modulated data over GSM voice (was Re: Data over normal GSM call)
ken at gmx.ch
Mon Apr 14 22:15:06 CEST 2008
Harald Welte wrote:
> Just to give you a "summary judgement":
> Running any kind of voice-encoded data over a regular voice channel of a
> GSM phone is _extremely_ unlikely to work.
> There are a number of different codecs in use. Which codec is
> determined by the network. There is echo cancellation at potentially
> multiple locations during the call. There might be one or multiple
> transcoders of the voice codec along the road.
> If you can manage to design a modulation and coding scheme that survives
> all (or even most) of the stages above, I think you have achieved
> something great. I doubt you will get more than 300bps though :)
Somebody already has. May I point you towards the paper "Real Time End
to End Secure Voice Communications over GSM Voice Channel" by N.N.
Katugampala, K.T. Al-Naimi, S. Villette, and A.M. Kondoz .
The authors claim to have achieved a throughput of 3 kbps with a 2.9%
BER. By adding error correction codes the throughput went down to 1.2
kbps with a BER of 0.03%. Unfortunately they have not released any code
and I could not find much detail beyond a couple more papers found at
. Nevertheless highly interesting to read :)
 - http://personal.ee.surrey.ac.uk/Personal/N.Katugampala/
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