Phase Keying (PSK) - definition

*Phase Shift Keying (PSK) is a digital modulation technique in which binary information is carried by changing the phase of a carrier wave. Instead of modifying the amplitude or frequency, the digital signal affects the phase shift of the sine wave by specific angles that correspond to successive logical states or combinations of bits. The phase shift occurs in discrete steps and is synchronised to the clock of the transmission system, allowing the receiver to read the data based on an analysis of the phase differences between successive symbols.

The simplest form of phase keying is BPSK (Binary Phase Shift Keying), where two opposite phases are used: 0° and 180°, representing the logical values 0 and 1. More advanced variants, such as QPSK (Quadrature PSK), 8-PSK or 16-PSK, use a larger number of phase states, allowing more bits to be transmitted per symbol, increasing the spectral efficiency of transmission. In these cases, the signal is represented as a vector in complex space, and the individual states are encoded as points in a phase (constellation) diagram.

The advantage of phase keying is that it is immune to amplitude interference, which makes the technique particularly useful under conditions of limited transmission channel quality. However, as the number of phase levels increases, the susceptibility to errors due to phase shifts caused by noise and distortion increases. Therefore, the design of PSK systems requires the use of appropriate filters, error correction and phase synchronisation of the carrier signal between the transmitter and the receiver.

Phase keying is widely used in modern communication systems, including the standards Wi-Fi, LTE, Bluetooth, satellite TV and data transmission in optical and microwave links. The technology is the foundation of many modern multilevel and adaptive modulation methods.

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