Error correction code: Difference between revisions

Revision as of 10:27, 28 June 2025

Revision as of 10:30, 28 June 2025

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This provides single-bit error correction and 2-bit error detection.

Hamming codes are only suitable for more reliable [[single-level cell]] (SLC) NAND.

Denser [[multi-level cell]] (MLC) NAND may use multi-bit correcting ECC such as [[BCH orcode|BCH]], Reed–Solomon, or [[Low-density parity-check code|LDPC]].<ref name="spansion">{{cite web|url=http://www.spansion.com/Support/Application%20Notes/Types_of_ECC_Used_on_Flash_AN.pdf|title =What Types of ECC Should Be Used on Flash Memory?|publisher=Spansion|format=Application note|year=2011|quote=Both Reed–Solomon algorithm and BCH algorithm are common ECC choices for MLC NAND flash. ... Hamming based block codes are the most commonly used ECC for SLC.... both Reed–Solomon and BCH are able to handle multiple errors and are widely used on MLC flash.}}</ref><ref>{{cite web|author=Jim Cooke|url=https://cushychicken.github.io/assets/cooke_inconvenient_truths.pdf |title=The Inconvenient Truths of NAND Flash Memory|date=August 2007|page=28|quote=For SLC, a code with a correction threshold of 1 is sufficient. t=4 required ... for MLC.}}</ref> Later, the [[Multi-level cell|MLC]] NAND flash used more complex ECC such as [[BCH code|BCH]] and [[Low-density parity-check code|LDPC]].<ref>https://www.thinkmind.org/articles/icons_2015_5_20_40055.pdf</ref> NOR flash typically does not use any error correction.<ref name="spansion"/>

Classical block codes are usually decoded using '''hard-decision''' algorithms,<ref>{{cite journal |author-last1=Baldi |author-first1=M. |author-last2=Chiaraluce |author-first2=F. |title=A Simple Scheme for Belief Propagation Decoding of BCH and RS Codes in Multimedia Transmissions |journal=[[International Journal of Digital Multimedia Broadcasting]] |volume=2008 |pages=1–12 |date=2008 |doi=10.1155/2008/957846 |doi-access=free }}</ref> which means that for every input and output signal a hard decision is made whether it corresponds to a one or a zero bit. In contrast, convolutional codes are typically decoded using '''soft-decision''' algorithms like the Viterbi, MAP or [[BCJR algorithm|BCJR]] algorithms, which process (discretized) analog signals, and which allow for much higher error-correction performance than hard-decision decoding.