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I'm interested in sending digital data over ultrasound.

My initial thought is that it should be first converted to BMC:

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And then phase shift encoded (PSK):

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I initially thought to use a Goertzel filter to decode it, but this runs into trouble: Extracting phase using Goertzel filter in Python

What would be a practical mechanism?

Is there a more intelligent way to encode the data, maybe using two frequencies and taking the relative strength at any moment in time?

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  • Just a basic question: Why do you use BMC if you use PSK? Since you use PSK, a DC component is obviously no issue. What would be the disadvantage of using PSK right away? – Matt L. Mar 15 '14 at 10:16
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    Without additional info, I would suggest that to simplify things you consider using a scheme like Bell 202 does: http://en.wikipedia.org/wiki/Bell_202_modem – John Mar 15 '14 at 12:02
  • A good strategy will depend greatly on channel characteristics, such as S/N, bandwidth, multipath distortion, fading, and etc. as well as the data rate. – hotpaw2 Mar 15 '14 at 19:07
  • Multipath distortion, I take it this is echoes as the sound bounces off objects. I hadn't thought of this! This could really mess up any kind of phase shifting approach... – P i Mar 15 '14 at 19:16
  • Multipath interference can also put a deep notch right at your audio carrier frequency. – hotpaw2 Mar 15 '14 at 22:39

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