WO2005006593A1

WO2005006593A1 - Method and apparatus for communication of gps ephemeris

Info

Publication number: WO2005006593A1
Application number: PCT/US2004/013201
Authority: WO
Inventors: Mark Roh; Chang Row; Jeff Wong
Original assignee: Qualcomm Incorporated
Priority date: 2003-06-27
Filing date: 2004-04-30
Publication date: 2005-01-20
Also published as: EP1639723A4; JP2011047946A; JP2007521481A; CN1930791A; BRPI0411920A; KR20060065590A; MXPA05014053A; EP1639723A1

Abstract

Satellite ephemeris data associated with satellite vehicles in a Global Positioning System (GPS) based position location system can be selectively transmitted to a mobile station within a wireless communication system. The mobile station can selectively request satellite ephemeris data from a Position Determination Entity (PDE) that is in communication with one or more GPS satellite vehicles (SV). The mobile station forecasts the satellite vehicles that theoretically are available. Then, the mobile station checks to see if valid ephemeris data is locally stored. If ephemeris data is desired and not locally available, the mobile station transmits a selective ephemeris request to the PDE and receives, in response to the request, the ephemeris corresponding to the SV identified in the ephemeris request. The selective ephemeris request and selective satellite update method can be implemented in accordance with presently available position location standards.

Description

METHOD AND APPARATUS FOR COMMUNICATION OF GPS EPHEMERIS

Background Related Applications

[0001] This application claims priority to U.S. Provisional No. 60/483,209, filed on June 27, 2003.

Field

[0002] The disclosed method and apparatus relates to the field of position determination. More specifically, this disclosure relates to communication of GPS ephemeris data.

Description of the Related Art

[0003] Wireless position determination systems are used to determine the location of a device. Often, the device is a mobile or portable device that may operate firom battery power, and the device may not be tethered to any stationary location by a wired cornmunications link.

[0004] There are a number of design concerns in a wireless position determination system. Position location accuracy is, of course, one of the concerns. System sensitivity, acquisition time, and power dissipation are also design concerns that are addressed in a position determination system. Wireless position determination systems typically incorporate a trade-off of design constraints in an attempt to obtain a relative optimization of each of the system concerns.

[0005] As v ireleεα communication systems become more popular, the desire to incorporate some type of position location capability has emerged, hi a wireless communication system, such as a wireless telephone system, it may be desirable to be able to locate the position of a mobile device such as a wireless telephone handset. Indeed, in the United States, enhanced emergency wireless service having the capability of determining the location of a handset has been mandated for wireless phone providers. Wireless service providers, in conjunction with equipment manufacturers, have devised a variety of position location systems that are able to provide the location of a mobile device, such as a portable handset. [0006] A position location system that may be utilized by a mobile device maybe based on the Global Positioning System (GPS). In the Global Positioning System, there are approximately twenty-four satellites that orbit the earth. Each of the satellites transmits a carrier frequency that is modulated with a pseudo random noise (PRN) code sequence. The PRN code that is commonly used by civilian-based GPS receivers is termed the Coarse Acquisition (C/A) code. Each satellite transmits a different PRN code. In the GPS, a GPS receiver receives the signals from multiple satellites and determines the distance from each satellite in order to trilaterate the position of the receiving device. [0007] The satellite orbits can be generally determined using a predictive algorithm. However, to obtain accurate position location using GPS, accurate satellite location is desired. The GPS satellites transmit ephemeris data that accurately identifies the position of the satellite in its orbit. However, because the position of the satellite typically varies according to a number of factors, the satellite periodically updates the ephemeris data. The satellite vehicle (SV) can update the ephemeris data each hour. However, satellite ephemeris data is typically valid for a period of approximately four hours. The ephemeris data transmitted by a SN includes a "time of ephemeris" field, and the ephemeris data is typically valid for the four hour period centered about the time of ephemeris.

[0008] The time required for GPS SNs to transmit SN ephemeris data as well as almanac data associated with SN locations can be rather lengthy. For example, the time to transmit one GPS frame having the sub-frames that contain SN ephemeris and SN almanac data can take over 12.5 minutes. A mobile device, such as a mobile station in a wireless communication system, may need to receive all SV ephemeris and almanac data prior to establishing an initial position determination. Additionally, the mobile device typically needs to identify available satellites and determine a pseudo range to each of the available satellites in order to make the initial position determination. The initial position determination can also be referred to as a first or initial fix. For a mobile station, the delay associated with receiving SN almanac and ephemeris data, plus the time required to make a position determination, may be greater than a desired time or specified maximum time.

