Abstract:
A method and apparatus for transmitting a location service message between a location server and a mobile station or LMU in a GPRS wireless communications system. The location server generates a location service message and transmits the location service message to a base station subsystem; the base station subsystem forwards the location service message to a serving GPRS support node; the serving GPRS support node then forwards the location service message to a mobile station or LMU), passing transparently back through the base station subsystem. This approach to system routing of location messages allows existing circuit-switched wireless communications systems to support location services in a GPRS environment with a minimum of alterations to existing hardware and software protocols.

Description:
This application claims benefit of U.S. Provisional Application 60/268,468, filed Feb. 13, 2001. 

   BACKGROUND OF THE INVENTION 
   The present invention relates generally to the field of wireless communications systems, and specifically to Location Services for use with General Packet Radio Service. 
   Global System for Mobile Communications (GSM) is a global standard for wireless telecommunications. Various GSM defined standards (GSM 900, GSM 1800, GSM 1900, etc.) have been deployed to provide cellular radiocommunication services in many countries around the world. The GSM standard was developed primarily for voice communications, but is also used to provide circuit-switched data services that require a continuous connection. The General Packet Radio Service (GPRS) is a recent extension of the GSM standard to provide packet switched data services to GSM mobile stations. Packet-switched data services are used for transmitting small amounts of data or for data transfers of an intermittent or bursty nature. Typical applications for GPRS include Internet browsing, wireless e-mail, and credit card processing. GPRS is described more fully in “3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; General Packet Radio Service (GPRS); Service description; Stage 2 (Release 1999),” the disclosure of which is incorporated herein by reference. 
   The GSM standard is capable of providing a variety of information services to subscribers. Location Services (LCS) is one example of an information service that GSM provides. LCS allows a subscriber or client to obtain or determine the location of a GSM mobile station operating within the GSM network. The location may be determined by the network, based on measurements supplied by the mobile station, or may be determined by the mobile station itself and communicated to the network. Various approaches to position estimation may be used, including Uplink Time of Arrival (TOA), Enhanced Observed Time Difference (E-OTD), and assisted Global Positioning System (GPS). LCS is described more fully in “Digital cellular telecommunications system (Phase 2+); Location Services (LCS); (Functional description)—Stage 2 (GSM 03.71 version 8.0.0 Release 1999).” 
   In the current GSM standard, a centralized server known as the Serving Mobile Location Center (SMLC) manages the overall coordination and scheduling of resources required to perform positioning of a mobile station. In order to perform these functions, the SMLC must exchange information with other entities within the network, such as the mobile station and/or a Location Measuring Unit (LMU). This location information may be the position of the mobile station, measurements from which the position of the mobile station may be determined, or data otherwise useful in determining the position of the mobile terminal. For instance, the location information may be that discussed in “3rd Generation Partnership Project; Technical Specification Group GSM EDGE Radio Access network; Mobile Station (MS)—Serving Mobile Location Centre (SMLC) Radio Resources LCS Protocol (RRLP)” (Release 1999, v8.3.1), incorporated herein by reference. 
   Communication protocols permit the orderly exchange of information between nodes or entities within a network. Communication protocols to support LCS information exchange in conventional circuit-switched GSM networks have been developed. In contrast, communication protocols for GPRS networks are still in development and have not been finalized. Thus, many aspects of the communication protocol needed to support LCS in a GPRS network remain unresolved. 
   SUMMARY OF THE INVENTION 
   The present invention provides a method and apparatus for transmitting a location service message between a location server and a mobile station in a GPRS wireless communications system. The location server generates a location service message and transmits the location service message to a base station subsystem; the base station subsystem forwards the location service message to a serving GPRS support node; the serving GPRS support node then forwards the location service message to a mobile station, passing transparently back through the base station subsystem. The flow of location service messages from the mobile station to the location server may follow the reverse path. This approach to system routing of location messages allows existing circuit-switched wireless communications systems to support location services in a GPRS environment with a minimum of alterations to existing hardware and software protocols. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a functional block diagram of a GPRS packet data network according to the present invention. 
