In this contribution we investigate the bit-error-rate (BER) performance of a downlink direct-sequence code-division multiple-access (DS-CDMA) system, where a set of relays are chosen to assist a mobile terminal (MT) in order to improve its communications reliability with the base-station (BS). In our relay-aided DS-CDMA system, the downlink signal is detected at the relays based on the minimum mean-square-error (MMSE) principles, since the MMSE detector can be implemented with the aid of low-complexity adaptive techniques. At the destination MTs (DMTs) the signals are combined according to the maximum signal-to-interference-plus-noise ratio (MSINR) criterion. The BER performance of the relay-aided DS-CDMA downlink is investigated, when the communications channels are assumed to experience both propagation pathloss and fast Nakagami-m fading. Furthermore, we consider the impact of the relays' locations and that of the power-allocation among the BS and relays on the achievable BER performance. From our study and simulation results, it can be shown that full relay-diversity gain can be achieved, after the multiuser interference (MUI) and inter-relay interference (IRI) are suppressed by the MMSE and MSINR detectors.
['Wei Fang', 'Lie-Liang Yang', 'Lajos Hanzo']
Performance of Relay-Aided DS-CDMA Downlink Systems Communicating over Nakagami-m Fading Channels