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.
|
 |