Optimal relay precoder for non-regenerative MIMO cognitive relay systems with underlay spectrum sharing

A study is presented of an optimal relay precoder design for non-regenerative MIMO cognitive relay systems where all the nodes are equipped with multiple antennas. With underlay spectrum sharing, the authors derive the optimal structure of the relay station (RS) precoding matrix to maximise the capacity subject to the transmit power constraint at the RS and the interference power constraint at the primary user (PU). Simulation results demonstrate the effectiveness of the proposed precoder.