On the prospects of MIMO SatCom systems: The tradeoff between capacity and practical effort

The optimization of the channel capacity in MIMO SatCom systems predominantly requires orthogonal up- and downlink channels, which in practice are formed by distinct antenna arrangements and configurations onboard the satellite(s) as well as at the terminals on earth ground [1]. However, in many applications a significant effort has to be spent at times, not only to identify adequate antenna setups but also to preserve them when imposing practical restrictions, e.g. satellite station keeping maneuvers. This paper analyzes and quantifies any capacity degradations encountered for the case when the orthogonality of the MIMO channel is violated due to practical constraints. Furthermore, the effort for suitable countermeasures is indicated. In the end it is concluded that all potential sources for capacity shortfalls can be handled at a reasonable effort. The analysis is performed for both types of satellite payloads, the transparent as well as the regenerative transponder.