HK1088760A - Method and apparatus for performing position determination in a wireless communication network with repeaters - Google Patents

Description

Method and apparatus for position determination in a wireless communication network with repeaters

Cross Reference to Related Applications

This application claims priority from U.S. provisional application No.60/452,182 filed 3/2003.

Technical Field

The present invention relates generally to position determination, and more particularly to a method and apparatus for position determination in a wireless communication network (e.g., a cellular network) with repeaters.

Background

One common technique for determining the location of a terminal is to determine the amount of time required for signals transmitted from multiple transmitters at known locations to reach the terminal. The propagation time of a signal is typically converted to a "pseudorange," which is an estimate of the distance between the terminal and the transmitter. The position of the terminal may be estimated based on pseudoranges to transmitters and the locations of the transmitters using a process commonly referred to as "trilateration.

One system that provides signals from multiple transmitters (satellites) at known locations is the well-known Global Positioning System (GPS). An accurate three-dimensional position estimate (or "fix") can be obtained for a terminal based on signals received by the terminal from a sufficient number of GPS satellites (typically four). However, in some operating environments (e.g., indoors) the required number of GPS satellites may not be available to obtain such a position fix. Another system that provides signals from a plurality of transmitters (base stations) at known earth-bound locations is a wireless (e.g., cellular) communication network. A two-dimensional (2-D) position estimate may be obtained for a terminal based on signals received by the terminal from a sufficient number of base stations, typically three or more.

Many cellular networks employ repeaters to provide coverage to a specified area within the network or to extend the network coverage. For example, one repeater may be used to cover a geographical area that is not covered by a base station due to a fading condition (i.e., a "hole" in the network). Repeaters may also be used to cover 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 and reverse links. The forward link refers to the communication link from the base stations to the terminals, and the reverse link refers to the communication link from the terminals to the base stations.

Determining the location of a terminal in a network employing repeaters encounters various challenges. On the forward link, each repeater transmits a repeated signal to the terminal within its coverage area with high power and with additional delay. A terminal located within the coverage area of a repeater often cannot receive signals from a base station due to the high power of the repeated signal plus the isolation normally associated with the coverage area of the repeater. Furthermore, in many cases where repeaters are used (e.g., in buildings, tunnels, subways, etc.), the signals from the GPS satellites do not have sufficient power levels and cannot be received by the terminal either. In this way only a limited number of signals (possibly only one from the repeater) can be used to determine the location of the terminal.

Moreover, the additional time delay introduced by the repeater can skew the measurements made by the terminal on the signals received from the repeater. Therefore, measurements of signals received by the repeater are typically discarded and not used for position determination. In some cases, only a few measurements may be used to compute a position estimate for the terminal. If the signals from the repeaters are discarded, the accuracy of the position estimate based on the remaining signals is very poor.

There is therefore a need in the art for a method and apparatus for providing a position estimate for a terminal in a wireless communication network employing repeaters (or other transmission sources having similar characteristics).

Disclosure of Invention

A method and apparatus for position determination in a wireless communication network (e.g., a cellular network) with repeaters is provided. As described below, the method and apparatus utilizes a repeater database that contains various types of information for repeaters in the network. A location estimate for a terminal may be obtained based on (1) measurements made by the terminal on signals received by the terminal, (2) information in the repeater database, and (3) other information available.

According to one embodiment of the disclosed method and apparatus, for position determination in the network with repeaters, it is first identified that a signal received by the terminal is from a repeater. Obtaining (e.g., from a repeater database) the location of the identified repeater and providing the location of the repeater as an estimate of the location of the terminal if a more accurate estimate of the location of the terminal cannot be obtained. The location uncertainty of the identified repeater can also be obtained (again, from a repeater database) and provided as an estimate of the location of the terminal. For various reasons, for example, (1) lack of additional latency information associated with the repeater and/or (2) lack of a sufficient number of measurements required for trilateration for a terminal may not result in a more accurate position estimate for the terminal.

It may also be determined whether the terminal is in an indoor or an outdoor environment. It may further be determined whether the terminal is located sufficiently close to the identified repeater. This may be accomplished by comparing the received signal strength of the identified repeater to a threshold. The location of the identified repeater is provided as an estimate of the location of the terminal if the terminal is deemed (1) to be in an indoor environment or (2) to be located sufficiently close to the identified repeater (i.e., received signal strength exceeds a threshold).

If additional delay information associated with the identified repeater is available, the time measurements for that repeater reported by the terminal may be processed to remove the additional delay. A more accurate position estimate for the terminal may thus be derived based on the "compensated" time measurements (i.e. with the additional time delay removed) of the identified repeater and the time measurements of at least two further transmitters received by the terminal.

Various aspects and embodiments of the invention are described in more detail below.

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. 1 illustrates a wireless communication network with repeaters;

figure 2 shows a process for deriving a terminal position estimate based on signals received by the terminal from base stations and/or repeaters in the network;

figure 3 shows a process for obtaining a position estimate for a terminal that has received a signal from at least one repeater; and

fig. 4 shows a block diagram of a base station, a relay, a terminal and a Position Determination Entity (PDE) in the network.

