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I'm calculating the max doppler frequency of a fading channel in an in-room environment and looking at different carrier frequencies. Calculated as follows:

F = vf/c

Where F -> max doppler shift
v -> Velocity of object
f -> carrier freq
c -> speed of waves in medium

At lower frequencies (ultrasound), I use the speed of sound. At higher frequencies (GSM range), I use the speed of light. How do I know when the acoustic medium ends and the light medium begins?

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  • $\begingroup$ What's a "fading channel"? $\endgroup$ Dec 19, 2013 at 13:58
  • $\begingroup$ A fading channel is a model of a wireless transmission environment where the channel response changes (or fades) over time. $\endgroup$
    – user36049
    Dec 20, 2013 at 14:22
  • $\begingroup$ Ah, thank's, I probably should have checked Wikipedia (en.wikipedia.org/wiki/Fading) before asking. In any case, wireless communications are done using light, not sound, so using the speed of sound to calculate Doppler spread fading is incorrect; use the speed of light. $\endgroup$ Dec 21, 2013 at 2:59

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Acoustic and electromagnetic waves are totally different. There is no overlap whatsoever. You can obviously have very long EM waves, but best example I can think of would be old long wave radio. In my country they still transmit at 225 kHz which is quite easy to achieve with sound wave too, but their nature is different. EM wave propagates in vacuum while the sound wave does not. EM is transverse wave while sound is longitudal wave (mostly).

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