Application of correlation-aided DSA(CDSA) technique to fast cell search in IMT-2000 W-CDMA systems

Abstract

In this paper, we introduce the correlation-aided distributed sample acquisition (CDSA) scheme for fast cell search in IMT-2000 W-CDMA cellular systems. The proposed scheme incorporates the state symbol correlation process into the comparison-correction based synchronization process of the original DSA scheme to enable fast acquisition even under very poor channel environment. For its realization, each mobile station (MS) has to store in its memory a set of state sample sequences, which are determined by the long-period scrambling sequences used in the system and the sampling interval of the state samples. CDSA based cell search is carried out in two stages: First, the MS first acquires the slot timing by using the primary synch code (PSC) and then identifies the igniter code which conveys the state samples of the current cell. Secondly, the MS identifies the scrambling code and frame timing by taking the comparison-correction based synchronization approach and, if the identification is not done satisfactorily within preset time, it initiates the state symbol correlation process which correlates the received symbol sequence with the pre-stored state sample sequences for a successful identification. As the state symbol SNR is relatively high, the state symbol correlation process enables reliable synchronization even in very low chip-SNR environment. Simulation results show that the proposed CDSA scheme outperforms the 3GPP 3-step approach, requiring the signal power of about 7 dB less for achieving the same acquisition time performance in low-SNR environment. Furthermore, it turns out very robust in the typical synchronization environment where large frequency offset exists.