search

Lora-net / LoRaMac-node

Reference implementation and documentation of a LoRa network node.
Other
1.88k stars 1.09k forks source link

[Question] Why CAD is not being used for carrier sensing/LBT #335

Closed hasnainvirk closed 6 years ago

hasnainvirk commented 7 years ago

Radio drivers provide channel activity detection mechanism by doing a CAD. Why this feature is not being used for LBT ? Why an attempt is being made to use IsChannelFree() to determine if RSSI is above a certail level ? Couldn't this be achieved by CAD ?

mluis1 commented 6 years ago

The CAD can't be used because it only detects LoRa modulation preambles (it is not able to detect LoRa modulated data). The CAD feature is most useful on point to point communications where the node transmitting sends very long preambles and the receiver side wakes up time to time.

This is the reason why only the RSSI is used for the LBT.

hasnainvirk commented 6 years ago

Understood. Thanks.

gnob417 commented 6 years ago

@mluis1 However, it seems StartCad function is not even implemented in sx1272/6 driver source. why is that? maybe there is a way to improve LBT mechanism using CAD.

mluis1 commented 6 years ago

@gnob417 The drivers do contain a function named SX1272StartCad or SX1276StartCad.

As previously said the LoRa CAD is of no use for a LoRaWAN end-device implementation.