METHOD AND APPARATUS FOR PAGING IN A CELLULAR RADIO ACCESS SYSTEM

Abstract: A method and apparatus for paging a single mode MS terminal in a system having cells from more than one radio access system in the same LA. By utilizing Classmark information (CM1, CM2, CM3 or a new common Classmark) carrying information relating to the band capability of the MS, the MSC can be informed as to the band capabilities of the MS and thereby enable paging in only those cells (e.g., GSM or UMTS) for which the MS is operable. The CM information can be transmitted to the MSC during the initial LA update upon access to the system (activation of the MS) or during another mobility management (MM) message.

Description: Method And Apparatus For Paging In A Cellular Radio Access System BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communications systems and more particularly, to paging in systems having cells belonging to more than one cellular radio access network in the same location area/radio area/paging area. 2. Description of the Related Art In cellular radio systems, tracking the mobility of the mobile station (MS) is of utmost importance in order to provide continuous capability to reach the MS. In a Global System for Mobile Communication (GSM) , this has been solved with two registers, one permanent (i.e., home location register (HLR) ) , and one temporary (e.g., visitor location register (VLR)) . The temporary register (e.g., the VLR) is located in the serving network. The permanent HLR contains the subscriber data that is copied to the temporary VLR when needed, and also contains the address of the VLR . The temporary VLR contains a copy of the permanent subscriber data and the location of the subscriber in the form of a location area/routing area (LA/RA) which is typically composed of more than one radio cell. LA/RA represents the most accurate information stored in the network while the MS is not engaged in a connection but is deemed reachable via paging (i.e., MS is listening to paging channels) . The size of the LA/RA is a compromise between LA/RA update vs. paging signaling load. The larger the LA/RA, the fewer location area updates (LAUs) /routing area updates (RAUs)are encountered but the area where paging must be performed to complete the call is larger. Referring to Figures la and lb, when the radio cells (e.g., GSM and UMTS) do not belong to the same LA and the dual mode MS moves, each new cell in a different system reguires an LAU, even if the cells were co-located. Figures lc and Id, show the scenario when the radio cells (e.g., GSM and Universal Mobile Telephone System (UMTS)) are part of the same location area LA3. LA3 is larger than both LAI and LA2 in that it contains more co-located cells of difference systems, therefore requiring less LAUs, but as mentioned previously, the area where paging is to be performed to complete the call (i.e., LA3) is much larger. Thus, in this environment, when the MS call is first routed, an inquiry is made to the permanent register (HLR) which provides a pointer to the address of the temporary register (i.e. VLR) . This is performed with well known GSM procedures. Once the call arrives to the serving network (i.e., core network), the LA/RA stored in the temporary register is utilized to page the MS. The paging of the MS is then directed to a subset of cells served by the CN . Referring to Figures lc and Id, the paging of the MS would be directed to LA3 which comprises a GSM and a UMTS cell. The termination of calls in the environment shown in Figures lc and Id is performed by also using the information stored in the registers (i.e., the HLR and VLR) . A determination is made (or has already been made) as to the VLR of the MS, and the LA is derived from the VLR. Once this information is known, the call can be terminated using procedures well known in the art . In an effort to reduce the amount of signaling required in different radio access systems (e.g., GSM and UMTS systems) connected to the same CN, it has been proposed to have each system' s cells within the same Location Area/Radio Area (LA/RA) . Figures lc and Id show this proposed solution using GSM and UMTS systems to optimize the LUs for paging in these systems. One of the reasons for the "co-habitation" of GSM and UMTS cells in the same LA/RA is to reduce location updating when changing radio access systems, which may occur frequently, especially at the beginning of UMTS service. UMTS coverage is expected to extend into hot spots such as, for example, airports where a large number of LA/RA updates would occur when people are leaving or arriving at the airport or even moving inside. This "cohabitation" of cells is specifically designed to support multiple mode terminals -- i.e., mobile stations (terminals) having the capability of operating in more than one radio access system (e.g., both GSM and UMTS systems) . A single mode terminal or MS can only access one or the other of the two systems . By way of example, let us consider the movement of a single mode UMTS or