Joint Beamforming and Antenna Subarray Formation for Nonregenerative MIMO Relay Networks

Antenna subarray formation (ASF) is a complexity-reducing technique for multiple-input-multiple-output (MIMO) receivers. For nonregenerative MIMO relay networks, we propose a joint beamforming and ASF scheme in this paper, which maximizes the achievable rate subject to transmit power constraints at the source and the relay, as well as a limited number of nonzero elements in the ASF matrix. By relaxing the constraint of limited number of nonzero elements in the ASF matrix, we decouple the joint beamforming and ASF design problem into three problems and propose to alternatively optimize beamforming matrices at the source, the relay, and the ASF matrix. We also propose a gradient projection (GP) algorithm to solve nonlinear programming of the relay beamforming design problem. Simulation results demonstrate that the proposed joint beamforming and ASF scheme outperforms the antenna selection (AS) scheme.