Abstract:
A system provides GSM service over distributed mobile networks. A Network Area Controller (NAC) allows Global Titles (GT) and Mobile Station Roaming Numbers (MSRN) of the GSM network to be shared within a private GSM network. A processor within the Mobile Switching Center (MSC) of a mobile network transcodes voice data and maps the data to the proper bearer QoS to allow the use of Mobile Satellite Services (MSS) such as Iridium and Inmarsat.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to a private network within the Global System for Mobile Communications (GSM) network. More particularly, the present invention relates to a GSM private network that provides communication over distributed mobile networks. 
       BACKGROUND OF THE INVENTION 
       [0002]    GSM is a set of telecommunication standards created by the European Telecommunications Standards Institute (ETSI) specifying the infrastructure of a digital cellular service. At the top level, the GSM system comprises a small number of networks that provide service around the world through interconnect agreements with each other. Access to the networks via sub-networks of service providers, which ultimately offer service to users, is usually accomplished through signaling brokers. 
         [0003]    A GSM network includes a Home Location Register (HLR), which is a database of mobile subscriber information for a service provider&#39;s subscriber base. The information includes, for example, the International Mobile Subscriber Identity (IMSI), service subscription information, and location information, which includes the current Visitor Location Register (VLR) serving the subscriber, and service restriction and supplementary service information. 
         [0004]    A VLR is a database that includes information about a mobile subscriber (user device) currently located in a given Mobile Switching Center (MSC) serving area when that serving area does not include the subscriber&#39;s HLR. Typically, there is one VLR per MSC, and the VLR and HLR exchange information regarding a user device. A network served by an MSC/VLR pair can be referred to as a mobile network. A mobile network may be, for example, ship-based such that the mobile network itself, as well as each of the user devices it serves, is mobile. A mobile network may instead be land-based with only the user devices being mobile. 
         [0005]    In GSM, the Mobile Station International Subscriber Directory Number (MSISDN) is used to locate and route calls to a given user device. In addition, during each call setup phase, a user device is temporarily assigned a Mobile Station Roaming Number (MSRN) by its current MSC, which is used to help locate the user device when it receives a call by allowing the gateway system to route the call to the current serving MSC. 
         [0006]    Traditionally, a service provider operates mobile networks that each require their own GT and set of MSRNs. However, the number of GTs and MSRNs available from a signaling broker is limited, which can limit the number of mobile networks a service provider can operate. Typically, a signaling broker buys a set of GTs and MSRNs from a GSM network and leases them to private GSM network providers. Thus, each additional GT and MSRN, even if available, represents an additional cost to the service provider. 
         [0007]    The mobile networks may use a Very Small Aperture Terminal (VSAT) to relay voice data via satellite. For example, a ship-based mobile network may communicate via satellite. While the VSAT system offers a dedicated data channel with quality of service (QoS), or service and/or subscription based prioritization of traffic, VSAT equipment is expensive in relation to equipment for other Mobile Satellite Services (MSS) such as IRIDIUM and INMARSAT. 
         [0008]    However, conventional use of MSS such as IRIDIUM and INMARSAT has also presented problems. Traditional implementations of GSM using MSS have used a Foreign Exchange Office (FXO) interface, which is a connector that allows an analog connection to the public switched telephone network (PSTN). For example, the Globe i250 from Globe Wireless, which included an INMARSAT FleetBroadband (FBB) terminal coupled with the MSC/VLR, also included an FXO interface to allow analog call transmission from a mobile network using the FBB to the PSTN. 
         [0009]    The use of the FXO interface presents issues because the call is never routed back through the core GSM network throughout its duration. As a result, the service provider cannot easily and accurately track the duration of the call in order to properly bill the call based on usage. Additionally, the call recipient not within the mobile network (the recipient of a call placed from a ship using FBB, for example) sees the MSS number rather than the MSISDN of the calling user device. Related to this, user devices within the mobile terminal using FBB cannot cost-effectively receive calls. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention addresses at least the issues discussed above. 
         [0011]    A private GSM network refers to a sub-network within a GSM network that includes a set of mobile networks that all share a single Network Area Controller (NAC). The addition of the NAC to the private GSM network architecture shifts the intelligence from the core GSM network to the mobile network level. The NAC facilitates this change in the network architecture through a sharing scheme for GTs and MSRNs. 
         [0012]    Including a processor in the MSC that can transcode incoming voice data and map the output to one of a plurality of bearer channels allows mobile networks to transmit via MSS without the conventional billing and call termination issues discussed above. 
         [0013]    In accordance with one embodiment of the present invention, a private communication network within the (Global System for Mobile communications) GSM network, the private communication network comprising a plurality of mobile networks, each of the mobile networks comprising a local Global Title (GT) and each comprising a plurality of user devices and all of the plurality of user devices of all of the plurality of mobile networks sharing one or more GTs of the GSM network, the one or more GTs being less than a number of the plurality of mobile networks, and a controller configured to translate between a local GT of one of the plurality of mobile networks and the real GT, the plurality of mobile networks of the private communication network sharing the controller. 
