ldpc

A simple small library for experimenting with LDPC codes

This codec uses the quasi-cyclic (QC) LCPC checksum arrays used in IEEE Std 802.11-2016, Annex F. These are currently used for forward error correction for 802.11 n, ac, and h devices. Why? Not only because they have of course been tested extensively, but the spec also has test data to validate any new software implementation.

The codec uses the Log Likelihood Sum-Product algorithm, so should prove to be very effective in signal reconstruction and sensitivity.

Adding to your npm project

npm i --save https://github.com/ishmal/ldpc

Using in an app

import { Ldpc } from "ldpc";

const codec = new Ldpc.LdpcCodec();
codec.withCrc = true/false;   //defaults to true

Pick a code rate and length

codec.setCode("1/2", "648");  // default
codec.setCode("1/2", "1296");
codec.setCode("1/2", "1944");

codec.setCode("2/3", "648");
codec.setCode("2/3", "1296");
codec.setCode("2/3", "1944");

codec.setCode("3/4", "648");
codec.setCode("3/4", "1296");
codec.setCode("3/4", "1944");

codec.setCode("3/4", "648");
codec.setCode("3/4", "1296");
codec.setCode("3/4", "1944");

Encode

codec.encodeBytes(byteArray);

codec.encodeText(string);

will break the input data into chunks that fit in codewords, encode each one, are return an array of bit arrays for transmitting over an AWGN channel.

Decode

This kind of transport is called a "binary input channel." What comes out of the encoder as 1's and 0's is turned into analog levels for transmission.

On the receiving side, we expect arrays of floats for each message, centered around 0, < 0 for 1, >= 0 for 0.

codec.decode(array of bits);  //returns an array of bytes

codec.decodeText(array of bits); // returns a string

More information

Look at the tests to see how it is done.
Feel free to ask me any questions.

Final

Hope that this helps you in your signal processing project. If you have any ideas on how to improve this library, please let me know.

Thanks!

ishmal/ldpc802-js