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Low-density parity-check (LDPC) codes are a class of highly efficient linear block codes made from many single parity check (SPC) codes. They can provide performance very close to the channel capacity (the theoretical maximum) using an iterated soft-decision decoding approach, at linear time complexity in terms of their block length.
The on-line textbook: Information Theory, Inference, and Learning Algorithms, by David J.C. MacKay, contains chapters on elementary error-correcting codes; on the theoretical limits of error-correction; and on the latest state-of-the-art error-correcting codes, including low-density parity-check codes, turbo codes, and fountain codes.
Compute forward probabilities Compute backward probabilities β {\displaystyle \beta } Compute smoothed probabilities based on other information (i.e. noise variance for AWGN , bit crossover probability for binary symmetric channel )
This process is implemented by Reed–Solomon codes, with code words constructed over a finite field using a Vandermonde matrix. Most practical erasure codes are systematic codes-- each one of the original k symbols can be found copied, unencoded, as one of the n message symbols. [12]
In this example, code block 1 shows loop-dependent dependence between statement S2 iteration i and statement S1 iteration i-1. This is to say that statement S2 cannot proceed until statement S1 in the previous iteration finishes. Code block 2 show loop independent dependence between statements S1 and S2 in the same iteration.
Classes of codes, and their subset relation: e.g., block codes -> linear codes -> cyclic codes -> BCH codes -> RS codes I'm sure I'm still missing a lot, but this came to my mind right away... Anyway, I'm sure I'll not be able to tackle this (rather big) task anytime soon, but maybe someone else will give it a shot.
Hardware-wise, this turbo code encoder consists of two identical RSC coders, C 1 and C 2, as depicted in the figure, which are connected to each other using a concatenation scheme, called parallel concatenation: In the figure, M is a memory register. The delay line and interleaver force input bits d k to appear in different sequences.
LDPC codes have no limitations of minimum distance, [34] that indirectly means that LDPC codes may be more efficient on relatively large code rates (e.g. 3/4, 5/6, 7/8) than turbo codes. However, LDPC codes are not the complete replacement: turbo codes are the best solution at the lower code rates (e.g. 1/6, 1/3, 1/2). [35] [36]