Cooperative downlink MC-CDMA system aided by transmitter preprocessing: Performance results

This paper investigates the performance of a cooperative downlink (DL) multi-carrier code division multiple access (MC-CDMA) system, where each of the K user's mobile station (MS) is supported by a group of MSs acting as relays in order to achieve the relay diversity. In a cooperative DL communication, multi-user interference (MUI) at the relays precludes the achievement of the relay diversity. In this correspondence, the DL MUI at the relays is suppressed by invoking the transmitter preprocessing (TP) at the base station (BS). Further, the inter-relay interference (IRI) at the destination mobile station (DMS) is suppressed with the aid of preprocessing operated at the relays. Specifically, 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. 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.