HK1172770A - Method and apparatus for determining location of a base station using a plurality of mobile stations in a wireless mobile network - Google Patents

Abstract

A method and apparatus for determining a position of a base station in a wireless communication network that includes a mobile station in communication with base stations. A BTS calibration server is networked with the base stations. A BTS calibration program is programmed into a group of mobile stations that have position location capabilities. Using the BTS calibration program, calibration information may be requested by the BTS calibration server, or a session may be initiated by the mobile station. The BTS calibration program also provides privacy features that allow user of the mobile station to prevent it from being used for base station location. If authorized, the BTS calibration program determines the position of the mobile station, and provides calibration information, such as position and base station phase measurements, to the server. The calibration information may be used to calibrate the base station almanac.

Description

Method and apparatus for determining base station location using multiple mobile stations in a wireless mobile network

Divisional application

The present application is a divisional application of the original Chinese invention patent application entitled "method and apparatus for determining base station position using multiple mobile stations in wireless mobile network". The original application having application number 2005800276222; the application date of the original application is 6/2005 and 20/th.

Related application

This application claims priority to U.S. provisional application No. 60/580,929, filed on 6/18/2004.

Technical Field

The present invention relates generally to wireless communication systems in which base stations communicate with a number of mobile stations having position location capabilities, and more particularly to the determination of the location of base stations in a mobile communication network.

Background

In a wireless communication network, one or more base stations communicate wirelessly with a number of mobile stations (e.g., wireless devices such as handsets). Mobile stations typically provide standard voice and/or data communications; as an additional feature, some mobile stations have positioning capabilities, which allow the user of the mobile station to determine its position. These position determination capabilities are becoming increasingly useful and important; for example, regulatory requirements for authority may require a network operator to report the location of the mobile station when the mobile station places a call to an emergency service (e.g., a 911 call in the united states). Alternatively, the user may wish to know their location only for the purpose of locating a nearby restaurant or movie theater.

One well-known type of position location system uses satellites in earth orbit to triangulate the position of a mobile station. An example of such a system is the Global Positioning Satellite (GPS) system in current implementations. Another type of position location system utilizes radio signals from base stations whose locations are known. For example, in one type of communication network, Code Division Multiple Access (CDMA) digital cellular networks, position location capability may be provided by Advanced Forward Link Trilateration (AFLT), a technique that calculates the position of a Mobile Station (MS) by the time of arrival of radio signals from cellular base stations as measured by the mobile station: AFLT-enabled wireless mobile stations (AFLT-enabled mobile stations) make Pilot Phase Measurements (PPM) of radio signals from base stations with which they communicate and use these measurements to determine the position of the mobile station. A more advanced technique is hybrid position location, where the mobile station also employs a GPS receiver and the position is calculated based on AFLT and GPS measurements.

Message protocols and formats suitable for CDMA position location using AFLT, GPS and hybrid receivers based on MS and MS assistance scenarios have been published in TIA/EIA standard IS-801-.

Thus, in an AFLT-enabled wireless communication system, a wireless base station may be used as a reference point to assist in fixing the position of the base station. However, one prerequisite for using a base station as a reference is an accurate knowledge of the base station antenna position. Timing information about the base station is also important. Once the base station antenna position and timing information is known, it can be recorded in a Base Station Almanac (BSA) database for use by a Position Determination Entity (PDE). However, obtaining accurate antenna position and timing information for a base station can be tedious and expensive.

To further elaborate on the position determination system, data on calibration and recalibration of base station time offsets, base station antenna positions and other parameters are typically stored in a so-called "base station almanac". The base station almanac database provides information to determine an initial position estimate for the mobile station to initiate a GPS pseudorange search. Due to PN reuse, the base station almanac database provides information to resolve ambiguities as to which observed Pseudorandom Noise Sequences (PNs) correspond to which physical sectors of a CDMA network base station. The base station almanac database provides the cellular base station sector antenna location from which the signal is present. AFLT range measurements are made for these antenna positions.

In some cases, the position of the base station antenna may change slightly or over a large distance, and in that case the corresponding almanac information must be updated. For example, the base station antenna may be relocated, or the base station transceiver may be repaired or replaced, and a new cable may be placed between the transceiver and the antenna, resulting in a change in the base station antenna position or timing information. In another example, when, for example, two physical base stations exchange their identification information, the base stations may be logically (but not physically) mobile, and in such an environment, the two base stations will appear to have exchanged locations, even though neither base station is physically moving.

In these cases, the corresponding information in the database may become erroneous if the information is not updated; the almanac database must be updated before resuming service from the base station. However, updating the almanac database using conventional techniques can be time consuming and expensive: for example, conventionally the antenna position may be determined by measuring or referring to coordinates read from a map, and if the antenna coordinates are manually entered into a database, the likelihood of human error rises. Base station timing information is also subject to human error where custom hardware is used to measure timing information and timing offsets are manually entered into the database.

In a local area network, the enormous number of base stations (millions), deployment practices, and the ease of moving portable base stations from one physical location to another make it impossible to locate and maintain base station almanac using conventional measurement techniques.

In summary, deployment of base station time differences to reach ranging solutions (e.g., AFLT or hybrid AFLT) requires accurate Base Station Almanac (BSA) information, which includes base station antenna position and forward link calibration parameters (e.g., time corrections), which are key components of BSA information. Today, the popularization of BSA parameters is done individually for each base station, which is a manual, laborious and expensive process, and thus hinders the deployment and expansion of LBS services. It would be advantageous to provide a practical system that can calculate base station locations and forward link calibration parameters using data from mobile devices in an area to update BSA parameters in real time.

Disclosure of Invention

A method and apparatus for determining the position of a base station in a wireless communication network including a plurality of mobile stations in communication with one or more base stations. The method includes programming a set of mobile stations with a BTS calibration program to provide a plurality of calibration-enabled mobile stations (BTS calibration-enabled mobile stations), and providing a BTS calibration server in network connection with the base stations. Calibration information is requested from at least one of the calibration-enabled mobile stations in communication with a base station, and a location of the calibration-enabled mobile station is determined. Signals from base stations are received at the mobile station and such signals may be used to measure the travel time of signals from the base stations to the mobile station, e.g., it may measure the path delay of signals transmitted between the base stations and the mobile station to determine the distance between the base stations and the mobile station, and may include measuring the relative time of arrival in a TDOA system, or the round trip delay in an RTD system. If authorized, calibration information indicating the location is transmitted from the mobile station to the BTS calibration server. In the BTS calibration server, the calibration information is compared to base station almanac information associated with the base stations, and the position and timing of the base stations may be calibrated in response thereto.

