System and method for providing location services in parallel to existing services in general packet radio services architecture

A telecommunications system and method is disclosed for enabling a General Packet Radio Service (GPRS) node, namely a Serving GPRS Support Node (SGSN) within a cellular network, to be able to handle requests for Location Services (LCS) for a GPRS mobile station (MS) in parallel to other existing transactions such as delivering short messages or engaging in session management activity, e.g., data call connection. A new LCS transaction type can be introduced in the Connection-Management (CM) sub-layer of GPRS in the SGSN and the GPRS MSs to handle requests for LCS in parallel to other offered services. LCS can be multiplexed together with other existing functions in GPRS by allocating a new Service Access Point Identifier (SAPI) to LCS within the Logical Link Control (LLC) sub-layer of the GPRS. Alternatively, when a common LLC SAPI is used between different CM-sublayer functions, then a different protocol discriminator (PD) can be allocated for LCS.

BACKGROUND OF THE PRESENT INVENTION
 1. Field of the Invention
 The present invention relates generally to telecommunications systems and
 methods for positioning a mobile station within a cellular network, and
 specifically to offering location services in parallel to other existing
 services for mobile stations capable of handling data communications.
 2. Background and Objects of the Present Invention
 Cellular telecommunications is one of the fastest growing and most
 demanding telecommunications applications ever. Today it represents a
 large and continuously increasing percentage of all new telephone
 subscriptions around the world. A standardization group, European
 Telecommunications Standards Institute (ETSI), was established in 1982 to
 formulate the specifications for the Global System for Mobile
 Communication (GSM) digital mobile cellular radio system.
 With reference now to FIG. 1 of the drawings, there is illustrated a GSM
 Public Land Mobile Network (PLMN), such as cellular network 10, which in
 turn is composed of a plurality of areas 12, each with a Mobile Switching
 Center (MSC) 14 and an integrated Visitor Location Register (VLR) 16
 therein. The MSC 14 provides a circuit switched connection of speech and
 signaling information between the MS 20 and the PLMN 10. The MSC/VLR areas
 12, in turn, include a plurality of Location Areas (LA) 18, which are
 defined as that part of a given MSC/VLR area 12 in which a mobile station
 (MS) (terminal) 20 may move freely without having to send update location
 information to the MSC/VLR area 12 that controls the LA 18. Each Location
 Area 18 is divided into a number of cells 22. Mobile Station (MS) 20 is
 the physical equipment, e.g., a car phone or other portable phone, used by
 mobile subscribers to communicate with the cellular network 10, each
 other, and users outside the subscribed network, both wireline and
 wireless.
 The MSC 14 is in communication with at least one Base Station Controller
 (BSC) 23, which, in turn, is in contact with at least one Base Transceiver
 Station (BTS) 24. The BTS is the physical equipment, illustrated for
 simplicity as a radio tower, that provides radio coverage to the cell 22
 for which it is responsible. It should be understood that the BSC 23 may
 be connected to several BTS's 24, and may be implemented as a stand-alone
 node or integrated with the MSC 14. In either event, the BSC 23 and BTS 24
 components, as a whole, are generally referred to as a Base Station System
 (BSS) 25.
 With further reference to FIG. 1, the PLMN Service Area or cellular network
 10 includes a Home Location Register (HLR) 26, which is a database
 maintaining all subscriber information, e.g., user profiles, current
 location information, International Mobile Subscriber Identity (IMSI)
 numbers, and other administrative information, for subscribers registered
 within that PLMN 10. The HLR 26 may be co-located with a given MSC 14,
 integrated with the MSC 14, or alternatively can service multiple MSCs 14,
 the latter of which is illustrated in FIG. 1.
 A Serving General Packet Radio Service Support Node (SGSN) 30, which is
 part of the General Packet Radio Service (GPRS) architecture, connects
 with the MSC 14 to provide packet switching of high and low speed data and
 signaling in an efficient manner to and from the MS 20. When the MS 20 is
 engaged in a data call, e.g., the MS 20 has an Internet connection (not
 shown) for sending and receiving data, data is sent from the MS 20 to the
 SGSN 30. The SGSN 30 provides a packet-switched connection for the data.
 Received data is transmitted from the SGSN 30 to the MS 20.
 Determining the geographical position of an MS 20 within a cellular network
 10 has recently become important for a wide range of applications. For
 example, location services (LCS) may be used by transport and taxi
 companies to determine the location of their vehicles. In addition, for
 emergency calls, e.g., 911 calls, the exact location of the MS 20 may be
 extremely important to the outcome of the emergency situation.
