Additive Scrambler

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Scramble an input stream using a Linear Feedback Shift Register (LFSR).

This block scrambles up to 8 bits per byte of the input data stream, starting at the LSB. The scrambler works by XORing the incoming bit stream by the output of the LFSR. Optionally, after bits have been processed, the shift register is reset to the value. This allows processing fixed length vectors of samples.

Alternatively, the LFSR can be reset using a reset tag to scramble variable length vectors. However, it cannot be reset between bytes.

For details on configuring the LFSR, see gr::digital::lfsr.

Parameters

(R): Run-time adjustable

Mask
Polynomial mask for LFSR
Seed
Initial shift register contents
Length
Shift register length
Count
Number of bytes after which shift register is reset, 0=never
Bits per byte
Number of bits per byte
Reset tag key
When a tag with this key is detected, the shift register is reset (when this is set, count is ignored!)

Example Flowgraph

Additive Scrambler fg.png

The state diagram for this flowgraph:

Additive Scrambler State Diagram.png

This flowgraph can be downloaded from Media:Additive Scrambler.grc.

Generating Gold Codes

Gold Codes can be generated using LFSRs, as explained here.

Additive Scrambler Gold Code fg.png

Output:

Additive Scrambler Gold Code Plot fg.png

This flowgraph can be downloaded from Media:Additive Scrambler Gold Code.grc.

Source Files

C++ files
additive_scrambler_impl.cc
Header files
additive_scrambler_impl.h
Public header files
additive_scrambler.h
Block definition
digital_additive_scrambler_bb.block.yml