Multi-degree adaptive cyclic delay diversity with multi-user scheduling

Multi-carrier based radio access schemes have been widely accepted as one of the PHY candidates in many standards, for their capabilities not only to combat multi-path propagation, but also to support multiple user access aided by multi-user scheduling. The performance of multi-user wireless system with multi-user scheduling depends on the fluctuation of independent channel response across different users. However, the channel selectivity may be limited in some channel conditions, e.g., light-of-sight (LOS) or spatial correlation, which may limit the multi-user diversity gain. Multi-degree random cyclic delay diversity (MD-RCDD) [9] scheme is introduced to obtain opportunistic beamforming gain with intensified frequency fluctuation of channel response. However, the available delay sets in MD-CDD are randomly generated, not fully utilizing the spatial resources. Therefore, multi-degree adaptive cyclic delay diversity (MD-ACDD) scheme is proposed in this paper to further optimize the system performance, in which the available delay sets are channel-dependent, and generated based on the feedback information of all users. Moreover, the detailed working procedure and overhead analysis are presented, and simulation results show that proposed scheme can achieve significant performance gain compared with conventional MD-RCDD.