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comm.RectangularQAMModulator System object

Package: comm

Modulate using rectangular QAM signal constellation

Description

The RectangularQAMModulator object modulates using M-ary quadrature amplitude modulation with a constellation on a rectangular lattice. The output is a baseband representation of the modulated signal. This block accepts a scalar or column vector input signal.

To modulate a signal using quadrature amplitude modulation:

  1. Define and set up your rectangular QAM modulator object. See Construction.

  2. Call step to modulate the signal according to the properties of comm.RectangularQAMModulator. The behavior of step is specific to each object in the toolbox.

Construction

H = comm.RectangularQAMModulator creates a modulator object, H. This object modulates the input using the rectangular quadrature amplitude modulation (QAM) method.

H = comm.RectangularQAMModulator(Name,Value) creates a rectangular QAM 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.RectangularQAMModulator(M,Name,Value) creates a rectangular QAM modulator object, H. This object has the ModulationOrder property set to M, and the other specified properties set to the specified values.

Properties

ModulationOrder

Number of points in signal constellation

Specify the number of points in the signal constellation as scalar value that is a positive integer power of two. The default is 16.

PhaseOffset

Phase offset of constellation

Specify the phase offset of the signal constellation, in radians, as a real scalar value. The default is 0.

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 requires a column vector of bit values. The length of this vector must an integer multiple of log2(ModulationOrder). This vector contains bit representations of integers between 0 and ModulationOrder1. When you set this property to false, the step method input must be a column vector of integer symbol values between 0 and ModulationOrder1.

SymbolMapping

Constellation encoding

Specify how the object maps an integer or group of log2(ModulationOrder) input bits to the corresponding symbol as Binary | Gray | Custom. The default is Gray. When you set this property to Gray, the System object™ uses a Gray-coded signal constellation. When you set this property to Binary, the object uses a natural binary-coded constellation. When you set this property to Custom, the object uses the signal constellation defined in the CustomSymbolMapping property.

CustomSymbolMapping

Custom constellation encoding

Specify a custom constellation symbol mapping vector. The default is 0:15. This property is a row or column vector with a size of ModulationOrder. This vector has unique integer values in the range [0, ModulationOrder1]. These values must be of data type double. The first element of this vector corresponds to the top-leftmost point of the constellation, with subsequent elements running down column-wise, from left to right. The last element corresponds to the bottom-rightmost point. This property applies when you set the SymbolMapping property to Custom.

NormalizationMethod

Constellation normalization method

Specify the method used to normalize the signal constellation as Minimum distance between symbols | Average power | Peak power. The default is Minimum distance between symbols.

MinimumDistance

Minimum distance between symbols

Specify the distance between two nearest constellation points as a positive, real, numeric scalar value. The default is 2. This property applies when you set the NormalizationMethod property to Minimum distance between symbols.

AveragePower

Average power of constellation

Specify the average power of the symbols in the constellation as a positive, real, numeric scalar value. The default is 1. This property applies when you set the NormalizationMethod property to Average power.

PeakPower

Peak power of constellation

Specify the maximum power of the symbols in the constellation as a positive real, numeric scalar value. The default is 1. This property applies when you set the NormalizationMethod property to Peak power.

OutputDataType

Data type of output

Specify the output data type as double | single | Custom. The default is double.

 Fixed-Point Properties

Methods

cloneCreate rectangular QAM modulator object with same property values
constellationCalculate or plot ideal signal constellation
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
stepModulate using rectangular QAM method

Examples

Modulate data using rectangular QAM modulation, and visualize the data in a scatter plot.

% Create binary data for 32, 3-bit symbols
    data = randi([0 1],96,1);
% Create a rectangular 8-QAM modulator System object with bits as inputs and Gray-coded signal constellation
    hModulator = comm.RectangularQAMModulator(8,'BitInput',true);
% Rotate the constellation by pi/4 radians
    hModulator.PhaseOffset = pi/4;
% Modulate and plot the data
    modData = step(hModulator, data); 
    constellation(hModulator)

Algorithms

This object implements the algorithm, inputs, and outputs described on the Rectangular QAM Modulator Baseband block reference page. The object properties correspond to the block parameters.

See Also

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