Phase-shift keying (PSK) is a
digital modulation scheme that conveys data by changing, or modulating, the
phase of a reference
signal (the
carrier wave).Any digital modulation scheme uses a number of distinct signals to represent digital data. PSK uses a finite number of phases, each assigned a unique pattern of
binary bits. Usually, each phase encodes an equal number of bits. Each pattern of bits forms the
symbol that is represented by the particular phase. The
demodulator, which is designed specifically for the symbol-set used by the modulator, determines the phase of the received signal and maps it back to the symbol it represents, thus recovering the original data. This requires the receiver to be able to compare the phase of the received signal to a reference signal — such a system is termed coherent.
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Phase-shift keying in which four different phase angles are used. (
188 ) Note: In QPSK, the four angles are usually out of phase by 90°. Synonyms quadriphase, quaternary phase-shift keying.
QUADRATURE PHASE SHIFT KEYING. QPSK
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