Performance analysis of cell search in W-CDMA systems over Rayleigh fading channels

The three-step cell search has been considered for fast acquisition of the scrambling code unique to a cell in wideband code-division multiple-access (W-CDMA) systems. In this paper, the performance of the cell-search scheme is analyzed in Rayleigh fading channels. The system parameters for the cell-search scheme and the design parameters for the receivers are examined. Probabilities of detection, false alarm, and miss for each of the three steps are derived in closed form based on the statistics of CDMA noncoherent demodulator output. Through the analysis, the effect of threshold setting and post-detection integration for each step is investigated and the power allocation for the channels is considered. The optimal number of post-detection integrations for each step may depend on not only the power allocation for the channels related to the cell search, but also the false-alarm penalty time. Our analysis can be utilized for determining the values of the parameters. Also, the cumulative probability distribution of the average cell-search time is obtained. Finally, it is shown that the analysis could be used to obtain the distribution of the cell-search time graphically according to the distance between a mobile station and a base station by considering the propagation models for pass loss and the traffic distribution models.