Downlink dual modes multiple user MIMO Cognitive radio system

This paper focuses on maximizing Cognitive radio (CR) system capacity by flexible Multiple input multiple output (MIMO) system, while maintaining the interference to primary user (PU) within a limit. It is proposed that MIMO implemented in CR can not only increase throughput but also avoid interference to PU, so two corresponding multi-user MIMO schemes are given and a parameter called transition radius is defined to help select two schemes optimally. Simulation shows that by using the proposed scheme system can achieve higher throughput gain over single antenna system, while the interference to PU is limited and no matter where the PU receiver is.