The digital voice terminal for slow-FH radio application

The authors present a real-time digital voice terminal (DVT) for slow frequency-hopping (slow-FH) radio applications to ensure a reliable radio link. Slow-FH technologies have been introduced for ECCM communications as a near-term solution which will not disturb the usage of the present conventional radio spectrum. Digital secure algorithms with digital speech codec are known to achieve a high degree of security. The DVT is composed of a speech codec and a voice-band modem. The speech codec that is used for the DVT is a 4.8 kbit/s pitch predictive coder using adaptive transform coding (PP-ATC). The modem is a QAM voice-band modem. This modem has a specific signal format to allow waveform shaping by a hopping transmitter to keep RF compatibility with conventional radio. The authors address aspects of the DVT architecture, the implementation of algorithms in the signal processors, and the system performance