Transceiver Design in Full-Duplex MIMO Cognitive Radios under Channel Uncertainties

In this paper, the operation of a full-duplex (FD) multiple-input multiple-output (MIMO) underlay cognitive radio (CR) network is studied. Each pair of secondary users (SUs) operate in FD mode, and each SU communicates with its peer within the coverage area of multiple primary users (PUs). Each SU suffers from self-interference, along with interference created by all other SUs and, in its turn, generates interference towards the PU. We assume that the channel-state-information (CSI) of the interference links between the SUs and the PU is imperfectly known and the channel estimation errors are norm bounded. Under such channel uncertainties, we address the problem of robust minimization of the aggregate mean-squared-error (MSE) of all estimated symbols, subject to a set of transmit power constraints, as well as interference constraints, with the aim of protecting PU communication. It is shown that the problem can be cast as a semidefinite programming problem and the optimal precoding matrices can be obtained via an iterative algorithm. By means of simulation, the proposed FD precoding scheme is shown to outperform the standard half-duplex scheme.