Differential phase shift keying (DPSK) is a type of phase shift keying in which information is transmitted by changing the phase of the carrier frequency
. With DPSK keying, as with quadrature phase shift keying (QPSK), ambiguities can occur if the phase changes during transmission. For this reason, in Differential Binary Phase Shift Keying (DBPSK), the phase position is changed with the signal
and is not fixed.
For example, in DBPSK, a digital "1" is transmitted by rotating the phase position by 180°, and a binary "0" is transmitted by adding one of 0° to the current phase position. If two "ones" are transmitted one after the other, the first can have a phase angle of 0°, the second is in any case rotated by 180°.