Comparison of managed decode-and-forward scheme and common decode-and-forward scheme in cooperative communication systems

In this paper, the symbol error rate of M-PSK modulation in managed relay scheme is computed. In the conventional technique, the relay always decodes the received signal and re-sends it to the destination. In the destination, the two copies of the signal will be combining in MRC manner. In another method, the relay will partially participate in the signal transmission. In this way, If the destination is not able to decode the source signal properly then requests the relay to re-send signal. Therefore, the average power consumption of the system can be reduced. In this paper, the M-PSK modulation error rate in Rayleigh channels is accurately obtained. Then, an approximation of the symbol error rate in the medium and high signal to noise ratio is achieved. Based on this approximation the power allocation coefficient is derived. The symbol error rates of two schemes are compared. Finally, it is showed that in the equal average power consumption, the symbol error rate of the managed scheme is lower than other scheme.