Discontinuous Transmission
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Discontinuous transmission (DTX) is a method of momentarily powering-down, or muting, a mobile or portable wireless telephone set when there is no voice input to the set. This optimizes the overall efficiency of a wireless voice communications system. In a typical two-way conversation, each individual speaks slightly less than half of the time. If the transmitter signal is switched on only during periods of voice input, the duty cycle of the telephone set can be cut to less than 50 percent. This conserves battery power, eases the workload of the components in the transmitter amplifiers, and frees the channel so that time-division multiplexing (TDM) can take advantage of the available bandwidth by sharing the channel with other signals.
A DTX circuit operates using voice activity detection (VAD). Sophisticated engineering is necessary to ensure that circuits of this type operate properly and do not swallow parts of words which were mistaken as background noise. Usually comfort noise is used to fill phases of discontinued transmission.
In wireless transmitters, VAD is sometimes called voice-operated transmission (VOX).
