Title of Invention	METHOD AND APPARATUS FOR REGISTERING A MOBILE STATION
Abstract	A communication system (200) provides for a mobile station (MS) (202) to pre-register with a Serving GPRS Support Node (SGSN) (250) servicing a neighboring Routing Area (RA) (208) that is a handoff candidate. In pre-registering with the neighboring RA and SGSN, the MS at least partially registers with the RA and SGSN, that is, at least a portion of the MS's registration information is conveyed to the neighboring SGSN serving the neighboring RA, prior to the MS being served by an associated neighboring BSS (230), for example, prior to an initiation of a handoff of the MS to the neighboring BSS. By pre-registering with the candidate SGSN, a duration of a registration process and the corresponding service disruptions when the MS is handed off to such an SGSN are reduced.

Title of Invention

METHOD AND APPARATUS FOR REGISTERING A MOBILE STATION

Abstract

A communication system (200) provides for a mobile station (MS) (202) to pre-register with a Serving GPRS Support Node (SGSN) (250) servicing a neighboring Routing Area (RA) (208) that is a handoff candidate. In pre-registering with the neighboring RA and SGSN, the MS at least partially registers with the RA and SGSN, that is, at least a portion of the MS's registration information is conveyed to the neighboring SGSN serving the neighboring RA, prior to the MS being served by an associated neighboring BSS (230), for example, prior to an initiation of a handoff of the MS to the neighboring BSS. By pre-registering with the candidate SGSN, a duration of a registration process and the corresponding service disruptions when the MS is handed off to such an SGSN are reduced.

