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In pure phase modulation, the phase of the modulating symbol is the phase of the carrier itself and this is the best representation of the modulated signal. A 'signal space diagram' is an ideal constellation diagram showing the correct position of the point representing each symbol.
Phase modulation (PM) is a modulation pattern for conditioning communication signals for transmission. It encodes a message signal as variations in the instantaneous phase of a carrier wave . Phase modulation is one of the two principal forms of angle modulation , together with frequency modulation .
The phase modulation (φ(t), not shown) is a non-linearly increasing function from 0 to π /2 over the interval 0 < t < 16. The two amplitude-modulated components are known as the in-phase component (I, thin blue, decreasing) and the quadrature component (Q, thin red, increasing).
Frequency modulation and phase modulation are the two complementary principal methods of angle modulation; phase modulation is often used as an intermediate step to achieve frequency modulation. These methods contrast with amplitude modulation , in which the amplitude of the carrier wave varies, while the frequency and phase remain constant.
Consequently, a VCO can be used for frequency modulation (FM) or phase modulation (PM) by applying a modulating signal to the control input. A VCO is also an integral part of a phase-locked loop . VCOs are used in synthesizers to generate a waveform whose pitch can be adjusted by a voltage determined by a musical keyboard or other input.
If the phase-offset/delay of the multiply-filter-divide system is known, it can be compensated for to recover the correct phase. In practice, applying this phase compensation is complicated. [4] In general, the modulation's order matches the nonlinear operator required to produce a clean carrier harmonic. As an example, consider a BPSK signal.
A modified constellation diagram of 16-APSK. Typically 16-APSK will have 15 degree phase offset on the outer ring, which is not depicted here. Symbols can be easily distinguished from each other and, moreover, varying of the space between rings is a way to counteract transmission distortions. [4]
This diagram describes the four-wave mixing interaction between frequencies f 1, f 2, f 3 and f 4. When three frequencies (f 1 , f 2 , and f 3 ) interact in a nonlinear medium, they give rise to a fourth frequency (f 4 ) which is formed by the scattering of the incident photons, producing the fourth photon.
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