HK1070523B - Method and apparatus for estimating the position of a terminal based on identification codes for transmission sources - Google Patents

Description

Method and device for estimating terminal position according to identification code of transmission source

Technical Field

The present invention relates generally to position determination, and more particularly to techniques for providing a position estimate of a terminal within a wireless communication system based on an identification code assigned to a transmission source, such as a repeater.

Background

A common technique for locating a terminal is to determine the amount of time it takes to transmit a signal from multiple transmitting transmitters at known locations to reach the terminal. One system that provides signals from multiple transmitters of known location is the well-known Global Positioning Satellite (GPS) system. The satellites within the GPS system are located on precise orbits according to the GPS control plan. The position of a GPS satellite can be determined from different sets of information transmitted by the satellite itself (commonly referred to as "ephemeris" and "ephemeris"). Another system that provides signals from transmitters at known locations within terrestrial range, such as base station … …, is a wireless (e.g., cellular telephone) communication system.

Many wireless communication systems use repeaters to provide coverage to a specified area within the system or to extend the coverage of the system. For example, a repeater may be used to cover an area that a base station cannot cover due to fading conditions (i.e., a "hole" in the system). Repeaters may also be used to extend coverage to rural areas (e.g., along highways) outside the coverage area of the base station. The repeater receives, conditions, and retransmits signals on both the forward link (i.e., from the base station to the mobile unit) and the reverse link (i.e., from the mobile unit to the base station).

Various challenges are encountered in determining the location of a terminal within a system that employs one or more repeaters. Typically, signals from a single base station are processed by repeaters and retransmitted by interrupters at relatively high power with some delay. The combination of the high power of the relayed signal plus the isolation associated with the repeater coverage area generally prevents the terminal from receiving signals from other base stations. Moreover, in many instances where repeaters are used (e.g., in buildings, tunnels, subways, etc.), the signal power level from the GPS satellites is insufficient to be received by the terminal. In this case, a limited number of signals (possibly only one signal from the repeater) may be used to determine the terminal location. In addition, the additional delay introduced by the repeater distorts the round trip delay/time of arrival (RTD, TOA) measurements as well as the TDOA measurements, which results in inaccurate position estimates from these measurements.

Fig. 1A is a diagram of a wireless communication system 100 that uses repeaters in accordance with the disclosed method and apparatus. System 100 may be designed to conform to one or more commonly known industry standards such as IS-95, published by the telecommunications industry association/electronic industries association (TIA/EIA), and other industry standards such as W-CDMA, CDMA2000, or combinations thereof. System 100 includes a plurality of base stations 104. Each base station serves a particular coverage area 102. Only three base stations 104a through 104c are shown in fig. 1A for simplicity, and those skilled in the art will appreciate that there are typically such base stations in such a system. For the sake of disclosure, a base station, together with its coverage area, is referred to as a "cell".

System 100 may use one or more repeaters 114 to provide coverage to areas that cannot be covered by a base station (e.g., due to fading conditions, such as area 112a shown in fig. 1A) or to extend the coverage area of the system (such as areas 112b and 112 c). For example, repeaters are commonly used to improve the indoor coverage of cellular systems at a relatively low cost. Each repeater 114 is coupled to the "serving" base station 104 via a wireless and wired (e.g., coaxial or fiber optic) link (e.g., coaxial or fiber optic cable) either directly or through other repeaters. Any number of base stations within the system may be relayed depending on the particular system design.

A plurality of terminals 106 are typically dispersed throughout the system (only one terminal is shown in fig. 1A for simplicity). Each terminal 106 may communicate with one or more base stations on the forward and reverse links at any given moment, depending on whether the system supports soft handoff and whether the terminal is actually in soft handoff. Those skilled in the art will appreciate that "soft handoff" refers to the situation where a terminal is communicating with more than one base station at the same time.

The plurality of base stations 104 are typically coupled to a Base Station Controller (BSC) 120. The BSC 120 coordinates the communication with the base stations 104. The base station controller 120 may also be coupled to a Position Determination Entity (PDE)130 for determining the position of the terminal. PDE 130 receives time measurements and/or identification codes from the terminals and provides control and other information related to position determination, as will be described in detail below.

For position determination, a terminal may measure the arrival times of signals transmitted from multiple base stations. For a CDMA network, these times of arrival may be determined from the phase of a Pseudonoise (PN) code used by the base station to spread its data before transmitting it on the forward link to the terminal. The PN phase detected by the terminal may then be reported to the PDE (e.g., via IS-801 signaling). The PDE then uses the reported PN phase measurements to determine pseudoranges, which are then used to determine the position of the terminal.

The location of the terminal can also be determined using a hybrid scheme where the time of arrival of the signal (i.e., time of arrival TOA) is measured for any combination of base station 104 and Global Positioning System (GPS) satellites 124. Measurements derived from GPS satellites may be used as primary measurements or to supplement measurements derived from base stations. Measurements from GPS satellites are generally more accurate than measurements from base stations. However, a clear line of sight to the satellites is generally required to receive the GPS signals. Accordingly, the use of GPS satellites for position determination is generally limited to unobstructed outdoor environments. GPS signals are generally not received indoors or in other environments where there are obstacles such as foliage and buildings. However, GPS has extended coverage and four or more GPS satellites can potentially receive from places without any obstructions.

In contrast, base stations are typically located in multiple areas of a person and their signals can penetrate buildings and obstacles. Thus, it may be used by a base station to determine the location of a device capable of receiving and/or transmitting such signals within a city and potentially a building. However, measurements derived from base stations are generally less accurate than measurements from GPS satellites, since multipath effects may receive multiple signals at a terminal from a particular base station. Multipath refers to the situation where a signal is received over multiple transmission paths between a transmitter and a receiver. Multiple paths result from the reflection of a signal on various objects, such as buildings, mountains, etc. It is to be noted that in the best case, the signal is also received on the direct path (straight line) from the transmitter to the receiver. However, this is not necessarily true.

In the hybrid scheme, each base station and each GPS satellite represents a transmission source. To determine a two-dimensional estimate of the position of a terminal, transmissions from three or more spatially misaligned sources are received and processed. The fourth source is used to provide altitude (third dimension) and may also provide increased accuracy (i.e., reduced uncertainty in the measured arrival time). The signal arrival time can be determined for the transmission source and used to calculate a pseudorange, which may be used (e.g., via trilateration) to determine the terminal location. Position determination may be by well known means, such as described in 3GPP25.305, TIA/EIA/IS-801, and TIA/EIA/IS-817 standard documents.

In the example shown in fig. 1A, terminal 106 may receive transmissions from GPS satellites 124, base stations 104, and/or repeaters 114. The terminal measures the time of arrival of signals transmitted from these transmitters and may report these measurements to PDE 130 through BSC 120. PDE 130 can then use these measurements to determine the location of terminal 106.

As described above, a repeater may be used to provide coverage in areas not covered by a base station, such as within a building. Repeaters are more cost effective than base stations and can be advantageously used where additional capacity is not required. However, repeaters are associated with additional time delays due to circuitry and cabling within the repeater and/or additional transmissions associated with the repeater. As an example, Surface Acoustic Wave (SAW) filters, amplifiers, and other components within repeaters introduce additional time delays that are equal to or even greater than the propagation delay from the base station to the terminal. Time measurements of signals from repeaters cannot be used to reliably determine terminal position if repeater delay is not accounted for.

Fig. 1B is a diagram illustrating the use of repeaters 114x to provide indoor coverage for building 150. In the illustrated example, the repeater 114x includes a Main Unit (MU)115 coupled to a plurality of Remote Units (RUs) 116. On the forward link, the master unit 115 receives one or more signals from one or more base stations and transmits all or a subset of the received signals to each of the remote units. And on the reverse link, the master unit 115 receives, combines, and relays signals transmitted on the reverse link from the remote units 116 back to one or more base stations. Each remote unit 116 provides coverage (e.g., one floor) of a particular area within the building and relays forward and reverse signals for its coverage area.

Various challenges are encountered in estimating the location of terminals located within a building covered by repeaters. First, in many indoor applications, a terminal may not be able to receive signals from base stations or GPS satellites, or may receive signals from fewer transmitters than are needed to enable trilateration. To provide in-building coverage, repeaters typically retransmit signals from a single base station at relatively high power and with a time delay. The combination of the high power of the relayed signal plus the isolated indoor location of the terminal generally prevents the terminal from receiving other signals from other base stations and satellites.

Second, if the delay introduced by the repeater is unknown, the signal from the repeater cannot be used for one of the reliably trilaterated signals. This prevents an entity (e.g., a PDE or a terminal) from using the relayed signals to derive a position estimate using as few as one satellite or base station signal. Third, GPS signals cannot be received in many environments where repeaters are used (e.g., subways, buildings, etc.), even if the terminals use receiver units with enhanced sensitivity. Fourth, the entity that determines the location of the terminal has no way to determine whether the terminal uses an incorrect time reference (due to uncertain repeater delay), which can affect the accuracy of Round Trip Delay (RTD) measurements as well as the time stamp on GPS measurements.

There is therefore a need in the art for techniques to provide terminal position estimates in a wireless communication system using repeaters (or other transmission sources with similar characteristics).