Detailed Description

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

Fig. 1 shows a diagram of a wireless communication network 100 with repeaters. Network 100 may be a cellular network that supports one or more CDMA standards (e.g., IS-95, IS-2000, W-CDMA, etc.) and/or one or more TDMA standards (e.g., GSM). All of these standards are well known in the art. The network 100 may include a plurality of base stations 104. However, for simplicity, only three base stations 104a, 104b, and 104c are shown in FIG. 1. Each base station 104 serves a particular coverage area 102 and provides communication for terminals 106 located within its coverage area. A base station, or its coverage area, or both, is often referred to as a "cell" depending on the context in which the term is used.

Repeaters 114 may be deployed in network 100 to provide coverage to areas that would not otherwise be covered by base stations 104. For example, repeaters 114 may be deployed in areas of poor reception of signals from base stations 104, such as area 112a in fig. 1. The poor reception may be due to a fading condition or some other phenomenon. Repeaters 114 are also typically deployed within buildings to improve indoor coverage. The repeater 114 may also be used to extend the coverage of the network 100, such as areas 112b and 112c in fig. 1. Repeaters are generally more cost effective than base stations and may be more advantageously deployed where additional coverage is needed but no additional capacity is needed. Any number of base stations in the network may be relayed depending on the deployment of the network.

Multiple terminals 106 may be distributed throughout the network. For simplicity, only one terminal 106 is shown in FIG. 1. Each terminal may communicate with one or more base stations on the forward and reverse links at any given moment. If the network supports "soft handoff" and if the terminal is actually in soft handoff, the terminal may be communicating with multiple base stations simultaneously.

A plurality of base stations 104 are typically connected to and controlled by a Base Station Controller (BSC) 120. The BSC 120 coordinates communication with the base stations under its control. A Position Determination Entity (PDE)130 may be coupled to the BSC 120 and used for position determination. PDE 130 may receive measurements from terminals 106 and may determine the location of the terminals based on the received measurements, as described in further detail below.

For a CDMA network, each base station is assigned a Pseudorandom Noise (PN) sequence with a particular offset or start time. The base station uses the PN sequence to spread its data prior to transmission on the forward link. Each base station also transmits a pilot, which is a simple all-one (or all-zero) sequence and is spread with the PN sequence assigned to that base station. The signal transmitted by each base station thus comprises spread spectrum data and pilot.

For position determination, a pseudorange to a given base station may be estimated based on signals received by a terminal from the base stations. The time of arrival of the signal at the terminal may be determined based on the phase of the PN sequence used by the base station for spreading. Since this PN phase information is typically obtained by processing pilots, the measurements obtained by the terminal are commonly referred to as "pilot phase" measurements (PPM). The pilot phase measurement is used to estimate the amount of time it takes for a signal to propagate from the base station to the terminal. The time of flight may be converted to a pseudorange comprising the "true" or actual distance between the terminal and the base station plus the measurement error.

In the following description, the term "time measurement" is used to represent (1) a measurement obtained based on a signal received from a transmitter (e.g., a base station) and (2) a measurement that may be used to compute a pseudorange to the transmitter. The time measurement may be a pilot phase measurement, a time of arrival (TOA) measurement, a Round Trip Delay (RTD) measurement, or a time difference of arrival (TDOA) measurement. All of these different types of measurements are known in the art and are not described herein.

As described above, repeaters may be used to provide coverage to areas not covered by a base station, such as in a building. Each repeater 114 is connected to a "donor" base station 104 by a wireless or wired link (e.g., a coaxial or fiber optic cable), either directly or through another repeater. On the forward link, a repeater receives a "donor" signal from the "donor" base station, conditions the "donor" signal to obtain a "repeater donor signal" and transmits the repeater donor signal via a "serving" antenna to terminals in its coverage area. On the reverse link, the repeater receives an "uplink" signal from the serving antenna, conditions the "uplink" signal to obtain a "repeated uplink" signal, and transmits the repeated uplink signal to the donor base station. The uplink signal includes a reverse link signal transmitted by the terminal to the repeater. A repeater typically includes a hardware unit for signal conditioning of donor and uplink signals and a serving antenna for transmitting the repeated donor signal to the terminal and receiving the reverse link signal from the terminal. The service antenna and the hardware unit may be located at different locations or co-located at the same location. In any case, the location of the serving antenna is typically used as the location of the repeater.

Each repeater is associated with an additional delay that includes (1) the transmission delay between the donor base station and the repeater and (2) internal delays caused by circuitry within the repeater receiving, conditioning and repeating signals from the donor base station. For example, Surface Acoustic Wave (SAW) filters, amplifiers, and other components within a repeater can introduce time delays to the repeating donor signal transmitted by the repeater. In some cases, this additional delay may be comparable to the transmission delay from the donor base station to the terminal, or may be greater. Thus, time measurements of signals received by the terminal from the repeater cannot be reliably used to determine the location of the terminal without taking into account the additional delay of the repeater.

A method and apparatus for position determination in a wireless communication network (e.g., a cellular network) with repeaters is provided. As described below, the method and apparatus utilize a repeater database that includes various types of information for repeaters in the network. A position estimate for a terminal is obtained based on (1) measurements made by the terminal, (2) information in the repeater database, and (3) other information that may be available.

