Abstract:
A method and system for providing the active members of a Voice Group Call Service with additional information. The additional information is transmitted in a message on the associated control channel for the downlink traffic channel of the voice group. The additional information is transmitted simultaneously to an ongoing voice group call.

Description:
BACKGROUND  
   1. Field of the Invention 
   The present invention generally relates to the field of voice group services in mobile communication networks, and in particular to Voice Group Call Services (VGCS). 
   2. Discussion of Prior Art 
   Voice Group Call Service allows the establishment of a call between members of a group in numerous cells of the mobile telecommunication network simultaneously. These cells define the service area. All subscribers belonging to the group have the possibility to listen to the call in the service area. It is also possible to participate in the call individually. Service subscribers of the radio network can become group members on a network-wide basis to one or more groups pre-defined in the network by a corresponding group identification (group ID). The membership enables them to receive voice group calls associated with that group ID. 
   In addition, certain group members are entitled by their subscription to initiate Voice Group Calls (VGC). In addition to subscriber details in the Home Location Register (HLR), it is necessary for the mobile station (MS) to be aware of its group membership by storing details on the Subscriber Identity Module (SIM). This is required because it responds to notification messages which include only the group call relevant information, that is, no IMSI or TMSI details. Having become a group member, each service subscriber can set to active state or deactive state the group ID or any one out of his several group IDs on the SIM. In active state the subscriber can initiate VGCs to that group ID. When in deactive state the subscriber cannot make VGCs to the group and the mobile station ignores any notification for that group ID. 
   A group call area can be restricted to a single Mobile Switching Center (MSC) area or can exceed one MSC area (implementation option). A voice group call is initiated by a calling subscriber by a related man machine interface action for the service selection and the group ID dialed. The MSC in which the voice group call is initiated obtains by requesting a Group Call Register (GCR) the group call attributes. The GCR is functionality in the network containing the group call attributes. This GCR interrogation after call initiation also determines whether the MSC acts as group call Anchor- or as group call Relay-MSC. A group call Anchor-MSC is responsible for managing and maintaining a particular VGC. The group call Anchor-MSC is determined as the one controlling the cells of the group call area. For VGCSs where the group call area exceeds an MSC area, the group call Anchor-MSC is predefined in the network. A group call Relay-MSC controls cells of a group call area which are not under control of the group call Anchor-MSC for those voice group call services where the group call area exceeds one MSC area. 
   If the MSC is not the Anchor-MSC then the call will be “forwarded” from the Relay-MSC to the respective Anchor-MSC (information also delivered by GCR) and further “call-establishment” is done by the Anchor-MSC. 
   When a calling subscriber (talker) initiates a voice group call, one voice group call channel is established in each cell of the group call area and notifications for that call is sent in each of these cells. A voice group call channel is a downlink to be allocated in each cell of the group call area for a particular voice group call. All mobile stations being service subscribers for that Voice Group Call in one cell listens to the common downlink. All mobile stations of the listening service subscribers in one cell only listens to the same common downlink (voice group call channel). Of course it is possible to change the talker at any time, so that one of the listeners of the group becomes the talker and the previous talker becomes a listener. 
   The standards of Voice Group Call Service are specified in the technical specification ETSI TS 143 068, V5.2.0, December 2002: Digital Cellular telecommunication system (Phase 2+); Voice Group Call Service (VGCS); Stage 2; 3GPP TS 43.068 version 5.2.0 Rel. 5. 
   US patent publication 2003/0100326 A1 relates to a group location and route sharing system for communication units in a trunked communication system, wherein the communication units are engaged in a group voice call communication. Subscription and location data can be sent as a supplementary information to the group voice call communication by using an underlying packet transport layer. 
   SUMMARY OF THE INVENTION 
   It is a purpose of the invention to enhance the conventional voice group call service by providing an additional communication service without changing the general architecture of the communication network. 
   The additional information for Voice Group Call Service (VGCS) is designed to provide all active members of a VGCS in parallel, that is, simultaneous to an ongoing voice group call, with additional information, for example, the tactical addresses of the current talker. The information contained here may have a text-oriented or binary-oriented character. 
   The transmission of the additional information shall be realized only in acknowledged mode and is sent on the Slow Associated Control Channel (SACCH), which represents an associated control channel for the downlink traffic channel of the voice group call. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     The objects, advantages and features of the invention will be more clearly perceived from the following detailed description, when read in conjunction with the accompanying drawing, wherein: 
       FIG. 1  shows a functional voice group call architecture with a group call register; and 
       FIG. 2  shows a transfer of additional information to members of a VGCS. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The general architecture of GSM is maintained in this invention. With reference to  FIG. 1 , in addition, a network function is required which is used for registration of the group call attributes, the group call register (GCR)  10   a ,  10   b ,  10   c . The GCR function is mainly a database function, holding information about voice group calls. The signalling between the entities shown in  FIG. 1  shall be as defined in the following. 