SUMMARY

The disclosed method and apparatus determine the location of a terminal communicating through a repeater within a wireless communication system. The disclosed methods and apparatus recognize that repeaters for providing indoor coverage are generally designed to cover relatively small geographic areas (e.g., buildings, a floor of a building, etc.). If the coverage area of a repeater is small, the position estimate of the terminal under the coverage of the repeater may be reported as the indicated position within the coverage area, which may be the center of the coverage area. In many, if not most, cases, the reported position estimate of the terminal is within 50 meters of the actual position of the terminal. This accuracy is sufficient for enhanced emergency 911(E-911) services as specified by the Federal Communications Commission (FCC).

In accordance with one embodiment of the disclosed method and apparatus, an identifier uniquely associated with each relay is transmitted by each relay within a particular coverage area (e.g., cell). The identification code may then be used by the terminal (or PDE) to unambiguously identify the relay. Various types of codes may be used as the identification code. In one embodiment, the identification code includes a Pseudo Noise (PN) sequence at a defined offset that is specifically reserved for repeater identification.

In the case of a repeater covering a small geographical area, the identification of the particular repeater through which the signal is received can be used to estimate the terminal location, for example the centre of the repeater coverage area. For the case where a repeater covers a large area, the identity of the particular repeater through which the signal is received can be used to adjust the measurements according to the time delay of the repeater.

In another embodiment, the identification code of each repeater is transmitted using a spread spectrum signal. The spread spectrum identifier signal can be designed to have minimal impact on the performance of the CDMA system and can be recovered in a similar manner as a forward modulated signal transmitted from a base station or repeater. In this way, the terminal does not need additional hardware to recover the identifier signal. In another embodiment, the spread-spectrum identifier signal IS generated in accordance with and in compliance with the IS-95CDMA standard.

In another disclosed embodiment of the method and apparatus, when a signal is determined to have passed through a repeater, the signal is not used for position location calculations. This provides a simple and inexpensive way of ensuring that the time delay added to the signal transmission time from the base station to the terminal does not cause errors in the position location calculation. That is, since the propagation delay between the time a signal is transmitted from a base station and the time the signal is received by a terminal does not accurately reflect the distance between the base station and the terminal, the delay should not be used for position location calculation. If additional information is available regarding the identity of the repeater through which the signal passes and the location of the repeater, this information can be used for the calculation. However, it is noted that there may be enough information from other signals that do not pass through the repeater so that the location of the terminal can not be calculated using information from the signals that pass through the repeater. In both cases it is important to know that the fact that the signal passes through the repeater is such that the additional delay imposed on the signal by the repeater can be taken into account, either by not using the timing information of the signal or by adjusting it appropriately.

Brief description of the drawings

The features, nature, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:

FIG. 1A is a diagram of a wireless communication system that employs repeaters and is capable of implementing various aspects and embodiments of the disclosed methods and apparatus;

FIG. 1B is a diagram illustrating the use of repeaters to provide coverage for a building;

FIG. 2 is a diagram showing the indices of the PN sequences used to generate the pilot reference and spread the data at the base station;

FIG. 3 is a diagram of an embodiment of a repeater in which one embodiment of the disclosed method and apparatus can be implemented;

FIGS. 4A through 4C illustrate three embodiments of a module for generating an identifier signal and combining the identifier signal with a forward modulated signal to provide a combined signal;

FIG. 5A is a diagram showing signals that may be received from a remote unit of a particular repeater;

fig. 5B is a diagram illustrating signals that may be received from a remote unit of a donor base station and a particular repeater;

FIGS. 5C and 5D are diagrams illustrating identifier signals for a plurality of remote units that are time delayed by different chip offsets derived according to two different schemes;

FIG. 6A is a geometric limit graph illustrating the time difference of arrival (TDOA) measurements;

fig. 6B to 6E are diagrams illustrating four different cases of the terminal according to the use of the neighbour list PNs of identifiers PNs;

FIG. 7 is a block diagram of a terminal capable of implementing various aspects and embodiments of the disclosed method and apparatus;

FIG. 8 is a block diagram of an embodiment of a Position Determining Entity (PDE) for use with the disclosed method and apparatus.

Detailed Description

Aspects of the disclosed methods and apparatus provide techniques for determining a location of a terminal under the coverage of a repeater in a wireless communication system. In an aspect, techniques are provided for each repeater to send an identification code that can be used by a terminal (or PDE) to determine the identity of the repeater. This information can then be used to estimate the terminal position, as described below.

The disclosed methods and apparatus indicate that repeaters for providing indoor coverage are generally designed to cover a relatively small geographic area (e.g., a building, a floor of a building, etc.). In an embodiment, since the coverage area of the relay is relatively small, the position estimate of the terminal within the coverage of the relay may be reported as a designated position within the coverage area, which may be the center of the coverage area. In many, if not most, cases, the reported terminal position estimate will be within 50 meters of the actual position of the terminal. This accuracy is sufficient for enhanced emergency services 911(E-911) as specified by the Federal Communications Commission (FCC), which requires that the location of the terminal within the 911 call be transmitted to a Public Safety Answering Point (PSAP). For cell phone terminals, E-911 mandates that a position estimate be required to be within 50 meters in 67% of cases and 150 meters in 95% of cases. These needs can be met by the techniques described above.

Various schemes are possible for identifying the repeater to the terminal. In one arrangement, each repeater within a particular coverage area (e.g., a cell) is assigned a unique identification code for unambiguously identifying the repeater. Multiple identification codes may be assigned to multiple repeaters within a particular coverage area. This may be applied, for example, to large buildings where multiple repeaters are used to provide coverage and are separated by some distance (e.g., greater than 100 meters). Alternatively, if the repeaters are located within a sufficiently small area, multiple repeaters may be assigned a common identification code. A single position estimate may be used for all of these repeaters.

For each repeater, the identification code assigned to the repeater and the position estimate provided to the terminal within the repeater coverage (e.g., the center of the repeater coverage area) may be stored in a table. The table may be maintained in the PDE. In this case, the terminal can receive the identification code from the repeater and send the code back to the PDE (e.g., in an encoded format), which can provide a position estimate for the terminal based on values stored in the table (e.g., coverage center). Or alternatively or additionally, the table may be maintained at the terminal or at some other entity (e.g., base station, BSC, etc.).

Schemes for transmitting the repeater identification code to the terminal may be designed according to a variety of criteria. First, the identification code should be transmitted in a manner that IS compatible with the CDMA standards supported by the existing system (e.g., IS-95, CDMA2000, W-CDMA, IS-801, etc.). Second, the solution should be compatible with the capabilities of the terminals used and deployed in the field, which enables existing terminals to perform location determination based on identification codes. Third, the identification codes should be transmitted to the terminals within the same frequency band of the terminal tone so that the relayed signals and the corresponding identification codes can be received simultaneously using a single receiver unit. Fourth, the signal used to transmit the identification code should minimally impact system performance.

In another aspect, the identification code of each repeater is transmitted using spread spectrum signals, which may provide a number of benefits. First the spread spectrum identifier signal can be designed to have minimal impact on CDMA performance. Second, the spreading identifier signal is similar to the forward modulated signal from the base station or repeater and can be recovered in a similar manner. In this way, the terminal does not need additional hardware to recover the identifier signal. Existing terminals that are already deployed in the field and are capable of receiving and processing CDMA signals can also receive and process the identifier signal from the repeater.

In one embodiment, the spread-spectrum identifier signal of the repeater IS generated in accordance with and in compliance with the IS-95CDMA standard. However, the identifier signal may also be generated to conform to some other CDMA standard or design.

In one embodiment, the identification code of the repeater includes a Pseudo Noise (PN) sequence at a defined offset. In a typical CDMA system, each base station spreads its data with a PN sequence to generate a spread-spectrum signal, which is then transmitted to the terminal (and possibly to a repeater). The PN sequence is also used to spread pilot data (typically an all-zero sequence) to generate a pilot reference, which is used by the terminal to perform coherent demodulation, channel estimation, and possibly other functions.

Fig. 2 is a diagram illustrating an index of a PN sequence used to generate a pilot reference and spread data at a base station. For IS-95 and some other CDMA systems, the PN sequence has a particular data format and a fixed length of 32768 chips. The PN sequence is repeated in succession to generate a continuous spreading sequence that is then used to spread the pilot and traffic data. The start of the PN sequence is defined by the CDMA standard and is compared to a defined absolute time reference (T)_ABS) And synchronizing, which serves as a system time reference. Each chip of the PN sequence is assigned a corresponding PN chip index, the beginning of the PN sequence is assigned a PN chip index value of 0, and the end of the PN sequence is assigned a PN chip index value of 32767.

The PN sequence may be divided into 512 different "PN INC offsets," numbered from 0 to 511, with consecutively numbered PN INC offsets separated by 64 chips. In practice, 512 different PN sequences may be defined based on 512 different PN INC offsets, each of the 512 PN sequences having a different on at an absolute time reference based on its PN INC offsetAnd (4) starting. Thus, the PN sequence with 0PN INC offset is at T_ABSStarting at PN chip index 0, the PN sequence with 1PN INC offset is at T_ABSStarting at PN chip index 64, a PN sequence with a 2PN INC offset at T_ABSStarting at PN chip index 128, etc., with a 511PN INC offset PN sequence at T_ABSBeginning at PN chip index 32704.

