Performance of a Tracking Status Detector for a Digital Delay Lock Loop

Abstract

A tracking status detector, operating on the principal of detecting the instantaneous phase error is considered in conjunction with a noncoherent τ-dither loop. This detector offers a significant improvement in performance as compared to the conventional loop lock detector. The out-of-lock detection when the loop is not in lock is modeled as a Markov process and the detection probability is the probability that the phase error accumulator (or a digital counter) exceeds a preset threshold in a fixed T seconds. The other performance parameter, the probability of false alarm, is also obtained using a Markov model. The results indicate that at a signal-to-noise ratio of 6 dB, the probability of out-of-lock detection of 0.9999 is attainable. The probability of one or more false alarms in one year was less than 10⁻⁵. A brief discussion on the frequency drift estimator based on the same principal is also included.