To provide a method for a mobile station user to prevent it from being used for base station location, mobile station calibration software can determine whether it is authorized to transmit calibration information. If not authorized, the operation is exited at any time prior to the transmission of the calibration information, otherwise the operation is completed. For example, a user of a calibration-enabled mobile phone may utilize a BTS calibration program to generate security settings to indicate authorization to provide calibration information, and the step of determining whether the mobile station is authorized to communicate calibration information further comprises verifying the security settings to verify that the mobile station is authorized to provide calibration information.

Calibration information may be requested by the BTS calibration server or by the mobile station, which is triggered upon the occurrence of a particular event. For example, the calibration request may be initiated by the BTS calibration software when communicating with the target base station. As another example, the BTSCS may select a target base station, and the BTS calibration server requests calibration information from at least one of software-enabled mobile stations (software-enabled mobile stations) in communication with the target base station. In yet another example, the BTSCS can provide the identity of the target base station to the mobile station for processing by BTS calibration software.

The location of the mobile station is determined by any suitable method. For example, if the mobile station has a global satellite receiver, the location of the mobile station may be determined by signals the mobile station receives from global satellites. Alternatively, or in addition to GPS, the position of a mobile station may be determined by Advanced Forward Link Trilateration (AFLT) of each mobile station from base stations with accurately known positions. A mobile station may comprise a hybrid telephone handset including a global satellite receiver, a location of the mobile station may be determined from signals received by the mobile station from global satellites, and a time difference of arrival, time of arrival, or round trip delay system may be used to determine the location of the base station from the location of the mobile station.

Various embodiments are disclosed. The mobile station may comprise a hybrid telephone handset including a global satellite receiver. The location of the mobile station may be determined by signals received by the mobile station from global satellites and/or the base station comprises at least one wireless LAN (local area network) base station and/or the location of the wireless LAN base station may be determined from the location of the mobile station communicating with the wireless LAN base station using wireless LAN signals (e.g., a WiFi access point).

Drawings

For a more complete understanding, reference is now made to the following detailed description of embodiments as illustrated in the accompanying drawings, in which:

FIG. 1 is a perspective view of a plurality of cellular base stations, GPS satellites, and a user holding a wireless mobile device such as a cell phone;

FIG. 2 is a block diagram of one example of fixed components residing in the cellular network shown in FIG. 1;

FIG. 3 is a block diagram of one embodiment of a mobile device incorporating a communication and position location system;

FIG. 4 is a diagram of a BTS calibration routine illustrating features of one embodiment;

FIG. 5 is a flow chart of an operation of calibrating a position of a base station;

FIG. 6 is a flow diagram of an example mobile device initiated calibration process; and

fig. 7 is a flow chart of an example mobile-terminated calibration process that differs from fig. 6 in that the request originates from the BTSCS.

Detailed Description

In the drawings, the same reference numerals are used to designate the same or similar elements.

Glossary of terms and abbreviations

The following terms and abbreviations are used in the detailed description:

AFLT (advanced forward link trilateration): a technique implemented in a CDMA system calculates the position of a Mobile Station (MS) by the time difference of arrival of radio signals from base stations measured by the mobile station.

BSA (base station almanac): an almanac that includes location information and time correction information (among other information) for one or more base stations.

BSA message: the BSA message (e.g., the provide base station almanac message of the IS-801-1 protocol) includes fields that describe the BTS, including its position and time correction values (among other information). The BSA message is typically sent to the MS upon request by the MS.

BTS (base transceiver subsystem): (a/k/a base station or cell site): a fixed-location station includes a transmitter and a receiver (transceiver) for communicating with mobile stations. Including antennas for transmitting and receiving wireless communication signals from mobile stations.

BTSCS (BTS calibration server): a server is connected to a network of base stations (base stations of BTSs). BTSCS provides services related to calibrating base station location and timing using one or more mobile phones in communication with the base station.

CDMA (code division multiple access): a high-capacity digital wireless technology is provided, which is composed of QUALCOMM^TMIncorporated pioneers and commercial developments.

Calibration enabled mobile station: a mobile station having an installed, operational BTS calibration program.

Honeycomb type: one type of communication service, in which an MS communicates with one or more base stations in a cellular network, each base station being in a different wireless wide area network or wireless local area network "cell" that covers a relatively small area. As the MS moves from one cell to another, there is a "hand-off" from cell to cell. "cellular" is used herein in its broadest sense to include at least digital and/or analog systems.

GPS fixed point: the final result of the process of satellite measurements and subsequent calculations, from which the position of the MS (GPS user) is determined.

GPS (global positioning system): although the term GPS is commonly used to refer to the United states Global positioning System, the meaning of this term includes other satellite-based global positioning systems, such as the Russian Glonass system and the planned European Galileo system.

GSM (global system for mobile): a widely used digital wireless communication technology.

MS (mobile station): a portable electronic device, such as a cell phone, PDA, or laptop computer, having means (e.g., a modem) for communicating with one or more base stations. For example, it is sometimes referred to as a mobile handheld unit, portable device, mobile device, handheld device, personal station, wireless device, subscriber unit, mobile terminal, or user terminal. The MS referenced in this disclosure has position determination capabilities.

MTSO (mobile telephone switching office): control and commands are provided to the mobile station. Connectivity is also provided to the PSTN.

PDE (position determination entity): a system resource (e.g., a server), typically in a CDMA network, that works in conjunction with one or more GPS reference receivers, is capable of exchanging location information with an MS. For example, in an MS-assisted a-GPS session, the PDE may send GPS and/or cellular assistance data to the MS to enhance the satellite and base station pseudorange signal acquisition process. The MS returns the pseudorange measurements to the PDE, which is then able to calculate the position of the MS. Alternatively, in an MS-based A-GPS session, the MS sends the computed position results back to the PDE. The PDE may also provide assistance data regarding other network-connected entities, such as identification information, location information, and types of wireless base stations (access points) that may be in the vicinity of the MS.

PSTN (public switched telephone network): providing connectivity to wired telephones in homes and stores, for example.

RSSI (received signal strength indicator): a parameter indicative of the radio signal strength between the base station and the mobile station.

RTD (round trip delay): a method of measuring distance by measuring the two-way travel time (distance) between a base station and a mobile station, for example, the base station sends a signal to the mobile station which returns to the base station, and the base station then measures the time between transmitting the signal and receiving the return signal, which can then be divided by 2 to provide an indication of the distance between the base station and the mobile station. Alternatively, the RTD may be measured by the mobile station.

