LoRa/LoRaWAN tutorial 6: Radio Propagation and Free Space Loss

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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
Check out all my other LoRa/LoRaWAN tutorial videos:
• LoRa/LoRaWAN tutorials
Subscribe to my RU-vid channel:
/ @mobilefish
The presentation used in this video tutorial can be found at:
www.mobilefish.com/developer/...
#mobilefish #lora #lorawan

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24 сен 2018

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Комментарии : 19

@vaibhavsugandhi2668 2 года назад

😍 amazing tutorials, thanks for sharing knowledge.

@resatyuzbasic1908 3 года назад

Thanks very much for the wonderful explanation.

@tsvetelindimitrov6990 4 года назад

Thanks mate, you're gonna help me pass my exam!

@omiiishirke8049 3 года назад

Thanks, sir for helping in an easy way .....

@widya2550 4 года назад

Thank u Sir, ur channel are really helpfull

@samuelwondemu6972 3 года назад

best

@nazmierazali7748 5 лет назад

Hi, if I just have a transmitter and receiver without using gateway, can I calculate the free space loss using the distance between transmitter and receiver? because you mentioned in the video that D represent the distance between the end node and the gateway.

@thienbui7052 3 года назад

How does the end node know the direction of the gateway, so that they can reflect builidng or diffraction big obstacles the right way to come to the gateway?

@quentinjames981 3 года назад

The end node does not know anything, it emits in all directions. Look up "omni-directional antenna"

@stepannovotny4291 8 месяцев назад

Pine trees are really bad at specific UHF frequencies because of the length of their needles.

@peubouzon 4 года назад

Hi Sir, I'm using a SX1276-915 LoRa module with maximum tx power of 20dB and minimum sensitivity of -148dB (7.8 Khz bw). Calculating the D value on the presented equation with f = 915, and L = -168 dB (20 - (-148)) gives me a value of 6548 km, which is pretty high. Even if i use a loss (L) of 148dB (sensitivity) it yields a distance of 654 km. The manufacturer claims only 4 to 8 km. Am i doing something wrong?

@Mobilefish 4 года назад

Pedro, you can not use this equation to calculate D. Use this equation to calculate the free space loss. See: www.mobilefish.com/download/lora/lora_part8.pdf page 4, for a better understanding of TX power, path loss and receiver sensitivity.

@Mobilefish 4 года назад

Your sensor can transmit over a distance of 4 to 8 km ONLY when: 1) Your sensor has a direct line of sight with the gateway 2) Your sensor has a "good" antenna (preferably outdoors and VSWR < 2)

@Mobilefish 4 года назад

The gateway antenna must be outdoors and must also have a good antenna (omidirectional, VSWR

@peubouzon 4 года назад

@@Mobilefish Thank's for your answers. Is there any equation which can be used to calculate D? It would be interesting to know how the manufacturers specifies the maximum range.

@Mobilefish 4 года назад

To be honest, I do not think the manufacturer knows the actual maximum range. The manufacturer just specified this range. There is probably an equation to calculate this, but it theoretical. You will never reach this distance! As I said it depends on the line-of-sight, the antennas used and other factors. If you read this article: www.thethingsnetwork.org/article/lorawan-distance-world-record a distance of 766 km could be reached, but they had "perfect" line-of-sight AND they were using a directional antenna. I have build this simple end node: www.mobilefish.com/developer/lorawan/lorawan_quickguide_build_lora_node_rfm95_arduino_pro_mini.html and I was able to reach a distance of 14 km BUT ONLY IF CERTAIN CONDITIONS WERE MET: 1) good line-of-sight (few obstacles, just trees) 2) end node (altitude = 11m) and gateway (altitude=40m), think Fresnel zone! 3) nice weather 4) end device had a directional antenna But when using a simple omnidirectional antenna (and in all weather conditions) I could only reach gateways 2 km away. By the way in both cases, the gateway antenna was outdoors and my end device antenna was indoors (this is not good)! If you look at my example the distance depends largely on other factors than the end device it self.