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Modulate using BPSK method


The comm.BPSKModulator object modulates using the binary phase shift keying method. The output is a baseband representation of the modulated signal. The input signal must be a discrete-time binary-valued signal. If the input bit is 0 or 1, then the modulated symbol is exp(jθ) or -exp(jθ), respectively. The PhaseOffset property specifies the value of θ in radians.

To modulate a signal using BPSK method:

  1. Create the comm.BPSKModulator 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?




bpskmodulator = comm.BPSKModulator creates a modulator System object™ to modulate input signals using the binary phase shift keying (BPSK) method.

bpskmodulator = comm.BPSKModulator(Name,Value) creates a BPSK modulator object 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).

bpskmodulator = comm.BPSKModulator(phase,Name,Value) creates a BPSK modulator object with the PhaseOffset property set to phase, and the other specified properties set to the specified values.


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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 constellation in radians, specified as a scalar.

Data Types: double

Output datatype, specified as 'double', 'single' or 'Custom'.

Data Types: char

Fixed-Point Properties

Fixed-point data type of the 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'.




waveform = bpskmodulator(data) applies BPSK modulation to the input data and returns the modulated BPSK baseband signal.

Input Arguments

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Input signal data, specified as a column vector or matrix.

Data Types: double

Output Arguments

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BPSK modulated baseband signal, returned as a column vector or matrix of the same size as the input signal. For more information about the output datatype, see the OutputDataType property.

Data Types: double | single | fi
Complex Number Support: Yes

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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This example creates binary data, modulates it, and then displays the data using a scatter plot.

Create binary data symbols

data = randi([0 1],100,1);

Create a BPSK modulator System object

bpskModulator = comm.BPSKModulator;

Change the phase offset to pi/16

bpskModulator.PhaseOffset = pi/16;

Modulate and plot the data

modData = bpskModulator(data);

Figure Scatter Plot contains an axes object. The axes object with title Scatter plot contains an object of type line. This object represents Channel 1.


Phase modulation is a linear baseband modulation technique in which the message modulates the phase of a constant amplitude signal. Binary Phase Shift Keying (BPSK) is a two phase modulation scheme, where the 0’s and 1’s in a binary message are represented by two different phase states in the carrier signal


for (n1)TbtnTb, n=1,2, 3,where:

  • ϕn = πm, m∈{0,1}.

  • Eb is the energy per bit.

  • Tb is the bit duration.

  • fc is the carrier frequency.

In MATLAB®, the baseband representation of a BPSK signal is


The BPSK signal has two phases: 0 and π. The probability of a bit error in an AWGN channel is


where N0 is the noise power spectral density.

Extended Capabilities

Introduced in R2012a