       FIG. 2  is a protocol model for communications between a location server and a mobile station according to the present invention. 
       FIG. 3  is a protocol model for communications between a location server and a Type A location measurement unit according to the present invention. 
       FIG. 4  is a protocol model for communications between a location server and a Type B location measurement unit according to the present invention. 
       FIG. 5  is a protocol model for communications between a location server and a base station subsystem according to the present invention. 
       FIG. 6  is a call flow diagram illustrating signaling between a location services client and location server. 
       FIG. 7  is a call flow diagram illustrating a procedure for requesting position information from a mobile station. 
       FIG. 8  is a call flow diagram illustrating a procedure for providing assistance data to a mobile station. 
       FIG. 9  is a call flow diagram illustrating a procedure for providing assistance data to an LMU. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows the logical architecture of a packet-switched network  30  implementing General Packet Radio Service (GPRS) developed for Global System for Mobile Communications (GSM). The packet-switched network  30  of  FIG. 1  comprises at least one Serving GPRS Support Node (SGSN)  32 , a Gateway GPRS Support Node (GGSN)  34 , a Home Location Register (HLR)  36 , a Serving Mobile Location Center (SMLC)  38 , a Gateway Mobile Location Center (GMLC)  40 , a Base Station Subsystem (BSS)  60 , an optional Location Measuring Unit (LMU)  70 , and a mobile station (MS)  80 . 
   The SGSN  32  contains the functionality required to support GPRS. SGSN  32  provides network access control for packet-switched network  30 . Network access is the means by which a user is connected to a telecommunications network in order to use the services of the network. The SGSN  32  connects to the BSS  60 , typically by a Frame Relay Connection. In the packet-switched network  30 , there may be more than one SGSN  32 . 
   The GGSN  34  provides interworking with external packet-switched networks, referred to as packet data networks (PDN)  50 , and is typically connected to the SGSN  32  via a backbone network using the X.25 or TCP/IP protocol. The GGSN  34  may also connect the packet-switched network  30  to other public land mobile networks (PLMN). The GGSN  34  is the node that is accessed by the external packet data network  50  to deliver packets to a mobile station  80  addressed by a data packet. Data packets originating at the mobile station  80  addressing nodes in the external PDN  50  also pass through the GGSN  34 . Thus, the GGSN  34  serves as the gateway between users of the packet-switched network  30  and the external PDN  50 , which may, for example, be the Internet or other global network. The SGSN  32  and GGSN  34  functions can reside in separate nodes of the packet-switched network  30  or may be in the same node. 
   The HLR  36  stores subscriber information and the current location of the subscriber. As the mobile station  80  moves about within the network, it periodically registers with the network so that the network can track the whereabouts of the mobile station  80 . The network updates the location information in the HLR  36  when needed. When a call intended for a mobile station  80  is received at the SGSN  32 , the SGSN  32  sends a query to the HLR  36  to get the current location of the mobile station  80  to use in routing the call. 
   The SMLC  38  contains functionality required to support LCS. The SMLC  38  manages the overall coordination and scheduling of resources required to perform positioning of a mobile station  80  and is therefore sometimes referred to as the location server. The SMLC  38  may calculate the final location estimate of the mobile station  80  and the accuracy thereof. The overall functionality of the SMLC  38  may be that set forth in “Digital cellular telecommunications system (Phase 2+); Location Services (LCS); (Functional description)—Stage 2 (GSM 03.71 version 8.0.0 Release 1999),” the disclosure of which is incorporated herein by reference. In the packet-switched network  30 , there may be more than one SMLC  38 . 
