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DPSK modulation, DPSK demodulation, Differential Phase Shift Keying

This page on DPSK (Differential Phase Shift Keying) describes DPSK basics, DPSK modulation and DPSK demodulation with block diagram. DPSK modulator and DPSK demodulator circuits used for DPSK modulation/demodulation respectively are described. It mentions benefits or advantages of DPSK over BPSK.

What is DPSK ?
DPSK stands for Differential Phase Shift Keying. It is the version of BPSK. In DPSK, there is no absolute carrier phase reference, instead transmitted signal itself used as phase reference. There are various applications of DPSK such as WLANs, Bluetooth and RFID communication. The most popular among them is its use of Bluetooth where π/4 - DQPSK and 8-DPSK modulation variants of DPSK has been employed.

In DPSK demodulation, phase of the received bit is compared with phase of the previous bit.

DPSK modulation using DPSK modulator

DPSK modulation using DPSK modulator

Figure-1 depicts the process of DPSK modulation using DPSK modulator in the form of a block diagram. In DPSK modulation, serial binary data pass through X-NOR gate and the output is fed back via 1 bit delay. The resulting bit stream is applied to the balanced modulator to produce DPSK signal.

DPSK demodulation using DPSK demodulator

DPSK demodulation using DPSK demodulator

Figure-2 depicts the process of DPSK demodulation using DPSK demodulator in the form of a block diagram. In DPSK demodulation, DPSK signal is passed to the balanced modulator and 1 bit delay circuit. The resulting signal is passed to the LPF which produces binary data. This is passed to comparator circuit (or Schmitt trigger circuit) to produce clean and high speed binary levels.

Advantages of DPSK

Following are the benefits or advantages of DPSK over BPSK.
➨DPSK modulation does not require carrier at its receiver circuit. Hence complex circuits are not needed.
➨Bandwidth requirement of DPSK is less compared to BPSK modulation.
Following are the disadvantages of DPSK.
➨Probability of error or BER (Bit Error Rate) is higher in DPSK compare to BPSK.
➨Noise interference in DPSK is more.
➨DPSK modulation uses two successive bits for its reception. Hence error in first bit creates error in second bit and consecutively error propagates.
➨Also refer advantages and disadvantages of DPSK modulation over BPSK modulation.


Modulation related links

what is modulation
MSK and GMSK modulation
8-PSK modulation
QAM modulation
BPSK modulation

RF and Wireless Terminologies


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