Single-User Performance of Relay-Assisted DS-CDMA with Power Allocation and Inter-Relay Interference Suppression

In this contribution we investigate the single-user-bound performance of a direct-sequence code-division multiple-access (DS-CDMA) system, where one source mobile terminal (MT) communicates with its base-station (BS) with the assistance of multiple relays. We assume that the communications channels experience both propagation pathloss and fast fading, and that the channels from the source MT to the BS and relays as well as from the relays to the BS may experience different fast fading modeled correspondingly by the Nakagami-m distributions. In our study we assume a multiuser combining (MUC) scheme, which suppresses the inter- relay interference under the criterion of maximum signal-to-interference-plus-noise ratio (MSINR). The bit-error-rate (BER) performance of the DS-CDMA is investigated associated with considering the locations of the relays as well as the power allocation among the source MT and relays. From our study and simulation results, it can be shown that the achievable BER performance of the DS-CDMA depends on the locations of the relays and also on the power allocation among the source MT and relays. When the relays of a source user are chosen from a different area, the power allocation should also be adjusted correspondingly in order to achieve the minimum BER. Furthermore, when optimum power allocation is assumed, the BER performance of the DS-CDMA can be significantly improved, when increasing the number of relays of a source MT.