A Soft Decodable Concatenated LDPC Code

Abstract

In this paper, a concatenated low-density-parity-check (LDPC) coding scheme that is suitable for iterative soft decoding is introduced for magnetic recording systems. The concatenated code is constructed as the product of two linear codes, in which a conventional 4 kB LDPC code is used as the inner code and a single-parity check code serves as the outer code. The outer code in this concatenated construction spans many sectors, possibly an entire track, and the code rate and the block size can be flexibly configured. While individual sectors can be read and decoded independently, the full decoding power of the concatenated code can only be achieved by reading all the data sectors that are involved in the outer code. The concatenated code produces significant signal-to-noise gain over the baseline 4 kB LDPC. The soft decoding for the single-parity check code is very simple compared with the 4 kB LDPC code, and the concatenated code has a similar decoding complexity as the baseline 4 kB LDPC code. When the individual sectors within the outer code are updated in place, a read-modify-write procedure must be employed.