comm.PhaseFrequencyOffset

Apply phase and frequency offsets to input signal

Description

The PhaseFrequencyOffset object applies phase and frequency offsets to an incoming signal.

To apply phase and frequency offsets to the input signal:

1. Define and set up your phase frequency offset object. See Construction.

2. Call step to apply phase and frequency offsets to the input signal according to the properties of comm.PhaseFrequencyOffset. The behavior of step is specific to each object in the toolbox.

Note

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.

Construction

H = comm.PhaseFrequencyOffset creates a phase and frequency offset System object, H. This object applies phase and frequency offsets to an input signal.

H = comm.PhaseFrequencyOffset(Name,Value) creates a phase and frequency offset 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).

Properties

PhaseOffset	Phase offset Specify the phase offset in degrees. The default is 0. If the step method input is an M-by-N matrix, the PhaseOffset property can be set to a numeric scalar, an M-by-1, or 1-by-N numeric vector, or an M-by-N numeric matrix. For more information, see Interdependent Property-Input Dimensions. Tunable: Yes
FrequencyOffsetSource	Source of frequency offset Specify the source of the frequency offset as one of Property | Input port. The default is Property. If you set this property to Property, you can specify the frequency offset using the FrequencyOffset property. If you set this property to Input port, you specify the frequency offset as a step method input.
FrequencyOffset	Frequency offset Specify the frequency offset in Hz. The default is 0. If the step method input is an M-by-N matrix, then the FrequencyOffset property is a numeric scalar, an M-by-1, or 1-by-N numeric vector, or an M-by-N numeric matrix. For more information, see Interdependent Property-Input Dimensions. This property applies when you set the FrequencyOffsetSource property to Property. Tunable: Yes
SampleRate	Sample rate Specify the sample rate of the input samples in Hz as a double-precision, real, positive scalar value. The default is 1.

Methods

step	Apply phase and frequency offsets to input signal

Common to All System Objects
release	Allow System object property value changes

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™. Set 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)';
modData = qammod(data,M);

Plot the 16-QAM constellation.

scatterplot(modData);
title(' Original Constellation')
xlim([-5 5])
ylim([-5 5])

Introduce a phase offset using pfo and plot the offset constellation. Note that it has been shifted 30 degrees.

impairedData = pfo(modData);
scatterplot(impairedData);
title('Constellation after phase offset')
xlim([-5 5])
ylim([-5 5])

More About

Interdependent Property-Input Dimensions

This table outlines the interdependency of property-to-input argument dimensions.

Number of Dimensions	Data I/O Dimension	Frame Size	Number of Channels	Frequency/Phase Offset Property Dimension	Frequency Offset Input Argument Dimension
Any	Scalar	1	1	Scalar	Scalar
2	M-by-1	M	1	M-by-1 1-by-M 1-by-1	M M-by-1 1 1-by-1
2	1-by-N	1	N	N-by-1 1-by-N 1-by-1	N 1-by-N 1 1-by-1
2	M-by-N	M	N	M-by-N N-by-1 1-by-N M-by-1 1-by-M 1-by-1	M-by-N N 1-by-N 1 1-by-1 M M-by-1

For example:

• When you specify a scalar offset property, the object applies the same offset to all elements of the input signal

• When you specify a 2-by-1 offset property for a 2-by-3 input signal (one offset value per sample), the object applies the same sample offset across the three channels.

• When you specify a 1-by-3 offset property for a 2-by-3 input signal (one offset value per channel), the same channel offset is applied across the two samples of a channel.

• When you specify a 2-by-3 offset property for a 2-by-3 input signal (one offset value per sample for each channel), the offsets are applied element-wise to the input signal.

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).