Comparison of threshold setting rules for the mean acquisition times of a DS spread spectrum receiver in certain type of fading

This paper describes the meaning of different threshold setting rules for the code acquisition process of a DS spread spectrum receiver. The consideration is made in an AWGN channel where the signal power is assumed to be considerably lower, i.e., faded, part of the time. The performance measure is the mean acquisition time, T_MA. A matched filter acquisition is used without any verification mode. In the comparisons, fixed thresholds, thresholds based on constant false alarm (CFAR) criteria and optimal thresholds in the sense to give the minimum T_MA are used. The results of a method of using the maximum value at the output of the matched filter are also compared to the threshold cases. The comparisons are made using coherent acquisition. The results indicate that CFAR-method or maximum selection method offers the best performance. By a proper selection of the probability of false alarm in the CFAR-method, the same performance is obtained as by using the optimal thresholds. The selection depends on code length and false alarm penalty time