HK1070776B - System and method for identification of transmitters with limited information - Google Patents

Description

System and method for identifying transmitter with limited information

Background

RELATED APPLICATIONS

This application has priority to U.S. provisional application No. 60/318661, filed on 9/10/2001.

Technical Field

The present invention relates generally to transmitter identification, and more particularly to a system and method for identifying a transmitter with limited information.

Description of the related Art

Existing position location technologies based on the Global Positioning System (GPS) use a network of satellites in the sky that transmit signals at known times. A GPS receiver on the ground measures the time of arrival (TOA) of the signal from each satellite it can detect. The TOA of the signals from the satellites and the accurate location of the satellites and the accurate time at which the signals are transmitted from each satellite are used to triangulate the position of the GPS receiver. A typical GPS receiver requires four satellites to triangulate and the performance of the resulting calculations increases as the number of satellites that can be detected increases.

Alternatively to or in addition to GPS, existing cellular base station networks may be considered a satellite network for position determination purposes. Similar to GPS technology, the exact location of each base station, the exact time at which the base station transmits a signal, and the TOA of the base station signal at the mobile unit may be used to triangulate the location of the mobile unit. This technique is described by some service providers as Advanced Forward Link Trilateration (AFLT). The wireless network may also be used in conjunction with GPS to determine the location of the mobile unit.

An important issue facing mobile stations is measuring the TOA of the signals received from each base station. Different wireless technologies may take different approaches to make TOA measurements. Code Division Multiple Access (CDMA) is one such technique. CDMA modulation is one of several techniques that may allow a large number of system users to share a communication system. It may be possible to determine the position of a mobile unit using AFLT techniques using measurements from conventional CDMA modulation techniques.

The end of CDMA modulation is disclosed in U.S. Pat. No. 4901307, filed on 1990, 13.2, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USENGSTATELLITE OR TERRESTRIAL REPEATERS", assigned to the assignee of the present invention and incorporated herein by reference. The above-cited patents disclose phase-coherent and chip-synchronous chip sequences, i.e., defined as pilot chip sequences or pilot signals. The pilot signal may be used to provide phase and timing acquisition and tracking as well as multipath correction.

Methods of acquiring pilot signals are disclosed in the above referenced patents and in the following patents: (1) U.S. patent No. 5781543, filed on 14/7/1998 AND entitled "POWER-EFFICIENT ACUISITIONOF A CDMA PILOT SIGNAL", AND (2) U.S. patent No. 5805648, filed on 8/9/1998 AND entitled "METHOD AND APPARATUS FOR PERFORMING SEARCH authorization in CDMA COMMUNICATION SYSTEM", both assigned to the assignee of the present invention AND incorporated herein by reference.

When a mobile unit is first powered on, it must establish a communication link with a Base Transceiver Station (BTS). A mobile unit typically receives pilot signals from a plurality of BTSs. The mobile unit searches for signals from the BTSs and establishes a communication link with the selected BTS to receive and transmit data, such as audio signals, over the established communication link. The actual process of selecting a particular BTS and communicating between the mobile unit and the selected BTS is known in the art and need not be discussed in detail herein.

As discussed in the above referenced patents, each BTS periodically broadcasts the same pseudo-noise (PN) code pilot signal, but with a different time offset. I.e., each BTS transmits the same PN code, but the start of transmission of the PN code from the transmitter in each BTS is delayed in time by an accurately known offset. The time offset is measured in multiples of 64 chips. As will be understood by those skilled in the art, a "chip" is a single piece of data in a PN sequence. Since the data is transmitted at a known rate, the chips can be used as a time measurement. Although the present description may use actual time units, it is more convenient to use chips or portions of chips as time units because TOA delay due to PN offset and propagation delay measurements can be calculated in units of chips.

To obtain the pilot signal, the mobile unit must be time offset and frequency synchronized with the signal transmitted by the BTS. The goal of the "searcher" within the wireless device is to find the time offset of the received signal. The searcher uses the estimated frequency. If the estimated frequency is not sufficiently close to the frequency of the pilot signal, the received signal may not be acquired.

When the BTS is properly detected, the output of the searcher is a pulse, which can be considered a correlation pulse. The correlation pulse may be used to measure the TOA of the signal from the BTS. TOAs from multiple BTSs must be measured to accurately determine the location of the mobile unit. In a typical environment, TOAs from at least four BTSs are calculated to determine the location of a mobile unit. The determination may be more accurate if TOA signals are received from additional BTSs.

Accurate determination of the location of the mobile unit requires accurate identification of each BTS from which the received signal came and accurate time at which the signal was transmitted from each BTS. However, mobile units often cannot accurately identify the BTS because of the limited information received from the BTS. I.e., the mobile unit does not always receive complete information from each BTS to make a unique identification for each BTS. Multiple BTSs may have the same PN sequence in a particular geographic region, resulting in ambiguity in the identification of the BTS from which the signal was received. This ambiguity leads to inaccuracies in the location determination process. Therefore, it can be appreciated that there is a great need for a technique: the transmitter may be identified using limited information received by the mobile unit. This and other advantages are provided by the present invention and will become apparent from the detailed description and drawings that follow.

Brief summary of the invention

In an example embodiment, the method of the present invention includes receiving transmissions from a plurality of base stations, wherein the transmissions include full identification data and only partial identification data from a first base station, the partial identification data being insufficient to identify at least a portion of the plurality of base stations. A candidate list is generated to provide an identification of candidate base stations from which transmissions may be received containing only part of the identification data. The candidate base station is analyzed with respect to the base station that has been uniquely identified, and the identification of the base station is determined based on the analysis of the candidate base station. The analysis may include analysis of an area of coverage overlap between the known coverage area of the uniquely identified base station and the coverage area of the selected one of the candidate base stations. It is also possible to implement an analysis of the relative phase delay between one or more uniquely identified base stations and a selected candidate base station.

Brief description of the drawings

Fig. 1 is a diagram illustrating the relative position of a mobile unit with respect to a plurality of Base Transceiver Stations (BTSs).

Fig. 2 is a functional block diagram of a wireless communication device implementing the system of the present invention.

Fig. 3 is an illustration illustrating identification of candidate BTSs by analyzing cell coverage area overlap.

Fig. 4 is an illustration illustrating identification of candidate BTSs by analyzing the relative phase delays of the candidate BTSs.

Fig. 5A-5D are diagrams illustrating cell sector coverage and coverage models for a typical BTS in accordance with the present invention.

Fig. 6 is a flow chart illustrating the operation of the present invention.

Detailed description of the preferred embodiments

The present invention uses data analysis techniques to identify the transmitters from where they receive signals. The location of a wireless unit is based on the time of arrival (TOA) of signals transmitted from a plurality of identified Base Transceiver Stations (BTSs). The delay in the TOA depends on the PN offset and the transmission propagation delay. The TOA offset may be easily determined. However, a unique identification for each BTS is required due to transmission delay so that the location of each BTS is accurately known.

In many cases, the only information available to the mobile unit is the PN offset. As is known in the art, the PN offset is typically a multiple of 64 chips. However, some service providers use more than 64 chips to separate within the PN offset. Given the length of the PN code within the pilot signal, there are only 512(0-511) possible PN offsets for a PN offset separation using 64 chips. This results in very severe ambiguity in uniquely identifying the BTS, as described below.

