A study of polar codes for MLC NAND flash memories

The increasing density of NAND flash memories makes data more prone to errors due to severe process variations and disturbance. The urgency to improve NAND flash reliability encourages searching for optimal channel coding methods. This paper reports our efforts towards a read channel for flash memories using polar coding. Our contributions include the solutions to several challenges raised when applying polar codes to NAND flash memories in practice. We propose efficient schemes for shortening both non-systematic and systematic polar codes, making polar codewords be easily adapted to flash page of any size. We demonstrate that the decoding performance of the shortened polar codes and LDPC codes are comparable using the data obtained by our NAND flash characterization platform. We show the feasibility of a practical adaptive decoding framework where it is not necessary to construct new polar codes for different channel parameters. Experimental results show that the decoding performance approaches the optimized performance where different codes are constructed for different channel conditions. To the best of our knowledge, this work is the first study of polar codes for error correction in flash memories.