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Demodulate using DBPSK method


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

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

  1. Define and set up your DBPSK demodulator object. See Construction.

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

H = comm.DBPSKDemodulator(Name,Value) creates a DBPSK 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.DBPSKDemodulator(PHASE,Name,Value) creates a DBPSK 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 bits in radians as a real scalar. The default is 0. This value corresponds to the phase difference between previous and current modulated bits when the input is zero.


Data type of output

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


stepDemodulate using DBPSK method
Common to All System Objects

Allow System object property value changes


Reset internal states of System object


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Create a DBPSK modulator and demodulator pair.

dbpskmod = comm.DBPSKModulator(pi/4);
dpbpskdemod = comm.DBPSKDemodulator(pi/4);

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-bit frames

  • DBPSK modulate

  • Pass through AWGN channel

  • DBPSK demodulate

  • Collect error statistics

for counter = 1:100
    txData = randi([0 1],50,1);
    modSig = dbpskmod(txData);
    rxSig = awgn(modSig,7);
    rxData = dpbpskdemod(rxSig);
    errorStats = errorRate(txData,rxData);

Display the error statistics.

ber = errorStats(1)
ber = 0.0040
numErrors = errorStats(2)
numErrors = 20
numBits = errorStats(3)
numBits = 4999


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

Extended Capabilities

Version History

Introduced in R2012a