Relay Precoder Design for Non-Regenerative MIMO Relay Networks with Imperfect Channel State Information

This paper studies the relay preceding design for a MIMO relay network, where the relay only possesses imperfect channel state information (CSI). We consider a downlink nonregenerative MIMO relay network comprised of a base station (BS, or the source S), a fixed relay (the relay R) and a mobile station (MS, or the destination D). We model the discrepancy between the CSI of the R-D link available at the relay and the actual R-D link gain as a Gaussian random matrix. An upper bound of the mutual information of the considered MIMO relay network is first obtained assuming imperfect CSI knowledge of the R-D link at the relay. The relay precoder to maximize this upper bound is then derived. Numerical results show that by choosing a proper feedback rate, the proposed preceding design is able to achieve ergodic capacity nearly approaching that of the optimal precoder obtained under perfect CSI if a = f_d · T ≤ 0.01. With fewer antennas used, the loss in capacity is less significant.