Fig. 1 is a diagram illustrating the operation of a wireless system that uses Advanced Forward Link Trilateration (AFLT) to determine the position of a mobile unit. As illustrated in fig. 1, a mobile unit 10 is within range of a plurality of BTSs 12-22. For normal communications, such as voice communications, the mobile unit 10 establishes communication links with one or more BTSs 12-22, respectively. Information derived in establishing the communication link may be used to estimate the TOA and, thus, the location of the mobile unit 10 relative to the BTSs 12-22. In fig. 2, a communication link 24 is established between the mobile unit 10 and the BTS 12. It is worth noting that a communication link does not need to be established with the BTS to measure its TOA. The mobile unit 10 may actually measure the TOA simply by listening to all base stations. However, accurate position determination requires identification of each BTS so that TOA based on propagation delay can be used in the AFTL procedure. The present invention provides techniques for uniquely identifying BTSs based on limited information available to the mobile unit 10.

In a communication system, signals from BTSs are often propagated beyond their normal coverage areas through the use of repeaters. The repeater receives the signal from the BTS and retransmits the same signal. Fig. 1 illustrates a repeater 30 coupled to the BTS18 by a communication link 32. The communication link 32 may be a wireless communication link, optical fiber, hard wire, or other known signal communication link. The BTS with the repeater (e.g., BTS18) is referred to as a donor BTS because it "sheds" its signal to the repeater. Fig. 1 also illustrates a repeater 34 coupled to the repeater 30 by a communication link 36. As described above with respect to communication link 32, communication link 35 may be a wireless communication link, optical fiber, hard wire, or the like. The use of repeaters 30 and 34 effectively extends the range of the BTS 18. A mobile unit, such as mobile unit 10, measures a signal from a donor BTS, which it may receive directly from the BTS or may receive through a repeater. It is often difficult for the mobile unit 10 to determine whether the measured signal is coming through a repeater.

The present invention is implemented within a system 100, which is illustrated in the functional block diagram of FIG. 2. The system 100 includes a Central Processing Unit (CPU)102 that controls system operation. Those skilled in the art will appreciate that CPU102 is intended to encompass any processing device capable of operating a telecommunications system. This includes microprocessors, embedded controllers, Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), state machines, dedicated discrete hardware, and the like. The invention is not limited to the particular hardware components selected to implement the CPU 102.

The system also preferably includes memory 104, which may include Read Only Memory (ROM) and Random Access Memory (RAM). Memory 104 provides instructions and data to CPU 102. A portion of the memory 104 may also include non-volatile random access memory (NVRAM).

In one embodiment, the location of the mobile unit 10 may be determined solely by processing that occurs within the mobile unit itself. In other embodiments, the mobile unit sends the data it receives to the BTS (e.g., BTS12) to determine the position calculation by the BTS. In still other embodiments, the mobile unit transmits data to a BTS (e.g., BTS12), which in turn transmits the data to a Position Determining Entity (PDE) 26. Fig. 1 illustrates the PDE26 coupled to the BTS12 by a communication link 28. The communication link 28 may be a land line or other wireless connection. In addition, the PDE26 may be coupled to a large number of BTSs (e.g., the BTSs 12-22) and may receive data related to the present invention from any one of the BTSs. An advantage of a centrally located position determination entity such as PDE26 is that statistical analysis, base station queries, and other processing (described below) may be more efficiently handled by the centrally located unit rather than the mobile unit. It will be appreciated that the amount of information needed regarding the location of all BTSs may be more efficiently stored in the central PDE rather than providing increased storage requirements for the mobile unit 10. However, the present invention is not limited by the particular location at which the location of the mobile unit 10 is determined.

In one embodiment, the system 100 is implemented within a wireless communication device, such as a cellular telephone, and further includes a housing 106 containing a transmitter 108 and a receiver 110 to allow transmission and reception of data, such as audio communications, between the system 100 and a remote location, such as a BTS (e.g., BTS12 of fig. 1). Transmitter 108 and receiver 110 may be combined into transceiver 112. An antenna 114 is attached to the housing 106 and is coupled to the transceiver 112. The operation of the transmitter 108, receiver 110 and antenna 114 is well known in the art and need not be described herein unless it is specifically relevant to the present invention.

In an implementation of a CDMA device, the system further includes a searcher 116 to detect and quantify the level of the signal received by the receiver 110. The searcher 116 detects one or more parameters such as total energy, pilot energy per Pseudonoise (PN) chips, power spectral density, and other parameters, as is well known in the art. The searcher 116 performs a correlation analysis to determine the time of arrival (TOA) from a location, such as the BTS12 (see fig. 1).

The searcher 116 performs a correlation analysis between the reference signal and the received signal and generates a correlation output signal. Some different metric, such as total energy, pilot energy per PN chip, or power spectral density, may be used as a correlation value. One common simple metric is received signal strength, such as indicated by a Received Signal Strength Index (RSSI).

A signal analyzer or model processor 120 analyzes the correlated signals and uses a statistical model 122 to uniquely identify the BTS from which the mobile unit 10 received the signals. As noted above, the location of the mobile unit may be determined by processing within the mobile unit itself or by an external entity, illustrated in fig. 1 as PDE 26. The signal analyzer 120 and statistical model 122 may not be required within the mobile unit 10 if the location is determined by an external entity, such as the PDE 26. For the case where position is determined by the PDE26, the signal analyzer 120 and statistical model 122 may be located within the PDE26 and remotely from the mobile unit 10, as indicated by the dashed lines in FIG. 2. The operation of the signal analyzer 120 and the statistical model 122 will be described in detail below. The system 100 includes a timer 124 to provide system timing for measuring delay times in the arrival of signals from different sources, such as the BTSs 12-22 and one or more GPS satellites. The timer 124 may be a stand-alone device or part of the CPU 102.

The various components of system 100 are coupled together by a bus system 126, which may include a power bus, a control signal bus, and a status signal bus in addition to a data bus. However, for clarity of disclosure, a different bus is illustrated in FIG. 2 as bus system 126.

Those skilled in the art will appreciate that the system 100 illustrated in FIG. 2 is a functional block diagram rather than a listing of specific components. For example, although the searcher 116 and the signal analyzer 120 are illustrated as two separate modules within the system 100, they may actually be within the same physical component, such as within a Digital Signal Processor (DSP). They may also reside as program code in memory 104, such as code operated on by the CPU102 or a processor (not shown) within the PDE 26. The same considerations may apply to other components listed within the system 100 of fig. 2, such as the statistical model 122.

The operation of the components shown within the system 100 of fig. 2 will be explained in detail. To assist in a proper understanding of the present invention, a brief description of TOA processing, for example, using a CDMA mobile unit, is provided. A mobile unit implementing the system 100 of fig. 2, such as the mobile unit 10 of fig. 1, is first assigned a pseudo-noise (PN) code. The PN code may be stored in memory 104 as a local reference. When a base station (e.g., BTS12) transmits data to mobile unit 10, the base station transmits a PN code. The system 100 continuously searches for a correlation between the local reference (i.e., the stored PN code) and the transmitted data (i.e., the transmitted PN code).

