Integrated voice-data communications over narrowband PMR channels

The use of narrowband PMR channels for voice and data transmission is becoming attractive as spectral constraints and demand for mobile services continues to increase. The technology, in terms of channel utilisation, keeps on improving and efficient modulation techniques continually increase the data rates possible on such channels. Most mobile applications still employ speech transmission, hence it is necessary to encode speech in a way that uses as little spectrum as possible. Improved speech coding techniques are making toll quality voice transmission possible at 2.4 kbps.