LoRa specifics


(Mike Syr) #1

I’m new to TTN but I’ve done a fair bit of research on LoRa/LoRaWAN and have a few basic questions for which I have been unable to find answers - or at least what appear to be definitive answers.

  1. There are combinations of SF and BW that appear to yield the same chirp rate (e.g., SF7/125k vs SF9/250k) and are therefore not orthogonal. If so, I take it they don’t play well together. Is this the case?
  2. I’ve seen SF6-SF12 mentioned as well as bandwidths of 62.5, 125, 250, and 500 kHz. However it appears that SF6 and 62.5kHz (and 500kHz?) are not always implemented or perhaps are not “legal”. Can you explain?

Thanks!
Mike


#2

SF6 … LoRaWAN ? where did you see that if I may ask

‘x’ represents the non orthogonal combinations
source


(Mike Syr) #3

Re: SF6. It’s apparently part of the LoRa capability (it’s in Semtech’s docs) , but is NOT part of LoRaWAN (I never said it was). So why is it left out of LoRaWAN?

Thanks for the chart but I’ve seen it. My question stands - what do network architects do about this? Does LoRaWAN somehow take care of the non-orthogonality? Is the ADR mechanism smart enough to not ask for changes to SF that would break orthogonality?


(LoRaTracker) #4

Packet size is fixed, so its not very flexible in use …


(LoRaTracker) #5

Because of the low cost devices used in nodes they can sometimes be outside the frequency capture capability of LoRa if there are significant temperature differences between devices.


#6

AFAIK, new SX1261/2 chip supports also SF5. And SF6 implementation in this chip is incompatible with SX1272/6 one…


(LoRaTracker) #7

What is the issue here, in what context could SF7/125k SF9/250k not ‘play well together’ ?


(Mike Syr) #8

Looking at the chart supplied above, it appears that there’s an issue with two devices transmitting simultaneously, using a combination of SF/BW that creates the same chirp rate. Is that true (it seems the point of the chart), and if true, is that not a problem for the receiver?


#9

yes there he is… I was expecting it :sunglasses:

SEMTECH Q&A forum


#10