# Documentation

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# comm.Scrambler System object

Package: comm

Scramble input signal

## Description

The `Scrambler` object scrambles a scalar or column vector input signal.

To scramble the input signal:

1. Define and set up your scrambler object. See Construction.

2. Call `step` to scramble the input signal according to the properties of `comm.Scrambler`. 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.Scrambler` creates a scrambler System object, `H`. This object scrambles the input data using a linear feedback shift register that you specify with the Polynomial property.

`H = comm.Scrambler(Name,Value)` creates a scrambler 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.Scrambler(N,POLY,COND,Name,Value)` creates a scrambler object, `H`. This object has the `CalculationBase` property set to `N`, the `Polynomial` property set to `POLY`, the `InitialConditions` property set to `COND`, and the other specified properties set to the specified values.

## Properties

 `CalculationBase` Range of input data Specify calculation base as a positive, integer, scalar value. Set the calculation base property to one greater than the number of input values. The `step` method input and output integers are in the range [0, CalculationBase–1]. The default is `4`. `Polynomial` Linear feedback shift register connections Specify the polynomial that determines the shift register feedback connections. The default is `'1+ z^-1 + z^-2 + z^-4'`. You can specify the generator polynomial as a character vector or as a numeric, binary vector that lists the coefficients of the polynomial in order of ascending powers of z–1, where p(z–1) = 1 + p1z-1 + p2z-2 + ... is the generator polynomial. The first and last elements must be `1`. Alternatively, you can specify the generator polynomial as a numeric vector. This vector must contain the exponents of z–1 for the nonzero terms of the polynomial, in order of ascending powers of z–1. In this case, the first vector element must be `0`. For example, `'1+ z^-6 + z^-8'`, ```[1 0 0 0 0 0 1 0 1]```, and `[0 -6 -8]` specify the same polynomial $p\left({z}^{-1}\right)=1+{z}^{-6}+{z}^{-8}$. `InitialConditionsSource` Source of initial conditions Specify the source of the `InitialConditions` property as either `Property` or `Input port`. If set to `Input port`, the initial conditions are provided as an input argument to the `step` function. The default value is `Property`. `InitialConditions` Initial values of linear feedback shift register Specify the initial values of the linear feedback shift register as an integer row vector with values in [0 CalculationBase–1]. The default is `[0 1 2 3]`. The length of this property vector must equal the order of the `Polynomial` property vector. This property is available when `InitialConditionsSource` is set to `Property`. `ResetInputPort` Scrambler state reset port Specify the creation of an input port that is used to reset the state of the scrambler. If `ResetInputPort` is `true`, the scrambler is reset when a nonzero input argument is provided to the `step` function. The default value is `false`. This property is available when `InitialConditionsSource` is set to `Property`.

## Methods

 clone Create scrambler 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 scrambler object step Scramble input signal

## Examples

expand all

Scramble and descramble 8-ary data using `comm.Scrambler` and `comm.Descrambler` System objects™ having a calculation base of 8.

Create scrambler and descrambler objects while specifying the generator polymomial and initial conditions using name-value pairs. Note that the scrambler and descrambler polynomials are specified with different but equivalent syntaxes.

```N = 8; scrambler = comm.Scrambler(N,'1 + z^-2 + z^-3 + z^-5 + z^-7', ... [0 3 2 2 5 1 7]); descrambler = comm.Descrambler(N,[1 0 1 1 0 1 0 1], ... [0 3 2 2 5 1 7]); ```

Scramble and descramble random integers. Display the original data, scrambled data, and descrambled data sequences.

```data = randi([0 N-1],5,1); scrData = scrambler(data); deScrData = descrambler(scrData); [data scrData deScrData] ```
```ans = 6 7 6 7 5 7 1 7 1 7 0 7 5 3 5 ```

Verify the descrambled data matches the original data.

```isequal(data,deScrData) ```
```ans = logical 1 ```

Scramble and descramble quaternary data while changing the initial conditions between function calls.

Create scrambler and descrambler System objects™. Set the `InitialConditionsSource` property to `Input port` to be able to set the initial conditions as an argument to the object.

```N = 4; scrambler = comm.Scrambler(N,'1 + z^-3','InitialConditionsSource','Input port'); descrambler = comm.Descrambler(N,'1 + z^-3','InitialConditionsSource','Input port'); ```

Allocate memory for `errVec`.

```errVec = zeros(10,1); ```

Scramble and descramble random integers while changing the initial conditions, `initCond`, each time the loop executes. Use the `symerr` function to determine if the scrambling and descrambing operations result in symbol errors.

```for k = 1:10 initCond = randperm(3)'; data = randi([0 N-1],5,1); scrData = scrambler(data,initCond); deScrData = descrambler(scrData,initCond); errVec(k) = symerr(data,deScrData); end ```

Examine `errVec` to verify that the output from the descrambler matches the original data.

```errVec ```
```errVec = 0 0 0 0 0 0 0 0 0 0 ```

## Algorithms

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