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wlanScramble

Scramble and descramble binary input sequence

Syntax

y = wlanScramble(bits,scramInit)

Description

example

y = wlanScramble(bits,scramInit) scrambles or descrambles the binary input bits for the specified initial scramble state, using a 127-length frame-synchronous scrambler. The frame-synchronous scrambler uses the generator polynomial defined in IEEE® 802.11™-2012, Section 18.3.5.5 and IEEE 802.11ad™-2012, Section 21.3.9. The same scrambler is used to scramble bits at the transmitter and descramble bits at the receiver.

Examples

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Create the scrambler initialization and the input sequence of random bits.

scramInit = 93;
bits = randi([0,1],1000,1);

Scramble and descramble the bits by using the scrambler initialization.

scrambledData = wlanScramble(bits,scramInit);
descrambledData = wlanScramble(scrambledData,scramInit);

Verify that the descrambled data matches the original data.

isequal(bits,descrambledData)
ans = logical
   1

Input Arguments

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Input sequence to be scrambled, specified as a binary column vector or matrix.

Data Types: double | int8

Initial state of the scrambler, specified as an integer from 1 to 127, or a corresponding 7-by-1 column vector of binary bits.

The scrambler initialization used on the transmission data follows the process described in IEEE Std 802.11-2012, Section 18.3.5.5 and IEEE Std 802.11ad-2012, Section 21.3.9. The header and data fields that follow the scrambler initialization field (including data padding bits) are scrambled by XORing each bit with a length-127 periodic sequence generated by the polynomial S(x) = x7+x4+1. The octets of the PSDU (Physical Layer Service Data Unit) are placed into a bit stream, and within each octet, bit 0 (LSB) is first and bit 7 (MSB) is last. The generation of the sequence and the XOR operation are shown in this figure:

Conversion from integer to bits uses left-MSB orientation. For the initialization of the scrambler with decimal 1, the bits are mapped to the elements shown.

ElementX7X6X5X4X3X2X1
Bit Value0000001

To generate the bit stream equivalent to a decimal, use de2bi. For example, for decimal 1:

de2bi(1,7,'left-msb')
ans =

     0     0     0     0     0     0     1

Same scramInit is applied across all the columns of bits when the input is a matrix.

Example: [0 0 0 0 0 0 1]'

Data Types: double

Output Arguments

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Scrambled or descrambled output, returned as a binary column vector or matrix with the same size and type as bits.

Extended Capabilities

Introduced in R2017b

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