QoS (quality of service): a measure of a desired service parameter, such as the accuracy of the position location information.

SV (satellite): one of the main elements of the global positioning system is the set of SVs orbiting the earth, broadcasting uniquely identifiable signals.

TDOA (time difference of arrival): a system for measuring distance by measuring the relative time of arrival of radio signals from base stations; for example, in a CDMA network, AFLT systems provide PPM measurements using TDOA, with time differences of arrival indicated by pilot phase measurements relative to a reference pilot used to set the mobile station timing. Another example of a TDOA system is the uplink TDOA system, which uses the time difference between mobile station signal transmission and base station reception.

TOA (time of arrival): a system for measuring the time of arrival of a unidirectional signal; such as a GPS system that measures the time of arrival of satellite signals.

WLAN (wireless local area network): a limited range wireless communication network; examples include WiFi, WiMAX, Bluetooth (Bluetooth), etc.

Determining base station location using mobile station

U.S. patent publication US2003/0125046Al entitled "Use of Mobile Stations for Determination of Base station location Parameters in a Wireless Mobile Communication System," published 3/7/2003, discloses a System in which a network uses known locations of one or more Mobile Stations to verify, update and/or determine the location of a Base station, and which publication is assigned to the same assignee as the present application. For example, the publication discloses a method that enables AFLT-enabled wireless handsets to provide a Pilot Phase Measurement (PPM) to the network that can be used to determine base station positions and associated forward link calibration parameters. For example, to address the issue of base station location, an algorithm would require PPMs for the base stations measured by at least three different geographically separated mobile devices, each located at a known location; knowledge of the location of the mobile station can be determined via GPS. An alternative approach is to manually survey the base station antenna and use the GPS fix to calculate the error of the PPM measurements by calibrating the handset collection measurements with a dedicated base station in the area in close proximity to the base station.

In particular, the system disclosed in publication US2003/0125046A1 describes methods that use a mobile station in communication with a base station to determine location parameters of the base station. For example, the location of the mobile station is determined, and then the location of the base station is determined from the location of the mobile station and the signals transmitted between the base station and the mobile station. Despite erroneous base station location parameters of at least one of the base stations, the position of the mobile station can often be accurately determined from base station location parameters of other base stations, or from global satellite signals received by the mobile station when the mobile station is equipped with a global satellite receiver.

In addition, whenever the location of a mobile station is determined independently of the location of the base station with which the mobile station is communicating, the base station location information in the database may be checked during normal position location sessions. This may be accomplished by determining the distance between the base station and the mobile station from signals transmitted between the base station and the mobile station. When this distance is inconsistent with the base station location information in the database, the database may be modified to include corrected base station location information. In this way, erroneous base station information may be discovered before the correct location of the base station becomes known, and its use for position location services interrupted.

Once a sufficient number of independent distances are determined between the base station and mobile stations having known locations, erroneous base station location information may be automatically corrected. With a sufficient number of independent distance measurements, the base station position can be determined with a degree of certainty comparable to the position of a single mobile station. In this way, base station location information in the database may be automatically maintained and improved. This can be done while providing conventional position location services without any modification to the communication protocol between the base station and the mobile station.

What is needed is a practical system and apparatus that can bring these base station location concepts into widespread use while making the solution economically viable.

SUMMARY

The position location system described herein utilizes information from calibration-enabled mobile stations to determine the position of the base station and update the base station almanac on-the-fly. This system is useful for a number of reasons: for example, handset-based information can be utilized to shorten the time for new base station business services and provide immediate improvements in location performance. Advantageously, the system can be implemented without hardware modifications and with very little modification to the basic subscriber service elements; providing this network preparation and improvement capability requires only very little cost.

Each handset that is part of the system communicates with and responds to the calibration server using a calibration program. The calibration program may be, for example, BREW, Java, or similar technology based and may be downloaded or embedded into the handset.

In one embodiment, in a CDMA system, to calibrate or recalibrate a base station, GPS and AFLT position measurement data may be obtained from a mobile station and then sent to the BTSCS during a conventional position location session (such as when the mobile station user is normally engaged in a telephone call), or when a regional service person drives to a selected location and places a call in order to obtain position measurement data that was not otherwise obtained from the conventional position location session. In this way, the BTSCS may then use this information to internally calculate calibration data and continuously store the calibration data in the base station almanac database. Additionally, to alleviate any privacy concerns, a conventional position location session may occur only when a user of a location-enabled mobile station places or answers a wireless telephone call. In this case, the CDMA system does not determine the location of the user without the user's knowledge and consent. In another example, a user of a mobile station (handset) authorizes the use of the mobile station as a calibration device, allowing the BTSCS to request calibration information from the device.

Description of the invention

Fig. 1 is a perspective view of a wireless communication network 10, the wireless communication network 10 comprising: a plurality of wide area network base stations 10 including first, second and third base stations 10a, 10b and 10c, respectively; a plurality of local area network base stations (access points) 20 including first and second base stations 20a, 20b, respectively; GPS satellites collectively shown at 11; and a plurality of mobile stations 14 including first, second, third and fourth mobile stations 14a, 14b, 14c and 14d, respectively. Fig. 1 is for illustrative purposes, it being understood that in an actual implementation, additional (or fewer) base stations and MSs may operate at any time.

In one embodiment, Satellites (SVs) 11 include any set of satellites used to position a satellite receiver. In the GPS system, the satellites transmit off-the-air GPS signals 12, which off-the-air GPS signals 12 are time-synchronized with the GPS system, are generated at a predetermined frequency, and have a predetermined format. The GPS reference receiver may be physically located in any of the base stations 10, which may communicate with the PDE18 to provide useful information in determining position using satellites, such as GPS satellite navigation data, differential corrections, and GPS system time.

The MS may be in the form of an electronic device (not shown) held by the user, for example the user may be walking, as shown, or may be traveling in a car or on a public transport. Each MS 14 (as described in more detail with reference to fig. 3) includes a position location system 27. The position location system may include a GPS system that utilizes GPS signals to determine the position of the MS, and/or it may include an AFLT system. The MS also includes a two-way communication system 32, such as a handset receiver, which communicates with the cellular base station 10 using the two-way communication signal 13. Alternatively, or in addition to the cellular communication system, the communication system in the MS may include another wireless communication system, such as WiFi, WiMAX, or bluetooth, that communicates with the access point 20 of a wireless local area network, such as an 802.11 network, using communication signals.

