Bedrosian's derivation of the Hilbert product rule,
H[f(x)g(x)]=f(x)H[g(x)], where g is often the high frequency carrier
cos(w_0t+P), stipulates that either F(w) and G(w) don't overlap, or f(x)
and g(x) are both analytic.
A few questions:
A) does non-overlapping mean that F(w) and G(w) don't overlap, or that
F(w)*G(w) goes to zero at some point in between the two spectra (like a
Nyquist-type arrangement?
B) What happens when they overlap? Is the result of a Hilbert-based
demodulation technique for overlapping F(w) and G(w) a simple aliasing?
C) (this one might be tough) The original Bedrosian paper refers to a
more general form than the r(t)cos(w_0t +P) type modulation, which is
r(t)cos(w_0t+P(t)), where the phase offset is a function of time (derived
by Kelly). Bedrosian points out that the Hilbert product rule for a
carrier with constant phase offset requires non-overlapping signals or
two analytic signals, while the less specific form requires no spectral
restriction. This suggests that the less specific form is not subject to
aliasing. Is this true? What does this mean practically? Does it mean
that if you have access to the actual carrier, instead of doing a sort of
carrier recovery, that you don't need to worry about aliasing? Does it
mean something else entirely? I have the Kelly J Soc Indust App Math
paper, but its a little dense, and I'm hoping that some facile person
could help me find a shortcut through this.
BTW, my motivation is that I'm trying to analyze a physiological systems
output w/ envolope detection, where the output really seems to be an AM
signal. The problem is that the carrier frequencies are very low
(<10Hz), and I have no way of knowing for a fact that the message signal
is non overlapping (though most of the energy must be nonoverlapping).
This isn't a huge worry, but I'd like to have some more grip on how this
impacts the methodology.
Thanks in advance,
--
Scott
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