Polar codes for NAND-based SSD systems: A joint source channel coding perspective

Polar codes [1] are a class of provably capacity-achieving error correcting codes (ECC) for memoryless symmetric channels with low-complexity code structures; they have been shown to enjoy better decoding performance over LDPC and Turbo codes under certain scenarios. In this work, we study the application of polar codes for NAND-based SSDs, and mainly focus on the joint source channel coding (JSCC) aspect of polar codes for flash data protection. In a practical SSD system, in addition to the host data, both flash translation layer (FTL) and host side will write on NAND a small amount of non-host data (a.k.a. metadata) for system managing purposes. We demonstrate that the metadata information can be readily and efficiently utilized by polar codes, whereas such property is lacking in LDPC-based systems. With the help of the side information provided by metadata, the decoding capability of polar codes can be further enhanced with little or no modifications on the decoder side. Simulation results verify the performance improvement of metadata-based JSCC scheme, and indicate that polar codes have competitive advantages over LDPC codes on flash memories.