[0009] Thus, what is desired is a method and apparatus for reducing the time for position determination in a GPS based position determination system. The method and apparatus should reduce the time required to obtain a first fix. Additionally, it would be particularly advantageous to be able to implement the method and apparatus into presently available wireless communication position determination systems in a manner that is compliant with existing standards.

Summary [0010] The disclosed method and apparatus is for selectively requesting and downloading ephemeris data based, at least in part, on availability of satellite vehicles (SNs). A mobile station can determine available SNs from a set of SNs. The mobile station can then determine if current ephemeris data associated with each of the available SNs is valid. The mobile station can then selectively request ephemeris data for those SNs for which the current ephemeris data is invalid. [0011] One aspect of the disclosed method of selectively requesting position determination data comprises determining in a mobile station a plurality of available position location signal sources and determining whether current position determination data associated with the plurality of available position location signal sources is valid. The mobile station can selectively request position determination data when the current position determination data is invalid. [0012] The method can include receiving an almanac of position determination data corresponding to the set of position location signal sources and estimating a position of each of the signal sources based on the almanac data. The mobile station can determine the available signal sources based on a predetermined elevation mask. [0013] The position location signal sources can be GPS SNs and available SNs can be , determined by determining the positions of the SNs relative to an elevation mask. The available SVs can also be determined to include SVs for which the position at a future tim eis compared to an elevation mask. [0014] The method of selectively requesting the position determination data can include generating a standard compliant message. The method can include generating a manufacturer specific Position Determination Data Message that requests satellite ephemeris data. The message can identify the satellites for which ephemeris data is requested. [0015] An aspect of the disclosed apparatus is the configuration to selectively request GPS satellite ephemeris data from a Position Detemiination Entity. The apparatus comprises an almanac that stores GPS SN almanac, an ephemeris module that stores ephemeris data corresponding to one or more GPS SNs, and an ephemeris update module that determines a plurality of available GPS SNs based at least in part on the almanac data. The ephemeris update module determines whether valid ephemeris data is stored in the ephemeris module and selectively requests ephemeris data for those GPS SNs that do not have valid ephemeris data in the ephemeris module. [0016] In another aspect, the disclosed method and apparatus is the use of a position determination entity that includes an almanac and an ephemeris module. The position determination entity also includes a position record update module that can receive a selective ephemeris request message and transmit, in response to the request, the ephemeris data for GPS satellites identified in the selective request message.

Brief Description of the Drawings [0017] The above-described aspects and other aspects, features and advantages of the disclosed method and apparatus will be apparent upon review of the following detailed description and the accompanying drawings. In the drawings, like reference characters identify identical or functionally equivalent elements.

[0018] Figure 1 is a functional block diagram of a wireless communication system with position determination capabilities.

[0019] Figure 2 is a flowchart of a method of selectively updating ephemeris data. [0020] Figure 3 is a table showing the fields in a selective ephemeris request message.

Detailed Description of the Preferred Embodiment

[0021] One embodiment of the disclosed method and apparatus updates the SN ephemeris in a mobile station thai is in communication with a wireless commumcation system. The mobile station determines a number of GPS SVs that theoretically are available for position detemiination. The mobile station determines if it has already received satellite ephemeris for the available SNs. The mobile station also determines if the satellite ephemeris is valid over a predetermined period of time. The mobile station can generate a standard compliant ephemeris request that selectively requests the ephemeris for those SNs for which no valid ephemeris data exists. The mobile station can also selectively request ephemeris for those SVs for which the ephemeris data will not be valid over the predetermined period of time. This prevents the mobile station from repeatedly downloading ephemeris data that it has already received, and prevents the mobile station from downloading ephemeris data for SVs that will likely not be available for position location.

[0022] Figure 1 is a functional block diagram of a wireless communication system 100. The wireless communication system 100 can be a wireless telephone system having position location capabilities. For example, the wireless communication system 100 can be a Code Division Multiple Access (CDMA) wireless system in accordance with Telecommunications Industry Association (TIA)/Electronics Industries Alliance (EIA)- 95-B, MOBILE STATION-BASE STATION COMPATIBILITY STANDARD FOR DUAL MODE SPREAD SPECTRUM SYSTEMS or TIA/EIA/IS-2000, including TIA/EIA/IS-2000-5, UPPER LAYER (LAYER 3) SIGNALING STANDARD FOR cdma2000 SPREAD SPECTRUM SYSTEMS. Additionally, the position location capabilities of the wireless communication system 100 can operate, for example, in accordance with TIA/EIA IS-801, POSITION DETERMINATION SERVICE STANDARDS FOR DUAL MODE SPREAD SPECTRUM SYSTEMS. Of course, although the wireless communication system 100 is described as a wireless CDMA telephone system, the wireless communication system 100 need not be a CDMA system, nor does the wireless communication system 100 need to be a telephone system. Alternative systems can include, for example, wireless position location systems, Bluetooth commumcation systems, Institute of Electrical and Electronic Engineers (IEEE) 802.11 compliant wireless networks, wireless dispatch systems, wireless radio systems, and the like, or some other means for communicating.