Full Text	Field of the Invention The present invention relates generally to cellular communication systems, and, in particular, to mobile station registration in a cellular communication system. Background of the Invention The General Packet Radio Service (GPRS) standard provides a compatibility standard for cellular mobile telecommunications systems. The GPRS standard ensures that a mobile station (MS) operating in a GPRS system can obtain communication services when operating in a system manufactured according to the standard. To ensure compatibility, radio system parameters and call processing procedures are specified by the standard, including call processing steps that are executed by an MS and a base station subsystem serving the MS in order to provide for cell reselection. FIG. 1 is a block diagram of an exemplary GPRS communication system 100 of the prior art. Communication system 100 includes multiple Base Station Systems (BSSs) 110, J20. Each BSS 110, 120 includes a respective transceiver 112, 122 that is coupled to a respective controller 114,124. Each BSS 110,120 is coupled to a respective Serving GPRS Support Node (SGSN) 116,126. In turn, each SGSN 116, 126 is further coupled to a Gateway GPRS Support Node (GGSN) 130 and, via the GGSN, to an external network 132. BSSs 110,120, SGSNs 116,126, and GGSN 130 are collectively referred to as an infrastructure of communication system 100. Communication system 100 further includes an MS 102 that resides in a first Routing Area (RA) and is provided communication services by a serving, or source, BSS 110 and a serving, or source, SGSN 116 serving the first RA. Typically, data is transferred between MS 102 and the serving BSS 110 over an air interface, or wireless communication link, 104 that includes a forward link and a reverse link. As MS 102 moves around in communication system 100, the MS may experience deterioration in radio frequency (RF) signal conditions or congestion conditions with respect to the communication services provided to the MS by BSS 110. As a result, the MS 102 may decide to perform a cell reselection. In GPRS communication systems, such as communication system 100, the burden of cell selection is imposed on the MS. That is, in a GPRS communication system, the MS initiates a cell reselection and selects a target cell. During cell reselection, the MS may decide to abandon a serving RA, that is, the RA serviced by BSS 110 and SGSN 116, and to move to a neighboring, or target, RA, such as an RA serviced by BSS 120, and SGSN 126. In the current implementation of a GPRS system such as system 100, when MS 102 switches RAs, that is, is handed over from the source RA to the target RA, the MS establishes a wireless communication link 106 with the target BSS 120 serving the target RA and terminates the communication link. 104 with the source RA. Upon estabhihing communication link 106, MS 102 must then register with the target SGSN 126 servicing the target RA. Upon establishing communication link 106 with BSS 120, MS 102 ceases listening to the forward link associated with source BSS 110. As a result, MS 102 does not receive any data packets that may be conveyed by source BSS 110 to MS 102 subsequent to the MS establishing communication link 106 with target BSS 120. Any such data packets must be reconveyed to SGSN 126 and then conveyed by SGSN 126 to MS 102 via BSS 120. However, MS 102 must first register with SGSN 126 before the SGSN conveys any data packets to the MS. As a result, all data flows are put on hold while MS 102 registers with the new SGSN 126, which registration process may take several seconds. Initially, GPRS did not support real-time services and a data flow disruption of several seconds during cell reselection was not an important issue. However, as real-time services are added to GPRS communication systems, the need has arisen for minimizing the disruption to data flows during a cell reselection involving a switch of RAs. Therefore, a need exists for a method and apparatus that reduces a length of time that data flows are disrupted during a cell reselection involving a switch of RAs in a GPRS communication system. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS FIG. 1 is a block diagram of a wireless communication system of the prior art. FIG. 2 is a block diagram of a wireless communicatioh system in accordance with an embodiment of the present invention: FIG. 3 is a logic flow diagram of a process by which a mobile station of FIG. 2. pre-registers with a potential target Serving GPRS Support Node (SGSN) of FIG. 2 in accordance with an embodiment of the present invention. FIG. 4 is a block diagram of an exemplary, modified System Information message in accordance with an embodiment of the present invention. FIG. 5 is a logic flow diagram of a mobile station-initiated pre-registration process in accordance with various embodiments of the present invention. FIG. 6A is a logic flow diagram of an infrastructure-initiated pre-registration process in accordance with various embodiments of the present invention. FIG. 6B is a continuation of the logic flow diagram of FIG. 6A depicting an infrastracture-inititiated pre-registration process in accordance with various embodiments of the present invention. Detailed Description of the Invention To address the need for a method and apparatus that reduces a length of time that data flows are disrupted during a cell reselection involving a switch of Routing Areas (RAs) in a General Packet Radio Service (GPRS) communication system, a communication system provides for a mobile station (MS) to pre-register with a Serving GPRS Support Node (SGSN) servicing a neighboring Routing Area (RA) that is a handoff candidate. In pre-registering with the neighboring RA and SGSN, the MS at least partially registers with the RA and SGSN, that is, at least a portion of the MS's registration information is conveyed to the neighboring SGSN serving the neighboring RA, prior to the MS being served by an associated neighboring BSS 230, for example, prior to an initiation of a handoff of the MS to neighboring BSS 230. By pre-registering with the candidate SGSN, the duration of a registration process and the corresponding service disruptions when the MS is handed off to such an SGSN are reduced. Generally, an embodiment of the present invention encompasses a method for registering a mobile station comprising registering the mobile station with a first Serving GPRS Support Node (SGSN), wherein the first SGSN services a first Base Station System (BSS) that provides communication services to the mobile station, assembling a Neighbor List that comprises a plurality of communication channels, wherein a communication channel of the plurality of communication channels is associated with a second BSS that is serviced by a second SGSN that is different than the first SGSN, and at least partially registering the mobile station with the second SGSN prior to the mobile station being served by the second BSS. Another embodiment of the present invention encompasses an apparatus for pre- registering a mobile station, the apparatus comprising a first Serving GPRS Support Node (SGSN) having at least one memory device that maintains registration information concerning a mobile station and a processor operably coupled to the memory device that pre-registers the mobile station with a second SGSN, wherein the processor pre-registers the mobile station with the second SGSN prior to the mobile station being served by a Base Station System associated with the second SGSN. Still another embodiment of the present invention encompasses a mobile station comprising at least one memory device and a processor operably coupled to the memory device that receives a Neighbor List, stores the Neighbor List in the at least one memory device, and conveys, to a Base Station System associated with a Serving GPRS Support Node, a request to pre-register the mobile station. The present invention may be more fully described with reference to FIGs. 2-6B. FIG. 2 is a block diagram of a wireless communication system 200 in accordance with an embodiment of the present invention. Communication system 200 includes multiple Base Station Systems (BSSs) 220, 230 (two shown). Each BSS 220, 230, includes a respective at least one transceiver 222, 232, such as a Base Transceiver Station (BTS), that is operably coupled to a respective controller 224,234. As is known in tide art, each BSS 220, 230 may include elements such as a Base Station Controller (BSC), and a Packet Control Unit (PCU) or a Packet Control Function (PCF). When a BSS, such as BSS 220 or 230, includes such elements, controller 224 may be implemented in any one of such elements or may be distributed among such elements. Each BSS 220, 230 is coupled to a respective Serving GPRS Support Node (SGSN) 240, 250 by an interface, for example by a Gb interface or an Iu-ps interface, that includes a bearer path and a signaling interface. In turn, each SGSN 240, 250 is further coupled to a Gateway GPRS Support Node (GGSN) 260 and, via the GGSN, to an external network 280. BSSs 220, 230, SGSNs 240,250, and GGSN 260 are collectively referred to as an infrastructure 270 of communication system 200. Each SGSN 240, 250 provides communication services via an associated BSS 220, 230 to a respective Routing Area (RA) 206, 208. Communication system 200 further includes an MS 202 that resides in a first Routing Area (RA) 206 serviced by a first serving, or source, BSS 220 and a first serving, or source, SGSN 240. Data is transferred between MS 202 and serving BSS 220 via an air interface 210 that includes a forward link 211 and a reverse link 212. Forward link 211 comprises multiple . communication channels including at least one broadcast channel, at least one traffic channel, and at least one control channel. Reverse link 212 also comprises multiple communication channels, including an access channel, at least one traffic channel, and at least one control channel. Each of MS 202, controllers 224,234 and SGSNs 240,250 includes a respective processor 203, 226,236,242,252 operably coupled to, or associated with, a respective at least one memory device 204,228,238, 244,254. Each of processors 203,226,236,242, and 252 comprises one or more microprocessors, microcontrollers, digital signal processors (DSPs), combinations thereof or such other devices known to those having ordinary skill in the art. Each of the at least one memory devices 204,228,238,244, and 254 comprises at least one memory device such as a random access memory (RAM), a dynamic random access memory (DRAM), and/or a read only memory (ROM) or equivalents thereof, that maintains data and programs that may be executed by the corresponding processor. In addition, each of the at least one memory devices 244 and 254 of respective SGSNs 240 and 250 may further maintain a list of BSSs, such as BSSs 220 and 230, operating in communication system 200 in association with an SGSN, that is, SGSNs 240 and 250, servicing each BSS. Furthermore, each of the at least one memory devices 228 and 238 of respective controllers 224 and 234 and/or each of the at least one memory devices 244 and 254 of respective SGSNs 240 and 250 may further, maintain a record of a geographical location of each BSS 220, 230 in communication system 200. Communication system 200 comprises a wireless packet data communication, system. In order for MS 202 to establish a packet data connection with an external network such as external network 280, each of MS 202 and multiple BSSs 220, 230, multiple SGSNs 240, 250, and GGSN 260 operates in accordance with the General Packet Radio Service (GPRS) standard, and in particular with 3GPP (Third Generation Partnership Project) TS (Technical Specification) 23.060 v5.0.0,3GPP TS 44.060 v4.4.0, 3GPP TS 45.008 v5.4.0, 3GPP TS 04.18 v8.12.0, which standards are hereby incorporated by reference herein and copies of which may be obtained from the 3GPP via. the Internet or from the 3GPP Organization Partners' Publications Offices at Mobile Competence Centre 650, route des Lucioles, 06921 Sophia-Antipolis Cedex, France. The. GPRS standard specifies wireless telecommunications system operating protocols, including radio system parameters and call processing and handoff procedures, for GPRS communication systems. By operating in accordance with the GPRS standard, a user of MS 202 can be assured that MS 202 will be able to communicate with infrastructure 270 and establish a packet data communication link with an external network, such as network 280, via infrastructure 270. In communication system 200, a communication channel comprises one or more time slots of multiple time slots transmitted in a frequency bandwidth. However, those who are of ordinary skill in the art realize that communication system 200 may operate in accordance with any one of a variety of wireless packet data communication systems, such as a Global System for Mobile Communication (GSM) communication system, a Time Division Multiple Access (TDMA) communication system, a Code Division Multiple Access (CDMA) - communication system, or an Orthogonal Frequency Division Multiple Access (OFDM) communication system. Each controller 224,234 maintains a record, in an associated at least one memory device 228, 238, of each MS that is active in communication system 200 and is serviced by the controller. Preferably, the controller maintains the records of active MSs by storing an MS identifier (MS ID) uniquely associated with each such MS in an associated at least one memory device 228,238. For example, when MS 202 initiates a packet data session, the MS conveys a request for a channel assignment, preferably a Channel Request message, to a BSS servicing the MS, that is, BSS 220. The channel assignment request is received by BSS 220, and in particular transceiver 222, and forwarded to controller 224. In response receiving the request, controller 224 assigns to MS 202 one or more communication channels, including a traffic channel, in air interface 210 at transceiver 222 and conveys to transceiver 222 an Uplink Immediate Assignment (ULIA) message informing of the one or more assigned communication channels. Transceiver 222 then forwards the ULIA message to MS 202. Channel Request messages and ULIA messages are well known in the art and will not be described in detail herein. Upon receiving the ULlA message from BSS 220, MS 202 conveys a message including uplink . data (ULData) and an MS identifier (MS ID) uniquely associated with the MS, such as a Temporarily Logical Link Identifier (TLLI), to serving BSS 220. BSS 220 stores the received MS ID in the least one memory device 228 and forwards the message to associated serving SGSN 240. Upon receiving the message, SGSN 240 stores the received MS ID in the at least one memory device 244 of the SGSN. SGSN 240 further establishes communication links between the SGSN and GGSN 260 for conveyance of data and other messages to and from MS 202, such as GPRS Tunneling Protocol (GTP) tunnels and flow identifiers for Packet Data Protocol (PDP) contexts. In addition, serving BSS 220 assembles and maintains, in the at least one memory device 244 and in association with MS 202, a Neighbor List 216 comprising communication channels associated with BSSs, such as BSS 230, that are potential handoff candidates for MS 202. In another embodiment of the present invention, Neighbor List 216 may be assembled by serving SGSN 240. BSS 220 or SGSN 240, whichever is appropriate, then conveys the assembled Neighbor List to MS 202. Upon receiving Neighbor List 216, MS 202 monitors one or more of the communication channels included in the Neighbor List. As MS 202 moves around in communication system 200, the MS may experience deterioration in radio frequency (RF) signal conditions or congestion conditions with respect to the communication services provided to the MS by serving BSS 220. Alternatively, MS 202 may be informed of a preferred cell reselection candidate, such as a neighboring cell in target RA 208 and/or an associated neighboring BSS 230, by infrastructure 270. As a result, the MS 202 may decide to perform a cell reselection. During cell reselection, MS 202 may decide to abandon a first, source RA, that is, RA 206, and to move to a neighboring, target RA, such as a second RA 208 serviced by a second BSS 230 and a second SGSN 250. ■ ■ ■ In a prior art communication system such as communication system 100, when an MS is handed off from a first, source RA to a second, neighboring RA, and in particular from, a first, source SGSN to a second, target SGSN, the MS must re-register in the second, neighboring RA, that is, with the second, target SGSN. The re-registration may cause a disruption in the data flow of several seconds and as many as seven to eight seconds, which disruption is unacceptable for real time services such as voice services. As a result, communication system 200 provides for an MS, such as MS 202, to pre- register with an SGSN, such as SGSN 250, servicing a neighboring RA, that is, RA 208, that is a handoff candidate. In pre-registering in a neighboring RA 208 with SGSN 250, the MS at least partially registers with the SGSN, that is, at least a portion of the MS's registration information is conveyed to the neighboring SGSN serving the neighboring RA, prior to the MS being served by an associated neighboring BSS 230, for example, prior to an initiation of a handoff of the MS to neighboring BSS 230. By pre-registering with a potential target SGSN, the duration of a registration process and the corresponding service disruptions when the MS is handed off to such an SGSN are reduced. FIG. 3 is a logic flow diagram 300 of a process whereby an MS in communication system 200, such as MS 202, pre-registers in a potential target RA, and in particular with a potential target SGSN, such as SGSN 250, in accordance with an embodiment of the present invention. Logic flow diagram 300 begins (302) when an MS, such as MS 202, initially registers (304) with a serving BSS and a serving SGSN, that is, BSS 220 and SGSN 240. As part of the registration process, serving BSS 220, and in particular controller 224 of serving BSS 220, assembles (306) Neighbor List 216 and conveys (308) the assembled Neighbor List to MS 202. In another embodiment of the present invention, Neighbor List 216 may be assembled by serving SGSN 240 and conveyed by the SGSN to MS 202. Unless otherwise specified herein, all functions performed herein by MS 202, controller 224, controller 234, SGSN 240, or SGSN 250 are respectively performed by processor 203, 226, 236, 242, and 252. Furthermore, unless otherwise specified herein, all functions performed herein by BSS 220 or BSS 230 are respectively performed by controllers 224 and 234, and specifically by processors 226 and 236 of controllers 224 and 234. In one embodiment of the present invention, Neighbor List 216 may be a typical Neighbor List of the prior art, comprising a list of broadcast channels (BCCH) associated with each of multiple neighboring BSSs, such as a broadcast channel associated with BSS 230. In such an embodiment of the present invention, each BSS of the multiple neighboring BSSs broadcasts information concerning an RA and or SGSN associated with the BSS via the associated broadcast channel. In response to receiving Neighbor List 216, MS 202 monitors the listed broadcast channels and receives the RA and/or SGSN information from each BSS included in the Neighbor List. In another embodiment of the present invention, Neighbor List 216, in addition to including a list of broadcast channels (BCCH) associated with each of multiple- neighboring BSSs, further includes, in association with each broadcast channel listed in the Neighbor List, an indicator of an RA or SGSN associated with the corresponding BSS. For example, in one embodiment of the present invention, Neighbor List 216 may include a single bit that indicates whether the BSS is a member of a same RA 206 as the first, serving or source, BSS 220. That is, from another perspective, Neighbor List 216 may indicate, for each listed broadcast channel, whether the corresponding BSS is serviced by a same SGSN as the SGSN 240 servicing the serving BSS 220. For example, Neighbor List 216 may include, in association with each listed broadcast channel, an RA membership data field. When the corresponding BSS is included in a same RA as source BSS 220, that is, is serviced by a same SGSN 240 as source BSS 220, then serving SGSN 240 may embed a value of '1' in the RA membership data field. When the corresponding BSS is included in an RA, such as RA 208 with respect to BSS 230 and SGSN 250, different from the RA serviced by source BSS 220 and source SGSN 240, then serving SGSN 240 may embed a value of '0' in the RA membership data field. For example, Neighbor List 216 may be conveyed to MS 202 via a modified version of a System Information (SI) message, such as a modified SI 2, SI2bis, SI5, or an SI5bis message. La order to provide an indicator of an RA or SGSN associated with each BSS in the Neighbor List, infrastructure 270 may modify the SI message to include the RA or SGSN indicator. An example of such a modified SI message is depicted in FIG. 4. As shown in FIG. 4, an exemplary, modified SI message 400 may include a Layer 2 Pseudo Length data field 402, a Protocol Discrirninator data field 404, a Skip Indicator data field 406, a Message Type data field 408, a Neighbor Cell Description data field 410 that informs of multiple neighbor cells and associated BSSs, such as a list of broadcast frequencies of each of multiple neighboring BSSs, a Network Colour Code (NCC) Permitted data field 412, and a Random Access Channel (RACH) Parameters data field 414. Such data fields are typical of an SI message. However, unlike a typical SI message, SI message 400 further includes an RA Membership data field 416 informing of an RA/SGSN associated with, or not associated with, each of the multiple neighbor cells and associated BSSs. SGSN 240 may then embed the RA/SGSN indicators in data field 416. In another embodiment of the present invention, instead of an indicator indicating a 'same' or 'different' RA or SGSN, each indicator may comprise an identifier associated with the RA in which the corresponding BSS located or an identifier associated with the SGSN servicing the corresponding BSS. For example, the identifier may comprise a code mat is uniquely associated with the RA or may comprise an identifier, such as a routing address such as an Internet Protocol (IP) address, that is uniquely associated with the SGSN. However, an advantage of using an indicator comprising a single bit is that a mere 16 bits, or two octets, are consumed in indicating an RA, or SGSN, associated with each of 16 broadcast channels typically included in a Neighbor List. Referring again to FIG. 3, in response to receiving (310) Neighbor List 216, MS 202 stores (312) the received Neighbor List in the at least one memory device 204 of the MS. Based on Neighbor List 216 and/or in response to at least one of a change in channel conditions between MS 202 and BSS 220, a change in channel conditions between MS 202 and a neighboring BSS associated with an SGSN other than serving SGSN 240, such as BSS 230 and SGSN 250, and a movement of MS 202, MS 202 then pre-registers (314) in at least one RA, such as RA 208, and with an associated SGSN, that is, SGSN 250, that is associated with a BSS 230 corresponding to a channel in the Neighbor List and that is different than the RA 206/SGSN 240 associated with serving BSS 220. In pre- registering with a neighboring RA 208/SGSN 250, MS 202 at least partially registers with such an RA/SGSN prior to MS 202 being served by the associated neighboring BSS 230. . In pre-registering MS 202 with neighboring RA 208/SGSN 250, at least a portion of the registration information associated with the MS is conveyed to, and received by, neighboring SGSN 250. In response to receiving the registration information, SGSN 250 stores (316) the registration information in the at least one memory device 254 of the SGSN and logic flow 300 then ends (318). In one embodiment of the present invention, the step of pre-registering (314) with RA 208/SGSN 250 may be initiated.by MS 202. FIG. 5 is a logic flow diagram 500 depicting an MS-initiated pre-registration in accordance with various embodiments of the present invention. Logic flow diagram 500 begins (502) when MS 202 determines (504) to pre-register with a neighbor SGSN, that is, SGSN 250. In one embodiment of the present invention, step 504 may comprise the following steps. In response to receiving , Neighbor List 216, MS 202 determines whether any neighbor BSS, that is, a BSS associated with a communication channel in the Neighbor List, is further associated with an RA or SGSN different than the RA 206 or SGSN 240 associated with serving BSS 220. In response to determining that a BSS, such as BSS 230, associated with a communication channel in the Neighbor List is further associated with a neighbor RA or SGSN, such as RA 208 and SGSN 250, different than the serving RA 206 or serving SGSN 240, MS 202 determines to pre-register with the neighbor RA or SGSN. In another embodiment of the present invention, step 504 may comprise the following steps. In response to receiving Neighbor List 216, MS 202 may monitor each broadcast channel identified in the Neighbor List. MS 202 determines a signal quality metric, such as a signal strength, a signal-to-noise ratio (SNR), or a bit error rate (BER), with respect to each monitored channel and compares each determined signal quality metric to a pre-registration signal quality metric threshold that is maintained in the at least one memory device 204 of the MS. When a determined signal quality metric compares favorably with the pre-registration signal quality metric threshold, for example, exceeds a signal strength threshold or a SNR threshold, then MS 202 determines to pre-register with a neighbor SGSN associated with the monitored broadcast channel and an associated BSS. MS 202 may further determine that the neighbor RA/SGSN is different than the serving RA/SGSN, or the serving SGSN, that is, SGSN 240, may determine that the neighbor RA/SGSN associated with the neighbor BSS is different than the serving RA/SGSN. In response to detennining to pre-register with a neighbor SGSN, that is, SGSN 250, MS 202 conveys (506) a pre-registration request to infrastructure 270. In one embodiment of the present invention, MS 202 may convey a pre-registration request to infrastructure 270 by conveying a first pre-registration request 218 to BSS 220 via the at least one control channel in reverse link 212, and via BSS 220 to serving SGSN 240. First pre-registration request 218 requests that infrastructure 270 pre-register