comm.GeneralQAMModulator

Modulate using arbitrary QAM constellation

Description

The GeneralQAMModulator object modulates using quadrature amplitude modulation. The output is a baseband representation of the modulated signal.

To modulate a signal using quadrature amplitude modulation:

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

2. Call step to modulate a signal according to the properties of comm.GeneralQAMModulator. 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.GeneralQAMModulator creates a modulator System object, H. This object modulates the input signal using a general quadrature amplitude modulation (QAM) method.

H = comm.GeneralQAMModulator(Name,Value) creates a 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.GeneralQAMModulator(CONST,Name,Value) creates a General QAM modulator object, H. This object has the Constellation property set to CONST, and the other specified properties set to the specified values.

Properties

Constellation

Signal constellation Specify the constellation points as a vector of real or complex double-precision data type. The default is exp($$2\times \pi \times 1i\times \raisebox{1ex}{$(0:7)$}\!\left/ \!\raisebox{-1ex}{$8$}\right.$$). The length of the vector determines the modulation order. The step method inputs requires integers between 0 and M–1, where M indicates the length of this property vector. The object maps an input integer m to the (m+1)st value in the Constellation vector.

OutputDataType

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

 Fixed-Point Properties

CustomOutputDataType

Fixed-point data type of output Specify the output fixed-point type as a numerictype (Fixed-Point Designer) object with a signedness of Auto. The default is numerictype([],16). This property applies when you set the OutputDataType property to Custom.

Methods

step	Modulate using arbitrary QAM constellation

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

Examples

Modulate data using an arbitrary 3-point constellation. Then, visualize the data in a scatter plot

       hQAMMod = comm.GeneralQAMModulator;     
  % Setup a three point constellation
       hQAMMod.Constellation = [1 1i -1];
       data = randi([0 2],100,1);
       modData = step(hQAMMod, data);
       scatterplot(modData)

Algorithms

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

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