In general, cellular base station 10 comprises any set of cellular base stations used as part of a wireless communication network that communicates with MSs using wireless signals 13. In the example of fig. 1, the cellular base station is network connected with a cellular infrastructure network 15a, which cellular infrastructure network 15a is then network connected with other communication networks and network entities by any suitable network protocol, such as TCP/IP over the internet as appropriate, or SS7 shown as a direct connection, for example. Thus, the cellular infrastructure network 15a provides communication services between the base stations and a plurality of other communication networks, such as the public telephone system 16, the computer network 17 and any of various other entities and communication systems. The network and the network entities may be connected by a hard-wired connection or by any other suitable connection for transferring data.

The land-based cellular infrastructure network 15 typically provides communication services that allow a handset user to connect to another telephone using the telephone system 16; however, cellular base stations may also be used for communication with other devices and/or for other communication purposes, such as an internet connection with a handheld Personal Digital Assistant (PDA) or a laptop computer. In one embodiment, the cellular base station 10 is part of a CDMA communications network; however, in other embodiments, the cellular base station may utilize other types of access technologies (e.g., GSM, WCDMA, TDMA, OFDM, etc.).

In addition to the cellular base stations 10a, 10b and 10c, other types of base stations, such as wireless access points, may be implemented using any suitable protocol, such as WiFi, WiMAX and bluetooth. As shown in fig. 1, the access points 20a and 20b (collectively referred to as 20) are network connected to a network 15b suitable for the particular implementation of the wireless access point. Similar to the cellular infrastructure network 15a, the wireless access point network 15b connects to other communication networks and physical networks through any suitable network protocol, such as TCP/IP over the internet as appropriate, or SS7, shown as a direct connection, for example. Thus, the wireless access point network 15b provides communication services between the wireless access point and a plurality of other communication networks, such as the public telephone system 16, the computer network 17, and any of various other entities and communication systems. The network and the network entities may be connected by a hard-wired connection or by any other suitable connection for transferring data.

The network also includes a Position Determination Entity (PDE)18, shown connected to the cellular infrastructure network 15. For example, for the a-GPS approach, the PDE includes system resources (e.g., servers) typically located within the network, operating in conjunction with one or more GPS reference receivers on the ground, which are capable of exchanging GPS-related information with the MS. In an MS-assisted a-GPS session, the PDE may send GPS assistance data to the MS to enhance the satellite signal acquisition process. The MS returns pseudorange measurements to the PDE, which can then calculate the position of the MS. Alternatively, in an MS-based A-GPS session, the MS sends the computed position results back to the PDE. In yet another example, in autonomous mode, the MS may determine its location without any assistance from a server. In another example, the PDE may be connected to the wireless access point network 20.

Also part of the cellular network is a BTS calibration server 19 (BTSCS). BTSCS is a system resource connected to a cellular infrastructure network and may operate in conjunction with PDE18, as described herein, or may be implemented in part or in whole in the PDE in certain embodiments. BTSCS uses one or more mobile stations in communication with one or more base stations to provide services related to calibration of the base stations, as described herein. In one embodiment, BTSCS is a dedicated server for BTS calibration purposes and is not associated with E-911 services. Similarly, the BTSCS may be part of, or connected to, a wireless access point network. In this case, BTSCS supports calibration of the base stations (access points) of the local area network. In another example, one BTSCS may serve both a cellular network and a wireless access point network.

Fig. 2 is a block diagram of one example of fixed components residing in the cellular network shown in fig. 1. A Mobile Switching Center (MSC)21 performs switching functions (i.e., circuit-switched voice and data routing) for mobile stations within its coverage area. A Mobile Switching Center (MSC)21 interfaces voice signals and telecommunications data between the base station 10 and a plurality of telephone lines 22, such as copper wires or optical fibers. A Mobile Positioning Center (MPC) 23 is connected to a Mobile Switching Center (MSC) 21. The Packet Data Serving Node (PDSN) 24 and/or interworking function (IWF) connected to the MSC 21 are primarily responsible for the establishment, maintenance and termination of packet-switched data sessions for mobile stations in the cellular network. The MPC 23 manages the position location application and interfaces the location data to an external location services client or external data network through a data network link 25. In the simplest form, a Position Determining Entity (PDE)18 collects and formats satellite reference data. The PDE18 provides wireless assistance to the mobile station and performs position calculations in the MS-assisted mode. The BTSCS19 provides services related to calibration of base station location using one or more mobile phones in communication with one or more base stations, as described in more detail herein. The PDE18 and BTSCS19 are connected to the MPC 23 and MSC 21, and also to the IWF/PDSN 24. In the example of packet switched mode, the PDE18 and BTSCS19 are connected to the IWF/PDSN 24 through an IP network 28. PDE18 and BTSCS19 access base station almanac database 27 managed by base station almanac database server 26. The PDE18, BTSCS19, and base station almanac database server 26 are implemented, for example, using conventional digital computers or workstations. The base station almanac 27 is stored in any suitable location, such as in the hard disk of a computer for the base station almanac database server 26.

Mobile station

Fig. 3 is a block diagram of one embodiment of a mobile station 14 incorporating a communication and position location system. The primary elements in this embodiment include one or more two-way communication systems 32, a position location system 34, an MS control system 35, and a user interface 36. For the sake of a brief description, communication system 32 may be discussed as a single system in a cellular scenario as an example, it being understood that the basic structure may be repeated for any other wireless communication system that may be implemented in a mobile station (e.g., WiFi, WiMAX, bluetooth) where appropriate. The example shown also does not preclude implementing multiple wireless communication systems with different levels of integration, whereby the microprocessor, baseband processor, and RF front end may be shared or integrated on a single chip.

The cellular communication system 32 is connected to a cellular antenna 31 which communicates with the base station using bidirectional radio signals 13. It is important to note that the wireless signals 13 need not be bi-directional to support positioning. The cellular communication system 32 includes any suitable means, such as a modem 33, as well as other hardware and software for communicating with base stations and/or detecting signals 13 from base stations. The cellular communication system 32 also includes appropriate hardware and software for processing transmitted and received information.

Position locating system 34 (FIG. 3) includes any suitable position locating system; for example, it may comprise a WAN TDOA system such as AFLT, a satellite positioning system such as a GPS receiver, or a hybrid GPS/AFLT system. In the hybrid system embodiment shown in fig. 3, the position location system 34 includes: antennas 31 and 38 which receive cellular signals 13 and GPS signals 12, respectively, a GPS receiver 39, a LAN positioning system 40a, a WAN TDOA system 40b, and any suitable hardware and software for receiving and processing GPS, cellular, and wireless LAN signals and for performing any necessary or useful calculations to determine position using any suitable position location algorithm.