         [0014]    In accordance with another embodiment of the present invention, a private communication network within the (Global System for Mobile communications) GSM network, the private communication network comprising a plurality of mobile networks, each of the mobile networks comprising a plurality of local mobile station roaming numbers (MSRN) and each comprising a plurality of user devices and all of the plurality of user devices of all of the plurality of mobile networks sharing one or more real MSRNs of the GSM network, a number of the plurality of real MSRNs being less than a number of the plurality of user devices of the plurality of mobile networks; and a controller configured to translate between a local MSRN and one of the one or more real MSRNs, the plurality of mobile networks of the private communication network sharing the controller. 
         [0015]    In accordance with yet another embodiment of the present invention, a satellite communication system comprises a base transceiver station (BTS) in communication with a plurality of user terminals; and a processor configured to transmit signaling data at a first quality of service (QoS) level and voice data at one of a plurality of second QoS levels, the first QoS level being less than any of the plurality of second QoS levels. 
         [0016]    There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
         [0017]    In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
         [0018]    As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a block diagram of an exemplary private GSM network, according to a preferred embodiment of the invention; 
           [0020]      FIG. 2  is a signal flow diagram of a call to a user device within a private GSM network, according to an embodiment of the invention; 
           [0021]      FIG. 3  is a block diagram of an exemplary mobile network communicating over MSS, according to an embodiment of the invention; and 
           [0022]      FIG. 4  depicts transcoding operations performed by the processor of the MSC, according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  shows an exemplary private GSM network  10  according to a preferred embodiment of the invention. Although only two mobile networks  100  are shown, any number of mobile networks  100  included within a private GSM network  10  is contemplated. Each mobile network  100  includes a MSC/VLR pair  130 , one or more BTS  120  based on expected usage, and numerous user devices  110 . For explanatory purposes, a private GSM network  10  is defined as one within which all the mobile networks  100  share a NAC  160 . Although shown together in this exemplary embodiment, the MSC/VLR pair  130  may be housed separately in one or more elements that communicate with each other.  FIG. 1  also shows an HLR  170  and GMSC  180  on the core network side. 
         [0024]    The NAC  160  stores the real GTs and MSRNs obtained for the private GSM network  10 . The “real” GT and “real” MSRN refer to those obtained from a signaling broker, for example, and recognized by the small number of networks at the top level of the GSM system as being part of their interconnect agreements. In the present embodiment of the invention, the number of real GTs is fewer than the number of mobile networks  100  in the private GSM network  10 , and the number of real MSRNs is less than the number of user devices  110  registered within the private GSM network  10 . In order to operate the private GSM network  10  with fewer GTs than the number of mobile networks  100  and with fewer MSRNs than the number of user devices  110 , the NAC  160  facilitates a sharing scheme within the private GSM network  10 . 
         [0025]    The sharing scheme facilitates a change in the network architecture, from the conventional GSM arrangement, within the private GSM network  10 . The network architecture facilitated by the sharing of real GTs and MSRNs is more efficient that the network architecture of the conventional GSM arrangement because the intelligence is shifted down to the mobile network level from the core network level. 
         [0026]    An exemplary private network  10  may have 8 real GTs and 20 real MSRNs shared among 10,000 user devices  110  (or MSISDNs) and 600 mobile networks  100  (600 local GTs). The example shows that the number of real MSRNs may not only be less than the number of user devices  110  in the private GSM network  10  but may also be less than the number of mobile networks  100  within the private GSM network  10 . 
         [0027]    The NAC  160  assigns a local GT to each mobile network  100  and requests, on an as-needed basis during call setup, local MSRNs from a mobile network  100  for call termination to a user device  110  within the mobile network  100 . The term “local” is used to mean within the private GSM network  10  only. The NAC  160  maintains a registry  163  of the correspondence between each assigned local GT and MSRN and the real GT and MSRN of the GSM network that were obtained for use within the private GSM network  10 . The NAC  160  can change the local GT assignment and update the registry  163 , as needed. For example, based on the addition of a mobile network  100  to the private GSM network  10 , the NAC  160  may assign a local GT to the new mobile network  100  and update the registry  163  accordingly. As another example, based on a network configuration change, such as a new provider assigning new real GTs to the private GSM network  10 , the NAC  160  can re-assign local GTs and update the registry  163 . In one example, all of the local GTs assigned to the mobile networks  100  of the private GSM network  10  may correspond to a single real GT. Alternately, more than one real GT may be shared among the mobile networks  100 , as shown by Table 1, below. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 local GT 
                 real GT 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Mobile Network 1 
                 local GT 1 
                 real GT 1 
               