   The GMLC  40  also contains functionality required to support LCS. The GMLC  40  is the first node an external LCS client accesses in a GSM network  30 . The GMLC  40  may request routing information from the HLR  36  via an appropriate interface. The overall functionality of the GMLC  40  may be that set forth in “Digital cellular telecommunications system (Phase 2+); Location Services (LCS); (Functional description)—Stage 2 (GSM 03.71 version 8.0.0 Release 1999),” referenced above. In the packet-switched network  30 , there may be more than one GMLC  40 . The BSS  60 , which includes a Base Station Controller (BSC)  62  and one or more Base Transceiver Stations (BTS)  64 , provides an interface between mobile stations  80  and the network  30 . The BTS  64  contains radio transmission and reception equipment, up to and including the antennas, and also contains the signal processing specific to the radio interface. The BSC  64  connects the BTS  62  with the SGSN  32  and performs most management and control functions of the BSS  60 . The main functions of the BSC  64  include allocation and release of radio channels, and handover management. 
   The optional LMU  70  makes radio measurements to support one or more positioning methods, in fashions well known in the art. The LMU may be of a type A, wherein the LMU  70  is accessed over the normal GSM air interface. Alternatively, the LMU may be type B, wherein the LMU  66  is accessed over a special interface (known as Abis). While type B LMUs  66  may be stand-alone network elements, they may also be integrated into a BTS  64  as shown in  FIG. 1 . 
   The mobile station  80  may take any form known in the art. For purposes of discussion herein, the mobile station  80  is assumed to be a GSM adapted mobile station with LCS and GPRS capability. The mobile station  80  registers with the SGSN  32  to receive packet data services in a conventional fashion. Registration is the process by which the mobile terminal ID is associated with the user&#39;s address(es) in the packet-switched network  30  and with the user&#39;s access point(s) to the external PDN  50 . After registration, the mobile station  80  typically camps on a Common Control Channel (CCCH) or a Packet Common Control Channel (PCCCH). 
   As discussed above, location service messages flow between the mobile station  80  and the SMLC  38 . These location service messages may aid the mobile station  80  in determining it position, aid the mobile terminal in taking position related measurements, and/or aid the SMLC  38  in estimating the position of the mobile station  80 , depending on the location measurement approach taken. For instance, the location service messages may comprise so-called assistance data, such as GPS almanac data, GPS ephemeris data, or the like, provided by the SMLC  38  to the mobile station  80 . Alternatively, the location service messages may be timed signal measurements, or the like, provided by the mobile station  80  to the SMLC  38 . While the SMLC  38  communicates with the mobile station  80  using the physical layer air interface provided by the BSS  60 , the particular protocol and routing used for the location service messages may vary. The present invention provides one such protocol and routing used for communicating location service messages between the mobile station  80  and the SMLC  38 . 
     FIG. 2  shows a protocol model used for transmitting location service messages between a location server and a mobile station  80 . Location service messages are messages used to transmit data and signaling information related to LCS. The protocol model shown in  FIG. 2  uses a layered protocol stack, with each layer performing defined functions. The protocol stack includes transfer control procedures (e.g., flow control, error detection, error correction, and error recovery) to facilitate information transfer between the various entities. 
   The Radio Resource LCS Protocol (RRLP) is the protocol used to transfer LCS related information between the mobile station  80  and a location server, such as the SMLC  38 . RRLP messages, referred to herein generically as location service messages, are used by the location server, for example, to send a Position Request Message or to send assistance data to a mobile station  80 . The mobile station  80  may use location service messages, for example, to request assistance data from the location server or to transmit position information to the location server in response to a Position Request Message. The RRLP is an application-level protocol. All RRLP messages are transmitted transparently between the location server and mobile station  80 . 
   The BSS LCS Assistance Protocol (BSSLAP) and the BSSAP LCS Extension (BSSAP-LE) support LCS signaling between the SMLC  38  and BSS  60 . BSSLAP supports specific LCS functions (e.g., positioning measurements, assistant measurements) and is independent of lower protocol layers. The BSSLAP layer may be absent if its functions are supported in the BSSAP-LE layer. The BSSAP-LE layer is an extension of the BSS Assistance Protocol. This layer carries the BSSLAP signaling units. The functions of the BSSAP-LE layer include identification of the BSSLAP version and identification, where not provided by the network layer, of the two end points. This layer supports segmentation of BSSLAP messages that exceed the message size limitations of lower layer protocols. 
