LBT (Listen Before Talk)
LBT is the method whereby a transmitter listens briefly to the channel it will use before transmitting and confirms that it is free. If there is energy above a defined threshold in the channel, transmission is postponed. It is defined as an alternative to the transmission duty ratio limit; it is not an additional condition that has to be applied on top of it.
The logic of LBT is simple: listen to the environment before you talk. The transmitter switches its receiver circuit on for a short period and measures the energy level in the channel.
- If the channel is free: transmission takes place immediately.
- If the channel is busy: transmission is postponed; usually it is retried after a random wait, or another channel is used.
- Gain: the probability of collision drops, the channel is shared more efficiently, and more transmissions can be made without being tied to a fixed hourly budget.
- Cost: a listening period is added before every transmission, latency increases somewhat, and keeping the receiver circuit on raises consumption.
In a remote control application LBT is especially valuable when many sets work on the same site; the sets talk in turn instead of transmitting over one another. The form in which the applied method and thresholds are implemented in your product is defined in the conformity documentation.
Context in which this term is used: Wireless remote control installation: pairing, relay, safety