Additive Scrambler: Difference between revisions

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[[Category:Block Docs]]
[[Category:Block Docs]]
[[Category:Stub Docs]]
Scramble an input stream using a Linear Feedback Shift Register (LFSR).
This is the template for the [[:Category:Block_Docs|"Page-per-block Docs"]].  This first section should describe what the block does and how to use it, using however many paragraphs necessary.  Note that the title of the wiki page should match the block's name in GRC, i.e. the one defined in the block's .grc file.  Look at the [[FFT]] Block for a good example.


As this is a basic template, it's also in the [[:Category:Stub_Docs|"Stub Docs category"]]. Please improve it.
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 [https://www.gnuradio.org/doc/doxygen/classgr_1_1digital_1_1lfsr.html gr::digital::lfsr].


== Parameters ==
== Parameters ==
(''R''): <span class="plainlinks">[https://wiki.gnuradio.org/index.php/GNURadioCompanion#Variable_Controls ''Run-time adjustable'']</span>
(''R''): <span class="plainlinks">[https://wiki.gnuradio.org/index.php/GNURadioCompanion#Variable_Controls ''Run-time adjustable'']</span>


; Param 1 (''R'')
; Mask : Polynomial mask for LFSR
: Description of parameter, provide any tips or recommended values.  Note that the name of the parameter above should match the param's label that shows up in grc (e.g. Sample Rate).
; 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 ==
 
[[File:Additive_Scrambler_fg.png|800px]]
 
The state diagram for this flowgraph:
 
[[File:Additive_Scrambler_State_Diagram.png|500px]]
 
<p>This flowgraph can be downloaded from [[Media:Additive Scrambler.grc]].</p>
 
=== Generating Gold Codes ===
 
[https://en.wikipedia.org/wiki/Gold_code Gold Codes] can be generated using LFSRs, as explained [https://natronics.github.io/blag/2014/gps-prn/ here].


; Param 2
[[File:Additive Scrambler Gold Code fg.png|800px]]
: blah blah blah


== Example Flowgraph ==
Output:
 
[[File:Additive Scrambler Gold Code Plot fg.png|800px]]


Insert description of flowgraph here, then show a screenshot of the flowgraph and the output if there is an interesting GUI.  Currently we have no standard method of uploading the actual flowgraph to the wiki or git repo, unfortunately. The plan is to have an example flowgraph showing how the block might be used, for every block, and the flowgraphs will live in the git repo.
<p>This flowgraph can be downloaded from [[Media:Additive Scrambler Gold Code.grc]].</p>


== Source Files ==
== Source Files ==


; C++ files
; C++ files
: [https://github.com/gnuradio/gnuradio TODO]
: [https://github.com/gnuradio/gnuradio/blob/main/gr-digital/lib/additive_scrambler_impl.cc additive_scrambler_impl.cc]


; Header files
; Header files
: [https://github.com/gnuradio/gnuradio TODO]
: [https://github.com/gnuradio/gnuradio/blob/main/gr-digital/lib/additive_scrambler_impl.h additive_scrambler_impl.h]


; Public header files
; Public header files
: [https://github.com/gnuradio/gnuradio TODO]
: [https://github.com/gnuradio/gnuradio/blob/main/gr-digital/include/gnuradio/digital/additive_scrambler.h additive_scrambler.h]


; Block definition
; Block definition
: [https://github.com/gnuradio/gnuradio TODO]
: [https://github.com/gnuradio/gnuradio/blob/main/gr-digital/grc/digital_additive_scrambler_bb.block.yml digital_additive_scrambler_bb.block.yml]

Latest revision as of 19:47, 26 May 2025

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
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