GPS positioning: the mobile station can also locate its position using well-known GPS techniques with the aid of system resources, such as the PDE 18. For example, in a CDMA system, each base station 10 may have a GPS receiver that receives a pseudorandom code sequence of at least one of a carrier wave and a GPS satellite that provides system time base that is referenced to GPS system time. When the mobile station is engaged in a position location session using a CDMA network, the serving base station may provide an accurate GPS time reference and send GPS acquisition data to the hybrid mobile station. The mobile station may use the GPS time and GPS acquisition data to obtain measurements of pseudoranges between each GPS satellite and the mobile station. In the case of MS-assisted solutions, the mobile station transmits pseudorange measurements to the serving base station. The PDE may be used to assist the MS in calculating the geographic position of the mobile station based on three or more of the pseudorange measurements. Alternatively, in the case of an MS-based solution, the geographical location of the mobile station may be calculated by the mobile station itself.

AFLT positioning: the CDMA network can measure the relative times of arrival of so-called pilot radio signals from base stations to locate the position of the mobile station 14 using the well-known mobile station tdoa (aflt) technique. The time difference of arrival is indicated by a pilot phase measurement relative to a reference pilot used to set the timing of the mobile station. In most cases, each difference locates the mobile station on a particular hyperbola. The intersection of the hyperbolas provides an estimate of the location of the mobile station.

Specifically, in one embodiment of the AFLT system, pilot phase measurements are calculated for all base stations that can be heard by the handset during a position fix. The base stations are typically at least three or more base stations depending on the environment, and in dense urban environments, often as many as twenty or more base stations. Thus, each positioning event may result in a number of relative distance estimates, at least some of which may be used in the calibration process described herein.

Positioning operation: to determine the position of a mobile station with the assistance of a PDE, the PDE may compute a final position using any of several methods, sequentially or in parallel, and select the method that is most likely to achieve the smallest position error. In one embodiment, the GPS fix is attempted first, as the desired accuracy is better than any other method. If the GPS-only fix fails (in one example, the GPS fix does not meet the selected QoS), the PDE selects from among several other methods and uses the result with the smallest association error estimate. These other methods include (for example): AFLT only; enhanced cell ID, where location is determined by knowing the sector orientation, received signal strength, and approximate range using RTD measurements (when available); "hybrid cell sector" positioning, determined using knowledge of the sectors seen by the mobile device and the location and orientation of each sector; current serving sector coverage area barycentric location determination (or, if the current serving sector cannot be determined, the initial serving sector); the center of gravity position of the current network ID/system ID coverage area; and finally a default position stored in the PDE profile. In the example of a wireless local area network, similar techniques can be applied whereby relative and absolute distance measurements, signal travel times, signal strength measurements, identification and/or address of access points, and coverage information thereof can all be used to determine an estimate of the location of a mobile station.

Calibration of the base station: in TDOA and TOA systems, base station timing should be calibrated when a base station is installed or modified, or periodically. In a CDMA system, each base station has a respective time offset between GPS system time and CDMA system time transmitted with CDMA signals due to variations in propagation delay or phase shift from the GPS antenna to the GPS receiver, from the GPS receiver to the CDMA transceiver, and from the CDMA transceiver to the CDMA antenna. Therefore, to reduce wireless ranging errors, each base station should be calibrated after completion of the base station installation by, for example, storing the base station's time offset in the base station almanac database 27 for use by the PDE 18. The base station needs to be recalibrated and the database updated for any subsequent hardware changes. In addition, because the base stations may be physically moved, or assigned a different identifier, it may be important to periodically or even continuously recalibrate the location information associated with each base station.

A mobile device control system: the mobile device control system 35 is connected to the two-way communication system 32 and the position location system 34. The mobile device control system 35 includes any suitable structure, such as a microprocessor, memory, other hardware, firmware, and software to provide the appropriate control functions for the system to which it is connected. It should be appreciated that the process steps described herein are implemented in any suitable manner using one or more of hardware, software, and firmware under microprocessor control.

The control system 35 is also connected to a user interface 36, which includes any suitable components for interfacing with a user, such as a keypad, a microphone/speaker for voice communication services, and a display, such as a backlit LCD display. A mobile device control system 35 and a user interface 36 connected to the position location system 34 and the two-way communication system 32 provide operational functions such as controlling user input/output and displaying results.

The MS 14 may include one or more external interfaces 41 for connecting with other devices. For example, a USB or IEEE 1394 port may be provided, or a wireless port (e.g., bluetooth, USB, infrared) may be included for interfacing and communicating with other electronic devices.

The software application program: a number of software applications may be stored in the MS 14 and connected to the MS control system 35 to run using the microprocessor and the code found therein. The software application is based on any suitable platform, such as BREW, Java, or other technology. The software application is stored in any suitable memory, such as a disk drive, SIM card, flash memory, RAM, firmware, or Read Only Memory (ROM).

BTS calibration program 37: the BTS calibration program 37 is included in the software application. The BTS calibration procedure comprises code adapted to perform the operations described herein (e.g., with reference to fig. 4 and 5) to allow a group of mobile stations to be used for calibration purposes in a controlled manner. For example, calibration program 37 may run in the background without active participation by the user and without identifying the user. The BTS calibration program resides anywhere that is accessible by the microprocessor, e.g., the program may be embedded in firmware or software stored in memory, or may be downloaded from a remote application server connected to the base station, for example. But may also be implemented at least partially in hardware, for example, in a computer chip.

Fig. 4 is a conceptual diagram of a BTS calibration procedure illustrating features that may be implemented in the procedure. In general, one purpose of the BTS calibration procedure described herein is to provide a mechanism that takes advantage of position measurements made at a mobile station that is used as a calibration tool to determine and calibrate the position and time reference of one or more base stations. The BTS calibration program is installed in the mobile station and performs the operations described herein.

Install in MS (42): specifically, as shown at 42, the BTS calibration program is typically installed in the mobile station as software. The BTS calibration program may be a downloadable software program and/or it may include firmware embedded or programmed into a handset or any other suitable system for storing instructions. Although BTS calibration procedures typically use pre-existing systems in the handset, such as a position location system, in certain embodiments, additional hardware features may be useful or necessary for efficient operation.

Immediate operation, may operate in the background (43): once installed, the BTS calibration program may operate on-the-fly, as shown at 43, under the control of the user discussed below. Furthermore, the calibration procedure may operate in the background whenever the mobile station is powered up, in view of privacy concerns (such as discussed below), and thus, in such embodiments, the user is not aware of its operation. For example, the user may make a call and download other information when performing calibration.

