Comparison of two dwell code acquisition of DS signal using different threshold setting rules

This paper introduces analysis results of a DS spread spectrum system in which code acquisition is performed using a two dwell method. The acquisition process includes matched filter acquisition in the first stage and a longer integration interval as a verification mode, the second stage. The performance measure is the mean acquisition time, T _MA. The equations for the mean acquisition times when the integration time of the verification mode and the number of uncertainty cells are parameters are derived in two cases, i.e., when the first stage decision is based on threshold comparison at the matched filter output or on selecting the maximum at the matched filter output. Different threshold setting rules, i.e., fixed thresholds, constant false alarm rate (CFAR) criteria and the optimum threshold in the sense of minimising the mean acquisition time are compared to the case when no threshold is used (maximum selection). The comparisons are made in an AWGN channel as a function of the signal-to-noise ratio E_b/N ₀. The comparisons are mainly performed using coherent acquisition but also a consideration for the practical noncoherent case is given. The results indicate that the best performance is obtained by using the CFAR-criteria when the probability of false alarm is selected properly