Search strategies for the acquisition of DS spread spectrum signals

Abstract

The performance, in terms of the mean acquisition time, of a direct sequence (DS) serial-search acquisition scheme that employs different search strategies is analysed. The mean value of the search length for the considered Z-search strategies is computed. This is then used to compute the mean acquisition time for each search strategy using the unified time domain method. In the presence of a priori information about the code phase, which is modelled as a truncated gaussian probability density function, various search strategies namely, Z-search, expanding window (EW) and alternate search strategies are analysed, evaluated and their performances compared. The performances are compared in the presence of narrowband interference, from which the DS spread spectrum suffers most, in addition to additive white gaussian noise (AWGN). Results have shown that the non-uniform expanding window (NUEA) search strategy outperforms other strategies, particularly at high interference-to-signal ratios (ISR). However, among the various Z-search strategies, the offset-Z-search strategy has been found to exhibit a mean acquisition time 3.3 times faster than that of the continuous centre (CC) Z-search strategy. An experimental serial-search DS acquisition scheme that employs different Z-strategies has been designed, implemented and tested. Experimental results compare very well with the theoretical results obtained.