Multigateway Precoded NOMA in Multibeam Satellite Multicast Systems

Abstract

In this paper, we consider multibeam satellite non-orthogonal multiple access (NOMA) multicast systems deploying multigateway. We investigate improving spectral efficiency and accessibility by superimposing multiple signals to each beam in the same frequency and time resource employing NOMA, where multiple gateways transmit precoded signals to alleviate inter-beam interference caused by full frequency reuse. We formulate an optimization problem of maximizing the sum rate while satisfying the transmit power constraints of the gateways and satellite, where precoding vector and power allocation for superposition coding as well as the decoding order for successive interference cancellation are optimized. This optimization problem is challenging to solve due to mixed-integer nonlinear programming, but a suboptimal solution can be obtained with block coordinate descent algorithm. In the simulation results, the proposed NOMA technique is compared with rate-splitting multiple access and orthogonal multiple access techniques, and it is shown that the proposed technique outperforms them.