[0023] The wireless communication system 100 includes a Mobile Switching Center (MSC) 120 in communication with a Base Transceiver System (BTS) 110 that is in turn in communication with a mobile station 140. The MSC 120 is also in communication with a Position Determination Entity (PDE) 130. Although only one MSC 120, BTS 110, mobile station 140, end PDE 130 are shown in the system 100, a system 100 may have a plurality of each of the elements and the number of BTS 110 or mobile stations 140, for example, need not be provided in any particular ratio or numerical relationship. [0024] The mobile station 140 alternatively can be a terminal, a remote station, a user equipment (UE), an access terminal, a wireless phone, a cellular telephone, a handset, a mobile device, a mobile unit, a personal digital assistant (PDA), a computer, and the like, or some other means for communicating. The mobile station 140 need not be mobile, but can be stationary. However, the need for position location capabilities greatly diminishes for stationary terminals that are rarely repositioned. [0025] The mobile station 140 includes a transceiver 142 that can be an RF wireless transceiver. The transceiver 142 allows the mobile station 140 to receive forward link signals from the base station 110. The transceiver 142 also typically allows the mobile station to transmit reverse link signals to the base station 110. The transceiver 142 can also be configured to receive signals from a position determination system. The transceiver 142 can be, for example, configured to receive signals from GPS satellite vehicles (SVs).

[0026] The transceiver 142 typically converts the forward link signals received by the mobile station 140 to baseband signals. The baseband signals can be data, such as position location information.

[0027] A processor 152 is coupled to the transceiver 142 and can process the received data and may also perform functions associated with the transceiver 142. The processor 152 is coupled to memory 154. The processor 152 can store and access data in memory 154. The processor 154 can also operate according to processor readable instructions that are stored in memory 15 .

[0028] The mobile station 140 also includes a clock 144 that can track time relative to time standard. For example, the clock 144 can be used to track GPS time, CDMA system time, or Universal Coordinated Time (UTC). The clock 144 can be used, for example, in determining the time of arrival of a forward link signal, such as a forward link pilot signal.

[0029] The mobile station 140 also includes an almanac 146 that is a set of data that describes generally the position of the GPS SV constellation. The mobile station 140 can use the almanac information to approximate the locations of each of the GPS SV. The mobile station 140 can use the information stored in the almanac 146, along with knowledge of GPS time from the clock 144, to predict the availability of a GPS SV. Each GPS SV periodically transmits the almanac data. The mobile station 140 can receive the almanac data directly by receiving and decoding the GPS SV transmissions. However, as noted earlier, the data rate from a GPS SV may be low relative to a data rate achievable through the wireless communication system 100. Thus, the mobile station 1 0 can alternatively receive the data for the almanac 146 from the PDE 130 in the wireless commumcation system 100. For example, the mobile station 140 can download the almanac data from the PDE 130 and store it in the almanac 146. Alternatively, the almanac 146 can be implemented in memory 154 and the mobile station can store the almanac data in a predetermined portion of memory 154. [0030] The almanac 146 includes data that roughly predicts the position of each SV. Ephemeris data is used to augment the almanac data to provide an accurate determination of the position of a particular SV. The mobile station 140 includes an ephemeris module 148 coupled to the transceiver 142 and processor 152 to store the ephemeris data. Similar to the almanac data, the mobile station 140 can receive the ephemeris data directly from a GPS SV and store it in the ephemeris module 148. The ephemeris module 148 can be implemented as a portion of memory 154. [0031] Alternatively, the mobile station 140 can receive the ephemeris data from the PDE 130 via the base station 110. As will be described in further detail below, the mobile station 140 can selectively request ephemeris data for those SVs that are determined to be available. The mobile station's ability to selectively request ephemeris data minimizes the amount of ephemeris data transmitted. Additionally, the combination of the almanac 146 and ephemeris module 148 in the mobile station 140 allows the mobile station 140 to independently compute its position in instances where the mobile station 140 is outside the coverage area of a base station 110, or otherwise not in commumcation with a PDE 130.

[0032] The mobile station 140 also includes an ephemeris update module 150. The ephemeris data transmitted by the SV includes a "time of ephemeris" field, t_oe. The time of ephemeris is a time stamp that indicates a midpoint of ephemeris validity. Typically, ephemeris data is valid for four hours, although in extreme cases the ephemeris data may be valid for up to six hours. Thus, typically, the ephemeris data is valid for a period of two hours prior to the time of ephemeris and two hours following the time of ephemeris.

