Title of Invention	METHOD OF AND SYSTEM FOR CALIBRATING A REPEATER
Abstract	A method of and system for calibrating a repeater in a wireless communications system are provided. The one or more calibration parameters for the repeater are derived from (a) time measurements derived from one or more signals relayed by the repeater and received at a plurality of different measurement positions, and (b) the positions of the measurement locations. In one application, the one or more parameters are used in determining the positions of subscriber stations in the wireless communications system.

Title of Invention

METHOD OF AND SYSTEM FOR CALIBRATING A REPEATER

Abstract

A method of and system for calibrating a repeater in a wireless communications system are provided. The one or more calibration parameters for the repeater are derived from (a) time measurements derived from one or more signals relayed by the repeater and received at a plurality of different measurement positions, and (b) the positions of the measurement locations. In one application, the one or more parameters are used in determining the positions of subscriber stations in the wireless communications system.

Full Text	METHOD OF AND SYSTEM FOR CALIBRATING A REPEATER Related Applications [0000] ITiis application claims the benefit of provisiCHial U.S. Application Serial No. 60/408,611, entitled "Method of and System for Calibrating a Repeater," filed on September 5, 2002, assigned to the assignee of the present application, and incorporated herein by reference in its entirety for all purposes. Fidd of the Invention [0001] llie disclosed subject matter relates to the fields of position determination and wireless communications, and more specifically, to position determination in a wireless communications system that employs repeaters. Related Art [0002] Repeaters are a flexible and cost effective way to extend coverage or fill coverage gaps in wireless communications systems. They may also be used to render a particular pilot dominant within a coverage area of a CDMA system that is subject to many pilots. Examples of areas where repeaters typically prove useful for adding or extending coverage are terrain variations such as valleys, tunnels and buildings. For a small fiaction of the cost of full base stations, repeaters are appropriate for use in new as well as well-established and mature networks. [0003] There are several implementations of repeaters. In the most common implementation, the repeater acts as a bi-directional amplifier as shown in Figure 1. On the forward (dowTi) link, the repeater 104 receives a transmission from donor cell base station (BTS) 102, amplifies it and sends it to the subscriber station (SS) 106. The BTS 102 may be an omni station or a sector in a multi-sector cell. On the reverse link, the SS 106 sends a signal to the repeater 104. The repeater 104 amplifies the signal and sends it to the BTS 102. As can be seen, the repeater relays a reliable signal between the donor cell and the subscriber station in an area that may not otherwise have reliable coverage. [0004] Pursuant to an FCC mandate, efforts are underway to equip subscriber stations with the capability of determining their locations from transmissions received from various reference sources, such as GPS satellites, base stations, or combinations of GPS satellites and base stations. The subscriber station receives transmissions from four or more references sources whose precise positions are known. These reference sources are synchronized to system time. The subscriber station then derives a time measurement from each of the transmissions. The time measurement represents the amount of time required for the signal to travel along a line-of-sight path between the reference source and the subscriber station. This time is commonly referred to as the "propagation time". The subscriber station then provides these time measurements to a position determination entity (PDE). In response, the FDE estimates the location of the subscriber station from (a) these time measurements, (b) the known speed of light, and (c) the known locations of the reference sources. Alternatively, the subscriber station uses this information to determine its own position. [0005] The presence of repeaters in a wireless communications system can render the position determination process ambiguous. For example, due to the presence of repeaters, there is a danger that a subscriber station will erroneously assume a transmission originating from a base station but relayed by a repeater is a line-of-sight transmission from the base station. Since a time measurement derived from this transmission will overstate the propagation time between the base station and the subscriber station, an estimate of the location of the subscriber station based on this time measurement vnll be erroneous. [0006] This problem may be further explained with reference to Figure 2. As shown, subscriber station 212 receives transmissions from four reference sources, comprising GPS satellite 202, BTS 204, GPS satellite 206, and BTS 206. Each of flie transmissions from sources 202, 204, and 206 is a line-of-sight transmission. Howevear, there ate two transmissions received from BTS 208. TTie first, identified with numeral 214, is received directly from BTS 208. The second, identified with numeral 216, is routed thiough repeater 210. Both transmissions from BTS 208 are modulated with the same PN code uniquely identifying BTS 208. The transmission 216 routed through the repeater 210 is stronger than transmission 214, and hence is chosen by the subscriba: staUon 212 for use in the position determination process in lieu of the transmission 214. [0007] Hw subscribe- station 212, upon receivir^ the transmissions, erroneously identifies the transmission 216 relayed by repeater 210 as a line of sight transmission from BTS 208. Therefore, it also erroneously identifies the time measurement derived from this transnassion as being representative of the propagation time between the BTS 208 and the subscriber station 212. However, this time measurement is aotiqjresentative of this propagation time, but in fact overstates it. Consequently, a posiljon estimate based on this time measurement will be erroneous. SUMMARY [0008] A method of caliloating a repeater in a wireless communications system is described In one embodiment, the method begins by receiving a signal at each of several difSsrent measurement locations. Each signal originates bom the same originadDg tmtsnattsT and is tdayed by the repeater prior to being necdved at the measurement location. Time measurements are then derived from each of the signals. Each of the time measurements represents the time betweai transmission of the signal at the originating transmitter, and arrival of the signal at the measurement locatjon. The positions of the measurement locations are either known or obtained Calibration parameters for (he repeater are then derived from (a) the time measurements, and (b) the positions of the measureraent locations. [fl00?J In one implementation, the calibrsrtion parameters for fee repeato-comprise (a) a time correction for the nepealer, and (b) the position of the repeats. Both parameters are derived throu^ appHcation of an inverse triangulatkxi procedure to time measuTBinentg derived from signals nsceived at four different measiaement locations. The signals all originate from the same donor base station and are each relayed by the repeater before being teceived at the measurement locations. [0010] Tne time measurements derived at these four locations may be refaxed to as mj, where 1 ^ i 5 4. Each time measurennent mj can be expregsed as: jr^ = A4-ti+"tJ( + T2i (1) where: x\ = the forward link delay between the originating transmitter and the repeater tR= the repeater self delay T2i = the forward link delay between the repeater and the receiver at measurement location i A = the offset between system time and time at the originating transmitter [0011] Assuming that the position of the n^eater has the unknown coordinates (XR, yR. ZR). and the position of measurement location i has the known coordinates (X], yi, Zi), Ihe relationship between the time measurement m, the coordinates of the position of the repeater, and the coordinates of the position of measurement legation i may be expressed as follows: m, = A+T, +r, +-^(x, -xj" +(y, - yj" + (z, -zj (2) c where c is the speed of light [0012] Note that (2) represents four separate equations, one for each of the measurement locations. These foxir equations can be solved for four unknowns. The first three unknowns are the coordinates of the position of the repeater (XR, yR, ZR). The fourth unlcnown is the time correction xj associated with the repeater, where TT = A + TJ Solving equations (3), (4) and (5) yields (XR, ys, ZR), the coordinates of the position of the repeater. Substituting these coordinates into any of the four equations represented by equation (2) yields the time correction TT- The position of the repeater and the time correction for the repeater form the calibration parameters for the repeater. [0014] In one application, these calibration parameters are stored for subsequent use in determining the positions of subscriber stations. In this application, the subscriber station receives a signal that is typically a composite of several component signals from reference sources visible to the subscriber station. The subscriber station derives a time measurement from one of the component signals. This time measurement represents the time between transmission of the component signal by the reference source and anival of the signal at the subscriber station. The subscriber station also analyzes the signature of the composite signal to determine whether the component signal was relayed by a repeater. [0015] If so, a PDE in communication with the subscriber station obtains the calibration parameters for the repeater from a database. In one embodiment, these calibration parameters consist of a time correction for, and position of, the repeater. The PDE corrects the time measurement using the time correction for the repeater. The corrected time measurement then represents the amount of time required for the signal to travel between tiie repeater and the subscriber station (commonly referred to as the "propagation time"). If to refers to the original time measurement, TT refers to the time correction for the repeater, and TC refers to fee coirected time measurement. then the PDE derives tc by subtracting Vr from XQ- The relationship between these values can be expressed as: TC = TO-TT (6) [0016] The PDB then detemaines the position of the subscriber station from the conected time measurement tc and the repeater position (XR, y&, ZR). It uses these values to determine the position of the subscriber station in lieu of the original time measurement To and reference source position. [0017] If the component signal was not relayed by a repeater, the PDE determines the location of the subscriber station from the uncorrected time measurement To and reference source position. [0018] Related systems are also described BRIEF DESCMFnON OF THE DRAWINGS [0019] The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosed subject matter. In the figures, like reference numerals designate corresponding parts throughout the different views. [0020] Figure 1 is a block diagram of an embodiment of a repeater in a wireless communications system relaying signals between a base station and a subscriber station. [0021] Figure 2 is a block diagram illustrating die ambiguity that may be introduced by a repeater into the process of determining the position of a subscriber station. [0022] Figure 3A is a flowchart of an embodiment of a method of calibrating a repeater. [0023] Figure 3B illustrates an example of the format of a database record for storing the calibration parameters for a repeater. [0024] Figure 4A illustrates an example of measurement locations which may be employed in the method of Hgure 3 A. [0025] Figure 4B illustrates an example where the measurement locations employed in the method of Figure 3A are situated along a route driven by a vehicle. [0026] Figure 4C illustrates an example where the time measurements employed in the method of Figure 3A are concurrently derived from a plurality of dispersed measurement locations. [0027] Figure 5 illustrates an example in which time measmements taken from different sets of measurement locations are used to calibrate different repeaters in a wireless communication system. [0028] Rgure 6 is a timing diagram illustrating the various components of a propagation time measurement for a signal relayed by a repeater. [0029] Figure 7A is a flowchart of an embodiment of a method of determining the position of a subscriber station in a wireless communications system employing repeaters. [0030] Figure 7B is a flowchart of an implementation of the method of Figure 7A. [0031] Figure 8A is a block diagram of an embodiment of a system for calibrating a repeater in a wireless communications system. [0032] Figure 8B is an example format of a database record which may be employed in the system of Figure 8A for storing one or more calibration parameters for the repeater. [0033] Figure 9 is a block diagram of an implementation of a subscriber station particularly suited for use in a wireless communications system employing repeaters. [0034] Figure 10 is a diagram of an example of a position determination system in which one or more calibration parameter for a repeater are stored in a database, and subsequently used for determining the positions of subscriber stations. [0035] Rgure H is a diagram illustrating calibration of a base station according to an embodiment of the disclosed subject matter. DETAILED DESCRIPTION [0036] As used herein, the term "memory" refers to any processor-readable medium, including but not limited to RAM, ROM, EPROM, PROM, EEPROM, disk, floppy disk, hard disk, CD-ROM, DVD, or the like, on which may be stored a series of instructions executable by a processor. [0037] The term "processor" refers to any device capable of executing a series of software instructions and includes, without limitation, a general- or special-purpose microprocessor, finite state machine, controller, computer, or digital signal processor. [00381 Figure 3A is a flowchart of an embodiment of a method of calibrating a repeater in a wireless communications system. In step 302, a signal relayed by a repeater is received at a plurality of different measurement locations. Step 304 follows step 302. In step 304, time measurements are derived from each of the measurement locations. Each time measurement represents the time between transmission of the signal by an originating transmitter and arrival of the signal at the measurement location (commonly referred to as the "propagation time"), [0039] From step 304, the metihod proceeds to step 306. In step 306, one or more calibration parameter for the repeater are derived from (a) the time measurements, and (b) the positions of the measurement locations. [0040] This method may be furfljer explained with refaence to Figure 4A, which illustrates an example of a wireless communications system in which a signal from base station 402 is transmitted over transmission medium 406 to repeater 404. Transmission medium 406 is any medium capable of transmitting the signal from transmitter 402, including by way of example and not limitation, an optical fiber, a conventional wireline link, or a wireless linL [0041] Repeater 404 receives the signal, amplifies it and re-transmits it over a wireless communications link. The repeater 404 re-transmits the signal over a covers area which includes measurement locations 408a, 408b, 408c, and 408d. A measuring device (not shown) at each of the measurement locations receives the signal as transmitted by base station 402 and relayed by repeater 404. The device flien derives time measurements from the received signals. The time measurements are representative of the time elapsed between transmission of the signal by the base station 402 and arrival of the signal at the measurament location. These time measurements include the repeater self-delay and donor base station/repeater forward link delay. [0042] Thus, in Figure 4A, the time measurement derived at measurement location 408a is representative of the time between transmission of the signal by base station 402, and arrival of Uie sipial at measurement location 408a. Similarly, the time measurement derived at measurement location 408b is representative of the time between transmission of the signal by base station 402, and airiva] of the signal at measuremeait location 408b. The same applies to measurement locations 408c and 408d. [0043] In one example, the signal relayed by a repeater is a pilot signal that originates from a base station in a CDMA wirisless communications system. The pilot signal comprises a cairier sipal modulated vsdth a repeating PN code uniquely identifying the base station that originated the signal. A measuring device located at a measurement