Performance of relay-assisted MC-CDMA downlink system using quantized CIRs feedback based transmitter preprocessing

We investigate the achievable bit-error-rate performance of a cooperative downlink (DL) multicarrier code division multiple access system aided by transmitter preprocessing. Specifically, a group of mobile stations (MSs) acting as relays is chosen to assist a destination mobile station (DMS) in order to improve the communication reliability. In a cooperative DL communication, multi-user interference (MUI) at the relays proscribes the achievement of the relay diversity. Hence, in this correspondence, the DL MUI at the relays is suppressed with the aid of the transmitter preprocessing (TP) operated at the base station (BS). Further, the inter-relay interference (IRI) at the DMS is suppressed with the aid of the preprocessing operated at the relays. The preprocessing operated at the BS is based on constructing a subspace that is orthogonal to the interfering subspace, while that operated at the relays relies on the transmit minimum mean square error approach. Furthermore, the channel impulse responses (CIRs) required for concocting the TP is based on the quantized feedback more than ever at the BS while at the relays rely on perfect CIRs. Our study shows that TP assists in achieving the diversity gain by efficiently removing the DL MUI and IRI at the relays and the DMSs, respectively under perfect CIRs assumption at the transmitter. Also, it is inferred that the resultant BER performance of the quantized CIRs feedback based TP at the BS combined with perfect CIRs based TP at the relays remains close to that attained with the perfect CIRs knowledge.