PSK manipulates the carrier phase information in conformance with the digital information to be transmitted, by advancing or delaying the phase of the carrier.
As equipment sophistication increased, phase keying became more common and is now in use on modern high-speed HF radio links, e.g., in MIL or STANAG based systems. In satellite communication PSK is the main modulation method; for instance Inmarsat C uses BPSK (2PSK), and other Inmarsat systems use QPSK (4PSK).