Contents

comm.DQPSKModulator System object

Package: comm

Modulate using DQPSK method

Description

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

To modulate a signal using differential quaternary 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.

Construction

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.

Properties

PhaseRotation

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.

BitInput

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.

SymbolMapping

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).

OutputDataType

Data type of output

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

Methods

cloneCreate DQPSK modulator object with same property values
getNumInputsNumber of expected inputs to step method
getNumOutputsNumber of outputs from step method
isLockedLocked status for input attributes and nontunable properties
releaseAllow property value and input characteristics changes
resetReset states of DQPSK modulator object
stepModulate using DQPSK method

Examples

Modulate data using DQPSK modulation and visualize the data in a scatter plot.

 % Create binary data for 100, 4 bit symbols
    data = randi([0 1],400,1);
 % Create a DQPSK modulator System object with bits as inputs,phase rotation of pi/8, and Gray-coded constellation
    hModulator = comm.DQPSKModulator(pi/8,'BitInput',true);
 % Modulate and plot the data
    modData = step(hModulator, data);
    scatterplot(modData)

Algorithms

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.

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