Doppler spread measurements for tuning pilot-assisted channel estimation

In pilot assisted channel estimation, pilots are sent at a rate sufficient to track channel variations under every operating condition. For this reason some pilot redundancy is present when Doppler spread is lower than the expected maximum. So it is worth providing a Doppler spread estimate to tune the channel estimation and exploit the possible aforementioned redundancy. This work presents a method to adaptively tune the pilot-aided channel estimation on the basis of the channel Doppler spread in turn estimated by means of a modified zero-crossing method. Zero-crossing method is very attractive be cause of its low complexity, but it suffers from bias in the case of noise. In this study the method has been modified to face very noisy conditions by introducing a correcting factor depending on the SNR. The application of this method in a RAKE receiver designed for UMTS FDD base station is presented herein.