Incentive plan (44): in one embodiment, the user may be registered in an incentive programme as shown at 44. For example, a user who authorizes a BTSCS or mobile service manager such as MPC to utilize a mobile device for base station calibration may be granted financial credits or other financial compensation, credits for future services, or additional services in exchange to allow the BTSCS to use location-related information provided by the mobile station. Any suitable basis for compensation may be configured: for example, the user may be compensated on a per-use basis, a per-session basis, or a flat rate basis.

Privacy issues (45, 46, 47): it is expected (although not required) that the BTS calibration procedure prevents unrestricted access by the BTSCS; specifically, access may be restricted as shown at 45. Features may be implemented that allow the handset to be used for calibration purposes only in a controlled, secure manner as shown at 46 and with the user's consent as shown at 47. This consent may be obtained in any suitable manner, for example, it may be pre-authorized and once authorized, the location determination may be done in the background without active participation by the handset user. Pre-authorization may be obtained, for example, over a particular period of time (e.g., 10 or 30 days), or only for a particular session (or sessions), or when a user subscribes to a service.

Authorization may be implemented in any of a variety of ways: generally, there is some secret information (settings) stored in the mobile station and/or a private proxy server residing in the network of the service provider that indicates the user's willingness to allow the mobile station to be used as a calibration device through the network. This information may also indicate rules that may be used to reveal user identity and location information. For example, the user may wish to be informed of each instance that the BTSCS or any other entity requests location-related information. For example, a privacy flag may be set in software or hardware, and the user will change the flag via any suitable interface (e.g., select via a drop down menu) depending on whether authorization is provided. In another example, the secret information may indicate allowable frequencies, durations, and/or times when the mobile device may be used as a calibration tool.

To address privacy concerns, the calibration program may run in a secure manner in the background to prevent unauthorized interception. One goal of the secure operation as shown at 46 is to avoid revealing the identity of the handset user, and in particular to avoid associating the user with a location when the handset is used for calibration purposes. For these purposes, the calibration procedure may disable transmission of the handset user's identity, the mobile station's electronic identity, to the BTSCS, and any other identifying information (non-position location information) to the BTSCS. Alternatively, the information may be encrypted using any suitable encryption system.

Communicating with BTSCS (48): the BTS calibration program also communicates with the BTSCS19, as shown at 48. For example, a calibration-enabled mobile station (a mobile station with an operational BTS calibration procedure is referred to as "calibration-enabled") may communicate with a base station connected to a BTSCS network; thus, the calibration procedure communicates with the network-connected BTSCS via the cellular communication system of the mobile station. For example, the calibration procedure may initiate a mobile-originated call flow (as described in more detail with reference to fig. 6) to report the required information to the BTSCS for BTS calibration. Alternatively, as described in more detail with reference to fig. 7, the calibration procedure may be responsive to a network-initiated (mobile-terminated) call flow from the BTSCS and report the requested calibration information back to the network. The BTSCS may then store calibration measurements associated with location (in CDMA networks, these would include base station PN codes and pilot phase residuals) for post-processing.

Interfacing with a position location system (49): the BTS calibration program 19, as shown at 49, may interface with the position location system 34 via the mobile device control system 35 (fig. 3). For example, a BTS calibration procedure in the mobile station may request calibration information (such as PPM and other position related measurements) from the position location system and then provide it to the BTSCS for post-processing. If the requested calibration information is not available or is not acceptable, for reasons such as poor quality of service (QoS), the BTS calibration procedure may request the position location system to determine the position of the mobile station and may also request the position location system to take Pilot Phase Measurements (PPMs) (residuals) associated with at least one base station. For time savings, the BTS calibration procedure may request PPM measurements from only one or more target base stations specified by the BTSCS, rather than all base stations in range of the mobile station. In selecting PPM measurements, the calibration procedure may select only robust (direct) PPMs that are better suited for accurate base station positioning and calibration. To select a good desired PPM, the QoS may be set to a desired accuracy threshold (e.g., meters), or set according to other parameters such as signal strength, power, SNR, SIR, etc.

Fig. 5 is a flowchart of an operation of calibrating a position of a base station.

At 50, a set of mobile stations is programmed with a BTS calibration program. Each of these mobile stations is referred to as a "calibration-enabled" mobile station.

At 51, communication is established between a target base station, such as may be selected by BTSCS, and at least one of the calibration enabled mobile stations. It should be noted that at any time, there may be more than one calibration-enabled mobile station within the coverage area of the target base station, and the operations of fig. 5 may be repeated in each of these calibration-enabled mobile stations. Furthermore, it should be noted that the exact time at which the calibration information is provided is not related to the location of the base station; thus, a moving mobile station may be used multiple times at different locations to provide calibration information at each of the multiple locations. Information from multiple geographically distinct locations is useful for determining the location of a base station.

At 52, calibration information is requested. The request may be generated in any of a variety of ways; the calibration information may be requested by BTSCS19, for example, or may be requested by a BTS calibration program. For example, the BTS calibration program may be programmed to transmit calibration information when certain events occur. For example, one such specific event may be associated with a mobile station communicating with a target base station or responding to an unrelated positioning event while communicating with the target base station. The calibration information may be related to a particular target base station that may be selected (provided to the mobile station) by the BTSCS, the calibration information may be related to one or more target base stations, or the calibration information may be related to all mobile stations within range of a particular base station, or the calibration information may be related to mobile stations that meet a particular criteria (e.g., may be predetermined or established by the BTSCS).

At 53, the secret information is checked to determine whether the mobile station is authorized to transmit calibration information. This step may take various forms; for example, the security token may be verified by a calibration procedure before beginning communication with the BTSCS. In one example, the privacy flag may be set in software or hardware, and the user will change the flag via any suitable interface (e.g., selecting via a drop down menu) depending on whether authorization has been provided.

At 53a, if authorization is not given, then operation is exited as shown at 53b, and communication of calibration information with the BTSCS or network is not allowed. If, however, authorization is given, then operation proceeds to the next step 54.

At 54, the location of the mobile station is determined. This information may already be available if a location measurement has been made recently; if not, the BTS calibration program requests the mobile station to determine its position by any suitable method, such as through a satellite, a cellular network, a local area network, or a combination thereof.