[0033] The ephemeris update module 150 periodically verifies the validity of the ephemeris data. For example, the ephemeris update module 150 can verify the validity of the ephemeris data at predetermined time intervals, such as every ten minutes. Alternatively, the ephemeris update module 150 can verify the validity of the ephemeris data at predetermined occurrences, such as originating or incoming telephone calls. In other embodiments, the ephemeris update module 150 can verify the validity of the ephemeris data according to an algorithm that may generate a fixed, random, or pseudorandom verification and update interval.

[0034] During the verification process, the ephemeris update module 150 accesses the data in the almanac 146 to determine which SVs are likely to be above a predetermined elevation mask. The elevation mask can be used, for example, to screen SVs that are likely unavailable. Unavailable SVs can include those SVs that are below a predicted horizon or that are very near a predicted horizon. Thus, a zero degree elevation mask can be used by the ephemeris update module 150 to determine which SVs are above a predicted horizon.

[0035] The ephemeris update module 150 may also use a predetermined independence time, which may, for example, be stored in memory 154. The independence time represents a duration for which the mobile station 140 should be able to accurately determine its location independent of assistance from the PDE 130. The independence time can be, for example, 30 minutes or 60 minutes.

[0036] The ephemeris update module 150 also determines which SVs will be above the elevation mask at a future time equal to the present time plus the independence time. Thus, the ephemeris update module determines which of the SVs are available by determining which SVs are currently above the elevation mask and which SVs will be above the elevation mask at an independence time later.

[0037] The ephemeris update module 150 accesses the ephemeris module 148 to determine if ephemeris data is available for any of the identified available SVs. If valid ephemeris data is unavailable for any of the identified SVs, the ephemeris update module 150 generates a request for the ephemeris data, which is transmitted to the PDE 130. If valid ephemeris data is available for a SV but will become invalid prior to the expiration of independence time, the ephemeris update module 150 generates a request for the ephemeris data for that SV. The ephemeris update module 150 can determine that the ephemeris data is invalid for a SN if more than 120 minutes has elapsed since the time of ephemeris associated with the data.

[0038] An embodiment of an algorithm performed by the ephemeris update module 150 can be summarized in the following pseudocode: loop over all SVs in almanac { if (ephemeris is unavailable) or (time since t_oe + PDE__IΝDEPEΝDEΝCE_TΓME > 120) { compute SV position for current time if (position above elevation mask) { set bit to request ephemeris for this SV } else { compute SV position for current time +

PDE_ΓNDEPENDENCE_TΓME if (position above elevation mask) { set bit to request ephemeris for this SV } } } }

[0039] The mobile station 140 is in communication with the base station 110. The base station 110 can be, for example, a BTS, an access point, a central dispatch, and the like, or some other centralized means for communicating. The communication link between the base station 110 and the mobile station 140 is typically a wireless link. The base station 110 transmits the ephemeris and almanac data requested from the PDE 130 to the mobile station 140 on one or more forward link channels. The mobile station 140 transmits requests for almanac and ephemeris data to the base station 110 on one or more reverse link channels. The base station 110 communicates the requests to the PDE 130. The base station 110 can be, for example, a wireless telephone base station compliant with a wireless communication standard such as TIA/EIA-95-B or TIA/EIA/IS-2000.

[0040] The base station 110 is in communication with a mobile switching center (MSC 120 that serves as the interface between the wireless communication system 100 and external commumcation systems, such as a Public Switched Telephone Network (PSTN) not shown. Alternatively or additionally, the MSC 120 can provide an interface between the tireless communication syslem 100 and a data net /oil", such 33 the Internet.

[0041] The MSC 120 is also in communication with a PDE 130. The link between the PDE 130 and the MSC 120 can be a wireless link or a wired link. Additionally, although the PDE 130 is shown coupled with the MSC 120, the PDE 130 may be coupled to the base station 110 and the communication link between the PDE 130 and the MSC 120 may occur through the base station 110. Other configurations are also possible. The PDE 30 includes an almanac 132, ephemeris 134, a position record update module 136, and a position determination module 138. [0042] The PDE 130 can be used to determine the position of the mobile station 140 based in part on information provided by the mobile station 140. For example, the mobile station 140 can determine pseudoranges to multiple position determination sources, such as GPS satellites, and can transmit the pseudorange information to the PDE 130. The PDE can then determine the position of the mobile station 140 in the position determination module 138.