   The Signaling Connection Control Part (SCCP) is the protocol used to transport messages over an SS 7  network. SCCP provides end-to-end routing of messages over a network. The SCCP layer contains addressing data necessary to deliver data to the specified destination. This addressing information is used at each signaling point or node in the network to determine how the message should be routed. SCCP is described in ANSI T1.112 and/or ITU-T Q.711. 
   The Message Transfer Part (MTP) comprises three layers that correspond to the physical layer (layer  1 ), data link layer (layer  2 ), and network layer (layer  3 ) of the OSI reference model. The MTP layer acts as an interface between the SCCP layer and the physical channel. Layer  1  is responsible for converting data signals into a bit stream suitable for transmission over the network. Layer  2  is responsible for delivery of messages over a signaling link between two adjacent signaling points or nodes in the network. Functions performed at this level include error detection and correction and sequencing of data that has been broken up for transmission over the network. Layer  3  performs several functions, including message discrimination, message distribution, message routing, and network management. Message discrimination determines to whom a message is addressed. If the message is addressed to the local node, the message is passed to message distribution. If the message is not addressed to the local node, it is passed to message routing. The message distribution function routes messages to the designated entity within the node. Message routing determines which length to use to transmit a message and sends the message back to Layer  2  for transmission on the designated length. Layer  3  also performs network management functions. These functions are not material to the invention and are not described herein. The MTP is described in ANSI publication T1.111 and/or ITU-T Q.701. 
   The BSS GPRS Protocol (BSSGP) conveys routing and quality of service (QOS) related information between the BSS  60  and SGSN  32 . In the present invention, the BSSGP provides transport of RRLP messages between SMLC  38  and SGSN  32 . BSSGP also provides transport of LLC frames between SGSN  32  and BSS  60 . In the BSC  62 , RRLP messages are unpacked from BSSLAP frames and placed into BSSGP frames. The RRLAP messages are unpacked from BSSGP frames at SGSN  32  and placed into LLC frames. LLC frames, in turn, are carried in a BSSGP message to BSS  60  where the LLC frame is unpacked and placed in RLC/MAC frames. This process is reversed in uplink communications from the mobile station  80  to the SMLC  38 . The BSSGP is specified in GSM 08.18. 
   The existing BSSGP protocol does not provide for transport of RRLP messages between the BSS  60  and SGSN  32 . The BSSGP can be easily modified by those skilled in the art to provide this transport function by adding an additional message to the BSSGP message set or, possibly, by modifying existing messages within the BSSGP message set to include new information elements. Messages used to transport RRLP messages between the BSS  60  and SGSN  32  are referred to herein as RRLP transport messages. 
   The Network Service (NS) layer transports BSSGP signaling units between the BSS  60  and SGSN  32 . Services provided by this layer are typically based on a Frame Relay Connection between the BSS  60  and SGSN  32 , but may alternatively be based on an IP connection such as that described in 3GPP TS 28.016. The frame relay circuits may be multi-hop and traverse a network of Frame Relay switching nodes. Frame Relay is used for signaling and data transmission. The NS layer is described in GSM 08.16. 
   The RLC/MAC layer contains two functions: the Radio Link Control function and Medium Access Control function. The Radio Link Control function provides a radio solution dependent reliable link. The Medium Access Control function controls the access signaling (request and grant) procedures for the radio channel and the mapping of LLC frames onto the GSM physical channel. RLC/MAC is defined in GSM 04.60. 
     FIG. 3  shows a protocol model used for transmitting location service messages between a location server and Type A LMU  70 . This protocol model is similar to that shown in  FIG. 2 . However, the top level protocol of the protocol model shown in  FIG. 3  is the LMU LCS Protocol (LLP). The LLP is the protocol used to transfer LCS-related information between a location server, such as the SMLC  38 , and a LMU, such as Type A LMU  70  or type B LMU  66 . Thus, LLP messages are another type of location service messages used by the SMLC  38  for communication with an LMU. The protocol model for communications between the SMLC  38  and Type A LMU  70  omits the BSSLAP layer shown in  FIG. 2 . The functions of the BSSLAP layer in  FIG. 2  are incorporated into the BSSAP-LE layer in  FIG. 3 . The BSSGP protocol is used to transport LLP messages between the BSS  60  and SGSN  32 . The BSSGP would need to be modified to perform this transport function as previously described by adding a new message to the BSSGP message set, or by adding new information elements to existing BSSGP messages. 