Fig. 2 shows a flow diagram of one embodiment of a process 200 for deriving a position estimate for a terminal based on signals received by the terminal from base stations and/or repeaters in a cellular network.

Initially, measurements of one or more signals received by the terminal from one or more transmitters in the network are obtained (step 212). Each received signal is from a different transmitter, which may be a base station or a repeater. One or more measurements may be obtained for each received signal. Each measurement may be a time measurement (e.g., a pilot phase measurement), a signal strength measurement, or some other type of measurement. For example, one time measurement and one signal strength measurement may be obtained for each received signal.

For each received signal, it is determined whether the received signal is from a repeater or a base station (step 214). Step 214 is referred to as a repeater identification process and may be accomplished based on (1) one or more measurements obtained for each received signal and (2) information in the repeater database. As part of the repeater identification process, if a signal is received from a repeater, it may also be determined whether it is an indoor repeater or an outdoor repeater. An indoor repeater is a repeater deployed within a building and an outdoor repeater is a repeater deployed outside a building. If the transmitter of a given received signal cannot be identified, then that signal may be discarded from use in position determination. The repeater identification process will be described in detail below.

It is then determined whether a sufficient number (e.g., three or more) of measurements for the base station are available (step 218). If the answer is in the affirmative, then a position estimate for the terminal is obtained based solely on measurements of the base stations (step 220). For step 220, the measurements for the repeater are discarded. Techniques for deriving location estimates for the terminal based on measurements of base stations in a cellular network are known as advanced forward link trilateration (a-FLT), observed time difference of arrival (OTDOA), enhanced observed time difference (E-OTD), and uplink time of arrival (U-TOA). These techniques are described in U.S. patent application No. XXX, entitled "XXX", filed XXX, which is assigned to the assignee of the present application and incorporated herein by reference. In general, position determination may be accomplished by well-known means, such as those described in the publicly available 3GPP25.305, TIA/EIA/IS-801, and TIA/EIA/IS-817 standard documents.

If the answer to step 218 is negative, then a determination may be made as to whether a signal is from a repeater (step 228). If the answer is in the affirmative, then a location estimate for the terminal may be derived based on measurements of the identified relays and possibly measurements of the base station (step 230). Step 230 will be described in further detail below.

If the answer to step 228 is negative, then a sufficient number of measurements for the base station are not obtained from the terminal and measurements for the repeater are not obtained from the terminal. In this case, the location of the terminal may be estimated using cell identification or enhanced cell identification techniques based on measurements of the received base stations. Cell identification techniques provide the identity of a cell in which the terminal is deemed to be located based on available measurements. Enhanced cell identification techniques provide the identity of the sector in which the terminal is deemed to be located. Thus, the accuracy of cell identification and enhanced cell identification techniques depends on the size of the cell and sector, respectively, in which the terminal is deemed to be located. Fig. 3 shows a flowchart of one embodiment of a process 230x for obtaining a location estimate for a terminal that has received a signal from at least one repeater in the cellular network. Each of the at least one repeater is identified by the repeater identification process in step 214 in fig. 2. Process 230x may be used for step 230 in fig. 2.

Initially, a determination is made as to whether the repeater database contains "coarse" or "full" information for the at least one identified repeater (step 312). A description of what constitutes coarse and complete information is provided below. In summary, the repeater database is considered to contain coarse information for a given repeater if (1) the location and location uncertainty of the repeater is available and (2) the delay information associated with the repeater is not available. If the repeater database contains coarse information for the at least one identified repeater, then an identified repeater is first selected. If only one repeater is identified, the selected repeater is simply the single identified repeater. If multiple repeaters are identified, one of the identified repeaters (e.g., the repeater with the strongest received signal strength) is selected. The location of the selected repeater is then provided as an estimate of the location of the terminal (step 314). The process then ends.

If the answer to step 312 is negative, then a determination is made as to whether the terminal is in an indoor or outdoor environment (step 322). The determination may be made based on signals received from the repeater and/or other available information. For example, if a signal is received from at least one indoor repeater, the terminal is considered to be indoors. The repeater identification process in step 214 of fig. 2 may indicate whether an identified repeater is an indoor repeater or an outdoor repeater. The determination of the indoor/outdoor environment of the terminal will be described in further detail below.

If the terminal is deemed to be indoors, the location of the selected repeater is provided as an estimate of the location of the terminal (step 324). In an indoor environment, the location of the repeater is typically sufficient as a location estimate for the terminal. Furthermore, in an indoor environment, a more accurate position estimate for the terminal may not be available because the required number of signals from base stations and/or GPS satellites may not be available for trilateration.

If the terminal is not in an indoor environment, then a determination is made as to whether the received signal strength or power from any of the identified repeaters exceeds a particular signal strength threshold (step 332). If the answer is in the affirmative, the terminal is considered to be located close enough to the repeater. In this case, the location of the identified repeater with strong received signal strength is provided as the location estimate for the terminal (step 334). The selection of the signal strength threshold may be based on a variety of factors, as will be described in further detail below.

For steps 314, 324 and 334, the uncertainty of the terminal position estimate may be set equal to the position uncertainty of an identified repeater whose position has been taken as the terminal's position estimate. For example, for a repeater covering a large building and connected to the donor base station via a leaky cable, a large position uncertainty may be associated with the repeater. In this case, a considerable uncertainty can be used for the terminal position estimate, which has been set to the position of this repeater.

