Research on cooperative diversity communication systems with adaptive modulation technique

In order to improve the spectral efficiency of cooperative diversity systems, adaptive modulation technique for Decoded-and-Forward cooperative communication systems is proposed in this paper. Cooperation is adopted when the signal to noise ratio of the source user is lower than a threshold. MQAM modulation scheme is used and a suitable modulation order is selected based on the source-destination, source-relay and relay-destination channels. Simulation results show that the proposed cooperative diversity method can improve the spectral efficiency effectively with a suitable threshold and relay, and the spatial diversity gain can be obtained, too.