Phase Shift Keying (PSK) is a digital modulation scheme used in communication systems to transmit digital data by varying the phase of a carrier signal. In PSK, different phase shifts are used to represent different symbols or bits of information. PSK is widely used in various wireless communication technologies due to its efficiency, spectral robustness, and ability to transmit multiple bits per symbol.

Key characteristics of Phase Shift Keying (PSK) include:

**Modulation Process**: In PSK, the phase of the carrier signal is modulated to represent digital data. The carrier signal is usually a sinusoidal waveform with a fixed frequency.**Binary Representation**: PSK is commonly used to transmit binary data, where different phase shifts correspond to different binary values. The number of phase shifts determines the number of symbols that can be transmitted.**Phase Shifts**: PSK employs different phase shifts to represent different symbols. For example, Binary Phase Shift Keying (BPSK) uses a phase shift of 180 degrees (π radians) for one binary value and no phase shift for the other binary value.**Constellation Diagram**: PSK can be visualized using a constellation diagram, where each point on the diagram represents a specific phase shift corresponding to a symbol.**Higher-Order PSK**: Higher-order PSK schemes, such as Quadrature Phase Shift Keying (QPSK), 8PSK, and 16PSK, use more phase shifts to transmit multiple bits per symbol. QPSK, for example, uses four phase shifts to transmit two bits per symbol.**Robustness**: PSK is robust against changes in amplitude, making it less sensitive to amplitude variations caused by noise and signal degradation.**Spectral Efficiency**: PSK offers high spectral efficiency by transmitting multiple bits per symbol, allowing for efficient use of the available bandwidth.**Applications**: PSK is used in a wide range of communication systems, including wireless LANs (Wi-Fi), satellite communication, digital television broadcasting, and more.**Coherent Detection**: PSK requires coherent detection at the receiver, where the phase of the received signal is compared to a reference phase to determine the transmitted symbol.**Differential PSK**: Differential PSK (DPSK) is a variant of PSK that encodes data based on the difference in phase between consecutive symbols. DPSK reduces the sensitivity to phase changes, making it suitable for noisy environments.

PSK modulation is well-suited for applications requiring high data rates and robust communication. It strikes a balance between efficiency and noise immunity. The choice of PSK variant depends on factors such as data rate requirements, available bandwidth, and noise conditions.