If the answer to step 332 is negative, this indicates that (1) the terminal is not in an indoor environment, (2) a sufficiently strong signal has not been received from any identified repeater and (3) the repeater database includes delay information for at least one identified repeater. In this case, the position estimate for the terminal may be derived based on (1) time measurements for signals received from the base station and (2) a "compensated" time measurement for signals received from the relay (block 340). Time measurements of a signal received from a repeater (i.e., reported by the terminal) include (1) the transmission delay from the donor base station to the repeater, (2) the internal delay of the repeater, and (3) the propagation delay from the repeater to the terminal. A compensated time measurement for the repeater may be obtained by processing the time measurement for the repeater to remove additional time delay associated with the repeater (step 342). The backoff time measurement for a given repeater i can be expressed as:

equation (1)

Wherein: p is a radical of_iTime measurements for repeater i reported by the terminal;

τ_int，iinternal delay for repeater i;

τ_br，iis the transmission delay from the donor base station to repeater i; and

is the compensated time measurement for repeater i.

The additional delay of the repeater i is the internal delay τ_int，iAnd transmission delay tau_br，iCombinations of (a) and (b). For each repeater that knows its additional delay (i.e., available in the repeater database), its compensated time measurement can be obtained.

Compensated time measurements for a repeater may be used to derive a pseudorange to the repeater. Accordingly, a time measurement for a base station may be used to derive a pseudorange to the base station. The terminal position estimate may then be derived based on (1) the pseudorange to the base station and the position of the base station and (2) the pseudorange to the repeater and the position of the repeater (step 344). Step 344 may be implemented using the A-FLT method. The process then ends.

Fig. 2 and 3 represent particular embodiments for position determination in a cellular network with repeaters. Various modifications may be made to the disclosed embodiments and this is within the scope of the invention. For example, the steps of the process shown in FIG. 3 may be rearranged. As an example, block 340 may move between steps 312 and 322. In this case trilateration can be used to derive a position estimate for the terminal if available (i.e. if time measurements and compensated time measurements for a sufficient number of base stations and repeaters, respectively, are available). Typically, using trilateration to obtain the terminal position estimate requires pseudoranges to three or more transmitters, where each transmitter may be a base station or a repeater. If a sufficient number of pseudoranges are not available to the transmitter, the position of an identified repeater may be used as a position estimate for the terminal. As another example, steps 322 and 324 and/or steps 332 and 334 may be eliminated.

Certain steps in fig. 2 and 3 will be described in further detail below.

Repeater identification

Various methods may be used to determine whether a signal received by a terminal is from a base station or a repeater. These methods include a legacy network (legacy network) method, a modulation method, and an identifier PN method.

For conventional network approaches, the transmitter of each signal received by the terminal is identified, one signal at a time, based on obtained measurements of the signals and available information of base stations and repeaters in the network. The method is iterative, with each iteration identifying a transmitter that receives the signal. Two embodiments of the conventional network method are described below-a coverage overlap method and a relative phase method.

The coverage overlap method identifies each transmitter receiving a signal based on an identified coverage area (described below) of the terminal and the coverage areas of a series of candidate transmitters of the identified signal. First, the signal from the reference base station or repeater is identified from all received signals. This may be done, for example, based on the PN offset/sequence of the received signal, the time of arrival of the received signal, the power level of the received signal, some other measurement, or a combination thereof. For each iteration, one of the remaining received signals is selected for identification. For the first iteration, the identified coverage area is set to the coverage area of the reference base station or repeater. For each subsequent iteration, the identified coverage area is formed as a composite of the coverage areas of all base stations and repeaters identified in the previous iteration. The PN sequence of the signal identified in the current iteration is then determined. A list of base stations and repeaters to which this same PN sequence is assigned is then obtained. The coverage area of each base station and relay in the list is then determined. The coverage area of a repeater can be obtained based on the repeater's location uncertainty or maximum antenna range, and the repeater location, stored in the repeater database. Each base station and relay in the list is then evaluated. The base station or repeater having a coverage area that most greatly overlaps the identified coverage area is then selected as the transmitter of the signal identified in the current iteration.

The relative phase method identifies the transmitter of each received signal based on the identified coverage area of the terminal and a time measurement of a series of candidate transmitters. Similar to the overlay method, in each iteration, one of the received signals is selected for identification. For each iteration, as described above, an identified coverage area is obtained, the PN sequence of the signal identified in the current iteration is determined, and a list of base stations and repeaters to which this PN sequence is assigned is obtained.

A time delta measurement (Δ p) is then calculated for each candidate base station and repeater in the list_i) And an increment of distance (Δ d)_i). The time delta measurement for a given candidate transmitter i is the time measurement (p) at the identified signal_i) Time measurement (p) with a selected transmitter_s) Difference therebetween (i.e. Δ p)_i＝p_i-p_s). Should chooseThe transmitter of the selection may be any one of the base station and the repeater identified in the previous iteration. The distance increment of the candidate transmitter i is the difference between the following distances: (1) distance (d) from candidate transmitter i to the center of the identified coverage area_i) And (2) the distance (d) from the selected transmitter to the center of the identified coverage area_s) (i.e. Δ d)_i＝d_i-d_s). Distance d_iIs determined based on the location of the candidate transmitter i, which is available from the repeater database. Each base station and repeater in the list is evaluated. The delta time measurement is then selected to be closest to the delta distance (i.e., smallest (Δ p)_i-Δd_i) Either the base station or the repeater as the transmitter of the signal identified in the current iteration. As is known in the art, a time measurement can be converted to a distance by multiplying by the constant of speed of light C.