PN offsets are selectively assigned to BTS transmitters so that offsets within a geographic area are spread out as much as possible to avoid interference between transmitters. The transmitter (e.g., within the BTS 12-22) may be identified by the transmitted identification data, but sometimes only by its PN offset time. For example, the transmitter within the BTS12 may be denoted as PN 4 to indicate that it transmits a PN code at an offset of 4x64 chips. In this example, transmitters 14 and 16 may be identified as PN 12 (i.e., 12x64 chips) and PN 25 (i.e., 25x64 chips), respectively, to indicate the offset time at which each transmitter transmits a PN code.

It is to be understood, however, that regardless of how the BTS transmitters are labeled, each relative offset with respect to the others may be derived from information encoded within the signal. A receiver 110 (see fig. 2) within the mobile unit 10 will detect the PN offset from each transmitter (e.g., within the BTSs 12-22) within the geographic region.

When a PN code is transmitted from a BTS (e.g., BTS12), there may be a delay due to the PN offset assigned to each transmitter. In addition, there is a transmission delay that indicates the distance between the transmitter and the mobile unit 10. The transmission delay may be measured by the system 100 to determine the location of the mobile unit 10. For example, the correlation pulse from the BTS with the lowest PN offset will arrive at the mobile unit 10 before the arrival of the signal from any other BTS. The system 100 must accurately measure the TOA of this first signal and arbitrarily assign it a time offset of zero. Successive correlation pulses from other BTSs and/or GPS satellites (not shown) will also be detected by the mobile unit 10, but with additional delay as a result of the PN offset and propagation delay. The delay associated with the PN offset is accurately known. The residual delay is the propagation delay, which is a result of the distance between the BTS and the mobile unit 10.

As will be appreciated by those skilled in the art, the propagation delay can only be used to determine the MS location if each BTS is uniquely identified. However, most of the information received from the BTS simply indicates the PN offset. Because of the limited number of possible PN offsets, the mobile unit 10 cannot always uniquely identify a particular BTS. For example, assume that mobile unit 10 only receives an offset value identifying a particular BTS as PN 25 (i.e., a 25x64 chip offset). There are thousands of BTSs with the same offset nationwide. Therefore, it is not possible to uniquely identify a specific BTS based on only this information.

The system 100 uses this limited information and generates additional information to build a list of possible candidates and to select the most likely candidate. As will be discussed in detail below, system 100 then uses various techniques to analyze the possible candidate list to uniquely identify a particular BTS.

The mobile unit 10 does have additional information derived from at least one BTS. Returning briefly to fig. 1, the mobile unit 10 initially establishes a communication link with a selected BTS. As mentioned above, the process of selecting a BTS with which to communicate is well known in the art and will not be described herein. However, the first BTS with which the mobile unit 10 communicates is referred to in the industry as the "serving" BTS. In the example of fig. 1, mobile unit 10 establishes a communication link 24 with BTS 12. In this example, the BTS12 would be considered the serving BTS. The data received by the mobile unit 10 uniquely identifies the BTS12 when establishing the communication link 24.

Under the telecommunication standards TIA-801 (location determination) and TIA-801-1 (location determination (hereafter TIA-801)), a serving BTS (e.g., BTS12 of FIG. 1) provides a number of parameters including NID, SID, BAND _ CLASS, CDMA _ FREQ, and BASE _ ID. As will be recognized by those skilled in the art, NID refers to network identification, SID refers to system identification, BAND _ CLASS refers to a set of channels allocated to the communication system and schemes for the communication system, CDMA _ FREQ refers to the operating frequency at which the BTS and MS communicate, and BSE _ ID refers to a particular BTS (e.g., BTS12 of fig. 1) and includes sector identification. This information may uniquely identify the BTS. With this information, the exact location (e.g., longitude and latitude) of the serving BTS can be determined.

As will be appreciated by those skilled in the art, a typical BTS actually includes a pair of independent transmitters and receivers that control the sectors. Each sector is essentially an independent BTS. Thus, the sector identification provided under TIA-801 uniquely identifies the serving BTS (e.g., BTS12 of fig. 1) and the particular sector of the serving BTS with which the communication link 24 is established.

Another telecommunications industry standard, J-STD-036(E)911 (phase 2), J-STD-036(E)911 (phase 2-annex 1) (hereinafter J-STD-036), provides information about the serving BTS, including market ID, switch number, band class, CDMA frequency, and cell ID. The market ID in the telecommunications standard J-STD-036 is typically the same as BASE _ ID in TIA-801. Thus, under the telecommunications standard J-STD-036, the mobile unit 10 receives sufficient information to uniquely identify the serving BTS.

Given this minimal information, system 100 can uniquely identify the other BTSs from which signals are received. For purposes of the present invention, the location of the mobile unit 10 is determined by measuring the TOAs from a "reference" BTS and three or more "measurement" BTSs. In most cases, the reference BTS is the same as the serving BTS unless a handoff occurs. However, for simplicity of illustration and understanding of the present invention, the serving BTS will be considered the same as the reference BTS. In the example of fig. 1, the serving/reference BTS is BTS 12. The BTSs 14-22 are considered measurement BTSs for purposes of this disclosure.

As noted above, the mobile unit 10 has sufficient data to uniquely identify the BTS 12. However, the signal from a measuring BTS (e.g., BTSs 14-22) typically includes only PN offset, BAND _ CLASS, and CDMA _ FREQ (within the telecommunication standard TIA-801).

The set of possible BTSs includes all BTSs within the country, except for the reference BTS (e.g., BTS12), before any information is received. With the PN data received from the measuring BTSs (e.g., BTSs 14-22), the set of possible BTSs is reduced to those with matching PN offsets and transmit frequencies within the country. However, this data set is not sufficient for the system to uniquely identify the measuring BTS.

To further narrow down the set of possible BTSs, the system 100 uses location information about a reference BTS (e.g., BTS12 of fig. 1). For example, if the reference BTS12 is located in Seattle, Washington, it may be known that the measuring BTSs 14-22 must be within that geographic area. System 100 implements statistical analysis to determine the amount of overlap in coverage areas between known BTSs and possible measuring BTSs and implements relative phase measurements to uniquely identify each measuring BTS. Overlay and relative phase measurements are detailed below.

The system 100 generates a large candidate BTS list of all BTSs that match the detected PN offset number, BAND _ CLASS, and frequency. The candidate list may be stored, for example, in memory 104 (see fig. 2) if the position determination entity is in memory within the mobile unit 10 or within the PDE26 (not shown). The system 100 may restrict the candidate list to include only BTSs located near known coverage areas. The known coverage area is based on the reference BTS. The known coverage area may further be based on any measuring BTS that has been previously identified by the system. As will be described in detail below, the process implemented by the system 100 is iterative. I.e. when the first measuring BTS is uniquely identified, this information can be used to uniquely identify the successive measuring BTS. As more and more measuring BTSs are identified, it provides more information to system 100, which uses information from the newly identified measuring BTS to help identify the remaining measuring BTSs.