512 possible PN sequences may be used for assignment to base stations in a CDMA system and for use in other base stations than other functions. Each base station is assigned a particular PN INC offset so that pilot references from neighboring base stations can be distinguished, which enables the terminal to identify each received base station by its PN INC offset.

The closest PN INC offset that may be assigned to neighboring base stations is determined by the CDMA standard. For example, the IS-95 and IS-856 standards define a minimum value of one for the parameter "PN _ INC". The assigned PN INC of one indicates that neighboring base stations may be assigned PN sequences separated by a minimum PN INC offset of one (or 64 chips). A lower assigned PN INC value (e.g., one) results in more available PN offsets (e.g., 512) that may be assigned to the base station. Conversely, a larger particular PN INC value (e.g., four) may result in less available PN offsets that may be assigned to a base station.

In an aspect, a PN sequence at a particular offset is used for repeater identification. As used herein, the identifier PN (ipn) is a PN sequence, code, bit pattern, or some other pattern used to identify a repeater. A variety of PNs may be used as identifiers PNs. The identifier PNs may be categorized as follows:

● private IPNs-one or more PN sequences at a particular PN INC offset are reserved for use by the repeater identification;

● neighbor list IPNs-the PN sequences of the base stations in the neighbor list are used for repeater identification.

Each of these IPN categories corresponds to a different scheme for selecting a PN sequence for use as the identifier PNs. These PN selection schemes are described in detail below. Other schemes of selecting PN sequences for use as IPNs are also contemplated and are within the scope of the present invention.

For the dedicated IPNs scheme, one or more of the 512 possible PN INC offsets (if PN _ INC is designated one) or 128 possible PN INC offsets (if PN _ INC is designated four) are dedicated to repeater identification. The PN sequence at each such dedicated PN INC offset may be used to identify the repeater.

The use of the identifier PN enables the terminal to unambiguously identify the repeater within the cell. If multiple repeaters are used for a particular cell, the repeaters may be assigned the same or different identifiers PNs depending on various factors. In an embodiment, different identifiers PNs at different PN INC offsets are assigned to repeaters within the same cell. In another embodiment, different chip offsets for the same identifier PN are assigned to repeaters within the same cell. These offsets are defined relative to the system time determined by the offset of the repeated PN. For example, if a 2-chip offset is used, 11 different PN sequences can be generated from a single identifier PN within a 20-chip window. The PN assigned to repeaters within the same cell thus have mutually different PN INC or chip offsets so that the repeaters can be specifically identified.

Fig. 3 is an embodiment of a repeater 114y that can implement aspects and embodiments of the disclosed method and apparatus. Repeater 114y is effectively a high gain bi-directional amplifier for receiving, amplifying, and retransmitting modulated signals on the forward and reverse links. On the forward link, the modulated signals from the serving base station 104 (which are also referred to as "donor" cells or sectors) are received by the repeater through either a (e.g., directional) antenna or a (e.g., coaxial or fiber optic) cable. Repeater 114y then filters, amplifies, and retransmits the forward modulated signal to the terminals within its coverage area. Accordingly, on the reverse link, repeater 114y receives signals from terminals within its coverage area, conditions them, and transmits the reverse modulated signals back to the serving base station.

In the particular embodiment shown in fig. 3, the repeater 114y includes a repeater unit 310 coupled to an identifier signal generator 320. Repeater unit 310 performs signal conditioning to generate repeated signals for the forward and reverse links. The identifier signal generator 320 generates one or more spread spectrum identifier signals that include an identification code (e.g., identifier PN) assigned to the repeater 114 y.

In the illustrated embodiment, the repeater unit 320 includes a receiver module 322 coupled to a PN generator and upconverter module 324. Coupler 308 provides a portion of the forward modulated signal from the serving base station to a receiver module 322. The receiver module 322 processes the coupled portions of the forward modulated signal and provides a timing reference and a frequency reference, which are used to generate the spread-spectrum identifier signal for the repeater 114 y. The PN generator and upconverter module 324 generates an identifier PN of the repeater from the timing reference and also upconverts the identifier PN to an appropriate Intermediate Frequency (IF) or Radio Frequency (RF) based on the frequency reference to generate a spread spectrum identifier signal. The operation of the identifier signal generator 320 is described in further detail below.

In the illustrated embodiment, repeater unit 310 includes a pair of duplexer 312a and 312b coupled to antennas 302a and 302b, respectively, for communicating with the serving base station and the terminal, respectively. Duplexer 312a routes the forward modulated signal from the serving base station to a conditioning unit 314 and couples the conditioned reverse modulated signal from conditioning unit 318 to antenna 302a for transmission back to the serving base station. The conditioning unit 314 conditions the forward modulated signal and provides a conditioned forward modulated signal to the combiner 316. Signal conditioning may include amplification, frequency down conversion of the forward modulated signal to an Intermediate Frequency (IF) or baseband, filtering, up conversion of the signal to IF or Radio Frequency (RF). Combiner 316 (which may be implemented with a hybrid coupler) further receives the spread spectrum identifier signal from identifier signal generator 320, combines the identifier signal with the conditioned forward modulated signal, and provides a combined signal to duplexer 312 b. The combined signal is then routed to antenna 302b and transmitted to the terminal.

As shown in fig. 3, the repeater unit 310 may receive a frequency reference from the identifier signal generator 320. This frequency reference may be needed IF the identifier signal is added at IF or baseband (BB). This frequency reference may be used to ensure that the IF/BB of the repeater is accurate. In this case, the adjustment unit 314 receives the frequency reference and the combiner is comprised in the adjustment unit 314.

On the reverse link, the reverse modulated signal from the terminal is received by antenna 302b, routed through duplexer 312b, and conditioned by a conditioning unit 310. The adjusted reverse modulated signal is then routed through the duplexer and transmitted via antenna 302a to the serving base station. In general, the processing of the forward and reverse modulated signals within repeater 310 is not affected by the processing and addition of the spread spectrum identifier signal.

As shown in the embodiment of fig. 3, the identifier signal is added to the conditioned forward modulated signal (e.g., at IF or RF) within repeater unit 310. In general, the identifier signal can be added at any point in the signal path from antenna 302a to antenna 302 b. For example, an identifier signal can be generated and added to the received forward modulated signal, and the combined signal can be provided to repeater unit 310. Alternatively, the identifier signal can be added to the conditioned forward modulated signal from repeater unit 310, and the combined signal can be transmitted from antenna 302 b. The identifier signal can thus be added to the forward modulated signal either external or internal to repeater unit 310. This functionality may be obtained external to the repeater for repeaters that have been deployed in the field and that do not include the appropriate circuitry (e.g., combiner 316 of fig. 3) to combine the identifier signal with the forward modulated signal. Also, the coupler 308 may be located before (at the input) or after (at the output) the repeater unit 310. Alternatively, the coupled portion of the forward modulated signal may be obtained within the repeater unit 310 at RF, IF, or baseband, depending on the particular implementation of the repeater.

Fig. 4A illustrates an embodiment of a module 400a that can be used to generate an identifier signal and combine this signal with a forward modulated signal to provide a combined signal. The module 400a can be implemented as a separate unit coupled to an input port or an output port of the repeater unit. If coupled to an input port, the combined signal from module 400a can be conditioned by a repeater unit and retransmitted in a manner similar to the forward modulated signal. And if coupled to an output port, the identifier signal can be combined with the adjusted forward modulated signal from the repeater unit to generate a combined signal for transmission to the terminal. In both cases, the repeater unit can operate in a normal mode as if the identifier signal were not present.

In the embodiment shown in fig. 4A, within module 400a, the forward modulated signal (i.e., the forward RF input) is coupled through coupler 408, routed through isolator 412, and provided to combiner 416, which may be implemented with a hybrid coupler. The combiner 416 also receives the identifier signal from the identifier signal generator 420a, combines the forward modulated signal with the identifier signal and provides the combined signal to the output (i.e., the forward RF output).

Fig. 4A also shows an embodiment of an identifier signal generator 420a, which is also possible for the identifier signal generator 320 of fig. 3. The coupled portion of the forward modulated signal is provided to a receiver module 422 and processed to provide a timing and frequency reference, as described above. In one embodiment, receiver module 422 includes receiver processing elements similar to those included in a terminal that can demodulate forward modulated signals from a serving base station. In particular, receiver module 422 filters, amplifies, frequency downconverts, and digitizes the forward modulated signal to provide samples. The samples are despread with the locally generated PN sequences at different chip offsets to recover the pilot reference transmitted by the serving base station.

Pilot SEARCH AND demodulation is well known, as shown IN U.S. Pat. No. 5764687 entitled "MOBILE DEMODULATOR ARCHITECTURE FOR A SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM", U.S. Pat. Nos. 5805648 AND 5644591 entitled "METHOD AND PARATUS FOR PERFORMING SECRETION IN A CDMA COMMUNICATION SYSTEM", AND U.S. Pat. No. 5577022 entitled "PILOT SIGNAL SEARCHING TECHNIQUE FOR A CELLULAR COMMUNICATION SYSTEM".