     FIG. 4  is a protocol model for communications between a location server, such as the SMLC  38 , and Type B LMU  66 . The top level protocol in this protocol model is the LLP. The BSSAP-LE is used to transport LLP messages between the SMLC  38  and BSC  62 . Layer  1  (L 1 ) and Layer  2  (L 2 ) protocols provide transport for LLP messages between the BSC  62  and Type B LMU  66 . This protocol model is the same as the protocol model used in circuit-switched GSM networks, which is well known to those skilled in the art, and would not require modifications. 
     FIG. 5  is the protocol model for communications between the location server, such as SMLC  38 , and BSS  60 . This protocol model is used when the BSC  62  is one end point for the communication and the SMLC  38  is the other end point. The top level protocol in this protocol model is the BSSLAP. Note that in this protocol model, the SCCP and MTP provide transport for messages in the higher protocol layers. The SCCP and MTP layers could be replaced by IP transport. The protocol model shown in  FIG. 5  is currently used in circuit-switched GSM networks and does not require modification for the present invention. 
   An exemplary situation where the present invention may advantageously be employed is shown in  FIG. 6 . An LCS client, such as an external LCS client, sends a LCS service request to the GMLC  40  (arrow  1 ). The GMLC  40  sends a routing information request to the HLR  36  (arrow  2 ), which responds by returning the appropriate routing information to the GMLC  40  (arrow  3 ). The GMLC  40  then sends a provide subscriber location request to the SGSN  32  (arrow  4 ). If the GMLC  40  is located in another PLMN or another country, the SGSN  32  may authenticate that a location request is allowed from that PLMN (or that country) before proceeding, with appropriate error response if the location request is not authorized. The SGSN  32  may then verify that any restrictions on location requests associated with the mobile station  80  are satisfied, once again with appropriate error messages/responses if they are not met. If the mobile station  80  is suspended or not attached, the SGSN  32  may return an error response to the GMLC  40 . If the mobile station  80  is in stand-by mode, the SGSN  32  and the mobile station  80  perform a page/response (arrow  5 ). The mobile station  80  should return the current cell identification in the BSSGP message of the page response. In addition, if the mobile station  80  supports any mobile station-based or mobile station-assisted positioning methods, the mobile station  80  may also provide the SGSN  32  with an indication of which positioning methods it supports during the attach procedure. Because the mobile station  80  may place restrictions on the dissemination of its location, the SGSN  32  may be required to send a LCS Location Notification Invoke message to the mobile station  80  (arrow  6 ) to notify the mobile station  80  of the identity of the entity requesting the mobile station&#39;s location and/or wait for user to grant or withhold permission for the information to be released (“privacy verification”). Next, the mobile station  80  responds to the notification/permission request by sending an appropriate message to the SGSN  32  (arrow  7 ). If the mobile station  80  does not respond within a predetermined time, the SGSN  32  may infer a “no response” condition and notify the GMLC  40  appropriately, such as indicating a permission denial. Optionally, the SGSN  32  may continue the location process in parallel, without waiting for the mobile station  80  to respond to the notification/permission request (with appropriate later safeguards in the later case). 
   Assuming the inquiry is authorized, the SGSN  32  sends a “perform location request” command to the BSS  60  as a BSSGP layer message (arrow  8 ). The existing BSSGP protocol does not currently define such a “perform location request” command; however, the BSSGP can be easily modified by those skilled in the art to provide this by adding an additional message to the BSSGP message set or, possibly, by modifying existing messages within the BSSGP message set to include new information elements. 
