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Modulate using DQPSK method


The DQPSKModulator object modulates using the differential quadrature phase shift keying method. The output is a baseband representation of the modulated signal.

To modulate a signal using differential quadrature phase shift keying:

  1. Define and set up your DQPSK modulator object. See Construction.

  2. Call step to modulate a signal according to the properties of comm.DQPSKModulator. The behavior of step is specific to each object in the toolbox.


Starting in R2016b, instead of using the step method to perform the operation defined by the System object™, you can call the object with arguments, as if it were a function. For example, y = step(obj,x) and y = obj(x) perform equivalent operations.


H = comm.DQPSKModulator creates a modulator System object, H. This object modulates the input signal using the differential quadrature phase shift keying (DQPSK) method.

H = comm.DQPSKModulator(Name,Value) creates a DQPSK modulator object, H, with each specified property set to the specified value. You can specify additional name-value pair arguments in any order as (Name1,Value1,...,NameN,ValueN).

H = comm.DQPSKModulator(PHASE,Name,Value) creates a DQPSK modulator object, H. This object has the PhaseRotation property set to PHASE and the other specified properties set to the specified values.



Additional phase shift

Specify the additional phase difference between previous and current modulated symbols in radians as a real scalar value. The default is pi/4. This value corresponds to the phase difference between previous and current modulated symbols when the input is zero.


Assume bit inputs

Specify whether the input is bits or integers. The default is false. When you set this property to true, the step method input must be a column vector of bit values. The length of this vector is an integer multiple of two. This vector contains bit representations of integers between 0 and 3. When you set this property to false, the step method input must be a column vector of integer symbol values between 0 and 3.


Constellation encoding

Specify how the object maps an integer or group of two input bits to the corresponding symbol as one of Binary | Gray. The default is Gray. When you set this property to Gray, the object uses a Gray-encoded signal constellation. When you set this property to Binary, the input integer m, between 0m3 shifts the output phase. This shift is (PhaseRotation + 2×π×m4) radians from the previous output phase. The output symbol is exp(j×PhaseRotation + j×2×π×m4)×(previously modulated symbol).


Data type of output

Specify output data type as one of double | single. The default is double.


stepModulate using DQPSK method
Common to All System Objects

Allow System object property value changes


Reset internal states of System object


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Create a DQPSK modulator and demodulator pair. Create an AWGN channel object having two bits per symbol.

dqpskmod = comm.DQPSKModulator('BitInput',true);
dqpskdemod = comm.DQPSKDemodulator('BitOutput',true);
channel = comm.AWGNChannel('EbNo',6,'BitsPerSymbol',2);

Create an error rate calculator. Set the ComputationDelay property to 1 to account for the one bit transient caused by the differential modulation

errorRate = comm.ErrorRate('ComputationDelay',1);

Main processing loop steps:

  • Generate 50 2-bit frames

  • 8-DPSK modulate

  • Pass through AWGN channel

  • 8-DPSK demodulate

  • Collect error statistics

for counter = 1:100
    txData = randi([0 1],100,1);
    modSig = dqpskmod(txData);
    rxSig = channel(modSig);
    rxData = dqpskdemod(rxSig);
    errorStats = errorRate(txData,rxData);

Display the error statistics.

ber = errorStats(1)
ber = 0.0170
numErrors = errorStats(2)
numErrors = 170
numBits = errorStats(3)
numBits = 9999


This object implements the algorithm, inputs, and outputs described on the DQPSK Modulator Baseband block reference page. The object properties correspond to the block parameters.

Extended Capabilities

Version History

Introduced in R2012a