Precoding and Scheduling in Multibeam Multicast NOMA based Satellite Communication Systems

In this paper, we propose a multibeam multicast non-orthogonal multiple access-based (MB-MC-NOMA) scheme for satellite communication systems. Building upon the multibeam transmission, we exploit precoding and NOMA techniques to deal with inter-and intra-beam interference, respectively. Combining these two techniques in the multicast transmission is not trivial as both scheduling, and the precoding design shall be reconsidered. Indeed, it is shown there is a contradiction between criteria for efficient user scheduling in MC-NOMA and MClinear precoding: while the first one requires a strong channel gain imbalance between user terminals, the latter seeks user channel vector similarities. To tackle this problem, we propose a user scheduling in MB-MC-NOMA, which provides a good balance between these two criteria. Besides, the MC-linear precoding is designed with aid of a mapping function that deals with the lack of spatial degrees of freedom. The numerical simulation results show that the performance of the MB-MC-NOMA scheme is improved by using the proposed user scheduling and a novel precoding design based on the singular value decomposition (SVD). Moreover, the MB-MCNOMA scheme outperforms its orthogonal version scheme. In particular, we observe that the throughput of the MB-MC-NOMA is increased a 25% with respect to MB-MC-OMA scheme under certain fair conditions.