Range between Lora to LoRa and LoRa to Gateway

LoRaWAN LoRaWAN Discussions
1

Hi,

Let’s say I have a LoRa End Device communicating with a Gateway at a particular distance. Now if I remove the Gateway and replace it with another LoRa End Device. Then change the firmware for P2P communication will both the nodes be able to communicate at the same distance.

I know P2P does not fall in LoRaWAN and is less secure but will the range be same for both?

2

At the radio level, which determines range and distance, the LoRa device does not know if its connected to a TTN node, TTN Gateway or whatever.

So two LoRa devices with the same settings should have the same range, regardless of what type of microcontroller they are connected to.

3

The gateway has better sensitivity -142.5 dBm vs -137 dBm, the P2P range should be less compared to Device to GW.

https://www.semtech.com/products/wireless-rf/lora-transceivers/sx1272
https://www.semtech.com/products/wireless-rf/lora-gateways/sx1301

4

Now, I dont know if Semtech have ever revealed how they measure the sensitivity, I would guess in an RF quiet environment, faraday shielded etc.

I have not tested a Gateway, but for the SX127X devices I have never got anwhere near the quoted sensitivity outside in the real World. The real World failure point does however get very close to the quoted SNR figure, and real World noise levels will be in the -105dBm region. So you might get reception at -125dBm for SF12, but -142.dBm, maybe by Pluto.

So whilst a Gateway might be able to quote a better ‘sensitivity’ can it be achieved in an RF noisy World ?

5

The sensitivity is measured through a cable: this way you get an accurate measurement of performance, independent of external condition. But, if you see a better sensitivity in a product compare to another, it basically means that you need less SNR for the same performance, and so this should translate as well in real life.

But in this particular case, don’t be fooled by the front-page datasheet number: the sensitivity given is basically the lowest achievable with the chip, but the condition can be very different:

  • looking at the SX1301 datasheet if you use the reference design you get -139.5 dBm and not the -142dBm (this one might require an external LNA I believe, so it depends on the product.
  • If you look at SX1276 you can see -146dBm sensitivity, but here, it is because the lowest bandwidth is different…
  • And even the definition can be different: the gateway sensitivity is for 10% PER , CR 4/5 and 32B while for the 1272 it is 1% for code rate 4/6 and 10B

In the end, it is difficult to fully compare both because the node contains the radio while the gateway depends of external front-end: so on a gateway you can get very different performances depending of the front-end used, presence of external LNA, … But at the LoRa demodulator level, those two chip are basically the same.

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6

Difference in sensivity relates to reception only and not to transmission. So it really depends on the type of communication whether difference in sensitivity on one end will make any practical difference.