MS 202 with neighbor SGSN 250. Pre-registration request 218 may specifically identify the neighbor SGSN, that is, SGSN 250, or an RA, that is, RA 208, associated with the neighbor BSS 230 and neighbor SGSN, or serving SGSN 240 may determine the neighbor SGSN by retrieving Neighbor List information stored in the at least one memory device 244 of the serving SGSN in response to receiving the pre-registration request. In response to receiving pre-registration request 218, serving SGSN 240 conveys (508) registration information associated with MS 202 to the neighbor SGSN, that is, SGSN 250. In one embodiment of the present invention, serving SGSN 240 may convey to SGSN 250 at least a portion of the registration information associated with MS 202 and maintained by the serving SGSN in the at least one memory device 244. In another embodiment of the present invention, pre-registration request 218 may further include registration information intended for SGSN 250. In response to receiving pre-registration request 218, serving SGSN 240 forwards the received registration information to SGSN 250. In yet another embodiment of the present invention, in response to receiving pre- registration request 218, serving SGSN may request registration information from MS 202, for example, by conveying a registration request to MS 202. In response to receiving the registration request, MS 202 may convey registration information to SGSN 240, which registration information is forwarded by SGSN 240 to SGSN 250. Serving SGSN 240 may convey the registration information to SGSN 250 via GGSN 260 or, in response to receiving pre-registration request 218, may establish a point-to-point communication with SGSN 250 and convey the information via the established point-to- point communication. In response to receiving the registration information from SGSN 240, SGSN 250 stores (510) the registration information in the at least one memory device 254 of the SGSN. In addition, in response to receiving registration information for MS 202 from SGSN 240, SGSN 250 may also establish (518) communication links with BSS 230 and/or GGSN 260 for transmission of data to and from MS 202. Logic flow 500 then ends (520). In another embodiment of the present invention, instead of conveying first pre- registration request 218 to serving BSS 20, MS 202 may convey a second pre-registration request 219 to neighbor BSS 230 via a control channel in a reverse link 214 between the MS and BSS 230, and via BSS 230 to SGSN 250. Second pre-registration request 219 requests that BSS 230 and associated SGSN. 250 pre-register MS 202. In one embodiment of the present invention, second pre-registration request 219 may identify serving SGSN 240. In response to receiving pre-registration request 219, SGSN 250 may request (512), from serving SGSN 240, at least a portion of registration information associated with MS 202. The request maybe conveyed by SGSN 250 to SGSN 240 via GGSN 260 or via a communication link established between SGSN 250 and SGSN 240. In response to receiving the request for at least a portion of the registration information, SGSN 240 then conveys (514) the requested information to SGSN 250 and SGSN 250 stores the received registration information in the at least one memory device 254. In another embodiment of the present invention, second pre-registration request 219 may not identify SGSN 240. In such an embodiment of the present invention, in response to receiving the second pre-registration request, SGSN 250 may initiate (516) a pre- registration process with MS 202 that comprises steps of a typical registration process involving an exchange of registration information between MS 202 and SGSN 250. In yet another embodiment of the present invention, pre-registration request 219 may further include registration information associated with MS 202. In response to receiving pre- registration request 219, serving SGSN 250 stores the received registration information in the at least one memory device 254. Logic flow 500 then ends (520). In each of the above embodiments of an MS initiated pre-registration, in addition to obtaining registration information concerning MS 202, neighboring SGSN 250 may also establish (518) communication links with BSS 230 and/or GGSN 260 for transmission of data to and from MS 202 as part of the pre-registration process. In still other embodiments of the present invention, the step of pre-registering (314) MS 202 with RA 208/SGSN 250 may be initiated by infrastructure 270. Referring now to FIGs. 6A and 6B, a logic flow diagram 600 is depicted of an infrastructure-initiated pre- registration in accordance with various embodiments of the present invention. In one embodiment of an infrastructure-initiated pre-registration process, logic flow diagram 600 begins (602) when infrastructure 270 receives (604), from MS 202, signal quality information corresponding to Neighbor List communication channels monitored by the MS. In one such embodiment, similar to the MS-imtiated pre-registration embodiment, in response to receiving Neighbor List 216, MS 202 monitors each broadcast channel identified in the Neighbor List. MS 202 determines a signal quality metric, such as a signal strength, a signal-to-noise ratio (SNR), or a bit error rate (BER), with respect to each monitored channel and conveys the signal quality metrics to infrastructure 270 via serving BSS 220. Based on the received signal quality information, serving BSS 220, and in particular serving controller 224, or serving SGSN 240 then determines (606) whether to pre-register MS 202 with a neighboring RA 208/SGSN 250 associated with a communication channel of Neighbor List 216. In one embodiment of the present invention, wherein infrastructure 270 receives signal quality metrics from MS 202, serving BSS 220 or serving SGSN 240 then compares each received signal quality metric to a pre-registration signal quality metric threshold. In another embodiment of the present invention, MS 202 may perform the comparison and convey the results of the comparison to infrastructure 270. When serving BSS 220 performs the comparison or receives comparison results from MS 202 and a determination of whether to pre-register MS 202 with a neighboring RA/SGSN resides in serving SGSN 240, the serving BSS conveys the comparison results to serving SGSN 240. When a determined signal quality metric compares favorably with the pre-registration signal quality metric threshold and serving BSS 220 or serving SGSN 240, whichever element of communication system 200 is making the pre-registration decision, further determines that the SGSN associated with the monitored signal, such as SGSN 250, is different than the serving SGSN, then the serving BSS or SGSN determines to initiate a pre-registration of MS 202 with such neighbor SGSN. In another infrastructure-initiated embodiment of the present invention, serving BSS 220, and in particular serving controller 224, or serving SGSN 240 may determine whether to pre-register MS 202 based on a location of the MS. In such an embodiment, logic flow diagram 600 may begin (602) when a location of MS 202 is determined (608). In one such embodiment, MS 202 may self-determine its geographical location and convey the determined geographical location to infrastructure 270. Methods by which an MS may self-determine its geographical location are well-known in the art and will not be described in detail herein. For example, MS 202 may self-determine its geographical location based on location information received from each of multiple BSSs in communication system 200, such as based on a time difference of arrival (TDOA) of pilot signals received from each of the multiple BSSs. By way of another example, MS 202 may further include a Global Positioning System (GPS) receiver (npt shown) and may self-determine its geographical location by reference to a constellation of GPS satellites. MS 202 then conveys its determined geographical location, or at least the received location information, to infrastructure 270 via serving BSS 220, which geographical location or location information is routed to SGSN 240 or to controller 224 of BSS 220. Upon receiving the location information from MS 202, serving SGSN 240 or serving BSS 220 determines a geographical location of the MS based on the geographical location determined by MS 202 or based on the location information received from MS 202 and further retrieves the geographical locations of the BSSs associated with the Neighbor List of MS 202 from a respective at least one memory device 228,244. When controller 224 determines the locations of MS 202 and/or BSSs 220 and 230, the controller may convey each such location determination to SGSN 240. Based on the determined locations of MS 202 and at least one of BSSs 220 and 230, serving BSS 220 or serving SGSN 240 then determines (610) whether to initiate a pre-registration of MS 202 with SGSN 250. For example, serving BSS 220 or serving SGSN 240 may determine, based on multiple determinations of a geographical location of MS 202, that MS 202 is headed in a direction toward BSS 230. In response to determining that MS 202 is headed toward BSS 230, BSS 220 or SGSN 240 may determine (612) to initiate a pre-registration of MS 202 with SGSN 250. By way of another example, based on a determined location of MS 202 and BSS 230, BSS 220 or SGSN 240 may determine that MS 202 has moved to within a predetermined distance of BSS 230. In response to deterrnining that MS 202 has moved to within the predetermined distance, BSS 220 or SGSN 240 may determine (612) to initiate a pre-registration of MS 202 with SGSN 250. By way of yet another example, the at least one memory device 228, 244 of BSS 220 or SGSN 240 may maintain a geographical location of a border, for handoff purposes, between a coverage area associated with BSS 220 and a coverage area associated with BSS 230. When BSS 220 or SGSN 240 determines that MS 202 has moved to within a geographical distance of the border, the BSS or SGSN may determine (612) to initiate a pre-registration of MS 202 with RA 208/SGSN 250. In response to deterrnining to initiate a pre-registration of MS 202 with RA 208/SGSN 250, BSS 220 or SGSN 240 may either instruct (616) the MS to pre-register or may pre-register (614) the MS with SGSN 250. In an embodiment of the present invention wherein serving BSS 220 or serving SGSN 240 pre-registers (614) MS 202 with RA 208/SGSN 250, serving BSS 220 may instruct serving SGSN 240 to pre-register MS 202, or serving SGSN 240 may on its own pre-register MS 202, with neighboring SGSN 250 as is described in detail above. For example, serving SGSN 240 may pre- register MS 202 by conveying to neighboring SGSN 250 at least a portion of the registration information associated with MS 202 and maintained in the at least one memory device 244 of the serving SGSN. Serving SGSN 240 may convey the information via GGSN 260 or may establish a point-to-point communication with SGSN 250 and convey the information via the established point-to-point communication. In an embodiment of the present invention wherein BSS 220 or SGSN 240 instructs (616) the MS to pre-register, serving BSS 220 or serving SGSN 240 may convey a pre-registration instruction to MS 202 via the broadcast channel or the at least one control channel in forward link 211. The pre-registration instruction instructs MS 202 to pre-register. In one such embodiment, in response receiving the pre-registration instruction, MS 202 conveys (618) to serving SGSN 240 via serving BSS 220, and the serving SGSN receives (620) from the MS, a pre-registration request such as pre- registration request 218. In response to receiving me pre-registration request, serving SGSN 240 then pre-registers (622) MS 202 with neighbor SGSN 250 as described above, for example, by conveying to SGSN 250 registration information stored in the at least one memory device 244 of serving SGSN 240 or by forwarding registration information received by the serving SGSN from MS 202. Logic flow 600 then ends (636). In another embodiment of the present invention, in response receiving the pre- registration instruction, MS 202 may identify (624) neighboring SGSN 250 or an associated RA 208 based on the Neighbor List maintained in the at least one memory device 204 of the MS and convey (626) a pre-registration request, such as pre-registration request 219, to the neighboring SGSN. In response to receiving the pre-registration request, neighboring SGSN 250 pre-registers (628) MS 202 as described above, for example, by obtaining registration information associated with MS 202 from SGSN 240, by engaging in a registration procedure with MS 202, or by storing registration information that may be included in the received pre-registration request Logic flow 600 then ends (636). In still another embodiment, the pre-registration instruction may include an identifier associated with neighboring SGSN 250. In response to receiving the pre- registration instruction, MS 202 identifies (630) neighboring SGSN 250 based on the received instruction and conveys (632) a pre-registration request to the neighboring SGSN. In response to receiving the pre-registration request, SGSN 250 pre-registers (634) MS 202 as described above and logic flow 600 men ends (636). In each of the above embodiments, as part of the pre-registration of MS 202 with SGSN 250, SGSN 250 may further establish communication links with BSS 230 and/or GGSN 260 for transmission of data to and from MS 202. By providing for a pre-registration of MS 202 with a neighboring SGSN 250 serving a neighboring RA 208 and a neighboring BSS 230 that are handoff candidates for MS 202, communication system 200 reduces a duration of a registration process and the corresponding service disruptions when the MS is handed off to such an RA and SGSN. In pre-registering in the neighboring RA 208 with SGSN 250, MS 202 at least partially registers with SGSN 250, that is, at least a portion of the MS's registration information is conveyed to the neighboring SGSN prior to the MS being served by an associated neighboring BSS 230, for example, prior to an initiation of a handoff of the MS to the neighboring BSS 230. In various embodiments of the present invention, the at least a portion of the MS's registration information may be conveyed by the serving SGSN 240 to the neighboring SGSN 250 in response to a self-initiated transfer by the serving SGSN or in response to a request received by the serving SGSN from MS 202 or from the neighboring SGSN. In other embodiments of the present invention, the at least a portion of the MS's registration information may be conveyed by MS 202 to neighboring SGSN 250 in response to a self-initiated pre-registration by the MS or in response to an instruction received by the MS from either serving BSS 220 or SGSN 240. While the present invention has been particularly shown and described with reference to particular embodiments thereof, it will be understood by those skilled in the art that various changes may be made and equivalents substituted for elements thereof without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather then a restrictive sense, and all such changes and substitutions are intended to be included within the scope of the present invention. Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any elements) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or element of any or all the claims. As used herein, the terms "comprises," "comprising," or any variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. It is further understood that the use of relational terms, if any, such as first and second, top and bottom, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. WE CLAIM: 1. A method for registering a mobile station (202) comprising: registering (304) the mobile station with a first Serving GPRS Support Node (240), wherein the first Serving GPRS Support Node services a first Base Station System (220) that provides communication services to the mobile station and wherein the method is characterized by: assembling (306) a Neighbor List (216) that comprises a plurality of communication channels, wherein a communication channel of the plurality of communication channels is associated with a second Base Station System (230) that is serviced by a second Serving GPRS Support Node (250) that is different than the first Serving GPRS Support Node and wherein the Neighbor List informs of a Routing Area RA (208) associated with each communication channel of the plurality of communication channels; determining (504) the second BSS that is serviced by the second Serving GPRS Support Node (SGSN) and that is different than the first SGSN based on the Routing Area (208) associated with each communication channel of the plurality of communication channels included in the Neighbor List; and partially registering (314, 508) the mobile station with the second Serving GPRS Support Node based on the determined second BSS and prior to the establishment of a control channel between the mobile station and the second Base Station System. 2. The method as claimed in claim 1, wherein partially registering comprises conveying, by at least one of the mobile station and the first Serving GPRS Support Node to the second Serving GPRS Support Node, at least a portion of registration information associated with the mobile station. 3. The method as claimed in claim 1, wherein partially registering the mobile station with the second Serving GPRS Support Node comprises: receiving registration information from the mobile station; and conveying the received registration information to the second Serving GPRS Support Node. 4. The method as claimed in claim 1, wherein partially registering comprises: receiving, by the first Serving GPRS Support Node from at least one of the mobile station, the first Base Station System, and the second Serving GPRS Support Node, a request to pre-register the mobile station with the second Serving GPRS Support Node; and in response to receiving the request, conveying, by the first Serving GPRS Support Node to the second Serving GPRS Support Node, at least a portion of registration information associated with the mobile station. 5. The method as claimed in claim 4, wherein receiving comprises: receiving, by the second Serving GPRS Support Node from the mobile station, a request to pre-register the mobile station with the second Serving GPRS Support Node; conveying, by the second Serving GPRS Support Node to the first Serving GPRS Support Node, a request for at least a portion of registration information associated with the mobile station; receiving, by the first Serving GPRS Support Node from the second Serving GPRS Support Node, the request for at least a portion of the registration information; and wherein conveying comprises, in response to receiving the request from the second Serving GPRS Support Node, conveying, by the first Serving GPRS Support Node to the second Serving GPRS Support Node, at least a portion of the registration information associated with the mobile station. 6. The method as claimed in claim 1, wherein each communication channel of the plurality of communication channels is associated with a Base Station System (BSS) and wherein partially registering comprises: broadcasting, by each BSS associated with a communication channel of the plurality of communication channels, information concerning a Routing Area associated with the BSS; determining the second BSS that is serviced by the second SGSN that is different than the first SGSN based on the Routing Areas broadcast by each BSS associated with a communication channel of the plurality of the communication channels; and partially registering the mobile station with the second SGSN based on the determined second BSS and prior to the mobile station being served by the second BSS. 7. The method as claimed in claim 1, wherein partially registering comprises: determining at least one of a signal quality metric for me communication channel of the plurality of communication channels that is associated with the second Base Station System, a signal quality metric for a communication channel that is associated with the first BSS, and a geographical location of the mobile station; detennining to pre-register the mobile station with the second serving GPRS Support Node based on the determined at least one of the signal quality metric for the communication channel that is associated with me second Base Station System, the signal quality metric for the communication channel that is associated with the first Base Station System, and the geographical location of the mobile station; partially registering the mobile station with the second Serving GPRS Support Node prior to the mobile station being served by the second Base Station System. 8. An apparatus for pre-registering a mobile station, the apparatus comprising a first Serving GPRS Support Node (240) having a processor (242) that assembles a Neighbor List (216) corresponding to a mobile station (202) and comprising a plurality of broadcast channels, wherein the Neighbor List comprises a Routing Area (208) associated with at least one broadcast channel of the plurality of broadcast channels and, while currently serving the mobile station, partially registers the mobile station with a second Serving GPRS Support Node (250) based on the Routing Area (208) associated with each communication channel of the plurality of communication channels included in the Neighbor List and prior to the establishment of a control channel between the mobile station and a Base Station System (230) associated with the second Serving GPRS Support Node. 9. The apparatus as claimed in claim 8, wherein the processor pre-registers the mobile station by receiving registration information from the mobile station and conveying the received registration information to the second Serving GPRS Support Node (SGSN). 10. The apparatus as claimed in claim 8, wherein the processor receives a request to pre-register the mobile station from at least one of the mobile station, a Base Station System (BSS) associated with the first Serving GPRS Support Node (SGSN), and the second SGSN, and in response to receiving the request, pre-registers the mobile station by conveying registration information to the second SGSN. 11. The apparatus as claimed in claim 8, wherein the apparatus comprises a controller associated with a Base Station System serviced by the first Serving GPRS Support Node (SGSN), wherein the controller is in communication with the first SGSN, wherein the controller assembles a Neighbor List corresponding to the mobile station and comprising a plurality of broadcast channels, and wherein the Neighbor List comprises a Routing Area associated with at least one broadcast channel and of the plurality of broadcast channels. 12. The apparatus as claimed in claim 8, wherein the processor determines to pre- register the mobile station with the second Serving GPRS Support Node (SGSN) based on at least one of a quality of a communication channel associated with a Base Station System that is associated with the first SGSN, a quality of a communication channel associated with the Base Station System that is associated with the second SGSN, and a location of the mobile station. 13. The apparatus as claimed in claim 8, wherein the apparatus comprises the second Serving GPRS Support Node (SGSN), wherein the second SGSN receives registration information associated with the mobile station from the first SGSN and stores the received registration information in an at least one memory device of the second SGSN prior to the mobile station communicating with the second SGSN. 14. The apparatus as claimed in claim 13, wherein the second Serving GPRS Support Node (SGSN) further establishes a communication link with at least one of a Gateway GPRS Support Node (GGSN) and a Base Station System associated with the second SGSN prior to the mobile station communicating with the second SGSN. 15. The apparatus as claimed in claim 8, wherein the apparatus comprises the second Serving GPRS Support Node (SGSN) and wherein the second Serving GPRS Support Node (SGSN) conveys a message to the mobile station informing of a Routing Area associated with the second SGSN and, in response to conveying the message informing of the Routing Area, receives registration information associated with the mobile station. 16. A mobile station {202) comprising: at least one memory device (204); and a processor (203) operably coupled to the memory device that receives a Neighbor list (216) comprising a plurality of communication channels and a Routing Area (208) associated with at least one broadcast channel of the plurality of broadcast channels, stores the Neighbor List in the at least one memory device, and initiates a partial registration of the mobile station by conveying to an infrastracture (270) a request to pre-register the mobile station in a Routing Area (208) associated with a Serving GPRS Support Node (250) and further associated with a communication channel of the plurality of communication channels prior to the establishment of a control channel between the mobile station and a Base Station System (230) associated with the communication channel of the plurality of communication channels. 17. The mobile station as claimed in claim 16, wherein the Neighbor List comprises information concerning the Routing Area, wherein the Routing Area is different than a Routing Area associated with a serving Base Station System (BSS), and wherein the mobile station conveys the request to pre-register to at least one of the serving BSS and the BSS associated with the communication channel of the plurality of communication channels. 18. The mobile station as claimed in claim 16, wherein the mobile station receives information concerning the Routing Area from the Base Station System (BSS) associated with the communication channel of the plurality of communication channels. ABSTRACT "METHOD AND APPARATUS FOR REGISTERING A MOBILE STATION" A communication system (200) provides for a mobile station (MS) (202) to pre-register with a Serving GPRS Support Node (SGSN) (250) servicing a neighboring Routing Area (RA) (208) that is a handoff candidate. In pre-registering with the neighboring RA and SGSN, the MS at least partially registers with the RA and SGSN, that is, at least a portion of the MS's registration information is conveyed to the neighboring SGSN serving the neighboring RA, prior to the MS being served by an associated neighboring BSS (230), for example, prior to an initiation of a handoff of the MS to the neighboring BSS. By pre-registering with the candidate SGSN, a duration of a registration process and the corresponding service disruptions when the MS is handed off to such an SGSN are reduced.

