Quadrature Phase Shift Keying (QPSK) is a widely used modulation scheme in digital communication systems to transmit digital data over a carrier wave. It is a type of phase modulation where the phase of the carrier signal is shifted to represent different combinations of digital bits. QPSK is particularly popular because it strikes a balance between spectral efficiency and robustness against noise and interference.
In QPSK, there are four possible phase shifts, each corresponding to a unique pair of binary bits. These phase shifts are typically represented as 0 degrees, 90 degrees, 180 degrees, and 270 degrees, as you’ve described:
- 00: 0 degrees phase shift
- 01: 90 degrees phase shift
- 11: 180 degrees phase shift
- 10: 270 degrees phase shift
Each pair of bits is mapped to a specific phase shift, and these phase shifts are evenly spaced around a circle in the complex plane. The carrier wave is modulated by shifting its phase according to the bit pairs to be transmitted. This allows two bits of information to be conveyed in each symbol, making QPSK more bandwidth-efficient than simpler modulation schemes like Binary Phase Shift Keying (BPSK), which transmits one bit per symbol.
QPSK is used in various communication systems, including satellite communication (such as DVB-S), digital radio, and wireless communication standards like Wi-Fi and some cellular technologies. It offers a good compromise between spectral efficiency and the ability to cope with noise and interference, making it suitable for a wide range of applications where reliable data transmission is essential.