Mani Raj Paul - DPSK



In Differential Phase Shift Keying DPSK
the phase of the modulated signal is shifted. No reference signal is considered here.

, if the data bit is Low i.e., 0, then the phase of the signal is not reversed
.If we observe the above waveform, we can say that the High state represents an M in the modulating signal and the Low state represents a W in the modulating signal.
 
DPSK Modulator
DPSK is a technique of BPSK, in which there is no reference phase signal. Here, the transmitted signal itself can be used as a reference signal.
DPSK encodes two distinct signals, i.e., the carrier and the modulating signal with 180° phase shift each. The serial data input is given to the XNOR gate and the output is again fed back to the other input through 1-bit delay. The output of the XNOR gate along with the carrier signal is given to the balance modulator, to produce the DPSK modulated signal.

DPSK Demodulator
In DPSK demodulator, the phase of the reversed bit is compared with the phase of the previous bit.
, it is evident that the balance modulator is given the DPSK signal along with 1-bit delay input. That signal is made to confine to lower frequencies with the help of LPF. Then it is passed to a shaper circuit, which is a comparator or a Schmitt trigger circuit, to recover the original binary data as the output.

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