This paper presents a BER performance derivation considering imperfect channel estimation for a pilot-aided coherent forward link of W-CDMA system under multipath Rayleigh fading channels. In the forward link of the W-CDMA system, pilot signal is usually used for coherent demodulation. In this paper, the maximum likelihood estimator, Wiener filter, and moving average filter are applied to estimate the channel effect due to mobile speed and frequency offset. Then, we concentrate on determining optimal parameter values of the estimators such as the observation length, delay parameters for causal/non-causal filter, and filter resolution. Also it is verified that these parameters are closely associated with the performance, hardware complexity, and characteristics of OVSF code. In particular, effect of data rate and filter resolution on the BER performance is analyzed in more detail. In addition, we show the performance comparison between the estimators considering various imperfections. Finally, we verify the derived BER by using an extensive Monte-Carlo computer simulation.