At 55, in the CDMA network, PPM from at least one base station to a mobile station is determined. This phase shift information may already be available if the PPM measurements have been used recently for position measurements; if not, the BTS calibration program requests the mobile station to determine this information. To save time, the BTS calibration procedure may only request PPM measurements from one or more target base stations specified by BTSCS, rather than all base stations in range of the mobile station. In selecting PPM measurements, the calibration procedure may select only the stronger (direct) PPMs, which are better suited for accurate base station positioning and calibration. To select a good PPM, the QoS may be set to a desired accuracy threshold (e.g., meters) or set according to other parameters such as signal strength, power, SNR, SIR, etc. To ensure that the position information corresponds exactly to the PPM measurements, the PPM measurements should be made close in time if not at the same time as the position fix. In the MS-assisted mode, position information may be determined by the PDE.

At 56, calibration information is transmitted from the mobile station to the BTSCS. In a CDMA network, this calibration information includes at least the mobile station's location information, PN code, and PPM measurements from one or more base stations, which can be used to determine the range from the target base station to the mobile station. In the MS-assisted mode, calibration information may be transmitted from the PDE to the BTSCS.

At 57, in response to the calibration information, the distance from the mobile station to the base station is calculated. The position of the target base station may also be calculated if multiple mobile stations are providing calibration information and/or if multiple positions have been reported by a single mobile station. In general, once a sufficient number of measurements have been received or accumulated over time and on the device, the location and/or timing information for the base station may be determined.

At 58, the base station almanac is consulted for location information of the base station whose distance and/or location from the mobile station has been calculated in the previous step 57. The almanac information is then checked for consistency with the calculated information. A consistency check may be performed for a particular target base station.

At 59, the base station location in the base station almanac may be updated in response to a correspondence between the almanac and the calculated information. Whether it is actually updated depends on many factors and the almanac information will not typically be updated without a high degree of assurance of accuracy, for example, by multiple consistent measurements over a period of time and/or the distances and/or locations of base stations to calibration-enabled mobile stations calculated from many different mobile stations.

Finally, it should be noted that BTS location and calibration can be an immediate process as long as there is a handset reporting calibration measurements. It should also be appreciated that steps 56 and 57 may be performed in a mobile station that enables calibration, whereby the calibration information transmitted to the BTSCS may also include errors in the distance measurements from the mobile station to the target base station.

Fig. 6 is a flow chart of an example of a mobile-initiated MS-based (or autonomous) calibration procedure. In one example, once the calibration procedure determines that the target base station is in the base station neighbor list, the mobile station may initiate a mobile-initiated calibration procedure. The mobile station initiates communication at 61 and then establishes two-way communication at 62. At 63, the MS queries the BTSCS whether calibration information can be provided, and if the BTSCS sends its ready signal, the location of the MS is determined and a calibration (PPM) measurement is made at 64. At 65, the MS location information is transmitted to the BTSCS, and at 66, the calibration (PPM) measurements are transmitted to the BTSCS. At 68, communication between the MS and the base station 10 is closed, which is particularly useful in the case where a private base station calibration session is established for the purpose of sending calibration information, and which is now satisfied.

Fig. 7 is a flow chart of an example of a mobile terminated MS-based (or autonomous) calibration process that differs from fig. 6 in that the calibration request is initiated in the BTSCS. At 71, two-way communication is established. At 72, the BTSCS19 requests calibration information from the MS 14. At 73, the position of the MS is determined and a PPM measurement is made. At 74, MS location information is transmitted to the BTSCS, and at 75, PPM measurements are transmitted to the BTSCS. In one example, steps 74 and 75 may be combined. At 76, communication between the MS and the base station 10 is closed, which may be useful where a dedicated connection is established, for example for calibration purposes.

Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.

Claims (38)

1. A method of maintaining accurate base station location information in a wireless communication system, comprising:

receiving, at a mobile station, a request to report location calibration information associated with at least one base station to a base station location calibration server, the requested location calibration information comprising at least one location estimate for the mobile station and information indicative of a range of the mobile station to the at least one base station;

determining location information sufficient to calculate the location estimate for the mobile station;

determining information indicative of a distance of the mobile station to the at least one base station;

and sending the requested position calibration information to the base station position calibration server.

2. The method of claim 1, further comprising:

determining whether the mobile station is authorized to send the requested calibration information to the base station location calibration server,

wherein the transmitting step is performed if the mobile station is authorized.

3. The method of claim 1, wherein the receiving step receives the request from a calibration procedure executing on the mobile station.

4. The method of claim 3, wherein the calibration procedure generates the request in response to a detected event.

5. The method of claim 4, wherein the detected event corresponds to a mobile station communicating with the at least one base station.

6. The method of claim 1, wherein the receiving step receives the request from a calibration server at the base station.

7. The method of claim 1, wherein the at least one base station comprises a currently serving base station of the mobile station.

8. The method of claim 1, wherein the at least one base station comprises each base station detected at the mobile station.

9. The method of claim 1, wherein a Position Determination Entity (PDE) assists the mobile station in determining the position estimate.

10. The method of claim 1, wherein the mobile station determines the position estimate without assistance from a Position Determination Entity (PDE).

11. The method of claim 1 wherein the base station position calibration server is separate from a Position Determination Entity (PDE) configured to assist mobile stations in determining their positions.

12. The method of claim 1, wherein determining the location estimate of the mobile station is based on a Wide Area Network (WAN) time difference of arrival (TDOA) protocol, a Satellite Positioning System (SPS) protocol, or a hybrid system.

13. A method as recited in claim 12, wherein the WAN TDOA protocol corresponds to an advanced forward link trilateration, AFLT, protocol, an SPS protocol corresponds to a global positioning system, GPS, protocol, and the hybrid system corresponds to a hybrid GPS/AFLT protocol.

14. The method of claim 1, wherein the mobile station comprises a hybrid telephone handset comprising a global satellite receiver, the location of the mobile station is determined from signals received by the mobile station from global satellites, the at least one base station comprises at least one wireless LAN base station, and the location of the wireless LAN base station is determined from the location of the mobile station in communication with the wireless LAN base station using wireless LAN signals.

15. The method of claim 14, wherein the wireless LAN base station includes a WiFi access point.

16. The method of claim 1, wherein the information indicative of the distance of the mobile station to the at least one base station is determined based on: (i) measuring a phase shift of one or more downlink pilot signals from the at least one base station according to an advanced forward link trilateration, AFLT, protocol; (ii) measuring time of arrival (TOA) of one or more downlink signals according to a time of arrival (TOA) protocol; and/or (iii) measuring a round trip delay of one or more signals exchanged between the mobile station and the at least one base station.

17. The method of claim 1, wherein the step of transmitting comprises:

establishing a private base station calibration session with the base station location calibration server with the primary purpose of sending the requested calibration information.

