BER performance analysis and optimum power allocation for a cooperative diversity system based on quadrature signaling

In this paper, an adaptive cooperative diversity system based on quadrature signaling is proposed. With the decode-and-forward (DF) relaying protocol, a tight closed-form approximate bit error rate (BER) for binary phase shift keying (BPSK) constellation modulation is derived, and the effect of inter-user channel quality and power scale factor on system performance is investigated. Theoretical and simulation results show that the proposed system with equal power allocation strategy offers substantial performance gain over non-cooperative system under the channel scenarios of interest, and the full diversity order of two is achieved at high inter-user channel signal-to-noise ratios(SNRs). Furthermore, the derived BER expression makes it possible to optimize the system performance numerically, by finding an optimum power scale factor, which can provide additional benefits when compared to the equal power allocation system.