modulated data over GSM voice (was Re: Data over normal GSM call)

Adrian-Ken Rueegsegger ken at
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 [1].

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 
[2]. Nevertheless highly interesting to read :)


[1] -
[2] -

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