Error correction apparatus, error correction method, and memory system

An error correction method implemented by a computer, the error correction method comprising:

• determining first likelihood information being a piece of likelihood information corresponding to a first received word as a target of decoding among multiple pieces of likelihood information, the first likelihood information being determined by using first correspondence information in which read values included in a received word and the multiple pieces of likelihood information are correlated with each other;
• executing iterative processing of repeating soft-decision decoding using the first likelihood information until a termination condition is satisfied;
• executing update processing of updating the first correspondence information to second correspondence information in a case where the termination condition is satisfied and the soft-decision decoding is failed;
• calculating an evaluation value that increases with increase in a difference between the first correspondence information and the second correspondence information;
• executing change processing of changing, in accordance with the evaluation value, at least one of a first parameter to be used in the iterative processing or a second parameter to be used in the update processing;
• and
• executing further the iterative processing after executing the change processing.

A memory system comprising:

• a nonvolatile memory configured to store data and an error correction code generated by using the data;
• and
• a memory controller configured to
• read a received word from the nonvolatile memory,
• determine first likelihood information being a piece of likelihood information corresponding to a first received word as a target of decoding among multiple pieces of likelihood information, the first likelihood information being determined by using first correspondence information in which read values included in the received word read from the nonvolatile memory and the multiple pieces of likelihood information are correlated with each other,
• execute iterative processing of repeating soft-decision decoding using the first likelihood information until a termination condition is satisfied,
• execute update processing of updating the first correspondence information to second correspondence information in a case where the termination condition is satisfied and the soft-decision decoding is failed,
• calculate an evaluation value that increases with increase in a difference between the first correspondence information and the second correspondence information,
• execute change processing of changing, in accordance with the evaluation value, at least one of a first parameter to be used in the iterative processing or a second parameter to be used in the update processing, and
• execute further the iterative processing after executing the change processing.