location first tunes to the pilot channel of the CDMA system, and then attempts to acquire the pilot signal being transmitted by the base station. [0044] The measuring device attempts to acquire the signal by correlating tiie received signal with the PN code for the donor base station over a range of code phase shift hypotheses and over a range of Doppler frequency shift hypotheses. Each correlation is performed over an integration time I, that is the product of Nc and M, where Nc is the coherent integration time, and M is the number of coherent integrations that are non-coherently combined to form the correlation value, [0045] The device then locates the peak in the correlation function that corresponds to a line of sight transmission by the repeater. In one implementation, the PN code of the donor base station is known, and the measurement locations are located far enouj^ ftom the donor base station that a line sight transmission from the donor base station cannot be detected at the measuring device. The earliest "non-sidelobe" peak in the correlation function thus represents the line of sight transmission from the repeater. It will be understood by those skilled in the art that a sidelobe is a relatively small peak occurs close to, and is related to, another relatively larger peak. [0046] The device derives a time measurement from the location of the early non-sidelobe peak along the code phase dimension of the correlation function, A system time reference is obtained from a GPS receiver included in the device. The system time refraence is used to adjust the time measurement so that the time measurement is in terms of system time. [0047] The positions of the measurement locations are derived by the GPS receiver included with tiie device. The time measurements and positions of the measurement locations are then provicted to a position determination entity (PDE). The PDE determines the calibration parameters for the repeater 404 responsive to this information. Alternatively, the subscriber station determines its own calibration parameters, or the collected data is stored for further processing at later time to determine the calibration parameters. [0048] In one implementation, the calibration parameters for the repeater 404 include a time conection for the repeater and the position of the repealer. In this implementation, an inverse triangulation procedure is used to derive the time correction for and position of the repeater from time measurements taken at four different measurement locations. These four time measurements may be referred to as mi, 1 S i [0049] Each of the time measurements represents the time between transmissi on of the signal by the originating transmitter and arrival of the signal at the measurement location. Included are the repeater self-delay and donor base station/repeater forward link delay. Thus, in Figure 6, the time measurement mi is the time between time of transmission 602 and time of arrival 604, and can be expressed as: mi = A + Ti + TR + Ta (7) where: A = offset between system time and time at the originating (donor) transmitter necessary to decompose this parameter into its constituent pieces for accurate position determination. [0054] A number of approaches are possible for collecting the time njeasurements nn, 1 5 i to the equations (8) above. [0055] In one embodiment, illustrated in Figure 4B, a vehicle is driven along a path 420. The measurement locations 408a, 408b, 408c, and 408d are arbitrary locations situated along the path 420. Tlie positions of these measurement locations are not known a priori. [0056] A measuring device (not shown) accompanies the vehicle. The device includes a GPS receiver. As the vehicle is driven along the path 420, each of the measurement locations is successively encountered. A time measurement is derived by the measuring device at each such measurement location. In addition, a system time reference and position of each measurement location is obtained from the GPS receiver included in the device. The system time reference is used to adjust the time measurements so they are in terms of system time. [0057] In a second embodiment, illustrated in Figure 4C, a plurality of subscriber stations 422a, 422b, 422c and 422d are situated at dispersed measurement locations 408a, 4085,408c, and 408d. A system time reference is derived from a GPS receiver located in the subscriber station. In addition, the position of the measurement location is obtained from the GPS receiver. A time measurement is derived by the subscriber station from a signal relayed by the repeater. The time measurement for the location is adjusted by the system time reference so it is terms of system time. [0058] In a third embodiment, the locations of the measurement locations are predetermined, and thus known beforehand. Fixed measuring devices are mounted at each of the measurement locations. Bach device determines a time measurement from a signal relayed by the repeater. A system time refaiencc is obtained and used to adjust the time measurements that are used in the calibration process. [0059] The method of Figure 3A may be applied to calibrate multiple repeaters in a wireless communications system. Figure 5 illustrates an example of this process. Time measurements and positional infoimation for each of the measurement locations 506a(l). 506b(l), 506c(l), and 506d(l) are used to calibrate repeater 504a. Similarly, time measurements and positional inframation for each of the measurement locations 506a(2), 506b(2), 506c(2), and 506d(2) are used to calibrate repeater 504b. [OOfiO] Note that, in the particular example illustrated in Figure 5, there is no overlap between the measurement locations 506a(l), 506b(l), 506c(l), and 506d(l) used for calibrating repeater 504a and the measurement locations 506a(2), 506b(2), 506c(2), and 506d(2) used for calibrating repeater 504b. However, it should be appreciated that embodiments are possible where there is complete or partial overlap in tiiese locations. Moreover, since the pilot signals originating from base stations 504a, 504b are modulated with different PN codes, a time measurement for both signals can be derived by the same measuring device located at a single measurement location. [0061] Referring back to Kgure 3A, in optional s^ 308, the one or more calibration parameters are stored for subsequent use in determining the positions of subscriber stations. In one implementation, the one or more calibration parameters comprise a time correction for and position of the repeater. These two values are embodied as a database record that is indexed by the PN code of the donor base station. Similar records are present in the database for all repeaters in the network. Each of the records is indexed with the PN code for the corresponding donor base station. The result is an almanac for all repeaters in the network that is updated every time a calibration procedure is performed. To ensure that the almanac is up to date, the calibration procedure is preferably performed periodically or at least every time a change is made to the network, such as the addition of a repeater. In one embodiment, the database is accessible to a PDE that determines the positions of subscriber stations. In an alternative embodiment, the database is accessible to subscriber stations that determine their own positions. [0062] Figure 7A illustrates an embodiinent of a method for detaraiining the location of a subscribor station in a wireless commuiiications system employing repeatoB. [0063] The method begins with step 702. Step 702 comprises deriving a time measurement from a received signal. The received signal is generally a composite of several component signals transmitted by reference sources visible to the receiver, but can comprise only a single component. The time measurement is representative of the time between transmission of one of the componait signals by the corresponding reference source, and arrival of the signal at the receiver. [0064] From step 702, the method proceeds to step 704. In step 704, the method analyzes the "signature" of the composite signal to deteamine whether or not the componeait signal was relayed by a repeater. [0065] In general, the "signature" of the composite signal comprises (a) the number of component signals visible to the receiver, (b) characteristics of each component, (c) the relative strength of these signals, and (d) the relative delay of these signals. The "signature" of the composite signal preferably conveys mformation sufficient to detennine whether a repeater relayed the compcxnoit signal. [0066] In one implementation, the component signals are pilot signals, and the "signature" of the composite signal includes: (1) the total number of pilot sipals visible to the receivrar, (2) characteristics of each pilot signal, (3) their relative signal strength, and (4) their relative times of arrival at the receiver. The detection of other pilots at the receiver generally identifies the donor cell as the immediate source of the received signal. On the other hand, the lack of any otiier pilots at the receiver generally identifies the repeater as flie immediate source of the component signal. A certain pattern of pilots from other cells, their relative signal strength and time of arrivals can be used to rule out or identify specific repeaters. [0067] For example, if there is an overlap m coverage area between the donor cell and the repeater, and the receiver is present in this area of overlap, the line of sight (LOS) signal received directly from the donor cell and that relayed by the repeater are marked with the same PN code. Consequently, both signals will give rise to peaks in the correlation function. If neither signal is subject to multi-path, tiie peak hi the correlation function due to the repeatCT will be delayed relative to that due to flie LXDS signal. The peak resulting from flie repeater can thus be identified cm the basis of this relative delay. [0068] As a second example, if the LOS signal ftom the donor cell is subject to multi-path, it may be difficult to distinguish the peaks due to multi-path from the peak due to the repeater. However, this ambiguity can be resolved during the design and deployment phase by ensuring that the delay due to transmission through the repeater exceeds that associated wi(h any multi-path produced by the RF envircmment In this case, the repeater will leave a signature footprint in the correlation function in the form ■ of a peak that is delayed beyond that due to multi-path. [0069] As a third example, if there is only a single peak in the correlation function for the PN code in question, and no other pilots are visible to the receiver, it can be assumed that the receiver is in an area that is only accessible to signals relayed by the repeater. The single peak at the PN code in question can therrfore be assumed to be due to a repeater. [0070] As a fourth example, the calibration parameters for a particular PN code can be used to detemrine whether a repeater relayed a particular compcment signal. More specifically, if the time correction Vr for the PN code greatly exceeds the corrected time measurement derived using this time correction, it can be assumed that a repeater relayed the component signal. [0071] Returning to Figure 7A, from step 704, the method proceeds to step 706. In step 706, the method queries whether a repeater relayed the component signal. If so, step 708 is performed. In step 708, the method comprises obtaining one or more calibration parameters for the repeater. In one implementation, this step comprises retrieving pre-determined calibration parameters from a database. In one example, these values are obtained by retrieving these parameters from a database record using the PN code of the donor cell as an index to the database. In a second implementation, this step comprises determining these parameters "on the fly." [0072] From step 708, the method proceeds to step 710. Step 710 comprises dctetmining the position of the subscriber station from the one or more calibration parameters obtained in step 708. [0073] In step 706, if the received signal was not relayed by a repeater, step 712 is performed. In step 712, the position of the subscriber station is determined from the time measurement derived in step 702, and the position of the ori^nating transmitter. [0074] Figure 7B illustrates an implemHitation of the method of Figure 7B. Steps 702,704,706, and 712 were already explained in the context of Figure 7A. Only steps 720-724 are explained here. [0075] In step 720, a time correction for and the position of the repeater are obtained. In one implementation, these parameters are retrieved dtora a database using the PN code of the donor cell as an index. [0076] From step 720, the method proceeds to step 722, St^ 722 comprises correcting the time measurement derived in step 714 using the time correction for the repeater obtained in step 720. In wie implementation, this step comprises subtracting the time correction Vx from the time measurement XQ to form a corrected time measurement it. where zc = To-tr- [0077] From step 722, the method proceeds to step 724. There, the position of the subscriber station is determined ftom the corrected time measurement tc and the position of flie repeater. [0078] Figure 8A illustrates an embodiment of a system for calibrating one or more parameters for a repeater in a wireless communications system. The system comprises a processor 810 that is configured to delennine the one or more calibration parameters for the repeater from time measurements and measurement location positions obtained throu^ any of the previously discussed methods. [0079] In one implementation, Ae processor is located within a PDE, and is configured to determine a time correction and position of the repeater by solving the four equations represented by (8) above. In this implementation, the processor 810 is configured to derive the parameters by executing software in the form of a series of instructions stored in memory 812. [0080] Jn one implemaitation, once these parameters have been deteimined, the processor 810 is configured to store them as a record in database 814, indexed using the PN code of the donor cdl. [0081] The record has the format shown in Figure 8B. Held 816 is the PN code of the donor cell. Field 818 is the time correction for the repeater. Field 820 is the position of the repeater. [0082] Figure 9 is a block diagram of a subscriber^stadon that is particularly suited for use in a wireless communications system onploying repeaters. [0083] ProcesscMT 902 is configured to execute software instructions, and memory 904 is configured to hold the software instcuctions and data that ace accessible by the processor 902. [0084] Persistent storage 906 is configured to hold provisioning information useful for acquiring wireless communications services, and can be implemented as a combination of devices such as a non-volatile EEPROM combined with a SIM card. [0085] Keypad 908 and display 910 are both typically provided as part of a user interface. Similarly, microphone 912 and speaker 914 are both typically provided to support use of the device for receiving and transmitting voice. [0086] Radio transceiver (Tx/Rx) 916 is provided for receiving and transmitting information over a wireless communications link, Modem 918 is provided for modulating baseband information, such as voice or data, onto an RF carrier, and demodulating a modulated RF carrier to obtain baseband information. Antenna 922 is provided far transmitting a modulated RF carrier over a wireless communications link and receiving a modulated RF carrier over a wireless communications link. [0087] Correlator 920 is provided for deriving correlation functions from a received signal comprising a composite of pilot sipals transmitted by various reference sources visible to the subscriber station. For a given PN code, the correlator 920 derives a correlation function by correlating the received signal with the PN code over a range of code phase shift hypotheses and a range of Doppler frequency shift hypotheses, It then locates a predetermined number of the peaks of the correlation function. [0088] Processor 902 is configured to analyze this information to det^mine the eariiest non-sidelobe peak of the correlation functioii. If such a peak is detected, the ptxxessor 902 is also configmed tx> draive a time measurement from the location of this peak in the code phase dimension. If a system time reference is available, the processor 902 adjusts the time reference using the system time reference so that the time measurement is in terms of system time. [0089] Processor 902 is also configured to analyze the signature of the received signal to determine if the peak relates to a pilot agnal received directly from the reference source or if it relates to a signal that was relayed by a repeater. This process was previously described in relation to Figure 7A. [009O] Figure 10 illustrates an example of a system for detennining the position of a subscriber station in a wireless