LoRa/LoRaWAN tutorial 16: SNR Limit and Receiver Sensitivity

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This is part 16 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 an SNR limit is and how to calculate the receiver sensitivity.
For each spreading factor there is a SNR limit, if this limit is reached the receiver will not be able to demodulate the signal.
In the table below, the SNR limit can be found for each Spreading Factor:
SF=7, SNR limit = -7.5 dB
SF=8, SNR limit = -10 dB
SF=9, SNR limit = -12.5 dB
SF=10, SNR limit = -15 dB
SF=11, SNR limit = -17.5 dB
SF=12, SNR limit = -20 dB
Note: If the SF increases by 1, the SNRlimit changes by -2.5 dB
To calculate the receiver sensitivity:
S = -174 + 10xlog10(BW) + NF + SNRlimit [3]
Receiver sensitivity (S) in dBm
Bandwidth (BW) in Hz
Receiver Noise Figure (NF) in dB
NF is fixed for a given hardware implementation
For LoRa end node transceiver chips SX1272 and SX1276 use NF = 6 dB [1]
Signal-to-Noise limit (SNRlimit) in dB
For example: BW=125kHz, NF=6dB [1]
Lets calculate the receiver sensitivity for SF 7-12.
Use the SNRlimit from the previous table.
SF=7: SNRlimit=-7.5dB
S = -174 + 10xlog10(125000) + 6 -7.5 = -125 dBm
SF=8: SNRlimit=-10dB
S = -174 + 10xlog10(125000) + 6 -10 = -127 dBm
SF=9: SNRlimit=-12.5dB
S = -174 + 10xlog10(125000) + 6 -12.5 = -130 dBm
SF=10: SNRlimit=-15dB
S = -174 + 10xlog10(125000) + 6 -15 = -132 dBm
SF=11: SNRlimit=-17.5dB
S = -174 + 10xlog10(125000) + 6 -17.5 = -135 dBm
SF=12: SNRlimit=-20dB
S = -174 + 10xlog10(125000) + 6 -20 = -137 dBm
If the distance between end node and gateway increases the signal gets weaker and therefore an increase spreading factor is needed for a lower receiver sensitivity to be able to demodulate the received signal. The Spreading Factor ranges from 7 when close to a gateway to 12 when far away from a gateway.
Check out all my other LoRa/LoRaWAN tutorial videos:
• LoRa/LoRaWAN tutorials
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The presentation used in this video tutorial can be found at:
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[@manvendrasingh5853]

This series helped a lot to get started up with LoRa. This playlist is the best one on the internet that can help a beginner to get the idea of LoRa. One can understand the concepts and terminologies of LoRa in an hour through your videos that later helps one to read Research Papers, application notes, specs and data sheet efficiently. A big thanks to you! :)

[@HarpreetSingh-sg5un]

Thank you for the videos , great information

[@Riot837]

Hi I noticed that you have a reference number for the values in the SNR_limit table. Could you share the source.

[@youngkevinsmith]

At 50secs snr drop per sf drop

[@andreyzhalo732]

Hello. Thank you for your videos! What does -174, in the sensitivity calculation formula?

[@ajienayakanikicio3261]

-174 = -228.6 + 30 + 10*log(288.4) where -228.6 is Boltzmann's constant, +30 is to convert from dB to dBm, and 288.4 K is the effective noise temperature

[@youngkevinsmith]

Would you recommend adr for non static devices?

[@youngkevinsmith]

With a sf of 7 and Snr if -7.5dB limit and an rssi and rx sensitivity of -125dBm, does that mean the signal will always get there? Or is this theoretical?

[@kti5682]

Depends on how the sensitivity was measured. If the sensitivity is the RSSI at 5% packet loss 95% of the packets will get through. You can determine the sensitivity with Rx, Tx and a switchable attenuator yourself to test your setup.

[@arnehovind3596]

What is the "spreading" factor?

[@tube_de_siguro]

Hi, I can't find where you have a references list. What's the reference for [2]

[@Mobilefish]

Watch tutorial 1 for the references www.mobilefish.com/download/lora/lora_part1.pdf

[@fenilmangukiya8482]

What is the difference between RSSI and receiver sensitivity?

[@manvendrasingh5853]

I think the RSSI is the signal power received and receiver sensitivity is the minimum power required by the receiver to further process the signal. As said in the video, receiver sensitivity varies with SF.