What is Differential Phase Shift Keying : Modulation and Demodulation

The digital modulation like PSK (phase shift keying) is one kind of modulation which is used to change the phase of the carrier signal to convey the data. Generally, it is used for wireless communication of LANs, Bluetooth, and RFID. In digital modulation, digital data can be represented by using a fixed number of discrete signals. Phase shift keying utilizes a fixed number of phases, where each phase can be allocated a unique outline of binary digits. Usually, every phase encodes an equivalent digit of bits. Each outline of bits can form the symbol that is signified through the specific phase. The demodulator is specially designed for the symbol-set which is utilized by the modulator. The original data can be recovered by decoding the received signal’s phase. This article discusses an overview of differential phase-shift keying or DPSK.

What is Differential Phase Shift Keying?

Definition: The DPSK stands for “Differential phase-shift keying”. It is one type of phase modulation used to transmit data by altering the carrier wave’s phase. In this, the modulated signal’s phase is moved e to the element of an earlier signal. The phase of the signal tracks the low or high state of the earlier element. This kind of phase-shift keying doesn’t require a synchronous carrier on the demodulator.


The binary bits input series can be changed so that the next bit depends upon the earlier bit. So, the earlier received bits in the receiver are utilized for detecting the current bit.

The above-shown figure is the DPSK waveform. From the above waveform, once the data-bit is ‘0’, the signal’s phase will not be inverted as well as continued. Once the data-bit is a ‘1’, then the signal’s phase will be inverted.

dpsk-waveforms
dpsk-waveforms

In the above waveforms, the high-state is represented by an’ within the modulating signal & the low -state represented by a modulating signal.

DPSK Modulation and Demodulation

The DPSK modulation & demodulation discusses what DPSK modulation? & what is DPSK demodulation?

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DPSK Modulation

DPSK is a method of BPSK, where there is no reference phase signal. Here, the signal which is transmitted is used as a reference signal. The DPSK modulator diagram is shown below. This modulation encodes two separate signals namely the carrier signal as well as the modulating signal. The phase shift of each signal is 180°.

dpsk-modulation
dpsk-modulation

In the above figure, the serial input data can be applied to the XNOR gate & the o/p of the logic gate is fed back again to the input via 1-bit delay. Both the carrier signal as well as XNOR gate output is applied to the balanced modulator so that the modulated signal of DPSK can be generated.

DPSK Demodulation

In this demodulator, both the previous bit and the reversed bit are compared with each other. The DPSK demodulator block diagram is shown below. From the above block diagram, it is clear that the DPSK signal is applied to a balanced modulator using a 1-bit delay input.

dpsk-demodulation
dpsk-demodulation

That signal is ready to release in the direction of lower frequencies using a low pass filter. After that, it is transmitted toward a shaper circuit for improving the unique binary data like the output. Here shaper circuit is a Schmitt trigger or comparator circuit.

DPSK Advantages and Disadvantages

The advantages of DPSK include the following.

  • This modulation doesn’t need the carrier signals at the end of the receiver circuit. Therefore compound circuits are not required.
  • The BW of DPSK requirement is low evaluated to BPSK modulation.
  • Non-consistent receivers are simple and inexpensive to construct, therefore extensively used in wireless communication.

The disadvantages of DPSK include the following.

  • The bit error rate or chance of error is high in DPSK contrast to BPSK.
  • The interference of noise in DPSK is more.
  • This modulation employs two consecutive bits intended for its response. Thus error in primary bit makes error within a subsequent bit as well as consecutively error spreads.

Differential Phase Shift Keying Applications

The applications of DPSK include the following.

The applications of differential phase-shift keying mainly include wireless communications like RFID, WLANs, and Bluetooth. The famous application among them is Bluetooth wherever alternatives of DPSK has been used like 8-DPSK, and π/4 – DQPSK modulation

Thus, DPSK is a general type of phase modulation and it is used to transmit data through the carrier wave by changing its phase. This type of PSK removes the need for a consistent reference signal at the end of the receiver by adding two fundamental operations at the end of the transmitter. Here is a question for you, what is the difference between DPSK and BPSK?

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