Network and signalling aspects of satellite personal communication networks.

The use of satellites for mobile communication applications has become a global issue. The use of handheld, vehicle mounted and transportable terminals is a key feature of Satellite Personal Communication Networks (S-PCNs). Due to the higher eirp requirements on the Earths surface and also because of their inherent delay, geostationary (GEO) satellites are not considered suitable for such applications. Instead, constellations of satellites at lower altitudes have been proposed for use in what are termed 2nd generation mobile satellite communication systems. Low intensity regions in the Earths surrounding trapped radiation bands, have resulted in two altitude bands of specific interest, resulting in two constellation types - LEO (Low Earth Orbit) constellations at around 1,000 km and MEO (Medium Earth Orbit) constellations at around 10,000 km. A satellite constellation consists of a number of satellites orbiting at the same altitude and inclination and phased in a specific way. The work reported in this thesis proposes a network control architecture for LEO or MEO based S-PCN systems. Air-interface signalling aspects are then considered for mobility management and call setup signalling. LEO and MEO constellation design aspects and properties are initially considered. Important implications on the control network are drawn based on constellation coverage and connectivity properties. Other system constraints such as terrestrial network interworking considerations as well as user, network operator and regulator requirements are also considered. Finally network and more specifically satellite control signalling is examined before a S-PCN architecture is proposed. The reference architecture results in constellation control being distributed globally with individual satellite control, at any one time, being located at a specific earth station. The use of two earth station types allows network administration to be separated from traffic channel carrying aspects. In order to reduce system setup cost and delay, the reuse of network related standards from the GSM terrestrial mobile communication system is envisaged. An equivalence is made between the S-PCN architecture and the GSMs terrestrial architecture. Network implementation aspects are considered for a 14 satellite MEO constellation. Network implications resulting from the use of LEO and MEO constellations are considered. After an examination of S-PCN traffic demand on a MEO constellation, mobility management signalling is considered. A new approach is proposed based on the use of a positioning system. The performance of this approach is examined from a system signalling viewpoint for both LEO and MEO constellations and a method to minimise the required amount of signalling is described. The air interface signalling procedure for location update, based on a modified GSM network layer protocol, is simulated from a delay point of view for both LEO and MEO constellations. User-originated, user-terminated and user-to-user call setup signalling were also simulated and their delay performance examined. The importance of random access channel delay and of user cooperation with the link were highlighted as aspects which have a significant influence on the average signalling delay. Finally, the effect of common and dedicated control channel system signalling on satellite power consumption, based on busy hour call setup and mobility management signalling estimates, was examined for a MEO constellation. From this, conclusions can be made on the signalling power efficiency of S-PCN systems