If delay information for a given candidate repeater is available, the additional delay for that repeater is subtracted from the time measurement reported by the terminal to obtain the time measurement p for that repeater_i. Conversely, if such delay information is not available for the candidate repeater, the additional delay for the repeater may be estimated based on the Round Trip Delay (RTD) measured at the candidate base station for the terminal. This RTD measurement is about twice the sum of: (1) distance (d) from donor base station to repeater_br) And (2) the distance (d) from the repeater to the terminal_rt) (i.e., RTD/2 ≈ d)_br+d_rt). For the distance d_rtThe terminal is estimated to be located at the center of the identified coverage area. The distance d is then subtracted from the time measurement reported by the terminal_brTo obtain a time measurement p of the repeater_i。

For the modulation method, the relayed uplink signal transmitted by the relay to the donor base station on the reverse link is modified by the relay to include an identification signature (identification signature). The signature may be in the form of a recognizable change in amplitude, frequency, and/or time delay of an uplink signal received at a serving antenna of the repeater. For the time delay modulation method, the relayed uplink signal transmitted by the repeater to the donor base station may include the uplink signal and one or more time delayed versions of the uplink signal. Each delayed version may be generated by delaying the upstream signal by a certain amount of time. The signature of the terminal may be obtained in various ways. For example, the signature may be obtained based on (1) a set of specific delays for the delayed versions of the upstream signal, (2) a specific frequency for switching between the delayed versions of different upstream signals, or (3) a specific pattern or code sequence for switching between the delayed versions of the upstream signal.

For the frequency modulation method, the signature can be obtained by applying a slight disturbance to the carrier frequency of the relay signal in some specific manner. For the amplitude modulation method, the signature may be obtained by applying a perturbation to the amplitude of the relayed signal.

The relay uplink signal from the relay may be received and processed by the donor base station to detect a signature included in the relay uplink signal by the relay. The signature can be evaluated to determine the identity of the particular repeater transmitting the relayed upstream signal. All reverse link signals included in this relayed uplink signal are associated with the identified repeater.

For the identifier PN method, a repeater generates an identifier signal by spreading a pilot with the PN sequence assigned to the repeater. This PN sequence may be one of a plurality of PN sequences specifically reserved for repeater identification. The identifier signal may be summed with a donor signal received from a donor base station on the forward link. The identifier signal is set at a power level low enough (e.g., -15dBc) so that it does not cause excessive interference to the donor signal. In addition, the identifier signal may be suitably time delayed to allow the terminal to detect that the identifier signal is from a particular repeater. A relayed donor signal comprising the donor signal and the identifier signal is transmitted by the relay to the terminal.

The relay donor signal from the relay is received and processed by a terminal to detect the identifier signal. The detected identifier signal is then evaluated to determine the identity of the particular repeater transmitting the relaying donor signal.

Repeater database

The integrity and accuracy of the repeater database has a tremendous impact on the accuracy of the location estimation of the terminal in the cellular network with repeaters. A complete and accurate repeater database is preferred. However, it may be difficult or impossible to organize such databases. The repeater database may be classified as "coarse" or "complete" depending on the type of information available for the repeaters in the network.

A coarse repeater database may contain all or some of the parameters listed in table 1.

TABLE 1

Parameter(s)	Description of the invention
		Repeater ID	A unique ID assigned to the repeater.
Corresponding PN	The PN offset/sequence assigned to the donor base station of the repeater.
		Location and location uncertainty	The location of the repeater and the uncertainty of this location. The location of the repeater may be provided by latitude, longitude and altitude coordinates.
Indoor/outdoor indicator	Indicating whether the repeater is an indoor repeater or an outdoor repeater.

The repeater ID may be any code used to identify the repeater. For example, the repeater ID may correspond to a signature in a repeating uplink signal transmitted by the repeater to the donor base station (for a modulation method), the PN sequence used to generate the identifier signal (for an identifier PN method), and so on.

For a coarse repeater database, repeater location may be coarse and may further be associated with a large location uncertainty. Thus, the coarse repeater database may be used for applications that require only a coarse terminal position estimate.

A complete repeater database may contain all or some of the parameters listed in table 2.

TABLE 2

Parameter(s)	Description of the invention
		Repeater ID	A unique ID assigned to the repeater.
Corresponding PN	The PN offset/sequence assigned to the donor base station of the repeater.
		Location and location uncertainty	The location of the repeater and the uncertainty of the location. A more accurate version of the same parameters in the coarse repeater database.
Maximum Antenna Range (MAR)	The range within which the terminal is likely to receive signals from the repeater, measured from the repeater's serving antenna.
		Indoor/outdoor indicator	Indicating whether the repeater is an indoor repeater or an outdoor repeater.