In one embodiment, the receiver module 422 includes a timing tracking loop and a carrier tracking loop (not shown in fig. 4A for simplicity). The frequency tracking loop locks the frequency of a local reference oscillator (e.g., a temperature compensated crystal oscillator TCXO) to the pilot reference frequency (i.e., the signal to be repeated) within the received forward modulated signal. The timing reference may then be derived by detecting the beginning of the PN sequence at the extraction from the recovered pilot reference. The timing reference may be provided by the receiver unit 422 by a timing signal with pulses that coincide with a deterministic periodic offset from the system time (as derived from the recovered pilot reference), which enables the identifier PN to be aligned with the system time.

The carrier tracking loop locks the Local Oscillator (LO) to the carrier frequency of the forward modulated signal. A frequency reference can be derived from the locked local oscillator. The frequency reference may be provided by having a clock signal that is related to (e.g., 1/N times) the recovered carrier frequency.

In the embodiment shown in fig. 4A, PN generator and upper sideband module 424 includes a controller 430, a PN generator 432, and an upconverter 434. The PN generator 432 receives the timing reference from the receiver module 422 and may further be provided with other signals that may be needed to generate the identifier PN. For example, a clock signal at a multiple of the PN chip rate (e.g., a clock signal at 16 times the chip rate, Chipx16) and another signal having Chipx16 cycles number for another particular period (e.g., 2 seconds) may be provided to PN generator 432. PN generator 432 then generates one or more identifiers PNs at the desired offsets according to the particular implementation, and may further implement pulse shaping of each identifier PN using digital filters to generate the appropriate wave shaped PN sequence.

An upconverter 434 receives the frequency reference from the receiver module 422 and the (waveform shaped) identifier PN from the PN generator 432 and generates one or more spread spectrum identifier signals, each corresponding to a different carrier frequency and/or PN offset. Some applications may require multiple identifier signals, as described below. Using the frequency reference from the receiver module 422, each identifier signal may be provided at a carrier frequency with negligible frequency error (e.g., a few hertz or less) relative to the retransmitted forward modulated signal. The negligible frequency error allows the terminal to receive the identifier signals and recover the identifier PN even if they are locked to the forward modulated signal. The generation of the identifier signal may be effected digitally using analog and/or digital circuitry or by some other means.

The controller 430 can communicate with the receiver module 422, the PN generator 432, and the upconverter 434 for a variety of functions. For example, controller 430 may direct receiver module 422 to lock onto a particular one of a plurality of forward modulated signals that have been received, to search for a forward modulated signal within a particular frequency window, and so on. The controller 430 may direct the PN generator 432 to generate an identifier PN at a particular offset that has been assigned to the repeater. The controller 430 may also direct the upper sideband mixer 434 to generate an identifier signal at a particular carrier frequency and at a particular transmit power level.

In one embodiment, the power level of each identifier signal is controlled such that it does not affect system capacity. For CDMA systems, each transmitted signal (e.g., the identifier signal) is interference to other transmitted signals (e.g., the forward modulated signal) and may degrade the quality of the other transmitted signals when received by the terminal. Degradation in signal quality may affect the transmission capacity of the forward link. To minimize this degradation, the power level of the identifier signal may be controlled below a certain (e.g., 15dB) level that is lower than the total signal power of the relayed forward modulated signal. The power level of the identifier signal is also controlled to be within the reception range of most terminals. This ensures that the identifier signal can be properly received by the terminal.

In one embodiment, only one identifier PN is used to specifically identify each repeater regardless of the number of forward modulated signals retransmitted by the repeater. However, multiple identifier signals may be generated by module 400a for multiple reasons. For example, if the forward modulated signal is to be retransmitted over multiple frequency bands, the identifier PN can be up-converted to multiple carrier frequencies corresponding to the carrier frequencies of the relayed signal. The plurality of identifier signals may also be generated digitally, for example at a lower IF (e.g., at 10 MHZ), and then up-converted to the desired RF or IF. Since the identifier PN is used for repeater identification rather than base station identification, only one identifier PN is assigned to each repeater, even though a plurality of forward modulated signals from a plurality of base stations may be repeated.

Fig. 4B illustrates an embodiment of another module 400B capable of generating an identifier signal and combining with a forward modulated signal to provide a combined signal. Module 400b is similar in some respects to module 400a of fig. 4A, but also includes a transmitter module 426 for providing confirmation of remote configuration by the reverse modulated signal. Remote configuration of the repeater may be carried out, for example, by the PDE. In this case, the transmitter module 426 may be used to send configuration-related information back to the PDE. This information may include a command determination sent by the PDE to change the identifier signal (e.g., the offset and/or associated power of the identifier signal). The feedback from the repeater then enables the PDE to monitor and verify such remote configuration. The positions of the combiner 416 and isolator 412 may be swapped, which enables the receiver module 422 to monitor the identifier signal itself. In this way, the receiver module 422 can receive the identifier signal, similar to a terminal, and thus can monitor for added signals.

Fig. 4C illustrates an embodiment of another module 400C that can be used to generate an identifier signal and combine with the forward modulated signal to provide a combined signal. Module 400c is similar in some respects to module 400B in fig. 4B, but also includes units 450a and 450B for combining the forward and reverse modulated signals at the input and output ports, respectively, of responsive module 400c, making it possible to use a single cable at each port of the forward and reverse links. In the illustrated embodiment, each unit 450 includes a pair of bandpass filters (BPFs) 452 and 454 for filtering the backward and forward modulated signals, respectively. The circulator 456 routes the forward and reverse modulated signals to their appropriate destinations and further provides isolation of the forward and reverse links. It is also possible that units 450a and 450b are each implemented within a duplexer.

A repeater may be associated with a plurality of Remote Units (RUs) that provide coverage to their respective areas. For the indoor application shown in fig. 1B, repeater 114x includes a main unit 115 and a plurality of remote units 116, each providing coverage for a respective floor of the building. The identifier signal to be transmitted by the remote unit may be generated in a variety of ways and according to a variety of considerations (e.g., whether the remote unit needs to be individually identified).

Fig. 5A to 5D illustrate a particular implementation of generating identifiers PN for a plurality of remote units of a repeater. For some CDMA systems (such as those conforming to the IS-95CDMA standard), the terminal reports only the pilot signal that arrives earliest with respect to the reference time (i.e., the first signal instance available for demodulation). The IS-801 standard also now supports reporting only the earliest arriving pilot. Since the pilot data is a series of all zeros or all ones, the pilot signal is essentially a PN sequence. For these systems, a particular offset of the identifier PN may be assigned to each remote unit so that the remote units may be specifically identified as described below. For other systems that may support reporting multiple pilots (i.e., pilot scenarios), the reported pilot scenario may be used to specifically identify the remote unit. Fig. 5A to 5D show illustrative examples. The concepts described herein may be extended and/or modified for other scenarios and are within the scope of the disclosed methods and apparatus.

The relayed signals transmitted from the remote units of a particular repeater are typically time delayed such that they are not received with equal power and equal time delays, but with opposite phase, so that they cancel. Since the area covered by the remote units is typically small, a two chip delay between remote units is typically sufficient.

In the following description of fig. 5A to 5D, it is assumed that dedicated IPNs are used for repeater identification. Extensions to the concepts described with reference to fig. 5A through 5D, including neighbor list IPNs, are next described.

Fig. 5A is a graph illustrating signals that may be received from a remote unit of a particular repeater. As shown in fig. 5A, the identifier PN is time delayed (i.e., PN from the relayed donor base station) by a predetermined offset d from the relayed donor PN (rdpn), and the relayed and identifier signals of each remote unit are time delayed by two chips from each other. If the terminal receives only signals from the repeater (i.e., the remote unit of one or more repeaters) and not from the donor base station, the terminal will report a time delay (or offset) relative to the identifier PN of the repeated donor PN, within the following ranges:

R_RIPN∈[d；2(n-1)+d]formula (1)

Equation (1) indicates that the offset of the earliest identifier PN reported by the terminal falls within the range from d (if the relayed identifier signal from the first remote unit is received) to 2(n-1) + d (if the relayed signal from the first remote unit and the identifier signal from the nth remote unit are received). Possibly offset R_RIPNBecause the terminal reports the earliest received identifier PN and the earliest received relayed and identifier signal may be from the same or different remote unit.

Fig. 5B is a diagram illustrating signals that may be received from a remote unit of a donor base station and a particular repeater. If the terminal is able to receive the forward modulated signal directly from the donor base station and the relayed signal from the relay, the terminal will report the donor PN (dpn) received from the base station and the earliest identifier PN of the relay. The offset of the identifier PN associated with the donor PN may fall within the following ranges:

R_IPN∈[d+x；2(n-1)+d+x]formula (2)

Where x is the time delay between the donor base station and the first (earliest) remote unit of the repeater.

From equations (1) and (2), it is noted that the predetermined offset d of the identifier PN is for two ranges R_RIPNAnd R_IPNThe same is true. If the time delay x between the donor base station and the earliest remote unit matchesWith the condition x > 2n, it can be determined whether the terminal receives a forward modulated signal from the donor base station or the repeater. This information may be useful in some situations, such as when the terminal is within the coverage of the repeater but still able to receive signals from the donor base station, or when the terminal is located far from the repeater coverage area but able to receive leakage from the repeater.

