Parallel frequency and code acquisition based on Walsh-Hadamard transform in DS-CDMA

A parallel frequency and pseudo-noise (PN) code searcher for direct-spread (DS)-CDMA is proposed and its performance in multipath Rayleigh fading channels is analyzed. The proposed method uses a two-step acquisition procedure: in the first PN search step, energies in multiple frequency hypotheses are tested in parallel against a threshold. When one or more frequency hypotheses pass the test, the searcher accepts the PN hypothesis and enters the next frequency search step where the searcher looks for the strongest frequency hypothesis. The proposed method uses a pre-calculated correlation matrix to extract frequency information from the Walsh-Hadamard transform of a received signal. One advantage of this method is that it utilizes the fast WHT that is already used in many DS-CDMA receivers for decoding orthogonal channels.