Several administrations have studied and developed distress alerting systems using geostationary satellites, which are called as satellite EPIRB (Emergency Position Indicating Radio Beacon) systems. In order to evaluate L-band (1.6GHz) satellite EPIRB systems, international cooperative tests coordinated by the CCIR (International Radio Consultative Commitee) were conducted through 1982 and early in 1983.
We have developed an experimentel satellite EPIRB system and participated in these tests which consist of laboratory tests, land tests, simulation tests and sea trials. This report describes the details of the satellite EPIRB system and the results of laboratory tests.
The experimental satellite EPIRB is of a buoy type. The antenna is a quadrifilar helical one and is contained in the top of the buoy. The transmitter and storage batteries are enclosed in its lower half. The transmitting frequency is 1642.375 MHz and the maximum transmitting power is 9 dBW. Modulation is FSK with a frequency shift of ± 120 Hz and the transmission rate is 63 bps.
In the satellite EPIRB demodulator, received signals are detected by a pair of FSK asynchronous detectors. The detected signals are converted to the digital form and superposed. After superposition is repeated by a specified number of times, bit and frame synchronization are performed, and error correction by BCH code is carried out.
Laboratory tests were conducted to evaluate and optimise the design, including the analysis of performances in fading conditions, and to ensure the C/N0 range for further tests. In laboratory tests, the IF signals of the satellite EPIRB transmitter are sent to the demodulator after down conversion. These tests show that the satellite EPIRB transmitter and the demodulator operate properly in both non-fading and fading conditions. Furthermore, 99% error free message probability was found to be achieved within 60 sec at C/N0 of 19 dBHz. It also gives that the optimum C/N0 range was 18∼24 dBHz.
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