Listen Before Talk (LBT)
Often required in Asian countries, Listen Before Talk when applied to LoRaWAN is forcing to listen for a short duration on the transmitting channel before sending a message.
LBT is device and gateway implementation only, this is not managed by the network server.
In practice:
- Device, upon sending a message, will listen on the selected channel for 128µs to make sure there isn't any other transmission.
- Gateways don't have the luxury to be able to wait on each transmission. To solve this, they usually embark an additional piece of hardware that contently listen on every channel and give a yes/no answer when the gateway want to transmit on this channel.