Spreading factors and Coverage

  • 10 augustus 2016
  • 6 reacties
  • 2820 keer bekeken

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This post has become obsolete as it was incorporated in the Spreading factor (SF), Time on Air and (Adaptive) Data Rate topic.

LoRa uses more spreading (and repeating messages) when there is a weak signal or a lot of noise. Usually, getting further away from a gateway will decrease signal and therefore increase the needed spreading factor. The Spreading Factor (SF) ranges from SF7 when close to a Gateway to SF12 when far away from a gateway or shielded by walls or buildings.

Coverage


KPN designs it’s network to have SF10 or better outdoor in The Netherlands, where KPN includes presence of buildings and other important objects. Walls and buildings typically reduce a signal by 2 SFs, creating a typical value of SF12 indoor in The Netherlands. Actual indoor coverage largely depends on type of building material, rule of thumb should be “you should have LoRa coverage when you see (reflected) daylight”. Note however that certain kinds of window coatings can also have a significant blocking effect on radio signals.

Time on Air


An important consequence of using a higher spreading factor for LoRa is a longer time on air (ToA). The LoRa Radio module needs more time to send the same amount of data. This ranges from 50 ms for a 10 byte payload on SF7 to a ToA of 1600 ms for the same packet on SF12. This means that power consumption increases with increasing Spreading Factor. To optimize spreading factor, Adaptive Data Rate ADR should be used.

6 reacties

Reputatie 1
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Hoi,

Hoi,

Ik lees:
This ranges from 50 ms for a 10 byte payload on SF7 to a ToA of 1.6 ms for the same packet on SF12.

Is dat niet andersom of in ieder geval algemeen gesteld dat een lage SF > korte tijd, hoge SF > langere tijd? Of lees ik het verkeerd?

groet.
Reputatie 7
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Hoi NoelTrain,

Ik lees het ook zo, en als ik logisch nadenk lijkt me dat jouw bevinding klopt. Dit check ik nog even intern na.

Logica:
lage SF + hoge snelheid = korte tijd
hoge SF + lage snelheid = langere tijd
Reputatie 1
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Time on Air


....This ranges from 50 ms for a 10 byte payload on SF7 to a ToA of 1.6 ms for the same packet on SF12.


Guess you meant 1.6 seconds, not 1.6 milliseconds.
Reputatie 1
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Agree, 7 > 12 = 2^5 = 32. 32 x 50 ms = 1600 ms = 1.6 seconds, nice!
Reputatie 7
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Hi NoelTrain & hobo,

SF12 definitely has a higher ToA time. I'll edit Michiel his post. Thanks all for the feedback.

"LoRa uses more spreading (and repeating messages) when there is a weak signal or a lot of noise. Usually, getting further away from a gateway will decrease signal and therefore increase the needed spreading factor."


Reputatie 3
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Mag ik deze link even toevoegen aan jullie discussie: ADR altijd afgedwongen door KPN development environment

Dus mocht je met een specifieke SF willen sturen op het dev netwerk. Dan zul je deze op bepaalde chips elke keer moeten instellen voor het versturen van een bericht.

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