statistics of stored signals are also useful in the decision procedure for executing a transfer to other antennas.

The handover procedure for the BT cable network is based on the signal received from each of the antennas. The central processor receives information about the quality of the links in both directions. In the direct link, it receives information from the user CDMA receiver, which operates on that link during an assigned time slot that is identified with a particular antenna. In the reverse link, you receive information about independent paths through different antennas. Information about the quality of the paths that pass through a specific antenna can be evaluated and compared with other current paths through different antennas, and with other new paths that the user terminal is continuously searching for. When a current path within a specific time slot continues to deteriorate and a better path is available, the central controller assigns a new path (antenna) to the user terminal and notifies the user terminal that it has done so.

The transfer procedure for the transfer station is similar, except that the transfer is, in general, between transfer stations, rather than between antennas. When transferred from one transfer station to another transfer station, the three antennas associated with a particular transfer station are transferred with the transfer station. A few transfer stations can be implemented with widely separated antennas. In the case that there are transfer stations with widely separated antennas, the transfer procedure described for the BT module can also be used.

Operational description: A new subscriber turns on his CDMA user terminal and performs a scan of the synchronization codes until it captures a synchronization code. The CDMA user terminal then initiates a registration message. The transfer station receives this message and passes it to the central controller, which acknowledges it with an acknowledgment message sent back to the user terminal. The central controller goes to the home registry of the new terminal and obtains the user profile, and places it in the archive for active users. The new user is now registered and all calls will be forwarded to this new service region.

There are 28 different synchronization codes, and a synchronization code is assigned to each area. The 28 areas make up one region and the codes are repeated in the next region. Transfer stations contained in an area are provided with different displacements or starting points for their particular code. Therefore, each transfer station, or widely separated antenna, has an identifiable code. The central controller knows through which antenna, or transfer station, the new user was registered, so that the controller will route all the information to the new user through that node. The central controller will also provide the new user with a set of codes, or different starting points in their current code, to search in order to identify diversity paths or candidates for transfer. The new user continues to monitor the synchronization and control channel for half of their time slots. In the other half of its time slots, it scans for better synchronization channels.

The user is remotely searched on the control channel and is provided with a CDMA and a time slot assignment that he starts, so that he is ready for the start of the call. When the user requests service, this is also provided with a CDMA code and a time slot assignment for the entire duration of the call. The user terminal remains in this state until the end of the call, unless the signal is weakened by one or all of the diverse paths. Because the user receiver is continuously evaluating incoming signals and exploring for better new paths, he will know if a path is deteriorating and will notify the controller of this situation, as well as a list of the best candidates. The central controller will indicate a handover and the user terminal will go to the new CDMA code and time slot. No part of this activity is detectable by the end user.

At the beginning of each time slot, there is a short section without modulation, lacking user information, which is used for resynchronization and range adjustment, followed by a short section of control message. These short bursts are sent whether or not user information is sent. If there is no user information to send, the control message confirms this and the transmitter power is reduced by 10 dB for the user information portion of the time slot. It should be noted that four time slots are available in the direct channel to pass user information, depending on the agreements reached between the user and the central controller. These slots as described above can be deactivated so that other users have access to additional capacity. Multiple time slots can be used to improve diversity or to send increased data rates, multiple data channels or a graphics channel, along with a voice channel. It is also possible to extend to several parties in a conference call.

LOCATION PROCESSING; Figures 20, 21, 22, 23

Figure 20 shows the radio links of Figure 1 or Figure 4, and in it the car and its antenna are represented by the user antenna U. The radio links have been structured in time slots as shown in Figure 10A The radio link AU is structured in time slots and is represented during time slot 1. The radio link BU has also been structured in time slots and is present during time slot 2. The radio link CU has also been structured in time slots and is present during time slot 4. The radio link AU establishes the absolute distance from U to antenna A. The distance to antenna A is a reference to measure the difference in path lengths between the AU and BU radio links. Similarly, the path length of the radio link AU is also used as a reference to measure the difference in path lengths between the radio links AU and CU.

