Articles
Weaknesses of Margulis and Ramanujan-Margulis Low-Density Parity-Check Codes

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Abstract

We report weaknesses in two algebraic constructions of low-density parity-check codes based on expander graphs. The Margulis construction gives a code with near-codewords, which cause problems for the sum-product decoder; The Ramanujan-Margulis construction gives a code with low-weight codewords, which produce an error-floor.

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