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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 contribution, we investigate the performance of a cooperative communication aided downlink (DL) multi-carrier code division multiple access (MC-CDMA) system with the aid of transmitter preprocessing (TP) realized based on vector quantized (VQ) channel state information (CSI) acquired via feedback channels. In our work, we assume that each of the 7{ destination mobile stations (DMS) is supported by a group of mobile stations (MSs) acting as relays to achieve the relay diversity. Specifically, we employ preprocessing at the base station (BS) to suppress the multi-user interference (MUI) at the relays that precludes in achieving the relay diversity. Further, inter-relay interference (IRI) at the destination mobile stations (DMSs) is mitigated with the support of the preprocessing operated at the relays. To be specific, the preprocessing operated at the BS is based on the maximum-signal-to-interference-plus noise ratio (MSINR) approach, while that operated at the relays is based on the classical minimum-mean-square error principle. Both the preprocessing approaches are formulated based on the VQ-CSI acquired via feedback channels. Our study demonstrates that TP-aided cooperative DL MC-CDMA system results in better achievable bit-error-rate (BER) as the TP assists in achieving the relay diversity by eliminating the DL-MUI and IRI at the relays and the DMSs, respectively. Furthermore, our study reveals that the attainable BER of the VQ-CSI based TP remains close to that attained with the perfect CSI based TP.Index Terms-MC-CDMA, transmitter preprocessing, relay diversity, multi-user interference.