   The BSS  60  forwards this “perform location request” message to the SMLC  38  by using an appropriate BSSMAP-LE layer message (arrow  9 ). From this point, suitable messages are exchanged to facilitate the individual positioning method (box  10 ), as described in more detail with reference to  FIG. 7  below. Once the SMLC  38  has the appropriate information, the SMLC  38  sends a “perform location response” message to the BSS  60  as a BSSMAP-LE layer message (arrow  11 ). The BSS  60  in turn forwards the information to the SGSN  32  as a BSSGP layer message (arrow  12 ). The SGSN  32  forwards the information to the LCS client via GMLC  40  (arrows  13 – 14 ). 
   Referring to  FIG. 7  for greater detail on the messages exchanged to facilitate the individual positioning method, the SMLC  38  generates a location service message and transmits the same to the BSS  60  in a BSSLAP layer message (arrow  2 ). It will be assumed for this example that the location service message includes a “position request” command. The BSS  60  forwards the location service message to the SGSN  32  in a BSSGP layer message (arrow  3 ). The SGSN  32  forwards the location service message to the mobile station  80  in a LLC UI frame (arrow  4 ). It should be noted that the SGSN  32  may apply ciphering to the location service message as desired prior to forwarding. The Network layer Service Access Point Identifier NSAPI value for LCS may be used by the LLC. This communication of the location service message between the SGSN  32  and the mobile station  80  is via the BSS  60 , but is basically transparent to the BSS  60 . The mobile station  80  receives the location service message and responds thereto. In this simple example, the mobile station  80  performs the necessary position-related measurements (e.g., E-OTD measurements or GPS measurements) known in the art, and prepares an uplink location service message containing the measurement results and/or a mobile station-computed location estimate. This uplink location service message is transmitted to the SGSN  32  in a LLC UI frame (arrow  5 ). Once again, this communication between the mobile station  80  and the SGSN  32  is via the BSS  60 , but is basically transparent to the BSS  60 . The SGSN  32  forwards the location message to the BSS  60  in a BSSGP message (arrow  6 ), which then forwards it to the SMLC  38  in a BSSLAP message for appropriate processing (arrow  7 ). 
   A location command/response scenario has been used for the discussion of  FIG. 7  immediately above. However, the same basic flow may be used for supply/acknowledgement of location assistance data, as shown in  FIG. 8 . That is, the location service message from the SMLC  38  may contain location assistance data (e.g., GPS almanac or ephemeris data, position of other BSSs  60 , etc.) and the uplink location message may contain a simple acknowledgement of receipt. It should also be noted that that the SMLC  38  may optionally precede the position request command/response cycle with a supply/acknowledgement cycle (using the process as shown in  FIG. 8 ) to provide location assistance information determined to be useful by the SMLC  38  to the mobile station  80 , as desired. 
   The discussion above has assumed that the location service messages are flowing between a SMLC  38  and a mobile station  80 ; however, the same basic approach can be used for the flow of location service messages between an SMLC  38  and a type A LMU  70  by simply replacing the mobile station  80  with a Type A LMU  70  as shown in  FIG. 3 . It should be noted that for the flow of location service messages between an SMLC  38  and a type A LMU  70 , there may not be an analogous flow to that of  FIG. 6 . For instance, the LMU  70  may be relatively continuously contacted by the SMLC  38 , as appropriate; or, alternatively, the LMU  70  may be contacted by the SMLC  38  in connection with a position request, such as that shown in  FIG. 6 . Assuming a triggered connection approach, the the flow of location service messages between an SMLC  38  and the LMU  70  may advantageously take place between step  10  and step  11  of  FIG. 6 , and the SMLC  38  may ask one or more LMUs  70  about timing information that the mobile station  80  reported in step  10  of  FIG. 6 . The process flow of  FIG. 7  may advantageously be altered as shown in  FIG. 9  for the flow of location service messages between an SMLC  38  and a type A LMU  70 . As shown in  FIG. 9 , the SMLC  38  generates a location service message (e.g., an LLP message) and transmits the same to the BSS  60  in a BSSLAP layer message (arrow  1 ). It will be assumed for this example that the location service message includes a “report BSS timing information” command. The BSS  60  forwards the location service message to the SGSN  32  in a BSSGP layer message (arrow  2 ). The SGSN  32  forwards the location service message to the LMU  70  in a LLC UI frame (arrow  3 ). This communication of the location service message between the SGSN  32  and the LMU  70  is via the BSS  60 , but is basically transparent to the BSS  60 . The LMU  70  receives the location service message and responds thereto. In this simple example, the LMU  70  performs the necessary position-related measurements (e.g., E-OTD measurements or GPS measurements) known in the art, and prepares an uplink location service message containing the measurement results. This uplink location service message is transmitted to the SGSN  32  in a LLC UI frame (arrow  4 ). Once again, this communication between the LMU  70  and the SGSN  32  is via the BSS  60 , but is basically transparent to the BSS  60 . The SGSN  32  forwards the location message to the BSS  60  in a BSSGP message (arrow  5 ), which then forwards it to the SMLC  38  in a BSSLAP message for appropriate processing (arrow  6 ). 
