Fading characteristics of maritime propagation channel for beyond geometrical horizon communications in C band
The design of a maritime communication system requires the understanding of the wireless propagation channel above the sea. For broadband communication systems, a carrier frequency in the C band is of interest because of allocatable spectrum. Therefore, the German Aerospace Center performed a long distance channel measurement campaign at 5.2 GHz on the North sea to investigate large and small scale fading characteristics. The results show that our measurement data conforms with the ITU R and the Bullington's path loss model to predict the power loss caused by diffraction over the Earth's surface. Further, the first tap of the channel impulse response experiences Rician fading due to superposition of a strong line of sight (LoS) path and multipath components originating from the sea surface and ship body. We found that the fading of the second tap follows a Rician distribution, but with a much smaller K factor compared to the first tap. The K factor showed a dependence on the distance between the transmitter and receiver. Particularly, the K factor of the first tap decreases significantly when the distance between the transmitter and receiver is larger than the clearance distance of the first Fresnel zone. Therefore, we propose a distance dependent K factor model for the first and the second tap.