A baseband processor for SARSAT signals

Search and rescue satellite-aided tracking (SARSAT) is a method of employing satellites in low polar orbits to relay the emergency signals of distressed aircraft and marine vessels to an earth station. At the earth station, the signals are processed using spectral estimation techniques, which permit the calculation of the location of the distressed vehicle. In this paper, we describe a baseband implementation for processing distress signals, which employs both the periodogram and the maximum entropy method (MEM). It is shown, theoretically and by computer simulation, that the minimum detectable carrier-to-noise density ratio for a coherent ELT signal is approximately 21 dB-Hz when the 512 complex-point FFT is applied to 50 blocks comprising ls of data. By applying rate-reduction filtering to the data sequence, improved resolution and an increase in carrier-to-noise density ratio are obtained. The baseband implementation also offers flexibility not found in the bandpass processor.