p/4 DQPSK (Digital Demod)

p/4 DQPSK (Differential Quadrature Phase-Shift Keying) is a differential format where the bits for a given symbol are determined by the phase change from the previous symbol. "p/4" adds an p/4 offset to the phase changes compared with the phase changes in plain DQPSK Differential Quadrature Phase Shift Keying: QPSK modulation using differential encoding of the digital information stream.. This means there are a total of 8 ideal state positions (compared to the 4 for DQPSK). The ideal state positions for symbols alternate between the four 45-degree states normally used by QPSK Quadrature phase shift keying and four on-axis states. Due to this alternation, the ideal trajectory between symbols never crosses through zero.

The following table shows the mapping of phase change to bit pattern:

Phase Change	Bit Pattern
p/4	00
3p/4	01
-p/4	10
-3p/4	11