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 :)
It has been done - for the minimal case of going through two actual real
phones.
1300bps.
Basically a voice synthesizer driven by data, and a voice recognition
system on the other end.
It uses the very properties that GSM/... codecs for speech are intended
to preserve in the face of small amounts of bit errors - synthesizing an
artificial throat, and exciting this model with data, so you don't get
into parts of the codec that are chaotic or horribly lossy.
Unfortunately, I can't find the original paper I found.
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