Logical Paging Areas
BACKGROUND OF THE INVENTION
Technical Field of the Invention
The present invention relates in general to wireless communication systems, and in particular, to paging mobile terminals within wireless communication system.
Description of Related Art
Today's wireless telecommunications networks provide telephone subscribers with the ability to access telecommunications services from almost anywhere in the world. The key to facilitating such world-wide access is mobility management. With mobility management, wireless networks are able to track the location of luuhllc HubHciibcrs so that mobile services can be delivered to them.
A wireless network is typically formed of a number of Cells, each covering a small geographic area within which a mobile device, such as a mobile station, may receive mobile service. each cell is equipped with a base station that provides radio coverage to the cell, thereby enabling communication with mobile devices located within the cell. By integrating the coverage of multiple base stations, a wireless network is able to provide radio coverage to mobile subscribers over a large geographic area.
A traditional wireless network 10a is illustrated in FIGURE 1. The coverage area of a collection of neighboring base stations is commonly referred to as a location area (LA) 70. Each LA 70 (i.e., LA1-LA5) is served by a Radio Access Node (RAN) 50 (i.e., RANl-RAN5) and a mobile switching center/visitor location register (MSC/VLR) 30 (i.e., MSCA^LRl and MSCA^LR2) via a respective connectivity network 40a and 40b. In addition, each MSCA'LR 30 may serve multiple LAs 70, which together form an MSC coverage area 60. For example, LA1-LA3 form MSCl coverage area that is served by MSCA^LRl, while LA4 and LAS form MSC2 coverage area that is served by MSCA^LR2.
The MSCA^'LR 30 is the network node that provides circuit-switched calling, mobility management and other telecommunications/mobile services to mobile subscribers. In particular, the MSCA^LR 30 maintains subscriber data for all mobile subscribers that are currently located within one of the location areas 70 served by the MSCA^LR 30. For example, the subscriber data for each mobile subscriber typically includes the location area

and serving base station of the mobile subscriber, which allows the MSCA^LR 30 to page, communicate with and connect incoming calls to that mobile subscriber.
When a mobile subscriber moves or "roams" into a new location area 70 (e.g., from LAI to LA2), the mobile device must inform the wireless network of the change in location area by performing what is commonly referred to as a location update procedure. Each mobile device is responsible for maintaining the location area code (LAC) of the current location area and comparing the stored LAC with subsequent LAC's that are broadcast and received by the mobile device. If the mobile device finds that the received LAC is different from the stored LAC, the mobile device sends a location update request to the wireless network.
If the new location area is sers'ed by a different MSCA^LR than the previous location area, an inter-VLR location update is performed. For example, if the mobile device roams from LA3, which is served by MSC,A/LR1 into LA4, which is served by MSCA/LR2, an inter-VLR location update is performed. During the inter-VLR location update, the new MSCA/LR that receives the location update request from the mobile subscriber transmits an update location message to the Home Location Register (HLR) 20 of the mobile subscriber. Tiie HLR 20 is a database that maintains permanent Hubscribor records for mobile subscribers. Upon receiving the update location message, the HLR 20 forwards the subscriber data associated with the mobile subscriber to the new MSC/VLR (i.e., MSCA^LR2) for temporary storage in the new MSC/VLR while the mobile subscriber is within the MSCA^LR coverage area and updates its records to indicate that the mobile subscriber is now present in a location area served by the now MSC/VLR, in addition, the HLR 20 asks the old MSC/VLR (i.e., MSC/VLRl) to delete its Niil)scriber record for this mobile subscriber since the mobile subscriber is no longer localoil In ii loudljoii area served by the old MSC/VLR.
Once the location update procedure is complete, the mobile Hiibsuilbei uiui continue to receive mobile services through the new MSC/VLR (i.e., MSC/VLR2). For example, in a typical mobile terminated call scenario, an incoming call to the mobile subscriber is first routed to a gateway mobile switching center (GMSC). Upon receiving the mobile terminated call, the GMSC queries the HLR to determine the current location of the mobile subscriber. For example, the HLR typically requests routing information from MSCVLR and returns it to

