Estimation of time-varying wireless channels and application to the UMTS W-CDMA FDD downlink

In this paper we consider the estimation of mobile channels that are modeled as autoregressive processes with a bandwidth commensurate with the Doppler spread. Pilot based estimation leads to brute FIR channel estimates on a slot by slot basis. These estimates are then refined by Wiener filtering across slots that performs the opti-mal compromise between temporal decorrelation due to Doppler spread and slot-wise estimation error. We furthermore propose adaptive filtering techniques to imple-ment the optimal filtering. For structured multipath channels, we introduce 2D filtering in which the refined FIR channel estimates are optimally approximated by a mutipath model in every slot. The techniques are illustrated with applications from downlink channel estimation in the 3G UMTS W-CDMA FDD system.