Following generation of the candidate list, the system 100 selects the most likely candidate. In some cases, the geographical area analysis described above may be sufficient to uniquely identify one or more candidate BTSs as the measuring BTS. For example, only one candidate BTS with a particular PN offset may be located in the state in which the reference BTS is located. The unique identification of the measuring BTS can be used to provide data that further uniquely identifies additional BTSs as described above.

In addition, system 10 selects candidates for measuring the BTS based on coverage overlap between a known coverage area and the possible candidate coverage areas. In the example of fig. 1, the reference BTS12 has a known coverage area based on data generated at the time the BTS is installed, such as transmitter power, antenna pattern, land/terrestrial usage data. The system 100 computes a statistical measure of possible coverage overlap between the known coverage area and the coverage of possible candidate measuring BTSs.

Fig. 3 provides an example of the operation of system 100 to analyze coverage area overlap. In the example illustrated in fig. 3, the known coverage area 150 corresponds to the coverage area of a uniquely identified BTS, such as a reference BTS (e.g., BTS12 of fig. 1). Using an iterative process, as described above, the system 100 may use information from any other uniquely identified measuring BTS (e.g., the BTSs 14-22 of fig. 1). Thus, the known coverage area 150 described with respect to fig. 3 may refer to the coverage area of any uniquely identified BTS.

For the sake of convenience, the coverage areas are illustrated in fig. 3 as circular patterns. Those skilled in the art will appreciate that geographic features and/or artifacts may alter the actual coverage area. It is not unreasonable to use a coverage of circular areas, which simplifies the mathematical process. However, the present invention is not limited to analysis of circular areas.

System 100 uses statistical techniques to determine the probability (likelihood) that a mobile unit will detect a signal from a particular BTS. The system 100 uses a statistical model 122 (see fig. 2) to determine the probability of coverage area overlap between a known BTS and a candidate BTS and the relative phase difference between the known BTS and the candidate BTS. A normal gaussian distribution (sometimes referred to as a bell curve) is used to illustrate the probability, the center or mean of which is the peak point of the gaussian distribution. One standard deviation from the mean (sometimes referred to as one-time σ) results in a probability that a particular measurement falls approximately 68% within the gaussian distribution. Two ranges of standard deviation (sometimes referred to as one-time σ) result in a 95% probability of being included in the distribution.

The system 100 calculates the probability that the mobile unit 10 is within a particular coverage area. It is relatively simple to perform a one-dimensional probability statistics calculation using the gaussian distribution described above. However, the system 100 must compute probabilities in two dimensions to accommodate the mobile unit position changes in the north-south and east-west directions. To accommodate such two-dimensional probabilities, the system 100 calculates a Horizontal Estimated Position Error (HEPE) from the possible errors in both directions. In the example of fig. 3, the HEPE of the known coverage area 150 is calculated as the square root of the sum of the squares of the errors within each of the two dimensions. If the mean of the rate Gaussian distribution is assumed to be one time σ (i.e., one standard deviation), the HEPE can be expressed as follows:

wherein sigma_N ²One time error of sigma, in north-south direction_E ²Refers to a one-time sigma error in the east-west direction. Those skilled in the art will appreciate that the HEPE represents the diagonal of the rectangle surrounding the error ellipse. Since the coverage area is illustrated as a circle, the HEPE represents the diagonal of the square.

As illustrated in fig. 3, the known coverage area 150 has a HEPE distance referred to as r₁This is based on a deviation of one time σ from the gaussian mean. Also illustrated in fig. 3 are three candidate BTSs, each with the same PN offset of 25 (i.e., 25x64 chips). PN 25 candidates 1 and 3 in fig. 3 have corresponding coverage areas 152 and 156 that do not overlap with the known coverage area 150. In contrast, there is an overlap between the known coverage area 150 and the candidate coverage area 154 corresponding to PN 25 candidate 2. The one-time σ distance for PN 25 candidate 2 is illustrated in FIG. 3 as the value r₂. Distance r₁And r₂Indicating the relative sizes of the coverage areas of the known coverage area 150 and the candidate coverage area 154. The distance between the center of the known coverage area 150 and the center of the candidate coverage area 154 is illustrated in fig. 3 as reference D.

The statistical model 122 (see fig. 2) of the system 100 uses the relative sizes of the coverage areas to calculate the coverage overlap measure and the distance D between the centers of the coverage areas. This overlap can be represented by:

all of which are defined above. The normal distribution statistical estimate may consist of the terms of equation (2) to generate a probabilistic statistical measure of overlap within the known coverage area 150 and the candidate coverage area 154.

The normal distribution density function is sometimes calculated using the following formula:

where x is the number of standard deviations from the ideal overlap between the known coverage area 150 and the candidate coverage area 154. For relative probability, the equation can be simplified as follows:

wherein all items have been defined above.

As an example of applying the overlay model described above, consider distance r in FIG. 3₁And r₂2.0 and 1.0, respectively, and the distance D is 1.1. It is noted that these distances may be measured in convenient units, such as kilometers or kilometersMiles. Inserting these values into equation (2) provides a result of 0.49. Substituting this result into x in equation (4) yields a result of 0.886. This indicates that the probability of ideal overlap between the known coverage area 150 and the candidate coverage 154 is 88.6%. It is noted that ideal overlap gives a result of 1.0 to 100%.

In contrast, one time σ size of coverage area 152 yields a value r₂Which is a result of 1.5, and the distance D between the center of the coverage area 152 and the center of the known area 150 is 4.0 units. Applying these values to equation (2) provides a result of 1.6. Substituting this value into equation (4) yields a result of 0.278, which indicates that the ideal overlap probability between the known coverage area 150 and the candidate coverage 152 is 27.8%. Thus, it can be seen that it is more likely (i.e., likelihood) that the candidate BTS uniquely identified only as PN 25 is PN 25 candidate 2 rather than PN 25 candidate 1.

The system 100 may remove candidate BTSs based only on the coverage area overlap model. However, one skilled in the art will appreciate how small, there is still a probability that the BTS is, for example, PN 25 candidate 1. Accordingly, the system 100 will only remove candidates if the probabilities calculated using equation (4) differ by a factor of 10 or other selected value for the relative confidence ratio. I.e., only if some other candidates are at least 10 times more likely to be detected BTSs, the candidates are only removed based on coverage area overlap. In the example described above, PN 25 candidate 2 is slightly three times larger than PN 25 candidate 1 and is more likely to be a BTS detected by mobile unit 10. Thus, the system 100 may implement additional analysis to uniquely identify candidate BTSs.

Although not described herein, the system 100 will implement a similar analysis with respect to PN 25 candidate 3. In an exemplary embodiment, if the result of equation (2) is less than 8, the system 100 may analyze any candidate BTSs using equation (4). The first step of the analysis ensures that even candidates with lower probability of coverage overlap will be analyzed using equation (4). If the one-time σ overlap amount in equation (2) is equal to 8, the probability calculated using equation (4) is approximately equal to 1.26 × 10^-14. In fact, the system 100 will remove any candidate that is twice the σ overlap value. This is probably as followsThis typically occurs when the candidate coverage area is separated from the known coverage area by a large distance. For example, if the known coverage area 150 is in Seattle, Washington, and the candidate BTS is in san Francisco, Calif., the distance D separating the two BTSs is so large that the probability of reception from the BTS in san Francisco is negligible.

