Non-Orthogonal Broadcast and Unicast Joint Transmission for Multibeam Satellite System

Due to its extensive coverage, promising satellite communication can provide seamless information services. Meanwhile, the promising rate-splitting multiple access (RSMA) technology has flexible multiple access modes and high spectrum efficiency. To meet various types of information services and improve SE, we consider a downlink non-orthogonal broadcast and unicast (NOBU) joint transmission scheme by combining the promising RSMA and multibeam satellite system. In this paper, we first establish the NOBU joint transmission model using the 1-layer rate-splitting (RS) strategy, where broadcast data and unicast data are encoded into two parts, common data, and private data. Meanwhile, we introduce a zero-forcing precoding matrix to suppress inter-beam interference. Furthermore, we also propose a general NOBU (GNOBU) joint transmission using the 2-layer RS strategy. Then, we consider the quality of service of rate requirements of all terminals and formulate the optimization problems of the NOBU and the GNOBU transmission schemes. An alternating optimization algorithm based on weighted minimum mean square error is proposed to solve the non-convex weighted sum rate problems of the two transmission models. Simulation results show that the proposed NOBU and GNOBU joint transmission schemes perform better than the conventional orthogonal transmission schemes.