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LoRa/Rules, sharing and the battery/Shared spectrum and collisions
Lesson 8 of 12 · in 3D and VR

Shared spectrum and collisions

LoRa nodes send when they have something to say, without asking. This lesson shows when two packets overlap, when both are lost and when the stronger one survives, and why no setting makes delivery certain.

Lonely BinaryUpdated 2026-10-144 min readNo board required

View it in VR

Lesson 8 of the LoRa course opens in a VR headset, on a table in front of you, and a voice starts three seconds after you arrive. Type this short address into the browser on a headset such as Meta Quest or Apple Vision Pro, and press Enter VR. No headset? Press Start the lesson: the same lesson, full screen.

learn.lonelybinary.com/vr/lora/8

Nobody asks first

The LoRaWAN MAC has no listen-before-talk step. A node simply sends when it has a reading, and two probes on the farm each have their own idea of when a report is due. Most of the time that is fine, because a six byte report is about 124 milliseconds on the air and a probe sends a few times an hour.

When two reports overlap

Two packets on the same channel and the same setting overlap when one starts within one airtime of the other. The gateway cannot ask one to wait. It hears the sum of both signals, and with similar levels usually both are lost. A gateway with several receive paths hears different channels at once, but it cannot make two packets on one channel not overlap.

Capture is a condition

Sometimes the much stronger packet gets through. The bench uses a margin of about six decibels as an example, and the figure depends on the radio and the setting. The weaker packet is still lost, and its sender does not learn it.

Different spreading factors

Packets on different spreading factors mostly coexist. Mostly is the word to keep: a packet that is very much stronger can still damage a weaker one on another setting.

What the rules do

The licence and the regional plan limit power, and in some regions the share of time a device may transmit. They do not cause collisions. A lower duty cycle lowers the chance of an overlap without taking it to zero, which is why a report that matters needs a confirmation, a repeat or a tolerance for loss in the application. The next lesson shows what each of those costs a battery.

Common mistakes

  • Reading a different spreading factor as a separate channel. The separation is partial, and a much stronger packet can still get through the isolation.
  • Counting on capture. It depends on the relative levels at the gateway, which change with the weather, the antenna and the position of the node.
  • Blaming the rules for collisions. Regulation limits how much anyone sends. Overlaps happen because nodes send without being scheduled.

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