Modulation optimization for green radios in cooperative networks

Green radios have drawn much attention in recent years. This paper derives the energy per good-bit expressions for MQAM and MPSK in DF relay networks under AWGN and Rayleigh fading channels. The energy per good-bit is defined as the energy per correctly received bit, which indicates that the energy consumed per bit as well as the link reliability and retransmission probabilities are considered. An energy efficient mode switching transmission is proposed. Constrained by a given probability of bit error, the optimal constellation size of MQAM and MPSK to achieve energy efficiency is obtained. Finally, computer simulations are also carried out to analyze the energy efficiency performance with respect to system parameters such as relay position and transmission distance.