comm.PhaseFrequencyOffset

Apply phase and frequency offsets to input signal

Description

The comm.PhaseFrequencyOffset System object™ applies phase and frequency offsets to an input signal.

To apply phase and frequency offsets to an input signal:

1. Create the comm.PhaseFrequencyOffset 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?

Creation

Syntax

pfo = comm.PhaseFrequencyOffset

pfo = comm.PhaseFrequencyOffset(Name=Value)

Description

pfo = comm.PhaseFrequencyOffset creates a phase and frequency offset object.

pfo = comm.PhaseFrequencyOffset(Name=Value) specifies additional properties using name-value arguments. For example, comm.PhaseFrequencyOffset(SampleRate=20) creates a phase and frequency offset object and sets a sample rate of 20 Hz. You can specify additional name-value pair arguments in any order as (Name1=Value1,...,NameN=ValueN).

Properties

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.

PhaseOffset — Phase offset

0 (default) | scalar | vector | matrix

Phase offset in degrees, specified as a scalar, vector, or matrix. For more information, see Interdependent Offset-I/O Dimensions.

Tunable: Yes

FrequencyOffsetSource — Frequency offset source

"Property" (default) | "Input port"

Frequency offset source, specified as one of these values.

• "Property" — Specify the frequency offset using the FrequencyOffset property.

• "Input port" — Specify the frequency offset in the fOffset input argument.

FrequencyOffset — Frequency offset

0 (default) | scalar | vector | matrix

Frequency offset in Hz, specified as a scalar, vector, or matrix. For more information, see Interdependent Offset-I/O Dimensions.

Tunable: Yes

Dependency

To enable this property, set the FrequencyOffsetSource property to "Property".

SampleRate — Sample rate

1 (default) | positive scalar

Sample rate of the input signal in Hz, specified as a positive scalar.

Usage

Syntax

Y = pfo(X)

Y = pfo(X,fOffset)

Description

Y = pfo(X) applies phase and frequency offsets to an input signal. To use this syntax, set the FrequencyOffsetSource to "Property".

Y = pfo(X,fOffset) specifies the frequency offset to apply to X. To use this syntax, set the FrequencyOffsetSource to "Input port".

Input Arguments

X — Input signal

scalar | vector | matrix

Input signal, specified as a scalar, vector, or matrix. For more information, see Interdependent Offset-I/O Dimensions.

This object accepts variable-size inputs. After the object is locked, you can change the size of each input channel, but you cannot change the number of channels. For more information, see Variable-Size Signal Support with System Objects.

Data Types: single | double

fOffset — Frequency offset

scalar | vector | matrix

Frequency offset in Hz, specified as a scalar, vector, or matrix. For more information, see the description of the FrequencyOffset property and Interdependent Offset-I/O Dimensions.

Dependency

To enable this input, set the FrequencyOffsetSource property to "Input port".

Data Types: single | double

Output Arguments

Y — Output signal

scalar | vector | matrix

Output signal, returned with the same dimensions and data type as X.

Data Types: single | double

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:

release(obj)

Common to All System Objects

step	Run System object algorithm
release	Release resources and allow changes to System object property values and input characteristics
reset	Reset internal states of System object

Examples

Introduce Phase Offset to 16-QAM Signal

Introduce a phase offset to a 16-QAM signal and view its effect on the constellation.

Create a phase frequency offset System object™, setting the phase offset to 30 degrees.

pfo = comm.PhaseFrequencyOffset(PhaseOffset=30);

Generate random symbols and apply 16-QAM modulation.

M = 16;
data = (0:M-1)';
x = qammod(data,M);

Plot the 16-QAM constellation.

scatterplot(x);
title("Original Constellation")
xlim([-5 5])
ylim([-5 5])

Introduce a phase offset and plot the offset constellation.

y = pfo(x);
scatterplot(y);
title("Constellation After Phase Offset")
xlim([-5 5])
ylim([-5 5])

More About

Interdependent Offset-I/O Dimensions

This table outlines the interdependency of offset impairment-to-input signal dimensions. M is the number of samples per channel in the input signal and N is the number of channels.

Data I/O Dimension	Frame Size	Number of Channels	Acceptable Dimension of Frequency Offset and Phase Offset Impairment
Scalar	1	1	Scalar
M-by-1	M	1	1-by-1 M-by-1
1-by-N	1	N	1-by-1 1-by-N
M-by-N	M	N	1-by-1 1-by-N M-by-1 M-by-N

For example when you specify a phase offset or frequency offset:

• As a scalar, the same offset is applied to all elements of the input signal.

• As a 10-by-1 vector for a 10-by-3 input signal, each input channel applies the same set of offsets per sample. Specifically, the same offset is applied across the three channels.

• As a 1-by-3 vector for a 10-by-3 input signal, channels can define a specific offset per channel to apply to all samples in each channel.

• As a 10-by-3 matrix for a 10-by-3 input signal, the offsets are applied element-wise to the input signal.

• When you vary the input signal length, the offset must be either a scalar or a 1-by-N vector.

Algorithms

If the input signal is u(t), then the output signal is

$$y(t)=u(t)\cdot \left(\cos \left(2\pi {\displaystyle {\int }_0^{t}f\left(\tau \right)d\tau +\phi (t)}\right)+j\sin \left(2\pi {\displaystyle {\int }_0^{t}f\left(\tau \right)d\tau +\phi (t)}\right)\right)\text{,}$$

where f(t) is the frequency offset, and φ(t) is the phase offset.

The discrete-time output is given by

$$\begin{array}{l}y(0)=u(0)\left(\cos \left(\phi (0)\right)+j\sin \left(\phi (0)\right)\right)\text{ and }\\ y(i)=u(i)\left(\cos \left(2\pi {\displaystyle \sum _{n=0}^{i-1}f\left(n\right)\Delta t}+\phi (i)\right)+j\sin \left(2\pi {\displaystyle \sum _{n=0}^{i-1}f\left(n\right)\Delta t}+\phi (i)\right)\right)\text{,}\end{array}$$

where i > 0, and Δt is the sample time.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

See System Objects in MATLAB Code Generation (MATLAB Coder).

Version History

Introduced in R2012a

R2025a: Variable-size support

This support enables you to vary the length of the input signal each time you call the object. To vary the input signal length, the offset properties must be either a scalar or a 1-by-N vector. For more information, see Variable-Size Signal Support with System Objects.

R2025a: Remove code generation limitation

Allows tunability of the PhaseOffset property in code generated from MATLAB^®.

R2025a: N-by-1 and 1-by-M impairment dimensions will not be supported

The comm.PhaseFrequencyOffset System object issues a warning that support for N-by-1 and 1-by-M frequency offset and phase offset impairment dimensions will be removed in a future release. M is the number of samples per channel in the input signal and N is the number of channels.

Instead transpose impairment vector dimension to 1-by-N and M-by-1.