Green modulation in selective-relay cooperative systems

Selective-relay cooperative systems have been proposed to save energy as well as improving bandwidth efficiency and reducing time delay in wireless systems. In this paper, energy consumption of two proposed Timer-based selection methods, opportunistic relay (OR) and selective cooperation (SC), are investigated for a decode and forward (DF) relay network. We consider the best modulation strategy, uncoded M-QAM, in terms of green in our system model. The motivation is to figure out which one of these two methods consume less energy by studying the green modulation. We also use Dinkel-bach´s concave-covex algorithm to minimize the total energy consumption required to send a given number of bits by optimizing transmission power and transmission time. By the optimization, a large amount of energy saving is achievable. The simulation and numerical results show that SC and OR will consume same amount of energy if threshold channel gain of source-relay be larger than relay-destination. However, energy consumption of OR will be much lower than SC if threshold channel gain of source-relay be smaller than relay-destination.