Abstract
The most active development in satellite communications, in the 1990s, lies in the area of mobile communications systems. With its large coverage area, satellites are ideally suited in providing mobile communications services. The challenges of a mobile satellite system lie in providing of a wide range of services within a limited bandwidth allocation, and in reducing the cost and complexity of mobile terminals. This thesis explores the application of on-board processing techniques in mobile satellite communications systems. The advantages and characteristics of various on-board processing techniques, including regeneration, switching, multiplexing, network control etc., are discussed. Also reviewed are a number of technologies required for an on-board processing payload, including transmultiplexers, switches, radiation hard components, software technology, payload architecture etc. Apart from geostationary orbit systems, the thesis also considered alternative orbital configurations, including Highly Inclined Elliptical orbits and Low Earth orbits. The application of on-board processing in such systems is discussed, especially in the area of hand-off strategies and network control. Details of two studies involving on-board processing payloads are also presented. The first, is an ESA feasibility study, which we carried out work on the power control, access schemes, network control, payload architecture and on-board software requirements. The second is the UK T-SAT program, which is a Molniya orbit based system. A prototype payload is developed for testing various on-board processing techniques. The areas of work presented include the development of the on-board control software, the signalling protocol, and the overall system design. A set of software tools is also developed for testing the protocol implementation.