communication system employing repeaters. Subscriber station 1002 receives signals transmitted by a plurality of reference sources 1004a, 1004b, 1004c, and 1004d, visible to the receiver in the subscriber station. As illustrated, the reference sources may be BTSs, GPS satellites, or combinations of BTSs and GPS satellites. [0091] Each of the reference sources transmits a signal that is modulated with an identification code that uniquely identifies the reference source. In one implementation, the identification codes are PN codes that may differ in length or periodicity according to the reference source involved. For IS-95 compliant CDMA systems, the PN code is a sequence of 32,768 chips that is repeated every 26.67 msec. In current GPS systems, the PN code is a sequence of 1,023 chips. The sequence is repeated every one millisecond. [0092] The signals transmitted by reference sources 1004a, 1004b, and 1004c, are all received directly by the subscriber station 1002. Thus, all are line of sight signals. However, the signal transmitted by base station 1004d is relayed by repeater 1006, and this is not a line of sight sipal from the standpoint of the donor cell 1004d. [0093] A database 1010 is accessible to position determination entity (PDE) 1008. The database 1010 contains entries for each of the repeaters that are present in the wireless communications system. Each of the entries comprises a record that contains the position of and time correction for the corresponding repeater. This information is derived using any of the methods for calibratkg a repeater that have been previously discussed. Each entry is indexed using the PN code of the donor cell. [005>4] The subscriber station 1002 is equipped with a correlator that, in conjunction with related software executable by a processor within the subscriber station, is configured to derive a time measurement for each of the pilot signals. If a system time reference is available, the subscriber station 1002 uses this information to adjust the time measurements so they are in terms of system time. Alternatively, this task is petfonned by the PDE1008. [0095] Tbst subscriber station 1002 then communicates the time measuranents to , PDE 1008. Upon receipt of this information, PDE 1008 checks the signature of the composite signal to determine if any of the pilot signals were relayed by a repeater. The process of analyzing the signature of a composite signal to determine the immediate origin of a composite signal was previously discussed in relation to the . method of Figure 7A. [0096] ff a time measurement derived from a signal relayed by a repeater is present, then the PDE 1008 uses the PN code for the donor cell to retrieve the calibration parameters for the repeater from the database 1010. In particular, the PDE 1010 retrieves a record containing the time correction for, and position of, the repeater. It then uses the time correction for the repeater to correct the time measurement. It also substitutes the position of the repeater for that of the donor cell. It performs these adjustments for each of the time measurements determined to involve signals relayed by a repeater. [0097] It then determines the position of the subscriber station 1002 using the corrected time measurements and updated positions. Again, in one implementation, known triangulation procedures are used to derive the position of subscriber station 1002. Once detennined, the position of the subscriber station 1002 may be communicated by the PDE 1008 to the subscriber station 1002 or some other network entity. [0098] Alternatively, the subscriber station 1002 detennines its own position using the database of calibration parameters that is accessible by the subscriber station 1002. [0099] While various embodiments of the disclosed subject matter have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible. [0100] In particular, embodiments are possible in which network entities other than rqepeates may be calibrated through application of the methods described. For example, Figure 11 illustrates the method of Figure 3A applied to the process of calibrating a base station. Referring to Figure 6, the time correction for a base station will comprise the component referred to as A, the offset between system time and time as maintained at the base station, but does not include the components referred to as TI or TR. Other than this difSaence, the approach for calibrating the base station is identical to that described previously in relation to a repeater. [0101] One or more signals are transmitted fh>m BTS 1102 over a wireless communications link. The transmission occurs over a coverage area that includes measurement locations 1104a, 1104bb, 1104cc, and 1104d. A receiver (not shown) at each of the measurement locations receives a signal as transmitted by BTS 1102. [0102] A time measurement is derived from the signal received at each of the measurement locations. In one hnplementation, the time measurement. is representative of the travel time between BTS 1102 and the receiver (commonly referred to as the "propagation time"). Thus, in the example illustrated in Figure 11, the time measurement derived at measurement location 1104a is representative of the propagation time from BTS 1102 to measurement location 1104a. Similarly, the time measurement derived at measurement location 1104b is representative of the propagation time from BTS 1102 to measurement location 1104b. The same applies to measurement locations 1104c and 1104d. [0103] One or more calibration parameters for BTS 1102 are then determined responsive to the time measurements and the locations of the measmement locations. In one implementation, the calibration parameters for BTS 1102 comprise a time correction for and position of BTS 1102. These parameters are determined from the time measurements and positions of the measurement locations using fee equations (8) refered to previously. [0104] Embodiments are also possible in which the calibration parameters are used for determining the positions of subscriber stations in any position determination system, including without limitation terrestrial systems, network-based or subscriber station based terrestrial systems, GPS satellite systems, or hybrids thereof. Moreover, any method of position deteniination may be employed, including without limitation AOA, TOA, cell ID, with or without TA or RTD enhancements, E-OTD, OTDOA, or A-GPS, with or without IPDL, TA-IPDL, or OTDOA-PE modifications. [0105] Accordingly, the invention is not to be restricted except by the appended claims. WE CLAIM : 1. A method of calibrating a repeater in a wireless communications system comprising the steps of: receiving a signal, transmitted by an originating transmitter and relayed by a repeater, at a plurality of different measurement locations; deriving time measurements from each of the received signals, each time measurement representative of the time between transmission of the signal by the originating transmitter and arrival of the signal at the measurement location; and deriving one or more calibration parameters for the repeater from (a) the time measurements, and (b) the positions of the measurement locations. 2. The method as claimed in claim 1, wherein the one or more calibration parameters comprise a time correction for the repeater, and the position of the repeater. 3. The method as claimed in claim 1, comprising storing the one or more calibration parameters. 4. The method as claimed in claim 1, wherein the plurality of different measurement locations comprise four or more different measurement locations. 5. The method as claimed in claim 1, wherein the time measurements are sequentially derived from signals sequentially received at successive ones of the measurement locations. 6. The method as claimed in claim 1, wherein the time measurements are concurrently derived from signals concurrently received at the measurement locations. 7. The method as claimed in claim 1, wherein the measurement locations are fixed and predetermined. 8. The method as claimed in claim 1, wherein the positions of the measurement locations are sequentially derived using a GPS receiver sequentially placed at successive ones of the measurement locations. 9. The method as claimed in claim 2, wherein the time measurements are obtained at four different measurement locations and may be referred to as mj, 1 where c is the speed of light. 10. The method as claimed in claim 3, wherein the one or more calibration parameters are stored in a database. 11. The method as claimed in claim 10, wherein the database includes one or more calibration parameters for each of a plurality of repeaters. 12. The method as claimed in claim 5, wherein the time measurements are sequentially obtained by driving around an area with a measuring device, and using the measuring device to sequentially obtain the measurements at successive ones of the measurement locations. 13. The method as claimed in claim 12, wherein the measuring device includes a GPS receiver, and the positions of the measurement locations are sequentially obtained by using the GPS receiver in the measuring device to sequentially obtain the positions of successive ones of the measurement locations. 14. The method as claimed in claim 6, wherein the time measurements are concurrently obtained from a plurality of dispersed measuring devices. 15. The method as claimed in claim 14, wherein the measuring device includes a GPS receiver, and the positions of the measurement locations are concurrently obtained from the GPS receivers included in the plurality of dispersed measuring devices. 16. The method as claimed in claim 1, wherein the signals received at the measurement locations all originate from the same transmitter. 17. A method of determining the position of a subscriber station in a wireless communications system employing repeaters comprising the steps of: receiving a composite signal at the subscriber station, the composite signal having a signature and comprising one or more component signals; determining from the signature of the composite signal whether a component signal was relayed by a repeater; obtaining one or more calibration parameters for the repeater if the component signal was relayed by the repeater; and determining the position of the subscriber station based at least in part on the one or more calibration parameters for the repeater. 18. The method as claimed in claim 17, wherein the one or more calibration parameters comprise a time correction for the repeater, and the position of the repeater. 19. The method as claimed in claim 17, wherein the one or more calibration parameters are retrieved from a database. 20. The method as claimed in claim 19, wherein the database includes one or more calibration parameters for a plurality of repeaters. 21. The method as claimed in claim 17, wherein the component signal originates with a reference source. 22. The method as claimed in claim 21, wherein the reference source is a base station in a wireless communications system. 23. The method as claimed in claim 21, wherein the reference source is a GPS satellite. 24. The method as claimed in claim 21, wherein the one or more calibration parameters are retrieved using a PN code for the reference source. 25. The method as claimed in claim 24, wherein the one or more calibration parameters comprise a time correction Xj for the repeater and position of the repeater. 26. The method as claimed in claim 21, wherein a time measurement TQ is derived from the component signal, the time measurement representing the time between transmission of the signal by the reference source, and receipt of the signal by the subscriber station, and this time measurement is corrected using the time correction TT for the repeater to form a corrected time measurement where 27. The method as claimed in claim 26, wherein the position of the subscriber station is determined from the corrected time measurement Xc and position of the repeater in lieu of the time measurement TQ and position of the reference source. 28. The method as claimed in claim 17, wherein the signature of the composite signal includes the number of component signals visible to the subscriber station. 29. The method as claimed in claim 28, wherein the signals are all pilot signals. 30. The method as claimed in claim 17, wherein the signature of the composite signal includes the relative strength of the component signals visible to the subscriber station. 31. The method as claimed in claim 17, wherein the signature of the composite signal includes the relative time of arrivals of the composite signals visible to the subscriber station. 32. A system for determining the position of a subscriber station (106) in a wireless communications system employing repeaters (104) comprising: a receiver (916) for receiving a composite signal (216) at the subscriber station, the composite signal have a signature and comprising one or more component signals; a processor (902) for determining from the signature of the composite signal whether a component signal was relayed by a repeater; and an entity (902) for obtaining one or more calibration parameters for the repeater if the component signal was relayed by the repeater, and determining the position of the subscriber station based at least in part on the one or more calibration parameters for the repeater. 33. The system as claimed in claim 32, wherein the one or more calibration parameters for the repeater comprise a time correction for the repeater, and the position of the repeater. 34. The system as claimed in claim 32, wherein the entity is configured to retrieve the one or more calibration parameters from a memory (904). 35. The system as claimed in claim 34, wherein the entity is configured to retrieve the one or more calibration parameters from a database (814). 36. The system as claimed in claim 35, wherein the one or more calibration parameters for the repeater are in the form of a record in a database that is accessible by the processor (810) using the PN code (816) for the originating transmitter of the signal as an index. 37. The system as claimed in claim 33, wherein the entity is configured to correct a time measurement derived from the signal using the time correction for the repeater, and determine the position of the subscriber station at least in part from the corrected time measurement for and the position of the repeater. 38. The system as claimed in claim 33, wherein the entity is a position determination entity (1008). 39. The system as claimed in claim 33, wherein the entity is a subscriber station. 40. A method of calibrating a repeater in a wireless communications system comprising: driving a vehicle along a route with a measuring device located on or within the vehicle; successively encountering a plurality of measurement locations having along the route; using the device to receive a signal, transmitted by an originating transmitter and relayed by a repeater, at each of the measurement locations; using the device to derive a time measurement from the received signal at each of the measurement locations; using a GPS receiver included with the device to determine a system time reference; using the system time reference to adjust the time measurements to produce adjusted time measurements, an adjusted time measurement for a measurement location representing the time, in terms of system time, between transmission of the signal by an originating transmitter and arrival of the signal at the measurement location; using the GPS receiver to determine the position of each of the measurement locations; and deriving a time correction for and position of the repeater from (a) the adjusted time measurements, and (b) the positions of the measurement locations. 41. A subscriber station comprising: a receiver for receiving a signal having a signature; a correlator (920) for deriving a correlation function from the signal, and identifying one or more peaks in the correlation function; a processor configured to derive a time measurement from a peak in the correlation function, analyze the signature of the signal to determine if the peak relates to a signal that was relayed by a repeater, and provide an indication whether the peak relates to a signal that was relayed by a repeater. 42. A method of calibrating an entity in a wireless communications system comprising: a step for receiving a signal, transmitted by an originating transmitter and relayed by a repeater, at each of a plurality of different measurement locations; a step for deriving time measurements from each of the received signals, each time measurement representative of the time between transmission of the signal by the originating transmitter and arrival of the signal at a measurement location; and a step for deriving one or more calibration parameters for the entity from (a) the time measurements, and (b) the positions of the measurement locations. 43. The method as claimed in claim 46, wherein the entity is a repeater. 44. The method as claimed in claim 46, wherein the entity is a base station.

