Enhancing cooperative communication spectral efficiency through signal space diversity

A high spectral efficiency cooperative communication system is proposed in this paper. The concept of signal space diversity (SSD) is utilized to double the spectral efficiency of opportunistic cooperative communication networks. SSD rotates the transmitted symbols by a certain angle at the source, before transmission, such that each in-phase and quadrature component of the rotated symbol contains enough information to retrieve the entire original data symbol. As such, parts of the rotated symbols are transmitted by the source and the other parts are transmitted by a relay. In opportunistic relaying, the best relay among all relays that decode the source signals correctly participates in forwarding a message to the destination. Optimum receiver along with detailed performance analysis are presented in this paper. Also, asymptotic analysis and optimum power allocations at the source and the active relay are given. It is shown that the proposed technique enhances the performance by about 2dB over the conventional opportunistic relaying. As well, optimum power allocation is shown to further enhance the error probability performance.