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Scramble input signal


The comm.Scrambler object applies multiplicative scrambling to input data.

This schematic shows the multiplicative scrambler operation. The adders operate modulo N, where N is the value specified by the CalculationBase property.

At each time step, the input causes the contents of the registers to shift sequentially. Using the Polynomial property, you specify the on or off state for each switch in the scrambler.


To apply additive scrambling to input data, you can use the comm.PNSequence System object™ and the xor function. For an example, see Additive Scrambling of Input Data.

To scramble an input signal:

  1. Create the comm.Scrambler object and set its properties.

  2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?



scrambler = comm.Scrambler creates a scrambler System object. This object scrambles the input data by using a linear feedback shift register that you specify with the Polynomial property.


scrambler = comm.Scrambler(base,poly,cond) creates the scrambler object with the CalculationBase property set to base, the Polynomial property set to poly, and the InitialConditions property set to cond.

Example: comm.Scrambler(8,'1 + x^-2 + x^-3 + x^-5 + x^-7',[0 3 2 2 5 1 7]) sets the calculation base to 8, and the scrambler polynomial and initial conditions as specified.


scrambler = comm.Scrambler(___,Name,Value) sets properties using one or more name-value pairs and either of the previous syntaxes. Enclose each property name in single quotes.

Example: comm.Scrambler('CalculationBase',2)


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Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

Range of input data used in the scrambler for modulo operations, specified as a nonnegative integer. The input and output of this object are integers from 0 to CalculationBase1.

Data Types: double

Connections for linear feedback shift registers in the scrambler, specified as a character vector, integer vector, or binary vector. The Polynomial property defines if each switch in the scrambler is on or off. Specify the polynomial as:

  • A character vector, such as '1 + x^-6 + x^-8'. For more details on specifying polynomials in this way, see Representation of Polynomials in Communications Toolbox.

  • An integer vector, such as [0 -6 -8], listing the scrambler coefficients in order of descending powers of x-1, where p(x-1) = 1 + p1x-1 + p2x-2 + ...

  • A binary vector, such as [1 0 0 0 0 0 1 0 1], listing the powers of x that appear in the polynomial that have a coefficient of 1. In this case, the order of the scramble polynomial is one less than the binary vector length.

Example: '1 + x^-6 + x^-8', [0 -6 -8], and [1 0 0 0 0 0 1 0 1] all represent this polynomial:

p(x-1) = 1 + x-6 + x-8

Data Types: double | char

  • 'Property' – Specify scrambler initial conditions by using the InitialConditions property.

  • 'Input port' – Specify scrambler initial conditions by using an additional input argument, initcond, when calling the object.

Data Types: char

Initial conditions of scrambler registers when the simulation starts, specified as a nonnegative integer vector. The length of InitialConditions must equal the order of the Polynomial property. The vector element values must be integers from 0 to CalculationBase1.


This property is available when InitialConditionsSource is set to 'Property'.

Scrambler state reset port, specified as false or true. If ResetInputPort is true, you can reset the scrambler object by using an additional input argument, reset, when calling the object.


This property is available when InitialConditionsSource is set to 'Property'.




scrambledOut = scrambler(signal) scrambles the input signal. The output is the same data type and length as the input vector.


scrambledOut = scrambler(signal,initcond) provides an additional input with values specifying the initial conditions of the linear feedback shift register.

This syntax applies when you set the InitialConditionsSource property of the object to 'Input port'.

scrambledOut = scrambler(signal,reset) provides an additional input indicating whether to reset the state of the scrambler.

This syntax applies when you set InitialConditionsSource to 'Property' and ResetInputPort to true.

Input Arguments

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Input signal, specified as a column vector.

Example: scrambledOut = scrambler([0 1 1 0 1])

Data Types: double | logical

Initial scrambler register conditions when the simulation starts, specified as a nonnegative integer column vector. The length of initcond must equal the order of the Polynomial property. The vector element values must be integers from 0 to CalculationBase1.

Example: scrambledOut = scrambler(signal,[0 1 1 0]) corresponds to possible initial register states for a scrambler with a polynomial order of 4 and a calculation base of 2 or higher.

Data Types: double

Reset the initial state of the scrambler when the simulation starts, specified as a scalar. When the value of reset is nonzero, the object is reset before it is called.

Example: scrambledOut = scrambler(signal,0) scrambles the input signal without resetting the scrambler states.

