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

[Eric A. Cottrell]

teka yemane wrote:
> Hi guys,
> Does any body has the source code and/or the algorithm for IMBE 
> vocoder to decode P25 signals?
> I am doing a project on P25 software radio receiver and I need the 
> IMBE vocoder source code.
> Thanks,
> Teka Yemane
>
>
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Hello,

In the P25 Training guide there is some information on the P25 frame 
structure.
http://www.p25.com/resources/P25TrainingGuide.pdf
When it describes the Voice Data (VC1 = VC9) in the frame on Page 48, 
the interleaving, error correcting, etc are done by the IMBE Codec.  
These are described in TIA-102.BABA.  The current Codec chips decode and 
encode to baseband so it handles the whole stream. 

Chapter 7 gives some overview on how the Codec works.  There are some 
other patents that describe IMBE used in other services and the error 
correcting techniques are similar.  I like using the Patent Search in 
Google.

Patent 5,805,612 Mechanism for repeater error mitigation  Partial 
discussion of how the P25 voice frames are encoded.
Patent 5,491,772 Methods for speech transmission  The appendix describes 
the IMBE codec used in INMARSAT M.  Different frame rate but the 
techniques are similar.

If you search on IMBE in the Google Patent search there are many other 
patents.

73 Eric