MIMO cognitive radio with channel covariance feedback

In MIMO cognitive radio networks, the secondary users are in cognizant of the spatial channels toward the primary users. Based on the knowledge of the interference channel toward the primary receivers and the channel toward its intended receiver, the secondary transmitter adjusts its transmission spatial spectrum in order to maximize its own information rate while limiting interference to the primary receivers. This paper considers the practical case where only the covariance of the time-varying channel matrix can be fed back to the secondary transmitter through a low-rate feedback channel. The optimal transmission is derived when either transmit power constraint or interference power constraint is imposed. Under both constraints, a suboptimal transmission scheme is proposed for the cognitive radio network. Simulation results show the average information rate per secondary user at the Nash equilibrium, which is compared with the rate in the case of perfect feedback of the channel state information.