Abstract:
A method is provided of registering a mobile terminal in an area of overlapping cell coverage by first and second networks for wireless mobile telecommunications. The networks are of different types. The method comprises: storing an identifier of the mobile terminal; storing in a controller a first record of in which cell or group of cells the mobile terminal is located in the first network and a second record of in which cell or group of cells the mobile terminal is located in the second network; and providing the mobile terminal with information of both records and said identifier.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to telecommunications, in particular wireless telecommunications. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    To date, a known solution to optimize mobility management signaling, across two different access technologies, is to have a single core network node that handles both the technologies and to share routing area identities between the two technologies. This approach has been used in systems having access technologies of a Universal Mobile Telecommunications System (UMTS) network and a Global System for Mobiles (GSM) network. This is not a flexible approach as it constrains deployment options. 
       SUMMARY OF THE INVENTION 
       [0003]    Methods and apparatus according to the present invention are set out in the appended claims, to which the reader is now referred. Preferred features are laid out in the dependent claims. 
         [0004]    A method is provided of registering a mobile terminal in an area of overlapping cell coverage by first and second networks for wireless mobile telecommunications. The networks are of different types. The method comprises:
       storing an identifier of the mobile terminal;   storing in a controller a first record of in which cell or group of cells the mobile terminal is located in the first network and a second record of in which cell or group of cells the mobile terminal is located in the second network; and   providing the mobile terminal with information of both records and said identifier.       
 
         [0008]    Accordingly, in preferred embodiments, a method is provided by which a dual-mode user terminal, which is capable of using different radio transmission technologies, can transfer connection between the two technologies while in Idle mode without generating large amounts of location update signalling. The two technologies may be, for example, on the one hand, Wideband Code Division Multiple Access (WCDMA)-based Universal Mobile Telecommunications System (UMTS) and, on the other hand, Orthogonal Frequency Division Multiple Access (OFDMA) based UMTS Long Term Evolution—also Known as LTE). User terminals are often referred to as User Equipment (UE). 
         [0009]    The proposed approach allows, in some embodiments, for independent allocation of routing area identities and network planning and also allows the usage of substantially independent core network nodes (albeit the two core nodes may interact with one another). 
         [0010]    A procedure is preferably provided to register the mobile in the two networks by means of just one registration by the user terminal, for the purpose of reducing location update signalling messages from the user terminal every time the user terminal transfers between the two networks. 
         [0011]    The radio access network (RAN) of the first network preferably holds a mapping record, for each of its cells of the tracking area, of the corresponding “overlay” cell of the other network. The RAN of the first network preferably provides the Tracking Area/Routing Area of the cells of both networks to the core network. 
         [0012]    The core network of one network preferably uses this information, on its own or along with temporary identifiers of the user terminal that are provided by the user terminal, to identify the core network of the other network. The core network of the first network preferably performs a proxy registration with the core network of the other network on behalf of the user terminal. 
         [0013]    Preferably, the Tracking Area/Routing Area, or a list of Tracking Areas and Routing Areas, are provided to the user terminal to inform of what may be considered as “Equivalent Tracking” areas, within which the mobile may roam without generating any location update signaling. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Preferred embodiments of the present invention will now be described by way of example and with reference to the drawing, in which: 
           [0015]      FIG. 1  is a diagram of a system according to the present invention, 
           [0016]      FIG. 2  is a more detailed diagram of the networks shown in  FIG. 1  showing the overlapping coverage areas, 
           [0017]      FIG. 3  is a sequence diagram illustrating a network attachment procedure in the LTE network shown in  FIG. 2 , 
           [0018]      FIG. 4  is a sequence diagram illustrating a first Tracking area update scenario in the LTE network, 
           [0019]      FIG. 5  is a sequence diagram illustrating a second Tracking area update scenario where the Serving GPRS Support Node (SGSN) has changed and the SGSN_old performing a proxy update towards the SGSN_new, 
           [0020]      FIG. 6  is a sequence diagram illustrating a third Tracking area update scenario where the SGSN has changed and the base station (eNB) performs a proxy update directly towards the SGSN_new, 
           [0021]      FIG. 7  is a sequence diagram illustrating a Routing area update procedure in UMTS, and 
           [0022]      FIG. 8  is a sequence diagram illustrating a paging procedure to deliver data to the user terminal. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    The system of networks will first be described followed by a description of the Attach procedure and Tracking and Routing Area update procedure used in the system. A description of the Paging procedure used in the network to deliver downlink data to the user terminal in Idle mode is also provided. 