GSM MS in an environment shown in Figures lc and Id. As the single mode MS moves, nothing happens (from an LU point of view) compared with the two LUs required for the environment shown in Figures la and lb. As shown in Figures lc and Id, a core network (CN) (e.g. MSC) supports both the GSM Radio access system (BSS) and UMTS radio access system or network (UTRAN) . Reference is made to GSM and UMTS systems as the two possible radio access systems having cells in the same LA. However, one of ordinary skill in the art will recognize that other radio access systems having cells in the same LA as another system also suffer from the aforementioned drawbacks with paging a single mode MS in the LA having cells from more than one radio access system. The location area LA3 covered by the respective BSS and UTRAN contains a corresponding GSM cell and a UMTS cell. Currently, when a single mode/band MS moves within the LA3 having both the GSM and UMTS cells, both systems will operate to page the single mode MS even though the MS can only access one of the two systems. As a result, the optimization for multi-mode terminals (i.e. co- location of cells of different systems in the same LA) has resulted in sub-optimal performance of the radio access systems for the single mode MS. Thus, since it is unnecessary for both systems to page the single mode MS, it becomes apparent that when paging a single mode MS operating in a LA/RA in which cells for both GSM and UMTS systems are present, the "co-habitation" of cells results in an inefficient use of the system resources. As mentioned previously, the larger the LA, the less LAUs required which results in paging in a very large area, and the opposite also applies -- i.e., the smaller the LA, the more LAUs required, and paging is performed in a smaller area. Table 1 summarizes the current paging scheme in a system having both GSM and UMTS cells in the same LA/RA, where * indicates totally unnecessary and inefficient use of system resources . Table 1 Referring to the flow chart of Figure le, when a single mode mobile station/terminal (MS) is activated (i.e., accesses the system), it starts its LA update (step 12) . In GSM (and also UMTS, for purposes of this discussion) , paging is performed according to the LA/RA. The LA is stored in the MSC/VLR or serving GPRS support node (SGSN) (step 14). This stored information does not contain any information relating to the band capabilities of the MS. Thus, when the need for a page arises (e.g., a call for the MS subscriber is forthcoming) , the LA previously stored in the MSC/VLR is accessed (step 18) and a page is issued in all cells contained within the LA regardless of whether the MS is dual mode or not (step 20) . Therefore, when both GSM and UMTS cells are located within the same LA (as shown in Figure la) , there is sub-optimal performance of the entire system resulting in the unnecessary issuance of a paging signal through the system' s cell for which the MS does not belong under any circumstance (i.e., either the GSM or UMTS cell) . Specifically, the core network (CN) (e.g., the MSC) currently has no mechanism by which it can optimize paging in an environment where cells from two radio access systems belong to the same LA/RA without unnecessarily restricting both systems. An example of such system is shown in Figure lc where GSM cells and UMTS cells are contained within the same LA3. Another example of such configuration would be when more than one GSM 900/1800 cells are located within the same LA. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for optimizing the paging of a single mode/band MS in a system having cells from more than one radio access system in the same LA/RA/Paging area. It is a further object of the invention to provide a method for paging a single mode MS where only those cells in the LA (paging area) corresponding to the system for which the single mode MS is adapted to operate will be used. This and other objects are achieved in accordance with the present invention wherein a method for paging a mobile station (MS) in a communication system having cells from more than one radio access system in the same location area (LA) using only those cells from a particular radio access system corresponding to the specific band capabilities (i.e., system capabilities) of the MS is provided. In a preferred embodiment, the mobile station transmits information to the core network of the system (e.g., MSC) relating to the system (e.g., band) capabilities of the mobile station during the LA update (LU in the preferred embodiment) . The capability to operate in other systems could also be achieved by attaching an adapter to the MS, even when powered on. Thus, in this case, the attachment should trigger the corresponding updating procedure (e.g, CM update) . This embodiment can be a procedure of its own (i.e., updating of Classmark information). The core network utilizes the system capability information of the MS to determine whether the MS is a single mode or multiple mode device