The parameters of the repeaters in table 2 are similar to the base station parameters in the Base Station Almanac (BSA). As described above, the MAR may be used to identify repeaters in one conventional network approach. For a full repeater database, the repeater location is more accurate and the location uncertainty is less compared to a coarse repeater database. In steps 324 and 334 of fig. 3, a more accurate location and less location uncertainty of the repeater may be provided as a terminal location estimate.

For repeater identification and location determination methods that are affected by the repeater's additional delay, the complete repeater database may also contain the parameters listed in table 3.

TABLE 3

Parameter(s)	Description of the invention
		Internal time delay of repeater	Due to the time delay caused by the repeater by the internal circuitry in the repeater.
Base station to repeater time delay	Due to the time delay of the transmission of the donor signal from the donor base station to the repeater. The transmission may be over the air, via coaxial or fiber optic cables, or by some other means.

The repeater internal delay and the base station to repeater delay make up the additional delay of the repeater. This delay information may be used in step 342 in fig. 3 to obtain a compensated time measurement for the repeater by removing the additional delay from the time measurement reported by the terminal.

The complete repeater database may also contain the parameters listed in table 4 for repeater identification and location determination methods that are affected by the signal strength or power transmitted by the repeater.

TABLE 4

Parameter(s)	Description of the invention
		Repeater service antenna information	The repeater serves various types of information of the antenna such as gain, orientation, horizontal beam width (antenna opening degree), vertical beam width, downtilt angle, and the like.
Donor base station to repeater path loss	Path loss from the donor base station to the repeater. For a repeater to communicate with a donor base station via a wireless link, it may also be derived based on information of the donor antenna used to transmit signals to the donor base station.
		Donor signal power	Donor signal power at the antenna of the donor base station.

The parameters listed in table 4 may be used to determine the power of the relay donor signal transmitted by the relay to the terminal.

Different repeater identification methods may rely on different information (e.g., latency or power information) to identify the repeater. Furthermore, different location determination methods may also rely on different information to derive a location estimate for the terminal.

The repeater database may be such that (1) only coarse information is available to each repeater in the network or (2) complete information is available to each repeater. The repeater database may also be "mixed" so that coarse information is available for some repeaters and complete information is available for other repeaters. For a hybrid repeater database, a coarse/full field may be provided for each repeater to indicate whether coarse or full information is available for the repeater. The position estimate for the terminal may be derived based on coarse or complete information available to each repeater received by the terminal.

The repeater database may be stored as a separate database or as part of the base station almanac. The base station almanac typically includes various types of information for the base stations in the network.

Indoor/outdoor repeater determination

For the location determination process shown in fig. 3, a distinction is made as to whether the terminal is in an indoor or an outdoor environment. This is because in fig. 3 a different procedure is used, depending on whether it is considered to be indoors or outdoors to get the terminal position estimate.

The environment of the terminal can be determined in various ways. In one embodiment, one indoor/outdoor field is included in the repeater database for each repeater. This field is used to indicate whether the repeater is an indoor repeater or an outdoor repeater. For each repeater in the database, this field may fill in the indoor/outdoor information for that repeater if such information is known, otherwise the field may be empty. The indoor/outdoor information for a given repeater may be obtained at the time of repeater deployment or at the time of examination of repeaters in the network. A terminal is considered to be indoors if it receives a signal from an indoor repeater. Otherwise, the terminal may be considered to be outdoors.

In another embodiment, the determination of whether the terminal is indoors or outdoors is made based on the number of signals received by the terminal. For example, since signals from GPS satellites are typically not received indoors, or are received at very low power levels, a terminal is considered to be indoors if no or very little signals are received from GPS satellites. A terminal is also considered to be indoors if (1) the received signal strength of the GPS satellites is low and/or (2) the angle of visibility of the GPS satellites is low. Similarly, a terminal may be considered to be indoors based on the number of signals received from the base station and/or the received signal strength of the base station.

Signal strength threshold

For the position determination process shown in fig. 3, if the terminal is outdoors but close enough to a repeater, the location of the repeater can be used as the position estimate for the terminal (steps 332 and 334). The determination of whether the terminal is sufficiently close to the repeater may be made by comparing the repeater received signal strength to a signal strength threshold. The threshold value may be set in various ways.

In one embodiment, the threshold for a given repeater is set at the signal strength expected to be received by a terminal at a particular range from the repeater. For example, the threshold may be set based on reports adopted by the Federal Communications Commission (FCC) on enhanced 911(E-911) and requirements specified in the rules. The FCC mandate that for handset-based technologies, the positioning accuracy of a terminal is within 50 meters for 67% of calls and within 150 meters for 95% of calls. The threshold may thus be set at the signal strength expected to be received by a terminal 50 or 150 meters from the repeater, depending on the uncertainty expected in the reported terminal position estimate. The threshold may also be set at the predicted worst case (i.e., weakest) power at 50 or 150 meters from the repeater. The signal strength threshold is typically selected to be higher than the add threshold conventionally used to add a new base station to a candidate set for the terminal. The candidate set includes all base stations whose signals are received by the terminal with sufficient strength and can be selected to transmit data to the terminal. Some exemplary values that may be used for the signal strength threshold are-6 dB, -10dB, and-13 dB. Other values may be used for the threshold, which is within the scope of the invention.

