A theoretical bound for the processing of SARSAT signals

Search and rescue satellite-aided tracking (SARSAT) has been responsible for saving the lives of many victims of airplane crashes and boating accidents. The system, in operation since 1982, employs satellites in low orbits which relay the emergency signals from distressed platforms to an Earth station where signal processing techniques are used to measure Doppler frequency shift. The author provides a theoretical bound which can be used to evaluate the performance of SARSAT signal processors. Results show that, for a processing duration of 125 ms, an emergency locator transmitter (ELT) signal can be detected within ±8 Hz when the carrier-to-noise density ratio is only 15 dB-Hz.