capable of operating in more than one mode/band (e.g., dual or triple mode/band) . Once the capabilities of the MS are determined, the core network identifies which radio access system in the LA correspond to the band capabilities of the MS, and when a need for a page arises, issues a paging signal to the MS only through the cells in the determined radio access system for which the MS is adapted to operate. Other contemplated embodiments provide for transmitting the band capability information of the MS to the core network at different points during communication between the MS and CN . For example, during a setup procedure as part of the connection establishment. However, this embodiment does not help in the initial establishment of a paging scheme for the MS. It does provide more efficient paging to the MS subsequent to performing the setup procedure. Also, the information sent by the MS may contain other variable parameters as well that are stored and utilized by the CN. Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings : Figures la and lb are block diagrams showing the movement of a MS from one LA to another LA in accordance with the prior art; Figures lc and Id are block diagrams showing the movement of a MS with the same LA having cells from two radio access systems; Figure le is a flow chart of a prior art method for paging in an exemplary system having both GSM and UMTS cells in the same LA; Figure 2 is a flow chart of the method for paging in the exemplary system having both GSM and UMTS cells in the same LA in accordance with an embodiment of the present invention; Figure 3 is a message sequence diagram of the location updating procedure in accordance with GSM Standard 04.08; and Figures 4a and 4b show message sequence diagrams of the location updating procedure for a UMTS system and a GSM system in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS In accordance with a preferred embodiment of the present invention, information relating to the MS capabilities is transmitted to the CN during location/routing area updating. In the following, the MSC/VLR is considered part of the CN . The MS capabilities referred to here are the system capabilities which provide the CN with information as to the specific system(s) (e.g., GSM, UMTS, etc) with which the MS is adapted to operate in. Referring to Figure 2, when the MS accesses the system (i.e., is activated), it performs its location area update (LAU) to the MSC handling the respective LA (step 12) . The MSC stores the location area (LA) into the VLR as described previously, and additionally stores information regarding aspects of the mobile equipment into the VLR (step 22) that describe the properties of the MS while the MS listens to the paging channel. Mobile Station Classmark (CM) information or other mode information stored in the VLR and provides the core network (e.g., MSC) with information concerning the operating characteristics of the MS while listening to the paging channel. The CM can be independent of the frequency band of the channel it is sent on. More specifically, the CM information includes, inter alia , the system/band capabilities of the MS. As such, this information can be stored in the MSC/VLR when the MS performs its LAU (either initially or when its LA changes from the initially registered LA) . Based on the band capabilities of the MS, it is easily determined what system or systems the MS is adapted to operate on (e.g., whether the MS is a dual mode (GSM and UMTS) or single mode terminal (e.g., GSM or UMTS)). Once the information is stored (step 22), the need for a page is determined (step 24) . The need for a page can be brought on, for example, by an incoming call for the MS subscriber. Once there is a need for a page, the MSC/VLR retrieves the previously stored LA and CM information from the VLR (step 26), and initially makes a determination as to whether the MS is a dual mode terminal (step 28) -- i.e. an MS capable of operating in both the GSM and UMTS systems. When the MS is a dual mode terminal, a page is usually issued in all cells contained within the LA (as in the prior art) . If however, the MS is not a dual mode terminal, the MSC determines which system the single mode MS is set up for (step 32) . Thus, when the MSC determines that the MS is a single mode GSM terminal, it proceeds to page the MS using only the GSM cells of the LA (step 34), and when the MSC determines, at step 32, that the MS is a single mode UMTS terminal, it proceeds to page the MS using only the UMTS cells of the LA (step 36) . Figure 3 shows a simplified message sequence diagram of the location area update (LAU) performed by a MS in a GSM system. The location update (LU) procedure is always initiated by the mobile station (e.g. when it finds itself in a different LA from the previously registered area) . Once the connection for LU is established, the MS sends the Location Updating Request (LUR) to the MSC. At this point, the MSC may optionally perform security functions such as, for example, authentication