An adaptive channel estimation scheme for DS-CDMA systems

We propose using decimation to estimate vehicle speed for adaptive channel estimation in pilot-aided transmission systems like DS-CDMA ones. It is shown that by passing the received pilot signal through a bandpass filter after decimation and computing its output energy, the current velocity of a mobile station can be accurately estimated. In addition, the proposed speed estimation unit is simple to implement. This allows us to use it accompanying a computationally efficient pilot filter for a forward link receiver. A structure for adaptive channel estimation based on the proposed velocity estimation unit is addressed. The optimal coefficients of the pilot filter are selected from a precalculated bank of coefficients based on the estimated mobile speed zone. Procedures for deriving the optimal coefficients and thresholds for the speed estimation unit are developed. The proposed method provides up to 0.75 dB improvement compared to conventional nonadaptive ones