Full Text

METHOD OF AND SYSTEM FOR CALIBRATING A REPEATER
Related Applications
[0000] ITiis application claims the benefit of provisiCHial U.S. Application Serial No. 60/408,611, entitled "Method of and System for Calibrating a Repeater," filed on September 5, 2002, assigned to the assignee of the present application, and incorporated herein by reference in its entirety for all purposes.
Fidd of the Invention
[0001] llie disclosed subject matter relates to the fields of position determination
and wireless communications, and more specifically, to position determination in a wireless communications system that employs repeaters.
Related Art
[0002] Repeaters are a flexible and cost effective way to extend coverage or fill
coverage gaps in wireless communications systems. They may also be used to render a particular pilot dominant within a coverage area of a CDMA system that is subject to many pilots. Examples of areas where repeaters typically prove useful for adding or extending coverage are terrain variations such as valleys, tunnels and buildings. For a small fiaction of the cost of full base stations, repeaters are appropriate for use in new as well as well-established and mature networks.
[0003] There are several implementations of repeaters. In the most common implementation, the repeater acts as a bi-directional amplifier as shown in Figure 1. On the forward (dowTi) link, the repeater 104 receives a transmission from donor cell base station (BTS) 102, amplifies it and sends it to the subscriber station (SS) 106. The BTS 102 may be an omni station or a sector in a multi-sector cell. On the reverse link, the SS 106 sends a signal to the repeater 104. The repeater 104 amplifies the signal and sends it to the BTS 102. As can be seen, the repeater relays a reliable