[0043] The PDE 130 is also in commumcation with position determination sources. For example, the PDE 130 can include a GPS receiver (not shown) to receive almanac and ephemeris data from the GPS SVs. The PDE 130 can then store the SV data in the almanac 132 and ephemeris 134. Because the PDE 130 can be in almost continuous communication with the SVs, the almanac 130 and ephemeris 134 in the PDE 130 is likely to contain the most current data. Additionally, the PDE 130 can typically communicate the almanac 132 and ephemeris 134 data to a mobile station 140 at a data rate that is greater than the rate used by the SVs. Thus, it may be quicker for the mobile station 140 to obtain the almanac and ephemeris data from the PDE 130 than it is to search for, acquire, and download the data from a SV. Of course, the almanac 132 need not be limited to SV data, but may include position location information for other position location signal sources, alternatively referred to as pseudo-lites. The pseudo- lites can include, for example, Differential GPS position location sources, or other position location beacons or sources.

[0044] The position record update module 136 can be configured to receive the selective data or record request from the mobile station 140. The position record update module 136 can determine, based on the request, the SV ephemeris data requested by the mobile station 140. The position record update module 136 can then access the ephemeris 134 and retrieve at least a portion of the ephemeris data requested by the mobile station 140. The position record update module can then generate a message having the requested data and transmit the message to the mobile station 140. In one embodiment, the position record update module 136 retrieves all ephemeris 134 data and prunes the data to exclude ephemeris data for any SV for which the mobile station 140 has not requested data.

[0045] An embodiment of an ephemeris update method 200 performed in a mobile station 140 is shown in Figure 2. The method 200 may be performed, for example, by the mobile station 140 in the wireless communication system 100 of Figure 1. The method 200 begins at block 202 where the mobile station initially requests almanac data. The mobile station can transmit an almanac data request message to the PDE. The mobile station may request almanac data periodically, or may request almanac data upon the occurrence of an event. For example, the mobile station may request almanac data upon power up or each time the mobile station is instructed to enter a position location mode.

[0046] The mobile station next proceeds to block 204 where it waits to receive the almanac data. The mobile station may receive the almanac data from the PDE or may receive some other indication that causes the mobile station to repeat the request for almanac data.

[0047] Once the almanac data is received, the mobile station proceeds to decision block 210 where the mobile station determines if it is in a position location mode. The position location mode can be one or more modes of operation in which the mobile station periodically updates the ephemeris in order to allow for relatively fast position fixes. For example, the position location mode may include a tracking mode in which the mobile station periodically performs a position determination. For example, in tracking mode, the mobile station may determine a fix every ten minutes. The position location mode may also include a stay warm mode in which the mobile station updates the ephemeris data to allow an accurate position fix without the delays associated with almanac and ephemeris download.

[0048] If the mobile station is not in position location mode, then the mobile station may be powered down or the position location capabilities may be turned off. In this case, the mobile station proceeds to block 260 where the method is done. [0049] If the mobile station is in position location mode, the mobile station proceeds to block 222 where the mobile station determines the positions of the SVs. The mobile station can, for example, use the almanac data to predict the rough positions of the SVs. After determining the SV positions, the mobile station proceeds to block 224 where the mobile station determines, based at least in part on the positions, which of the SVs are theoretically available. The mobile station determination of the availability of the SVs is only theoretical because the mobile station may not know its exact location or the type of terrain surrounding the mobile station and thus, may not know which of the SVs are below the horizon. Additionally, the mobile station may not be able to determine if the signal from one or more of the SVs is occluded or otherwise not available. [0050] The mobile station may determine the availability of the SVs based on a rough estimate of the mobile station location in combination with an elevation mask. The rough estimate of the mobile station location may be derived, for example, based on prior position fixes, or may be based on a location of a base station or repeater with which the mobile station is in communication. The elevation mask may be used to exclude those SVs not within the parameters of the mask. For example, only those SVs that are predicted to be above the horizon, or some other elevation, may be determined by the mobile station to be available.

[0051] After determining the available SVs, the mobile station proceeds to decision block 230 where the mobile station determines if the stored ephemeris data for the available SVs is valid. The mobile station may compare the "time of ephemeris" associated with the ephemeris data to determine if the ephemeris data is currently valid and to determine if the ephemeris will be valid a predetermined time, independence_time, in the future. Independence_time may be, for example 20, 30, 45, or 60 minutes, or some other time increment. Typically, independence_time is less than 120 minutes. If the ephemeris is valid for all the available SVs, the mobile station proceeds to block 260 and the method is done.