The system 100 also checks whether the probability of the most likely candidate is reasonable. If the probability of the most likely candidate is, for example, 0.001 (i.e., 0.1%), this indicates that the fit of the candidate BTS to other known information is quite poor and that the probability of the likely correct BTS not being in the original BTS database is higher. The system 100 will confirm that the best candidate fit is at least 0.01 (i.e., 1%) or other selected value for the minimum likelihood threshold to reduce the variance in matching the measurement to a potentially incorrect BTS.

In addition to the coverage area overlap analysis described above, the system 100 uses a relative phase model to further narrow the list of candidate BTSs. The term "relative phase" is used to indicate the distance from the candidate BTS to the mobile unit 10. As described above, each BTS transmits the same PN sequence, but with a known time delay or PN offset. When two candidate BTSs have the same PN offset, the signal is detected by the mobile unit (see fig. 1) at different times (or offsets) depending on the distance from the candidate BTS to the mobile unit. In the example of fig. 1, the mobile unit 10 is known to be within the coverage area of the reference BTS 12. If two candidate measuring BTSs are also within the coverage area, one candidate BTS may be removed based on the transmission delay, which indicates the relative phase. For example, if one candidate BTS is within two miles of the reference BTS, while the other candidate BTS is 20 miles away from the reference BTS, the relative phase between the two may be used to remove one candidate BTS.

In an example embodiment, the statistical model 122 (see FIG. 2) uses a double difference relative phase model, as follows:

ND([d_K-d_i)-(p_K-p_i)]/S_C) (5)

wherein d is_kIs covered from combinationDistance from the center of the area (i.e., the combined coverage area of the candidate BTS and the known BTS) to the known BTS, d_iDistance of time from the center of the combined coverage area to the candidate BTS, p_kIs a phase measurement, p, to a known BTS_iIs a phase measurement to a candidate BTS, S_CIs the expected double difference phase error from the combined coverage area. The term "double difference" refers to a statistical calculation based on two difference (i.e., the difference of the distance minus the phase difference) measurements.

Phase p_kAnd p_iOffsets to known BTSs such as forward link hardware delays are adjusted. Those skilled in the art will appreciate that hardware delays may occur due to circuitry, filters, processing within the connector cable, etc. Uncertainty in the phase measurement due to uncertainty in the BTS bias, and possible propagation delays and measurement errors, and the denominator (S) of the relative phase test_C) And (4) combining. In addition, if the known or candidate BTS has a repeater that greatly delays the relative phase measurement, the relative phase test can be removed, the weight given greatly reduced, or made unilateral. For measurement purposes, the phase of the signal passing through the repeater (e.g., repeater 30 of fig. 1) is delayed and appears to be further than the signal from the donor BTS (e.g., BTS 18). The delay of the repeater signal results from hardware delays due to filters, cables, etc. as compared to the normal direct signal, and there is further delay due to the fact that the signal path from the donor BTS may not be direct, which results in additional delay.

The relative phase test may be modified in two different ways when repeaters are present. In one case, the location and signal delay of all repeaters are known. In the second case, it is known that a given BTS may have one or more signal repeaters, but the location and/or signal delay of these repeaters is unknown. In the first case, some BTSs (e.g., BTS18 of FIG. 1) are known to have one or more repeaters (e.g., repeaters 30 and 34), and the location and signal delay of each repeater is known. In this case, each repeater for each BTS may be treated as another candidate BTS. The candidate repeater looks similar to the donor BTS except that it is in a different location and has a different hardware delay that is often much higher. In addition, each candidate repeater has a different sector center and maximum antenna range. The candidate repeaters are added to the candidate list in the same manner as normal BTSs in the same coverage area and phase tested as the other candidates. Assuming that such repeater information is available, this is the best way to handle the repeaters, as it increases the likelihood that the donor BTS and each repeater can be used as a source of the measurement.

In the second case, a BTS such as BTS18 of FIG. 1 may have one or more repeaters (e.g., repeaters 30 and 34), but the location and signal delay of the repeaters are unknown. If the signal is from a repeater, its delay is greater than the phase delay directly from the donor BTS. As a result, the relative phase test described above needs to be able to allow a phase equal to or greater than the signal directly from the donor BTS. In the case where a candidate BTS may have a repeater, the relative phase test is modified so that the double difference coincides with the much longer phase delay expected from the candidate BTS. For example, the relative probability is not recorded according to an approximation of equation (4), but is equal to the maximum value of equation (4) or 0.5, which ensures that the recording of long phase delays is not worse than 0.5. This effectively makes the phase test single-sided. Those skilled in the art will recognize that other techniques are possible for compensating for the long phase delay introduced by the repeater. In addition, it may be useful to avoid comparison with a BTS with a repeater when selecting a comparison BTS for relative phase delay measurements.

The combined coverage area is a probabilistic measure of the combined coverage area of the known BTS and the candidate BTS. Details of the measurement of the combined coverage area are provided below. The relative phase model is used to determine if the phase delay of the mobile unit 10 (see fig. 1) coincides with the distance between the known BTS and the candidate BTS. As described above, the known BTS may be a reference BTS (e.g., BTS12 of fig. 1) or any measuring BTS that has been uniquely identified.

The example shown here is a possible technique for determining this relative phase difference. Those skilled in the art will appreciate that other techniques may be used to determine this phase difference. The present invention is not limited to the specific analysis described above for determining the relative phase difference.

The relative phase calculation is illustrated in fig. 4, where the approximate center of the combined coverage area 160 is designated by reference numeral 164. Distance d_KIs the distance of the center 164 of the combined coverage area 160 and the known BTS 166. As noted above, the known BTS 166 may be a reference BTS, a serving BTS, or a uniquely identified measuring BTS.

The candidate BTS 168 has a coverage area 162 that is modeled as a circular coverage area. As shown in fig. 4, the candidate BTS 168 is not located at the center of the candidate coverage area 162. This is because a general BTS is not omni-directional, but is divided into a plurality of sectors. The sectors may be modeled as pie-shaped sectors by the system 100. However, such modeling is often inaccurate due to back-scattering of the antenna and reflections from buildings, natural terrain, and other objects. Thus, the candidate coverage area 162 may be modeled as a circle. Similarly, a known BTS 166 is not generally centrally located within a known coverage area (not shown in FIG. 4) for the reasons discussed above.

The coverage area of each BTS (or each cell sector) is determined at the time of installation and is known. The combined coverage areas, indicating the coverage areas of the known BTS 166 and the candidate BTS 168, may be linearly computed by computing the overlap area of the circular areas of coverage. Alternatively, the combined coverage area may be calculated by weighting the coverage areas. Determining the combined coverage area is described in more detail below.

The combined coverage area 160 is determined from the coverage areas mapped at the time of BTS installation and calibration. The combined coverage area 160 is a probabilistic estimate of the coverage areas of the known BTS 166 and the candidate BTS 168. As described above, a two-dimensional position error, referred to as HEPE, provides a measure of the statistical uncertainty of the measurement combined coverage area 160. Within the system 100, a distance S_CBased on HEPE coverage and represents one-fold σ uncertainty in relative phase.

