Two-Way Relaying with Multiple Antennas using Covariance Feedback

This paper studies two-way multi-antenna amplify- and-forward relaying using physical layer network coding. So far, the design of the relay matrix for sum rate maximization has been based on the assumption of complete channel state information (CSI). Designs for the relay matrix based on covariance feedback are proposed in this paper. The optimal relay matrix is estimated using the Monte Carlo method, in which a large number of channel realizations are generated. This requires a runtime linear in the number of channel samples used. Low-complexity methods are then proposed to calculate the relay matrix, without the need to generate multiple channel realizations. Simulations show that the low-complexity methods proposed have near-optimal performance. These methods exhibit much larger sum rates than direct relaying for small to moderate angular spreads. Furthermore, as the number of antennas increases, the low-complexity methods show significant improvements over direct relaying.