A Round Earth Loss Model and Small-scale Channel Properties for Open-Sea Radio Propagation

In this paper, a path-loss model for the open-sea environment is proposed, in which different propagation phenomena including effective reflection, shadowing, divergence, and diffraction, related to the sea surface and earth curvature in the open-sea environments, are taken into account. The channel model is parameterized and validated by experimental results from our measurement campaign at 2 GHz over a distance range of 45 km in calm, cold Norwegian ocean waters. Model and measurements show excellent agreement in terms of the root mean square error. By evaluating the channel model parameters like mean-square surface slope and standard deviation of surface height related to the sea surface roughness, it can be concluded that the effects of shadowing and scattering on the reflected rays will influence the fading amplitude within the distance range where the Line-Of-Sight (LOS) is tangential to the surface of the earth. It is also found that the diffraction loss starts to influence the path-loss results beyond the distance of 0.6 × the first Fresnel zone clearance. The amplitude probability density function (PDF) of fading is studied as well. By using the Akaike information criterion for model selection, it is found that the amplitude PDF can be modeled as Weibull distribution at short distances and very large distances. The two-wave with diffuse power distribution, Rician distribution, and Rayleigh distribution dominate at distances between 9 and 45 km. The correlation coefficient between the signal amplitudes at two antennas that are vertically separated by 3 m was studied, and found to be close to zero when the transmitter is below the horizon. This indicates the potential to employ multi-antenna techniques for maritime communication systems.