Re: [Discuss-gnuradio] Does any body has the source code and/or the algorithm for IMBE vocoder to decode P25 signals?

[LRK]

On Wed, Sep 24, 2008 at 08:49:08PM -0700, John Gilmore wrote:
> > IMBE is proprietary and the holder of the rights, DVSI, is very very
> > very unwilling to share.  You can try to license it from them, but
> > experience has shown that they are not interested.
> 
> According to:
> 
>   http://wiki.multimedia.cx/index.php?title=IMBE
> 
> the IMBE codec is patented, and here's the patent number: US 5,870,405.
> Which means you are free to read it and understand it, and maybe even
> implement it yourself to make sure you know how it works.  And if you
> live in a country without software patents, then you can probably 
> even distribute the software.

Best I can tell, this patent covers the use of error checking to send
bits generated by vocoders of several types including IMBE. I do not 
see a good description of IMBE vocoders.

Since the basic vocoder method of sampling speech and analyzing the
sample to produce a data stream to generate something sounding like
speech at the receiving end of the circuit was used in military systems
in the 1960's, it is not clear what was 'improved' to patent IMBE.

In any case, we built a prototype 'conference bridge' around 1966 to
connect three of these vocoders in a conference because they could not
be conferenced at an analog point. Doing the vocoder steps twice gave
an uninteligible collection of sounds.

Since analog patching of P-25 systems is part of the National Emergency
Communications Plan, I have tried to determine if any work has been done
on inteligibility of such patches but inquiries to APCO and SAFECOM have
been unproductive.

I would like very much to use GnuRadio to do simulations so if anybody
figures out how to do IMBE in software, please post it here.


-- 
LRK
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