Full Text

Field of the Invention
The present invention relates generally to cellular communication systems, and, in
particular, to mobile station registration in a cellular communication system.
Background of the Invention
The General Packet Radio Service (GPRS) standard provides a compatibility
standard for cellular mobile telecommunications systems. The GPRS standard ensures
that a mobile station (MS) operating in a GPRS system can obtain communication
services when operating in a system manufactured according to the standard. To ensure
compatibility, radio system parameters and call processing procedures are specified by the
standard, including call processing steps that are executed by an MS and a base station
subsystem serving the MS in order to provide for cell reselection.
FIG. 1 is a block diagram of an exemplary GPRS communication system 100 of
the prior art. Communication system 100 includes multiple Base Station Systems (BSSs)
110, J20. Each BSS 110, 120 includes a respective transceiver 112, 122 that is coupled
to a respective controller 114,124. Each BSS 110,120 is coupled to a respective Serving
GPRS Support Node (SGSN) 116,126. In turn, each SGSN 116, 126 is further coupled
to a Gateway GPRS Support Node (GGSN) 130 and, via the GGSN, to an external
network 132. BSSs 110,120, SGSNs 116,126, and GGSN 130 are collectively referred
to as an infrastructure of communication system 100. Communication system 100 further
includes an MS 102 that resides in a first Routing Area (RA) and is provided
communication services by a serving, or source, BSS 110 and a serving, or source, SGSN
116 serving the first RA. Typically, data is transferred between MS 102 and the serving