               
                   
                 Mobile Network 2 
                 local GT 2 
                 real GT 1 
               
               
                   
                 Mobile Network 3 
                 local GT 3 
                 real GT 2 
               
               
                   
                 Mobile Network 4 
                 local GT 4 
                 real GT 3 
               
               
                   
                 Mobile Network 5 
                 local GT 5 
                 real GT 3 
               
               
                   
                 Mobile Network 6 
                 local GT 6 
                 real GT 3 
               
               
                   
                   
               
             
          
         
       
     
         [0028]    A sharing scheme is also contemplated for MSRNs with two differences from the scheme discussed for sharing GTs: (1) the local MSRN assignment is temporary and on an as-needed basis during call setup and (2) the assigned local MSRN for a given user device  110  may change from one call setup to another. An MSRN is needed by a user device  110  within a mobile network  100  only when the user device  110  (which has a unique MSISDN) receives a call from outside its own mobile network  100 . A local MSRN and corresponding real MSRN are used to route and establish the call as shown in detail in the signal flow diagrams discussed below. The assignment of real MSRNs and their correspondence to local MSRNs is done on a rolling basis. That is, when a call is incoming to a user device  110 , the MSC of the MSC/VLR  130  pair of the mobile network  100  of the user device  110  assigns the next in the set of local MSRNs made available by the NAC  160 . The NAC  160  then associates that local MSRN with the next available real MSRN. For each subsequent incoming call to any user device  110 , the procedure is repeated (the MSC/VLR  130  associated with the user device  110  assigns the next available local MSRN and the NAC  160  associates that local MSRN with the next available real MSRN). 
         [0029]    The registry  163  of the NAC  160  may be implemented in the form of a look-up table, for example. The processor  165  of the NAC  160  translates a real GT and MSRN on the GSM network side to the corresponding local GT and MSRN assigned within the private GSM network  10 , as discussed in relation to  FIG. 2  below. 
         [0030]      FIG. 2  is a signal flow diagram of a call to a user device  110  within a private GSM network  10 , according to a preferred embodiment. S 210  is a signal from the external network  200  indicating an incoming call intended for a target user device  110  within a mobile network  100  of a private GSM network  10 . The Gateway Mobile Switching Center (GMSC)  180 , which is part of the core network equipment, cannot determine which NAC  160  the call should be directed to in order to reach the target user device  110 , identified by its MSISDN in S 210 . The GMSC  180  sends a Mobile Application Part (MAP) Send Routing Information message requesting routing information in S 220  to the HLR  170 . Based on the MSISDN of the target user device  110 , the HLR  170  determines the appropriate NAC  160  to contact regarding the call and sends a MAP Provide Roaming Number (PRN) message at S 230  to the NAC  160  that serves the target user device  110 . The signal S 230  includes the real GT and a request for a real MSRN. The NAC  160  forwards the MAP PRN message at S 240  to the MSC/VLR  130  in the mobile network  100  of the target user device  110  to request a roaming number. S 240  includes the local GT, which is associated with the real GT in the NAC  160 , and the IMSI of the target user device  110 . 
         [0031]    In response, the MSC/VLR  130  sends a MAP PRN Response message, at S 250 , back to the NAC  160 . S 250  includes the local GT and a local MSRN, which is the next free local MSRN from a pool of MSRNs made available to the MSC/VLR  130  by the NAC  160 . The processor  165  of the NAC  160  uses its registry  163  to associate the local GT in S 250  with the corresponding real GT and to assign the next available real MSRN to correspond with the local MSRN in S 250 . The NAC  160  sends a MAP PRN Response message at S 260  to the HLR  170  with the real GT and real MSRN. In turn, the HLR  170  sends a MAP Send Routing Information (SRI) message at S 270  to the GMSC  180 . The incoming call is then routed from the GMSC  180  to the NAC  160  with the real MSRN in S 280  and is forwarded from the NAC  160  to the MSC/VLR  130  with the corresponding local MSRN in S 290 . 