the GMSC. The GMSC uses the routing information to route the mobile terminated call to the MSC/VLR. The MSCA'^LR accesses its subscriber data for the mobile subscriber to detei-mine the location area of the mobile subscriber, and pages the mobile device of the mobile subscriber within that location area to set-up a call connection to the mobile device for the mobile terminated call,
However, if the MSC/VLR crashes, the MSC/VLR goes through a restart routine in which all temporary subscriber records are deleted. During the restart routine (or when the MSCA^'LR is in the maintenance stage), subscribers cannot make or receive new calls through the MSCA/LR. To prevent such a loss of service, service providers have begun implementing flexible wireless network architectures. An example of a flexible wireless network 10b is shown in FIGURE 2. In the flexible wireless network 10b, multiple MSCA^LRs 30 (i.e., MSCA^LRl and MSCA^LR2) service a large mobile pool area 80 that is made up of multiple location areas 70 (i.e., LAI-LAS). Each MSCA^'LR 30 is able to serve mobile subscribers within any of the location areas 70. A mobile subscriber located in the mobile pool area is registered and served in any one of the MSCA^'LRs 30.
However, in the flexible arcMtecture, when one MSCA^'LR goes down, another MSCAO-R can take over while the failed MSCA^LR restarts. For example, if a mobile subscriber within LA2 receives a mobile terminated call during the time that the serving MSCA^LR (i.e., MSCA^LRl) is restarting, the mobile temiinated call can be routed to MSCA^LR2 for connection of the mobile terminated call to the mobile subscriber. In this case, when the HLR 20 requests the routing infonnalion for the mobile temiinated call that identifies MSCA^LRl as the sen'ing MSCA/'LR from the HLR 20, fl Signal Transfer Point (STP) (within the SS7 network) can fonvnrd the request to MSC7VLR2. However, since the LAC of the LA that the mobile subscriber is cun-emly located in is only stored in the sei-ving MSCA^LR, here MSCA/LRl, MSC/VLR2 will not have biowledge of the cunent location nron (LA2) oflho mobile subscriber. Therefore, in order to connect the mobile tenninnted call to the mobile subscriber, MSC/VLR2 must page the mobile subscriber over the entire mobile pool lueii 80, n procedure commonly rcfciTcd to ns global paging.

IJnforfunately, global paging causes excessive traffic throughout the mobile pool area, U.S. Published Patent Application No. 2002/18779.'^ A I In papadimitrion clesciibes dividing a mobile pool area that is served by two or nunc MSCVVI.U'N into a number of global paging areas (each including two or more locution areas In order to avoid paging throughout the entire mobile pool area when a mobile station cannot be reached after paging in location area. In Papadimitriou, paging is first preformed in
the location area, and only if no response is received in the localion area is paging performed in the global paging area to which the location area belongs. Upon failure of an MSCA^LR, Papadimitriou suggests suppressing any global paging until a significant number of subscribers is re-registered in the MSC/VLR, which can delay connection of mobile terminated calls to awaiting mobile subscribers.
U.S. Published Patent Application No. 2005/0192005 Al describes a system where due to failure of a first/serving MSCA^LR, a second one is selected to page the mobile device in all location areas. Unfortunately, this leads to a high paging signaling load.
International Application WO 97/24898 Al describes a system,that uses logical paging areas (each including two or more location areas) to page a mobile station when an MSC/VLR loses the location area infonnation for a mobile .station. In WO 97/24898 Al, the logical paging area identity (ID) is stored in the HLR and is provided to the MSC./VLR to page the mobile station. However, this requires additional information to be stored in the HLR and additional signaling infonnation to be transmitted fi-om the MSC/VLR's to the HLR.
Therefore, what is needed is a paging solution in flexible wireless network that reduces the traffic within the mobile pool area.

