Reduced-Dimension Cooperative Precoding for MIMO Two-Way Relay Channels
Tao Yang, Xiaojun Yuan, Iain B. Collings · IEEE Transactions on Wireless Communications · 2012
We investigate efficient communications over MIMO two-way relay channels (TWRCs) of nTR, where nTdenotes the number of antennas at each user and nRdenotes that at the relay. We propose a new reduced-dimension (RD) cooperative precoding scheme. In the proposed scheme, the two users cooperatively create nTaligned eigen-modes, supporting nTstreams of physical-layer network coding. We investigate the design of the RD cooperative precoder and derive an asymptotically optimal solution. We analytically show that, in the worst case, the proposed scheme is within ½ bit per transmit antenna of the asymptotic sum-capacity of the MIMO TWRC. For fading MIMO TWRCs with i.i.d. Gaussian coefficients, we derive a closed-form expression of the average sum-rate of the proposed scheme using large system analysis. Our analytical result shows that, for a large system with nT/nR= ½, the proposed scheme is less than 0.16 bit per transmit antenna away from the capacity. Furthermore, this gap reduces as nT/nRincreases, and vanishes as nT/nRtends to 1. It is demonstrated that the proposed scheme can significantly outperform other existing schemes in the literature.