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This is part 6 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 radio propagation and free space loss are.
Propagation is the way how radio waves travels thru free space (also known as medium).
The way how these waves travels may impact its signal strength.
Line-of-sight propagation
The radio waves travels directly from sender to receiver without any obstacles.
If the distance between sender and receiver gets larger, the signal will get weaker.
This loss is known as Free Space loss.
If there are obstacles near its path (within the Fresnel zone), the radio waves reflecting off those objects may arrive out of phase with the signals that travel directly and reduce the power of the received signal.
Propagation thru obstacles
Radio waves may penetrate thru obstacles that appear in its path.
Radio waves loses strength if it travels thru obstacles made of more conductive materials.
Propagation thru reflection
Radio waves can be reflected by buildings which interfere with its direct signal.
Propagation thru diffraction
Diffraction is where radio waves are bent around sharp edges.
A signal from a transmitter may be received by the gateway even though it may be "shaded" by a large obstacle.
There are more types of propagations which impact the signal strength but the ones explained in this video:
- Line-of-sight propagation
- Propagation thru obstacles
- Propagation thru reflection
- Propagation thru diffraction
are the important ones.
The free space loss can be calculated as follow:
Lfs = 32.45 + 20xlog(D) + 20xlog(f)
Lfs = Free space loss in dB
D = Distance between end node and gateway in km
f = frequency in MHz
For example: f=868MHz
D=0.01 km, Lfs=32.45+20xlog(0.01)+20xlog(868) = 51 dB
D=0.05 km, Lfs=32.45+20xlog(0.05)+20xlog(868) = 65 dB
D=0.10 km, Lfs=32.45+20xlog(0.10)+20xlog(868) = 71 dB
D=0.50 km, Lfs=32.45+20xlog(0.50)+20xlog(868) = 85 dB
D=1.00 km, Lfs=32.45+20xlog(1.00)+20xlog(868) = 91 dB
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