Algebraic Codes‎ > ‎

LDPC and RS Codes

Modern communications and storage channels (such as hard drive channels shown below) use decoders such as Low-Density Parity Check (LDPC) decoders which input soft decisions in order to extract the maximum amount of information from received waveforms.

In order for a 2D-RS scheme to create failure tolerance across a number of channels, a RS decoder within each disk channel which corrects only a small number of symbols may be used in conjunction with the LDPC decoder. Many disk drive vendors already use a RS decoder in conjunction with the LDPC decoder so this is nothing new.

It is appropriate to use a RS code in conjunction with a LDPC code because the output of the LDPC decoder is a sequence of hard decisions (bits) with possibly some sort of decoder failure indications which can be used by the RS decoder as erasure indications.

Multiple disk channels can be transformed into a 2D-RS HDD by adding a parallel RS encoder and decoder as illustrated below.