A suitable architecture for personal communications systems based on small satellites

The strategic importance of developing a world-wide personal communication service through user´s hand-held terminals has been carried out by the space-industry. Therefore, next step of this process is the assessment of all system implementation aspects. This paper deals with a satellite system, based on a Low Earth Orbit constellation, offering an optimum system architecture based on small simple (transparent or purely regenerative) satellites. All major critical aspects relevant to the space segment and to the ground segment are examined. In particular, the orbital constellation parameters are discussed in order to minimise, with the assumed traffic distribution, the number of satellites and to offer high availability in terms of number of circuits and service time-continuity. Different hypotheses for the payload architecture are proposed: depending on the access method selected (CDMA, TDMA, and mixed are discussed), and taking into account the low complexity space-segment requirements to achieve the low cost goal for the overall system. A preliminary dimensioning of the derived spacecraft options is also presented. Finally, this paper addresses the major networking aspects, focusing on the impact and the integrability of the proposed satellite system with the existing or planned terrestrial infrastructure for Personal Communications. In particular, the main network requirements, in terms of functionalities, topology and architecture are pointed out