Noise spectral density
In communications, noise spectral density N0 is the noise power per unit of bandwidth; that is, it is the power spectral density of the noise. It has dimension of power/frequency (see dimensional analysis), whose SI coherent unit is watts per hertz, which is equivalent to watt-seconds. If the noise is one-sided white noise, i.e., constant with frequency, then the total noise power N in a bandwidth B is BN0. For double-sided white noise, this is doubled, so N is BN0/2. This is utilized in signal-to-noise ratio calculations.