       The Networks 
       [0024]    As shown in  FIG. 1 , there are two technologies (technology A and technology B) with overlapping cells and coverage area. The radio access network (RAN) of each technology keeps a mapping record of the Routing Area (RA)/Tracking Area (TA) for each of its cells and also the overlapping cell of the other technology. For example, a RAN of Technology A knows the Routing Area of each of its cells and also the corresponding Tracking Area of the cells of Technology B which overlap the cells of technology A. 
         [0025]    As shown in  FIG. 2 , in the networks, technology A is Long Term Evolution (LTE) and Technology B is Universal Mobile Telecommunications System (UMTS). The LTE and UMTS core networks are also shown connected to a Gateway and the Home Subscriber Server/Home Location Register (HSS/HLR). The core network of technology A is a LTE Core Node (LCN) and the core network of technology B is a Serving GPRS Support Node (SGSN), where GPRS denotes General Packet Radio System. A dual-mode, specifically LTE and UMTS capable, user terminal is also shown. The core network node (SGSN) in technology B is also linked by a tunnel towards the Gateway as shown in  FIG. 2  acting as an anchor (and in the remainder of this description referred to as Gateway Node), so that the user terminal can be reached by packets intended for that user terminal. 
         [0026]    Core network nodes in one technology need to keep a mapping table that relates the addresses of nodes in the core network of the other technology to the identities of the tracking/routing areas of the other technology. The mapping table is based on a list of tracking/routing areas associated to one (or more) addresses of the core network node that handles them. 
         [0027]    Alternatively, in an otherwise similar embodiment (not shown), the mapping table in one technology uses the user terminal identifiers of known type, namely UE identity (P-TMSI or LTE TMSI (referred to as L-TMSI)), of the other technology, in order to identify the core network identity of that other technology. 
       Network Attachment Procedure 
       [0028]    Basically speaking,  FIG. 3  relates to the situation where a user terminal (user equipment, UE) attaches in one technology (Technology A), and the Radio Access Network (RAN) of Technology A includes the Tracking Area (TA) of the cell of Technology A in which the user terminal is performing the Attach, as well as the routing area of Technology B of the overlapping cell of technology B, into the Attach request, before passing the Attach Request to the core network (CN) of technology A. The core network node of this technology A performs a proxy registration of the user terminal with the core network node of the other technology (Technology B). The Core network node of technology B is determined by the core network node in technology A based on the value of the routing area (RA)) identity of technology B included by the RAN of technology A in the attach message. In the example shown in  FIG. 3 , Technology A is Long Term Evolution (LTE), RAN of technology A is enhanced NodeB (eNB), Technology B is Universal Mobile Telecommunications System (UMTS). The core of technology B is the Serving GPRS Support Node (SGSN) and the core network node of technology A is the LTE core node (LCN). 
         [0029]    As shown in  FIG. 3 , more specifically, the Attach request is sent (step a) by the user terminal (user equipment, UE) towards the eNB. The Attach request contains the user terminal&#39;s International Mobile Subscriber Identity (UE IMSI). The enhanced NodeB (eNB) forwards (step b) this to the LTE core network (LCN); the eNB also includes the UMTS routing area identity (RAId) of the overlapping UMTS cell found by using the mapping table maintained in the eNB. The LCN determines, i.e., identifies the associated SGSN (step c) based on the UMTS RAId value received in step b using the core network mapping table. The LCN then sends (step d) a proxy Attach request including the UE IMSI to the Serving GPRS Support Node (SGSN). This is acknowledged by the SGSN in step e. The LCN then establishes (step f) a tunnel towards the gateway and also performs (step g) a Location update towards the Home Subscriber Server/Home Location Register (HSS/HLR). After completion of these procedures, the LCN sends (step h) an Attach Accept to the user terminal including the user terminal&#39;s temporary identity in UMTS (packet temporary mobile subscriber identity, P-TMSI), temporary mobile subscriber identity in LTE (L-TMSI), the UMTS Routing Area identity (RAId), and LTE Tracking Area Identity (TAId). 
         [0030]    Thus, after the process of attach in technology A and the proxy registration in technology B are complete, the user terminal will have acquired the Routing Area/Tracking Area identities in the two technologies and the temporary identities in the two technologies, which also bind the user terminal to a particular core network node (the identities implicitly identify the core node) in the two technologies. 
         [0031]    In this condition, the user terminal will not generate any location update signaling as long as it stays within the same Tracking Area/Routing Area as at the initial registration time, even if the user terminal changes the technology, A or B, to which it is connected, e.g. see  FIG. 2 . When the boundaries of the initial Tracking Area/Routing Area are crossed, then the user terminal will need to perform a Tracking Area/Routing Area update procedure with the Core network node of the technology that the user terminal is currently camping on. 
