Structured Bit-Interleaved LDPC Codes for MLC Flash Memory

Due to a structural feature in the programming process of MLC (two bits per cell) and TLC (three bits per cell) flash memory, the majority of errors that occur are single-bit errors. Moreover, the voltages used to store the bits typically result in different bit error probabilities for the two or three types of bits. In this work we analyze binary regular LDPC codes in the standard bit-interleaved coded modulation implementation, assuming different probabilities on the bits, to determine what ratio of each type of bit should be connected at the check nodes to improve the decoding threshold. We then propose a construction of nonbinary LDPC codes using their binary images, resulting in check node types that come close to these optimal ratios.