switching nodes. The mobile pool area includes a plurality of location areas, and is divided into multiple logical paging areas. Upon receiving a njobile terminated call for the mobile device, the logical paging area within which to page the mobile device is determined in order to deliver the mobile tenninated call to the mobile device.
In one embodiment, the mobile switching nodes are mobile switching center/visitor location registers (MSC/VT.,Rs). In another ombodiineni, (he mobile switching nodes are serving general packet radio service nodoKS (SGSNs). For example, the mobile device can be paged within said logical paging area by one of paged within said logical paging area by one of|said MSCA^LRs or one of the SGSNs when ihe mobile terminated call is received after a restart of one of (ho MSCA/1 MH or SGSNs.
In an exemplary embodiment, each logical paging area Is associuted with a logical MSC/VLR address identifying one of the MSCAVLRs. Th« lottlcal MHCA^I.R address is received with the mobile terminated call, and used to dcrivo H«lii U)gn'n\ pHging area within which to page the mobile device. For example, in one onilniitliiuM)!, llin iogiiinl MSC/VLR address is received within a Mobile Application Part (MAP) Provide Roaming Number message from a Home Location Register (HLR) associated with the mobile device. The logical MSCA^LR address is provided to the HLR within the MSCA^LR address parameter of a location update message each time the mobile device roams into a new logical paging area. In addition, if the mobile device moves to a new paging area within the same mobile pool area, and the mobile device is still served by the same MSC/VLRs, the location update message can further include a "skipSubscriberDataUpdate" parameter to prevent the HLR from downloading the subscriber data associated with the mobile device.
In another exemplary embodiment, each logical paging ai*ea has a unique paging area identity associated therewith. The paging area identity can be received, for example, within a Mobile Application Part (MAP) Provide Roaming Number message from a Home Location Register (HLR) associated with the mobile device. In addition, the update location message can include the paging area identity of the logical paging area (or the collection of location area identities (LAIs)) within wMch the mobile device is currently located. For example, the paging area identity can be included within a local mobile subscriber identity parameter of

the update location message. In addition, if the mobile device moves to a new paging area within the same mobile pool area, and the mobile device is still served by the same MSCA^LRs, the location update message can further include a "skipSubscriberDataUpdate" parameter to prevent the HLR from downloading the subscriber data associated with the mobile device.
Embodiments of the invention are also applicable to the MSCA^R restart case where all temporary subscriber records are deleted. In this case, the logical paging area (the PAl or set of LAIs) is received. BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention may be obtained by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein:
FIGURES 1 and 2 illustrate exemplary conventional traditional and flexible wireless networks;
FIGURE 3 illustrates an exemplary flexible wireless network utilizing logical paging areas to page mobile devices, in accordance with embodiments of the present invention;
FIGURE 4 illustrates an exemplary flexible wireless network for delivering a mobile terminated call to a mobile device using logical paging areas in accordance with cnibodiinents of the present invention; and
I'IGURE 5 is a flowchart illustrating an exemplary process for paging a mobile device using logical paging areas, according to embodiments of the present invention.
DETAILED DESCRIPTION OF THE DIUWINGS
FIGURE 3 illustrates an exemplary flexible wireless noiwiirk lOc iillli/.ing logical paging areas to page mobile devices, in accordance with eiuhndlincnlN of the present invention. The flexible wireless network 10c includes Mobile Swltclilnn ('oiUcr/Visitor Location Registers (MSC/VLRl and MSCA^LR2) 30, Radio ACCCHN NIHICN (U/VH I-KAS5) 50 and u Home Location Register (HLR) 20. MSCA^LRl and MSC/VLR2 each serve all of the location areas (LAI-LAS) 70 within the mobile pool area 80 via connectivity network 40.
In accordance with embodiments of the present invention, the mobile pool area 80 is divided into multiple logical paging areas (Paging Area 1 and Paging Area 2) 100. The term

