Fast Cell Search Algorithm for Overlay System with Cellular and Isolated Cells in Forward Link for OFCDM Broadband Wireless Access

Abstract

This paper proposes a new cell-specific scrambling code (CSSC) assignment method and a fast cell search algorithm in the forward link for Orthogonal Frequency and Code Division Multiplexing (OFCDM) wireless access that are suitable for a system incorporating coexisting isolated and cellular cells. In the proposed method, one or some CSSC groups and thereby the CSSCs belonging to the CSSC groups are exclusively assigned to isolated cells. By detecting the best CSSC assigned to an isolated cell with higher priority than the cellular cells, the best cell including the isolated cell obtaining the minimum path loss can be detected far faster than by using the conventional cell search method, which employs uniform CSSC assignment. Computer simulation results show that by using the proposed cell search method together with the exclusive CSSC assignment to the isolated cells, the isolated-cell detection probability of approximately 90% is achieved at the cell boundary after the cell search time of 10msec, while corresponding detection probability using conventional CSSC assignment is approximately 80% without notifying the user equipment of the cell type and its CSSC information of the surrounding cells via the broadcast channel, at the average received signal energy per bit-to-noise power spectrum density ratio (E b /N 0 ) of 10dB for the common pilot channel (CPICH) in the cellular cells, when the transmission power ratio of the CPICH to the packet data channel (PDCH) for a one-code channel is R CPICH = 9dB in a 20-cell layout model.