Combining the distances d from the center 164 of the coverage area 160 to the candidate BTS 168_iAnd (4) showing. Phase measurement p_KAnd p_iMeasured by the mobile unit 10 and provided to a PDE (e.g., PDE26 of fig. 1) via the BTS using the telecommunications standard TIA-801.

As described above, the system 100 can calculate the expected relative phase difference and compare the expected phase difference to the actual distance measurement. The system 100 may apply normal distribution equation (4) to calculate the probability that the candidate BTS is consistent with the phase and distance measurements. If multiple candidate BTSs (with the same PN) are detected by the system 100, one or more of the candidate BTSs may be dropped based on the relative phase difference. I.e., given the location of the known BTS from the center 164 of the combined coverage area 160 and the distance from the center of the combined coverage area to the candidate BTS, the candidate BTSs must have a reasonable phase difference. The inconsistent candidate BTSs may be removed from the candidate list.

The relative phase model is also applied to other candidate BTSs. For example, fig. 3 illustrates three candidates with the same PN 25 offset. The analysis process described above is applied to each candidate BTS (e.g., PN 25 candidates 1-3 of fig. 3) resulting in a probability calculated for each candidate BTS. As described above, a candidate BTS may only be removed according to a coverage area overlap model if the coverage overlap of another BTS is at least ten times greater than the coverage area likelihood of the BTS to be removed. Similarly, a particular candidate BTS may only be removed according to the relative phase model if the phase difference probability of another BTS is at least ten times greater than the likelihood of the phase difference probability of the BTS to be removed. This process ensures that the low probability candidate BTS is dropped with little likelihood of erroneously dropping the BTS.

The probability of coverage area overlap models and relative phase models may be combined to remove candidate BTSs. In one example, the probability of the coverage area overlapping the model is multiplied by the probability of the relative phase model. The combination of probabilities is used to further remove the unlikely BTSs from the candidate list.

In addition to the analysis described above, the system 100 may also use signal strength and cell sector coverage models to uniquely identify candidate BTSs. As described above, a typical BTS has multiple transmitters and multiple antenna elements, each for operating within a sector. In an exemplary embodiment, a BTS may have three sectors, each of which may be considered a separate BTS. The coverage area of a typical sector may have a pie-shaped coverage area, such as illustrated in fig. 5A-5D. The coverage area of a sector is typically determined by measurements at the time of installation of the BTS. The coverage area is based on factors such as maximum antenna range, maximum transmitter power, etc. In some installations, the BTS is divided into three sectors with wide coverage areas 170, such as illustrated in fig. 5A, 5C, and 5D. In other installations, a narrower sector is desired, such as coverage area 172 illustrated in fig. 5B.

The system 100 can model the coverage areas as pie-shaped coverage areas 170 and 172. However, it is most convenient to model the coverage area as a substantially circular distribution. As mentioned above, factors such as antenna backscattering and reflections from man-made objects, terrain, etc. cause the shape of the coverage area to be more circular than pie-shaped. Accordingly, in the example embodiment, the system 100 models the coverage area 170 in FIG. 5A as a circular coverage area 174, while the coverage area 172 in FIG. 5B is modeled as a circular coverage area 176. Coverage areas 170 and 172 are calculated when the BTS is installed and provide a 99% coverage probability within the area. The circular coverage areas 174, 176, 182, and 184 indicate areas where the mobile unit has a 99% probability within the circle. The centers of coverage areas 174 and 176 are indicated by reference numerals 178 and 180, respectively. In an example embodiment, the system 100 uses the circular model coverage areas 174 and 176, possibly to calculate a combined coverage area 160 (see FIG. 4).

As discussed above, the coverage areas 174 and 176 are used for probabilistic calculation of relative phase measurements. The combined coverage areas may be linearly combined or weighted according to a scale factor. The system 100 may calculate the scaling factor based on the received signal strength. One measure of received signal strength is E_c/I_oWhich is the pilot energy accumulated over a 1PN chip period (i.e., E)_c) To receivingTotal power spectral density (i.e., I) over the bandwidth of_o) A measure of the ratio. Those skilled in the art will recognize other power measurements that may be more satisfactory for use with system 100. Based on the signal strength, the system 100 assigns a scaling factor based on the strength of the received signal. The principle of the scale factor is illustrated in fig. 5C and 5D. In fig. 5C, the received signal strength is relatively weak. Thus, the mobile unit may be located in a relatively wide area with respect to the BTS. In this case, the circular coverage area 174 may be expanded by the scaling factor to generate a larger circular coverage area 182, as illustrated in fig. 5C. The larger circular coverage area 182 reflects the fact that the mobile unit 10 may be located anywhere within a larger range. The center of the circular coverage area 182 is designated by reference numeral 186.

In contrast, if the received signal strength is strong, the system 100 may reduce the coverage area. This indicates that the mobile unit is more likely to be close to the BTS than far away. This probability is illustrated in fig. 5D, where the reduced circular footprint 184 is smaller in diameter than the circular footprint 170. The reduced circular coverage area 184 reflects the fact that the probability of the mobile unit 10 being in close proximity to a BTS increases, depending on signal strength. The center of the circular coverage area 184 is designated by reference numeral 188.

In an example embodiment, the system may apply a scale factor of 0.9 to the stronger signal, above its pre-selected threshold, and may apply a scale factor of 1.1 to the weaker signal (below a predetermined threshold).

As previously described, the coverage area calculation is used to establish a combined coverage area (e.g., the combined coverage area of fig. 4). The cell sector models illustrated in fig. 5A-5D may also be used to calculate a known area (e.g., known area 150 of fig. 3). In a simple calculation, the coverage area of a single known BTS may be used as the known area of the coverage area overlay model. Similarly, a single known BTS may be used in combination with a single candidate BTS to generate a combined coverage area for use within the relative phase model. However, the system 100 can also perform calculations of known areas or combined coverage areas, which may be from mixed coverage areas of multiple cells. The cells may be combined in a linear fashion or may include weights such as scale factors applied to fig. 5C and 5D or the inverse of the area of each coverage area.

The identification process of system 100 is illustrated in the flow chart of fig. 6, where at start 200, mobile unit 10 has been powered on and a requested position determination has been made. In step 202, the system 100 identifies a reference BTS (e.g., BTS12 in fig. 1). As noted above, the serving BTS is the BTS with which the mobile unit 10 initially communicates. In some cases, a handoff may occur such that mobile unit 10 is now communicating with a different BTS. The handover procedure is well known in the art and will not be described here. To understand the present invention, it is only necessary to illustrate that the mobile station 10 is in communication with a reference BTS, which may or may not be the serving BTS and which has uniquely identified the reference BTS.

In step 204, the system 100 generates a candidate list. As previously described, the signals received from each measuring BTS are typically identified using only the corresponding PN offset of the measuring BTS. From the PN offsets, it is possible to identify multiple candidate BTSs. In the example discussed herein, a PN offset of 25 (i.e., 25x64 chips) is identified as the measuring BTS. In the example described herein, many candidate BTSs throughout the country may have the same PN 25 offset. Each of these candidate BTSs is added to the candidate list in step 204.

