# comm.PSKModulator System object

Package: comm

Modulate using M-ary PSK method

## Description

The `PSKModulator` object modulates using the M-ary phase shift keying method. The output is a baseband representation of the modulated signal. The M-ary number parameter, M, is the number of points in the signal constellation.

To modulate a signal using phase shift keying:

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

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

## Construction

`H = comm.PSKModulator` creates a modulator System object™, `H`. This object modulates the input signal using the M-ary phase shift keying (M-PSK) method.

`H = comm.PSKModulator(Name,Value)` creates an M-PSK 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.PSKModulator(M,PHASE,Name,Value)` creates an M-PSK modulator object, `H`. This object has the `ModulationOrder` property set to `M`, the `PhaseOffset` property set to `PHASE`, 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 a positive, integer scalar value. The default is `8`. `PhaseOffset` Phase of zeroth point of constellation Specify the phase offset of the zeroth point of the constellation, in radians, as a real scalar value. The default is `pi/8`. `BitInput` Assume bit inputs Specify whether the input is bits or integers. When you set this property to `true`, the `step` method input must be a column vector of bit values. This vector must have a length that is an integer multiple of log2(`ModulationOrder`). This vector contains bit representations of integers between `0` and `ModulationOrder`-`1`. When you set the `BitInput` property to `false`, the `step` method input must be a column vector of numeric data type integer symbol values. These values must be between `0` and `ModulationOrder`-`1`. The default is `false`. `SymbolMapping` Constellation encoding Specify how the object maps an integer or group of log2(`ModulationOrder`) input bits to the corresponding symbol as one of `Binary` | `Gray` | `Custom`. The default is `Gray`. When you set this property to `Gray`, the object uses a Gray-encoded signal constellation. When you set this property to `Binary`, the integer m, between `0` $\le m\le$`ModulationOrder`–`1`) maps to the complex value exp(j$×$`PhaseOffset` + j `2` $\pi$ m/`ModulationOrder`). 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. This property requires a row or column vector of size `ModulationOrder` and must have unique integer values in the range [`0`, `ModulationOrder`–`1`]. The values must be of data type `double`. The first element of this vector corresponds to the constellation point at an angle of `0` + `PhaseOffset`, with subsequent elements running counterclockwise. The last element corresponds to the constellation point at an angle of – /`ModulationOrder` + `PhaseOffset`. This property applies when you set the `SymbolMapping` property to `Custom`. The default is `0:7`. `OutputDataType` Data type of output Specify the output data type as `double` | `single` | `Custom`. The default is `double`.

## Methods

 clone Create PSK modulator object with same property values constellation Calculate or plot ideal signal constellation 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 step Modulate using M-ary PSK method

## Examples

Modulate data using 16-PSK modulation, and visualize the data in a scatter plot.

``` % Create binary data for 24, 4-bit symbols data = randi([0 1],96,1); % Create a 16-PSK modulator System object with bits as inputs and Gray-coded signal constellation hModulator = comm.PSKModulator(16,'BitInput',true); % Change the phase offset to pi/16 hModulator.PhaseOffset = pi/16; % Modulate and plot the data modData = step(hModulator, data); constellation(hModulator)```

## Algorithms

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

## See Also

#### Introduced in R2012a

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