Because the appearance in time of the vector of all ones (for synchronization) is the same in the three antennas, the distances to the three antennas can be deduced from the difference between the respective arrival times of the vector of all ones inside of each time slot. The location center, having the physical geographic coordinates of the three antennas, calculates the position of the antenna U of the users.

The geometry of the position determination has been shown in figures 20, 21, 22 and 23. The first distance measurement AU places the user somewhere in a circle A, in figure 21. The second distance determination locates the user also as located somewhere in a circle B. The only positions for which this may be true are where the circles intersect each other, at points X and Z. Therefore, their position has been reduced to two Possible points The third distance determination places the user somewhere in a circle

C. Because the user is also in circle C, it must be at point Z. Obtaining additional distances to other antennas confirms the first set of measurements and, in many cases, improves accuracy. If the terrain has significant height variations, the constant distance circles become constant distance spheres and the added measurements eliminate any ambiguity that could be caused by adding the third dimension. The processing center for the position location converts these coordinates into user-manageable instructions. The distance measurements by the CDMA system are obtained as follows:

<dl><dt>1. </dt><dd>The pseudocode of noise, as it is drawn between A and U to act as a measuring stick. The time required for propagation between A and U allows many chips, the propagation time in microseconds, multiplied by the speed of chips, in millions of chips, to represent the length of the link or to "store" in the link during propagation signal See figure 20.</dd></dl>

<dl><dt>2. </dt><dd>There are two ways to increase the number of chips that fit in the propagation path. One is to increase the length of the path and the other is to accelerate the speed of the chip generation clock. Increasing the speed of the chip generation clock is analogous to marking a ruler with a smaller scale. Therefore, an increase in the speed of the chip generation clock stores more chips in the path delay and allows the possibility of making more accurate measurements.</dd></dl>

<dl><dt>3. </dt><dd>The path length from the antenna A to the user terminal U and back to the antenna A can be measured by transmitting from A, then retransmitting the same PN code, with the arrival phase, from the user terminal U, and comparing the repeated signal as it is received back on antenna A, with the signal that had previously been transmitted from antenna A. If the original signal is delayed until it matches, chip by chip, with the received signal, in A, and the number of </dd></dl>

chips that are displaced, the total delay is proportional to twice the distance between antenna A and antenna U.

<dl><dt>4. </dt><dd>The precision of the distance measurement is approximately 1/4 of the number of feet (0.076 of the number of meters) that represents a single chip. The 1/4 chip factor is an implementation constraint determined by the degree of accuracy with which the correlation peak is detected and monitored. It is possible to reduce this error by autocorrelation techniques, but the 1/4 chip factor is a realistic resolution.</dd></dl>

<dl><dt>5. </dt><dd>To determine the path length between the antenna A and the user terminal U, as described in paragraph 3 above, Figure 22 shows the signals 2202 transmitted and the signals 2204 received on the antenna A. For a speed of chip generation clock of 10 million chips per second, each chip represents approximately 30.40 m (100 feet). The 51-chip delay between the transmitted, 2202, and received, 2204 signals represents the time required by a radio wave to complete a round trip between the subscriber station and the transfer station. Half of the round trip delay, or 25.5 chips, represents the distance to the antenna. Thus, the distance from the antenna A to the user terminal antenna U, for example, in Figure 22, is (51 x 30.48) / 2 = 777.24 meters ((51 x 100) / 2 = 2,550 feet). The distance measurement accuracy is plus or minus 7.62 m (25 feet (100 feet / 4)).</dd></dl>

<dl><dt>6. </dt><dd>Therefore, the distance AU is measured quite accurately. As described above, the receiver uses a single receiver for all time slots. Although the subscriber receiver is listening to time slot one, it is working in combination with the base station to repeat the received waveform, with the same phase and without delay through the user terminal. The base station receiver, as described above, compares the received phase with the transmitted phase to determine the absolute distance. The base station then transmits the distance value, measured in this way, to the user terminal, where it is stored for future recovery and use. As noted above, the important thing is the phase of the waveform, if the starting point, the vector of all ones, is maintained through the user terminal, a new similar PN code can be substituted in the reverse link. A similar code can include that same code, with a deviation from a defined offset.</dd></dl>