BSS 110 over an air interface, or wireless communication link, 104 that includes a
forward link and a reverse link.
As MS 102 moves around in communication system 100, the MS may experience
deterioration in radio frequency (RF) signal conditions or congestion conditions with
respect to the communication services provided to the MS by BSS 110. As a result, the
MS 102 may decide to perform a cell reselection. In GPRS communication systems, such
as communication system 100, the burden of cell selection is imposed on the MS. That
is, in a GPRS communication system, the MS initiates a cell reselection and selects a
target cell. During cell reselection, the MS may decide to abandon a serving RA, that is,
the RA serviced by BSS 110 and SGSN 116, and to move to a neighboring, or target, RA,
such as an RA serviced by BSS 120, and SGSN 126. In the current implementation of a
GPRS system such as system 100, when MS 102 switches RAs, that is, is handed over
from the source RA to the target RA, the MS establishes a wireless communication link
106 with the target BSS 120 serving the target RA and terminates the communication link.
104 with the source RA. Upon estabhihing communication link 106, MS 102 must then
register with the target SGSN 126 servicing the target RA.
Upon establishing communication link 106 with BSS 120, MS 102 ceases
listening to the forward link associated with source BSS 110. As a result, MS 102 does
not receive any data packets that may be conveyed by source BSS 110 to MS 102
subsequent to the MS establishing communication link 106 with target BSS 120. Any
such data packets must be reconveyed to SGSN 126 and then conveyed by SGSN 126 to
MS 102 via BSS 120. However, MS 102 must first register with SGSN 126 before the
SGSN conveys any data packets to the MS. As a result, all data flows are put on hold
while MS 102 registers with the new SGSN 126, which registration process may take
several seconds. Initially, GPRS did not support real-time services and a data flow
disruption of several seconds during cell reselection was not an important issue.
However, as real-time services are added to GPRS communication systems, the need has
arisen for minimizing the disruption to data flows during a cell reselection involving a
switch of RAs.

Therefore, a need exists for a method and apparatus that reduces a length of time
that data flows are disrupted during a cell reselection involving a switch of RAs in a
GPRS communication system.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 is a block diagram of a wireless communication system of the prior art.
FIG. 2 is a block diagram of a wireless communicatioh system in accordance with an embodiment of the present invention:
FIG. 3 is a logic flow diagram of a process by which a mobile station of FIG. 2.
pre-registers with a potential target Serving GPRS Support Node (SGSN) of FIG. 2 in
accordance with an embodiment of the present invention.
FIG. 4 is a block diagram of an exemplary, modified System Information message
in accordance with an embodiment of the present invention.
FIG. 5 is a logic flow diagram of a mobile station-initiated pre-registration process
in accordance with various embodiments of the present invention.
FIG. 6A is a logic flow diagram of an infrastructure-initiated pre-registration
process in accordance with various embodiments of the present invention.
FIG. 6B is a continuation of the logic flow diagram of FIG. 6A depicting an
infrastracture-inititiated pre-registration process in accordance with various embodiments
of the present invention.
Detailed Description of the Invention
To address the need for a method and apparatus that reduces a length of time that
data flows are disrupted during a cell reselection involving a switch of Routing Areas
(RAs) in a General Packet Radio Service (GPRS) communication system, a
communication system provides for a mobile station (MS) to pre-register with a Serving
GPRS Support Node (SGSN) servicing a neighboring Routing Area (RA) that is a
handoff candidate. In pre-registering with the neighboring RA and SGSN, the MS at least

partially registers with the RA and SGSN, that is, at least a portion of the MS's
registration information is conveyed to the neighboring SGSN serving the neighboring
RA, prior to the MS being served by an associated neighboring BSS 230, for example,
prior to an initiation of a handoff of the MS to neighboring BSS 230. By pre-registering
with the candidate SGSN, the duration of a registration process and the corresponding
service disruptions when the MS is handed off to such an SGSN are reduced.
Generally, an embodiment of the present invention encompasses a method for
registering a mobile station comprising registering the mobile station with a first Serving
GPRS Support Node (SGSN), wherein the first SGSN services a first Base Station
System (BSS) that provides communication services to the mobile station, assembling a
Neighbor List that comprises a plurality of communication channels, wherein a
communication channel of the plurality of communication channels is associated with a
second BSS that is serviced by a second SGSN that is different than the first SGSN, and
at least partially registering the mobile station with the second SGSN prior to the mobile
station being served by the second BSS.
Another embodiment of the present invention encompasses an apparatus for pre-
registering a mobile station, the apparatus comprising a first Serving GPRS Support Node
(SGSN) having at least one memory device that maintains registration information
concerning a mobile station and a processor operably coupled to the memory device that
pre-registers the mobile station with a second SGSN, wherein the processor pre-registers
the mobile station with the second SGSN prior to the mobile station being served by a
Base Station System associated with the second SGSN.
Still another embodiment of the present invention encompasses a mobile station
comprising at least one memory device and a processor operably coupled to the memory
device that receives a Neighbor List, stores the Neighbor List in the at least one memory
device, and conveys, to a Base Station System associated with a Serving GPRS Support
Node, a request to pre-register the mobile station.
The present invention may be more fully described with reference to FIGs. 2-6B.
FIG. 2 is a block diagram of a wireless communication system 200 in accordance with an
embodiment of the present invention. Communication system 200 includes multiple

Base Station Systems (BSSs) 220, 230 (two shown). Each BSS 220, 230, includes a
respective at least one transceiver 222, 232, such as a Base Transceiver Station (BTS),
that is operably coupled to a respective controller 224,234. As is known in tide art, each
BSS 220, 230 may include elements such as a Base Station Controller (BSC), and a
Packet Control Unit (PCU) or a Packet Control Function (PCF). When a BSS, such as
BSS 220 or 230, includes such elements, controller 224 may be implemented in any one
of such elements or may be distributed among such elements. Each BSS 220, 230 is
coupled to a respective Serving GPRS Support Node (SGSN) 240, 250 by an interface,
for example by a Gb interface or an Iu-ps interface, that includes a bearer path and a
signaling interface. In turn, each SGSN 240, 250 is further coupled to a Gateway GPRS
Support Node (GGSN) 260 and, via the GGSN, to an external network 280. BSSs 220,
230, SGSNs 240,250, and GGSN 260 are collectively referred to as an infrastructure 270
of communication system 200.
Each SGSN 240, 250 provides communication services via an associated BSS
220, 230 to a respective Routing Area (RA) 206, 208. Communication system 200
further includes an MS 202 that resides in a first Routing Area (RA) 206 serviced by a
first serving, or source, BSS 220 and a first serving, or source, SGSN 240. Data is
transferred between MS 202 and serving BSS 220 via an air interface 210 that includes a
forward link 211 and a reverse link 212. Forward link 211 comprises multiple .
communication channels including at least one broadcast channel, at least one traffic
channel, and at least one control channel. Reverse link 212 also comprises multiple
communication channels, including an access channel, at least one traffic channel, and at
least one control channel.
Each of MS 202, controllers 224,234 and SGSNs 240,250 includes a respective
processor 203, 226,236,242,252 operably coupled to, or associated with, a respective at
least one memory device 204,228,238, 244,254. Each of processors 203,226,236,242,
and 252 comprises one or more microprocessors, microcontrollers, digital signal
processors (DSPs), combinations thereof or such other devices known to those having
ordinary skill in the art. Each of the at least one memory devices 204,228,238,244, and
254 comprises at least one memory device such as a random access memory (RAM), a
dynamic random access memory (DRAM), and/or a read only memory (ROM) or

equivalents thereof, that maintains data and programs that may be executed by the
corresponding processor. In addition, each of the at least one memory devices 244 and
254 of respective SGSNs 240 and 250 may further maintain a list of BSSs, such as BSSs
220 and 230, operating in communication system 200 in association with an SGSN, that
is, SGSNs 240 and 250, servicing each BSS. Furthermore, each of the at least one
memory devices 228 and 238 of respective controllers 224 and 234 and/or each of the at
least one memory devices 244 and 254 of respective SGSNs 240 and 250 may further,
maintain a record of a geographical location of each BSS 220, 230 in communication system 200.
Communication system 200 comprises a wireless packet data communication,
system. In order for MS 202 to establish a packet data connection with an external
network such as external network 280, each of MS 202 and multiple BSSs 220, 230,
multiple SGSNs 240, 250, and GGSN 260 operates in accordance with the General
Packet Radio Service (GPRS) standard, and in particular with 3GPP (Third Generation
Partnership Project) TS (Technical Specification) 23.060 v5.0.0,3GPP TS 44.060 v4.4.0,
3GPP TS 45.008 v5.4.0, 3GPP TS 04.18 v8.12.0, which standards are hereby
incorporated by reference herein and copies of which may be obtained from the 3GPP via.
the Internet or from the 3GPP Organization Partners' Publications Offices at Mobile
Competence Centre 650, route des Lucioles, 06921 Sophia-Antipolis Cedex, France. The.
GPRS standard specifies wireless telecommunications system operating protocols,
including radio system parameters and call processing and handoff procedures, for GPRS
communication systems. By operating in accordance with the GPRS standard, a user of
MS 202 can be assured that MS 202 will be able to communicate with infrastructure 270
and establish a packet data communication link with an external network, such as
network 280, via infrastructure 270. In communication system 200, a communication
channel comprises one or more time slots of multiple time slots transmitted in a
frequency bandwidth. However, those who are of ordinary skill in the art realize that
communication system 200 may operate in accordance with any one of a variety of
wireless packet data communication systems, such as a Global System for Mobile
Communication (GSM) communication system, a Time Division Multiple Access
(TDMA) communication system, a Code Division Multiple Access (CDMA)

