Rayleigh quotient based interference alignment spectrum sharing in MIMO cognitive radio networks

An interference alignment (IA) spectrum sharing method based on Rayleigh quotient is proposed for distributed multi-user multi-antenna cognitive radio (CR) networks. The interference from cognitive users (CUs) to the primary (PR) system is constrained through the Rayleigh quotients of channel matrices to deal with the absence of PR users (PUs) in the IA process. As a result, the IA scheme can be applied in CR networks without harmful interference to PUs. Compared with existing IA based spectrum sharing methods, the proposed method is more general because of breaking the restriction that CUs can only transmit on the idle sub-channels of the PR system. Moreover, in comparison to other four spectrum sharing methods applicable in general scene, the proposed method leads to improved performance of achievable sum rate of the CR system as well as guarantees the transmission of PUs.