In some embodiments, multiple identifier signals may be generated from different chip offsets of a single identifier PN. For example, it may be desirable for a different identifier signal to be required to individually identify each of a plurality of remote units of a repeater. In this case, it is possible to generate one identifier signal for each remote unit, each identifier signal comprising an identifier PN at a particular chip offset assigned to that remote unit. Using chip offsets for different identifier signals for different remote units enables a more specific estimate of the terminal position. For example, different chip offsets can be used to estimate that the location of the terminal is within the coverage area of a particular remote unit (e.g., a floor of a building), as opposed to the coverage area of the main unit (e.g., a particular building).

Figure 5C is a graph illustrating the identifier signals of a plurality of remote units that are time delayed by a linearly increasing chip offset. The delay of the identifier signal may add to the delay of the relayed signal. For example, if the remote unit relayed signal is delayed by two chips, the remote unit's identifier signal may be delayed by four chips. In one embodiment, the chip offset assigned to a remote unit is defined as follows:

d_IPN(i) d +2(i-1), 1 ≦ i ≦ n equation (3)

Wherein d is_IPN(i) Is an offset assigned to the ith remote unit and d is an offset relative to the identifier PN of the relayed donor PN correlation of the first remote unit (i.e., d ═ d)_IPN(1)). As the particular example shown in fig. 5C, if the relayed signal of the remote terminal is delayed by two chips, d-8 and n-3, the offsets d for the three remote units_IPN(i) Can be calculated as 8, 10, 12.

By using different offsets for the remote units, the remote units can be specifically identified by the offset between the relayed and identifier signals if relayed and identifier signals from only one remote unit are received by the terminal at any given time.

Multiple identifier signals at different chip offsets may be generated (e.g., by the master unit) by: by delaying the identifier signal (e.g., at IF or RF) with differently delayed filters, by generating PN sequences with different chip offsets and upconverting these PN sequences, or with some other mechanism.

Fig. 5D is a graph illustrating identifier signals for a plurality of remote units that are non-linearly decremented by a chip offset delay. In one embodiment, the chip offset assigned to a remote unit is defined as follows:

d_IPN(i) d- (i-1) · (i +2), 1 ≦ i ≦ n equation (4)

Wherein d is_IPN(i) Is an offset assigned to the ith remote unit and d is an offset relative to the identifier PN of the relayed donor PN of the first remote unit (i.e., d ═ d_IPN(1)). As the particular example shown in fig. 5D, if the remote units' relayed signals have chip delays D-14 and n-5, the offsets D for the five remote units_IPN(i) Can be calculated as 14, 10, 4, -4, -4, -14.

The different offsets generated by equation (4) allow for the identification of the particular remote unit that detected the identifier signal (if only one remote unit was received) or the identification of two (or more) remote units that detected the identifier signal (if two or more remote units were received). Table 1 lists possible bias measurements for the terminal (in column 1), remote units that may be bias detection for the measurements (in column 2), and reported remote units (column 3).

TABLE 1

Measured bias	Remote Unit (RU) capable of being detected by terminal	Decision making
			d	RU1	RU1
d-2	(RU1，RU2)	(RU1，RU2)
			d-4	RU2	RU2
d-6	(RU1，RU3)，optional RU2	(RU1，RU3)
			d-8	(RU2，RU3)	(Ru2，RU3)
d-10	RU3	RU3
			d-12	(RU1，RU4)，optionalRU2，RU3	(RU1，RU4)
d-14	(RU2，RU4)，optional RU3	(RU2，RU4)
			d-16	(RU3，RU4)	(RU3，RU4)
d-18	RU4	RU4
			d-20	(RU1，RU5)，optional RU2，RU3，RU4	(RU1，RU5)
d-22	(RU2，RU5)，optional RU3，RU4	(RU2，RU5)
			d-24	(RU3，RU5)，optional RU4	(RU3，RU5)
d-26	(RU4，RU5)	(RU4，RU5)
			d-28	RU5	RU5

The remote units reported in table 1 (in column 3) may be derived as follows. For even values of D (e.g., the example D-14 shown in fig. 5D), the measured offset of the identifier PN associated with the relayed donor PN is first rounded to the nearest value and noted asThe remote unit for which the identifier signal is received may be identified as:

formula (5)

For odd values of d, the measured offset of the identifier PN is rounded to the nearest odd value, and the remote unit is then identified in a similar manner according to equation (5).

If multiple repeaters are used for a given coverage area (e.g., one sector or omni cell) of a donor PN, each repeater may have multiple remote units, the range of offsets reported by the terminal for each repeater may be expressed as:

R_k∈R_k，RIPN∪R_k，IPNequation (6)

Wherein:

R_kis the offset range that may be reported to the kth repeater,

R_k，RIPNis the offset range if the kth repeater is received but the donor base station is not,

R_k，IPNis the offset range if the kth repeater and donor base station are received, an

U is a merge operator.

If x_k＝2(n_k+1), then the range R_kCan be expressed as:

R_k∈[d_k；d_k+4·n_k]formula (7)

Wherein d is_kIs a predetermined offset between the identifier PN and the repeated PN of the kth repeater, and n_kIs the number of remote units for the kth repeater. Equation (7) is derived from equations (1), (2), and (6). Range R_kIs the lower limit value in equation (1) (i.e., d), and the end of the range is given by the upper limit value in equation (2) (i.e., 2(n-1) + d + x)). By replacing x with 2(n +1) and maintaining the condition x > 2n, range R_kIs calculated as 4n + d as shown in equation (7).

Selecting the time delay d_kSuch that the following equation is satisfied:

d_k+1＝d_k+4·n_k+2 formula (8)

If equation (8) is satisfied, the repeater that receives the repeated signal at the terminal may be specifically identified. It is possible to select the time delay d₁Such that the identifier signal is within the search window used to search for the pilot.

In general, if a biased range is used for the identifier signal, range information is provided to the terminal so that the search window can be appropriately set.

If multiple repeaters are used for coverage, multiple PNs may also be used to individually identify each repeater. Each repeater may be assigned a respective identifier PN. It is also possible that a repeater is assigned two or more identifiers PNs. For example, if two identifiers PNs are available, a first identifier PN may be assigned to a first repeater, a second identifier PN may be assigned to a second repeater, and a combination of the first and second identifiers PNs may be assigned to a third repeater. Various combinations of offsets for these identifiers PNs may also be generated and used.

In a typical CDMA system, each base station may be associated with a corresponding neighbor list, which includes the neighbor base stations for soft handoff candidates. A terminal is provided with a neighbor list associated with the base station with which it is communicating. The terminal may query the list as it continuously searches for strong signals (or multipath components) to determine if a soft handoff is required.

For the neighbor list IPN scheme, the PN sequences used by the base stations in the neighbor list (i.e., the neighbor list PNs) are also used for repeater identification. There are a number of considerations in selecting neighbor lists PNs for use in IPNs, IPNs transmission, and IPN measurement usage. These considerations ensure that measurements of IPNs are distinguished from measurements of neighbor lists PNs for IPNs. The use of neighbor list IPNs is similar to the use of private IPNs, if considered appropriate, as described above.

Some selection criteria may be used to determine what neighbor lists PNs are likely to be used for IPNs. One criterion is that the relayed neighbor lists PNs are not used for IPNs. Without such a restriction, the terminal may receive the same PN as (1) a relayed donor PN from one repeater i and (2) an IPN from another repeater. Since the terminal reports a single measurement for each PN for the corresponding earliest arriving path, there may be ambiguity in the point at which the reported PN is from one or the other repeater. In another criterion, for a given donor base station associated with one or more repeaters, only IPNs that are not in the neighbor list of base stations detected by any of the associated repeaters can be used as IPNs for those repeaters. This limitation may be ensured, for example, by obtaining PN search results from units located within each repeater and using them for remote configuration and generating IPNs.

IPNs should be transmitted at a particular power level so that they can be reliably detected at the terminal while minimally impacting communication and system performance. As a consideration, the IPN should transmit at a power level low enough so that it is not added to the candidate list of terminals. As a specific example, the IPN may be transmitted at 15dB less power than the relayed donor PN. For a lightly loaded cell with a relayed pilot Ec/Io of-5 dB, the IPN may be transmitted at an Ec/Io corresponding to-20 dB.

For IS-95 networks, which have a lower threshold (T ADD) for adding new base stations to the candidate list, the IPN may be transmitted at a lower power level. The headroom may reduce the likelihood of IPN measurements that are suddenly raised by noise and exceed T _ ADD (since pilot power may be estimated by a short integration period). For IS-95B networks with "dynamic" summing thresholds, a larger difference in pilot power across the relayed donor PN and IPN will result in a lower likelihood of adding the IPN to the candidate list.

In some examples, a terminal may be in a soft handover region between (1) a repeater that transmits donor PN and IPN and (2) neighboring base stations whose PN is used by the repeater as an IPN. The PN from the neighboring base station is referred to as a "neighboring PN" (NPN). In these examples, the terminal may attempt to (non-coherently) combine transmissions from the donor base station with transmissions from neighboring base stations to improve demodulation performance. In this case, the terminal may view the IPN as another multipath component of the neighboring base station and may attempt to combine the non-existing traffic channel associated with the IPN (since only the IPN is transmitted from the repeater) with the traffic channel of the neighboring base station.