- communication system, or an Orthogonal Frequency Division Multiple Access (OFDM)
communication system.
Each controller 224,234 maintains a record, in an associated at least one memory
device 228, 238, of each MS that is active in communication system 200 and is serviced
by the controller. Preferably, the controller maintains the records of active MSs by
storing an MS identifier (MS ID) uniquely associated with each such MS in an associated
at least one memory device 228,238. For example, when MS 202 initiates a packet data
session, the MS conveys a request for a channel assignment, preferably a Channel Request message, to a BSS servicing the MS, that is, BSS 220. The channel assignment
request is received by BSS 220, and in particular transceiver 222, and forwarded to
controller 224. In response receiving the request, controller 224 assigns to MS 202 one or
more communication channels, including a traffic channel, in air interface 210 at
transceiver 222 and conveys to transceiver 222 an Uplink Immediate Assignment (ULIA)
message informing of the one or more assigned communication channels. Transceiver
222 then forwards the ULIA message to MS 202. Channel Request messages and ULIA
messages are well known in the art and will not be described in detail herein. Upon receiving the ULlA message from BSS 220, MS 202 conveys a message including uplink . data (ULData) and an MS identifier (MS ID) uniquely associated with the MS, such as a Temporarily Logical Link Identifier (TLLI), to serving BSS 220. BSS 220 stores the
received MS ID in the least one memory device 228 and forwards the message to
associated serving SGSN 240.
Upon receiving the message, SGSN 240 stores the received MS ID in the at least
one memory device 244 of the SGSN. SGSN 240 further establishes communication
links between the SGSN and GGSN 260 for conveyance of data and other messages to
and from MS 202, such as GPRS Tunneling Protocol (GTP) tunnels and flow identifiers
for Packet Data Protocol (PDP) contexts. In addition, serving BSS 220 assembles and
maintains, in the at least one memory device 244 and in association with MS 202, a
Neighbor List 216 comprising communication channels associated with BSSs, such as
BSS 230, that are potential handoff candidates for MS 202. In another embodiment of
the present invention, Neighbor List 216 may be assembled by serving SGSN 240. BSS
220 or SGSN 240, whichever is appropriate, then conveys the assembled Neighbor List to

MS 202. Upon receiving Neighbor List 216, MS 202 monitors one or more of the
communication channels included in the Neighbor List.
As MS 202 moves around in communication system 200, the MS may experience
deterioration in radio frequency (RF) signal conditions or congestion conditions with
respect to the communication services provided to the MS by serving BSS 220.
Alternatively, MS 202 may be informed of a preferred cell reselection candidate, such as
a neighboring cell in target RA 208 and/or an associated neighboring BSS 230, by
infrastructure 270. As a result, the MS 202 may decide to perform a cell reselection.
During cell reselection, MS 202 may decide to abandon a first, source RA, that is, RA
206, and to move to a neighboring, target RA, such as a second RA 208 serviced by a
second BSS 230 and a second SGSN 250.
■ ■ ■
In a prior art communication system such as communication system 100, when an
MS is handed off from a first, source RA to a second, neighboring RA, and in particular
from, a first, source SGSN to a second, target SGSN, the MS must re-register in the
second, neighboring RA, that is, with the second, target SGSN. The re-registration may
cause a disruption in the data flow of several seconds and as many as seven to eight
seconds, which disruption is unacceptable for real time services such as voice services.
As a result, communication system 200 provides for an MS, such as MS 202, to pre-
register with an SGSN, such as SGSN 250, servicing a neighboring RA, that is, RA 208,
that is a handoff candidate. In pre-registering in a neighboring RA 208 with SGSN 250,
the MS at least partially registers with the SGSN, that is, at least a portion of the MS's
registration information is conveyed to the neighboring SGSN serving the neighboring
RA, prior to the MS being served by an associated neighboring BSS 230, for example,
prior to an initiation of a handoff of the MS to neighboring BSS 230. By pre-registering
with a potential target SGSN, the duration of a registration process and the corresponding
service disruptions when the MS is handed off to such an SGSN are reduced.
FIG. 3 is a logic flow diagram 300 of a process whereby an MS in communication
system 200, such as MS 202, pre-registers in a potential target RA, and in particular with
a potential target SGSN, such as SGSN 250, in accordance with an embodiment of the
present invention. Logic flow diagram 300 begins (302) when an MS, such as MS 202,

initially registers (304) with a serving BSS and a serving SGSN, that is, BSS 220 and
SGSN 240. As part of the registration process, serving BSS 220, and in particular
controller 224 of serving BSS 220, assembles (306) Neighbor List 216 and conveys (308)
the assembled Neighbor List to MS 202. In another embodiment of the present invention,
Neighbor List 216 may be assembled by serving SGSN 240 and conveyed by the SGSN
to MS 202. Unless otherwise specified herein, all functions performed herein by MS 202,
controller 224, controller 234, SGSN 240, or SGSN 250 are respectively performed by
processor 203, 226, 236, 242, and 252. Furthermore, unless otherwise specified herein,
all functions performed herein by BSS 220 or BSS 230 are respectively performed by
controllers 224 and 234, and specifically by processors 226 and 236 of controllers 224
and 234.
In one embodiment of the present invention, Neighbor List 216 may be a typical
Neighbor List of the prior art, comprising a list of broadcast channels (BCCH) associated
with each of multiple neighboring BSSs, such as a broadcast channel associated with BSS
230. In such an embodiment of the present invention, each BSS of the multiple
neighboring BSSs broadcasts information concerning an RA and or SGSN associated
with the BSS via the associated broadcast channel. In response to receiving Neighbor
List 216, MS 202 monitors the listed broadcast channels and receives the RA and/or
SGSN information from each BSS included in the Neighbor List.
In another embodiment of the present invention, Neighbor List 216, in addition to
including a list of broadcast channels (BCCH) associated with each of multiple-
neighboring BSSs, further includes, in association with each broadcast channel listed in
the Neighbor List, an indicator of an RA or SGSN associated with the corresponding
BSS. For example, in one embodiment of the present invention, Neighbor List 216 may
include a single bit that indicates whether the BSS is a member of a same RA 206 as the
first, serving or source, BSS 220. That is, from another perspective, Neighbor List 216
may indicate, for each listed broadcast channel, whether the corresponding BSS is
serviced by a same SGSN as the SGSN 240 servicing the serving BSS 220. For example,
Neighbor List 216 may include, in association with each listed broadcast channel, an RA
membership data field. When the corresponding BSS is included in a same RA as source
BSS 220, that is, is serviced by a same SGSN 240 as source BSS 220, then serving SGSN

240 may embed a value of '1' in the RA membership data field. When the corresponding
BSS is included in an RA, such as RA 208 with respect to BSS 230 and SGSN 250,
different from the RA serviced by source BSS 220 and source SGSN 240, then serving
SGSN 240 may embed a value of '0' in the RA membership data field.
For example, Neighbor List 216 may be conveyed to MS 202 via a modified
version of a System Information (SI) message, such as a modified SI 2, SI2bis, SI5, or an
SI5bis message. La order to provide an indicator of an RA or SGSN associated with each
BSS in the Neighbor List, infrastructure 270 may modify the SI message to include the
RA or SGSN indicator. An example of such a modified SI message is depicted in FIG. 4.
As shown in FIG. 4, an exemplary, modified SI message 400 may include a Layer 2
Pseudo Length data field 402, a Protocol Discrirninator data field 404, a Skip Indicator
data field 406, a Message Type data field 408, a Neighbor Cell Description data field 410
that informs of multiple neighbor cells and associated BSSs, such as a list of broadcast
frequencies of each of multiple neighboring BSSs, a Network Colour Code (NCC)
Permitted data field 412, and a Random Access Channel (RACH) Parameters data field
414. Such data fields are typical of an SI message. However, unlike a typical SI
message, SI message 400 further includes an RA Membership data field 416 informing of
an RA/SGSN associated with, or not associated with, each of the multiple neighbor cells
and associated BSSs. SGSN 240 may then embed the RA/SGSN indicators in data field
416.
In another embodiment of the present invention, instead of an indicator indicating
a 'same' or 'different' RA or SGSN, each indicator may comprise an identifier associated
with the RA in which the corresponding BSS located or an identifier associated with the
SGSN servicing the corresponding BSS. For example, the identifier may comprise a code
mat is uniquely associated with the RA or may comprise an identifier, such as a routing
address such as an Internet Protocol (IP) address, that is uniquely associated with the
SGSN. However, an advantage of using an indicator comprising a single bit is that a
mere 16 bits, or two octets, are consumed in indicating an RA, or SGSN, associated with
each of 16 broadcast channels typically included in a Neighbor List.
Referring again to FIG. 3, in response to receiving (310) Neighbor List 216, MS

202 stores (312) the received Neighbor List in the at least one memory device 204 of the
MS. Based on Neighbor List 216 and/or in response to at least one of a change in channel
conditions between MS 202 and BSS 220, a change in channel conditions between MS
202 and a neighboring BSS associated with an SGSN other than serving SGSN 240, such
as BSS 230 and SGSN 250, and a movement of MS 202, MS 202 then pre-registers (314)
in at least one RA, such as RA 208, and with an associated SGSN, that is, SGSN 250,
that is associated with a BSS 230 corresponding to a channel in the Neighbor List and
that is different than the RA 206/SGSN 240 associated with serving BSS 220. In pre-
registering with a neighboring RA 208/SGSN 250, MS 202 at least partially registers with
such an RA/SGSN prior to MS 202 being served by the associated neighboring BSS 230. .
In pre-registering MS 202 with neighboring RA 208/SGSN 250, at least a portion of the
registration information associated with the MS is conveyed to, and received by,
neighboring SGSN 250. In response to receiving the registration information, SGSN 250
stores (316) the registration information in the at least one memory device 254 of the
SGSN and logic flow 300 then ends (318).
In one embodiment of the present invention, the step of pre-registering (314) with
RA 208/SGSN 250 may be initiated.by MS 202. FIG. 5 is a logic flow diagram 500
depicting an MS-initiated pre-registration in accordance with various embodiments of the present invention. Logic flow diagram 500 begins (502) when MS 202 determines (504)
to pre-register with a neighbor SGSN, that is, SGSN 250. In one embodiment of the
present invention, step 504 may comprise the following steps. In response to receiving ,
Neighbor List 216, MS 202 determines whether any neighbor BSS, that is, a BSS
associated with a communication channel in the Neighbor List, is further associated with
an RA or SGSN different than the RA 206 or SGSN 240 associated with serving BSS
220. In response to determining that a BSS, such as BSS 230, associated with a
communication channel in the Neighbor List is further associated with a neighbor RA or
SGSN, such as RA 208 and SGSN 250, different than the serving RA 206 or serving
SGSN 240, MS 202 determines to pre-register with the neighbor RA or SGSN.
In another embodiment of the present invention, step 504 may comprise the
following steps. In response to receiving Neighbor List 216, MS 202 may monitor each
broadcast channel identified in the Neighbor List. MS 202 determines a signal quality