The same threshold may be used for all repeaters in the network. Alternatively, different thresholds may be used for different repeaters. In this case, the threshold for each repeater may be set based on the power level of the repeating donor signal at the repeater serving antenna. This output power level may be determined based on serving antenna and path loss information (e.g., as shown in table 4) stored in the repeater database. A threshold field may also be included in the repeater database for each repeater. This field may be used to store a signal strength threshold for the repeater.

Network entity

Fig. 4 shows a block diagram of an embodiment of base station 104x, relay 114x, terminal 106x, and PDE 130 in network 100. Base station 104x is an exemplary base station in the network, repeater 114x is an exemplary repeater, and terminal 106x is an exemplary terminal. Terminal 106x may be a cellular telephone, a handset, a computer with a wireless modem, or some other unit. Base station 104x is operatively connected to PDE 130 via BSC 120, BSC 120 not shown in fig. 4 for simplicity.

On the forward link, base station 104x transmits pilot, data, and signaling to terminals within its coverage area. These various types of data are processed (e.g., encoded, modulated, filtered, amplified, and upconverted) by a modulator/transmitter (Mod/TMTR)420 to provide a forward link signal. The forward link signal is routed through duplexer 422, processed by a splitter unit 424, and transmitted via an antenna 426 to terminals within the coverage area of base station 104 x.

Repeater 114x receives the forward link signal from splitter unit 424 in donor base station 104 x. In repeater 114x, the forward link signal is routed through duplexer 430, conditioned by conditioning unit 432, routed through duplexer 434 and transmitted via antenna 436 to terminals within the coverage area of repeater 114 x. Antenna 436 is the serving antenna of the repeater.

Terminal 106x receives forward link signals from zero or more base stations (e.g., base station 104x) and zero or more repeaters (e.g., repeater 114x) at antenna 452. The receiver input signal from antenna 542 thus may comprise multiple forward link signals received from multiple transmitters, each of which may be a base station or a repeater. The receiver input signal is routed through a duplexer 454 and processed by a receiver/demodulator (RCVR/Demod)456 to provide various types of information useful for repeater/base station identification and position determination. In particular, the RCVR/Demod 456 can provide a time measurement and a signal strength measurement for each forward link signal detected in the receiver input signal. RCVR/Demod 456 can be implemented as a rake receiver that can concurrently process multiple signal instances (or multipath components) for multiple base stations and repeaters. A rake receiver includes a plurality of demodulation processors (or fingers), each of which may be assigned to process and track a particular multipath component.

On the reverse link, terminal 106x may transmit data, pilot, and/or signaling to a reference base station (e.g., base station 104 x). For example, terminal 106x may send back time and signal strength measurements made on the forward link signal received by the terminal. Various types of data are processed by a modulator/transmitter (Mod/TMTR)464 to provide a reverse link signal, which is then transmitted through duplexer 454 and transmitted from antenna 452.

Repeater 114x may receive the reverse link signal from terminal 106x at antenna 436. A receiver input signal from antenna 436 is routed through duplexer 436, conditioned by conditioning unit 438, routed through duplexer 430, and transmitted to donor base station 104 x.

Base station 104x may also receive the reverse link signal from terminal 106x at antenna 426. A receiver input signal from antenna 426 is passed through a splitter unit 424, through a duplexer 422, and provided to a receiver/demodulator (RCVR/Demod) 428. The RCVR/Demod428 then processes the receiver input signal in a complementary manner to provide various types of information, which may then be provided to a processor 410. For example, the RCVR/Demod428 may recover the time and signal strength measurements transmitted by terminal 106 x. RCVR/Demod428 may also provide time and signal strength measurements taken on the reverse link signal received from terminal 106 x.

For the embodiment shown in fig. 4, communication (Comm) port 414 within base station 104x is operatively connected (e.g., via BSC 120) to communication port 476 within PDE 130. Communication ports 414 and 476 allow base station 104x to exchange information with PDE 130 regarding repeater/base station identification and position determination. Some of this information may be measurements received from terminal 106 x.

As noted above, relay and base station identification, as well as terminal location determination, may be performed by terminal 106x, base station 104x, PDE 130, or some other network entity, as a whole. The entity performing the repeater/base station identification and/or position determination is provided with relevant information. Such information may include, for example, a series of forward link signals received by terminal 106x, time and signal strength measurements for these forward link signals, pertinent information from a repeater database, and so forth.

The process of performing repeater and base station identification on the forward link signal received by terminal 106x and deriving a position estimate for the terminal may be performed by processor 460 in terminal 106x, processor 410 in base station 104x, or processor 470 in PDE 130. The memory units 462, 412, and 472 may be used to store various types of information for repeater/base station and location determination. This information may include, for example, a list of forward link signals received by terminal 106x, time and signal strength measurements for these signals, pertinent information from the repeater database and base station almanac, and so forth. Memory units 412, 462, and 472 may also store program codes and data for processors 410, 460, and 470, respectively. The repeater database in PDE 130 may be used to store information for repeaters in the network, such as the parameter information listed in tables 1-4 above. The base station almanac may be stored in a database 474 or memory 472.

