Performance of Relay-Aided DS-CDMA Experiencing Propagation Pathloss and Nakagami Fading

In relay-aided cellular wireless communications mobile terminals (MTs) near the base-station (BS) are usually preferred to being selected as relays for the sake of achieving the relay diversity while simultaneously obtaining a high power-efficiency. However, this strategy may result in a so-called ´bottleneck´ problem, when each source MT employs different relays, since the available relays near the BS are limited. In this contribution we propose and study a relay diversity scheme for uplink direct-sequence code-division multiple-access (DS-CDMA) systems. In the proposed scheme all the uplink source MTs share a set of relays chosen in the vicinity area of the BS, and the number of relays is independent of the number of source MTs. Therefore, the proposed relay scheme can significantly mitigate the above-mentioned ´bottleneck´ problem. In this contribution the performance of the uplink DS-CDMA using our proposed relay diversity scheme is investigated, when either the maximal ratio combining aided single-user combining (MRC-SUC) or maximum signal-to-interference-plus-noise ratio aided multiuser combining (MSINR-MUC) is employed. We assume that the channels experience both propagation pathloss and fast Nakagami-m fading. Our study and simulation results show that the diversity gain may be overwhelmed by the multiuser interference (MUI), when the MRC-SUC is employed. However, when the MUI is efficiently suppressed with the aid of the MSINR-MUC, then the full diversity gain can be achieved and the bit error rate (BER) performance of the DS-CDMA improves, when increasing the number of relays.