of the subscriber to prevent access of unregistered users, radio path ciphering (i.e., ciphering of all subscribed information to prevent third-party tapping) and the allocation of a new Temporary Mobile Subscriber Identity (TMSI) to protect the subscriber identity and to prevent subscriber location disclosure by not sending the International Mobile Subscriber Identity (IMSI) in clear over the radio. The MSC then sends a location updating accept message when the LU was ok. Once the LU is complete, the radio channel is released. In accordance with an embodiment of the present invention, the LUR sent by the MS can include information relating to the MS such as, for example, its power and band capabilities (i.e., the system bands at which it is designed to operate) . As mentioned previously, this information can be contained in the Classmark (CM) accompanied with the LUR. Classmark 1, Classmark 2 and Classmark 3 and GPRS type information are known in the art for GSM applications, and can be also utilized (in principle) in the UMTS systems as the aim is to re-use the GSM CN in UMTS. In other contemplated embodiments, a common new mode Classmark (i.e., common between both GSM and UMTS systems) can be used in the LUR to provide the necessary MS identifying information to the Core Network (i.e., MSC) via the respective BSS or UTRAN. The band capability information will inherently include or will enable the derivation of information relating to whether the MS is a multiple mode or single mode terminal, and by knowing what bands the MS operates in, the MSC (network) can easily identify which systems (e.g., GSM, UMTS) the MS is adapted to operate on. Thus, the information on the capability to operate in other systems or bands can be included in these CMs . For example, in prior art GSM the information on the MS's capability to operate on the other GSM band (i.e. 900 vs. 1800 in Europe) is coded in the CM3. For UMTS (or also for GSM), a totally new CM can be defined to carry the information on the MS band capabilities to the CN. The LUR is sent by the MS to the network to either request update of its location file (i.e., normal or periodic updating) or to request IMSI attachment. The initial message from the MS to the network includes the LUR. Table 2 provides a detailed look at the content of a LUR message according to GSM standards. Table 2 As shown in Table 2, the CM1 information is part of the LUR in the GSM system. However, multi-band mobile stations are relatively new and require support in the CM. Generally, CMs are two octets in length and therefore may provide sufficient space for the bits necessary to inform the CN as to the band capabilities of the MS. CM1 and CM2 have very rigid and inefficient coding which would result in the CM being very long, even if all bits for the capability information are not in their supported positions. CM3 has more flexible coding than CM1 and CM2 , thus enabling its preferred use for storing and transmitting the band capabilities of a single band or multi-band MS to the CN . Also, in the future since CM1 and CM2 do not provide all the MS information (e.g., multi-band), the CM3 must be present in order to provide this information to the CN . When dealing with multiband MS's however, the CM3 is not included in the initial message from the MS to the network. In order to compensate for this, GSM 04.08 provides for Early Classmark sending, which is generally when the MS sends, as early as possible after access, a "Classmark Change" message to provide the network with the additional Classmark information (e.g., with dual band terminals in GSM: CM3) . Figure 4a shows a message sequence diagram of the preferred embodiment of the transmission of the initial message (e.g. LUR) to the MSC from the MS in a UMTS (and GSM) system in accordance with a preferred embodiment of the present invention. As shown, the initial message is sent to the MSC (via the UTRAN or URAN) as would ordinarily be performed, however the initial message contains the CM information relating to the band capabilities of the MS (e.g., CM3 or new CM) in addition to the IMSI. As suggested above, the information necessary for identifying the band capability (and other relevant information for paging) relating to the MS can be carried by the CM which can be CM1, CM2 , CM3 or a GSM and UMTS common new CM (i.e., common to both GSM and UMTS systems) . The MSC/VLR of the UMTS/GSM system can then store the band info (in bits) in the MSC/VLR. Thus, when the need for a page arises (step 24 of Figure 2), the CM information relating to this MS and thereby the mode/band capabilities of the MS can be retrieved from the VLR (steps 26 and 28 of Figure 2) . In this example, the paging could then be performed in the UMTS cell within the previously registered (updated) LA, thus enabling the GSM cells in the same LA to remain free and capable of being used for other GSM related operations . Figure 4b shows another embodiment when there is a change in the classmark (CM) information or the "CM3 