FAST CELL SEARCH ALGORITHM IN INTERCELL ASYNCHRONOUS DS-CDMA MOBILE RADIO

Inter-cell asynchronous DS-CDMA cellular mobile radio allows continuou s system deployment from outdoors to indoors since no outer timing sou rce is required. All the forward link channels(control and traffic cha nnels)of each cell site are first spread by orthogonal short spreading codes and then randomized by a long random code uniquely assigned to each cell site. However, inter-cell asynchronous systems generally req uire much longer cell search time than inter-cell synchronous systems. This paper proposes a fast cell search algorithm based on the periodi c masking of the long random code when transmitting the control channe l(CCH) signal. The same short spreading code is used for the CCHs of a ll cell sites. The same short spreading code periodically appears in t he signals transmitted from all cell sites so the mobile station can d etect the long random code timing(or more precisely the masking timing )by using a matched filter. By grouping the long random codes used in the system and transmitting a group identification(GI) code from each cell site during the masking period, we can avoid searching all long r andom codes. This significantly reduces the cell search time. Simulati on results demonstrate that cell search can be accomplished in less th an 500 ms at 90% of the locations when the number of long random codes (having a repetition period of IO ms) is 512 and the number of those p er group is 32.