Comparison of threshold setting rules for the probability of acquisition in a DS spread spectrum receiver

This paper describes the meaning of different threshold setting rules in the code acquisition process of a DS spread spectrum receiver. The consideration is made in an AWGN channel. The performance measure is the probability of the acquisition, P_acq, in a given observation interval. A matched filter acquisition is used with or without a verification mode using an active integration. The equation of the P_acq is derived for both of the cases. In the comparisons, fixed thresholds, thresholds based on constant false alarm (CFAR) criteria and optimal thresholds in the sense to give the maximum P_acq, are used. The results of the method using the selection of the maximum value at the output of the matched filter is also compared to the threshold cases. The comparison are made using coherent acquisition and only a brief consideration for noncoherent case is given. The results indicate that it is reasonable to use the method of selecting the maximum value at the output of the matched filter instead of using some threshold setting criteria. If the signal-to-noise ratio is large, the CFAR-criteria with a properly selected P_fa gives also a good performance