[0052] However, if the ephemeris is not currently valid or will expire before independence_time, the mobile station proceeds to block 240 and requests the ephemeris for the SV for which the data is not, or will not, be valid. The mobile station may, for example, generate a standard compliant request that selectively requests the desired ephemeris data. The mobile station may then transmit the request to the PDE. [0053] The mobile station then proceeds to decision block 250 to determine if valid ephemeris data is received. The mobile station may perform the verification when a message is received from the PDE or may perform the validation a predetermined time out period after sending the request.

[0054] The mobile station may request ephemeris data from the PDE but may not receive it. This may occur, for example, if the PDE sends SV ephemeris data for a subset of the requested SVs. Alternatively, the mobile station may not receive the requested ephemeris data if the PDE sends a reject message to the mobile station. The PDE may deny ephemeris data to the mobile station if, for example, the SV is below the horizon and the PDE lacks the current ephemeris or if the SV is unhealthy. [0055] If valid ephemeris for all requested SVs is received by the mobile station, the mobile station proceeds to block 260 and the method 200 is done. Alternatively, if the mobile station did not receive valid ephemeris data for one or more requested SVs, the mobile station proceeds to block 252.

[0056] At block 252, the mobile station waits a predetermined wait period and then re- requests the ephemeris data for those SVs for which valid ephemeris was not received. The predetermined wait period maybe on the order of fractions of a second, seconds, or minutes.

[0057] The mobile station then returns to block 240 to re-request the ephemeris data that was previously unsuccessfully received. If the PDE reports that one of the SVs is unhealthy, the mobile station may re-request the ephemeris data associated with the unhealthy SV only if the mobile station will be requesting other SV ephemeris data. The selective ephemeris request message may be such that requests for ephemeris data for greater than one SV does not consume any additional bandwidth as compared to a request for ephemeris data for a single S V. Of course, the bandwidth required for the base station to transmit multiple SV ephemeris is typically greater than the bandwidth required to transmit ephemeris data for a single S V.

[0058] Other embodiments of the method 200 are envisioned. For example, once the mobile station successfully receives the almanac data, the mobile station may periodically check to see if it is in the position location mode and update the ephemeris data for available SVs. The mobile station may, for example, determine available SVs and update the ephemeris data every ten minutes.

[0059] hi another embodiment, in block 222, the mobile station may initially determine all satellite positions for a predetermined number of regular intervals beginning at the present time. The predetermined number of times may be sufficient to require the mobile station to determine the SV positions up to a time at least independence ime into the future. Then, at the next ephemeris update interval, the mobile station only needs to determine the SV positions for a time of independence-time into the future. [0060] Figure 3 is a table showing a portion of the fields in a selective ephemeris request message. The mobile station can be configured to generate a selective ephemeris request message that is compliant with current standards. For example, the selective ephemeris request message maybe compliant with TIA EIA/IS-801. [0061] The TIA/EIA/IS-801 standard defines a Position Determination Data Message (PDDM) 300 that can be sent by a mobile station. The PDDM 300 includes a Position Determination Message Type field, PD_MSG_TYPE 310 that identifies a type of position determination data message. The length of the field is eight bits. The default value for the field is 0X00, where the prefix "OX" denotes a hexadecimal number. However, the standard provides for manufacturer specific PDDM definitions. For example, a value of 0XC0 may represent a manufacturer proprietary message. [0062] The REQ_TYPE 320 field identifies the type of data requested by the mobile station. A REQ_TYPE value of "1001" indicates GPS ephemeris is requested. However, when this REQ_TYPE is used in conjunction with the predefined manufacturer proprietary PD_MSG_TYPE value identified above, the message may indicate that the request is a selective SV ephemeris request message. The message may indicate the SV specific ephemeris requested in the REQ_PAR_RECORD 340 field of the PDDM 300.

[0063] The REQ_PAR_RECORD 340 field has a length of forty bits. The value of the forty bits describes the SV ephemeris requested. The REQ_PAR_RECORD 340 field includes sub-fields that include AB_PAR_REQ 342, SV_MASK 344, and a reserved 346 field.

[0064] The AB_PAR_REQ 342 sub-field is only one bit in length and indicates whether the mobile station is requesting AlphaBeta parameters. If Alpha/Beta parameters are requested, the mobile station sets the filed to '1', otherwise the mobile station sets the filed to '0'.

[0065] <«Please provide a definition of the Alpha/Beta parameter§>» [0066] The SV_MASK 344 sub-field is thirty-two bits in length. The value of the sub- field identifies the subset of GPS satellites for which ephemeris is requested. For example, the least significant bit, bit 0, may represent SV 1 and the most significant bit, bit 31 , may represent S V 32. In one embodiment, a bit value of '' V indicates the data for that SV is requested.

