NONLINEAR DIGITAL PHASE-LOCKED LOOPS WITH APPLICATION TO LORAN-C RECEIVERS (ROBUST, ESTIMATION, MARKOV)
Abstract
This thesis is concerned with the application of nonlinear digital phase-locked loops (DPLL's) to the tracking of the Loran-C radio-navigation signal. This problem is characterized by the presence of nongaussian noise, which suggests the use of nonlinear processing to improve the performance of currently designed marine receivers to a level adequate for land-based uses of the Loran-C system. Several methods of determining the performance of a DPLL are reviewed. A detailed development of the finite Markov chain analysis of a DPLL is presented, along with a new performance measure and an extension of the results for a second-order loop. A computer simulation of the loop operations is also performed, and the close agreement between analytic and simulation results shows the value of such a simulation. Because the noise contaminating the Loran-C signal is atmospheric (heavy-tailed) and therefore nongaussian, the use of robust estimation is discussed, and then several robust estimators are incorporated into a DPLL and the resulting performance simulated in the presence of nongaussian noise. As a further demonstration of the power of the finite Markov chain technique, it is also used to analyze the performance of a DPLL including a robust estimator and operating in the presence of nongaussian noise. Finally the robust estimation procedures are applied to DPLL's designed for Loran-C signal tracking. An analysis method is presented which may be applied to a DPLL containing a robust estimator and operating in the presence of nongaussian noise; this method allows a fair comparison between different estimators to be made. It is shown that for some types of noise which may be encountered in actual practice, the use of nonlinear robust estimation procedures specifically designed for use in low signal-to-noise ratio situations can tremendously improve the performance of the loop over the performance obtained with common scale invariant robust estimators or linear procedures.
Degree
Ph.D.
Subject Area
Electrical engineering
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