Time-Variant Channel Estimation and Equalization for Wireless Mobile Applications

Abstract

Channel estimation in smart antennas for wireless and mobile applications is needed for equalization so as to reduce the ill effects of inter symbol interference (ISI). In our earlier work, it was shown that a time dispersive channel, which can be modeled as an FIR channel can be estimated effectively by using active tap detection NLMS algorithm. The channel was, however, assumed to be stationary; but, for the mobile communication applications, owing to the mobility involved, this assumption is not justifiable. This work undertakes estimation of non stationary or time variant channel for equalization. The time invariance is modeled by using the random walk method that works by varying the tap weights of the underlying adaptive filter. Simulated results show that as standard LMS and NLMS algorithm does not even converge, active tap detection LMS/NLMS algorithm works well for time variant channels as well.