Opportunistic cooperative spectrum sharing and optimal receive combiner for cognitive MU-MIMO systems

Cognitive multiple-input/multiple-output (MIMO) has been studied as a solution to improve spectrum utilization via dynamic spectrum sharing technology. In cognitive MIMO systems, it is most important to design a transceiver for minimizing interference from the cognitive base station (CBS) to primary users, and for maximizing the sum rate of cognitive users (CUs). In this paper, we first propose opportunistic cooperative spectrum sharing to improve the sum rate of the CR system through an increase of the achievable maximum number of serving CUs, while guaranteeing the quality of service of the primary system. Secondly, an optimal receive combiner (ORC) for the CR system is proposed to maximize the signal to interference plus noise ratio (SINR) of CUs. Utilizing the geometric analysis for a given MIMO channel, we propose a criterion for the beam-forming vector selection and then design the ORC scheme based on major factors that affect the SINR, i.e., multi-user interference among CUs, interference from the primary base station to CUs and the desired channel gain. Consequently, it is demonstrated that the ORC maximizes the sum rate of the cognitive MU-MIMO system.