   It should be noted that  FIG. 9  includes a dashed line figuratively separating the flow of messages from the SMLC  38  to the LMU  70  (above the line) and the flow of messages from the LMU  70  to the SMLC  38  (below the line). The process flow of  FIG. 9  described above is for both above and below the line, based on an inquiry-response model initiated by or through the SMLC  38 . However, in some instances, the LMU  70  may send one or more location messages to the SMLC  38 , not in response to a specific inquiry from the SMLC  38 , but instead at its own initiative, such as on a periodic basis or upon detection of a new satellite coming into view. Thus, the portion of  FIG. 9  below the line may occur without, or independent of, the portion of  FIG. 9  above the line in some instances. 
   The following documents are incorporated by reference herein and are part of the specification: 
   1. Digital cellular telecommunications system (Phase 2+); Location Services (LCS); (Functional description)—Stage 2 (GSM 03.71 version 8.0.0 Release 1999). 
   2. 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Functional stage 2 description of LCS (Release 2000). 
   3. 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; General Packet Radio Service (GPRS); Service description; Stage 2 (Release 1999). 
   4. 3rd Generation Partnership Project; Technical Specification Group GSM EDGE Radio Access Network; General Packet Radio Service (GPRS); Base Station System (BSS)—Serving GPRS Support Node (SGSN); BSS GPRS Protocol (BSSGP) (Release 1999). 
   5. 3rd Generation Partnership Project; Technical Specification Group GSM EDGE Radio Access Network; Location Services (LCS); Base Station System Application Part LCS Extension (BSSAP-LE) (Release 1999). 
   6. Digital cellular telecommunications system (Phase 2+); General Packet Radio Service (GPRS); Mobile Station—Serving GPRS Support Node (MS-SGSN) Logical Link Control (LLC) layer specification (GSM 04.64 version 8.4.0 Release 1999). 
   7. Digital cellular telecommunications system (Phase 2+); General Packet Radio Service (GPRS); Base Station System (BSS)—Serving GPRS Support Node (SGSN) interface; Network Service (GSM 08.16 version 8.0.0 Release 1999). 
   8. 3rd Generation Partnership Project; Technical Specification Group GSM EDGE Radio Access Network; Location Services (LCS); Mobile Station (MS)—Serving Mobile Location Centre (SMLC) Radio Resource LCS Protocol (RRLP) (Release 1999). 
   9. 3rd Generation Partnership Project; Technical Specification Group GSM EDGE Radio Access Network; Location Services (LCS); Serving Mobile Location Centre—Base Station System (SMLC-BSS) interface; Layer  3  specification (Release 1999). 
   10. BSS+ Protocol Architecture to Support LCS in GPRS. 
   Although the present invention has been described herein with respect to particular features, aspects and embodiments thereof, it will be apparent that numerous variations, modifications, and other embodiments are possible within the broad scope of the present invention, and accordingly, all variations, modifications and embodiments are to be regarded as being within the scope of the invention. The present embodiments are therefore to be construed in all aspects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.