## Differential QPSK (DQPSK)

#### As for BPSK, phase ambiguity in the carrier recovery process for QPSK requires the use of known preambles, differential encoding/decoding of the data, or differential encoding coupled with differential phase detection. As for BPSK, differential demodulation of QPSK (DQPSK) can be used in preference to coherent detection if simpler implementation is important. The DQPSK modulator uses the same differential data encoder for each parallel data stream as the DPSK binary counterpart, and likewise employs the same principle of using a 1 symbol delayed version of the received symbol stream to act as the reference for demodulation. |