DEFINITION POWER SPECTRAL DENSITY OF A RANDOM PROCESS
We consider the rules of power spectral density of a random process. The basis of a signal from a random initial phase. This narrow-band random process. If a random variable - current or voltage, the mean square of this function - is the average power emitted at 1 ohm resistance. This power is distributed in a certain frequency band. Average power spectral density is the power allocated to 1 Hz at a given frequency. If the spectral power density averaged over many implementations, it describes the whole process. In general, the spectral power density has a continuous part of the spectrum, corresponding to the fluctuation component and the delta function.