Precoding of Space-Time Block Codes for Relay Networks over Correlated MIMO Channels

In this paper, we consider the precoder design at both the source and relay nodes of MIMO relay networks to minimize the symbol error rate (SER) based on the statistical channel state information. First compact SER expressions are derived, then the optimization problem of designing the precoding matrices is formulated. This problem is highly nonlinear and nonconvex. We propose a two-step method by exploiting the correlations of the source-relay and relay-destination links. In the first step the two precoding matrices are proved to be in the eigenvector directions of the transmit correlation matrices. In the second step, the original joint problem is decomposed into two independent sub-problems which can be solved in lower complexity. Simulation results show that the precoding system combined with orthogonal space-time block codes (STBC) outperforms the STBC-only system in terms of SER, especially at low signal-to-noise ratios.