signal between the donor cell and the subscriber station in an area that may not otherwise have reliable coverage.
[0004] Pursuant to an FCC mandate, efforts are underway to equip subscriber stations with the capability of determining their locations from transmissions received from various reference sources, such as GPS satellites, base stations, or combinations of GPS satellites and base stations. The subscriber station receives transmissions from four or more references sources whose precise positions are known. These reference sources are synchronized to system time. The subscriber station then derives a time measurement from each of the transmissions. The time measurement represents the amount of time required for the signal to travel along a line-of-sight path between the reference source and the subscriber station. This time is commonly referred to as the "propagation time". The subscriber station then provides these time measurements to a position determination entity (PDE). In response, the FDE estimates the location of the subscriber station from (a) these time measurements, (b) the known speed of light, and (c) the known locations of the reference sources. Alternatively, the subscriber station uses this information to determine its own position.
[0005] The presence of repeaters in a wireless communications system can
render the position determination process ambiguous. For example, due to the presence of repeaters, there is a danger that a subscriber station will erroneously assume a transmission originating from a base station but relayed by a repeater is a line-of-sight transmission from the base station. Since a time measurement derived from this transmission will overstate the propagation time between the base station and the subscriber station, an estimate of the location of the subscriber station based on this time measurement vnll be erroneous.
[0006] This problem may be further explained with reference to Figure 2. As shown, subscriber station 212 receives transmissions from four reference sources, comprising GPS satellite 202, BTS 204, GPS satellite 206, and BTS 206. Each of flie transmissions from sources 202, 204, and 206 is a line-of-sight transmission. Howevear, there ate two transmissions received from BTS 208. TTie first, identified

with numeral 214, is received directly from BTS 208. The second, identified with numeral 216, is routed thiough repeater 210. Both transmissions from BTS 208 are modulated with the same PN code uniquely identifying BTS 208. The transmission 216 routed through the repeater 210 is stronger than transmission 214, and hence is chosen by the subscriba: staUon 212 for use in the position determination process in lieu of the transmission 214.
[0007] Hw subscribe- station 212, upon receivir^ the transmissions,
erroneously identifies the transmission 216 relayed by repeater 210 as a line of sight transmission from BTS 208. Therefore, it also erroneously identifies the time measurement derived from this transnassion as being representative of the propagation time between the BTS 208 and the subscriber station 212. However, this time measurement is aotiqjresentative of this propagation time, but in fact overstates it. Consequently, a posiljon estimate based on this time measurement will be erroneous.
SUMMARY
[0008] A method of caliloating a repeater in a wireless communications system is
described In one embodiment, the method begins by receiving a signal at each of several difSsrent measurement locations. Each signal originates bom the same originadDg tmtsnattsT and is tdayed by the repeater prior to being necdved at the measurement location. Time measurements are then derived from each of the signals. Each of the time measurements represents the time betweai transmission of the signal at the originating transmitter, and arrival of the signal at the measurement locatjon. The positions of the measurement locations are either known or obtained Calibration parameters for (he repeater are then derived from (a) the time measurements, and (b) the positions of the measureraent locations.
[fl00?J In one implementation, the calibrsrtion parameters for fee repeato-comprise (a) a time correction for the nepealer, and (b) the position of the repeats. Both parameters are derived throu^ appHcation of an inverse triangulatkxi procedure to time measuTBinentg derived from signals nsceived at four different measiaement locations.

The signals all originate from the same donor base station and are each relayed by the repeater before being teceived at the measurement locations.
[0010] Tne time measurements derived at these four locations may be refaxed
to as mj, where 1 ^ i 5 4. Each time measurennent mj can be expregsed as:
jr^ = A4-ti+"tJ( + T2i (1)
where:
x\ = the forward link delay between the originating transmitter and the repeater
tR= the repeater self delay
T2i = the forward link delay between the repeater and the receiver at measurement location i
A = the offset between system time and time at the originating transmitter [0011] Assuming that the position of the n^eater has the unknown coordinates (XR, yR. ZR). and the position of measurement location i has the known coordinates (X], yi, Zi), Ihe relationship between the time measurement m, the coordinates of the position of the repeater, and the coordinates of the position of measurement legation i may be expressed as follows:
m, = A+T, +r, +-^(x, -xj" +(y, - yj" + (z, -zj (2)
c
where c is the speed of light
[0012] Note that (2) represents four separate equations, one for each of the
measurement locations. These foxir equations can be solved for four unknowns. The
first three unknowns are the coordinates of the position of the repeater (XR, yR, ZR). The
fourth unlcnown is the time correction xj associated with the repeater, where TT = A + TJ

Solving equations (3), (4) and (5) yields (XR, ys, ZR), the coordinates of the position of
the repeater. Substituting these coordinates into any of the four equations represented
by equation (2) yields the time correction TT- The position of the repeater and the time
correction for the repeater form the calibration parameters for the repeater.
[0014] In one application, these calibration parameters are stored for subsequent
use in determining the positions of subscriber stations. In this application, the subscriber station receives a signal that is typically a composite of several component signals from reference sources visible to the subscriber station. The subscriber station derives a time measurement from one of the component signals. This time measurement represents the time between transmission of the component signal by the reference source and anival of the signal at the subscriber station. The subscriber
station also analyzes the signature of the composite signal to determine whether the
component signal was relayed by a repeater.
[0015] If so, a PDE in communication with the subscriber station obtains the
calibration parameters for the repeater from a database. In one embodiment, these calibration parameters consist of a time correction for, and position of, the repeater. The PDE corrects the time measurement using the time correction for the repeater. The corrected time measurement then represents the amount of time required for the signal to travel between tiie repeater and the subscriber station (commonly referred to as the "propagation time"). If to refers to the original time measurement, TT refers to the time correction for the repeater, and TC refers to fee coirected time measurement.

then the PDE derives tc by subtracting Vr from XQ- The relationship between these values can be expressed as:
TC = TO-TT (6)
[0016] The PDB then detemaines the position of the subscriber station from the conected time measurement tc and the repeater position (XR, y&, ZR). It uses these values to determine the position of the subscriber station in lieu of the original time measurement To and reference source position.
[0017] If the component signal was not relayed by a repeater, the PDE
determines the location of the subscriber station from the uncorrected time
measurement To and reference source position.
[0018] Related systems are also described
BRIEF DESCMFnON OF THE DRAWINGS
[0019] The components in the figures are not necessarily to scale, emphasis
instead being placed upon illustrating the principles of the disclosed subject matter. In
the figures, like reference numerals designate corresponding parts throughout the
different views.
[0020] Figure 1 is a block diagram of an embodiment of a repeater in a wireless
communications system relaying signals between a base station and a subscriber
station.
[0021] Figure 2 is a block diagram illustrating die ambiguity that may be
introduced by a repeater into the process of determining the position of a subscriber
station.
[0022] Figure 3A is a flowchart of an embodiment of a method of calibrating a
repeater.
[0023] Figure 3B illustrates an example of the format of a database record for
storing the calibration parameters for a repeater.
[0024] Figure 4A illustrates an example of measurement locations which may be
employed in the method of Hgure 3 A.

[0025] Figure 4B illustrates an example where the measurement locations
employed in the method of Figure 3A are situated along a route driven by a vehicle.
[0026] Figure 4C illustrates an example where the time measurements employed
in the method of Figure 3A are concurrently derived from a plurality of dispersed
measurement locations.
[0027] Figure 5 illustrates an example in which time measmements taken from
different sets of measurement locations are used to calibrate different repeaters in a
wireless communication system.
[0028] Rgure 6 is a timing diagram illustrating the various components of a
propagation time measurement for a signal relayed by a repeater.
[0029] Figure 7A is a flowchart of an embodiment of a method of determining
the position of a subscriber station in a wireless communications system employing
repeaters.
[0030] Figure 7B is a flowchart of an implementation of the method of Figure
7A.
[0031] Figure 8A is a block diagram of an embodiment of a system for
calibrating a repeater in a wireless communications system.
[0032] Figure 8B is an example format of a database record which may be
employed in the system of Figure 8A for storing one or more calibration parameters
for the repeater.
[0033] Figure 9 is a block diagram of an implementation of a subscriber station
particularly suited for use in a wireless communications system employing repeaters.
[0034] Figure 10 is a diagram of an example of a position determination system
in which one or more calibration parameter for a repeater are stored in a database, and
subsequently used for determining the positions of subscriber stations.
[0035] Rgure H is a diagram illustrating calibration of a base station according
to an embodiment of the disclosed subject matter.

