Phase-Shift Keying (PSK)

Phase-shift keying (PSK) in a digital transmission refers to a type of angle modulation in which the phase of the carrier is discretely varied to represent data being transmitted—either in relation to a reference phase or to the phase of the immediately preceding signal element.

For example, when encoding bits, the phase shift could be 0° for encoding a 0 and 180° for encoding a 1, or the phase shift could be -90° for 0 and +90° for a 1, thus making the representations for 0 and 1 a total of 180° apart. In PSK systems designed so that the carrier can assume only two different phase angles, each change of phase carries one bit of information, that is, the bit rate equals the modulation rate. If the number of recognizable phase angles is increased to four, then 2 bits of information can be encoded into each signal element; likewise, eight phase angles can encode 3 bits in each signal element.