Maximum likelihood data-aided phase estimation in CDMA communication systems with QPSK modulation

In CDMA communication systems, the received signal is the sum of contributions from several active users. Instead of dealing with these users separately, in a parallel way, this paper introduces maximum-likelihood (ML) joint phase estimation for a data-aided QPSK-modulated scenario. Joint phase estimation is first defined by means of the ML method. Then, in a two-user case, its performance is compared to that of the conventional single user technique considering their estimation errors. Closed forms of the errors are derived, their variances are computed and, finally, the resistance against a near-far situation is analyzed