         [0032]    Tracking Area Update Procedures 
         [0033]    Three tracking area update scenarios will now be described.  FIG. 4  shows the user terminal performing a tracking area update towards the Long Term Evolution (LTE) radio access network (RAN). The LTE core network performs a proxy registration with the UMTS core network where the SGSN is unchanged. The eNB appends the UMTS Routing Area while forwarding the Tracking Area update towards the LCN. The user terminal is provided with the list of Tracking Area and RAs in the Tracking Area update Accept within which it does not need to perform any update. In both  FIG. 5  and  FIG. 6 , the SGSN_new is different from the SGSN_old. In  FIG. 5 , the eNB performs a proxy registration towards the SGSN_old and the SGSN_old forward the proxy registration to the SGSN_new. In  FIG. 6 , the eNB performs the proxy registration directly towards the SGSN_new. 
         [0034]    These three scenarios are now described in turn, referring respectively to  FIGS. 4 ,  5  and  6 . 
       Tracking Area Update Where the Core Network of Technology B is Unchanged 
       [0035]    As shown in  FIG. 4 , say that the user terminal is camped on technology A, namely LTE. When the user terminal crosses the combined set of tracking areas provided in the Attach Accept message in shown in  FIG. 3 , the user terminal performs a Tracking area towards the eNB (step a 1 ). When the RAN (eNB) of the technology A (LTE) receives this message, it includes (step b 1 ) the RAId of the cell of technology B (UMTS) of the overlapping UMTS cell using the mapping table maintained in the eNB. Core network node (LCN) in technology A receives this Tracking Area/Routing Area update, identifies the core network node (SGSN_old) of technology B based on the temporary identity of the UE in technology B, or the RAId of technology B, using the mapping table maintained in the core network (step c 1 ). The LCN then sends a Proxy Routing Area update request (step d 1 ) towards the core network node (SGSN_old) in technology B. 
         [0036]    The core network node in technology B checks (step e 1 ) this Tracking Area/Routing Area identity value and if this value is compatible with the values that the core network node manages, the core network node will return one (or a list of) Tracking Area(s)/Routing Area(s) in technology B that can be considered valid for the user terminal to move within without generating signaling (step f 1 ). 
         [0037]    This set of information will then be sent (step g 1 ) to the user terminal in the Tracking Area/Routing Area update response along with one Tracking Area/Routing Area identity, or a list of Tracking Area/Routing Area identities, in technology A, within which the user terminal can move without generating signaling. Also, the Gateway Node is updated (step h 1  and i 1 ) with the address of the core network node in technology A if the address is different (that is, if there is a change in the CN node). As a result, the user terminal acquires a list of Tracking Area(s)/Routing Area(s) in both technologies, allowing the user terminal to move within the Tracking Area/Routing Area of the two technologies without generating Tracking Area/Routing Area update signaling. Also, the user terminal has now temporary identities consistent with the core node that is handling the user terminal in each technology. 
       Two Scenarios for Tracking Area Updates Where the Core Network of Technology B has Changed 
       [0038]    In  FIG. 5 , steps a 2  to d 2  and h 2  to k 2  are the same as in steps a 1  to d 1  and steps f 1  to i 1  respectively referred to above in respect of  FIG. 4 . If in the SGSN_old the Tracking Area/Routing Area identity value will point (step e 2 ) to the address of an alternate core network node (SGSN_new) in technology B, the SGSN_old will forward (step f 2 ) the proxy registration to this node. This node will then repeat the check of the Routing Area/Tracking Area value and will return (step g 2 ) to the core network node (LCN) in technology A, via (step h 2 ) the first core network node (SGSN_old) in technology B, one (or a list of) Tracking Area/Routing Area in technology B that can be considered valid for the user terminal to move within without generating signalling, along with a temporary identity in technology B to be used by the user terminal. 
         [0039]    In  FIG. 6 , steps a 3  to b 3  and h 3  to j 3  are the same as in steps a 1  to b 1  and steps g 1  to i 1  respectively referred to above in respect of  FIG. 3 . In an alternative embodiment, the core network node (LCN) of technology A sends (step d 3 ) the Proxy update to the new core network node (step c 3 ) of technology B identified by the TAId of technology B. The new core network node then retrieves (step e 3  and f 3 ) the user terminal&#39;s context signal from the old CN (SGSN_old) of technology B. The SGSN_new then sends (step g 3 ) the Proxy update response to the core network (LCN) of technology A. 