 Furthermore, LCS can be used to determine the location of a stolen car,
 for the detection of home zone calls, which are charged at a lower rate,
 for the detection of hot spots for micro cells, or for the subscriber to
 determine, for example, the nearest gas station, restaurant, or hospital,
 e.g., "Where am I" service.
 Circuit switched paging and identification of the MS 20 when the MS 20 is
 both IMSI and GPRS attached, e.g., registered with both the VLR 16 and the
 GPRS 30, is performed via the SGSN 30 instead of the MSC 14, due to the
 higher efficiency and capacity offered by the SGSN 30 as compared with the
 MSC 14. For similar reasons, it is more efficient to locate an MS 20 that
 is both IMSI and GPRS attached via the SGSN 30 rather than the MSC 14.
 Currently, when an MS 20, which is registered with the SGSN 30, is being
 positioned, the MS 20 is not always able to make or receive data calls or
 send or receive short messages. With reference now to FIG. 2 of the
 drawings, using the Open Systems Interconnection (OSI) model, which was
 developed by the International Standards Organization (ISO) in 1982, the
 inability of the MS 20 to engage in other activities involving the SGSN 30
 while being positioned can be explained by describing the connection
 between the MS 20 and the SGSN 30 as several functional layers arranged in
 hierarchical form. These consist of the physical layer 205, the data link
 layer 210 and the application layer 215, which are on both the SGSN 30 and
 the MS 20. The application layer 215 is composed of three sublayers: a
 Radio Link Control (RLC) sublayer 220, a Logical Link Control (LLC)
 sub-layer 225 and a Connection Management (CM) sub-layer 230, which is the
 highest sub-layer within the application layer 215.
 The CM protocol 235 controls two separate transaction types: session
 management (SS layer) 232, which handles data call delivery, such as
 activating, modifying and deleting the contents of packet data protocols,
 and short message handling delivery (SM layer) 234, which handles the
 delivery of Short Message Service (SMS) messages. Each transaction type
 232 and 234 can be allocated a separate Service Access Point Identifier
 (SAPI) 233 and 235, respectively, within the LLC sub-layer 225 for
 distinguishing between the transaction types 232 and 234. Alternatively,
 when a common LLC SAPI is used between different transaction types 232 and
 234, it is possible for a mobile subscriber to establish two
 CM-connections 230, using the same LLC-connection 220, by using different
 protocol discriminators (PDs) (not shown) to distinguish between the
 transaction types. Therefore, it is possible to provide SMS and data call
 services at one time and to change between the different services if
 necessary.
 Any transaction may be established in parallel to any combination of other
 transactions. However, for a given RLC-connection 220, LLC-connections 230
 can only be established once for each of the transaction types 232 and
 234. Thus, only one LLC-connection 230 is allowed at a time per
 transaction type 232 and 234. That implies that, if LCS were to be defined
 as part of either the SS layer 232 or SM layer 234, it would be impossible
 to offer an LCS transaction at the same time as another transaction if
 both transactions belonged to the same transaction type (SS 232 or SM
 234).
 It is, therefore, an object of the present invention to allow LCS
 transactions to be performed in parallel to other existing transactions
 such as data calls or short messages within a GPRS architecture.
 SUMMARY OF THE INVENTION
 The present invention is directed to telecommunications systems and methods
 for enabling a General Packet Radio Service (GPRS) node, namely a Serving
 GPRS Support Node (SGSN) within a cellular network, to be able to handle
 requests for Location Services (LCS) for a GPRS mobile station (MS) in
 parallel to other existing transactions such as delivering short messages
 or engaging in session management activity, e.g., data call connection. A
 new LCS transaction type can be introduced in the Connection-Management
 (CM) sub-layer of GPRS in the SGSN and the GPRS MSs to handle requests for
 LCS in parallel to other offered services. LCS can be multiplexed together
 with other existing functions in GPRS by allocating a new Service Access
 Point Identifier (SAPI) to LCS within the Logical Link Control (LLC)
 sub-layer of the GPRS in the SGSN and the GPRS MSs in order to support LCS
 services in parallel to other transaction types. Alternatively, when a
 common LLC SAPI is used between different CM-sublayer functions, then a
 different protocol discriminator (PD) must be allocated for LCS in order
 to be able to handle LCS transactions in parallel to other transactions.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS
 The numerous innovative teachings of the present application will be
 described with particular reference to the presently preferred exemplary
 embodiments. However, it should be understood that this class of
 embodiments provides only a few examples of the many advantageous uses of
 the innovative teachings herein. In general, statements made in the
 specification of the present application do not necessarily delimit any of
 the various claimed inventions. Moreover, some statements may apply to
 some inventive features but not to others.
