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Phase Shift Keying is used primarilly in digital microwave and satellite communications. It encodes data by shifting the phase of the radio wave form a specific number of degrees from its original value. Quadrature Phase Shift Keying shifts a frequency 90, 180 or 270 degrees out of phase from the current expected state. This produces four distinct values. Thus, when the radio signal is received a single radio frequency value indicates a possible binary value of two bits (four values is represented by two bits).

The simplest form of QPSK starts with zero phase and uses gray coding to organize the binary values so that any unintended shift in phase can be detected.

This file is a place holder for a tutorial on Phase Shift Keying.