In what scenario is it possible that collision happens between two packets. And if a collision happens, is it possible to demodulate? How? Regarding here it says there are two types of interference. Intra and internetwork for unlicensed networks. I suspect when a node from outside network interferes with signals inside network, it is recoverable. But how? Thanks.

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    In LoRaWAN any device can talk at any time, so if two devices send on the same frequency you may end up with a collision. There’s no carrier sense/listen before talk, no collision avoidance, no collision detection, no collision recovery. Whether two devices sending on the same frequency but using different data rates end up colliding or not is unclear to me, though. – jcaron May 29 at 11:10
  • @jcaron Does data rate even matter? In unlicensed networks there could be intra-network and inter-network interference. I want to know which is recoverable? Why did you say that all sort of interference is not recoverable? I suspect if collision comes from out of network node signal, the message ould be recovered? But how – m0ss Jun 3 at 18:02

Lora’s spreading and frequency chirps provide some level of de-confliction, but it’s not perfect. Lora devices transmit randomly on their own schedule, so there’s always the possibility of collision. If the Lora gateway cannot de-conflict both packets, then they’re dropped. The transmitting device won’t know that the packet was dropped, unless the device was requesting information or acknowledgement. You can implement a retry feature where the gateway requests packets that were missed based on sequence numbers. If the gateway receives packets 1, 2, 3, and 5, it can request packet 4 from the device. It’s up to your device to implement that feature.

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