In step 206, the system 100 narrows down the candidate list based on the comparison of coverage areas. As described above, this analysis includes removing those geographical locations from the BTS that make it unlikely to be a particular BTS that system 100 has detected. For example, if the mobile unit 10 is identified as being located in the Seattle area based on the communication link 24 with the reference BTS12 (see FIG. 1), BTSs in areas remote from the Seattle area may be removed.

As noted above, the analysis may be performed by the PDE26 (see fig. 1), which may be part of the BTS, or remote from the BTS, or may be implemented within the mobile unit 10. System 100 may also initially identify a reference BTS and may generally uniquely identify one or more measuring BTSs using the process described in step 206. I.e., the system 100 may remove candidate BTSs that are not within the same geographic region as the reference BTS. Alternatively, it may be the case that a particular geographic area may have only one BTS with a particular PN offset. In these cases, the unique identity of the candidate BTS is not ambiguous. The system 100 will identify the candidate BTS as the measuring BTS.

At step 210, the system 100 uses analysis techniques, such as coverage area overlap and relative phase difference, to further identify candidate BTSs. Additionally, system 100 may use analysis of signal strength and mixed cell sector location to identify candidate BTSs. At step 210, the system 100 identifies the most likely candidates based on the analysis in step 208. As described above, the most likely candidate may be selected based on one or more analysis techniques. These analyses, such as overlay and relative phase measurements, may be implemented separately, or probabilities may be combined to identify the most likely candidates.

In decision 212, the system 100 determines whether all of the measuring BTSs have been identified. If the candidate BTS has not yet been identified, the result of decision 212 is NO and system 100 proceeds to decision 214. As previously described, the process of identifying the measuring BTS uses information obtained from previous identifications of other measuring BTSs within the iterative process. Accordingly, fig. 6 illustrates the processing loop formed by steps 208 and 210 and decisions 212 and 214. In decision 214, the system 100 determines whether at least one new measuring BTS has been identified in the iteration through the loop. Assuming that the system 100 successfully identifies the measuring BTS, the result of decision 214 is YES and the process returns to step 208 to analyze the candidate BTS with respect to the known BTSs, including at least one new measuring BTS identified on the previous path over the loop. The process ends when either all measuring BTSs are identified by the system or when no new BTS can be identified. If all measuring BTSs have been identified, the result of decision 212 is YES and the process terminates at 216. If the BTS remains unidentified, but the system 100 cannot identify additional BTSs based on the available information, the result is decision 214 is NO and the process ends at 216.

Using the principles of the present invention, it is possible to identify all of the measuring BTSs detected by the mobile unit 10 (see fig. 1). As can be appreciated by those skilled in the art, the location determination may be more accurate when there are more measuring BTSs. It is unreliable for AFLT if it cannot uniquely identify a candidate BTS. However, using the techniques of the present invention, it is possible to identify many of these additional measurement BTSs, thereby providing additional sources of measurements that can be used to more reliably determine the location of mobile unit 10.

In the example provided above, the identification process is performed by the mobile unit 10. However, the identification of candidate BTSs may be performed by other entities, such as the PDE26 (see fig. 1). For example, the communications standard TIA-801 has provided for the transmission of relative phase measurements from a mobile unit to the PDE 26. Additional information, such as the exact location of the BTS, coverage area, etc., has been determined by any entity, such as the mobile unit 10, the BTS, or the PDE. Given this information, any location determining entity may perform the necessary calculations to uniquely identify each measuring BTS. Accordingly, the present invention is not limited to identifying candidate BTSs based solely on analysis by the mobile unit 10.

It is to be understood that even though numerous embodiments and advantages of the present invention have been set forth in the foregoing description, the foregoing disclosure is illustrative only, and changes may be made in detail, yet remain within the general principles of the invention. The invention is therefore to be limited only by the appended claims.

Claims (52)

1. A method for identifying a base station in a wireless communication system, comprising:

receiving complete identification data from the first base station;

receiving transmissions from a plurality of base stations, the transmissions containing only a portion of the identification data insufficient to identify at least a portion of the plurality of base stations;

generating a candidate list from the candidate base stations from which transmissions of only part of the identification data have been received, providing identifications for the candidate base stations;

analyzing the candidate base stations with respect to the uniquely identified base stations by at least one method selected from the group consisting of determining coverage overlap areas and determining relative phase delays; and

an identity of one of the plurality of base stations is determined from an analysis of the candidate base stations.

2. The method of claim 1, wherein the first base station is a serving base station with which the wireless device initially establishes a communication link.

3. The method of claim 1, wherein analyzing the candidate base stations is performed iteratively with respect to other ones of the candidate base stations that have been previously uniquely identified.

4. The method of claim 1, wherein analyzing the candidate base stations comprises analytically determining an area of coverage overlap between a known coverage area of the uniquely identified base station and a coverage area of the selected one of the candidate base stations.

5. The method of claim 4, wherein the probability statistic generated by said parsing determination is a probability of coverage area overlap between a known coverage area of said uniquely identified base station and a coverage area of the selected one of the candidate base stations, and wherein determining the identity of the base station is based on the probability statistic.

6. The method of claim 4, wherein determining the coverage overlap region further comprises transforming a coverage area model of the selected base station based on a received signal strength of a signal received from the selected base station.

7. The method of claim 1, wherein analyzing the candidate base stations comprises determining a probability that a coverage area of each candidate base station overlaps with a coverage area of a base station that has been uniquely identified.

8. The method of claim 7, further comprising removing the selected candidate base station from the candidate list if the probability of coverage overlap of the selected candidate base station is less than the probability of coverage overlap of the other candidate base stations by a predetermined amount.

9. The method of claim 7, wherein the candidate list includes candidate base stations that transmit substantially the same partial identification data.

10. The method of claim 1, wherein analyzing the candidate base stations comprises analytically determining relative phase delays between the uniquely identified base stations and the selected candidate base stations.

11. The method of claim 10, wherein determining the relative phase delay generates a probabilistic result, and wherein the determination of the base station identification is based on the probabilistic result.

12. The method of claim 10, wherein the at least one candidate base station comprises a repeater and the relative phase delay is adjusted to account for the repeater by compensating for a phase equal to or greater than a phase of a signal directly from the candidate base station comprising the repeater.

13. The method of claim 10, wherein at least one of the candidate base stations comprises a repeater with a known location and signal processing delay, the method further comprising adding the repeater to the candidate list as a candidate base station.

14. The method of claim 10, wherein analyzing the candidate base stations comprises determining a probability of the phase delay of each candidate base station relative to the phase delay of the uniquely identified base station corresponding to a distance from each candidate base station to the predetermined location relative to a distance from the uniquely identified base station to the predetermined location.

15. The method of claim 14, wherein the predetermined location for each candidate base station is approximately a center of a combined coverage area of each respective candidate base station and at least one uniquely identified base station.

16. The method of claim 15, wherein determining the relative phase delay further comprises altering a combined coverage area of the selected base stations based on a received signal strength of a signal received from the selected base stations.

17. The method of claim 14, further comprising removing the selected candidate base station from the candidate list if the probability of the relative phase delay corresponding to the relative distance of the selected candidate base station is less than the probability of the relative phase delay corresponding to the relative distance of the other candidate base stations by a predetermined amount.