metric, such as a signal strength, a signal-to-noise ratio (SNR), or a bit error rate (BER),
with respect to each monitored channel and compares each determined signal quality
metric to a pre-registration signal quality metric threshold that is maintained in the at least
one memory device 204 of the MS. When a determined signal quality metric compares
favorably with the pre-registration signal quality metric threshold, for example, exceeds a
signal strength threshold or a SNR threshold, then MS 202 determines to pre-register with
a neighbor SGSN associated with the monitored broadcast channel and an associated
BSS. MS 202 may further determine that the neighbor RA/SGSN is different than the
serving RA/SGSN, or the serving SGSN, that is, SGSN 240, may determine that the
neighbor RA/SGSN associated with the neighbor BSS is different than the serving
RA/SGSN.
In response to detennining to pre-register with a neighbor SGSN, that is, SGSN
250, MS 202 conveys (506) a pre-registration request to infrastructure 270. In one
embodiment of the present invention, MS 202 may convey a pre-registration request to
infrastructure 270 by conveying a first pre-registration request 218 to BSS 220 via the at
least one control channel in reverse link 212, and via BSS 220 to serving SGSN 240. First pre-registration request 218 requests that infrastructure 270 pre-register MS 202
with neighbor SGSN 250. Pre-registration request 218 may specifically identify the
neighbor SGSN, that is, SGSN 250, or an RA, that is, RA 208, associated with the
neighbor BSS 230 and neighbor SGSN, or serving SGSN 240 may determine the
neighbor SGSN by retrieving Neighbor List information stored in the at least one memory
device 244 of the serving SGSN in response to receiving the pre-registration request.
In response to receiving pre-registration request 218, serving SGSN 240 conveys
(508) registration information associated with MS 202 to the neighbor SGSN, that is,
SGSN 250. In one embodiment of the present invention, serving SGSN 240 may convey
to SGSN 250 at least a portion of the registration information associated with MS 202
and maintained by the serving SGSN in the at least one memory device 244. In another
embodiment of the present invention, pre-registration request 218 may further include
registration information intended for SGSN 250. In response to receiving pre-registration
request 218, serving SGSN 240 forwards the received registration information to SGSN
250. In yet another embodiment of the present invention, in response to receiving pre-

registration request 218, serving SGSN may request registration information from MS
202, for example, by conveying a registration request to MS 202. In response to
receiving the registration request, MS 202 may convey registration information to SGSN
240, which registration information is forwarded by SGSN 240 to SGSN 250. Serving
SGSN 240 may convey the registration information to SGSN 250 via GGSN 260 or, in
response to receiving pre-registration request 218, may establish a point-to-point
communication with SGSN 250 and convey the information via the established point-to-
point communication. In response to receiving the registration information from SGSN
240, SGSN 250 stores (510) the registration information in the at least one memory
device 254 of the SGSN. In addition, in response to receiving registration information for
MS 202 from SGSN 240, SGSN 250 may also establish (518) communication links with
BSS 230 and/or GGSN 260 for transmission of data to and from MS 202. Logic flow 500
then ends (520).
In another embodiment of the present invention, instead of conveying first pre- registration request 218 to serving BSS 20, MS 202 may convey a second pre-registration
request 219 to neighbor BSS 230 via a control channel in a reverse link 214 between the MS and BSS 230, and via BSS 230 to SGSN 250. Second pre-registration request 219
requests that BSS 230 and associated SGSN. 250 pre-register MS 202. In one
embodiment of the present invention, second pre-registration request 219 may identify serving SGSN 240. In response to receiving pre-registration request 219, SGSN 250 may
request (512), from serving SGSN 240, at least a portion of registration information
associated with MS 202. The request maybe conveyed by SGSN 250 to SGSN 240 via
GGSN 260 or via a communication link established between SGSN 250 and SGSN 240.
In response to receiving the request for at least a portion of the registration information,
SGSN 240 then conveys (514) the requested information to SGSN 250 and SGSN 250
stores the received registration information in the at least one memory device 254. In
another embodiment of the present invention, second pre-registration request 219 may not
identify SGSN 240. In such an embodiment of the present invention, in response to
receiving the second pre-registration request, SGSN 250 may initiate (516) a pre-
registration process with MS 202 that comprises steps of a typical registration process
involving an exchange of registration information between MS 202 and SGSN 250. In

yet another embodiment of the present invention, pre-registration request 219 may further
include registration information associated with MS 202. In response to receiving pre-
registration request 219, serving SGSN 250 stores the received registration information in
the at least one memory device 254. Logic flow 500 then ends (520).
In each of the above embodiments of an MS initiated pre-registration, in addition
to obtaining registration information concerning MS 202, neighboring SGSN 250 may
also establish (518) communication links with BSS 230 and/or GGSN 260 for
transmission of data to and from MS 202 as part of the pre-registration process. In still
other embodiments of the present invention, the step of pre-registering (314) MS 202
with RA 208/SGSN 250 may be initiated by infrastructure 270. Referring now to FIGs.
6A and 6B, a logic flow diagram 600 is depicted of an infrastructure-initiated pre-
registration in accordance with various embodiments of the present invention. In one
embodiment of an infrastructure-initiated pre-registration process, logic flow diagram 600
begins (602) when infrastructure 270 receives (604), from MS 202, signal quality
information corresponding to Neighbor List communication channels monitored by the
MS. In one such embodiment, similar to the MS-imtiated pre-registration embodiment,
in response to receiving Neighbor List 216, MS 202 monitors each broadcast channel
identified in the Neighbor List. MS 202 determines a signal quality metric, such as a
signal strength, a signal-to-noise ratio (SNR), or a bit error rate (BER), with respect to
each monitored channel and conveys the signal quality metrics to infrastructure 270 via
serving BSS 220.
Based on the received signal quality information, serving BSS 220, and in
particular serving controller 224, or serving SGSN 240 then determines (606) whether to
pre-register MS 202 with a neighboring RA 208/SGSN 250 associated with a
communication channel of Neighbor List 216. In one embodiment of the present
invention, wherein infrastructure 270 receives signal quality metrics from MS 202,
serving BSS 220 or serving SGSN 240 then compares each received signal quality metric
to a pre-registration signal quality metric threshold. In another embodiment of the present
invention, MS 202 may perform the comparison and convey the results of the comparison
to infrastructure 270. When serving BSS 220 performs the comparison or receives
comparison results from MS 202 and a determination of whether to pre-register MS 202

with a neighboring RA/SGSN resides in serving SGSN 240, the serving BSS conveys the
comparison results to serving SGSN 240. When a determined signal quality metric
compares favorably with the pre-registration signal quality metric threshold and serving
BSS 220 or serving SGSN 240, whichever element of communication system 200 is
making the pre-registration decision, further determines that the SGSN associated with
the monitored signal, such as SGSN 250, is different than the serving SGSN, then the
serving BSS or SGSN determines to initiate a pre-registration of MS 202 with such
neighbor SGSN.
In another infrastructure-initiated embodiment of the present invention, serving
BSS 220, and in particular serving controller 224, or serving SGSN 240 may determine
whether to pre-register MS 202 based on a location of the MS. In such an embodiment,
logic flow diagram 600 may begin (602) when a location of MS 202 is determined (608).
In one such embodiment, MS 202 may self-determine its geographical location and
convey the determined geographical location to infrastructure 270. Methods by which an
MS may self-determine its geographical location are well-known in the art and will not be
described in detail herein. For example, MS 202 may self-determine its geographical
location based on location information received from each of multiple BSSs in
communication system 200, such as based on a time difference of arrival (TDOA) of pilot
signals received from each of the multiple BSSs. By way of another example, MS 202
may further include a Global Positioning System (GPS) receiver (npt shown) and may
self-determine its geographical location by reference to a constellation of GPS satellites.
MS 202 then conveys its determined geographical location, or at least the received
location information, to infrastructure 270 via serving BSS 220, which geographical
location or location information is routed to SGSN 240 or to controller 224 of BSS 220.
Upon receiving the location information from MS 202, serving SGSN 240 or
serving BSS 220 determines a geographical location of the MS based on the geographical
location determined by MS 202 or based on the location information received from MS
202 and further retrieves the geographical locations of the BSSs associated with the
Neighbor List of MS 202 from a respective at least one memory device 228,244. When
controller 224 determines the locations of MS 202 and/or BSSs 220 and 230, the
controller may convey each such location determination to SGSN 240. Based on the

determined locations of MS 202 and at least one of BSSs 220 and 230, serving BSS 220
or serving SGSN 240 then determines (610) whether to initiate a pre-registration of MS
202 with SGSN 250.
For example, serving BSS 220 or serving SGSN 240 may determine, based on
multiple determinations of a geographical location of MS 202, that MS 202 is headed in a
direction toward BSS 230. In response to determining that MS 202 is headed toward BSS
230, BSS 220 or SGSN 240 may determine (612) to initiate a pre-registration of MS 202
with SGSN 250. By way of another example, based on a determined location of MS 202
and BSS 230, BSS 220 or SGSN 240 may determine that MS 202 has moved to within a
predetermined distance of BSS 230. In response to deterrnining that MS 202 has moved
to within the predetermined distance, BSS 220 or SGSN 240 may determine (612) to
initiate a pre-registration of MS 202 with SGSN 250. By way of yet another example, the
at least one memory device 228, 244 of BSS 220 or SGSN 240 may maintain a
geographical location of a border, for handoff purposes, between a coverage area
associated with BSS 220 and a coverage area associated with BSS 230. When BSS 220
or SGSN 240 determines that MS 202 has moved to within a geographical distance of the
border, the BSS or SGSN may determine (612) to initiate a pre-registration of MS 202
with RA 208/SGSN 250.
In response to deterrnining to initiate a pre-registration of MS 202 with RA
208/SGSN 250, BSS 220 or SGSN 240 may either instruct (616) the MS to pre-register or
may pre-register (614) the MS with SGSN 250. In an embodiment of the present
invention wherein serving BSS 220 or serving SGSN 240 pre-registers (614) MS 202
with RA 208/SGSN 250, serving BSS 220 may instruct serving SGSN 240 to pre-register
MS 202, or serving SGSN 240 may on its own pre-register MS 202, with neighboring
SGSN 250 as is described in detail above. For example, serving SGSN 240 may pre-
register MS 202 by conveying to neighboring SGSN 250 at least a portion of the
registration information associated with MS 202 and maintained in the at least one
memory device 244 of the serving SGSN. Serving SGSN 240 may convey the
information via GGSN 260 or may establish a point-to-point communication with SGSN
250 and convey the information via the established point-to-point communication.

