Research On The MLC Nand Flash Error Control Technology Based On Polar Codes

With the rapid development of information technology,storage technology plays an increasingly important role.The application of non-volatile storage technology makes Flash storage more reliable,and because of its low power consumption,anti-vibration,high performance,low cost and so on,it is widely used in digital products.However,with the upgradation of manufacturing technology,original single-level cell memory technology has progressed to multi-level cell and trinary-Level cell memory technology which has greater storage density.With the increasing of storage density of Nand Flash,the error probability of data in the process of storage is increasing,and the realiability requirements of data storage are also improving.Therefore,Nand Flash puts forward higher requirements for ECC.Conventional ECC schemes usually use BCH code,LDPC code,or a combination of both as an error correction codes.However,they either suffer from limited error correction capability,or have long decoding latency,so that they can not meet the requirements of Nand Flash error control.Therefore looking for new error control technology has become the primary task of Nand Flash.Polar codes are a significant breakthrough in coding theory.It can achieve the channel capacity of arbitrary binary input discrete memoryless channel,and has the advantages of flexible coding rate and low coding and decoding complexity.It can be applied to the future Nand Flash error control.The standard code length of the polar codes determines that it can not be applied to any page capacity of Flash directly.In order to make the polar codes suitable for any page of Flash,we need to design a length-compatible polar codes.This paper focuses on the coding and decoding algorithms of the shortened polar code,and proposes the optimized shortened codes,then constructs a series of shortened polar codewords which have high code rates for MLC Nand Flash error correction using the cut-off pattern.First,the basic cut-off pattern is obtained by bit reordering,and then the optimized cut-off pattern is composed of the frozen bits with lower channel capacity,so all the punctured bits are frozen bits,and the error correcting performance of the shortened code scheme can be greatly improved.Then,this paper proposes the methods to reduce the delay of polar code decoding.The delay reduction scheme uses recursive channel combined method to construct parallel decoding channel,and thereby effectively reduces the latency of decoders.And the delay reduction algorithm can be better applied to MLC Nand Flash error control and improve the transmission rate of MLC Nand Flash.Then,according to the asymmetry of MLC unit errors,this paper proposes one unequal error protection schemes for unequal error protection of MLC Nand Flash.Finally,by simulation and the result analysis,it fully verifies the possibility and superiority of those shortened codes which are proposed in this paper in the field of MLC Nand flash error-correcting.