 With reference now to FIGS. 3A and 3B of the drawings, in order to overcome
 the architectural restraint within the General Packet Radio Service (GPRS)
 architecture on initiating both Location Services (LCS) and either a call
 short message, or a data call in parallel, a new type of layer called LCS
 236 can be defined on the connection management (CM) sublayer level 230 of
 the application layer 215 within a GPRS mobile station (MS) 20 and a
 Serving GPRS Support Node (SGSN) 30. The LCS layer 236 or transaction type
 will be in parallel with a session management (SS) sub-layer 232 and a
 short message (SM) sub-layer 234. Therefore, an LCS transaction 236 can be
 performed in parallel to any other existing transaction for the same
 mobile subscriber at any one time.
 As between the MS 20 and the SGSN 30, the MS 20 can establish several
 Logical Link Control (LLC)-connections 225 with the SGSN 30, using the
 same Radio Link Control (RLC)-connection 220, which is the layer
 responsible for converting the digital data into bit streams for
 transmission across the air interface 240. Therefore, it is possible to
 provide several telecommunication services at one time and to change
 between different services if necessary. Any transaction may be
 established in parallel to any combination of other transactions. However,
 for a given RLC-connection 220, only one LLC-connections 225 can be
 established for each of the transaction types 232, 234 and 236. Thus, only
 one LLC-connection 225 is allowed at a time per subscriber per transaction
 type 232, 234 and 236.
 The MS 20 can establish such an LLC-connection 225 by the MS 20 transaction
 type layer, e.g., LCS 236, sending the request through it's LLC 225 and
 RLC 220 layers to establish an LLC-connection 225 with the LCS layer 236
 on the SGSN 30. The request is sent over the RLC-connection 220 between
 the MS 20 and the SGSN 30 using DTAP signaling. If, on the other hand, a
 transaction type layer 232, 234 or 236 on the SGSN 30 would like to
 establish an LLC-connection 225 with the associated transaction type layer
 232, 234, or 236, respectively, of the MS 20, the process is reversed.
 As shown in FIG. 3A of the drawings, the LLC-connection 225 can be
 established by allocating a separate Service Access Point Identifier
 (SAPI) 233,235 or 237 within the LLC sub-layer 225 for each transaction
 type layer 232, 234 or 236, respectively, in order to distinguish between
 the transaction types 232, 234 and 236. Alternatively, as shown in FIG. 3B
 of the drawings, when a common LLC SAPI 231 is used between different
 transaction types 232, 234 and 236, the LLC-connection 225 is established
 by using different protocol discriminators (PDs) 240, 242 and 244 to
 distinguish between the transaction types 232, 234 and 236, respectively.
 With the new LCS layer 236, when a positioning request for a particular MS
 20 that is GPRS attached, e.g., registered with a SGSN 30, is received by
 the SGSN 30, positioning of that MS 20 can be performed regardless of
 whether the MS 20 is currently engaged in a data call or is receiving or
 sending a short message. For example, as can be seen in FIG. 4 of the
 drawings, which will be described in connection with the steps listed in
 FIG. 5 of the drawings, positioning of a particular MS 20 typically begins
 by a requesting Location Application (LA) 280 sending a positioning
 request 285, which specifies the particular Mobile Station International
 Subscriber Identity Number(s) (MSISDN) associated with the particular MS
 20 to be positioned, to a Gateway Mobile Location Center (GMLC) 290 within
 the Public Land Mobile Network (PLMN) 10b of the LA 280 (step 500).
 When the GMLC 290 receives the positioning request 285 (step 500), the GMLC
 290 sends a request for routing information (step 505), e.g., the address
 of the SGSN 30 serving the PLMN 10a that the MS 20 is currently located in
 and positioning subscription information for the MS 20, to the MS's Home
 Location Register (HLR) 26, using the MS's 20 directory number as a global
 title. The signaling network, e.g., the Signaling System #7 (SS7) network
 (not shown), can perform a global title translation on the MSISDN and
 route the request to the appropriate HLR 26 for the MS 20.
 The HLR 26 checks its records to confirm that the MS 20 is registered in
 the HLR 26 (step 510), and that routing information for that MS 20 is
 available (step 515). If the MS 20 is not registered in the HLR 26 (step
 510) or the routing information is not available (step 515), the routing
 information request is rejected by the HLR 26 (step 520) and the GMLC 290
 sends a rejection message 295 to the requesting LA 280 (step 525).
 However, if the MS 20 is registered in the HLR 26 (step 510) and routing
 information for the SGSN 30 is available (step 515), the routing
 information, e.g., the SGSN 30 address, together with the positioning
 subscription information, is sent to the GMLC 290 (step 530).