The combination of non-existent traffic channels associated with IPNs with the traffic channels of neighboring base stations can be ignored for the following reasons. First, if the IPN selection criteria described above are met, the terminal has a low probability of being in soft handoff between the repeater and the neighboring base station. Second, the possibility of selecting an IPN as a combination may be small. To select a combination, the IPN pilot power may need to exceed the lock threshold. However, the IPN pilot power is relatively weak (e.g., 15dB below the relayed donor PN pilot power). Thus, the IPN will exceed the lock threshold only if the relayed donor PN is received at a stronger level for the terminal. Third, even if combined, the contribution of the IPN is small. Since the repeater transmits the pilot for the IPN without a traffic channel, it can only be combined as noise detected without a traffic channel. However, the noise is attenuated by a large amount. For the maximum combining ratio (typically used with rake receivers), the traffic channel from each finger is weighted by the pilot power received by that finger before combining. Since the IPN pilot power is relatively weak (e.g., 15dB or more below maximum power for fingers), the noise from the IPN is weighted with a smaller value. Fourth, IPNs can only be combined if there are spare fingers to track the weaker multipath components of the IPN.

If the IPNs of a repeater is selected from the neighbor list PNs, it may be necessary to determine whether the signal (or PNs) is received directly from the base station or through the repeater. In one embodiment, the determination may be based on geographic limitations.

FIG. 6 is a graph illustrating the geometric constraints of time difference of arrival (TDOA) measurements. In FIG. 6A, the terminal receives pilots from two base stations, and the two received pilots are used to derive a single TDOA measurement. The TDOA measurement indicates the difference between the arrival times of two received pilots, and the arrival time of the signal is proportional to the distance the signal travels. The distance between the terminal and the two base stations is denoted r₁And r₂The distance between two base stations is denoted by d₁₂. From FIG. 6A, it can be seen that r₁、r₂And d₁₂Forming a triangle. The following limitations may be established.

-d₁₂≤(r₁-r₂)≤d₁₂Formula (9)

The geometric test may be designed according to the geometric constraints noted in equation (9).

Equation (9) indicates the absolute value of each TDOA measurement (i.e. | r) assuming no receiver timing and estimation error₁-r₂I) is the distance d between two base stations₁₂. Thus, the set restriction of TDOA measurements may be used to (1) determine excessive latency of TDOA measurements and/or (2) determine whether a pilot is delayed by a repeater.

The IPN of each repeater may be delayed relative to the repeated donor signal by an amount greater than the distance of the donor and the neighboring base station plus some margin. This may be expressed as:

r_ipn-r_rdpn＞d_dn+d_mar，or r_ipn＞r_rdpn+d_dn+d_marformula (10)

Wherein r is_ipnIs an IPN measurement from the repeater;

r_rdpnis the RDPN measurement from the repeater;

d_dnis the distance between the donor base station and the neighboring base station whose PN is used as an IPN; and

d_maris a margin.

The geometric limitations of TDOA measurements may be used to determine whether a signal received at a terminal is from a repeater. Any non-relayed donor pn (dpn), non-relayed neighboring pn (npn), relayed donor pn (rdpn), and IPN detected by the terminal, or any combination of these PNs, will be described below.

Fig. 6B is a diagram illustrating a case where a terminal is under a relay coverage area. For this case, the terminal receives RDPN and IPN from the repeater, but not DPN or NPN. The terminal may then report the RDPN and IPN to the PDE, which may implement the geometry test. TDOA measurements between RDPN and IPN must be accurate because PNs originate from the same source. If IPN is delayed relative to RDPN by at least d_dn+d_marThen, as shown in equation (10), the difference between the IPN measurement and the RDPN measurement is greater than the distance between the donor and the neighboring base station by at least a margin (i.e., r)_ipn-r_rdpn＞d_dn+d_mar) The geometric tests of RDPN and IPN will fail. Failure of the geometry test may serve as an indication that the IPN was received from the receiver rather than the neighboring base station whose PN was used as the IPN.

Fig. 6C is a diagram illustrating a situation where a terminal is within the joint coverage area of a relay, a donor base station, and a neighboring base station. For this case, the terminal receives RDPN and IPN from the repeater, DPN directly from the donor base station and NPN directly from the neighboring base station. The terminal would then report the earliest arriving multipath component for each different PN, which would be the DPN and NPN received over the non-relaying path. The DPN and NPN may then be used in the normal manner for the PDE.

Fig. 6D is a diagram illustrating a situation where a terminal is within the joint coverage area of a relay and a donor base station. For this case, the terminal receives RDPN and IPN from the repeater and DPN directly from the donor base station. The terminal will then report the DPN and IPN, which are the earliest arriving multipath components of these PNs. If DPN delays repeater by d_repThen the TDOA measurements for the DPN and IPN are r_ipn-r_rdpn＞d_dn+d_mar+d_rep. The geometry test may fail, which may be used to indicate that the IPN was received through a repeater.

Fig. 6E is a diagram illustrating a case where a terminal is under joint coverage of a relay and a neighboring base station. For this case, the terminal receives the RDPN from the repeater and the NPN directly from the neighboring base station. The terminal may or may not receive the IPN from the repeater. The terminal then reports the NPN, which is the earliest arriving multipath component for that PN and RDPN. The TDOZ measurement for RDPN and NPN would be r_rdpn-r_npnOr r_dpn+d_rep-r_npn。

If repeater delay d_repLarge enough, the geometric test will fail and the failure may be used to discard the measurements obtained from the repeater. However, if the NPN delay is large enough or if the repeater delay is not large enough, then the TDOA measurement may not violate the geometric test. In this case, other techniques may be used to distinguish between (1) receiving the IPN through the repeater and (2) receiving the NPN directly from the neighboring base station with excessive delay on the NPN. For example, more than one IPN may be used to make this determination. The probability of this event occurring may be kept small by selecting the appropriate neighbor list PNs for use as IPNs.

The situation depicted in fig. 6E generally does not occur for indoor repeaters, but may occur for outdoor repeaters. This situation may occur whether private PNs or neighbor list PNs are used as IPNs.

In the above description, IPNs are assumed to be forward delayed with respect to RDPNs. This is notIs necessary. IPNs may also be delayed in the negative direction by a distance (d) greater than the distance between the donor and the neighboring base station_dn) Plus repeater time delay (d)_rep) Plus some margin (d)_mar) Also a large amount (d)_ipn). This can be expressed as:

d_ipn≥d_dn+d_rep+d_marformula (11)

It is noted that in one embodiment of the disclosed method and apparatus, when a signal is determined to pass through a repeater, the signal is not used for position determination. This provides a simple and inexpensive method to ensure that the delay in the propagation time of the joining signal from the base station to the terminal does not cause errors in the position determination. That is, since the propagation delay of a signal transmitted from a base station and a signal received for a terminal cannot accurately reflect the distance between the base station and the terminal, the delay is not applied to position determination. If there is additional information about identifying whether a repeater has a signal passing through and the location of the repeater, this information can be used to determine the location of the terminal. It is noted, however, that there may be enough information from other signals that do not pass through the repeater such that it is possible to determine the location of the terminal without using information from the signals that pass through the repeater. In both cases, knowing that the signal passes through and the repeater imposes additional time delays on the signal, or by not using the timing information of the signal or by appropriately adjusting the timing information allows these time delays to be taken into account.

In the case where the terminal provides the PDE with a code of the signal received by the terminal so that the PDE can determine whether the signal was transmitted from the repeater, the PDE determines whether to use the signal and may choose to ignore any signal transmitted by the repeater (not received directly by the terminal from the base station). In further embodiments, where the terminal determines position, or requires the terminal to make relevant measurements using the information to derive information to be transmitted to an external device, such as a base station or PDE, the terminal may choose to ignore information relating to signals received from the relay.

Fig. 7 is a block diagram of a terminal 106x capable of implementing aspects and embodiments of the disclosed methods and embodiments. On the forward link, signals from the GPS satellites, base stations, and/or repeaters are received by the antenna 712, routed through the duplexer 714, and provided to an RF receiver unit 722. RF receiver unit 722 conditions (e.g., filters, amplifies, and frequency downconverts) the received signal and digitizes it to provide samples. A demodulator 724 then receives and processes (e.g., despreads, decovers, and pilot demodulates) the samples to provide recovered symbols. Demodulator 724 may implement a rake receiver that can process multiple instances of the received signal and recover the symbols for multiple multipath combinations. Rx data processor 726 then decodes the recovered symbols, checks the received frame, and provides output data.

For position determination, the RF receiver unit 722 can be used to provide the controller 730 with the times of arrival of the strongest received multipath or multipaths with signal strengths that exceed a particular threshold. The samples from the RF receiver unit 722 may also be provided to a signal quality estimator 728, which estimates the quality of the received signal. Signal quality can be estimated using different known techniques, such as those described in U.S. patent nos. 5056109 and 5265119. For position determination, demodulator 724 may be used to provide the PN sequence recovered from the base station and the identifier PNs recovered from the repeater, if any.

The GPS receiver 740 receives and searches for GPS signals according to a search window provided by the controller 730. The GPS receiver 740 then provides the time measurements of the GPS satellites to the controller 730. In some embodiments, GPS receiver 740 is not included within terminal 106 x. The techniques described herein may be used in a position determination method that does not use a GPS receiver.