<dl><dt>7. </dt><dd>The same direct and reverse direction measurement procedures described above can be used to obtain the other two distances (to the antennas B and C), so that the results are also stored in the memory located in the user station. However, a direct distance measurement to the three antennas is not necessary. See figure 23. The same receiver retrieves information on all three paths. By doing this, the receiver adjusts to the difference in path lengths at the beginning of each time slot. Once the adjustment has been carried out, the first time the receiver uses this antenna as an information channel, the code is stored and stored in memory until the radio returns to this time slot, so that extracted from memory and used as a starting point for tracking loops. Therefore, the receiver is essentially maintaining three independent sets of receiver parameters, which emulate three different receivers, a set of parameters for time slot 1, a different set for time slot 2 and a different set more for time slot 3. The distances to antenna B and antenna C can be determined by adding or subtracting the offset, measured in chips, with respect to the average absolute distance value on the AU link. In fact, the displacement is determined before using the time slot for the first time as an information channel, and this determination is carried out in the process of finding new paths for the transfer. The delay and the measurement of the signal quality are determined and maintained in the archive of potential transfer objectives. These delay offset measures are also used as additional distance measurements in the position location procedure.</dd></dl>

In particular, continuing with the previous example, the signal 2302 transmitted on antenna A represents a distance of 25.5 chips from antenna A to user terminal antenna U. The signal 2304 received on the antenna U, from the antenna A, is used as a reference to measure the relative arrival time of the signals from the antennas B and C, adjusted for the different time slots in which they are Signals are located.

Because the synchronism for time slots 1, 2 and 3 is sequential, real-time chip patterns or configurations for slots 2 and 3 do not overlap. However, after the adjustment for the time slot delays, the synchronism ratio is as shown in Figure 23. Adjusted in this way for the difference in time slots, the received signal 2306, from the antenna B, in the user terminal antenna U, is received in advance (ie, offset with respect to signal from the antenna A) of 8 chips. Similarly, the signal 2308 received, from the antenna C, in the user terminal U is also received in advance (ie, offset with respect to the signal from the antenna C), but 6 chips . The received signals may be either delayed or advanced (that is, have a positive or negative delay) with respect to the reference signal 2304. A reception in advance indicates that the antenna (B or C) is closer to the antenna A. Conversely, late reception indicates that the antenna (B or C) is farther away than the antenna

TO.

In Figure 23, the distance from antenna B to antenna U is 25.5-8 = 17.5 chips. In meters, 17.5 chips are 17.5 x 30.48 = 533.40 meters (17.5 x 100 = 1,750 feet), the length of the BU path. The distance from antenna C to antenna U is 25.5 - 6 = 19.5 chips. In meters, 19.5 chips are 19.5 x 30.48 = 594.36 meters (19.5 x 100 =

1,950 feet) = CU path length. The user terminal may be located at Z, the intersection of circle A at 685.8 meters (2,250 feet) of antenna A, circle B at 533.4 meters (1,750 feet) of antenna B, and circle C at 594.36 meters (1,950 meters) from antenna C.

Alternatively, a position measurement can be carried out by calculating the intersection of two hyperbolas. The first hyperbola is the geometric place of all the points that have a fixed distance difference from two foci, which is proportional to the difference in delays between antenna A and antenna B. The second hyperbola is the geometric place of all points that have a fixed distance difference from two foci, which is proportional to the difference in delays between antenna B and antenna C (or between antenna A and antenna C). Antennas A and B are the foci of the first hyperbola, while the antennas B and C are the foci of the second hyperbola. In this way, the subscriber's position can be calculated without the need for a two-way exchange between the user terminal and the transfer station to establish a first distance measurement.

