Sub-band pre-channel compensation-at RS for MC-CDMA downlink relay system

In this paper, we consider a relay system for a downlink communication of multi carrier code division multiple access (MC-CDMA) to improve the performance of cell-edge. However since different signals from the base station and the relay station affect different frequency-selective fading channels, the use of frequency-domain equalization at a receiver cannot restore the orthogonality of these signals. Therefore, bit error rate (BER) performance severely degrades due to large multiaccess interference (MAI). We have proposed a channel compensation method at the relay station for MC-CDMA to improve the performance of the downlink relay system. In this method, the channel response from the relay station to the terminal is compensated to be the same channel response from the base station to the terminal at the receiver terminal. Therefore, MAI can be reduced and BER performance is improved. However, the compensation causes the problem of reducing the effect of frequency domain diversity gain by using relay station. Therefore, in this paper, we also propose a sub-band pre-channel compensation at the relay station for MC-CDMA downlink relay system to obtain the diversity gain.