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[aprssig] an off-topic query about statistical analysis indigital modes

Dave Baxter dave at emv.co.uk
Fri Sep 21 08:31:14 UTC 2007


As of course does Morse code!

Thanks for the book link btw Scott.

Dave G0WBX.
 

> -----Original Message-----
> From: Steve Noskowicz [mailto:noskosteve at yahoo.com] 
> Sent: Friday, September 21, 2007 2:30 AM
> To: TAPR APRS Mailing List
> Subject: Re: [aprssig] an off-topic query about statistical 
> analysis indigital modes
> 
> 
> 
> Perhaps you know that PSK31 has variable length symbols with 
> more common ones (letters e, t, a, o, i, n, s))  having shorter codes.
> 
> 73, Steve, K9DCI
> 
> 
> --- Scott Miller <scott at opentrac.org> wrote:
> 
> > http://www.tapr.org/pub_wdcdat.html
> > 
> > Wireless Digital Communications: Design and Theory, by Tom 
> McDermott, 
> > N5EG.
> > 
> > I'm sure there are plenty of other good texts out there, 
> but this one 
> > covers a lot of ground that's of particular interest to hams.
> > 
> > Also see the Wikipedia articles for convolutional code, viterbi 
> > decoder,
> >   and Hamming distance.  They have some good information 
> and plenty of 
> > references.
> > 
> > Scott
> > N1VG
> > 
> > w0ep at frii.com wrote:
> > > 
> > > Is there a good book to learn about these things?
> > > 
> > > 
> > > On Thu, 20 Sep 2007, Scott Miller wrote:
> > > 
> > >> I think what you're describing is basically a
> > convolutional code.
> > >>
> > >> Such things work better when you've got
> > side-channel information to work
> > >> from - like if you know one particular bit was
> > closer to the decision
> > >> threshold than the others, you know that one's
> > the most likely to be wrong.
> > >>
> > >> In APRS you might be able to recover more data by
> > knowing that certain
> > >> fields are always digits, or always alphanumeric,
> > and using that
> > >> knowledge to try flipping specific bits to see if
> > the new message
> > >> matches the checksum.
> > >>
> > >> Of course, you're still better off encoding it
> > with a proper
> > >> convolutional code in the first place...
> > >>
> > >> Scott
> > >> N1VG
> > >>
> > >> w0ep at frii.com wrote:
> > >>> We've kind of been on an off-topic swing and I know 
> this is a good 
> > >>> place to find people that
> > know
> > >>> about digital data transmission so:
> > >>>
> > >>> Are there any digital data transmission systems
> > that
> > >>> use a dictionary of expected terms and
> > statistical
> > >>> analysis that assigns probability to incoming raw data to match 
> > >>> against the dictionary?
> > >>>
> > >>> Sort of like what my BlackBerry does with
> > SureType mode?
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