Answers:

Discontinuous Transmission (DTx) technique is based on detecting voice activity and switching ON the transmitter only during periods when there is active speech to transmit and switching OFF the transmitter during silent period.

Advantages

• Switching off the transmitter during silent periods reduces interference in the air. This allows the use of smaller frequency reuse clusters leading to a gain in spectrum efficiency of up to 50%
• Battery power consumption is reduced in the mobile terminal since transmitter is OFF during silent periods.

An adaptive threshold voice activity detector(VAD) algorithm is used in the GSM radio equipment to detect silent periods and interrupt transmission. At the receiving end, the DTx is detected and empty frames are filled with comfort noise. The VAD algorithm and its implementation need to be carefully designed to minimise speech clipping and the resulting degradation in speech quality.