Adaptive modulation for cooperative communications with noisy feedback

Cooperative communication is an alternative way to generate spatial diversity. However due to the extra time slot required for relay transmission, the spectral efficiency (SE) is reduced. Adaptive modulation can optimize the spectral efficiency by adopting the transmission parameters to the channel conditions. This requires the perfect channel state information (CSI) feedback at the transmitter. However, in real life this is not practical. The feedback channel is noisy and fading which causes feedback errors. In this contribution, first we investigate the performance of adaptive modulation schemes for cooperative communications with perfect feedback, the adaptive modulation is applied both by the source and the relay. Then the impact of noisy feedback channels on the performance is analysed. The simulation results demonstrate the spectral efficiency improvement, and illustrates that the effect of the noisy feedback can be ignored when the feedback channel signal-to-noise ratio (SNR) is relatively high i.e. 10 dB.