Transceiver design for cognitive multi-user MIMO multi-relay networks using imperfect CSI

Cognitive radio is a promising technique to solve the spectrum shortage problem in wireless communications. Integrating wireless relaying into the cognitive radio networks can improve the spectrum efficiency. In this paper, a multi-user multiple-input multiple-output cognitive multi-relay network is considered, where the primary network (PN) consists of one transmitter-receiver pair and the secondary network (SN) consists of multiple active source–destination pairs and multiple non-regenerative relays. All nodes in the networks are deployed with multiple antennas. Transceivers in SN should suppress the interference from SN to PN and guarantee the quality of SN transmission simultaneously. We deal with the transceiver design problem with practical condition that the system only has imperfect channel state information (CSI). The transceivers in SN, i.e. source precoders, relay beamforming and destination receiving filters, are jointly designed to minimize the sum mean square error (MSE) subject to interference power constraints and individual transmit power constraints. We propose an algorithm to divide the design problem into three subproblems, which can be solved using the convex optimization methods. The algorithm solves them iteratively until convergence. The performances of the proposed design algorithm have been verified by computer simulations.