Doppler Compensation for WCDMA System in High-Speed Mobile Environments

In this paper we discuss issues about the downlink wideband code division multiple access (WCDMA) in high-speed mobile environments. When the carrier synchronization is considered in the RAKE receiver, it may induce the over Doppler shifting (ODS) problem to the high-speed mobile in a rural area where more than one specular component for the multipath channels exist. This makes the receiver difficult to track the rapidly time-varying channel for the time-multiplexed pilot symbols. To fix this problem, we propose a Doppler shift compensation (DSC) method in the 2nd finger of the RAKE receiver to remove the residual frequency offset hence facilitate the channel tracking by linearly interpolating the pilot-aided channel estimates. It can be shown that the performance is improved tremendously for both coded and uncoded systems, especially when the specular component for the 2nd finger is strong.