Zero-insertion adaptive minimum mean-square error (MMSE) receiver for asynchronous CDMA multiuser detection

This paper proposes an asynchronous code-division multiple-access multiuser detector, zero-insertion adaptive minimum mean-square error (ZA-MMSE) multiuser detector, in which a data stream is partitioned into blocks by inserted zero bits and detection proceeds block by block to ensure a balance between processing delay and detection efficiency. The bit error rate performance of the ZA-MMSE detector is evaluated under different multipath scenarios with varying severity characterized by average relative strength of the paths. The results are compared with decorrelator, revealing that the ZA-MMSE detector offers promising detection efficiency at a relatively low complexity, which is linear to the product of the number of users and block length. As an effort to implement it adaptively, the transient behavior of the ZA-MMSE detector with different recursive algorithms is studied. It is concluded that the least mean square algorithm is not suitable due to its power-dependent convergence; whereas the recursive least square algorithm offers a consistently fast convergence regardless of the received power, making it ideal for application in a time-varying channel with near-far effect