In this thesis, we evaluate the performance of multi-user detectors over an uplink using AWGN, Rayleigh flat fading single-input single-output (SISO) and multiple-input multiple-output (MIMO) channel models. First, we review the performance of three multiuser receivers; the decorrelator, the MMSE receiver and the multistage parallel interference cancellation receiver in an AWGN and Rayleigh flat fading SISO channel. Next, the V-BLAST algorithm is reviewed and the error propagation of this algorithm is investigated. Then, the V-BLAST algorithm is combined with multiuser receivers to achieve high channel capacity while sharing the spectral resources over a MIMO channel. A bias reduction technique is considered for multistage parallel interference cancellation receiver on both SISO and MIMO channel. Finally, the effect of channel estimation error and timing delay estimation error is evaluated for MIMO systems with multiple users.