G8A12

What is QPSK modulation?

1. AModulation using quasi-parallel to serial conversion to reduce bandwidth
2. BModulation using quadra-pole sideband keying to generate spread spectrum signals
3. CModulation using Fast Fourier Transforms to generate frequencies at the first, second, third, and fourth harmonics of the carrier frequency to improve noise immunity
4. DModulation in which digital data is transmitted using 0-, 90-, 180- and 270-degrees phase shift to represent pairs of bits

Pick an answer to check it.