Question
What is QPSK modulation?
Answer Options
- A) Modulation using quasi-parallel to serial conversion to reduce bandwidth
- B) Modulation using quadra-pole sideband keying to generate spread spectrum signals
- C) Modulation using Fast Fourier Transforms to generate frequencies at the first, second, third, and fourth harmonics of the carrier frequency to improve noise immunity
- D) Modulation in which digital data is transmitted using 0-, 90-, 180- and 270-degrees phase shift to represent pairs of bits
Correct Answer: D
Explanation
QPSK stands for Quadrature Phase Shift Keying. It is a form of phase modulation used in many digital data transmission systems (like PSK31 and other digital modes). QPSK is an improvement over simple Binary PSK (BPSK), which only shifts phase by 180^\circ to encode a single bit.
QPSK works by encoding two bits of digital data at a time, known as a symbol. It achieves this by shifting the carrier’s phase to one of four possible angles: 0^\circ, 90^\circ, 180^\circ, and 270^\circ. By encoding two bits per symbol, QPSK effectively doubles the data throughput (baud rate) over BPSK without increasing the required bandwidth.
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