Research On Reader Array And Signal Processing Technology For Two-dimensional Magnetic Recording

With the rapid development of information technology,the volume of digital information increases dramatically in modern society.According to the Data Age 2025 report released in November 2018 by International Data Corporation(IDC),the global total of all data will grow from 33 ZB in 2018 to 175 ZB in 2025.The storage demand of mass data has promoted the rapid expansion of the market scale of large capacity storage devices,and put forward higher requirements on the development of various storage technologies.Compared with optical storage,semiconductor storage,etc.,magnetic storage has lower unit storage cost and greater comprehensive performance advantages.The disks based on magnetic storage technology are expected to take a major share of the mass storage device market in the future.The magnetic recording areal density of the plate in a disk is one of the critical factors that determine the disk capacity.At present,the further increase of magnetic recording areal density is facing the dilemma of “trilemma”.To break through the growth bottleneck of the magnetic recording areal density with conventional perpendicular continuous thin film,it is urgent to introduce a new magnetic recording technology and cope with the problem from all aspects of magnetic recording system such as magnetic recording medium,read and write magnetic head,magnetic recording methods,signal processing,etc.Two-dimensional magnetic recording is a new magnetic recording technology which combines the shingled write recording and two-dimensional signal processing.It further increases the magnetic recording areal density from two aspects: magnetic recording mode and signal processing.The shingled write recording narrowed the track space,enhancing the inter-track interference of the read back signals.The intersymbol interference in the down-track direction combined with the inter-track interference in the cross-track direction gave the two-dimensional magnetic recording channel characteristic of two-dimensional interesymbol interference.In addition,the increase of magnetic recording density made the medium noise of two-dimensional magnetic recording channel the main noise source.Therefore,it is necessary to introduce the characteristics of two-dimensional intersymbol interference and medium noise into two-dimensional magnetic recording channel model.This paper intends to analyze the channel of two-dimensional magnetic recording and establish its model.The characteristics and related parameters of two-dimensional magnetic recording channel are discussed based on the Voronoi model.By studying the reader array,two-dimensional signal processing algorithm,channel decoding technology and interpolation timing recovery technology,it has provided theoretical and technical support for the realization of 10 Tbpsi ultrahigh density magnetic recording.As for the problem of two-dimensional signal detection,a 4-reader array design and signal detection algorithm are proposed.The two-dimensional signal detection needs to obtain the information of the target track and its adjacent tracks simultaneously.Since using a single reader will bring a delay,it is necessary to introduce the reader array into the twodimensional magnetic recording system.The existing 3-reader array is evenly arranged in the cross-track direction,and can effectively obtain the diversity of signals in the cross-track direction.In the design of 4-reader array,an auxiliary reader is added on the basis of 3-reader array in order to further obtain diversity of signal in the down-track direction,providing additional soft information for detecting bits on the track and improving detection performance.As for the problem of the medium noise in the two-dimensional magnetic recording channel,this paper proposes a two-dimensional modulation coding method to eliminate the isolated bit patterns that caused larger variance of the medium noise.As for the overwrite errors and channel detection errors,LDPC coding is used in the two-dimensional magnetic recording system for detection architecture design and performance evaluation.Medium noise is caused by change of adjacent magnetic particles polarity in the recording medium because of the transformation of input data.If the input data patterns cause more magnetic polarity reversal,then larger noise variance will be produced in the signal readback process,and it will not be conducive to signal detection.As a result,modulation coding is needed to eliminate these data patterns.Further more,the data-dependent noise prediction method is applied to further improve the detection performance of the system.Shingled write recording often accompanied with writing errors caused by magnetic head erase effect,that is partially written information bits are overridden and can't be detected and recovered.Therefore,it is necessary to apply the error control codes in two-dimensional magnetic recording channel to correct the errors in the process of writing and signal detection and recover the right information bits.For the timing recovery in two-dimensional magnetic recording channel,this paper proposes an iterative two-dimensional interpolation timing recovery and signal detection method,which uses two timing error detectors to estimate the timing errors in the downtrack direction and across-track direction respectively,and causes corresponding phase offset respectively.Since the estimated value of timing error on future sampling cannot be obtained at the current position,it will lead to invalid signal detection and timing error estimation at the current position.Therefore,the timing error estimation from previous iterations and the decision results of signal detectors are used to further improve the signal detection performance.