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Re: [Discuss-gnuradio] DV Dongle - AMBE USB Device

From: Eric Cottrell
Subject: Re: [Discuss-gnuradio] DV Dongle - AMBE USB Device
Date: Thu, 20 Mar 2008 14:24:38 -0400 (EDT)

----- Start Original Message -----
Sent: Wed, 19 Mar 2008 23:29:57 -0400
From: "David I. Emery" <address@hidden>
To: Rick Parrish <address@hidden>
Subject: Re: [Discuss-gnuradio] DV Dongle - AMBE USB Device

> On Wed, Mar 19, 2008 at 07:38:13PM -0500, Rick Parrish wrote:
> > Jeff Brower wrote:
> > >If you're looking at low bitrate codecs for GNU radio, why use a 
> > >hardware (dongle)dependent solution? You might look at MELPe, which 
> > >provides 600, 1200, and 2400 bps,and can be implemented as a software 
> > >solution. MELPe is a US/NATO standard (STANAG4591). Common 
> > >applications are HF radio and L band satellite apps where bandwidth is 
> > >very limited.
> > My interest is what is actually being used - which in the case of public 
> > safety communications is the P25 variant of IMBE. FWIW, a closed source 
> > PC hosted IMBE vocoder exists now.
>       Is this a DVSI licensed and publically available closed source
> module or something "unofficial" or not generally available to the world
> at large ?  It has obviously long been possible to recode some reverse
> engineered DSP chip based IMBE implemenation into C++ source code for
> Wintel/Unix/BSD use, but this would not be free of license and patent
> issues... and could not be made part of an open sourced project or
> product without a DVSI deal (and it appears they don't see this as in
> their interest).

In the case of the DV Dongle they buy the DVSI chips and designed a USB 
interface to connect to a PC.  DVSI gets paid for their work.  It is a neat 
solution for the problem of providing PC and Network support for D-Star.  The 
open source part is the interface to the CODEC chip.  It is similar to the 
MadWiFi drivers where there is a closed source HAL provided by Atheros and the 
open source part is the interface of the HAL to the OS.  Not the best solution 
but otherwise there would be nothing.

DVSI does make a PC solution for their licensees.  I have the APCO P25 Voice 
Module for my WinRadio G305e and it is keyed to the radio serial number.

Because the DV Dongle has a published API I was able to see that it should be 
possible to run the CODEC at different rates.  That is one area of exploration 
I want to do.

I also want to see if the AMBE codec can be used on a IMBE stream.  I have seen 
comments online that they are totally different yet I also see comments from 
the TIA P25 group that the AMBE codec is an improvement over the IMBE codec and 
it should be implemented by equipment makers.  This seems to indicate that the 
stream format is the same at least at P25 rates.  I find that new products of a 
company tend to be built on past products of the company.  Companies tend not 
to throw out stuff that works if it still works on the new products.  So the 
improvements could be in the quality of the encoding and decoding rather than 
changes in stream formats.

73 Eric

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