Transmitter Preprocessing Assisted Cooperative Downlink Transmission in DS-CDMA Systems Experiencing Propagation Pathloss and Nakagami-m Fading

In this contribution we propose and investigate a relay diversity transmission scheme for the direct-sequence code-division multiple-access (DS-CDMA) downlink, where each (destination) mobile terminal (MT) is aided by a cluster of relays for achieving the relay diversity. In the considered system downlink multiuser interference (MUI) is suppressed with the aid of transmitter preprocessing operated at the base-station (BS). Two transmitter preprocessing schemes are considered, which are operated in the principles of transmitter zero-forcing (TZF) and transmitter minimum mean-square error (TMMSE). At the MTs, signals received from the BS and relays are combined based on the principles of maximal ratio combining (MRC) or of maximum signal-to-interference-plus-noise ratio (MSINR). In this contribution the bit error rate (BER) performance of the relay-assisted DS-CDMA downlink is investigated, when the communications channels are assumed to experience both propagation pathloss and generalized Nakagami-m fading. Our study and simulation results show that the transmitter preprocessing can help to achieve the relay diversity by efficiently mitigating the MUI presenting at the relays and MTs. Furthermore, in our proposed relay diversity scheme the relays only require lowcomplexity signal processing for forwarding information to their served MTs.