2 Phase modulations: Differential Phase-Shift Keying, Quadrature Phase-Shift Keying
Differential Quadrature Phase-Shift Keying (DQPSK) is a multilevel format.
QPSK is effectively two independent BPSK systems, and therefore exhibits the same performance but twice the bandwidth efficiency.
- Pairs of bits are assigned a specific phase, as for example:
- 00 → 45°
- 01 → 135°
- 10 → 315°
- 11 → 225°
There are many options of QPSK – the pairs of bits can be assigned different phase and different pairs can be the neighbour pairs, which can be observed in the following constellation diagrams.
Transceiver’s construction:
The principle of QPSK modulation. Sample constellation diagram. Pairs of bits are assigned particular symbols; since there are four combinations of the pairs, the modulation has four states (levels).
Sample constellation diagrams for OOK and BPSK for comparison purposes. Phase and amplitude expressed by a constellation diagram.