The methods and apparatus described herein may be implemented by various means, such as hardware, software, or a combination thereof. For a hardware implementation, the methods and apparatus may be implemented within one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units, or a combination thereof, designed to perform the functions described herein.

For a software implementation, the methods described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit (e.g., memory unit 412, 462, or 472 in fig. 4) and executed by a processor (e.g., processor 410, 460, or 470). The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. 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 departing from the spirit or scope of the invention. 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 (25)

1. A method for position determination in a wireless communication network with repeaters, comprising:

identifying that a signal received by a wireless terminal is from a repeater;

obtaining a location of the repeater; and

if a more accurate position estimate for the terminal is not available, the location of the repeater is provided as a position estimate for the terminal.

2. The method of claim 1, further comprising:

providing a position uncertainty of the repeater as an uncertainty of the position estimate of the terminal if a more accurate position estimate of the terminal is not available.

3. The method of claim 1, wherein a more accurate position estimate for the terminal cannot be obtained due to a lack of additional latency information associated with the repeater.

4. The method of claim 1, wherein a more accurate position estimate for the terminal is not obtained due to a lack of a required number of measurements for trilateration of the terminal.

5. The method of claim 1, further comprising:

determining whether the terminal is in an indoor or an outdoor environment; and

if the terminal is deemed to be in an indoor environment, the location of the repeater is provided as an estimate of the location of the terminal.

6. The method of claim 5, wherein the terminal is considered to be in an indoor environment if the repeater is an indoor repeater.

7. The method of claim 5, wherein the determination is based on a number of signals received by the terminal from satellites and base stations.

8. The method of claim 1, further comprising:

comparing the received signal strength of the repeater to a threshold; and

providing the location of the repeater as a location estimate for the terminal if the received signal strength exceeds the threshold.

9. The method of claim 8, wherein the threshold is set based on a desired repeater signal reception strength at a particular range from the repeater.

10. The method of claim 1, wherein additional latency information associated with the repeater is available, the method further comprising:

processing the time measurements of the repeater to remove additional time delay associated with the repeater; and

a more accurate position estimate for the terminal is derived based on the time measurements of the repeater from which the additional time delay has been removed and the time measurements of at least two further transmitters received by the terminal.

11. The method of claim 1, wherein the identifying is based on a pseudo-random number (PN) sequence used for signals received from the repeater.

12. The method of claim 1, wherein the identifying is based on a modulation characteristic of a signal received from the repeater.

13. The method of claim 1, wherein the identifying is based on time measurements obtained at the terminal of signals received from the repeater.

14. The method of claim 1, wherein the identifying is based on signal strength measurements of signals received from the repeater obtained at the terminal.

15. The method of claim 1, wherein the wireless communication network is a CDMA network.

16. An apparatus in a wireless communication network with repeaters, comprising:

means for identifying that a signal received by a wireless terminal is from a repeater;

means for obtaining a location of the repeater; and

means for providing the location of the repeater as a location estimate for the terminal if a more accurate location estimate for the terminal is not available.

17. The apparatus of claim 16, further comprising:

means for determining whether said terminal is in an indoor or an outdoor environment; and

means for providing the location of the repeater as an estimate of the location of the terminal if the terminal is deemed to be in an indoor environment.

18. The apparatus of claim 16, further comprising:

means for comparing the received signal strength of said repeater with a threshold; and

means for providing the location of the relay as a location estimate for the terminal if the received signal strength exceeds the threshold.

19. The apparatus of claim 16, further comprising:

means for processing the time measurements of the repeater to remove additional time delay associated with the repeater; and

means for deriving a more accurate position estimate for the terminal based on the time measurements of the repeater from which the additional time delay has been removed and the time measurements of at least two further transmitters received by the terminal.

20. A program embodied on a tangible storage medium, the program comprising executable instructions to:

identifying that a signal received by a wireless terminal is from a repeater;

obtaining a location of the repeater; and

if a more accurate position estimate for the terminal is not available, the location of the repeater is provided as a position estimate for the terminal.

21. An apparatus in a wireless communication network with repeaters, comprising:

a storage unit that stores a database of information of the repeaters in the network; and

a processor that identifies that a signal received by a wireless terminal is from a repeater, obtains a location of the repeater from the database, and provides the location of the repeater as an estimate of the location of the terminal if a more accurate estimate of the location of the terminal cannot be obtained.

22. The apparatus of claim 21, wherein the database comprises a location and a location uncertainty for each of at least one repeater in the network.

23. The apparatus of claim 22, wherein the processor is further operative to obtain a location uncertainty of the relay and to provide the location uncertainty as an uncertainty of the location estimate of the terminal if a more accurate location estimate of the terminal is not available.

24. A method for position determination in a CDMA communication network with repeaters, comprising:

identifying a transmitter of each of at least one signal received by one wireless terminal as a repeater or a base station; and

if a signal is from an identified repeater while a more accurate position estimate of the terminal cannot be obtained or if the terminal is deemed to be in an indoor environment, then the position of the identified repeater is provided as the position estimate for the terminal.

25. The method of claim 24, further comprising:

if the received signal strength of the identified repeater exceeds a threshold, the location of the identified repeater is provided as a location estimate for the terminal.