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# comm.RectangularQAMTCMModulator System object

Package: comm

Convolutionally encode binary data and map using rectangular QAM signal constellation

## Description

The RectangularQAMTCMModulator object implements trellis-coded modulation (TCM) by convolutionally encoding the binary input signal and mapping the result to a rectangular QAM signal constellation.

To convolutionally encode binary data and map the result using a rectangular QAM constellation:

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

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

## Construction

H = comm.RectangularQAMTCMModulator creates a trellis-coded, rectangular, quadrature amplitude (QAM TCM) System object™, H. This object convolutionally encodes a binary input signal and maps the result to a rectangular QAM constellation.

H = comm.RectangularQAMTCMModulator(Name,Value) creates a rectangular QAM TCM 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.RectangularQAMTCMModulator(TRELLIS,Name,Value) creates a rectangular QAM TCM modulator object, H. This object has the TrellisStructure property set to TRELLIS and the other specified properties set to the specified values.

## Properties

 TrellisStructure Trellis structure of convolutional code Specify trellis as a MATLAB structure that contains the trellis description of the convolutional code. Use the istrellis function to check whether a structure is a valid trellis. The default is the result of poly2trellis([3 1 1], [ 5 2 0 0; 0 0 1 0; 0 0 0 1]). TerminationMethod Termination method of encoded frame Specify the termination method as Continuous | Truncated | Terminated. The default is Continuous. When you set this property to Continuous, the object retains the encoder states at the end of each input vector for use with the next input vector. When you set this property to Truncated, the object treats each input vector independently. The encoder is reset to the all-zeros state at the start of each input vector. When you set this property to Terminated, the object treats each input vector independently. For each input vector, the object uses extra bits to set the encoder to the all-zeros state at the end of the vector. For a rate K/N code, the step method outputs the vector with a length given by $y=N×\left(L+S\right)}{K}$, where S = constraintLength–1 (or, in the case of multiple constraint lengths, S = sum(constraintLength(i)–1)). L is the length of the input to the step method. ResetInputPort Enable modulator reset input Set this property to true to enable an additional input to the step method. The default is false. When you set the reset input to the step method to a nonzero value, the object resets the encoder to the all-zeros state. This property applies when you set the TerminationMethod property to Continuous. ModulationOrder Number of points in signal constellation Specify the number of points in the signal constellation used to map the convolutionally encoded data as a positive integer scalar value equal to 4, 8, 16, 32, or 64. The default is 16. The value of the ModulationOrder property must equal the number of possible output symbols from the convolutional encoder of the QAM TCM modulator. Thus, the value for the ModulationOrder property must equal 2N for a rate K/N convolutional code. OutputDataType Data type of output Specify the output data type as one of double | single. The default is double.

## Methods

 clone Create rectangular QAM TCM modulator object with same property values getNumInputs Number of expected inputs to step method getNumOutputs Number of outputs from step method isLocked Locked status for input attributes and nontunable properties release Allow property value and input characteristics changes reset Reset states of the rectangular QAM TCM modulator object step Convolutionally encode binary data and map using rectangular QAM constellation

## Examples

expand all

### Modulate Data Using Rectangular QAM TCM

Modulate data using rectangular 16-QAM TCM modulation and display the scatter plot.

Generate random binary data. The length of the data vector must be an integer multiple of the number of input streams into the encoder, log2(8) = 3.

```data = randi([0 1],3000,1);
```

Create a modulator System object™ and use its step function to modulate the data.

```hMod = comm.RectangularQAMTCMModulator;
modData = step(hMod,data);
```

Plot the modulated data.

```scatterplot(modData)
```

## Algorithms

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