The Influence of Environmental Noise Power on the Probability of Receiving GMDSS Alarm Signals

The article briefly presents the Global Maritime Distress and Safety System (GMDSS), which provides global emergency communication capabilities for maritime navigation through the use of satellite technologies (INMARSAT) and terrestrial VHF, MF, and HF frequency bands. In GMDSS-defined sea areas A3 and A4, particularly under conditions of severe satellite channel attenuation (greater than 100 dB), HF communication remains crucial. However, its effectiveness strongly depends on the signal-to-noise ratio (SNR), which may be significantly degraded by electromagnetic interference. The dominant noise source in the MF/HF range is man-made noise (MMN). ITU-R Recommendations and ITU-R Reports define standardized methodologies for noise measurement, including spectral analysis. Before installing a GMDSS station, and periodically during its operation, the interference environment must be assessed to ensure reliable reception of both voice and Digital Selective Calling alerts. The article presents a procedure for verifying changes in noise levels at the GMDSS antenna site.