Distributed Precoding Systems in Multi-Gateway Multibeam Satellites: Regularization and Coarse Beamforming

This paper deals with the problem of beamformer design in a multibeam satellite, which is shared by several clusters of terminals, each served by an earth station, or gateway. Each gateway precodes the symbols addressed to its respective users; the design follows an MMSE criterion, and a judiciously chosen regularization factor accounts for the presence of mutually interfering clusters, extending more classical results applicable to the case of a single centralized station. More importantly, channel statistics can be used instead of instantaneous channel state information, avoiding the exchange of information among gateways through backhaul links. The on-board satellite beamforming weights are designed to exploit the degrees of freedom of the satellite antennas to minimize the noise impact and the interference to some specific users. On-ground beamforming results are provided as a reference to compare the joint performance of MMSE precoders and on-board beamforming network. A non-adaptive design complements the results and makes them more amenable to practical use by designing a coarse beamforming network.