Additive Scrambler

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

The state diagram for this flowgraph:

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

Generating Gold Codes

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

Output:

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