         [0032]    In the above exemplary signal flow, the HLR  170  knows which NAC  160  serves a given target user device  110  and the NAC  160  knows which mobile network  100  the target user device  110  is currently served by in order to route the incoming call correctly. This knowledge is acquired because every user device  110  that will use a given mobile network  100  must first register the Subscriber Identity Module (SIM) card issued by the private GSM network provider with the mobile network  100 . Following that registration with the private GSM network  10 , any of the following scenarios is possible. 
         [0033]    If the user device  110  initiates a call to another user device  110  within the mobile network  100 , the call need not go beyond the MSC/VLR  130  and exit the mobile network  100 . Further, real/local MSRN is not necessary to set up the call. 
         [0034]    If the user device  110  initiates a call to another user device  110  outside of its mobile network  100  but within its private GSM network  10 , the call must still be routed beyond its MSC/VLR  130  through the NAC  160  that serves both mobile networks  100 . In this case, the MSC/VLR  130  of the user device  110  that is the call recipient must assign a local MSRN to set up the call, and the NAC  160  must associate a real MSRN with the local MSRN to complete the call setup procedure. 
         [0035]    If the user device  110  initiates a call to a device outside of its mobile network  100  and outside of its private GSM network  10 , the private GSM network  10  associated with the receiving user device  110  must assign a real MSRN for use during the call setup procedure. 
         [0036]      FIG. 3  shows a block diagram of an exemplary mobile network  100  communicating over exemplary MSS, IRIDIUM  140  and INMARSAT  150 , according to an embodiment of the invention. The processor  133  of the MSC in the MSC/VLR unit  130  transcodes outgoing signals from the BTS  120  based on a predetermined selection of the MSS bearer (IRIDIUM  140  or INMARSAT  150 , for example) to be used for transmission. Communication via VSAT is still contemplated with the processor  133 , and the processor  133  may transcode the voice data for transmission over VSAT, as well. The voice data is routed through the MSS gateway  190  but the call is terminated at the GMSC  180 . 
         [0037]      FIG. 4  shows exemplary transcoding operations performed by the processor  133  of the MSC in the MSC/VLR unit  130  according to a preferred embodiment. The transcoded signals S 420  from the MSC/VLR  130  are transmitted to MSS, such as IRIDIUM  140  and INMARSAT  150 , through the corresponding user terminal (UT)  140   a  or  150   a , respectively. The UTs  140   a  and  150   a  output signals S 430 , which may be further transcoded, for ultimate transmission over the corresponding satellite service,  140  or  150 . The UTs  140   a  and  150   a  may be incorporated within the MSC/VLR  130  or housed separately, in whole or in part. 
         [0038]    Voice data S 410  is transmitted from the BTS  120  to the MSC/VLR  130  as full rate, enhanced full rate, or adaptive multi-rate, for example. The MSC/VLR  130  then transcodes the voice data into a signal S 420 . For example, S 420  has an intermediate codec and the MSC/VLR  130  passes the call to the appropriate UT  140   a  or  150   a , based on pre-selection, via a standard circuit switched channel, or S 420  is streaming IP data. The MSC/VLR  130  not only transcodes the incoming voice data S 410  but also maps the data S 420  to the proper bearer channel (with corresponding QoS) for transmission via pre-selected MSS. The transcoding operation is done in reverse for incoming voice data. 
         [0039]    The signaling channel is on the Packet Data Network (PDN). Each of the bearer channels shown for voice data S 420  represents a different QoS. The processor  133  can perform dynamic switching of QoS, that is, the processor  133  can use the signaling channel, as needed, during voice call establishment and during the duration of the voice call. 
         [0040]    The NAC  160  and processor  133  resolve the issues related to call tracking (for purposes of billing) and call termination for traditional GSM over MSS systems. Previously, using the FXO interface resulted in the voice call being routed from the MSS gateway  190  to the PSTN and not having a voice path to the GMSC  180  for termination of the call. This resulted in the GMSC  180  not being directly aware of the call duration or the proper MSISDN of the user device  110  placing the call over the MSS. Because the NAC  160  allows the MSISDN of the user device  110  to be known to the GMSC  180  as shown by the signal flow diagram at  FIG. 2 , for example, and because the processor  133  allows the call over MSS to be terminated at the GMSC  180 , the duration of a call can easily and accurately be tracked for billing purposes, and the MSISDN of the user device  110  can be used to provide a callback number, rather than the MSS number, to the recipient of the call. 
         [0041]    The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.