Joint Source and Relay Precoding Designs for MIMO Two-Way Relaying Based on MSE Criterion

TL;DR

This paper proposes an iterative and structured precoding design for MIMO two-way relay systems based on MSE, improving spectral efficiency while reducing computational complexity and signaling overhead.

Contribution

It introduces a novel joint source and relay precoding approach using alternating optimization, structured design for parallelization, and antenna selection for single data streams.

Findings

Iterative precoding algorithm converges reliably.

Structured precoding reduces computational complexity.

Antenna selection algorithm lowers signaling overhead.

Abstract

Properly designed precoders can significantly improve the spectral efficiency of multiple-input multiple-output (MIMO) relay systems. In this paper, we investigate joint source and relay precoding design based on the mean-square-error (MSE) criterion in MIMO two-way relay systems, where two multi-antenna source nodes exchange information via a multi-antenna amplify-and-forward relay node. This problem is non-convex and its optimal solution remains unsolved. Aiming to find an efficient way to solve the problem, we first decouple the primal problem into three tractable sub-problems, and then propose an iterative precoding design algorithm based on alternating optimization. The solution to each sub-problem is optimal and unique, thus the convergence of the iterative algorithm is guaranteed. Secondly, we propose a structured precoding design to lower the computational complexity. The proposed precoding structure is able to parallelize the channels in the multiple access (MAC) phase and broadcast (BC) phase. It thus reduces the precoding design to a simple power allocation problem. Lastly, for the special case where only a single data stream is transmitted from each source node, we present a source-antenna-selection (SAS) based precoding design algorithm. This algorithm selects only one antenna for transmission from each source and thus requires lower signalling overhead. Comprehensive simulation is conducted to evaluate the effectiveness of all the proposed precoding designs.