Re: Additive White Gaussian Noise Question

Necronomicon wrote:

...

That depends on how you're amplitude modulating the carrier -- "amplitude
modulate" it with white noise & you'll get spectrally flat "side bands"
(actually you'll spread the carrier energy all over every place).


My point is that if you add the gaussian noise to the
amplitude, the side bands will not be spectrally flat.

Modulating and adding are very different. Think about what happens when addding 60 Hz to an AM radio signal.

...

_Any_ modulation will alter the frequency spectrum of a carrier, so I
don't see how AM is a misnomer.


My point is that pure FM does not alter the amplitude
while pure AM still alters the frequency spectrum.

Regardless of the modulation scheme, sending information requires bandwidth. When information is modulated onto an AM carrier, the result occupies a band of frequencies around the carrier. If a very narrow filter is used to leave only the carrier, it will no longer have amplitude variations.

...

How would you differentiate AWGN from
simple white noise + carrier?

You evidently recognize that noise can be white only within some interesting frequency band and not from DC to gamma rays and beyond.

As for your question, the difference is that your AWGN has no carrier.

AWGN is a particular kind of noise, and the concept assumes something about its introduction to the system. It is *white* and *Gaussian*, and of course it is *noise*. But before all, it is *additive*, which is to say, that the system behaves linearly at the point where the addition takes place. Does that clear anything up?

Jerry
--
Engineering is the art of making what you want from things you can get.
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.

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