Location services; figures 18, 19

Because the receiver of the subscriber station is receiving information on three different paths that start from known positions, the information for the location of the position is deduced by measuring the arrival time of the messages with respect to a fixed time reference. The measurement accuracy depends on the chip generation speed, but a chip generation speed of 10 million chips per second offers quite a bit of precision. There are several ways in which position measurement and display can be carried out, depending on how much processing capacity is available in the user terminal. The choice also depends on who will actually use the information. This can be quite passive, using only the relative displacement information of the chips, and obtaining a reference from the current cell. The user can deduce locally and visualize their position, similar to the use of a GPS satellite. A GPS receiver displays the longitude and latitude reading. Position information can also be sent back to a processing center that provides a service to a user. The processing center converts the coordinates of longitude and latitude into a position that has a geographical meaning, such as a block number of a specific street.

The measurement of the local geographical position is attractive, in particular, to people concerned about their safety or health problems. Or the service center manager can notify the police or a designated relative,

or the service center may include, as part of a special service fee, the appropriate staff to handle irregular circumstances. Of course, the service center can also, for a nominal fee, tell a person their position on the street and provide instructions on how to get to a desired destination address. These services can be provided to users who are pedestrians or who travel in vehicles. The destination instructions can be given in the form of a set of detailed addresses at once, or in specific indications that arise continuously at the crossings, as the user moves along the suggested route. The indications can take the form of a voice instruction or a text display that tells the user to turn right at the next intersection. A delivery truck, taxi, ambulance or fire truck can have a special screen that shows a local map with written instructions on it. Instructions can also be modified as traffic congestion varies. The benefits of this system are a significant increase in public safety, comfort and productivity.

In the system configurations described above, the separation between antennas is set so that it is sufficient to provide a precise position location capability. Thanks to the placement of the antennas to obtain independent paths that are sufficient to avoid flat fading as a result of interposed obstacles, then the separation is also sufficient to reduce the triangulation error to a very small number. The increase in costs as a result of including the optimization of a location capacity is nominal.

The processing for the location of the position is carried out by a third-party provider who owns and manages the location center of the position. The location service can perform in various ways. The preferred approach is to make the user terminal the repository for all location information, through the constitution and maintenance of a location file. The location location center asks the user terminal through the normal public switched telephone network (preferably, packet) when it needs information. Preferably, a provision for encryption or encryption is used during transmission, and an access code for privacy. The user terminal can also send location information to the location center, also through the public switched telephone network, sensitive to user activation. For example, when the user presses an alarm button, the radio will send the alarm message, along with the location information, to the location center. The location center will respond according to preset addresses and the level of service subscribed. Because the radio of the user terminal develops the code offset information internally, the only additional information that the cellular system needs to provide to the user terminal is distance, on a one-way trip or round trip , from the user to one of the base stations / antennas. The distance information, which will be provided as a service feature to the user, must identify the base station / antenna. All measurements must be made within a time window of 100 milliseconds, or the error resulting from the movement of the vehicle between measurements will be excessive. For stopped or pedestrian vehicles, the time window for location measurements can be much longer, because there is little or no movement between the measurements. Therefore, the distance measurement sent by the system to the user terminal includes the distance in feet (in meters), the time in milliseconds and the identity of the entity that performs the measurement. Upon receiving the distance message, the user terminal stores the message and performs code offset measurements for various different antennas, and, if the signal levels are adequate, stores the composite information in the location file. The location file is retained until a new distance message is received by the radio from the user terminal, whereby the radio of the user terminal again carries out the code offset measurements and updates the data file. Location.

When the location center asks the radio of the user terminal about its location or position, the radio sends the contents of the location file. The location center processes or processes this data and converts it into very accurate map or cartographic data, placing them on a specific street (which can be displayed on a typical street map). The system measures the distance to the subscriber normally once a minute when the subscriber is in the active reception mode, with the receiver connected, waiting for his paging. The period between measurements is variable and can be adjusted according to the user's needs. The system sends this new distance to the subscriber station, which places it in the file and introduces new code offset measurements with it. If the subscriber is having a conversation, the user terminal is transmitting, the base station makes a measurement every ten seconds and, if the distance changes more than 30.48 meters (one hundred feet), the system sends a message to the station subscriber. Whenever the user terminal receives a distance measurement, it adds the local code offset measurements and updates the file.

