Effect of new users on blind adaptive synchronous multiuser DS-CDMA detection

This paper studies the effect of arrival of new users to the synchronous blind multiuser receivers namely one based on the Minimum Output Energy (MOE) criterion and one based on the Constant Modulus algorithm (CMA). The perturbation caused by this sudden birth of interferers is examined from the viewpoint of the change of the cost function under the noiseless assumption. The CMA and MOE detectors are compared with the training-based minimum mean-squared-error (MMSE) detector. It is shown that in the vicinity of lock convergence, the CMA minimum stays in the neighborhood of the MMSE minimum if the perturbation is small enough. The changes in the MMSE and MOE costs are the same if all users are independent. It is observed that the transient behavior of the CMA detector deteriorates the fastest as the existing number of users approaches the processing gain.