Doppler-adaptive multipath window tracking for WCDMA FDD-uplink

A dynamic RAKE diversity combiner used in the 3rd Generation Partnership Project (3GPP) UTRA FDD (WCDMA) uplink (UL) mobile communication system includes a path searcher to estimate time delays of channel taps to be coherently combined. Due to varying propagation delay between mobile and base station, the channel taps change their position over time. The path searcher has to track these changes by adapting its search window. This paper describes the concept of adaptive window tracking algorithms (WTA) and presents different approaches for position adaptation of the search window with emphasis on the required search window size - a major index for implementation complexity of the path searcher. In addition, it introduces a novel Doppler-adaptive WTA and compares the behavior of the different algorithms by means of tracking accuracy, tracking speed, and required search window size. The simulation studies show that the proposed Doppler-adaptive algorithm reduces the implementation complexity, significantly.