Transceiver Design for Cognitive Full-Duplex Two-Way MIMO Relaying System

In this paper, we present the design of optimal precoders and receive filters for a full-duplex (FD) two-way amplifyand- forward (AF) multiple-input multiple-output (MIMO) relaying system in a cognitive radio network. The secondary user (SU) or cognitive nodes share the spectrum with the licensed primary user (PU) nodes while keeping the interference to PU nodes below a threshold. The cognitive transceivers communicate with each other with the assistance of a cognitive AF relay. The precoders for the cognitive transceivers are designed so as to maximize the signal to noise ratio (SNR) at the relay while limiting the interference to the PU node below a specified threshold. Due to FD mode of operation, all the nodes suffer from self-interference (SI). We assume the available channel state information (CSI) of loopback self-interference channels at relay and transceivers to be imperfect. We design the optimal relay precoder and transceiver receive filter, for suppressing the residual SI, by minimizing the sum of mean square error (SMSE) at the cognitive transceivers with constraint on transmit power at relay. The precoders and receive filters are updated at each time slot, taking into account the cumulative interference effect from all previous time slots, which enhances the performance of the system over time. The simulation results illustrate the effectiveness of the proposed design in terms of the achievable sum-rate.