Low cost call delivery for roamers of satellite based mobile systems

In the third generation of mobile systems several satellite systems are expected to be integrated with the terrestrial cellular network. A number of roles of satellites have been defined within third generation of mobile systems, for example, providing UNITS (universal mobile telecommunication systems) services in area lacking in terrestrial facilities, providing services to aeronautical users etc. This paper deals with the requirement of reducing the cost of call delivery to roamers within the satellite based mobile systems. We consider both mobile originated and PSTN originated calls to be optimally routed to roamers. For reducing the cost of PSTN originated calls, the notion of a "roamer location register" (RLR) is introduced, which maintains the information of all the roamers within the country. On the other hand for routing mobile originated calls optimally, caller is asked to register at the MSC which is nearest to the called subscriber's PSTN or PLMN switch, so as to minimize the usage of the network trunks. The biggest advantage of the proposed scheme is that it is simple to implement and all the calls from the visited country results in a local call.