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by roman_zeyde 2919 days ago
Indeed, I am using OFDM [1], which uses several carriers, each modulated via QAM [2].

[1] https://en.wikipedia.org/wiki/Orthogonal_frequency-division_...

[2] https://en.wikipedia.org/wiki/Quadrature_amplitude_modulatio...
1 comments
viraptor 2919 days ago
I'm a bit confused. How does QAM work with audio if you have only one channel rather than I/Q? Are you using multiple frequencies for that?
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roman_zeyde 2919 days ago
QAM is using both carrier's amplitude and phase to encode information, so I/Q can be thought as [1]:

  I = amplitude*cos(phase)
  Q = amplitude*sin(phase)
[1] http://whiteboard.ping.se/SDR/IQ
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viraptor 2919 days ago
I'm just sitting here and staring at this sentence: "The modulated signal rides on a carrier of a given frequency, but the base band signal got no fixed frequency at all. Because of this, we have the possibility to encode the two-dimensional I/Q signal onto the one-dimensional RF signal without losing anything." I may need to sleep on it...
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