DETAILED DESCRIPTION
[0036] As used herein, the term "memory" refers to any processor-readable
medium, including but not limited to RAM, ROM, EPROM, PROM, EEPROM, disk, floppy disk, hard disk, CD-ROM, DVD, or the like, on which may be stored a series of instructions executable by a processor.
[0037] The term "processor" refers to any device capable of executing a series
of software instructions and includes, without limitation, a general- or special-purpose
microprocessor, finite state machine, controller, computer, or digital signal processor.
[00381 Figure 3A is a flowchart of an embodiment of a method of calibrating a
repeater in a wireless communications system. In step 302, a signal relayed by a
repeater is received at a plurality of different measurement locations. Step 304
follows step 302. In step 304, time measurements are derived from each of the
measurement locations. Each time measurement represents the time between
transmission of the signal by an originating transmitter and arrival of the signal at the
measurement location (commonly referred to as the "propagation time"),
[0039] From step 304, the metihod proceeds to step 306. In step 306, one or
more calibration parameter for the repeater are derived from (a) the time
measurements, and (b) the positions of the measurement locations.
[0040] This method may be furfljer explained with refaence to Figure 4A, which
illustrates an example of a wireless communications system in which a signal from base station 402 is transmitted over transmission medium 406 to repeater 404. Transmission medium 406 is any medium capable of transmitting the signal from transmitter 402, including by way of example and not limitation, an optical fiber, a conventional wireline link, or a wireless linL
[0041] Repeater 404 receives the signal, amplifies it and re-transmits it over a
wireless communications link. The repeater 404 re-transmits the signal over a covers area which includes measurement locations 408a, 408b, 408c, and 408d. A measuring device (not shown) at each of the measurement locations receives the signal as transmitted by base station 402 and relayed by repeater 404. The device flien

derives time measurements from the received signals. The time measurements are representative of the time elapsed between transmission of the signal by the base station 402 and arrival of the signal at the measurament location. These time measurements include the repeater self-delay and donor base station/repeater forward link delay.
[0042] Thus, in Figure 4A, the time measurement derived at measurement
location 408a is representative of the time between transmission of the signal by base station 402, and arrival of Uie sipial at measurement location 408a. Similarly, the time measurement derived at measurement location 408b is representative of the time between transmission of the signal by base station 402, and airiva] of the signal at measuremeait location 408b. The same applies to measurement locations 408c and 408d.
[0043] In one example, the signal relayed by a repeater is a pilot signal that
originates from a base station in a CDMA wirisless communications system. The pilot
signal comprises a cairier sipal modulated vsdth a repeating PN code uniquely
identifying the base station that originated the signal. A measuring device located at a
measurement location first tunes to the pilot channel of the CDMA system, and then
attempts to acquire the pilot signal being transmitted by the base station.
[0044] The measuring device attempts to acquire the signal by correlating tiie
received signal with the PN code for the donor base station over a range of code phase shift hypotheses and over a range of Doppler frequency shift hypotheses. Each correlation is performed over an integration time I, that is the product of Nc and M, where Nc is the coherent integration time, and M is the number of coherent integrations that are non-coherently combined to form the correlation value, [0045] The device then locates the peak in the correlation function that corresponds to a line of sight transmission by the repeater. In one implementation, the PN code of the donor base station is known, and the measurement locations are located far enouj^ ftom the donor base station that a line sight transmission from the donor base station cannot be detected at the measuring device. The earliest "non-sidelobe" peak in the correlation function thus represents the line of sight transmission

from the repeater. It will be understood by those skilled in the art that a sidelobe is a
relatively small peak occurs close to, and is related to, another relatively larger peak.
[0046] The device derives a time measurement from the location of the early
non-sidelobe peak along the code phase dimension of the correlation function, A system time reference is obtained from a GPS receiver included in the device. The system time refraence is used to adjust the time measurement so that the time measurement is in terms of system time.
[0047] The positions of the measurement locations are derived by the GPS
receiver included with tiie device. The time measurements and positions of the measurement locations are then provicted to a position determination entity (PDE). The PDE determines the calibration parameters for the repeater 404 responsive to this information. Alternatively, the subscriber station determines its own calibration parameters, or the collected data is stored for further processing at later time to determine the calibration parameters.
[0048] In one implementation, the calibration parameters for the repeater 404
include a time conection for the repeater and the position of the repealer. In this implementation, an inverse triangulation procedure is used to derive the time correction for and position of the repeater from time measurements taken at four different measurement locations. These four time measurements may be referred to as mi, 1 S i [0049] Each of the time measurements represents the time between transmissi on
of the signal by the originating transmitter and arrival of the signal at the measurement location. Included are the repeater self-delay and donor base station/repeater forward link delay. Thus, in Figure 6, the time measurement mi is the time between time of transmission 602 and time of arrival 604, and can be expressed as:
mi = A + Ti + TR + Ta (7)
where:
A = offset between system time and time at the originating (donor)
transmitter

necessary to decompose this parameter into its constituent pieces for accurate position
determination.
[0054] A number of approaches are possible for collecting the time
njeasurements nn, 1 5 i to the equations (8) above.
[0055] In one embodiment, illustrated in Figure 4B, a vehicle is driven along a
path 420. The measurement locations 408a, 408b, 408c, and 408d are arbitrary
locations situated along the path 420. Tlie positions of these measurement locations
are not known a priori.
[0056] A measuring device (not shown) accompanies the vehicle. The device
includes a GPS receiver. As the vehicle is driven along the path 420, each of the
measurement locations is successively encountered. A time measurement is derived
by the measuring device at each such measurement location. In addition, a system
time reference and position of each measurement location is obtained from the GPS
receiver included in the device. The system time reference is used to adjust the time
measurements so they are in terms of system time.
[0057] In a second embodiment, illustrated in Figure 4C, a plurality of
subscriber stations 422a, 422b, 422c and 422d are situated at dispersed measurement
locations 408a, 4085,408c, and 408d. A system time reference is derived from a GPS
receiver located in the subscriber station. In addition, the position of the measurement
location is obtained from the GPS receiver. A time measurement is derived by the
subscriber station from a signal relayed by the repeater. The time measurement for the
location is adjusted by the system time reference so it is terms of system time.
[0058] In a third embodiment, the locations of the measurement locations are
predetermined, and thus known beforehand. Fixed measuring devices are mounted at
each of the measurement locations. Bach device determines a time measurement from
a signal relayed by the repeater. A system time refaiencc is obtained and used to
adjust the time measurements that are used in the calibration process.
[0059] The method of Figure 3A may be applied to calibrate multiple repeaters
in a wireless communications system. Figure 5 illustrates an example of this process.

Time measurements and positional infoimation for each of the measurement locations
506a(l). 506b(l), 506c(l), and 506d(l) are used to calibrate repeater 504a. Similarly,
time measurements and positional inframation for each of the measurement locations
506a(2), 506b(2), 506c(2), and 506d(2) are used to calibrate repeater 504b.
[OOfiO] Note that, in the particular example illustrated in Figure 5, there is no
overlap between the measurement locations 506a(l), 506b(l), 506c(l), and 506d(l) used for calibrating repeater 504a and the measurement locations 506a(2), 506b(2), 506c(2), and 506d(2) used for calibrating repeater 504b. However, it should be appreciated that embodiments are possible where there is complete or partial overlap in tiiese locations. Moreover, since the pilot signals originating from base stations 504a, 504b are modulated with different PN codes, a time measurement for both signals can be derived by the same measuring device located at a single measurement location.
[0061] Referring back to Kgure 3A, in optional s^ 308, the one or more
calibration parameters are stored for subsequent use in determining the positions of subscriber stations. In one implementation, the one or more calibration parameters comprise a time correction for and position of the repeater. These two values are embodied as a database record that is indexed by the PN code of the donor base station. Similar records are present in the database for all repeaters in the network. Each of the records is indexed with the PN code for the corresponding donor base station. The result is an almanac for all repeaters in the network that is updated every time a calibration procedure is performed. To ensure that the almanac is up to date, the calibration procedure is preferably performed periodically or at least every time a change is made to the network, such as the addition of a repeater. In one embodiment, the database is accessible to a PDE that determines the positions of subscriber stations. In an alternative embodiment, the database is accessible to subscriber stations that determine their own positions.
[0062] Figure 7A illustrates an embodiinent of a method for detaraiining the
location of a subscribor station in a wireless commuiiications system employing repeatoB.

[0063] The method begins with step 702. Step 702 comprises deriving a time
measurement from a received signal. The received signal is generally a composite of several component signals transmitted by reference sources visible to the receiver, but can comprise only a single component. The time measurement is representative of the time between transmission of one of the componait signals by the corresponding reference source, and arrival of the signal at the receiver.
[0064] From step 702, the method proceeds to step 704. In step 704, the method analyzes the "signature" of the composite signal to deteamine whether or not the componeait signal was relayed by a repeater.
[0065] In general, the "signature" of the composite signal comprises (a) the
number of component signals visible to the receiver, (b) characteristics of each component, (c) the relative strength of these signals, and (d) the relative delay of these signals. The "signature" of the composite signal preferably conveys mformation sufficient to detennine whether a repeater relayed the compcxnoit signal. [0066] In one implementation, the component signals are pilot signals, and the "signature" of the composite signal includes: (1) the total number of pilot sipals visible to the receivrar, (2) characteristics of each pilot signal, (3) their relative signal strength, and (4) their relative times of arrival at the receiver. The detection of other pilots at the receiver generally identifies the donor cell as the immediate source of the received signal. On the other hand, the lack of any otiier pilots at the receiver generally identifies the repeater as flie immediate source of the component signal. A certain pattern of pilots from other cells, their relative signal strength and time of arrivals can be used to rule out or identify specific repeaters.
[0067] For example, if there is an overlap m coverage area between the donor cell
and the repeater, and the receiver is present in this area of overlap, the line of sight (LOS) signal received directly from the donor cell and that relayed by the repeater are marked with the same PN code. Consequently, both signals will give rise to peaks in the correlation function. If neither signal is subject to multi-path, tiie peak hi the correlation function due to the repeatCT will be delayed relative to that due to flie LXDS signal. The peak resulting from flie repeater can thus be identified cm the basis of this relative delay.

