A memory device having a Low-Density Parity-Check (LDPC) decoder that is energy efficient and has a low error floor. The decoder is configured to determine syndromes of bits in a codeword, select bits in the codeword based at least in part on the syndromes according to a first mode, and flip the selected bits in the codeword. The decoder can repeat the bit selection and flipping operations to iteratively improve the codeword and reduce parity violations. Further, the decoder can detect a pattern in parity violations of the codeword in its iterative bit flipping operations. In response, the decoder can change from the first mode to a second mode in bit selection for flipping. For example, the decoder can transmit from a dynamic syndrome mode to a static syndrome mode in response to the pattern of repeating a cycle of bit flipping iterations.

Embodiments of the present disclosure provide a scheme for decoding over a small subgraph which highly likely includes some errors. A controller is configured to: control the first decoder to decode the data, read from the memory device, using a parity check matrix for the error correction code; extract one or more subgraphs from the entire bipartite graph of the parity check matrix, which is defined by a plurality of variable nodes and a plurality of check nodes when a particular condition satisfied; and control the second decoder to decode the decoding result of the first decoder using a submatrix of the parity check matrix corresponding to the extracted subgraphs.

A method and apparatus for decoding in which a first failed decode operation is performed on raw bit values of a FEC block by a LDPC decoder. When the FEC block is determined to be a trapped block an updated LLR map is generated; the updated LLR map and either the raw bit values of the FEC block or a failed-decode-output-block from a previous failed decode operation on the trapped block are provided to the LDPC decoder; a decode operation of the LDPC decoder is performed using the updated LLR map on the bit values of the FEC block or the failed-decode-output-block from the previous failed decode operation; and the generating, the providing and the performing are repeated until the decode operation is successful or until a predetermined number of trapped-block-decoding iterations have been performed. When the decode operation is successful in decoding the FEC block the codeword is output.

Techniques related to improving the error floor performance of a bit flipping (BF) decoder are described. In some examples, error floor performance is improved through determining a set of unreliable check nodes (CNs) and using information about the set of unreliable CNs to compute the flipping energies of variable nodes (VNs). In this manner, the flipping energies can be computed more accurately, thereby lowering the error floor. The set of unreliable CNs can be built through applying various criteria, such as criteria relating to the path length to an unsatisfied CN, the degree of a VN in a path to an unsatisfied CN, and/or checksum value. Path length and VN degree can be applied as selection criteria to determine which CNs qualify as members of the set of unreliable CNs. Checksum value can be applied as a trigger condition for building and/or using the set of unreliable CNs.

Methods, systems, and apparatuses for stall mitigation in iterative decoders are described. A codeword is received from a memory device. The codeword is iteratively error corrected based on a first bit flipping criterion. A stall condition in the multiple error correction iterations is detected. In response to the detection, the codeword is error corrected based on a second bit flipping criterion that is different from the first bit flipping criterion.

Methods, systems, and apparatuses for stall mitigation in iterative decoders are described. A codeword is received from a memory device. The codeword is iteratively error corrected based on a first bit flipping criterion. A stall condition in the multiple error correction iterations is detected. In response to the detection, the codeword is error corrected based on a second bit flipping criterion that is different from the first bit flipping criterion.

A bit interleaving method applying a bit permutation process to a QC LDPC codeword made up of N cyclic blocks of Q bits each, dividing the processed codeword into constellation words of M bits each, and applying an intra-cyclic-block permutation process to the cyclic blocks, where the codeword is divided into F×N/M folding sections of M/F cyclic blocks each and the constellation words are each associated with one of the folding sections, and the bit permutation process is applied such that the constellation words are each made up of F bits from each of M/F different cyclic blocks in the associated section, after the permutation process.

An LDPC decoding method of a received signal including a plurality of received symbols is provided. A decoding apparatus selects a perturbation space in which perturbation is to be performed based on a code length of the received signal and a maximum number of perturbation rounds indicating a number of perturbation rounds that can be performed, and performs a perturbation round. The decoding apparatus performs perturbation on a corresponding received symbol among the plurality of received symbols in each perturbation round, and decodes the received signal on which the perturbation has been performed. The decoding apparatus determines that decoding is successful when there is a perturbation round in which a decoding result of the received signal satisfies a predetermined condition.

A method for generating an LDPC (low-density parity check) code with a required error floor, comprising: using a parity generation circuit to generate an LDPC code; using a detection circuit to detect the LDPC code according to a plurality of trapping set cores in a database and to generate at least one piece of trapping-set-core information; using a verification circuit to perform an important sampling simulation according to the LDPC code and each trapping-set-core information separately to obtain an estimated error floor for each trapping-set-core information; using the verification circuit to separately compare each of the estimated error floors with an expected error floor; and when all of the estimated error floors are lower than or equal to the expected error floor, using the verification circuit to output the LDPC code.

A method of correcting data stored in a memory device includes: applying an iterative decoder to the data; determining a total number of rows in first data the decoder attempted to correct; estimating first visible error rows among the total number that continue to have an error after the attempt; estimating residual error rows among the total number that no longer have an error after the attempt; determining second visible error rows in second data of the decoder that continue to have an error by permuting indices of the residual error rows according to a permutation; and correcting the first data using the first visible error rows.