present" relating to the MS. The reason for the classmark change can be the fact that CM3 is there to inform the network about additional capabilities of the MS. The change is transmitted to the BSS from the MS. The change can be to another identified classmark (e.g., CM2 or CM3) , or can be the new common CM. The BSS sends the CM update to the MSC, which again stores the bits relating to the MS's band capabilities and any other relevant information for paging the MS in the VLR. As before, when the MSC has access to information relating to the MS's system operating capabilities (via the stored bits in the VLR) , more efficient paging of the MS within the updated LA can be performed. One of ordinary skill in the art will recognize that this can be applied in GSM, UMTS or other radio access systems as well. In other contemplated embodiments of the present invention, the actual bits containing the information relating to the operating characteristics of the MS can be transmitted to the MSC at several different points via several different mediums. For example, the bits can be incorporated into the LUR message or any other MM message itself without requiring the use of the CM information from the MS to the MSC during connection establishment. In another embodiment, the information relating to the band capabilities of the MS (and any other paging relevant information) can be stored in the HLR and downloaded from there when needed. This embodiment, however, is very rigid as every time the terminal is changed, the HLR must be informed. Generally, storing information about the MS that needs to be updated within short intervals in the HLR is not a good idea because the HLR serves to provide substantive data services, etc. Other embodiments would include transmitting the information relating to the MS system capabilities after a connection (e.g., voice call) is being established. In this embodiment, bearer capability (BC) information, which is also part of the setup procedure (or message) , can also be used to carry the bits necessary for identifying the MS band capabilities. BC generally provides information relating to the connection capabilities of the terminal (e.g., data), so the information relating to the band capabilities could be handled in a similar manner. It is important to note however, that BC is not present in LU. In the aforementioned embodiments, when the MS terminal is a single mode terminal, only those system resources allocated to the capabilities of the MS are utilized. Thus, the unnecessary paging in both the UMTS and GSM cells contained in the same LA is eliminated, and system efficiency is substantially increased. While there have shown and described and pointed out fundamental novel features of the invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims: CLAIMS 1. A method for paging a mobile station in a communication system having cells from more than one radio access system in the same location/routing/paging area comprising the steps of: transmitting information to a core network relating to system capabilities of the mobile station; determining the system capabilities of the mobile station from the transmitted information; identifying which cells in the location/routing/paging area correspond to the system capabilities of the mobile station; and issuing a paging signal to the mobile station through the determined cells of the system for which the mobile station is adapted to operate. 2. The method set forth in claim 1, further comprising the steps of: storing the transmitted information in a visitor location register of a mobile switching center; and retrieving the stored information from the visitor location register when a need to page the mobile station exists. 3. The method set forth in claim 1, wherein said step of transmitting is performed using Classmark information relating to the mobile station. 4. The method set forth in claim 1, wherein the more than one radio access system comprises a GSM and UMTS system. 5. The method set forth in claim 1, wherein said step of transmitting is performed during a mobility management message sent from the mobile station to the mobile switching center. 6. The method set forth in claim 1, wherein said step of transmitting is performed during a location area update request sent from the mobile station to the mobile switching center. 7. The method set forth in claim 1, wherein said step of transmitting further comprises establishing a connection between the mobile station and the mobile switching center and sending the system capability information during a setup procedure performed during connection establishment. 8. The method set forth in claim 3, wherein the Classmark information comprises one selected from a group consisting of general Classmark, Classmark 1, Classmark 2, Classmark 3 and a common Classmark. 9. The method set forth in claim 1, wherein the mobile station comprises a mobile cellular telephone. 10. The method set forth in claim 2, further comprising determining whether the mobile station is a dual mode mobile station. 