Hybrid Precoding for Multicast Downlink Transmit in LEO Satellite Communications

This paper investigated a hybrid precoding design in multigroup multicast scenario for low earth orbit (LEO) satellites communications (SATCOM). Compared with traditional multi-beam satellites, using massive MIMO in satellite communications enables us to have flexible beamforming capabilities and make better use of the degrees of freedom in Spatial domain. Due to the satellite power constraints, hybrid precoding design is used to reduces the number of RF chains required, thereby reducing the power consumed and costs of satellites. The proposed scheme is composed of two processes. Firstly, the sum rate maximization problem in multicast scenario with power constraint and signal to interference plus noise requirement is solved to get an optimal fully digital weights for precoder. The problem is reformulated and we relax the constrains to get a convex form of the problem. After solving the multicast optimization procedure, the problem becomes minimizing the Euclidean distance between the fully digital precoder and the product of baseband and RF band precoder. A fast alternative minimization method based on complex oblique manifold optimization is used for the design of baseband and RF band precoder. The simulation results suggest that the new hybrid precoding design has a considerable performance improvement compared with the traditional precoding scheme.