Multi-user Performance of Relay-Aided MC-CDMA Downlink System Employing Transmitter Preprocessing Based on Feedback of Vector Quantized CSI

The achievable bit-error-rate (BER) performance of a relay-aided downlink (DL) multi-carrier code division multiple access (MC-CDMA) cellular system, where multi-user interference (MUI) and inter-relay interference (IRI) are the dominant channel impairments is investigated in this paper, principally from a transmitter signal processing perspective. Specifically, in this paper, we investigate the considered system by employing three cooperation strategies. The MUI and IRI are mitigated with the aid of the transmitter preprocessing (TP) operated at the base station (BS) and relays, respectively. The TP operated at the BS that suppresses the MUI at the relays is based on the maximum-signal-to-interference-plus-noise ratio approach, while that operated at the relays that mitigates the IRI relies on the classical transmit minimum-mean-square-error principle. Further, the TP in our work is constructed with the aid of vector-quantized channel state information (VQ-CSI) acquired via feedback channels. Our simulation study shows that relay-aided cooperative DL MC-CDMA system employing TP, results in better achievable BER, as the TP helps in achieving the relay-diversity by mitigating the DL-MUI and IRI at the relays and DMSs, respectively. Furthermore, our study demonstrates that the resultant BER performance of the VQ-CSI based TP remains close to that achieved with the perfect CSI based TP. Hence, we advocate that the feedback of the VQ-CSI to the transmitter for conceiving the preprocessing can be considered as an efficient approach, particularly in a frequency division duplex type wireless system.