Coexistent transmission and user scheduling for CR-MIMO system based on interference alignment and cancellation

In this paper an interference alignment and cancellation (IAC) based coexistent transmission and user scheduling strategy is proposed for infrastructured cognitive radio (CR) multiple-input multiple-output (MIMO) system with multiple secondary users (SUs). By exploiting cooperative capability at primary base station (PBS) and secondary base station (SBS), spatial signal processing procedure is designed. With the scheme, interference alignment (IA) is firstly employed to adjust multiple cognitive transmissions to lie in the subspace orthogonal to the one spanned by the primary signal. Then primary information is recovered at PBS without interference and fed to SBS via inter-BS collaboration. Finally, SBS subtracts the primary part from the received mixed signal and extracts the secondary information separately. With regard to SU scheduling transmission difference of various channel realizations is exploited to achieve multiuser diversity gain. According to the IAC based mechanism the priority of primary is guaranteed, and interference-free coexistence of both primary and secondary transmission is achieved. Moreover, effective utilization of spatial channel resource is realized compared with traditional IA based scheme. Theoretical analysis and simulation results show that the achievable data rate of secondary transmission is significantly enhanced.