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.Keywords-MC-CDMA, transmitter preprocessing, relay diversity, multi-user interference.

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In this article, we revisit the performance of a downlink (DL) multi-carrier direct-sequence code-division multiple-access (MC-DS-CDMA) system when the destination mobile stations (DMSs) are aided by a group of relay stations for achieving the relay diversity. In our work, transmitter preprocessing is invoked at the base-station (BS) as well as at the relay stations to suppress the DL multi-user interference (MUI) and the inter-relay interference (IRI) at the relays and the DMSs, respectively. In particular, we investigate the achievable bit error rate (BER) performance of the relay aided MC-DS-CDMA downlink communication with transmitter preprocessing. Our study shows that the transmitter preprocessing efficiently mitigates the MUI at the relays and IRI at the DMSs, thereby significantly contributing to achieve the relay diversity. Further, the preprocessing approach results in low-complexity signal processing at the relay stations in the context of signal detection.Keywords-MC-DS-CDMA, transmitter preprocessing, relay diversity, multi user interference.

In this correspondence, 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 com bined with perfect CIRs based TP at the relays remains close to that attained with the perfect CIRs knowledge.Index Terms-MC-CDMA, transmitter preprocessing, relay diversity, multi-user interference.