The controller 730 receives measurements of base stations and/or GPS satellites, PN sequences of the base stations, identifiers PNs of the repeaters, estimated signal qualities of the received signals, or any combination thereof. In one embodiment, the measurement and identifier PNs are provided to TX data processor 742 for transmission back to the PDE, which uses the information to determine the location of terminal 106 x. Controller 730 may also provide signals to direct the units within terminal 106x for appropriate signal processing. For example, the controller 730 may provide a first signal to the demodulator to direct a PN search within a particular chip offset range, provide a second signal indicative of a search window used by the GPS receiver 740 to search for signals from GPS satellites, and so on.

Demodulator 724 searches for a strong instance of the pilot reference from the base station (possibly relayed) and the identifier PN (e.g., if detected). This may be accomplished by correlating the received samples with locally generated PN sequences at multiple offsets. The highly correlated result indicates a high likelihood of the PN being received at that offset.

If appropriate, different schemes may be implemented to ensure that the demodulator 724 searches for the identifier PNs from the repeater. In one arrangement, the identifier PNs is included in a neighbor list of PN sequences to be searched. The neighbor list maintained for each active terminal typically includes strong pilot references detected by the terminal. In another aspect, a neighbor list for each active terminal is sent by the PDE. In this case, the PDE can be provided with information about the base stations in the system, their associated repeaters, and the identifiers PNs of the repeaters. The PDE then ensures that the appropriate identifiers PNs are included in the neighbor list for each active terminal. In another arrangement, the PDE can automatically send to the terminal a list of PNs to search for, including the identifiers PNs. The list may be sent for location-related calls. In another arrangement, the PDE can send the identifier PNs to the terminal upon request, for example when a repeater is known to be present and there are not enough GPS measurements to enable position determination.

On the reverse link, the data is processed (e.g., formatted, encoded) by a Transmit (TX) data processor 742, further processed (e.g., covered, spread) by a Modulator (MOD)744, and conditioned (e.g., converted to analog signals, amplified, filtered, modulated, etc.) by an RF TX unit 746 to generate a reverse modulated signal. Information from controller 730, such as an identifier PN, may be multiplexed with the processed data by a modulator 744. The reverse modulated signal is then routed through duplexer 714 and transmitted via antenna 712 to a base station and/or repeater.

FIG. 8 is a block diagram of an embodiment of a PDE 130 capable of supporting aspects of the disclosed method and apparatus. PDE 130 interfaces with BSC 120 and exchanges information related to position determination.

On the reverse link, data within the reverse modulated signal for the terminal is sent to the repeater, transmitted to the base station, routed to the BSC, and provided to the PDE. Within the PDE, the inversely modulated signals from the terminals are processed by a transceiver 814 to provide samples, which are further processed by an RX data processor 822 to recover the data transmitted by the terminals. This data may include any combination of measurements reported by the terminal, identifiers PNs, and so forth. The data processor 822 then provides the received data to the controller 810.

The controller 810 may also receive additional data from the data storage unit 830 (e.g., information indicating whether the base station is relayed, the center of the coverage area, and the time delay associated with each relay, etc.) and estimate the location of the terminal based on the data from the terminal and the additional data from the storage unit 830. The storage unit 830 may be used to store a table of base stations, their associated repeaters (if any), and an identifier PN and a position estimate (e.g., the center of the coverage area) for each repeater.

In some embodiments, the controller 810 determines that the identifier PN is to be included in the neighbor list of terminals in all sectors. Alternatively, in the case where the identifier PNs is not included in the neighbor list, the identifier PN may be provided to the terminal by the controller 810. The identifier PN is then provided to a TX data processor 812, which formats and transmits the data as appropriate to a transceiver 814. The transceiver 814 further conditions and transmits the data to the terminal via the BSC, base station, and (possibly) repeater.

The techniques described herein may be advantageously used for position determination for indoor applications, where signals from other base stations and/or GPS satellites may not be received and the coverage area of the repeater is generally small. The techniques described herein may also be used for outdoor applications. In one embodiment, the outdoor repeater may be calibrated to determine the time delay associated with the repeater. The identifier signal transmitted by the outdoor repeater may be used to identify the repeater through which a particular repeated forward modulated signal passes and is received by the terminal. Measurements of terminals within the coverage of the repeater may be adjusted accordingly to obtain more accurate measurements. For example, the round trip delay from the location of the repeater may be adjusted based on the delay associated with the repeater. The time offset at the terminal may also be updated to reflect the time delay of the repeater, thus allowing more accurate time reference for the GPS measurements. The techniques described herein can also be used in cases where the terminal observes duplicate PNs.

As mentioned above, the coverage area of repeaters for indoor applications is typically small. If the center of the repeater coverage area is provided as an estimate of the location of the terminal within the repeater coverage, the error is small in many, if not most, cases and can comply with the FCC mandated E-911 mandates. In an embodiment, the entity responsible for position estimation (PDE or terminal) may also be provided with an estimate of the size of the repeater coverage area. In this case, the entity may be able to report a confidence in the accuracy of the position estimate (e.g., whether the E-911 requirements are met).

For clarity, the identification code of each repeater is implemented with a PN sequence at a specific (PN INC) offset as described above. The identification code of the repeater may also be implemented in a variety of other ways. For example, the identification code may be any PN sequence (and not necessarily the same PN sequence spread within a CDMA system), Gold code, any low data rate code that can be modulated on the signal to be relayed, etc. The identification code of the repeater may or may not be time aligned with the system, as observed at the terminal.

For clarity, various aspects and embodiments have been described in detail for an IS-95CDMA system. The techniques described herein may also be used for other types of CDMA systems and other non-CDMA systems. For example, identification codes (identifiers PNs) using repeater identification may also be used for W-CDMA systems, CDMA2000 systems, and the like. The identification code of the repeater identification is also used in the GSM system. For GSM systems, the identification code can be transmitted on a "dummy" channel (with or without an offset) at a different frequency than that used for the forward modulated signal. Different channels on different frequencies may be used for each repeater in a sector or geographic area, or repeaters may be distinguished by data transmitted on a given channel or by the offset of the channel.

The identification code may also be transmitted using any spread spectrum communication technique within the CDMA channel or using some other communication technique. In the above-described embodiment, the identification code of the repeater is transmitted by the repeater simultaneously with the forward modulated signal. In some other embodiments, the identification code of the repeater may be transmitted on another "local" system, such as, for example, a wireless system operating simultaneously. One such system may be a wireless LAN IEEE-802.11 system.

Other schemes may also be used to identify repeaters within a wireless communication system. In one aspect, if the system and terminal are capable of reporting multipath conditions, it may be established to identify the multipath conditions based on (e.g., on the forward modulated signal) and for repeater identification. A CDMA terminal is generally capable of processing multiple received signal instances generated from signal path reflections. The multipaths are typically demodulated and combined by the terminal to provide symbols that are then decoded. If multipath conditions can be reported, each repeater can correlate to a particular multipath condition instead of to the identifier signal.

The multipath conditions for each repeater may be generated in a number of ways. In an embodiment, the forward modulated signal is delayed (and possibly attenuated) by a plurality of specific values, and the plurality of delayed signals are combined and transmitted to the terminal. The number of multipaths and the amount of delay for each multipath may be selected such that a unique multipath scenario is established and can be used to specifically identify each repeater. In another embodiment, the identifier PN can be delayed by a number of specific chip offsets, and the delayed PN sequences can be combined to provide a multipath situation. For this embodiment, the PN sequence of the serving base station (rather than the identifier PN) may be used to generate a multipath scenario.

The repeater identifier can also be transmitted over a secondary low rate CDMA channel, which may be aligned with the CDMA channel from the serving base station. The identification code of the repeater may then be transmitted as data on the low rate channel.

In addition to the benefits of using an identifier signal as described above, an additional benefit is that a position estimate can be determined without interrupting the voice call. According to the IS-801 standard, pilot measurements are sent to the PDE when the terminal sends a request to assist the GPS to estimate the terminal's position. If the PDE identifies an identifier PN within the list of PN sequences reported by the terminal, it may not be necessary to perform GPS measurements since the terminal is within the coverage of the repeater and may not be able to receive GPS signals. Also, the position estimate of the terminal may be determined to a required accuracy based only on the identifier PN (e.g., the terminal position may be estimated as the center of the repeater coverage). In this case, the identifier PN is included in the neighbor list of all base stations using the repeater so that the terminal may search for the identifier PN. Alternatively, if the PDE has reason to suspect that the signal received by the terminal was transmitted by a repeater, a list of identifiers PN may be sent to the terminal before sending the GPS assistance information.

Some elements of a repeater, such as a PN generator, controller, and up-converter, used to implement the techniques described herein may be implemented with a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a processor, a microprocessor, a controller, a microcontroller, a Field Programmable Gate Array (FPGA) or other programmable logic device, or any combination thereof, to achieve the functionality described above. Some aspects of the disclosed methods and apparatus may be implemented in hardware, software, or a combination of both. For example, the process of forming a neighbor list for each active terminal, terminal location estimation, etc. may be implemented based on program code stored in a memory unit and executed by a processor (controller 810 of fig. 8).

