Asymmetric llr generation using assist-read

A method of operating a storage system, the storage system including memory cells and a memory controller coupled to the memory cells for controlling operations of the memory cells, wherein each memory cell is an m-bit multi-level cell (MLC), where m is an integer, the memory cells arranged in m pages, each of the m bits of a given memory cell providing data for a corresponding one of the m pages, the method comprising:

• determining initial LLR (log likelihood ratio) values for each of the m pages;
• comparing bit error rates in the m pages;
• identifying a programmed state in one of the m pages that has a high bit error rate (BER);
• selecting an assist-read threshold voltage of the identified page;
• performing an assist-read operation on the identified page using the assist-read threshold voltage;
• determining revised LLR values for the identified page based on results from the assist-read operation;
• and
• performing soft decoding using the revised LLR values for the identified page and the initial LLR values for other pages.

A storage system, the storage system including memory cells and a memory controller coupled to the memory cells for controlling operations of the memory cells, wherein each memory cell is an m-bit multi-level cell (MLC), where m is an integer, the memory cells arranged in m pages, each of the m bits of a given memory cell providing data for a corresponding one of the m pages, wherein the memory controller is configured to:

• determine initial LLR (log likelihood ratio) values for each of the m pages;
• compare bit error rates in the m pages;
• identify a programmed state in one of the m pages that has a high bit error rate;
• select an assist-read threshold voltage of the identified page;
• perform an assist-read operation on the identified page using the assist-read threshold voltage;
• determine revised LLR values for the identified page based on results from the assist-read operation;
• and
• perform soft decoding using the revised LLR values for the identified page and the initial LLR values for other pages.