Digital Voice Systems VC-20-ATC-10B Especificaciones descargar pdf (Pagina 28)

FAA20 Embedded NEXCOM Vocoder

Board Manual

This manual has been prepared for the Federal Aviation Administration.

FA100-00107 (March 2004) – Rev 1.0.0 Page 22

5.3 Voice Processing

The FAA20 voice processing flow includes the following major functional

blocks:

• AMBE+ Vocoder

• Linear Voice Mixer

• Packet Voice Router

• PCM Rate Adapter

• Tone Generator

• Gain, Attenuation, and Mute (GAM)

• Voice Peak/Activity Detectors

Figure 9 is a voice processing flow diagram. The diagram is divided into

two major areas: linear audio and compressed audio. The AMBE+ vocoder

is positioned between these two areas.

5.3.1 AMBE+ Vocoder

The FAA20 uses the optimized, fixed-point implementation of the DVSI 4.8

kbps Advanced Multi-Band Excitation Plus (AMBE+

) Vocoder for Air

Traffic Communication. The vocoder is used to compress speech for

transmission over low data rate channels. The AMBE+ algorithm has been

approved for use with the FAA Next Generation Air-to-Ground

Communication System (NEXCOM). The vocoder is also known as the

ATC10B vocoder.

The AMBE+ algorithm has been designed to be robust to both acoustic

background noise and channel errors. It generally contains sufficient

channel error protection to produce high quality speech at bit error rates up

to 1-2% and intelligible speech at bit error rates up to 4-5%.

The algorithm includes a number of advanced features such as automatic

Voice Silence detection (VAD), adaptive comfort noise generation, and soft-

decision decoding.

There are three sources of vocoder control:

• DIN Signal Conductors (GO, VAD)

• Control Nibble Bits (INIT, LOST, and MUTE bits)

• Terminal Command (VOC command)

The signal and bit states are sampled during the FMDE signal pulse. The

associated control is executed at the beginning of the next call to the

vocoder task. The terminal command states are implemented as soon as

the command is processed.

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Digital Voice Systems VC-20-ATC-10B Especificaciones Pagina 28