       Routing Area Update 
       [0040]    Basically speaking,  FIG. 7  relates to the user terminal performing a Routing area update towards the UMTS radio access network (RAN). The UMTS core network performs the proxy registration towards the LTE core network. The UMTS radio network controller (RNC) appends the LTE Tracking Area while forwarding the Routing Area update towards the Serving GPRS Support Node (SGSN). The user terminal is provided with the list of Tracking Areas and Routing areas within which it does not need to perform any update. 
         [0041]    As shown in  FIG. 7 , more specifically, the user terminal sends (step a 4 ) a Routing area update towards the UMTS RNC and the RNC then forwards (step b 4 ) it to the SGSN and also includes the overlapping LTE TAId using the mapping record stored in the RNC. The SGSN determines (step c 4 ) the LCN of the UE based on the L-TMSI using the mapping table maintained in the SGSN. The SGSN then performs (step d 4 ) a proxy Tracking area update towards the LCN. The LCN checks (step e 4 ) if the TAId provided belong to it. If the LCN corresponding to the TAId is different, the LCN_old forwards (step f 4 ) the Proxy TA update to the LCN_new. The LCN_new responds (step g 4 ) with a Proxy Tracking area update response to the LCN_new. The LCN_old sends (step h 4 ) a proxy Tracking area update response to the SGSN including the LTE user terminal identity (L-TMSI) and the list of tracking areas in which the user terminal is allowed to roam without generating a Tracking Area update. The SGSN finally sends (step i 4 ) a Routing Area update Accept to the user terminal including the information received from the LCN and the UMTS user terminal identity (P-TMSI) and the list of RAId in which the user terminal is allowed to roam without generating a Routing Area update. If there is a change of SGSN, the tunnel to the gateway is also updated (step j 4 ) by the SGSN and a location update is also performed (step k 4 ) towards the home subscriber server/home location register (HSS/HLR). 
         [0042]    In an alternative, otherwise similar, embodiment (not shown), the SGSN sends the proxy Tracking Area update of step d 4  directly to the LCN_new rather than via the LCN_old. 
       Downlink Data Transfer and Paging 
       [0043]      FIG. 8  relates to how the user terminal that is last registered in UMTS is paged in both UMTS and LTE systems when idle. The user terminal responds on the LTE system. On receipt of the paging response, the bearers (radio channels) are set up and the data sent to the user terminal via the LTE system. 
         [0044]    As shown in  FIG. 8 , when a downlink packet arrives (step a 5 ) at the Gateway (denoted GW in  FIG. 8 ), the packet is then sent on to the last registered core network node (SGSN) (step b 5 ). The SGSN triggers paging in both technologies (LTE and UMTS) by contacting the core network node (LCN) (step c 5  and d 5 ) in the other technology that was associated to the user terminal during the attach or Tracking Area/Routing Area update procedure. The SGSN sends (step e 5 ) a paging message to UMTS radio access network RAN, which is also known as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN). The LCN then also sends (step f 5 ) a paging message to the eNB. Both the UTRAN (step g 5 ) and eNB (step h 5 ) will then page the user terminal over the radio interface. The user terminal responds (step i 5 ) to the paging message over the technology it is currently camped on (i.e. LTE) to the eNB. The eNB forwards (step j 5 ) the paging response to its core network node (LCN). The LCN then forwards (step k 5 ) the paging response to the last registered core network node (SGSN) from which the LCN had received the paging request in step c 5 . The SGSN then forwards (step l 5 ) to the LCN data that the SGSN had received in step b 5 . Security functions are executed (step m 5 ) by the LCN. The gateway is updated (step n 5 ) to request that data be sent to the LCN. Bearers between the LCN and the user terminal over LTE are established in steps o 5 , p 5  and q 5 ). The LCN then forwards (step r 5 ) data to the eNB, and eNB sends (step s 5 ) data to the user terminal. 
       General 
       [0045]    The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope. 
       LIST OF ACRONYMS 
       [0000]    
       
         CN: Core Network 
         eNB: Enhanced NodeB 
         GPRS: General Packet Radio System 
         GW: Gateway 
         HSS/HLR: Home Subscriber Server/Home Location Register 
         LCN: LTE Core Network/ LTE Core Network node 
         LTE: Long Term evolution. 
         L-TMSI: LTE Temporary Mobile Subscriber Identity 
         P-TMSI: Packet Temporary Mobile Subscriber Identity 
         RA: Routing Area 
         RAId: Routing Area Identity 
         RAN: Radio access Network 
         RNC: Radio Network Controller 
         SGSN: Serving GPRS Support Node 
         TA: Tracking Area 
         TAId: Tracking Area Identity 
         UE: User Equipment 
         UMTS: Universal Mobile Telecommunications System 
         UTRAN; UMTS Radio Access Network