[0068] As a second example, if the LOS signal ftom the donor cell is subject to
multi-path, it may be difficult to distinguish the peaks due to multi-path from the peak
due to the repeater. However, this ambiguity can be resolved during the design and
deployment phase by ensuring that the delay due to transmission through the repeater
exceeds that associated wi(h any multi-path produced by the RF envircmment In this
case, the repeater will leave a signature footprint in the correlation function in the form
■ of a peak that is delayed beyond that due to multi-path.
[0069] As a third example, if there is only a single peak in the correlation function
for the PN code in question, and no other pilots are visible to the receiver, it can be assumed that the receiver is in an area that is only accessible to signals relayed by the repeater. The single peak at the PN code in question can therrfore be assumed to be due to a repeater.
[0070] As a fourth example, the calibration parameters for a particular PN code
can be used to detemrine whether a repeater relayed a particular compcment signal. More specifically, if the time correction Vr for the PN code greatly exceeds the corrected time measurement derived using this time correction, it can be assumed that a repeater relayed the component signal.
[0071] Returning to Figure 7A, from step 704, the method proceeds to step 706.
In step 706, the method queries whether a repeater relayed the component signal. If so, step 708 is performed. In step 708, the method comprises obtaining one or more calibration parameters for the repeater. In one implementation, this step comprises retrieving pre-determined calibration parameters from a database. In one example, these values are obtained by retrieving these parameters from a database record using the PN code of the donor cell as an index to the database. In a second implementation, this step comprises determining these parameters "on the fly."
[0072] From step 708, the method proceeds to step 710. Step 710 comprises
dctetmining the position of the subscriber station from the one or more calibration parameters obtained in step 708.

[0073] In step 706, if the received signal was not relayed by a repeater, step 712 is
performed. In step 712, the position of the subscriber station is determined from the
time measurement derived in step 702, and the position of the ori^nating transmitter.
[0074] Figure 7B illustrates an implemHitation of the method of Figure 7B. Steps
702,704,706, and 712 were already explained in the context of Figure 7A. Only steps
720-724 are explained here.
[0075] In step 720, a time correction for and the position of the repeater are
obtained. In one implementation, these parameters are retrieved dtora a database using
the PN code of the donor cell as an index.
[0076] From step 720, the method proceeds to step 722, St^ 722 comprises
correcting the time measurement derived in step 714 using the time correction for the
repeater obtained in step 720. In wie implementation, this step comprises subtracting
the time correction Vx from the time measurement XQ to form a corrected time
measurement it. where zc = To-tr-
[0077] From step 722, the method proceeds to step 724. There, the position of the
subscriber station is determined ftom the corrected time measurement tc and the
position of flie repeater.
[0078] Figure 8A illustrates an embodiment of a system for calibrating one or
more parameters for a repeater in a wireless communications system. The system
comprises a processor 810 that is configured to delennine the one or more calibration
parameters for the repeater from time measurements and measurement location
positions obtained throu^ any of the previously discussed methods.
[0079] In one implementation, Ae processor is located within a PDE, and is
configured to determine a time correction and position of the repeater by solving the
four equations represented by (8) above. In this implementation, the processor 810 is
configured to derive the parameters by executing software in the form of a series of
instructions stored in memory 812.
[0080] Jn one implemaitation, once these parameters have been deteimined, the
processor 810 is configured to store them as a record in database 814, indexed using the
PN code of the donor cdl.

[0081] The record has the format shown in Figure 8B. Held 816 is the PN code
of the donor cell. Field 818 is the time correction for the repeater. Field 820 is the
position of the repeater.
[0082] Figure 9 is a block diagram of a subscriber^stadon that is particularly suited
for use in a wireless communications system onploying repeaters.
[0083] ProcesscMT 902 is configured to execute software instructions, and memory
904 is configured to hold the software instcuctions and data that ace accessible by the
processor 902.
[0084] Persistent storage 906 is configured to hold provisioning information
useful for acquiring wireless communications services, and can be implemented as a
combination of devices such as a non-volatile EEPROM combined with a SIM card.
[0085] Keypad 908 and display 910 are both typically provided as part of a user
interface. Similarly, microphone 912 and speaker 914 are both typically provided to
support use of the device for receiving and transmitting voice.
[0086] Radio transceiver (Tx/Rx) 916 is provided for receiving and transmitting
information over a wireless communications link, Modem 918 is provided for
modulating baseband information, such as voice or data, onto an RF carrier, and
demodulating a modulated RF carrier to obtain baseband information. Antenna 922 is
provided far transmitting a modulated RF carrier over a wireless communications link
and receiving a modulated RF carrier over a wireless communications link.
[0087] Correlator 920 is provided for deriving correlation functions from a
received signal comprising a composite of pilot sipals transmitted by various
reference sources visible to the subscriber station. For a given PN code, the correlator
920 derives a correlation function by correlating the received signal with the PN code
over a range of code phase shift hypotheses and a range of Doppler frequency shift
hypotheses, It then locates a predetermined number of the peaks of the correlation
function.
[0088] Processor 902 is configured to analyze this information to det^mine the
eariiest non-sidelobe peak of the correlation functioii. If such a peak is detected, the
ptxxessor 902 is also configmed tx> draive a time measurement from the location of

this peak in the code phase dimension. If a system time reference is available, the processor 902 adjusts the time reference using the system time reference so that the time measurement is in terms of system time.
[0089] Processor 902 is also configured to analyze the signature of the received signal to determine if the peak relates to a pilot agnal received directly from the reference source or if it relates to a signal that was relayed by a repeater. This process was previously described in relation to Figure 7A.
[009O] Figure 10 illustrates an example of a system for detennining the position
of a subscriber station in a wireless communication system employing repeaters. Subscriber station 1002 receives signals transmitted by a plurality of reference sources 1004a, 1004b, 1004c, and 1004d, visible to the receiver in the subscriber station. As illustrated, the reference sources may be BTSs, GPS satellites, or combinations of BTSs and GPS satellites.
[0091] Each of the reference sources transmits a signal that is modulated with an
identification code that uniquely identifies the reference source. In one implementation, the identification codes are PN codes that may differ in length or periodicity according to the reference source involved. For IS-95 compliant CDMA systems, the PN code is a sequence of 32,768 chips that is repeated every 26.67 msec. In current GPS systems, the PN code is a sequence of 1,023 chips. The sequence is repeated every one millisecond.
[0092] The signals transmitted by reference sources 1004a, 1004b, and 1004c, are
all received directly by the subscriber station 1002. Thus, all are line of sight signals.
However, the signal transmitted by base station 1004d is relayed by repeater 1006, and
this is not a line of sight sipal from the standpoint of the donor cell 1004d.
[0093] A database 1010 is accessible to position determination entity (PDE)
1008. The database 1010 contains entries for each of the repeaters that are present in the wireless communications system. Each of the entries comprises a record that contains the position of and time correction for the corresponding repeater. This information is derived using any of the methods for calibratkg a repeater that have been previously discussed. Each entry is indexed using the PN code of the donor cell.

[005>4] The subscriber station 1002 is equipped with a correlator that, in
conjunction with related software executable by a processor within the subscriber
station, is configured to derive a time measurement for each of the pilot signals. If a
system time reference is available, the subscriber station 1002 uses this information to
adjust the time measurements so they are in terms of system time. Alternatively, this
task is petfonned by the PDE1008.
[0095] Tbst subscriber station 1002 then communicates the time measuranents to
, PDE 1008. Upon receipt of this information, PDE 1008 checks the signature of the composite signal to determine if any of the pilot signals were relayed by a repeater. The process of analyzing the signature of a composite signal to determine the immediate origin of a composite signal was previously discussed in relation to the
. method of Figure 7A.
[0096] ff a time measurement derived from a signal relayed by a repeater is
present, then the PDE 1008 uses the PN code for the donor cell to retrieve the calibration parameters for the repeater from the database 1010. In particular, the PDE 1010 retrieves a record containing the time correction for, and position of, the repeater. It then uses the time correction for the repeater to correct the time measurement. It also substitutes the position of the repeater for that of the donor cell. It performs these adjustments for each of the time measurements determined to involve signals relayed by a repeater.
[0097] It then determines the position of the subscriber station 1002 using the
corrected time measurements and updated positions. Again, in one implementation, known triangulation procedures are used to derive the position of subscriber station 1002. Once detennined, the position of the subscriber station 1002 may be communicated by the PDE 1008 to the subscriber station 1002 or some other network entity.
[0098] Alternatively, the subscriber station 1002 detennines its own position
using the database of calibration parameters that is accessible by the subscriber station 1002.

[0099] While various embodiments of the disclosed subject matter have been
described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible.
[0100] In particular, embodiments are possible in which network entities other
than rqepeates may be calibrated through application of the methods described. For
example, Figure 11 illustrates the method of Figure 3A applied to the process of
calibrating a base station. Referring to Figure 6, the time correction for a base station
will comprise the component referred to as A, the offset between system time and time
as maintained at the base station, but does not include the components referred to as TI
or TR. Other than this difSaence, the approach for calibrating the base station is
identical to that described previously in relation to a repeater.
[0101] One or more signals are transmitted fh>m BTS 1102 over a wireless
communications link. The transmission occurs over a coverage area that includes measurement locations 1104a, 1104bb, 1104cc, and 1104d. A receiver (not shown) at each of the measurement locations receives a signal as transmitted by BTS 1102. [0102] A time measurement is derived from the signal received at each of the measurement locations. In one hnplementation, the time measurement. is representative of the travel time between BTS 1102 and the receiver (commonly referred to as the "propagation time"). Thus, in the example illustrated in Figure 11, the time measurement derived at measurement location 1104a is representative of the propagation time from BTS 1102 to measurement location 1104a. Similarly, the time measurement derived at measurement location 1104b is representative of the propagation time from BTS 1102 to measurement location 1104b. The same applies to measurement locations 1104c and 1104d.
[0103] One or more calibration parameters for BTS 1102 are then determined
responsive to the time measurements and the locations of the measmement locations. In one implementation, the calibration parameters for BTS 1102 comprise a time correction for and position of BTS 1102. These parameters are determined from the time measurements and positions of the measurement locations using fee equations (8) refered to previously.

