Fresnel zone: LPWAN gateway in the middle of the North Sea

#Discussion(IoTStack) [ via IoTForIndiaGroup ]

Low frequencies in the 900 MHz range are a blessing and a curse for LPWAN. The low frequencies spread further in the open field and penetrate the walls of buildings better. But the curse of the low frequencies is the much wider Fresnel zone. To ensure undisturbed transmission, the space between the transmitter and receiver must be free of obstacles of all kinds. In this case, obstacles are not only objects in the direct line of sight between the two antennas, but also objects in a curved curve between the two antennas. Any obstructions lead to reflections and therefore to interference with the direct radio wave. This curved wave propagation follows an imaginary rotational ellipsoid. The area around the direct radio beam and the area around the rotational ellipsoid must be free of obstacles. This area, in the form of a rotational ellipsoid, is called the first Fresnel zone after the French engineer Augustine Jean Fresnel. Fresnel zones can be used to estimate the degree of additional attenuation caused by the obstacles.
The following figures illustrate the Fresnel zone above the earth’s surface. At the edge of the ellipsoid, the detour for the signal diffracted at obstacles is half a wavelength. Inside a Fresnel zone, the path difference, which is the difference between two propagation paths, is less than half a wavelength.
Key data for the simulation:
– Height of gateway antenna = 169 m, 85 m
– height of sensor antenna = 169 m, 85 m, 1m
– Sensor output power: 14 dBm
– Antenna gain sensor: 2.15 dBi
– Sensitivity Gateway: -137 dBm
– Antenna gain gateway: 5.15 dBi
– Sum of all profits and losses (link budget): 158.3 dB
Selected losses in the simulation:
– Margin, sum of the path loss through the first wall and fading: 28 dB
– Link budget minus loss in the wall and fading: 130.3 dB

References
Fresnel zone: https://en.wikipedia.org/wiki/Fresnel_zone
Fresnel zone calculator: https://www.everythingrf.com/rf-calculators/fresnel-zone-calculator
Fresnel zone calculator (1. to 4. zone) https://tomclegg.ca/fresnel

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