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

[John Gilmore]

> 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.

I've also read that a bunch of radios that use IMBE are *not*
interoperable with each other.  Perhaps the company tweaks the format for
different customers to avoid easy interoperability.  So after reading
the patent and writing some code and recording some over-the-air
traffic, you might still need to do a bit of sleuthing to figure out
exactly which bits go where in the signal.  That is, they might have
some "trade secrets" in addition to the patent.  The fun of trade
secrets is that once somebody figures them out without violating any
contract or law, they get no legal protection.

But that's the fun of having a "protocol analyzer" for the radio
spectrum -- the high and mighty can't just wave their hand and say
"proprietary, proprietary" and leave you stuck.  If they transmit a
signal, you can receive it in high resolution, and your mind and your
software can noodle about how to make sense of it -- whether the
manufacturer likes it or not.

        John