The above description of the preferred embodiments is provided to enable any person skilled in the art to make or use the methods and apparatus disclosed herein. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (58)

1. A method of determining a location of a device in a wireless communication system including a transmitter and a repeater, comprising:

receiving, from the repeater, a first signal including transmission data and a second signal including an identification code assigned to the repeater;

processing the second signal to recover the identification code of the repeater; and

a location estimate of the device is determined based on the recovered identification code.

2. The method of claim 1, wherein the second signal is a spread spectrum signal.

3. The method of claim 2, wherein the spread spectrum signal conforms to a CDMA standard.

4. A method as defined in claim 3, wherein the spread spectrum signal conforms to the IS-95CDMA standard.

5. The method of claim 1, wherein the identification code comprises a pseudo-random (PN) sequence at a particular offset.

6. The method of claim 1, wherein the identification code comprises a plurality of pseudo-random (PN) sequences.

7. The method of claim 6, wherein the plurality of PN sequences are at a particular offset.

8. The method of claim 1, wherein the identification code comprises a time-delayed and attenuated version of the first signal.

9. The method of claim 1, wherein the identification code comprises delayed and attenuated versions of the plurality of first signals and a representation of a particular multipath condition.

10. The method of claim 1, wherein the identification code comprises a signal transmitted at a frequency different from the frequency of the first signal.

11. The method of claim 1, wherein the identification code comprises a signal transmitted at a frequency different from the frequency of the first signal and at a particular transmission offset.

12. The method of claim 1, wherein the identification code comprises one or more sequences of Gold codes.

13. The method of claim 12, wherein each Gold code sequence is at a particular offset.

14. The method of claim 1, further comprising:

adjusting a set of position-determined parameters based on the recovered identification code.

15. The method of claim 1, wherein the location estimate for the device is a particular location within the coverage area of the repeater.

16. The method of claim 15, wherein the location estimate for the device is approximately the center of the coverage area of the repeater.

17. The method of claim 1, wherein the wireless communication system is a CDMA system.

18. The method of claim 1, wherein said wireless communication system is a TDMA system.

19. A method for generating a signal suitable for use in estimating a position of a device in a wireless communication system including a transmitter and a repeater, comprising:

receiving, at a repeater, a first signal including therein the transmitted data from a transmitter;

generating, at the repeater, a second signal including an identification code assigned to the repeater;

combining the first and second signals to provide a combined signal; and the number of the first and second groups,

the combined signal is transmitted from the repeater.

20. The method of claim 19, further comprising:

processing the first signal to recover the timing reference, and,

wherein the second signal is generated based on the recovered timing reference.

21. The method of claim 20, further comprising:

the first signal is processed to recover the frequency reference for the carrier signal of the first signal, and,

wherein the second signal is further generated in dependence on the recovered frequency reference.

22. The method of claim 19, further comprising:

the individual combined signals within the repeater units are adjusted, and,

wherein the adjusted signal from the repeater unit is transmitted from the repeater.

23. The method of claim 19, further comprising:

the first signal within the repeater unit is adjusted, and,

wherein the second signal is combined with the adjusted first signal within the repeater unit.

24. The method of claim 19, wherein: wherein the identification code is a Pseudo Noise (PN) sequence at a particular offset.

25. The method of claim 24, wherein: wherein the offset of the PN sequence used for the identification code is one of a plurality of possible offsets and is reserved for identification of the repeater.

26. The method of claim 24, wherein: wherein the timing of the PN sequence used to identify the code closely aligns with the timing of the PN sequence used to spread the transmitted data in the first signal.

27. The method of claim 19, wherein: wherein the carrier frequency of the second signal is close to the carrier frequency of the first signal.

28. The method of claim 19, wherein: wherein the second signal is a spread spectrum signal.

29. The method of claim 19, wherein: wherein the amplitude of the second signal is set to a particular level below the amplitude of the first signal.

30. The method of claim 19, wherein: wherein the wireless communication system is a CDMA system.

31. A method for generating a signal suitable for use in estimating a position of a terminal in a wireless communication system including a transmitter and a repeater, comprising:

receiving and processing, at a repeater, a first signal including therein transmitted data;

generating a second signal including an identification code assigned to the repeater;

transmitting a first signal from a repeater; and the number of the first and second groups,

the second signal is transmitted from the repeater to a plurality of terminals within the communication system.

32. The method of claim 31, wherein: wherein the second signal comprises a plurality of signals at different offsets and representing a particular multipath profile.

33. The method of claim 31, wherein: wherein the second signal includes a plurality of Pseudo Noise (PN) sequences at a plurality of offsets and representing a particular multipath profile.

34. A method for determining a position of a terminal in a wireless communication system including a transmitter and a repeater, comprising:

receiving, at the terminal, an indication of a particular identification code assigned to the repeater;

receiving a first signal and a second signal from the repeater, the first signal including the transmitted data, the second signal including the identification code; and the number of the first and second groups,

the second signal is processed to recover the identification code, and,

wherein the recovered identification code is used to identify the relay, and wherein the position of the terminal is estimated from a position estimate associated with the identification code.

35. The method of claim 34, wherein: wherein the list of identification codes is included in a contiguous list of codes to be searched.

36. The method of claim 34, wherein: wherein the list of identification codes is transmitted to the terminal in response to a call related to the position location.

37. The method of claim 34, wherein: wherein the list of identification codes is broadcast to the terminal via a broadcast channel.

38. The method of claim 34, wherein: wherein the list of identification codes is transmitted to the terminal according to a request of the terminal.

39. A repeater in a wireless communication system, comprising:

a first unit for receiving, adjusting and retransmitting signals on a forward link and a reverse link of a communication system; and the number of the first and second groups,

a second unit coupled to the first unit and comprising:

a first module for receiving and processing a first signal on a forward link including data to be transmitted,

a second module for generating a second signal including an identification code assigned to the repeater, and,

a third module for combining the first and second signals to provide a combined signal for transmission from the repeater.

40. The repeater of claim 39, wherein: wherein the first module is further to process the first signal to recover the timing reference; and wherein the second signal is generated in accordance with the recovered timing reference.

41. The repeater of claim 40, wherein: wherein the first module is further configured to process the first signal to recover a frequency reference for a carrier signal of the first signal; and wherein the second signal is further generated in dependence on the recovered frequency reference.

42. A method for determining a location of a device in a wireless communication system, comprising:

receiving a first signal including transmitted data and a second signal including a first identification code assigned to the first repeater from the first repeater, wherein the first identification code is selected from a list of identification codes used for nearby repeaters;

processing the second signal to recover the first identification code; and the number of the first and second groups,

a location estimate of the device is determined based on the recovered first identification code.

43. The method of claim 42, wherein: wherein it is determined whether to receive the first identification code from the first repeater or from another repeater based on geometric constraints.

44. The method of claim 43, wherein: wherein the geometric constraint relates to time difference of arrival (TDOA) measurements.

45. The method of claim 42, wherein: wherein only the identification codes in the list that are not forwarded by other repeaters are available as the first identification code for the first repeater.

46. The method of claim 42, wherein: wherein the first identification code comprises a plurality of identification codes in the list.

47. The method of claim 46, wherein: wherein the plurality of identification codes for the first identification code are associated with different offsets.

48. The method of claim 42, wherein: where nearby repeaters are neighboring base stations and the identification codes in the list are the PN sequences assigned to these neighboring base stations.

49. The method of claim 42, wherein: wherein the identification code assigned to the first repeater is delayed by a particular delay amount relative to the first signal.

50. The method of claim 49, wherein: wherein the amount of delay is selected to enable a determination of whether to receive the first identification code from the first repeater or from another repeater.

51. A wireless terminal, comprising:

a receiver for receiving a first signal including transmitted data from a first repeater and a second signal including a first identification code assigned to the first repeater, wherein the first identification code is selected from a list of identification codes used for nearby repeaters; and the number of the first and second groups,

a processor for processing the second signal to recover the first identification code, wherein a position estimate for the terminal is determined based on the recovered first identification code.

52. The terminal of claim 51, wherein: wherein it is determined whether the first identification code is received from the first repeater or from another repeater based on geometric constraints.

53. A method for determining a location of a device in a wireless communication system, comprising:

receiving a signal from the repeater including the transmitted data, wherein the signal is further processed according to the identification code assigned to the repeater;

processing the signal to recover the identification code; and the number of the first and second groups,

a location estimate of the device is determined based on the recovered identification code.

54. The method of claim 53, wherein: wherein the signal is modulated with this identification code.

55. The method of claim 53, wherein: wherein this identification code is a PN sequence used for repeater identification.

56. The method of claim 53, wherein: where this identification code is a PN sequence used by another repeater to spread the data over the spectrum.

57. A repeater in a wireless communication system, comprising:

a first unit for receiving and processing a first signal including transmitted data therein, and for generating a second signal including an identification code assigned to the repeater therein; and the number of the first and second groups,

a second unit, coupled to the first unit, for receiving and modulating the first signal with the second signal to provide a modulated signal for transmission from the repeater, wherein the identification code is used for position determination.

58. A wireless terminal, comprising:

a receiver for receiving a first signal including transmitted data from the repeater, wherein the first signal is further modulated with a second signal including an identification code assigned to the repeater, wherein the receiver is further for processing the first signal to recover the second signal; and the number of the first and second groups,

a processor for processing the second signal to recover the identification code, wherein a position estimate for the terminal is determined based on the recovered identification code.