Phase modulation

Phase modulation encodes information by varying a carrier wave’s phase while keeping its amplitude constant. Its instantaneous frequency changes when the phase changes over time.

Carrier wave: A periodic signal whose properties are varied to carry information. Phase modulation changes this signal’s phase while preserving its amplitude.
Phase (waves): The position of a periodic wave within its cycle, measured as an angle or fraction of a period. Phase modulation changes this position to represent the message.
Phase-shift keying: A digital modulation method that represents symbols with discrete carrier-phase values. It applies phase modulation using a finite set of phase states.
Amplitude modulation: A modulation method that encodes information by varying a carrier’s amplitude. It varies amplitude, whereas phase modulation keeps amplitude constant.
Instantaneous phase: The phase angle of an oscillating signal at a particular moment. Phase modulation encodes the message in changes to this angle.
Angular frequency: The rate of change of angular phase, measured in radians per unit time. Changes in phase over time produce changes in instantaneous frequency.
Quadrature phase-shift keying: A digital modulation scheme that encodes two bits per symbol using four carrier phases. It is a widely used phase-modulation scheme for digital transmission.
Frequency-shift keying: A digital modulation method that represents symbols with distinct carrier frequencies. It selects discrete frequencies rather than encoding symbols through phase states.
Frequency modulation: A modulation method that encodes information by varying a carrier’s instantaneous frequency. Its frequency deviations are directly controlled, unlike phase modulation’s phase deviations.
Sinusoidal wave: A smooth periodic waveform described by a sine or cosine function. A sinusoidal carrier provides the standard model for describing phase modulation.

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