It can be seen that the user terminal location file is updated at least every minute and more often if justified. Therefore, the system can know the position of any active user within a distance of approximately 30.48 meters (100 feet). Certainly better accuracy and more frequent updating are possible, but, due to the load on the data links, the number of subscribers receiving higher performance should be the exception rather than the rule. Whenever the user presses the alarm button on their portable terminal, the terminal transmits the contents of the location file three times, which is a sufficient duration for the system to read a new distance and send a message to the user terminal. The user terminal performs several offset measurements and sends the new location file three times. The alarm message repeats every thirty seconds, until the battery runs out. The user terminal radio may have an added module (with its own battery) that emits an audible tone each time the radio alarm message is transmitted.

The system generates unprocessed location information in the user terminal, which must be converted into cartographic data readable by a person. In general, the basic readings of longitude, latitude, or angle and distance are accurate. However, there is a need for a third party to translate this data into a format that the general public can use quickly, such as a service business. Because the user terminal has the basic location information, it can be provided to any authorized entity that requests it from the user terminal. The location processing center periodically asks subscriber user terminals and maintains a file about their location or position at that time. One of the possible services for subscribers with health problems is a monitoring system during the exercise. If the subscriber stops in an unusual position for an excessive period of time and does not press the alarm button, the operator of the location center could request vital signs or signs and send a medical professional to the detained subscriber. If it is an emergency, the location center operator knows the subscriber's position in order to send help. On the other hand, when the alarm button is pressed, the alarm message is directed to the location center, where they are equipped to handle such emergencies. The ability to track user terminals and provide help as a result of some action is useful for many applications. The tracking of stolen cars, the identification of traffic jams, the avoidance of ambulances being lost and the warning of vandalism are just a few examples of the application of the present invention.

The system certainly requires, in particular in its distributed configuration as described above, a consistent zero time reference across the different base station antennas. Having a zero time reference available significantly reduces the time required to resynchronize as the signal jumps from one antenna to another, and also helps in the search and transfer procedure. The ability to apply to the location described above allows the system to periodically perform a self-calibration, by placing several of the user terminals, as described above, in fixed positions and determining the appropriate zero time setting for these positions. By maintaining the correct response in the central processor, as the system scans these checkpoints, you will get an error indication in the event that the system is out of calibration. The same checkpoints are used to show the effective delay during the procedure where a variable delay is introduced by increasing or reducing the system delay in one or more of the signal paths, in the recalibration or adjustment procedure.

The calibration procedure can be automated easily. Automation can be implemented in two ways. The first approach is to explore the checkpoints every minute and determine any errors that have developed. If this error reaches a significant level, the communication system contacts the location center and provides the center with the corrections that need to be added as factors in the calculations for the location of the position. This last approach requires close coordination between the communication system and the position location center. A more autonomous approach would be desirable. The communication system itself can maintain the proper "zero" state by scanning the checkpoints, as described above and having the ability to insert or remove a delay 1806 on the path to the antenna.

Figure 18 illustrates a system with self-calibration. Once per minute, the system asks each checkpoint 1802. This results in a distance measurement that is sent to checkpoint 1802, where the checkpoint receiver adds the code offset measurements and sends the content from the location file to processor 1804, where the received file is compared to a file containing the correct measurements. If the difference exceeds the threshold, the processor 1804 calculates the delay changes that are required to bring the measurements within the tolerance and sends the correction to the controller. The controller maintains a file that includes variable delay 1806 to be inserted for each antenna. The controller modifies the file delay input and a new measurement is made to validate the calibration. Modifications that require significant changes in the delay are unlikely, but if this had to occur, the controller would not initiate any measurement that included the branch that is undergoing recalibration. In this way, the position location capability also provides a service for the communication system. Self-calibration results in a significant reduction in the cost of installation and allows the use of cheaper system components.

