#Noise mapping diagram series#

This principle of using two independently modulated carriers is the foundation of quadrature modulation. A coherent detector is able to independently demodulate these carriers. Thus each symbol can be represented by a complex number, and the constellation diagram can be regarded as a complex plane, with the horizontal real axis representing the I component and the vertical imaginary axis representing the Q component. The carrier representing each symbol can be created by adding together different amounts of a cosine wave representing the 'I' or in-phase carrier, and a sine wave, shifted by 90В° from the I carrier called the 'Q' or quadrature carrier. In a frequency or phase modulated signal, the signal amplitude is constant, so the points lie on a circle around the origin. The constellation diagram shows all the possible symbols that can be transmitted by the system as a collection of points. Each symbol is encoded as a different combination of amplitude and phase of the carrier, so each symbol is represented by a point on the constellation diagram, called a constellation point. So each sample encodes one of a finite number of 'symbols', which in turn represent one or more binary digits (bits) of information. During each sample, the carrier wave has a constant amplitude and phase, which is restricted to one of a finite number of values.

#Noise mapping diagram series#

In a digital modulation system, information is transmitted as a series of samples, each occupying a uniform time slot. The distance of a point from the origin represents a measure of the amplitude or power of the signal. The angle of a point, measured counterclockwise from the horizontal axis, represents the phase shift of the carrier wave from a reference phase. It displays the signal as a two-dimensional xy-plane scatter diagram in the complex plane at symbol sampling instants. Each symbol is encoded as a different phase shift of the carrier sine wave: 0В°, 45В°, 90В°, 135В°, 180В°, 225В°, 270В°, 315В°.ДЄ constellation diagram is a representation of a signal modulated by a digital modulation scheme such as quadrature amplitude modulation or phase-shift keying. Information transmitted according to the scheme described in the above diagram is encoded as one of 8 'symbols', each representing 3 bits of data.