Research On The Encoding And Decoding Of Polar Code In MLC NAND Flash

The proposed channel polarization theory shows that we can construct capacity-achieving code sequences in an arbitrary Binary-Input Discrete Memoryless Channel. According to this theory, Arikan gave the construction method of Polar codes, and proved that they have low encoding and decoding complexities. The good performance of Polar codes has opened up a new direction of the channel encoding technology.As a non-volatile memory, flash memory has high storage density, low power consumption, so it has been widely used as the main storage device in the market. Each cell of the MLC NAND flash memory can store two bits of data, reduce the unit cost, so that it is more suitable for large capacity storage devices. However, the increase in the number of levels within the cell makes the distribution of the threshold voltage more close, data are more prone to errors. Error correction codes is a technique that can improve the reliability and extend the life of flash memory.In this paper, we study the encoding and decoding method and the error control scheme in MLC NAND flash memory of Polar codes. The main work of this paper is summarized as follows:1. The basis of flash memory is introduced. Then the physical structure and storage principle of the cell of MLC NAND flash memory are summarized. And the common operation of flash memory is described. The error model of flash memory is studied in depth. And the cause of errors is analyzed. It is concluded that the retention error and program interference error are the most two common types in flash memory.2. The channel polarization phenomenon is described in detail. The simulation of encoding method and successive cancellation decoding algorithm of Polar codes in AWGN, BEC and BSC are given. The simulation results show that the lengths of Polar codes is longer, the performance of the decoding algorithm is better.3. The threshold voltage distribution of the cell of MLC NAND flash memory under P/E cycles is analyzed. Using the hard and soft sensing technology to read MLC, the simulation of encoding and decoding algorithm of Polar codes in NAND flash memory are given. Compared to the hard sensing technology, the simulation results show that the soft sensing technology significantly improves the endurance of MLC.