[0067] The REQ_PAR_RECORD 340 field also includes seven bits that are reserved 346. The reserved bits allow for future definition and expansion. The mobile station may set the reserved 346 bits to "0000000". The reserved bits may be, for example, appended to the SV_MASK 344 sub-field if there are sources other than GPS SVs for which ephemeris data is available. [0068] A PDE that receives the selective ephemeris request message can respond with an unsolicited Provide GPS Ephemeris message. However, in the response message, the PDE may prune the data for any SV not requested in the SVJVIASK 344 sub-field of the PDDM 300 message.

[0069] Thus, a method and apparatus for selectively updating the ephemeris data in a mobile station has been described. A method allows a mobile station to selectively request and receive ephemeris data. Selective request and transmission of ephemeris data allows for optimization of the communication bandwidth between the mobile station and base stations because repetitive ephemeris data, as well as data for SVs that are not available, are excluded from the communication messages. [0070] The mobile station can thus download the ephemeris data for available SVs and determine its position independent of a communication link with the system. The selective ephemeris request can be configured to be compliant with presently existing standards, thus allowing the method and apparatus to be implemented into existing systems.

[0071] Although the method and apparatus have been described with respect to wireless telephone systems, and in particular, CDMA telephone systems that utilize GPS satellites for position determination, the methods and apparatus can be implemented in other types of systems. The SVs are not limited to GPS SVs, and need not be satellites, but can be any type of position location signal source for which the source location varies. For example, the satellites may be Global Orbiting Navigation Satellite System (GLONASS) satellite vehicles.

[0072] Electrical connections, couplings, and connections have been described with respect to various devices or elements. The connections and couplings may be direct or indirect. A connection between a first and second device may be a direct connection or may be an indirect connection. An indirect connection may include interposed elements that may process the signals from the first device to the second device. [0073] Signal or process flows have been described with respect to various processes, methods, or flowcharts. The flow from one step or block to the next may be direct or indirect. An indirect connection may include interposed blocks that may process the signals from the one block prior to a subsequent block. Additionally, the arrangement of the blocks or steps shown in the figures is not necessarily an indication of order. The blocks, processes, steps, or methods may, in some instances, be re-ordered without affecting results of the process or methods.

[0074] Those of skill in the art will understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0075] Those of skill will further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled persons may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the disclosed method and apparatus.

[0076] The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0077] The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. [0078] The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the claimed invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the claimed invention. Thus, the claimed invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. WHAT IS CLAIMED IS:

Claims

1. A method of selectively requesting position determination data, the method comprising: determimng, in a mobile station, a plurality of available position location signal sources from a set of position location signal sources; determimng whether current position determination data associated with the plurality of available position location signal sources is valid; and selectively requesting position determination data associated with the plurality of position location signal sources for which the current position determination data is invalid.

2. The method of Claim 1, wherein determining the plurality of available position location signal sources comprises: receiving an almanac of position determination data corresponding to the set of position location signal sources; estimating a position of each of the signal sources in the set of position location signal sources; and determimng the plurality of available position location signal sources based at least in part on an elevation mask.

3. The method of Claim 1, wherein determining the plurality of available position location signal sources comprises: estimating a position of each of a plurality of GPS satellite vehicles based in part on an almanac of GPS satellite vehicle position data; and determining a plurality of available GPS satellite vehicles based in part on the position of each of the plurality of GPS satellite vehicles and an elevation ma sic

4. The method of Claim 3, wherein determining the plurality of available position location signal sources further comprises: estimating a position of each of the plurality of GPS satellite vehicles at a predetermined future time; and determining a plurality of available GPS satellite vehicles based in part on the position of each of the plurality of GPS satellite vehicles at the predetermined future time and the elevation mask.

5. The method of Claim 1, wherein determimng the plurality of available position location signal sources comprises: comparing positions of a plurality of GPS satellites to an elevation mask; and determining a plurality of available GPS satellites for which a satellite position corresponds to the elevation mask.

6. The method of Claim 1, wherein determining validity of position determination data associated with the plurality of position location signal sources comprises: retrieving a time of ephemeris associated with each of a set of available GPS satellite vehicles; and determining validity of position determination data based at least in part on the time of ephemeris and a predetermined position independence time.

7. The method of Claim 1, wherein determining validity of position determination data associated with the plurality of position location signal sources comprises determining validity of GPS satellite vehicle ephemeris at a predetermined independence time in the future.

8. The method of Claim 1, wherein selectively requesting position determination data comprises requesting satellite ephemeris data from a Position Determination Entity (PDE) for available GPS satellites for those available GPS satellites for which the satellite ephemeris data is invalid.

9. The method of Claim 1, wherein selectively requesting position determination data comprises: generating a manufacturer specific Position Determination Data Message (PDDM); identifying, in the manufacturer specific PDDM, a request for satellite ephemeris; and identifying, in the manufacturer specific PDDM, satellites for which ephemeris data is requested.

