Design of high-speed preamble searcher for RACH preamble structure in WCDMA reverse link receiver

In this paper, we propose a high speed preamble searcher adequate for RACH (random access channel) preamble structure in WCDMA reverse link receiver. Unlike IS-95, WCDMA system uses AISMA (acquisition indication sense multiple access) scheme. Because of the time limit between RACH preamble transmission and AI (acquisition indicators) and the restriction on the number of RACH signatures assigned to RACH preamble, fast acquisition indication is required for efficient operation. The preamble searcher proposed in this paper is based on 2-antenna system and has adopted FHT (fast Hadamard transform) algorithm that has the radix-2 16 point FFT (fast Fourier transform) structure. The acquisition speed using FHT is 32 times faster than the conventional method that correlates each signature. Based on this fast aquisition scheme, we improved the acquisition performance by calculating correlation up to the 4096 chips of the total preamble length. The performance is analyzed by using Neyman-Pearson method. The proposed algorithm has been applied for the implementation of the WCDMA reverse link receiver modem successfully.