On the threshold setting principles in code acquisition of DS-SSsignals

摘要

This paper compares the meaning of different threshold settingnprinciples in the code acquisition process of a direct sequence (DS)nspread spectrum (SS) receiver. The consideration is made mainly innone-path additive white Gaussian noise (AWGN) channel. A considerationnto a fixed multipath channel is given to see its effect on the results.nAlso, a consideration for a certain type of fading is given in a casenwhere the signal power is assumed to be considerably lower, i.e., faded,npart of the time. For the possible performance measures of codenacquisition, the main interest is in the mean acquisition time TMAn. The probability of the acquisition in a given observationninterval Pacq is also considered to see if different measuresnhave different demands. A matched filter (MF) acquisition is used withnand without a verification mode using an active integration. In thencomparisons, fixed thresholds, thresholds based on constant false alarmnrate (CFAR) criteria, and optimal thresholds in the sense to give eithernthe minimum TMA or the maximum Pacq are used. Thenresults, which are obtained by using a method of selecting the maximumnvalue at the output of the MF, are compared to the threshold cases. Thenresults can be summarized as follows: when the performance measure is TnMA, the best results are obtained by using CFAR-basednthreshold comparison. By a proper selection of the probability of anfalse alarm, the same performance is obtained as by using the optimalnthresholds. When the performance measure is Pacq, thenmaximum-selection method is the best choice