"logical paging area" is defined herein as a collection of location areas 70 to avoid global paging throughout the mobile pool area 80. Thus, each logical paging area 100 includes two or more location areas 70, but less than all of the location areas 70, within the mobile pool area 80. In FIGURE 3, the logical paging areas 100 correspond to the traditional MSC coverage areas shown in FIGURE 1. However, in other embodiments, the mobile pool area 80 can be divided into other logical paging areas 100, so that each logical paging area 100 can include any number of location areas 70.
Each logical paging area 100 has a paging area identity (PAI) associated therewith that uniquely identifies the paging area 100 within the mobile pool area 80. The PAI is used to determine the logical paging area within which to page a mobile device if the current location area 70 of the mobile device is unknown. For example, if one of the MSCA'LRs goes down and deletes all of its temporary subscriber records as a result of a restart procedure, the current location area 70 of each subscriber for whom the failed MSCA^LR kept a temporary subscriber record would be unknown. In this situation, instead of performing a global paging across the entire mobile pool area 80, for a mobile terminated call, the mobile device would be paged only in the location areas 70 included within the logical paging area 100 of the mobile device.
To enable the MSCA^LR 30 to determine the current logical paging area 100 of a mobile device, a paging area indicator is stored in the HLR 20. In one embodiment, the paging area indicator is the PAI of the paging area. In another embodiment, the paging area indicator is a logical MSC address that can be used to derive the PAI of the paging area. For example, each paging area 100 can be assigned an MSC address associated with the MSC currently serving the mobile device. As an example. Paging Area 1 can be assigned the address of MSC la when MSCA/LRl is serving a mobile device in Paging Area 1 and the address MSC2a when MSC/VLR2 is serving a mobile device in Paging Area 1. Likewise, Paging Area 2 can be assigned the address of MSClb when MSCA^LRl is serving a mobile ■ device in Paging Area 2 and the address of MSC2b when MSCA^LR2 is serving a mobile device in Paging Area 2.
During a location update, or each time a mobile device roams into n new paging area 100, the serving MSC/VLR 30 can update the HLR 20 with llic MSC: nddrcsH Ibr the logical paging area 100 in which the mobile device is currently located. For example, if a mobile

(k'vice roams from I,A3 into I,A4, but. is continued to he served by MSC/VLR I, MSCA^LRl ciiii update the IlLR 20 with the new MSC address, i.e., MS('lb. AH luiolhcr example, if a mobile device roams from LA4 to LA3, but continues to bo Morvcd liy MSC/VLR2, MS(VVLR2 can update the HLR 20 with the new MSC addre,si(, i.o , MM( '?h. An yet anotlier example, if a mobile device roams from LA4 to LAS, and pcrlbrinn an intci Vl,l< location update from MSCA^LIU to MSC/VLRl. MSCAVLRl cim update llai IILM J\) wllh )l»c new MSC address, i.e., MSCla.
When the mobile device roams into a new paging area, but the serving MSCAi'LR 30 does not change, to reduce traffic in the flexible wireless network 10c, the MSCA^LR 30 update location message to the HLR 20 can include a "skipSubscriberDataUpdate" parameter that informs the HLR 20 that there is no need to download the subscriber data for the mobile device to the MSCA^LR since the serving MSCA^LR has not changed. I'ypically, muUiple insert subscriber data (ISD) messages are sent from the HLR 20 to the MSC/VLR 30 during the location update process to provide the MSC/VLR with the subscriber data associated with the mobile device. By including the "skipSubscriberDataUpdate" parameter, the HLR 20 is prevented from sending the ISD messages, which reduces the network traffic.
In embodiments where the paging area indicator is the PAI, the MSC/VLR 30 can either send the PAI within a new information element (IE) or parameter of the update location message transmitted from the MSC/VLR 30 to the HLR 20 or include the PAI within a Local Mobile Subscriber Identity (LMSI) parameter of the update location message transmitted from the MSC/VLR 30 to the HLR 20. In the former embodiment, a new IE must be added to the update location message, while in the latter embodiment, an existing IE (i.e., the LMSI) is used to transmit the PAI. However, if the LMSI is already used ibr the LMSI or for another purpose, the LMSI parameter carmot be used to transmit the PAI and a new IE must be added to the update location message to transmit the PAI to the HLR 20.
In an exemplary operation, when a mobile device first enters one of the location areas 70 in the mobile pool area 80, for example, LA3, the mobile device receives the location area code (LAC) of LA3 that is broadcast by RAN3 50. The mobile device then sends a location update request to the wireless network 10c via RAN3. Upon receiving the location update request, RAN3 forwards the location update request to one of the MSC/VLRs 30, for example, MSC/VLRl, serving the mobile pool area 80. MSC/VLRl 30 then transmits an

