Adaptive receivers for mobile DS-CDMA communication systems

We investigate the performance of adaptive receivers for mobile DS-CDMA communication systems. Adaptive filters are known to effectively cope with both multiuser interference and multipath propagation in the case of static channels. A time-variant channel can be assumed static if the variations of the channel are slow compared with the convergence rate of the adaptive algorithm. However, in mobile communication where channels change very rapidly, this assumption is not valid. Therefore, we investigate the tracking performance of adaptive receivers in a mobile environment with realistic parameters. Different algorithms and receiver structures are compared. The results indicate that the convergence speed of the LMS algorithm is too slow. The NLMS yields good results if the velocity of the mobile is slow. The RLS yields good results if the number of users is relatively small. We propose a new adaptive multiuser receiver structure which allows one to increase the number of users.