Three-step cell search algorithm for broadband multi-carrier CDMA packet wireless access

This paper proposes a three-step cell search algorithm for a multi-carrier (MC)-CDMA broadband packet wireless access system with a 50-100 MHz bandwidth and evaluates the cell search time performance in a numerous-multipath fading channel. To achieve fast cell search, we introduce a continuously transmitted synchronization channel (SCH), which is multiplexed into sub-carriers with equal sub-carrier spacing and scrambled by the code common to all cell sites, and a common pilot channel (CPICH), which is continuously-transmitted in both the time and frequency domains and scrambled by a cell specific scrambling code (CSSC). In the proposed three-step algorithm, fast Fourier transform (FFT) window timing and packet frame timing are successively detected by using a guard interval and SCH and then, the CSSC of the target cell is identified by CPICH. Furthermore, in the proposed method, since the CSSC identification is performed for several candidates of the FFT window and packet frame timings, the best cell having the least path loss is precisely obtained despite the channel load, ie, the number of dedicated traffic channels (DTCH) in each cell. Computer simulation results show that by using the three-step cell search algorithm, the cell detection probability of 90% is achieved within approximately 77 msec (44 msec) when the number of DTCH with the information bit rate of 2 Mbit/s of each cell is distributed with the average of 20 and the standard deviation of 15 (0), when the FFT symbol-correlation of the SCH is averaged over N/sub PST//sup SCH/ = 20 (4) frames in the second step and the CPICH symbol-correlation is coherently averaged during N/sub CST//sup CPICH/ = 16 (10) symbols along the time axis and N/sub CSF//sup CPICH/ = 8 sub-carriers along the frequency axis CS-F in the third step.