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(To be removed) Modulate using QPSK method

comm.QPSKModulator will be removed in a future release. Use pskmod instead. For information on updating your code, see Version History.


The comm.QPSKModulator object modulates a signal using the quadrature phase shift keying (QPSK) method. The output is a baseband representation of the modulated signal.

To modulate using the QPSK method:

  1. Create the comm.QPSKModulator object and set its properties.

  2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?



qpskmod = comm.QPSKModulator creates a System object™ to modulate input signals using the QPSK method.


qpskmod = comm.QPSKModulator(Name,Value) sets properties using one or more name-value arguments. For example, 'OutputDataType'='single' specifies output of the modulated signal values in single precision data type.

qpskmod = comm.QPSKModulator(phase,Name,Value) sets the PhaseOffset property to phase and optional name-value arguments. Specify phase in radians.


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Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

Phase of zeroth point of the signal constellation in radians, specified as a scalar.

Example: 'PhaseOffset',0 aligns the QPSK signal constellation points on the axes, {(1,0), (0,j), (-1,0), (0,-j)}.

Data Types: double

Option to provide input in bits, specified as a logical 0 (false) or 1 (true).

  • When this property is set to false, the input values must be integer representations of two-bit input segments in the range [0, 3].

  • When this property is set to true, the input must be a binary vector of even length. Element pairs are binary representations of integers.

Data Types: logical

Symbol encoding mapping of constellation bits, specified as 'Gray' or 'Binary'.

SettingConstellation Mapping for IntegersConstellation Mapping for BitsComment


Integer order Q1: 0, Q2: 1, Q3: 3, and Q4: 2

Bit order Q1: 00, Q2: 01, Q3: 11 and Q4: 10

Map symbols using Gray-coded ordering.


Integer order Q1: 0, Q2: 1, Q3: 2, and Q4: 3

Bit order Q1: 00, Q2: 01, Q3: 10 and Q4: 11

Map symbols using natural binary-coded ordering. The signal constellation maps to the complex value ej(PhaseOffset + (2πm/4)), where m is an integer in the range [0, 3].

Data Types: char

Data type assigned to output, specified as 'double', 'single', or 'Custom'.

Data Types: char

Fixed-Point Properties

Fixed-point data type of output, specified as a numerictype (Fixed-Point Designer) object with a signedness of Auto.


This property applies when you set the OutputDataType property to 'Custom'.



y = qpskmod(x) returns baseband-modulated output.

Input Arguments

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Input signal, specified as an NS-element column vector of integers or bits, where NS is the number of samples.

The setting of the BitInput property determines the interpretation of the input vector.

Data Types: double | int8 | logical | fi

Output Arguments

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Output QPSK-modulated signal, returned as a complex-valued vector.

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:


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constellationCalculate or plot ideal signal constellation
stepRun System object algorithm
releaseRelease resources and allow changes to System object property values and input characteristics
resetReset internal states of System object


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Estimate the bit error rate of a QPSK modulated signal filtered through an AWGN channel.

Create a QPSK modulator and demodulator pair that operate on bits.

qpskModulator = comm.QPSKModulator('BitInput',true);
qpskDemodulator = comm.QPSKDemodulator('BitOutput',true);

Create an AWGN channel object and an error rate counter.

channel = comm.AWGNChannel('EbNo',4,'BitsPerSymbol',2);
errorRate = comm.ErrorRate;

Generate random binary data and apply QPSK modulation.

data = randi([0 1],1000,1);
txSig = qpskModulator(data);

Pass the signal through the AWGN channel and demodulate it.

rxSig = channel(txSig);
rxData = qpskDemodulator(rxSig);

Calculate the error statistics. Display the BER.

errorStats = errorRate(data,rxData);

ans = 0.0100

Extended Capabilities

Version History

Introduced in R2012a

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R2023a: To be removed

comm.QPSKModulator will be removed in a future release. Use the pskmod function with the modulation order set to 4 to QPSK modulate the input signal.