Advanced Signal Processing Strategies for Search and Rescue Satellite Aided Tracking

Abstract

<p>Search and rescue satellite aided tracking (SARSAT) involves the use of satellites in low-polar orbits which relay the emergency signals of distressed vehicles to an earth station for signal analysis. A significant number of lives have been saved by using SARSAT. The program originated from the efforts of the three member countries of Canada, the United States and France who formed a joint venture with the Soviet Union in a program referred to as COSPAS/SARSAT. Since then, the United Kingdom, Norway and Sweden have joined the program and is expected that the system will be used worldwide.</p> <p>In this thesis, three different models for emergency locator transmitter (ELT) signals are proposed. Some basic concepts and a theoretical analysis of the spectrum produced by these signal models are studied. The first model, the Ideal Coherent Model ELT, produces a highly idealized spectrum which does not exist in practice. The second model, the Non-Ideal Coherent Model ELT, is capable of producing a wide range of spectra which can he closely related to actual ELT signals. Mathematical analysis identifies a design problem not previously recognized and provides the basis for a new design specification which should become mandatory. The third model, the non-Coherent Model ELT, represents a class of ELT signals having very poor spectral properties. This type of ELT design should be avoided.</p> <p>The performance of several different signal processors is evaluated using real ELT signals. The periodogram gives good performance for coherent ELT signals. However, the linear spectral estimation technique is not suitable for determining carrier frequency for non-coherent ELT signals. Use of a modified maximum entropy method in detecting these type of signals is demonstrated. In addition, spectrum ranking, sub-group averaging and spectrum levelling are found to benefit the spectral performance of the signal processors.</p> <p>In SARSAT signal environment, it is possible to receive many simultaneous emergency beacon signals combined with interference of various types. The thesis also examines the sources or interference which enter the 121.5/243 MHz frequency bands of the SARSAT system.</p>