Robust joint optimization of nonregenerative MIMO relay channels with imperfect CSI

In this paper, we deal with the problem of joint optimization of the source precoder, the relay beamformer and the destination equalizer in a nonregenerative relay network with only a partial knowledge of the Channel State Information (CSI). We model the partial CSI using a deterministic norm bounded error model, and we use a system-wide mean square error performance measure which is constrained based on the transmit power regulations for both source and relay nodes. Most conventional designs employ the average performance optimization, however, we solve this problem from a worst-case design perspective. The original problem formulation is a semi-infinite trilinear optimization problem which is not convex. To solve this problem we extend the existing theories to deal with the constraints which are semi-infinite in different independent complex matrix variables. We show that the equivalent approximate problem is a set of linear matrix inequalities, that can be solved iteratively. Finally simulation results assess the performance of the proposed scheme.