11. The method set forth in claim 2, further comprising the steps of: determining whether the mobile station is a dual mode mobile station; and determining which system the mobile station is adapted to operate in when it is determined that the mobile station is a single mode mobile station. 12. The method set forth in claim 1, wherein the system information comprises information relating to band capabilities of the mobile station. 13. A method for paging a mobile station in a wireless communication system having a core network, a GSM Base Station Subsystem, a UMTS Radio Access Network, and corresponding GSM and UMTS cells in the same location area covered by the Base Station Subsystem and UMTS Radio Access Network, the method comprising the steps of: initiating a location area update from the mobile station to the mobile switching center to provide the mobile switching center with the location area information of the mobile station; transmitting information to the mobile switching center relating to system capabilities of the mobile station during the location area update; storing the location area information and transmitted information in a visitor location register of the master switching center; retrieving the stored location area information and transmitted system capability information from the visitor location register when a need for paging the mobile station is determined; identifying which system the mobile station is adapted to operate in based on the transmitted information; and issuing a paging signal in the cell or cells corresponding to the identified system for which the mobile station is adapted to operate in. 14. The method set forth in claim 13, wherein said step of transmitting is performed using Classmark information relating to the mobile station. 15. The method set forth in claim 13, wherein said step of transmitting is performed during a location area update request sent from the mobile station to the mobile switching center. 16. The method set forth in claim 13, wherein said step of transmitting further comprises establishing a connection between the mobile station and the mobile switching center and sending the system capability information during a setup procedure performed during connection establishment. 17. The method set forth in claim 16, wherein the Classmark information comprises one selected from a group consisting of general Classmark, Classmark 1, Classmark 2, Classmark 3 and a common Classmark. 18. An apparatus for paging a mobile station in a system having cells from more than one radio access system in the same location area comprising: a core network; at least one mobile station in communication with the core network; means for transmitting information to the core network relating to system capabilities of the mobile station; means for identifying which cells in the location area correspond to the system capabilities of the mobile station; and means for issuing a paging signal to the mobile station through the identified cells for which the mobile station is adapted to operate. 19. The apparatus in accordance with claim 18, wherein said at least one mobile station comprises a cellular telephone. 20. The apparatus in accordance with claim 18, wherein said means for transmitting comprises Classmark information contained in said at least one mobile telephone, wherein said at least one mobile telephone transmits the Classmark information to the core network during a location area update procedure. 21. The apparatus in accordance with claim 18, wherein said transmitting of information to the core network is performed during location area update by the at least one mobile station to the core network. 22. The apparatus in accordance with claim 20, wherein the Classmark information comprises one selected from a group consisting of general Classmark, Classmark 1, Classmark 2, Classmark 3 and a common Classmark. 23. A method for paging a mobile station in a communication system having cells from more than one radio access system comprising the steps of: transmitting information to a core network relating to operating capabilities of the mobile station; identifying which radio access system the mobile station is adapted to operate on based on the transmitted information; and issuing a paging signal to the mobile station through cells of the identified radio access system for which the mobile station is adapted to operate. 24. The method set forth in claim 23, wherein said step of transmitting is performed using Classmark information relating to the mobile station. 25. The method set forth in claim 24, wherein the Classmark information comprises one selected from a group consisting of general Classmark, Classmark 1, Classmark 2, Classmark 3 and a common Classmark.

Inventors: EINOLA HEIKKI, HAUMONT SERGE, KALLIO SUSANNA, SITCH PAUL, EINOLA, HEIKKI, HAUMONT, SERGE, KALLIO, SUSANNA, SITCH, PAUL
Applicants: NOKIA INC, NOKIA NETWORKS OY, NOKIA INC.
Application year: 2000
Main classification: H04Q7
IPC codes: H04W64