A Limited Feedback Joint Precoding for Dual-Hop MIMO Amplify-and-Forward Relay Systems

This paper investigates the limited feedback joint precoding design for dual-hop multiple-input-multiple-output (MIMO) amplify-and-forward (AF) relay systems. Assuming that full channel state information (CSI) of two hops is available and that a linear receiver is employed at the destination, a suboptimal joint precoding structure, which is based on the maximization of the minimum postprocessing signal-to-noise ratio (SNR), is presented. Based on a derived lower bound on the minimum postprocessing SNR, a joint codeword selection (JCS) scheme at the destination is proposed. To reduce feedback latency and computational complexity, the lemma of singular value inequalities of a product matrix and other lemmas are used to split the JCS into two independent codeword selections (ICSs). Thus, the codeword selections at the relay and the destination are concurrently carried out. Simulation results illustrate the effectiveness of the proposed limited feedback joint precoding design. They also show that the ICS scheme displays a bit error rate performance that is close to that of the joint scheme, while having shorter feedback latency and lower computational complexity.