PSK (phase shift keying)

Phase Shift Keying (PSK) is a modulation scheme used in digital communication systems to transmit data by varying the phase of a carrier wave. It is a popular modulation technique in applications such as wireless communication, satellite communication, and digital audio broadcasting.

In PSK, the phase of the carrier wave is changed to represent different symbols or bits of digital data. The carrier wave is typically a high-frequency sinusoidal waveform. By modifying the phase of this carrier wave, the information can be encoded and transmitted.

The basic principle behind PSK is to assign different phase shifts to different symbols or bits. The number of distinct phase shifts determines the number of possible symbols or bits that can be transmitted. The most common types of PSK include Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), and Quadrature Amplitude Modulation (QAM).

1. Binary Phase Shift Keying (BPSK): BPSK is the simplest form of PSK, where the phase of the carrier wave is shifted by 180 degrees (π radians) to represent binary symbols. Typically, a phase shift of 0 degrees represents a binary 0, while a phase shift of 180 degrees represents a binary 1. BPSK is often used in applications with low data rates and robustness requirements.
2. Quadrature Phase Shift Keying (QPSK): QPSK is an extension of BPSK that allows the transmission of two bits per symbol. In QPSK, the phase of the carrier wave is shifted in four possible ways: 0 degrees, 90 degrees, 180 degrees, and 270 degrees. These four phase shifts correspond to four different symbol combinations, and each combination represents two bits of data. QPSK enables higher data rates compared to BPSK.
3. Quadrature Amplitude Modulation (QAM): QAM is a more advanced form of PSK that combines both phase and amplitude modulation. It uses a combination of phase shifts and varying signal amplitudes to transmit multiple bits per symbol. QAM allows for a larger number of possible symbols and thus higher data rates. Common QAM schemes include 16-QAM, 64-QAM, and 256-QAM.

To demodulate the received PSK signal, the receiver must synchronize its local carrier wave with the received signal and then determine the phase of the carrier at specific time intervals. By comparing the phase of the received signal with the expected phase shifts for each symbol, the receiver can decode the transmitted symbols or bits.

PSK modulation offers several advantages. It is relatively simple to implement, requires less bandwidth compared to other modulation schemes, and is robust against noise and interference. However, it is more susceptible to phase errors and requires accurate carrier synchronization at the receiver.

In summary, PSK (Phase Shift Keying) is a modulation technique used in digital communication systems to transmit data by varying the phase of a carrier wave. It allows for the encoding and transmission of binary symbols or multiple bits per symbol by shifting the phase of the carrier wave. Different PSK schemes, such as BPSK, QPSK, and QAM, offer varying data rates and robustness characteristics.