Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request
From: Jeff Carroll <bcsaic!carroll@beaver.cs.washington.edu>
Newsgroups: comp.dcom.telecom
Subject: Re: IRIDIUM: Motorola's New Cellular Phone System
Message-ID: <11195@accuvax.nwu.edu>
Date: 21 Aug 90 22:55:26 GMT
Sender: news@accuvax.nwu.edu
Organization: Boeing Computer Services AI Center, Seattle
Lines: 29
Approved: Telecom@eecs.nwu.edu
X-Submissions-To: telecom@eecs.nwu.edu
X-Administrivia-To: telecom-request@eecs.nwu.edu
X-Telecom-Digest: Volume 10, Issue 586, Message 3 of 11


In article <10706@accuvax.nwu.edu> gronk!johnl@uunet.uu.net (John
Limpert) writes:

>mk59200@metso.tut.fi (Kolkka Markku Olavi) writes:

>>Does anybody know what kind of compression they plan to use to squash
>>8kHz bandwith sound through a 4800bps channel?

>The original article said that the system used vocoders, not telco
>style A/D converters.  A vocoder (voice encoder/decoder) can operate
>at very low data rates.  The Texas Instruments Speak and Spell toy
>used vocoder technology (linear predictive coding) to fit digitized
>voice into the toy's ROM chip.  A vocoder uses a model of the human
>vocal tract to transmit speech.  It continually adjusts the model to
>approximate the speech input and periodically transmits the parameters
>to the decoder on the other end.  

	The USAF has been using 10th order LPC vocoders for a number
of years. They operate at 2400 bps, with a couple of different
(incompatible) types in use. These are early '80s technology, and
everyone tends to sound a little bit like Donald Duck - but really not
much worse than analog cellular. (The signal/noise requirement in most
tactical voice comm systems is only 10 or 12 dB anyway.)


	Jeff Carroll
	carrol@atc.boeing.com