Single-User Performance of Uplink DS-CDMA using Relay-Assisted Diversity

In a wireless system with distributed mobile users, several mobile users may cooperate with each other in order to achieve the transmit diversity. In this contribution we investigate the single-user performance of an uplink direct-sequence code-division multiple-access (DS-CDMA) scheme, where one user is assisted by several other users (relays) so as to achieve the relay-assisted diversity. Specifically, the performance of the relay-assisted DS-CDMA is investigated, when communicating over generalized Nakagami-m fading channels, where signals from the transmitter to the relays and that from the relays to the base-station (BS) receiver may experience different fading. In our study two types of detection schemes are invoked. The first detection scheme is a maximal ratio combining (MRC) assisted single-user detection (SUD) scheme, which maximizes the output signal-to-noise ratio (SNR) without taking the interference among the relays into account. By contrast, the second detection scheme maximizes the output signal-to-interference-plus-noise ratio (MSINR), which is a multiuser detection (MUD) scheme that is capable of suppressing the interference among the relays. Our study and results show that, in a relay-assisted DS-CDMA without using orthogonal spreading codes, the relay-assisted diversity may only be achievable after suppressing the inter-relay interference