Joint user scheduling and beamforming for underlay cognitive radio systems

In this paper, we consider underlay cognitive radio systems in which secondary users coexist with users in primary networks whose radio band is licensed. The secondary subnetwork comprising the cognitive users utilizes the cognitive radio technology to make opportunistic access to the licensed spectrum that primary users own. In this scheme, we discuss the issue of joint user scheduling and beamforming in order to make sure that received interferences at the primary users maintain below an affordable threshold level. The user scheduling includes two procedures: 1) primary users scheduling; 2) secondary users scheduling. However, these two steps are carried out coordinately and the selected primary user and corresponding cognitive users can be obtained. In addition, Zero-forcing Beamforming (ZFBF) and antenna selection are integrated into our scheme where the former is used to support multiple concurrent streams transmission and the latter is used to reduce the feedback in the uplink of the secondary system. Our performance results show that the proposed scheme can significantly improve the throughput of the whole cognitive radio networks.