Noise spectral density
Encyclopedia
In communications, noise spectral density No 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 or joule
s. If the noise is white noise
, i.e., constant with frequency, then the total noise power N in a bandwidth B is BNo. This is utilized in signal-to-noise ratio
calculations.
The thermal noise density is given by No = kT, where k is Boltzmann's constant in joules per kelvin
, and T is the receiver system
noise temperature in kelvins.
No is commonly used in link budget
s as the denominator of the important figure-of-merit ratios Eb/N0 and Es/N0.
Electronic noise
Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects...
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
Dimensional analysis
In physics and all science, dimensional analysis is a tool to find or check relations among physical quantities by using their dimensions. The dimension of a physical quantity is the combination of the basic physical dimensions which describe it; for example, speed has the dimension length per...
), whose SI coherent unit is watts per hertz, which is equivalent to watt-seconds or joule
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
s. If the noise is white noise
White noise
White noise is a random signal with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency...
, i.e., constant with frequency, then the total noise power N in a bandwidth B is BNo. This is utilized in signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...
calculations.
The thermal noise density is given by No = kT, where k is Boltzmann's constant in joules per kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
, and T is the receiver system
System
System is a set of interacting or interdependent components forming an integrated whole....
noise temperature in kelvins.
No is commonly used in link budget
Link budget
A link budget is the accounting of all of the gains and losses from the transmitter, through the medium to the receiver in a telecommunication system. It accounts for the attenuation of...
s as the denominator of the important figure-of-merit ratios Eb/N0 and Es/N0.