A Novel Antenna Assignment Algorithm for Spectrum Underlay in Cognitive MIMO Networks

We consider a point-to-multipoint cognitive network sharing the same frequency band with a primary network assuming a spectrum underlay model. We investigate the scenario where a cognitive base station equipped with multiple antennas attempts to serve secondary users through an antenna assignment scheme. We consider quality of service constraints for secondary users and an interference constraint for the primary receiver. Hence, the cognitive base station performs both antenna assignment and optimal power allocation for the selected secondary users. Due to the high computational complexity of this problem, we propose a heuristic algorithm that separates the two tasks and tries to maximize the number of served secondary users with respect to the system constraints. The antenna assignment phase is performed using an efficient selection criterion followed by an optimal power allocation as a second phase. We show that the proposed algorithm has a very low computational complexity compared to the brute force algorithm. Furthermore, simulation results show that the proposed heuristic algorithm is able to achieve performance very close to that of the optimal solution.