n0/2 noise

in field of communication or PLL, single side noise power spectral density No and double side No/2 are used widely, what is the difference between them?

thanks!

ddt694

Generally, those symbols are used for measuring white noise power spectral density (ped). Both things are the same, however, you should be careful when using them: They are used to describe noise characteristics in different contexts.

When all signals and systems are considered for frequencies between + to - inf, you should use N0/2 [W/Hz].

In contrast, when signals and systems are considered for f>0, use N0 [W/Hz].

For example, if ideal white noise is applied to an ideal unitary gain band pass filter of B Hz bandwidth, the noise power at its output is N0xB. To get this result you can do the following:

For freq +/- inf:

Power = power for f<0 + power for f>0
= ped f<0 x BW f<0 + ped f>0 x BW f>0
= N0/2xB + N0/2xB
= N0xB

For freq >0:

Power = power for f<0 +power for f>0
= 0 + ped f>0 x BW f>0
= N0xB


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