This paper analyzes the performance of linear and nonlinear multi-user detection (MUD) for an asynchronous
OFDM-CDMA uplink transmission. Specifially, we regard linear MUD techniques such as the decorrelator (zero forcing, ZF) and the MMSE approach as well as the nonlinear parallel interference cancellation (PIC) and their combination. It is pointed out that OFDM-CDMA systems oer a great advantage over single carrier systems due to at fading conditions on each subcarrier. This leads to much lower implementation costs of MUD techniques. Furthermore, the combination of a linear MUD filter with successive PIC and FEC decoding results in a recursive
receiver structure. It will be demonstrated that the linear filter should only be active in the first iteration and should be removed for further iterations of FEC decoding and PIC.

Assuming perfectly known channel impulse responses for each user and a rough synchronization it turns out that solely linear interference cancellation is not able to reach the performance of a single user system. Nonlinear techniques like parallel interference cancellation supplies single user performance even for system loads of J=Gp = 1=2. Furthermore, the combination of linear MMSE equalization and PIC shows excellent performance even for J=Gp = 1.