10. The method of Claim 1, wherein the mobile station is selected from a wireless telephone, an access terminal, a computer, and a personal digital assistant.

11. A method of selectively requesting GPS satellite ephemeris data by a mobile station in a wireless communication system, the method comprising: determimng, at the mobile station, positions of GPS satellites; determining available GPS satellites based in part on the positions of GPS satellites and an elevation mask; determining whether ephemeris data for the available GPS satellites is invalid; and requesting, from a Position Determination Entity (PDE) in the wireless communication system, ephemeris data corresponding to the available GPS satellites for which the ephemeris data is determined to be invalid.

12. The method of Claim 11 , wherein requesting ephemeris data comprises: generating a Position Determination Data Message (PDDM) selectively requesting ephemeris data; and transmitting the PDDM from the mobile station to a base station in communication with the PDE.

13. A method of providing ephemeris data, the method comprising: receiving a manufacturer specific Position Determination Data Message (PDDM) from a mobile station in a wireless communication system; determimng if the manufacturer specific PDDM comprises a selective ephemeris request message; pruning a set of ephemeris data to generate satellite specific ephemeris data; and transmitting the satellite specific ephemeris data to the mobile station.

14. The method of Claim 13, wherein pruning the set of ephemeris data comprises: comparing the set of ephemeris data to a satellite vehicle mask included in the selective ephemeris request message; and excluding ephemeris data corresponding to those satellites vehicles not identified in the selective ephemeris request message.

15. One or more processor readable storage devices having processor readable code embodied on the processor readable storage devices, the processor readable code for programming one or more processors to perform a method of selectively requesting GPS satellite ephemeris data by a mobile station in a wireless commumcation system, the method comprising: determining, at the mobile station, positions of GPS satellites; determining available GPS satellites based in part on the positions of GPS satellites and an elevation mask; determining whether ephemeris data for the available GPS satellites is invalid; and requesting, from a Position Determination Entity (PDE) in the wireless communication system, ephemeris data corresponding to the available GPS satellites for which the ephemeris data is determined to be invalid.

16. One or more processor readable storage devices having processor readable code embodied on the processor readable storage devices, the processor readable code for programming one or more processors to perform a method of providing ephemeris data, the method comprising: receiving a manufacturer specific Position Determination Data Message (PDDM) from a mobile station in a wireless communication system; determimng if the manufacturer specific PDDM comprises a selective ephemeris request message; pruning a set of ephemeris data to generate satellite specific ephemeris data; and transmitting the satellite specific ephemeris data to the mobile station.

17. An apparatus configured to selectively request GPS satellite vehicle ephemeris data from a Position Determination Entity in a wireless communication system, the apparatus comprising: an almanac configured to store GPS satellite vehicle almanac data; an ephemeris module configured to store ephemeris data corresponding to one or more GPS satellites; and an ephemeris update module in communication with the almanac and the ephemeris module, the ephemeris update module configured to determine a plurality of available GPS satellites based at least in part on the almanac data, determine whether valid ephemeris data corresponding to the plurality of available GPS satellites is stored in the ephemeris module, and generate a selective ephemeris request that requests ephemeris data for those available GPS satellites for which valid ephemeris data is not stored in the ephemeris module.

18. The apparatus of Claim 17, further comprising a transceiver configured to wirelessly transmit the selective ephemeris request message to the PDE and receives ephemeris data from the PDE.

19. The apparatus of Claim 17, further comprising a clock synchronized to a system time, the ephemeris update module determining valid ephemeris data based in part on the system time and a time of ephemeris associated with each of the ephemeris data stored in the ephemeris module.

20. The apparatus of Claim 17, wherein the apparatus comprises an Application Specific Integrated Circuit (ASIC).

21. The apparatus of Claim 17, wherein the apparatus comprises a wireless telephone.

22. A Position Determination Entity (PDE) in a wireless communication system, the PDE comprising: an almanac configure to store GPS satellite almanac data; an ephemeris module configured to store GPS satellite ephemeris data; and a position record update module in commumcation with the almanac and the ephemeris module, and configured to receive a selective ephemeris request message from a mobile station, determine one or more GPS satellites for which ephemeris data is requested, and transmit to the mobile station, in response to the selective ephemeris request message, the ephemeris data for the one or more GPS satellites while excluding ephemeris data for at least one GPS satellite for which ephemeris data is not requested.

23. The PDE of Claim 22, wherein the position record update module is further configured to prune the ephemeris data stored in the ephemeris module prior to transmitting the ephemeris data for the one or more GPS satellites.