   The Mobile Switching Center (MSC)  12   a ,  12   b ,  12   c  containing the cell within which this voice group call is initiated performs subscription checking against Visitor, Location Register (VLR)  14   a ,  14   b ,  14   c  and Home Location Register  16  records. It then consults its GCR  10   a ,  10   b ,  10   c , respectively, to determine the group call attributes related to its MSC area and whether it is the group call Anchor-MSC  12   a  for that voice group call. If it is not, the GCR provides with the group call reference and the routing information identifying the group call Anchor-MSC  12   a  to the originating MSC. The originating MSC then routes the voice group call to the Anchor-MSC  12   a . If the originating MSC is the group call Anchor-MSC  12   a , along with the group call attributes, the respective GCR  10   a  provides information on all group call Relay-MSCs  12   b ,  12   c  to be involved. The group call Anchor-MSC  12   a  sets up links to all group call Relay-MSCs  12   b ,  12   c . Each MSC  12   a ,  12   b ,  12   c  involved in a voice group call obtains its proper group call attributes from the GCR  10   a ,  10   b ,  10   c  related to the respective MSC. 
   The GCR  10   a ,  10   b ,  10   c  holds for a related MSC area for each group ID and cells from which voice group calls can be established by service subscribers, the group call reference to be used for a voice group call to be established and an indication whether the originating MSC is the group call Anchor-MSC  12   a . If the originating MSC is the group call Anchor-MSC  12   a , the GCR  10   a  provides the group call attributes related to that group call reference to the originating MSC and the originating MSC establishes the voice group call. If the originating MSC is not the Anchor-MSC  12   a , the GCR  10   a  provides the group call reference plus the routing information identifying the Anchor-MSC  12   a  to the originating MSC and the originating MSC routes the voice group call to the Anchor-MSC  12   a.    
   According to the invention, an additional information can be forwarded to all group members during an ongoing voice group call. This is preferably done by transmitting a message containing the additional information on the associated control channel for the traffic channel of the voice group. 
   Referring now to  FIG. 2 , the MSC  12  (either Anchor- or Relay-MSC) triggers via an appropriate message, for example, an additional-information-request-message, on the A-interface the base station subsystem (BSS)  20  to send the additional information to the mobile stations MS  22 ,  24  of the group members, that is, one talker  22  and at least one listener  24 . The message contains at least the additional information itself. The VGC-ID or VGC-Reference represents an optional part of this message. 
   In the case where the message is sent on the controlling SCCP-connection (Signaling Connection Control Part connection) of the VGC, the addressing which VGC is meant is not necessary. 
   In addition to this, the message, that is, the additional-information-request-message, can be sent on the resource controlling SCCP-connections. 
   Afterwards, the BSS  20  transmits the additional information on the SACCH of all TCHs where the VGC is ongoing, so that the additional information can be received by all MS  22 ,  24  participating in the voice group. The provisioning of the additional information in radio cells which are belonging the VGC-area but in which a VGC-channel is not established is not necessary. 
   In the case that the additional information is sent on the controlling SCCP-connection, the BSS  20  is responsible to transmit the additional information on all SACCHs for this VGC. 
   After having sent the additional information, the BSS  20  provides an acknowledge information to the MSC  12  that the additional information was sent to the mobile stations  22 ,  24 . However, this acknowledge information does not confirm to the sender of the message that the individual members of a voice group call have received the message. 
   In order to give an indication that the additional information was at least received by the current talker  22 , the talker  22  may send an acknowledgement on the Uplink-SACCH for this VGC. 
   LIST OF REFERENCE NUMERALS AND ABBREVIATIONS  
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               10a, 10b, 10c 
               Group Call Register 
             
             
                 
               12a, 12b, 12c 
               Mobile Switching Center 
             
             
                 
               14a, 14b, 14c 
               Visitor Location Register 
             
             
                 
               16 
               Home Location Register 
             
             
                 
               18 
               Gateway Mobile Switching Center 
             
             
                 
               20 
               Base Station Subsystem 
             
             
                 
               22 
               MS (Talker) 
             
             
                 
               24 
               MS (Listener) 
             
             
                 
               BSS 
               Base Station Subsystem 
             
             
                 
               MS 
               Mobile Station 
             
             
                 
               MSC 
               Mobile Switching Centre 
             
             
                 
               SACCH 
               Slow Associated Control Channel 
             
             
                 
               SCCP 
               Signaling Connection Control Part 
             
             
                 
               TCH 
               Traffic Channel 
             
             
                 
               VGC 
               Voice Group Call 
             
             
                 
               VGCS 
               Voice Group Call Service