Regarding the working of listen-before-talk

Hello everyone,
I some confusion regarding LBT mode in LoRaWAN.
So, in LBT mode the end device opens a receive window before transmitting. I am confused that what is the configuration of that receive window.

In other words, during the receive window the end device listen to the entire channel (all spreading factors) or a specifically configured transmission on that channel?


LBT should be modulation/datarate agnostic and simply read the RSSI for the selected channel before transmitting.

An example implementation can be seen in the isChannelFree function for the Sx1272 driver.


Thanks for your response but why should LBT be datarate agnostic?

Suppose one of the end device transmits on channel-A SF7 and at the same time other device wants to transmit on channel-A but at SF-10, according to LBT the channel is busy, but practically the message can be sent successfully.

Am I missing something here?

The other use of the channel in progress might not even be LoRa

While it’s true that there is a limited degree of orthogonality of certain spreading factor / bandwidth combinations when the signal levels aren’t drastically different, that only protects the LoRa side. Another channel user might well be using a modulation which would be more readily interfered with by a LoRa transmission.

Essentially the answer to both questions is “because the spectrum is not reserved for LoRa alone”