18. A method of maintaining accurate base station location information in a wireless communication system, comprising:

receiving, at a base station calibration server, location calibration information associated with at least one base station, the location calibration information comprising at least one location estimate for one or more mobile stations and information indicative of distances of the one or more mobile stations to the at least one base station;

determining a location of the at least one base station based at least in part on the received location calibration information;

selectively updating a record of the location of the at least one base station in a base station almanac configured with locations of base stations in a wireless communication system based on the determined location of the at least one base station.

19. The method of claim 18, wherein the position calibration information is sent from the one or more mobile stations in response to a request initiated by a calibration procedure, the calibration procedure being performed on the one or more mobile stations.

20. The method of claim 18, further comprising:

sending a request for the position calibration information to each of the one or more mobile stations,

wherein the receiving step receives the location calibration information from the one or more mobile stations in response to the request.

21. The method of claim 20, wherein the first and second portions are selected from the group consisting of,

establishing a private base station calibration session with the one or more mobile stations with a primary purpose of receiving the requested calibration information.

22. The method of claim 18, wherein the at least one base station comprises a currently serving base station of one or more mobile stations.

23. The method of claim 22, wherein the at least one base station comprises each base station detected at the one or more mobile stations.

24. The method of claim 18, wherein the location estimate of the mobile station is based on a Wide Area Network (WAN) time difference of arrival (TDOA) protocol, a Satellite Positioning System (SPS) protocol, or a hybrid system.

25. A method as recited in claim 24, wherein the WAN TDOA protocol corresponds to an advanced forward link trilateration, AFLT, protocol, an SPS protocol corresponds to a global positioning system, GPS, protocol, and the hybrid system corresponds to a hybrid GPS/AFLT protocol.

26. The method of claim 18, wherein the information indicative of the distance of the mobile station to the at least one base station is determined based on: (i) measuring a phase shift of one or more downlink pilot signals from the at least one base station according to an advanced forward link trilateration, AFLT, protocol; (ii) measuring time of arrival (TOA) of one or more downlink signals according to a time of arrival (TOA) protocol; and/or (iii) measuring a round trip delay of one or more signals exchanged between the mobile station and the at least one base station.

27. The method of claim 18, wherein the determining step determines the location of the at least one base station based on multiple instances of the location calibration information to triangulate the location estimate for the at least one base station with multiple indications of the distance of a given mobile station from a particular geographic location to a given base station.

28. The method of claim 27, wherein the multiple instances of the position calibration information are received from (i) the same mobile station in different positions, or (ii) different mobile stations in different positions, (iii) or a combination of both.

29. The method of claim 18, wherein the step of selectively updating comprises:

comparing the determined location of the at least one base station with a previously stored location of the at least one base station in the base station almanac; and

replacing the previously stored location in the record with the determined location based at least in part on the comparing step.

30. The method of claim 18, wherein the base station position calibration server is separate from a Position Determination Entity (PDE) configured to assist a mobile station in determining its position.

31. The method of claim 18, wherein the one or more mobile stations comprise hybrid telephone handsets including global satellite receivers, the locations of the one or more mobile stations are determined from signals received by the one or more mobile stations from global satellites, the at least one base station comprises at least one wireless LAN base station, and the locations of the wireless LAN base stations are determined from the locations of the mobile stations in communication with the wireless LAN base station using wireless LAN signals.

32. The method of claim 31, wherein the wireless LAN base station includes a WiFi access point.

33. A mobile station in a wireless communication system, comprising:

means for receiving, at a mobile station, a request to report location calibration information associated with at least one base station to a base station location calibration server, the requested location calibration information comprising at least one location estimate for the mobile station, and information indicative of a range of the mobile station to the at least one base station;

means for determining location information sufficient to calculate the location estimate for the mobile station;

means for determining information indicative of a distance of the mobile station to the at least one base station;

means for sending the requested location calibration information to the base station location calibration server.

34. A base station calibration server configured to maintain accurate base station location information in a wireless communication network, the base station calibration server comprising:

means for receiving location calibration information associated with at least one base station, the location calibration information comprising at least one location estimate for one or more mobile stations and information indicative of a range of the one or more mobile stations to the at least one base station;

means for determining a location of the at least one base station based at least in part on the received location calibration information;

means for selectively updating a record of the location of the at least one base station in a base station almanac configured for the location of base stations in a wireless communication system based on the determined location of the at least one base station.

35. A mobile station in a wireless communication system, comprising:

logic configured to receive, at a mobile station, a request to report location calibration information associated with at least one base station to a base station location calibration server, the requested location calibration information comprising at least one location estimate for the mobile station, and information indicative of a range of the mobile station to the at least one base station;

logic configured to determine location information sufficient to calculate the location estimate for the mobile station;

logic configured to determine information indicative of a distance of the mobile station to the at least one base station;

logic configured to send the requested position calibration information to the base station position calibration server.

36. A base station calibration server configured to maintain accurate base station location information in a wireless communication system, the base station calibration server comprising:

logic configured to receive position calibration information associated with at least one base station, the position calibration

The information comprises at least one position estimate for one or more mobile stations and information indicative of the distance of said one or more mobile stations to said at least one base station;

logic configured to determine a location of the at least one base station based at least in part on the received location calibration information;

logic configured to selectively update a record of the location of the at least one base station in a base station almanac configured with the locations of base stations in a wireless communication system based on the determined location of the at least one base station.

37. A computer-readable storage medium comprising instructions, which, when executed by a mobile station in a wireless communication system, cause the mobile station to perform operations, the instructions comprising:

program code to receive, at a mobile station, a request to report location calibration information associated with at least one base station to a base station location calibration server, the requested location calibration information comprising at least one location estimate for the mobile station and information indicative of a range of the mobile station to the at least one base station;

program code for determining location information sufficient to calculate the location estimate for the mobile station;

program code for determining information indicative of a distance of the mobile station to the at least one base station;

program code to send the requested position calibration information to the base station position calibration server.

38. A computer-readable storage medium comprising instructions, which, when executed by a base station calibration server configured to maintain accurate base station location information in a wireless communication system, cause the base station calibration server to perform operations, the instructions comprising:

program code to receive location calibration information associated with at least one base station, the location calibration information comprising at least one location estimate for one or more mobile stations and information indicative of distances of the one or more mobile stations to the at least one base station;

program code to determine a location of the at least one base station based at least in part on the received location calibration information;

program code to selectively update a record of the location of the at least one base station in a base station almanac configured with locations of base stations in a wireless communication system based on the determined location of the at least one base station.