Adaptive filters in multiuser (MU) CDMA detection

The primary purpose of this work is to provide a perspective on adaptive code-division multiple-access (CDMA) MU receivers that have been proposed for future digital wireless systems. Adaptive receivers can potentially adapt to unknown and time-varying environmental parameters such as the number of users, their received powers, spreading codes and time-delays. Two adaptive receiver architectures are primarily considered – one in which the sampled received signal is filtered, and can be used in both the uplink (i.e., at the base station) and downlink (i.e., at the mobile handset), and another in which the spreading codes of users are filtered (assuming knowledge of users’ codes and its timing at the receiver) for use in the uplink. Relevant issues such as training-based and blind implementations of the adaptive receiver are discussed, as well as (transient) convergence rates and estimation noise in steady-state.