MMSE multiuser detection for cooperative diversity CDMA systems

Cooperative diversity transmission exploits the spatial diversity created by antenna sharing in a wireless network. The objective of this paper is to investigate the cooperative diversity technique performed in a multi-hop DS-CDMA system, where the limiting factor in the system is the multi-access interference (MAl). We focus on the use of minimum mean-square error (MMSE) multiuser detection (MUD) in the uplink of cooperative CDMA networks. MMSE detectors are designed to suitably combine the signals from the direct path and relaying path and minimize the signal in the interference-and-noise ratio at the receiver output. We evaluate the bit error rate (BER) performance of cooperative transmission in narrow-band block fading channel. Also, MMSE detection is applied in a random CDMA network and the average performance is presented through Monte-Carlo simulations. It is illustrated that, through using MMSE detection in a non-orthogonal CDMA system, cooperation is beneficial in terms of introducing additional diversity gain and thus ensuring a low bit error rate.