Full duplex using several channels
In most cases, Radio communication requires the use of the terminal’s antenna in alternate mode: reception or transmission. From this simple fact arises the obligation to interleave "incoming" and "outgoing" data and build dedicated protocols. This limitation is not a problem for currents systems (walkie-talkie, CB, etc.) and offers the possibility to multiply "listening" terminals that can alternately change their status to “emission” if the channel is free: this is the "half-duplex" mode. For cons, one’s terminal transition to the emission mode prevents the others to send data, which may be disadvantageous for "critical" or "security" uses. This discomfort is further enhanced with "the voice" trigger ("Vox") as the first to speak, or any external noise would trigger the emission and lock the others, which is why some choose the "full-duplex" mode, which allows everyone to intervene at any time, hands free.
To allow several terminals to transmit and receive at the same time, the Full-Duplex Radio generally uses two radio channels, the "up-stream" one and the "down-stream" one, which are mixed in a special terminal (“base”): DECT protocols, for example, uses a base without which two modules, even close cannot communicate.