V.V. Latyshev - Dr.Sc. (Eng.), Professor, Moscow Aviation Institute (National Research University). E-mail: lvv@mai.ru

The signal processing task of the GPS and radar receivers can be divided into two fundamental parts: signal acquisition and signal tracking. The most frequently acquisition scheme is the noncoherent correlator, which provides a coarse estimation of the code delay. The problem of accurate positioning is solved in the second stage with the tracking loops using discriminators. The article is devoted to a comparative analysis of common time discriminators for their potentially achievable accuracy. These are the discriminator, which is a solution of the maximum likelihood, its approximation in the form of two bipolar pulses, and a two-channel correlator with displaced to each other impulse responses. It is shown how to select the pulses durations and the early-late separation in the two-channel discriminator. The criterion is the Fisher - information about time delay contained in the output signals of the discriminators. For comparison, we also consider the properties of the correlator used for signal acquisition. The optimal choice of the early-late separation allows you to utilize the largest part of Fisher information contained in the observation. However, from the information point of view, the discriminator, which is a solution of the maximum likelihood, shows the best results among linear processing methods. It uses all of the Fisher-s information contained in the observation and guarantees a smaller value Cramer-Rao boundary with other linear discriminators. Although such a conclusion is based on particular case, the informational approach may be useful for other signals. The difference may lie in how well utilized the information content of the data being processed. But the general conclusion remains valid.

 

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