update location message to the HLR 20 to retrieve the subscriber data associated with the mobile device and to update the HLR 20 with the paging area indicator, e.g., the PAI or MSC address, identifying Paging Area 1.
If, during the time that MSCA'/LRl is serving the mobile device, MSCA'^LRl goes down, and a mobile terminated call comes into the flexible wireless network 10c during the time that MSCA^LRl is restarting, the mobile terminated call can be routed to MSCA''LR2 for connection of the mobile terminated call to the mobile subscriber. For example, referring now to FIGURE 4, when HLR 20 receives a Send Routing Infonnation (SRI) message from a Gateway Moliile Switching Center (GMSC) (not shown), the I ILK 20 HCCONSON llic Hubscriber record for the mobile device to determine the serving MSCA/LR, here MSC/VLRl, and transmits a Provide Roaming Number (PRN) message 310 via Signal Transler Point (STP) to MSC/VLRl. Since MSC/VLRl is down, STP will attempt to redirect Ihe PRN message to MStVVLR2.
The PRN message sent to MSC/VLR2 includes the logical MS(-' midrcrts or paging area identity (PAI) or the collection of LAIs, so that MSC/VLK2 will Im ^\hW, In iltjicrminc the logical paging area within which to page the mobile device. In respoiiHo to llio PUN message, \\w MSC/VLR2 sends a message including a Mobile Station KoitiiiliiH I liiiiilii'r (MHKN) back to the IJLR 20 and restores the subscriber data associated with the mobile device from HLR 20. The MSRN is an E. 164 number that is temporarily assigned to the mobile device for the mobile terminated call and can be used to route the mobile terminated call to MSC/VLR2. Upon receipt of the MSRN, the HLR 20 forwards the MSRN back to the GMSC, which uses the MSRN to route an Initial Address Message (lAM) for the mobile terminated call to MSC/VLR2. Upon receipt of the IAM[, MSC/VLR2 uses the logical MSC address or PAI or collection of LAIs to determine the logical paging area within which to page the mobile device, and pages the mobile device within that logical paging area.
If paging is successful, MSC/'*/LR2 can connect the mobile terminated call to the mobile device. If paging is unsuccessful (i.e., the paging timer expires), MSC/VLR2 can page the mobile device within the entire mobile pool area 80. If the mobile device responds from a new logical paging area, MSC/VLR2 updated the HLR 20 with the new paging area indicator (MSC address or PAI).

Logical paging areas can also be used for paging reattempts if the mobile device does not respond to location ai'ea (LA) paging. For example, if MSCA/'LRl does not go down, when the mobile terminated call comes into the GMSC, the call is routed to MSCA/'LRl as conventionally done. MSCA^LRl accesses the subscriber data for the mobile subscriber to which the mobile terminated call is addressed to retrieve the LA and logical paging area for the mobile subscriber. MSCA^LRl first pages the mobile device within the designated LA 70, and if there is no response, MSCA^LRl can page the mobile device within the logical paging area 100. Only if there is no response from logical paging of the mobile device will the MSCA/LRl perform a global page throughout the entire mobile pool area 80 for the mobile device.
In another embodiment of the present invention, the logical paging areas 100 can be used within a General Packet Radio System (GPRS), in which Serving General Packet Radio Services Nodes (SGSNs) service the flexible network 10c. In this embodiment, the MSCA'LRs 30 are replaced with SGSN's.
FIGURE 5 is a flowchart illustrating an exemplary process 500 for paging a mobile device using logical paging areas, according to embodiments of the present invention. At block 510, two or more mobile switching nodes are provided to service a mobile pool area that includes a plurality of location areas (LAs). At block 520, the mobile pool area is divided into logical paging areas, each including at least one of the LAN. During each location update that is performed by a mobile device within Iho mobile pool area, at block 5.TO, the HLR is updated with a paging area indicator that is used to uniquely identify the logical paging area within which the miobile device is currently located,
When a mobile terminated call arrives for a particular mobile device within the mobile pool area, at block 540, the HLR provides the paging urea iiulicatoi' of the mobile device to one of the mobile switching nodes for use by (luil inobllo Nwllcliliig node in connecting the mobile tenninated call to the mobile device, if, al block ^5I), llio LA of the mobile device is known by the mobile switching node, at block S()\), liiu luuhlle switching nude pages the mobile device within the LA to connect tlio iii