Distributed optimal relay selection for spectral efficiency improvement in underlay-paradigm based cognitive radio networks

A distributed best-relay node selection scheme is investigated for cooperative communications with adaptive modulation and coding (MAC) strategy over underlay-paradigm based cognitive radio (CR) networks. The scheme aims to maximize the average spectral efficiency and meanwhile to guarantee that the primary link is provided with a minimum-rate for a certain percentage of time. Simulation results demonstrate that the proposed scheme can significantly improve the spectral efficiency compared with other existing schemes.