SER of M-PSK modulation in incremental-selective decode-and-forward cooperative communications over Rayleigh fading channels

In this paper we consider a cooperative communication systems over Rayleigh fading channels. The system utilizes a combination of incremental and selective decode-and-forward (ISDF) relaying protocols. The symbol error rate (SER) of M-PSK modulation for the ISDF protocol is derived. Using an approximation of the SER expression, the optimal power allocation is investigated. In order to reduce the complexity of the receiver, we used a modified version of the ISDF protocol which does not use the storage or retransmission of the first phase signal. We also derived optimal power allocation coefficient for modified ISDF. It has been noted that for the optimal power allocation in the ISDF protocol, at least 2/3 of total power must be used by the direct link. For the modified ISDF protocol this portion should be reduced to 1/2. Also the optimal power allocation coefficient is not dependent on SNR.