Cooperative transmission protocols based on decode-and-forward (DF) relaying and multiuser detection (MUD) for the wireless uplink transmission in synchronous CDMA systems are proposed in this paper on the condition that channel state information (CSI) is available at the destination, as well to the relays. In order to mitigate the multiple access interference (MAI) due to the usage of non-orthogonal spreading codes, we develop minimum mean square error (MMSE) or parallel interference cancellation (PIC) multiuser detectors after matched filters at relays or destination and evaluate the bit error rate (BER) performance. We discuss four kinds of protocols in this paper, which are multiuser detectors at relays, multiuser detector at destination, multiuser detectors at both relays and destination, without relay (direct transmission). The system performance is presented through Monte-Carlo simulations which are developed for different locations of relay and different number of sources to compare these protocols. Simulation results show that the protocol with MUD at both relays and destination achieves the best performance when SNR increases. Several protocols obtain lowest BER when the relay is close to a certain location and system performance degrades when the number of sources increases.
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