Fast cell search using I/Q multiplexed code in asynchronous DS/CDMA cellular systems

For wireless multimedia services in cellular systems, it is desirable to asynchronously operate the cell sites because of flexible system deployment from outdoors to indoors. For this, we should be able to minimize the cell search time which is much longer than in case of synchronous operation. A new code assignment scheme is proposed for the forward pilot channel using short spreading codes, in which a group code is assigned to the in-phase (I) pilot channel of all cells belonging to the group, and a cell-specific code is assigned to the quadrature (Q) pilot channel of each cell in the group. Based on the code assignment, the mobile station first searches a group code by processing the I channel, and then detect a cell-specific code from the Q channel, resulting in fast cell search. As a decision algorithm, a SPRT (sequential probability ratio test) is used to further reduce the acquisition time of the I/Q multiplexed code. It is demonstrated through simulation that cell search can be finished in less than about 200 ms at 90% of the locations when 8 group codes and 64 cell-specific codes are assigned to 512 cell sites.