Multiple-Input Multiple-Output Two-Way Relaying: A Space-Division Approach

TL;DR

This paper introduces a space-division network-coding scheme for MIMO two-way relay channels that achieves near-capacity sum rates by dividing the signal space and applying different decoding strategies, outperforming existing methods.

Contribution

The paper presents a novel space-division approach for MIMO TWRCs that combines decoding and physical-layer network coding, achieving near-capacity performance with rigorous analysis.

Findings

Achieves within 0.161 bits per user-antenna of the sum rate capacity at high SNR.

Average sum-rate gap to capacity is at most 0.053 bits per relay-antenna.

Significantly outperforms existing MIMO TWRC schemes.

Abstract

We propose a novel space-division based network-coding scheme for multiple-input multiple-output (MIMO) two-way relay channels (TWRCs), in which two multi-antenna users exchange information via a multi-antenna relay. In the proposed scheme, the overall signal space at the relay is divided into two subspaces. In one subspace, the spatial streams of the two users have nearly orthogonal directions, and are completely decoded at the relay. In the other subspace, the signal directions of the two users are nearly parallel, and linear functions of the spatial streams are computed at the relay, following the principle of physical-layer network coding (PNC). Based on the recovered messages and message-functions, the relay generates and forwards network-coded messages to the two users. We show that, at high signal-to-noise ratio (SNR), the proposed scheme achieves the asymptotic sum rate capacity of MIMO TWRCs within 1/2log(5/4) = 0.161 bits per user-antenna for any antenna configuration and channel realization. We perform large-system analysis to derive the average sum-rate of the proposed scheme over Rayleigh-fading MIMO TWRCs. We show that the average asymptotic sum rate gap to the capacity upper bound is at most 0.053 bits per relay-antenna. It is demonstrated that the proposed scheme significantly outperforms the existing schemes.