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 :)
-Adrian
[1] -
http://personal.ee.surrey.ac.uk/Personal/N.Katugampala/pubs/eusipco05.pdf
[2] - http://personal.ee.surrey.ac.uk/Personal/N.Katugampala/
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