 The GMLC 290 verifies that the MS 20 allows positioning to be performed
 (step 535), e.g., by checking the positioning subscription information,
 sent by the HLR 26, and if the MS 400 does not allow positioning (step
 535), the positioning request 285 is rejected (step 520) and a rejection
 message 295 is sent to the LA 280 (step 525). However, if the MS 20 does
 allow positioning (step 535), the GMLC 290 can send the positioning
 request 285 to the SGSN 30 (step 540) to perform positioning of the MS 20.
 Normally, at this point, if the SGSN 30 determines that the MS 20 has
 established a data call connection or is receiving or sending a short
 message, the positioning request 285 would be rejected. However, with the
 new LCS layer 236 shown in FIGS. 3A and 3B, if, for example, the MS 20 is
 engaged in a data call connection over the Public Data Network (PDN) 260,
 which can be, for example, the Internet, via a Gateway General Packet
 Radio Service Node (GGSN) 265, the SGSN 30 can allow the positioning to
 occur by establishing an LCS 236 LLC-connection 225 between the SGSN 30
 and the MS 20 to be positioned (step 545) in addition to the SS 232
 LLC-connection 225 between the SGSN 30 and the MS 20 using either separate
 PD's 244 and 243, respectively or separate SAPI's 237 and 233,
 respectively.
 In order to complete the positioning process, the SGSN 30 can forward the
 positioning request 285 to a Base Station Controller (BSC) 23 (step 550)
 serving the MS 20. It should be noted that if the MS 20 is not engaged in
 a call connection, e.g., the MS 20 is in idle mode, the SGSN 30 must first
 page the MS 20 prior to forwarding the positioning request 285 to the BSC
 23 (step 550).
 The originating BSC 23 then determines which Base Transceiver Station (BTS)
 24a is currently serving the MS 20, and obtains a Timing Advance (TA)
 value (TA1 ), or other positioning data, from this serving BTS 24a, if
 possible. TA values corresponds to the amount of time in advance that the
 MS 20 must send a message in order for the BTS 24a to receive it in the
 time slot allocated to that MS 20. When a message is sent from the MS 20
 to the BTS 24a, there is a propagation delay, which depends upon the
 distance between the MS 20 and the BTS 24a. TA values are expressed in bit
 periods, and can range from 0 to 63, with each bit period corresponding to
 approximately 550 meters between the MS 20 and the BTS 24a.
 Thereafter, TA values are obtained from at least two target BTSs (24b and
 24c) (step 555) by performing a positioning handover. If the serving BTS
 24a does not support positioning, an additional target BTS (not shown)
 must be selected. It should be noted that positioning of the MS 20 can be
 performed using more than three BTSs (24a, 24b, and 24c).
 The TA values (TA1, TA2 and TA3) measured by the BTS's (24a, 24b and 24c)
 are then transmitted by the serving BSC 23 to the SGSN 30 (step 560).
 Finally, the TA values (TA1, TA2 and TA3) and the positioning request 285
 are forwarded to a serving Mobile Location Center (MLC) 270 from the SGSN
 30 (step 565), where the location of the MS 20 is determined using a
 triangulation algorithm (step 570). The MLC 270 then presents positioning
 information 275 representing the geographical position of the MS 20 to the
 requesting LA (node) 280 (step 575) without interrupting the data call
 connection between the positioned MS 20 and the Internet 260.
 It should be understood, however, that any estimate of time, distance, or
 angle for any cellular system can be used, instead of the TA value method
 discussed herein. For example, the MS 20 can have a Global Positioning
 System (GPS) receiver built into it, which can be used to determine the
 location of the MS 20. In addition, the MS 20 can collect positioning data
 based on the Observed Time Difference (OTD) between the time a BTS 24
 sends out a signal and the time the MS 20 receives the signal. This time
 difference information can be sent to the MLC 270 for calculation of the
 location of the MS 20. Alternatively, the MS 20, with knowledge of the
 location of the BTS 24, can determine its location and forward it to the
 MLC 270.
 In addition to providing a layer for Location Service features, the new LCS
 layer 236 in FIGS. 3A and 3B, which is defined on the CM-sublayer level
 230 can be used as a generic layer in the CM-sublayer 230 to cater for any
 network 10 and/or MS 20 feature not belonging to any existing layer 232 or
 234 in the CM-sublayer 230. A generic SAPI 237 or generic PD 244 can be
 used to distinguish the generic 236 sub-layer from the SS 232 and SM 234
 sub-layers. However, in this case, if the LCS layer 236 is used for
 another feature for a particular subscriber, positioning of that
 subscriber at the same time would not be possible.
 As will be recognized by those skilled in the art, the innovative concepts
 described in the present application can be modified and varied over a
 wide range of applications. Accordingly, the scope of patented subject
 matter should not be limited to any of the specific exemplary teachings
 discussed, but is instead defined by the following claims.