[0104] Embodiments are also possible in which the calibration parameters are
used for determining the positions of subscriber stations in any position determination
system, including without limitation terrestrial systems, network-based or subscriber
station based terrestrial systems, GPS satellite systems, or hybrids thereof. Moreover,
any method of position deteniination may be employed, including without limitation
AOA, TOA, cell ID, with or without TA or RTD enhancements, E-OTD, OTDOA, or
A-GPS, with or without IPDL, TA-IPDL, or OTDOA-PE modifications.
[0105] Accordingly, the invention is not to be restricted except by the appended
claims.

WE CLAIM :
1. A method of calibrating a repeater in a wireless communications system
comprising the steps of:
receiving a signal, transmitted by an originating transmitter and relayed by a repeater, at a plurality of different measurement locations;
deriving time measurements from each of the received signals, each time measurement representative of the time between transmission of the signal by the originating transmitter and arrival of the signal at the measurement location; and
deriving one or more calibration parameters for the repeater from (a) the time measurements, and (b) the positions of the measurement locations.
2. The method as claimed in claim 1, wherein the one or more calibration parameters comprise a time correction for the repeater, and the position of the repeater.
3. The method as claimed in claim 1, comprising storing the one or more calibration parameters.
4. The method as claimed in claim 1, wherein the plurality of different measurement locations comprise four or more different measurement locations.

5. The method as claimed in claim 1, wherein the time measurements are sequentially derived from signals sequentially received at successive ones of the measurement locations.
6. The method as claimed in claim 1, wherein the time measurements are concurrently derived from signals concurrently received at the measurement locations.

7. The method as claimed in claim 1, wherein the measurement locations are fixed and predetermined.
8. The method as claimed in claim 1, wherein the positions of the measurement locations are sequentially derived using a GPS receiver sequentially placed at successive ones of the measurement locations.
9. The method as claimed in claim 2, wherein the time measurements are obtained at four different measurement locations and may be referred to as mj, 1
where c is the speed of light.
10. The method as claimed in claim 3, wherein the one or more calibration
parameters are stored in a database.
11. The method as claimed in claim 10, wherein the database includes one or more
calibration parameters for each of a plurality of repeaters.
12. The method as claimed in claim 5, wherein the time measurements are sequentially obtained by driving around an area with a measuring device, and using the measuring device to sequentially obtain the measurements at successive ones of the measurement locations.
13. The method as claimed in claim 12, wherein the measuring device includes a GPS receiver, and the positions of the measurement locations are sequentially

obtained by using the GPS receiver in the measuring device to sequentially obtain the positions of successive ones of the measurement locations.
14. The method as claimed in claim 6, wherein the time measurements are concurrently obtained from a plurality of dispersed measuring devices.
15. The method as claimed in claim 14, wherein the measuring device includes a GPS receiver, and the positions of the measurement locations are concurrently obtained from the GPS receivers included in the plurality of dispersed measuring devices.
16. The method as claimed in claim 1, wherein the signals received at the measurement locations all originate from the same transmitter.
17. A method of determining the position of a subscriber station in a wireless communications system employing repeaters comprising the steps of:
receiving a composite signal at the subscriber station, the composite signal having a signature and comprising one or more component signals;
determining from the signature of the composite signal whether a component signal was relayed by a repeater;
obtaining one or more calibration parameters for the repeater if the component signal was relayed by the repeater; and
determining the position of the subscriber station based at least in part on the one or more calibration parameters for the repeater.
18. The method as claimed in claim 17, wherein the one or more calibration
parameters comprise a time correction for the repeater, and the position of the
repeater.

19. The method as claimed in claim 17, wherein the one or more calibration parameters are retrieved from a database.
20. The method as claimed in claim 19, wherein the database includes one or more calibration parameters for a plurality of repeaters.
21. The method as claimed in claim 17, wherein the component signal originates with a reference source.
22. The method as claimed in claim 21, wherein the reference source is a base station in a wireless communications system.
23. The method as claimed in claim 21, wherein the reference source is a GPS satellite.

24. The method as claimed in claim 21, wherein the one or more calibration parameters are retrieved using a PN code for the reference source.
25. The method as claimed in claim 24, wherein the one or more calibration parameters comprise a time correction Xj for the repeater and position of the repeater.
26. The method as claimed in claim 21, wherein a time measurement TQ is derived from the component signal, the time measurement representing the time between transmission of the signal by the reference source, and receipt of the signal by the subscriber station, and this time measurement is corrected using the time correction TT for the repeater to form a corrected time measurement where

27. The method as claimed in claim 26, wherein the position of the subscriber station
is determined from the corrected time measurement Xc and position of the repeater in
lieu of the time measurement TQ and position of the reference source.
28. The method as claimed in claim 17, wherein the signature of the composite
signal includes the number of component signals visible to the subscriber station.
29. The method as claimed in claim 28, wherein the signals are all pilot signals.
30. The method as claimed in claim 17, wherein the signature of the composite signal includes the relative strength of the component signals visible to the subscriber station.
31. The method as claimed in claim 17, wherein the signature of the composite signal includes the relative time of arrivals of the composite signals visible to the subscriber station.
32. A system for determining the position of a subscriber station (106) in a wireless communications system employing repeaters (104) comprising:
a receiver (916) for receiving a composite signal (216) at the subscriber station, the composite signal have a signature and comprising one or more component signals;
a processor (902) for determining from the signature of the composite signal whether a component signal was relayed by a repeater; and
an entity (902) for obtaining one or more calibration parameters for the repeater if the component signal was relayed by the repeater, and determining the position of the subscriber station based at least in part on the one or more calibration parameters for the repeater.

33. The system as claimed in claim 32, wherein the one or more calibration parameters for the repeater comprise a time correction for the repeater, and the position of the repeater.
34. The system as claimed in claim 32, wherein the entity is configured to retrieve the one or more calibration parameters from a memory (904).
35. The system as claimed in claim 34, wherein the entity is configured to retrieve the one or more calibration parameters from a database (814).
36. The system as claimed in claim 35, wherein the one or more calibration parameters for the repeater are in the form of a record in a database that is accessible by the processor (810) using the PN code (816) for the originating transmitter of the signal as an index.
37. The system as claimed in claim 33, wherein the entity is configured to correct a time measurement derived from the signal using the time correction for the repeater, and determine the position of the subscriber station at least in part from the corrected time measurement for and the position of the repeater.
38. The system as claimed in claim 33, wherein the entity is a position determination
entity (1008).
39. The system as claimed in claim 33, wherein the entity is a subscriber station.
40. A method of calibrating a repeater in a wireless communications system
comprising:

driving a vehicle along a route with a measuring device located on or within the vehicle;
successively encountering a plurality of measurement locations having along the route;
using the device to receive a signal, transmitted by an originating transmitter and relayed by a repeater, at each of the measurement locations;
using the device to derive a time measurement from the received signal at each of the measurement locations;
using a GPS receiver included with the device to determine a system time reference;
using the system time reference to adjust the time measurements to produce adjusted time measurements, an adjusted time measurement for a measurement location representing the time, in terms of system time, between transmission of the signal by an originating transmitter and arrival of the signal at the measurement location;
using the GPS receiver to determine the position of each of the measurement locations; and
deriving a time correction for and position of the repeater from (a) the adjusted time measurements, and (b) the positions of the measurement locations.
41. A subscriber station comprising:
a receiver for receiving a signal having a signature;
a correlator (920) for deriving a correlation function from the signal, and identifying one or more peaks in the correlation function;
a processor configured to derive a time measurement from a peak in the correlation function, analyze the signature of the signal to determine if the peak relates to a signal that was relayed by a repeater, and provide an indication whether the peak relates to a signal that was relayed by a repeater.

42. A method of calibrating an entity in a wireless communications system
comprising:
a step for receiving a signal, transmitted by an originating transmitter and relayed by a repeater, at each of a plurality of different measurement locations;
a step for deriving time measurements from each of the received signals, each time measurement representative of the time between transmission of the signal by the originating transmitter and arrival of the signal at a measurement location; and
a step for deriving one or more calibration parameters for the entity from (a) the time measurements, and (b) the positions of the measurement locations.
43. The method as claimed in claim 46, wherein the entity is a repeater.
44. The method as claimed in claim 46, wherein the entity is a base station.

Documents:

0317-chenp-2005 abstract-duplicate.pdf

0317-chenp-2005 abstract.jpg

0317-chenp-2005 abstract.pdf

0317-chenp-2005 claims-duplicate.pdf

0317-chenp-2005 claims.pdf

0317-chenp-2005 correspondence-others.pdf

0317-chenp-2005 correspondence-po.pdf

0317-chenp-2005 description (complete)-duplicate.pdf

0317-chenp-2005 description (complete).pdf

0317-chenp-2005 drawings.pdf

0317-chenp-2005 form-1.pdf

0317-chenp-2005 form-18.pdf

0317-chenp-2005 form-26.pdf

0317-chenp-2005 form-3.pdf

0317-chenp-2005 form-5.pdf

0317-chenp-2005 pct-search report.pdf

0317-chenp-2005 pct.pdf

0317-chenp-2005 petition.pdf

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Patent Number

218416

Indian Patent Application Number

317/CHENP/2005

PG Journal Number

21/2008

Publication Date

23-May-2008

Grant Date

01-Apr-2008

Date of Filing

04-Mar-2005

Name of Patentee

QUALCOMM INCORPORATED

Applicant Address

5775 Morehouse Drive, San Diego, California 92121,

Inventors:

#	Inventor's Name	Inventor's Address
1	SOLIMAN, Samir S	11412 Cypress Canyon Park Drive, San Diego, California 92131,

PCT International Classification Number

H04B 7/26

PCT International Application Number

PCT/US2003/028107

PCT International Filing date

2003-09-05

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/408/,611	2002-09-05	U.S.A.
2	10/366,960	2003-02-14	U.S.A.