Truncated sequential CFAR detectors using weighted sign and weighted conditional sign tests

In this paper we propose truncated sequential constant false alarm rate (CFAR) detectors which are approximations of the optimum sequential sign and sequential conditional sign detectors. The particular approximations used here allow exact evaluation of the performances. These detectors form a test statistic by taking the weighted sum of the outputs of a hard-limiter in one case and a dead-zone limiter in the other case. The test statistic, obtained after every observation, is compared with two constant thresholds. The tests terminate either when one of these thresholds is reached, or when the number of observations exceeds a predetermined truncation point. Design procedures which guarantee a CFAR are presented. Numerical comparisons with some reported detectors are given. The proposed truncated CFAR detectors gain improvement over their corresponding non-truncated CFAR detectors in reducing the average sample number under signal mismatch, at the expense of a more involved design process. The proposed truncated CFAR detector with conditional test is uniformly better than a previously reported CFAR detector.