Communications related to the location that occur between the antenna devices and the subscriber terminal may be fragmented into several different links. The functions performed by these different links are: 1, distance measurement (requires a link in both directions, but no traffic); 2, sending measurement information to the subscriber terminal (one-way data link, except for possible retransmission requests; 3, code offset measurement (only requires that the user terminal be listening; no any data is transferred); 4, the transmission of the location file to the location center or to the communication processor 1804 (the data links can be one way or both directions). The distance measurement can be done only by the system and, because it requires a two-way link, it can be done while a normal conversation channel has been established, or, if the terminal is in the listening mode, the system has to establish a short connection with round trip.

The two-way link is necessary because the base station measures the difference in code phases between the signal it sends to, and the signal it receives from, the user terminal. In Figure 18, the above function is carried out in processor 1804. In this sense, the system functions as a radar with an impulse the width of a PN chip. The one-way data link message that carries the message away to the user terminal is a single message that will usually include an error correction code and that may also require the sending of an acknowledgment message. back from the user terminal to the base station. The acknowledgment message can be sent independently or attached as part of the distance measurement function.

The code offset information is also placed in a file that is accessible from outside the system. As described above, the time of the user terminal shares a receiver for the three independent paths that start at different times from the three different antennas. Therefore, the receiver tracks three independent paths, one after the other. The PN code of each path is the same and, as described above, the code has the same starting time on each antenna but, due to the difference in distances to the three different antennas from the user terminal, the codes that arrive at the user terminal are of different code phases. However, because the system cycles very quickly from one antenna to another, the receiver cycles between the signals received from each of the antennas. Consequently, the receiver maintains three independent starting states and tracking loops for the different time slots. At the end of each time slot, the exact time is known in advance, and the previous state is stored by the computer and is restored at the beginning of the next time slot assigned to the same antenna. In this way, the processor is emulating three different receivers. The receiver quickly adjusts to any slight displacement or mismatch that occurs while the receiver is locked with the other antennas. Note that the receiver has a specific starting state. Therefore, the PN sequence has been shifted to compensate for the difference in distances between the path between the user terminal and the first antenna and the path between the user terminal and the second antenna. The difference is the code offset, because the code offset measures the difference in distances. In this way, the distance to the second antenna is known without having to perform a closed loop measurement (both ways). The same procedure is followed for the third antenna.

Additional entries, in numbers greater than three, are available in the location file, using the normal search mode used by the radio of the user terminal to identify potential candidates for handover. The radio of the user terminal searches for the pilot codes that start from the nearby antennas to determine if any of these antennas have better signals than one of the three that are currently being used. If so, the user terminal notifies the system that a good candidate is available. The search procedure starts in the state of the PN signal that enters from time slot number one and, if nothing is found in that state, the radio adds a chip to the path length and integrates again. The radio continues to add chips until it finds a signal or exceeds a distance threshold. If it exceeds the distance threshold, it restores the PN generator to a new pilot code and starts again at offset distance 0. Therefore, when the radio finds a new pilot signal, it knows how many chips it has added before it succeeds . The number of chips added is also the code offset. The code offset value, together with the code identity, which uniquely determines the antenna, and the time indication are entered in the location file. The radio places these entries in the location file even if they are no better than the current signals. As the radio scans and finds new antennas, it places the four best results in the location file. As you continue exploring, old entries are replaced by newer better entries.

Now that the necessary information is available in the user terminal location file, it can be made available to any authorized applicant. Location services can be provided by the communications operator or by a competitive independent service provider. In addition, there will also be large private location centers operated by large fleet owners. The location center 1902 receives the position files through the public switched network, see Figure 19. The network can be a circuit switched network or a packet switched network. A packet switched network is suitable and economical for this type of application.