Voice control of the pan-European digital mobile radio system

The DTX (discontinuous transmission) system that has been standardized by CEPT for the pan-European digital mobile radio system is described. In this mode the transmitter is switched on when a user begins to talk and switched off again when he or she stops. There are two reasons for using DTX: to increase the number of radio channels (by 100% or more) which can be accommodated in a given bandwidth and to reduce the power drain in hand portable equipment. It is noted that, while adding little degradation to the speech channel and very little additional cost, the DTX will increase considerably the capacity of the system. Particular attention is given to the voice activity detector, the comfort noise subsystem, speech frame substitution, objective and subjective testing, and complexity.<>