18. The method of claim 14, wherein the candidate list includes candidate base stations that transmit substantially the same partial identification data.

19. An apparatus for identifying a base station in a wireless communication system, comprising:

a receiver for receiving transmissions from a plurality of base stations, the transmissions comprising complete identification data from a first base station and comprising only a portion of the identification data, the portion of the identification data being insufficient to identify at least a portion of the plurality of base stations;

a candidate list providing identifications of candidate base stations from which transmissions containing only part of the identification data may be received; and

a signal analyzer for analyzing the candidate base station relative to the uniquely identified base station by at least one method selected from the group consisting of determining a coverage overlap area and determining a relative phase delay, the signal analyzer using a statistical model to determine the identity of the base station from the analysis of the candidate base station.

20. The apparatus of claim 19 wherein the first base station is a serving base station and the wireless device initially establishes a communication link with the first base station.

21. The apparatus of claim 19, wherein the signal analyzer analyzes the candidate base station in an iterative process with respect to other candidate base stations that have previously been uniquely identified.

22. The apparatus of claim 19, wherein the candidate list comprises candidate base stations that transmit substantially the same partial identification data.

23. The apparatus of claim 19, wherein the signal analyzer analyzes the candidate base stations to determine a probability that the coverage area of each candidate base station overlaps with the coverage area of the uniquely identified base station.

24. The apparatus of claim 23, wherein the signal analyzer alters the model of the coverage area of the selected base station based on a received signal strength of the signal received from the selected base station.

25. The apparatus of claim 23, wherein the signal analyzer is configured to: the selected candidate base station is removed from the candidate list if the coverage overlap probability of the selected candidate base station is less than the coverage overlap probabilities of the other candidate base stations by some predetermined amount.

26. The apparatus of claim 19 wherein the signal analyzer analyzes the candidate base stations to determine a probability that the phase delay of each candidate base station relative to the phase delay of the uniquely identified base station corresponds to the distance of each candidate base station to the predetermined location relative to the distance from the uniquely identified base station to the predetermined location.

27. The apparatus of claim 26 further comprising a repeater communicatively coupled to at least one of the candidate base stations, the signal analyzer varying the probability to compensate for the repeater by compensating for a phase that is equal to or greater than a phase of a signal directly from the candidate base station that includes the repeater.

28. The apparatus of claim 26 further comprising a repeater communicatively coupled to at least one candidate base station, wherein the repeater has a known location and signal processing delay, and wherein the analyzer analyzes the repeater in the same manner as the candidate base station.

29. The apparatus of claim 26, wherein the predetermined location for each candidate base station is approximately a center of a combined coverage area for each respective candidate base station and at least one uniquely identified base station.

30. The apparatus of claim 29 wherein the signal analyzer determines the relative phase delay by varying the combined coverage area of the selected base stations based on the received signal strength of the signals received from the selected base stations.

31. The apparatus of claim 26, wherein the signal analyzer is configured to: if the relative phase delay probability corresponding to the relative distance of the selected candidate base station is less than the relative phase delay probability corresponding to the relative distances of other candidate base stations by a predetermined amount, the selected candidate base station is deleted from the candidate list.

32. The apparatus of claim 26, wherein the signal analyzer further analyzes the candidate base stations to determine a probability that a coverage area of each candidate base station overlaps with a coverage area of a uniquely identified base station.

33. The apparatus of claim 32 wherein the signal analyzer combines the relative phase delay probability and the coverage overlap probability to determine the identity of the candidate base station.

34. In operating a mobile communication unit in a wireless communication system, a method of distinguishing a base station having partial identification data from a base station having the same partial identification data, comprising:

uniquely identifying a first base station;

receiving a transmission from at least one other base station, the transmission containing only the partial identification data;

generating a candidate list providing the identification of candidate base stations having the same partial identification data;

analyzing the candidate base stations on the candidate list according to the identification data of the first base station by at least one method selected from the group of methods consisting of determining a coverage overlap area and determining a relative phase delay; and

the base station having the partial identification data is distinguished from another base station having the same partial identification data based on an analysis of the candidate base stations.

35. The method of claim 34, wherein the first base station is a serving base station with which the wireless device initially establishes a communication link.

36. The method of claim 34, wherein the generating the candidate list that provides the identification of candidate base stations comprises: including at least one candidate base station outside the communication range of the first base station.

37. The method of claim 34, wherein said analyzing the candidate base stations is performed iteratively based on other ones of the candidate base stations that have been previously uniquely identified.

38. The method of claim 34, wherein the analyzing the candidate base stations comprises: resolving to determine a coverage overlap area between the known coverage area of the first base station and the coverage area of the selected one of the candidate base stations.

39. The method of claim 38, wherein the probabilistic statistic generated by said resolving determination is a probability of coverage area overlap between a known coverage area of said uniquely identified base station and a coverage area of a selected one of the candidate base stations, and wherein said uniquely identifying the candidate base station is based on the probabilistic statistic.

40. The method of claim 38, wherein said determining the coverage overlap area further comprises transforming a coverage area model of the selected candidate base station based on received signal strength of signals received from the selected candidate base station.

41. The method of claim 34, wherein analyzing the candidate base stations comprises determining a probability that one coverage area of each candidate base station overlaps with a coverage area of the first base station.

42. The method of claim 41, further comprising: if the coverage overlap probability of the selected candidate base station is less than the coverage overlap probabilities of the other candidate base stations by a predetermined amount, the selected candidate base station is removed from the candidate list.

43. The method of claim 42, wherein the predetermined amount is greater than 10 times.

44. The method of claim 34, wherein analyzing the candidate base stations comprises analytically determining a relative phase delay between the first base station and the selected candidate base station.

45. The method of claim 44, wherein the determining the relative phase delay comprises generating a probabilistic statistic, and wherein the uniquely identifying a base station is based on the probabilistic statistic.

46. The method of claim 44 further comprising, if the system includes any repeaters, adjusting the relative phase delay to account for any repeaters in the system by compensating for a phase equal to or greater than a phase of a signal directly from a candidate base station including the repeater.

47. The method of claim 44, wherein at least one candidate base station comprises a repeater with a known location and signal processing delay, the method further comprising adding the repeater to a candidate list as a candidate base station.

48. The method of claim 44, wherein analyzing the candidate base stations comprises determining a probability of the phase delay of each candidate base station relative to the phase delay of the first base station corresponding to a distance from each candidate base station to a predetermined location relative to a distance from the first base station to a predetermined location.

49. The method of claim 47, wherein the predetermined location for each candidate base station is approximately a center of a combined coverage area of each respective candidate base station and the first base station.

50. The method of claim 49, wherein determining the relative phase delay further comprises altering a combined coverage area of the selected base stations based on a received signal strength of a signal received from the selected base stations.

51. The method of claim 48, further comprising: if the probability of the relative phase delay corresponding to the relative distance of the selected candidate base station is less than the probability of the relative phase delay corresponding to the relative distance of the other candidate base stations by a predetermined amount, the selected candidate base station is deleted from the candidate list.

52. The method of claim 51, wherein the predetermined amount is greater than 10 times.