Robust transmit precoding for underlay MIMO cognitive radio with interference leakage rate limit

This paper addresses the problem of optimizing the information rate of a multiple-input multiple-output (MIMO) secondary user (SU) in an underlay cognitive radio (CR) network when channel state information (CSI) from the SU to the primary user (PU) is inaccurate. Rather than applying the commonly used interference temperature metric, the proposed SU transmit precoder limits the interference leakage rate (LR) to maintain the quality of service (QoS) for the PU. We model the uncertainty in CSI as deterministic with the Schatten norm and apply the worst-case principle to derive a robust solution. Two solution methods are proposed to address the design with the LR metric. The first simplifies the LR metric that is valid under the low interference-to-noise ratio (INR) condition and the second uses an iterative linearization technique. We demonstrate the performance of the proposed solutions by numerical simulations.