Performance of Cooperative Diversity aided Downlink MC-DS-CDMA System using Transmitter Preprocessing

In this letter, we investigate the bit error rate (BER) 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 in order to achieve relay diversity. In this work, we employ transmitter preprocessing (TP) both at the base-station (BS) and relay stations to suppress the downlink multi-user interference (MUI) and inter-relay interference (IRI) at the relays and the DMSs, respectively. In particular, the preprocessing employed at the BS is formulated by constructing a subspace that is orthogonal to the interfering subspace that results in zero forcing solution without depending on the eigen analysis, while that at the relays is based on the classical transmit zero forcing (TZF). Our study shows that the TP is capable of efficiently mitigating the MUI at the relays and IRI at the DMSs, thereby assisting in achieving the relay diversity.