Subject: [NEXTEL-1] Application of Vocoders to Wireless Communications

From: [email-masked]
Date: Mon, 17 Nov 2003 14:46:40 -0500

Application of Vocoders to Wireless Communications

The need for increased utilization of available wireless communication
spectrum has fueled the development of voice coding technology. From simple
waveform coding techniques operating at 64 kbps, the advance of speech
coding algorithms has produced communication quality systems at 2 kbps and
below. This allows up to 32 communications channels to operate in the
bandwidth formerly occupied by one channel. In addition to the increased
capacity, new digital communication systems offer enhanced security due to
the ease of implementing encryption algorithms.

The Makers of the Project-25 Vocoder
http://www.dvsinc.com/papers/app_voco.htm

Voice Coding Overview

The development of advanced model-based coders has had a significant impact
in a number of fields, including wireless communications, voice storage and
digital telephony, which require high quality combined with efficient
bandwidth utilization (i.e. low bit rate). Figure 1 provides an example of
the voice quality, as measured by a standard mean opinion score (MOS) test,
which is obtainable by DVSI's state of the art AMBE® vocoder. One can see
from this figure that the model based AMBE® vocoder operating at 2 kbps is
able to achieve better quality than the original GSM cellular waveform coder
operating at 13 kbps, a factor of 6.5 times higher. In a wireless system
this added coding efficiency is typically used to increase the number of
users which can be supported across a fixed bandwidth. In addition lowering
the data rate in a wireless application generally leads to smaller, less
expensive mobile equipment which uses less power and, with additional
forward error control (FEC), is more robust to bit errors found in a typical
mobile environment.

Link to full overview:
http://www.dvsinc.com/papers/vc_over.htm

Speech Samples:
http://www.dvsinc.com/samples.htm

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