## why do we consider zero mean for gaussian noise in a communication channel?

Hi all,
I got an idea why noise is having a gaussian pdf but didnot understood why it should be having zero mean. Why cant noise contain a dc content.

-Devanand T

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 in most cases we consider 0 mean awgn , is it so....

 Quote by dexterdev Why cant noise contain a dc content.
DC component means that there is energy (power) permanently leaving the source, i.e. the source is "evaporating" so it would eventually seize to exist.

## why do we consider zero mean for gaussian noise in a communication channel?

 Quote by FailedLaunch DC component means that there is energy (power) permanently leaving the source, i.e. the source is "evaporating" so it would eventually seize to exist.
Can you explain in simple english (Iam not good in english). I didnot got the idea of evaporate and seize etc..

 Quote by FailedLaunch DC component means that there is energy (power) permanently leaving the source, i.e. the source is "evaporating" so it would eventually seize to exist.
Actually, it looks like I'll need to take this explanation back since it doesn't appear to be to right reason while the used AWGN is zero-mean.

Check also this thread: White noise in communication channel

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 Quote by dexterdev Hi all, I got an idea why noise is having a gaussian pdf but didnot understood why it should be having zero mean. Why cant noise contain a dc content. -Devanand T
Your question is quite a reasonable one. It is largely a matter of semantics and practicalities, I think. In all analogue equipment, you can expect very low rate drifting of DC levels and these will mostly be due to other effects (due to thermal variations of gain etc.) than the normal Gaussian Noise that you can also expect. Most analogue channels are deliberately made 'AC' coupled so there is a lower frequency limit, below which we are not particularly interested and it is not very relevant, in any case. Also, if you think of noise power in W/Hz, there is very little of it in a small fraction of a Hz, compared with normal signalling rates.

 Thankyou for your helpful replies. but what does "matter of semantics" mean

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