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Demodulate using DQPSK method


The DQPSKDemodulator object demodulates a signal that was modulated using the differential quadrature phase shift keying method. The input is a baseband representation of the modulated signal.

To demodulate a signal that was modulated using differential quadrature phase shift keying:

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

  2. Call step to demodulate a signal according to the properties of DQPSKDemodulator. 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.DQPSKDemodulator creates a demodulator System object, H. This object demodulates the input signal using the differential quadrature phase shift keying (DQPSK) method.

H = comm.DQPSKDemodulator(Name,Value) creates a DQPSK demodulator 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.DQPSKDemodulator(PHASE,Name,Value) creates a DQPSK demodulator 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. The default is pi/4. This value corresponds to the phase difference between previous and current modulated symbols when the input is zero.


Output data as bits

Specify whether the output consists of groups of bits or integer symbol values. The default is false. When you set this property to true the step method outputs a column vector of bit values with length equal to twice the number of demodulated symbols. When you set this property to false, the step method outputs a column vector, of length equal to the input data vector, that contains integer symbol values between 0 and 3.


Constellation encoding

Specify how the object maps an integer or group of 2 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 integer m, between 0m3 maps to the current symbol as exp(j×PhaseRotation + j×2×π×m4)×(previously modulated symbol).


Data type of output

Specify the output data type as one of Full precision | Smallest unsigned integer | double | single | int8 | uint8 | int16 | uint16 | int32 | uint32. The default is Full precision. When you set this property to Full precision the output has the same data type as that of the input. In this case, the input data type is single- or double-precision value. When you set the BitOutput property to true, logical data type becomes a valid option.


stepDemodulate using DQPSK method
Common to All System Objects

Allow System object property value changes


Reset internal states of System object


collapse all

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 Demodulator Baseband block reference page. The object properties correspond to the block parameters.

Extended Capabilities

Version History

Introduced in R2012a