LBT

Listen Before Talk (LBT) or sometimes called Listen Before Transmit is a technique used in radiocommunications whereby a radio transmitters first sense its radio environment before it starts a transmission. LBT can be used by a radio device to find a network the device is allowed to operate on or to find a free radio channel to operate on. Difficulty in the latter situation is the signal treshold down to which the device has to listen.

LBT is used e.g in GSM by the mobile to find a network to connect to and in DECT to find a free radio channel.