| In an era where the personal communication character of the user is the main technology focus, the convergence of mobile satellite and mobile terrestrial systems seems not too distant. The extend of the integration of the satellite-based and the terrestrial-based systems introduces major architectural challenges. The first chapter of this thesis presents a general overview of the mobile satellite systems, presents the organisation of the thesis and details the main contributions. In the second chapter some background information relevant to the research is presented. Specifically, aspects of GSM and GPRS are presented. Additionally, after a brief description of S-PCSs, the subject of satellite and GSM integration is addressed. In the third chapter issues regarding timing synchronisation, when GSM is integrated with a satellite system, are examined, and solutions to mitigate parts of the problems identified are proposed. In the fourth chapter the GPRS system is examined in the satellite environment. The research is focused in the GPRSs RLC/MAC protocol, which is mainly responsible for the allocation of resources amongst the users. Dynamic Channel Allocation (DCA) techniques, are expected to improve dramatically the efficiency of the resources allocation issue, by allowing a more intelligent use of the limited spectrum available for mobile communications. In the fifth chapter, novel DCA algorithms are introduced and are examined for purposes of resources allocation for mobile satellite systems. In the sixth chapter heuristic algorithms are used in combination with the proposed DCA schemes in order to offer a further optimisation in the systems examined. Simulated annealing, is incorporated to the real-time system scenarios, in contrast to its conventional use for non-dynamic systems and major benefits to the systems are introduced. The final chapter brings the thesis to a conclusion by summarising the main results and proposing areas where further work may be fruitful. |