In an embodiment of the present invention wherein BSS 220 or SGSN 240
instructs (616) the MS to pre-register, serving BSS 220 or serving SGSN 240 may convey
a pre-registration instruction to MS 202 via the broadcast channel or the at least one
control channel in forward link 211. The pre-registration instruction instructs MS 202 to
pre-register. In one such embodiment, in response receiving the pre-registration
instruction, MS 202 conveys (618) to serving SGSN 240 via serving BSS 220, and the
serving SGSN receives (620) from the MS, a pre-registration request such as pre-
registration request 218. In response to receiving me pre-registration request, serving
SGSN 240 then pre-registers (622) MS 202 with neighbor SGSN 250 as described above,
for example, by conveying to SGSN 250 registration information stored in the at least one
memory device 244 of serving SGSN 240 or by forwarding registration information
received by the serving SGSN from MS 202. Logic flow 600 then ends (636).
In another embodiment of the present invention, in response receiving the pre-
registration instruction, MS 202 may identify (624) neighboring SGSN 250 or an
associated RA 208 based on the Neighbor List maintained in the at least one memory
device 204 of the MS and convey (626) a pre-registration request, such as pre-registration
request 219, to the neighboring SGSN. In response to receiving the pre-registration
request, neighboring SGSN 250 pre-registers (628) MS 202 as described above, for
example, by obtaining registration information associated with MS 202 from SGSN 240,
by engaging in a registration procedure with MS 202, or by storing registration
information that may be included in the received pre-registration request Logic flow 600
then ends (636).
In still another embodiment, the pre-registration instruction may include an
identifier associated with neighboring SGSN 250. In response to receiving the pre-
registration instruction, MS 202 identifies (630) neighboring SGSN 250 based on the
received instruction and conveys (632) a pre-registration request to the neighboring
SGSN. In response to receiving the pre-registration request, SGSN 250 pre-registers
(634) MS 202 as described above and logic flow 600 men ends (636).
In each of the above embodiments, as part of the pre-registration of MS 202 with
SGSN 250, SGSN 250 may further establish communication links with BSS 230 and/or

GGSN 260 for transmission of data to and from MS 202.
By providing for a pre-registration of MS 202 with a neighboring SGSN 250
serving a neighboring RA 208 and a neighboring BSS 230 that are handoff candidates for
MS 202, communication system 200 reduces a duration of a registration process and the
corresponding service disruptions when the MS is handed off to such an RA and SGSN.
In pre-registering in the neighboring RA 208 with SGSN 250, MS 202 at least partially
registers with SGSN 250, that is, at least a portion of the MS's registration information is
conveyed to the neighboring SGSN prior to the MS being served by an associated
neighboring BSS 230, for example, prior to an initiation of a handoff of the MS to the
neighboring BSS 230. In various embodiments of the present invention, the at least a portion of the MS's registration information may be conveyed by the serving SGSN 240
to the neighboring SGSN 250 in response to a self-initiated transfer by the serving SGSN
or in response to a request received by the serving SGSN from MS 202 or from the
neighboring SGSN. In other embodiments of the present invention, the at least a portion
of the MS's registration information may be conveyed by MS 202 to neighboring SGSN
250 in response to a self-initiated pre-registration by the MS or in response to an
instruction received by the MS from either serving BSS 220 or SGSN 240.
While the present invention has been particularly shown and described with
reference to particular embodiments thereof, it will be understood by those skilled in the
art that various changes may be made and equivalents substituted for elements thereof
without departing from the scope of the invention as set forth in the claims below.
Accordingly, the specification and figures are to be regarded in an illustrative rather then
a restrictive sense, and all such changes and substitutions are intended to be included
within the scope of the present invention.
Benefits, other advantages, and solutions to problems have been described above
with regard to specific embodiments. However, the benefits, advantages, solutions to
problems, and any elements) that may cause any benefit, advantage, or solution to occur
or become more pronounced are not to be construed as a critical, required, or essential
feature or element of any or all the claims. As used herein, the terms "comprises,"
"comprising," or any variation thereof, are intended to cover a non-exclusive inclusion,

such that a process, method, article, or apparatus that comprises a list of elements does
not include only those elements but may include other elements not expressly listed or
inherent to such process, method, article, or apparatus. It is further understood that the use
of relational terms, if any, such as first and second, top and bottom, and the like are used
solely to distinguish one entity or action from another entity or action without necessarily
requiring or implying any actual such relationship or order between such entities or
actions.

WE CLAIM:
1. A method for registering a mobile station (202) comprising:
registering (304) the mobile station with a first Serving GPRS Support Node
(240), wherein the first Serving GPRS Support Node services a first Base Station
System (220) that provides communication services to the mobile station
and wherein the method is characterized by:
assembling (306) a Neighbor List (216) that comprises a plurality of
communication channels, wherein a communication channel of the plurality of
communication channels is associated with a second Base Station System (230) that is
serviced by a second Serving GPRS Support Node (250) that is different than the first
Serving GPRS Support Node and wherein the Neighbor List informs of a Routing Area
RA (208) associated with each communication channel of the plurality of
communication channels;
determining (504) the second BSS that is serviced by the second Serving GPRS
Support Node (SGSN) and that is different than the first SGSN based on the Routing
Area (208) associated with each communication channel of the plurality of
communication channels included in the Neighbor List; and
partially registering (314, 508) the mobile station with the second Serving
GPRS Support Node based on the determined second BSS and prior to the
establishment of a control channel between the mobile station and the second Base
Station System.
2. The method as claimed in claim 1, wherein partially registering comprises
conveying, by at least one of the mobile station and the first Serving GPRS Support
Node to the second Serving GPRS Support Node, at least a portion of registration
information associated with the mobile station.
3. The method as claimed in claim 1, wherein partially registering the mobile
station with the second Serving GPRS Support Node comprises:
receiving registration information from the mobile station; and

conveying the received registration information to the second Serving GPRS
Support Node.
4. The method as claimed in claim 1, wherein partially registering comprises:
receiving, by the first Serving GPRS Support Node from at least one of the
mobile station, the first Base Station System, and the second Serving GPRS Support
Node, a request to pre-register the mobile station with the second Serving GPRS
Support Node; and
in response to receiving the request, conveying, by the first Serving GPRS
Support Node to the second Serving GPRS Support Node, at least a portion of
registration information associated with the mobile station.
5. The method as claimed in claim 4, wherein receiving comprises:
receiving, by the second Serving GPRS Support Node from the mobile station, a
request to pre-register the mobile station with the second Serving GPRS Support Node;
conveying, by the second Serving GPRS Support Node to the first Serving
GPRS Support Node, a request for at least a portion of registration information
associated with the mobile station;
receiving, by the first Serving GPRS Support Node from the second Serving
GPRS Support Node, the request for at least a portion of the registration information;
and
wherein conveying comprises, in response to receiving the request from the
second Serving GPRS Support Node, conveying, by the first Serving GPRS Support
Node to the second Serving GPRS Support Node, at least a portion of the registration
information associated with the mobile station.
6. The method as claimed in claim 1, wherein each communication channel of the
plurality of communication channels is associated with a Base Station System (BSS)
and wherein partially registering comprises:

broadcasting, by each BSS associated with a communication channel of the
plurality of communication channels, information concerning a Routing Area associated
with the BSS;
determining the second BSS that is serviced by the second SGSN that is
different than the first SGSN based on the Routing Areas broadcast by each BSS
associated with a communication channel of the plurality of the communication
channels; and
partially registering the mobile station with the second SGSN based on the
determined second BSS and prior to the mobile station being served by the second BSS.
7. The method as claimed in claim 1, wherein partially registering comprises:
determining at least one of a signal quality metric for me communication
channel of the plurality of communication channels that is associated with the second
Base Station System, a signal quality metric for a communication channel that is
associated with the first BSS, and a geographical location of the mobile station;
detennining to pre-register the mobile station with the second serving GPRS
Support Node based on the determined at least one of the signal quality metric for the
communication channel that is associated with me second Base Station System, the
signal quality metric for the communication channel that is associated with the first
Base Station System, and the geographical location of the mobile station;
partially registering the mobile station with the second Serving GPRS Support
Node prior to the mobile station being served by the second Base Station System.
8. An apparatus for pre-registering a mobile station, the apparatus comprising a
first Serving GPRS Support Node (240) having a processor (242) that assembles a
Neighbor List (216) corresponding to a mobile station (202) and comprising a plurality
of broadcast channels, wherein the Neighbor List comprises a Routing Area (208)
associated with at least one broadcast channel of the plurality of broadcast channels
and, while currently serving the mobile station, partially registers the mobile station
with a second Serving GPRS Support Node (250) based on the Routing Area (208)
associated with each communication channel of the plurality of communication

channels included in the Neighbor List and prior to the establishment of a control
channel between the mobile station and a Base Station System (230) associated with the
second Serving GPRS Support Node.
9. The apparatus as claimed in claim 8, wherein the processor pre-registers the
mobile station by receiving registration information from the mobile station and
conveying the received registration information to the second Serving GPRS Support
Node (SGSN).
10. The apparatus as claimed in claim 8, wherein the processor receives a request to
pre-register the mobile station from at least one of the mobile station, a Base Station
System (BSS) associated with the first Serving GPRS Support Node (SGSN), and the
second SGSN, and in response to receiving the request, pre-registers the mobile station
by conveying registration information to the second SGSN.
11. The apparatus as claimed in claim 8, wherein the apparatus comprises a
controller associated with a Base Station System serviced by the first Serving GPRS
Support Node (SGSN), wherein the controller is in communication with the first SGSN,
wherein the controller assembles a Neighbor List corresponding to the mobile station
and comprising a plurality of broadcast channels, and wherein the Neighbor List
comprises a Routing Area associated with at least one broadcast channel and of the
plurality of broadcast channels.
12. The apparatus as claimed in claim 8, wherein the processor determines to pre-
register the mobile station with the second Serving GPRS Support Node (SGSN) based
on at least one of a quality of a communication channel associated with a Base Station
System that is associated with the first SGSN, a quality of a communication channel
associated with the Base Station System that is associated with the second SGSN, and a
location of the mobile station.

13. The apparatus as claimed in claim 8, wherein the apparatus comprises the
second Serving GPRS Support Node (SGSN), wherein the second SGSN receives
registration information associated with the mobile station from the first SGSN and
stores the received registration information in an at least one memory device of the
second SGSN prior to the mobile station communicating with the second SGSN.
14. The apparatus as claimed in claim 13, wherein the second Serving GPRS
Support Node (SGSN) further establishes a communication link with at least one of a
Gateway GPRS Support Node (GGSN) and a Base Station System associated with the
second SGSN prior to the mobile station communicating with the second SGSN.
15. The apparatus as claimed in claim 8, wherein the apparatus comprises the
second Serving GPRS Support Node (SGSN) and wherein the second Serving GPRS
Support Node (SGSN) conveys a message to the mobile station informing of a Routing
Area associated with the second SGSN and, in response to conveying the message
informing of the Routing Area, receives registration information associated with the
mobile station.
16. A mobile station {202) comprising:
at least one memory device (204); and
a processor (203) operably coupled to the memory device that receives a
Neighbor list (216) comprising a plurality of communication channels and a Routing
Area (208) associated with at least one broadcast channel of the plurality of broadcast
channels, stores the Neighbor List in the at least one memory device, and initiates a
partial registration of the mobile station by conveying to an infrastracture (270) a
request to pre-register the mobile station in a Routing Area (208) associated with a
Serving GPRS Support Node (250) and further associated with a communication
channel of the plurality of communication channels prior to the establishment of a
control channel between the mobile station and a Base Station System (230) associated
with the communication channel of the plurality of communication channels.

17. The mobile station as claimed in claim 16, wherein the Neighbor List comprises
information concerning the Routing Area, wherein the Routing Area is different than a
Routing Area associated with a serving Base Station System (BSS), and wherein the
mobile station conveys the request to pre-register to at least one of the serving BSS and
the BSS associated with the communication channel of the plurality of communication
channels.
18. The mobile station as claimed in claim 16, wherein the mobile station receives
information concerning the Routing Area from the Base Station System (BSS)
associated with the communication channel of the plurality of communication channels.

ABSTRACT

"METHOD AND APPARATUS FOR REGISTERING A MOBILE STATION"
A communication system (200) provides for a mobile station (MS) (202) to pre-register with a Serving
GPRS Support Node (SGSN) (250) servicing a neighboring Routing Area (RA) (208) that is a handoff
candidate. In pre-registering with the neighboring RA and SGSN, the MS at least partially registers
with the RA and SGSN, that is, at least a portion of the MS's registration information is conveyed to
the neighboring SGSN serving the neighboring RA, prior to the MS being served by an associated
neighboring BSS (230), for example, prior to an initiation of a handoff of the MS to the neighboring
BSS. By pre-registering with the candidate SGSN, a duration of a registration process and the
corresponding service disruptions when the MS is handed off to such an SGSN are reduced.

METHOD AND APPARATUS FOR REGISTERING A MOBILE STATION

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