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Author: search.filters.author.Duangthong, ChatupornSubject: search.filters.subject.density evolution

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    Efficient Design of Read Voltages and LDPC Codes in NAND Flash Memory Using Density Evolution
    (2023-01-01)
    Duangthong, Chatuporn
    ;
    Phakphisut, Watid
    ;
    Wardkein, Paramote
    Low-density parity-check (LDPC) codes play an important role in the reliability enhancement of commercial NAND flash memory. Unfortunately, due to the requirement of the reading speed of NAND flash memory, the LDPC decoder will not obtain precise soft information to achieve high error-correcting capability. In this work, we use a density evolution (DE) algorithm to reveal the decoding threshold of the LDPC decoder affected by the read voltages. We propose the efficient design of read voltages so that the LDPC decoder has the lowest decoding threshold. Therefore, this method can guarantee that the designed read voltages are suitable for a given LDPC code. Moreover, since we found that the designed read voltages are related to the structure of the LDPC code, the joint design of the read voltages and LDPC code is then proposed to achieve the capacity of NAND flash memory. The simulation results demonstrate that our proposed design significantly improves the frame error rate (FER) performance of NAND flash memory.
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    Read Voltage Optimization in MLC NAND Flash Memory via the Density Evolution
    (2019-04-01)
    Duangthong, Chatuporn
    ;
    Phakphisut, Watid
    ;
    Supnithi, Pornchai
    The multi-level-cell (MLC) NAND flash memory can typically use multiple reads for obtaining soft information for the LDPC decoder. The multiple reads give the soft information which is quantized to a certain level. The major challenge is that the read voltages must be precisely selected to provide better soft information. In the previous work, the read voltages are selected so that the soft information has the maximum mutual information (MMI). However, the error-correction capability of LDPC decoder is not considered. Therefore, in this work, we analyze the performance of LDPC decoder by density evolution whereby the soft information is quantized. Then the optimal read voltages for given LDPC codes are obtained. As a result, for a regular LDPC code with the read voltages optimized by density evolution can provide the lower BER performance compared with the MMI technique.