Two-way relaying for 5G systems: Comparison of network coding and MIMO techniques

This paper studies the two-way wireless relaying with multiple antennas at the nodes, where data transfer takes place between the base station (BS) and the mobile station (MS) with the help of the relay station (RS). We consider the decode-and-forward protocol which is divided into two phases: Multiple Access phase and Broadcast phase. The main focus of this work is on the broadcast phase during which two data blocks received by the RS have to be sent to the BS and MS using the same channel resources. It may be achieved by incorporating network coding, where the binary sum of two data blocks is broadcast to both end nodes. In this paper, we demonstrate that when multiple antennas are available at the transmitter and receiver, applying network coding is not the optimal solution. We present a novel approach that exploits the MU-MIMO scheme and together with the proposed SVD precoding algorithm and interference cancellation receiver, provides a significant performance improvement. In the proposed scheme, we assume full channel state information at the transmitter (CSIT), which in a time division duplex (TDD) system may be obtained by exploiting the reciprocity of the wireless channel. The performance of the considered scenario is analyzed and verified through multi-link level simulations.