Abstract
In this study, the authors propose two schemes to enhance the spectral efficiency of the decode-and-forward adaptive relaying with adaptive modulation. The first scheme, called the minimum error rate scheme, uses cooperative transmission all the time to achieve transmit diversity whereas the second scheme, called the maximum spectral efficiency scheme, tries to avoid cooperative transmission if the spectral efficiency cannot be improved. For each scheme, the authors introduce a policy that depends on the channel state information of each link. They provide performance analysis in terms of average spectral efficiency, average bit error rate and outage probability over independent non-identically Rayleigh fading channels. Our analysis is verified by simulation results. These results show that our proposed schemes lead to an improvement in the performance of cooperative wireless systems.