Data Types: double

Output Arguments

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Scrambled output, returned as a column vector with the same data type and length as signal.

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:


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stepRun System object algorithm
releaseRelease resources and allow changes to System object property values and input characteristics
resetReset internal states of System object


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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, specifying the calculation base, polynomial, and initial conditions using input arguments. The scrambler and descrambler polynomials are specified with different but equivalent data formats.

N = 8;
scrambler = comm.Scrambler(N,'1 + x^-2 + x^-3 + x^-5 + x^-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 = 5×3

     6     7     6
     7     5     7
     1     7     1
     7     0     7
     5     3     5

Verify that the descrambled data matches the original data.

ans = logical

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

Create scrambler and descrambler System objects having a calculation base of 4. Set the InitialConditionsSource property to 'Input port' so you can 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');

Preallocate memory for the error vector which will be used to store errors output by the symerr function.

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 descrambling 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);

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

errVec = 10×1


Digital communications systems commonly use additive scrambling to randomize input data to aid in timing synchronization and power spectral requirements. The comm.Scrambler System object™ implements multiplicative scrambling but does not support additive scrambling. To perform additive scrambling you can use the comm.PNSequence System object. This example implements the additive scrambling specified in IEEE 802.11™ by scrambling input data with an output sequence generated by the comm.PNSequence System object. For a Simulink® model that implements a similar workflow, see the Additive Scrambling of Input Data in Simulink example.

This figure shows an additive scrambler, that uses the generator polynomial x7+x4+1, as specified in figure 17-7 of IEEE 802.11 Section [1].

Comparing the shift register specified in 802.11 with the shift register implementated using a comm.PNSequence System object, note that the two shift register schematics are mirror images of each other. Therefore, when configuring the comm.PNSequence System object to implement an additive scrambler, you must reverse values for the generator polynomial, the initial states, and the mask output. To take the output of the register from the leading end, specify a shift value of 7.

For more information about the 802.11 scrambler, see [1] and the wlanScramble (WLAN Toolbox) reference page.

Define variables for the generator polynomial, shift value for the output, an initial shift register state, a frame of input data, and a variable containing the 127-bit scrambler sequence specified in section of the IEEE 802.11 standard. Create a PN sequence object that initializes the registers by using an input argument.

genPoly = 'x^7 + x^3 + 1';   % Generator polynomial
shift = 7;                   % Shift value for output
spf = 127;                   % Samples per frame
initState = [1 1 1 1 1 1 1]; % Initial shift register state
dataIn = randi([0 1],spf,1);
ieee802_11_scram_seq = logical([ ...
    0 0 0 0 1 1 1 0 1 1 1 1 0 0 1 0 1 1 0 0 1 ...
    0 0 1 0 0 0 0 0 0 1 0 0 0 1 0 0 1 1 0 0 0 ...
    1 0 1 1 1 0 1 0 1 1 0 1 1 0 0 0 0 0 1 1 0 ...
    0 1 1 0 1 0 1 0 0 1 1 1 0 0 1 1 1 1 0 1 1 ...
    0 1 0 0 0 0 1 0 1 0 1 0 1 1 1 1 1 0 1 0 0 ...
    1 0 1 0 0 0 1 1 0 1 1 1 0 0 0 1 1 1 1 1 1 1])';

pnSeq = comm.PNSequence( ...
    Polynomial=genPoly, ...
    InitialConditionsSource="Input Port", ...
    Mask=shift, ...
    SamplesPerFrame=spf, ...
pnsequence = pnSeq(initState);

Compare the PN sequence object output to the IEEE 802.11 127-bit scrambler sequence to confirm the generated PN sequence matches the 802.11 specified sequence.

ans = logical

Scramble input data according to the 802.11 specified additive scrambler by modulo-adding input data with the PN sequence output.

scrambledOut = xor(dataIn,pnSeq(initState));

Descramble the scrambled data by applying the same scrambler and initial conditions to the scrambled data.

descrambledData = xor(scrambledOut,pnSeq(initState));

Verify that the descrambled data matches the input data.

ans = logical


[1] IEEE Std 802.11™-2020 (Revision of IEEE Std 802.11™-2016). "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications." IEEE Standard for Information technology — Telecommunications and information exchange between systems. Local and metropolitan area networks — Specific requirements.

Extended Capabilities

Version History

Introduced in R2012a