In this thesis, we propose a modified blind adaptive approach to MAI cancellation for synchronous DS-CDMA systems, termed PCMA Approach. It has the same advantage as MOE and CMA of suppressing MAI without the explicit knowledge of interference parameters. We study the effect of arrival and departure of new users to the synchronous blind multiuser receivers, namely MOE and CMA. The perturbation caused by this sudden birth or death of interferers is examined from the viewpoint of the change of the cost function under the noiseless assumption. It is shown that in the vicinity of lock convergence, the changes in the CMA and MOE costs are the same if the perturbation is small enough. But it is also observed that the transient behavior of the CMA detector becomes significantly less robust as the existing number of users approaches the processing gain. To overcome this question of the CMA detector, we employ a projection matrix P that can remove the desired signal from the received signal with other interferers unchanged. Finally its performance has been demonstrated by numerical results in comparison with CMOE, ANMMSE, BAMMSE and Linear MMSE. The proposed receiver can combat MAI, approach the performance of Linear MMSE and have a higher capacity and fast convergence rate for a time-varying user population.