Jean E. Adams and Kenneth H. Cavcey

Abstract: The combined communications probabilities (Cm) have been calculated for 56 Simulated Ship Positions (SSP's) in the North Atlantic to a network of 26 digital selective calling shore stations The Cm are based on individual circuit reliability data obtained from the ITS lonospheric propagation model "IONCAP". The 1456 circuit calculations were made for Zurich sun-spot numbers of 20 and 120, the months of January, April 1 and July for hours of 0600, 1200, 1800 and 2400 local time and for the 4 maritime frequencies 6, 8, 12 and 18 MHz. The resulting circuit data were then combined into the Cm assuming that the circuits from the SSP's to each shore station are statistically independent. In analyzing the Cm data, it has been determined that the probability of communication to the combined shore station network from any SSP in this region is at least 92%, and approaches 98% when all four frequencies are used.

Keywords: HF propagation; circuit reliability; communications probability (Cm); digital selective calling (DSC); signal to noise density ratio (SNR)

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