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This is part 7 of the LoRa/LoRaWAN tutorial.
In this video series different topics will be explained which will help you to understand LoRa/LoRaWAN.
It is recommended to watch each video sequentially as I may refer to certain LoRa/LoRaWAN topics explained earlier.
In this video I will explain what the Fresnel zone is.
The Fresnel zone is an elliptical shaped body around the direct line of sight path between the end node and the gateway.
Any obstacle within this volume, for example buildings, trees, hilltops or ground can weaken the transmitted signal even if there is a direct line of sight between the end node and the gateway.
The maximum radius of the Fresnel zone, located half the distance between end node and gateway is calculated as follow:
r = 8.657 x sqrt(D / f)
r = Fresnel zone radius in m
D = distance in km
f = frequency in GHz
The Fresnel zone equation r = 8.657 x sqrt(D / f) is based on a flat earth.
It does not take the curvature of the earth into consideration.
To calculate height H:
H = 1000 x D2 / (8 x Rearth)
H = Height (or earth curvature allowance) in m
D = Distance between end node and gateway in km
Rearth = Earth radius in km = 8504 km
As a rule of thumb Fresnel zone should always be clear of obstruction but this can be impractical so it is said that beyond 40% blockage, signal loss will become significant.
r = 8.657 x sqrt((0.6 x D) / f)
r = Fresnel zone radius in m
D = distance in km
f = frequency in GHz
For the best radio signal performance:
The gateway antenna must be placed outdoors at a high location (avoiding obstacles in the Fresnel zone).
The antenna design for both gateway and end nodes must be optimised for its regional frequency.
Keep the antenna polarisation vertical for both gateway and end nodes and use omnidirectional antenna to cover a large area.
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