The Error-Pattern-Correcting Turbo Equalizer

The error-pattern correcting code (EPCC) is incorporated in the design of a turbo equalizer (TE) with aim to correct dominant error events of the inter-symbol interference (ISI) channel at the output of its matching Viterbi detector. By targeting the low Hamming-weight interleaved errors of the outer convolutional code, which are responsible for low Euclidean-weight errors in the Viterbi trellis, the turbo equalizer with an error-pattern correcting code (TE-EPCC) exhibits a much lower bit-error rate (BER) floor compared to the conventional non-precoded TE, especially for high rate applications. A maximum-likelihood upper bound is developed on the BER floor of the TE-EPCC for a generalized two-tap ISI channel, in order to study TE-EPCC's signal-to-noise ratio (SNR) gain for various channel conditions and design parameters. In addition, the SNR gain of the TE-EPCC relative to an existing precoded TE is compared to demonstrate the present TE's superiority for short interleaver lengths and high coding rates.Comment: This work has been submitted to the special issue of the IEEE Transactions on Information Theory titled: "Facets of Coding Theory: from Algorithms to Networks". This work was supported in part by the NSF Theoretical Foundation Grant 0728676

Low-density parity-check coding for high-density magnetic recording systems.

Our strategy is to combine advanced signal processing techniques, the core of which is soft-decision iterative channel detection, with powerful low-density parity-check (LDPC) coding techniques.Magnetic recording channels (MRCs), including both longitudinal and perpendicular ones, are subject to a number of physical impairments, such as electronic/media noise, intersymbol interference (ISI), erasure, and intertrack interference (ITI). These impairments, if not appropriately handled, are barriers to achieving ultra-high densities. The goal of this dissertation is to study the impact of these multiple impairments on system performance, and to develop techniques to mitigate this impact such that the performance is as close to the theoretical limit of the channel as can be achieved by practical and implementable means.Specifically, the performance of regular LDPC codes on MRCs is first evaluated. Both randomly and structurally constructed codes are considered. Secondly, density evolution is used to analyze and design LDPC codes for MRCs. Results show that better irregular codes can be obtained. Afterwards, this algorithm is modified to include erasures, and erasure detection algorithms are studied. Fourthly, an improved algorithm for LDPC decoding, called signal-to-noise ratio (SNR) mismatch is unveiled. This algorithm may be useful for future practical applications. Finally, a channel detection algorithm for handling ITI in perpendicular recording is optimized, the eventual goal of which is to maximize the attainable track density

Error-correction coding for high-density magnetic recording channels.

Finally, a promising algorithm which combines RS decoding algorithm with LDPC decoding algorithm together is investigated, and a reduced-complexity modification has been proposed, which not only improves the decoding performance largely, but also guarantees a good performance in high signal-to-noise ratio (SNR), in which area an error floor is experienced by LDPC codes.The soft-decision RS decoding algorithms and their performance on magnetic recording channels have been researched, and the algorithm implementation and hardware architecture issues have been discussed. Several novel variations of KV algorithm such as soft Chase algorithm, re-encoded Chase algorithm and forward recursive algorithm have been proposed. And the performance of nested codes using RS and LDPC codes as component codes have been investigated for bursty noise magnetic recording channels.Future high density magnetic recoding channels (MRCs) are subject to more noise contamination and intersymbol interference, which make the error-correction codes (ECCs) become more important. Recent research of replacement of current Reed-Solomon (RS)-coded ECC systems with low-density parity-check (LDPC)-coded ECC systems obtains a lot of research attention due to the large decoding gain for LDPC-coded systems with random noise. In this dissertation, systems aim to maintain the RS-coded system using recent proposed soft-decision RS decoding techniques are investigated and the improved performance is presented

ADVANCED SIGNAL PROCESSING FOR MAGNETIC RECORDING ON PERPENDICULARLY MAGNETIZED MEDIA

In magnetic recording channels (MRCs) the readback signal is corrupted by many kinds of impairments, such as electronic noise, media noise, intersymbol interference (ISI), inter-track interference (ITI) and different types of erasures. The growth in demand for the information storage, leads to the continuing pursuit of higher recording density, which enhances the impact of the noise contamination and makes the recovery of the user data from magnetic media more challenging. In this dissertation, we develop advanced signal processing techniques to mitigate these impairments in MRCs.We focus on magnetic recording on perpendicularly magnetized media, from the state-of-the art continuous media to bit-patterned media, which is a possible choice for the next generation of products. We propose novel techniques for soft-input soft-output channel detection, soft iterative decoding of low-density parity-check (LDPC) codes as well as LDPC code designs for MRCs.First we apply the optimal subblock-by-subblock detector (OBBD) to nonbinary LDPC coded perpendicular magnetic recording channels (PMRCs) and derive a symbol-based detector to do the turbo equalization exactly. Second, we propose improved belief-propagation (BP) decoders for both binary and nonbinary LDPC coded PMRCs, which provide significant gains over the standard BP decoder. Third, we introduce novel LDPC code design techniques to construct LDPC codes with fewer short cycles. Performance improvement is achieved by applying the new LDPC codes to PMRCs. Fourth, we do a substantial investigation on Reed-Solomon (RS) plus LDPC coded PMRCs. Finally, we continue our research on bit-patterned magnetic recording (BPMR) channels at extremely high recording densities. A multi-track detection technique is proposed to mitigate the severe ITI in BPMR channels. The multi-track detection with both joint-track and two-dimensional (2D) equalization provide significant performance improvement compared to conventional equalization and detection methods

Multitrack Detection for Magnetic Recording

The thesis develops advanced signal processing algorithms for magnetic recording to increase areal density. The exploding demand for cloud storage is motivating a push for higher areal densities, with narrower track pitches and shorter bit lengths. The resulting increase in interference and media noise requires improvements in read channel signal processing to keep pace. This thesis proposes the multitrack pattern-dependent noise-prediction algorithm as a solution to the joint maximum-likelihood multitrack detection problem in the face of pattern-dependent autoregressive Gaussian noise. The magnetic recording read channel has numerous parameters that must be carefully tuned for best performance; these include not only the equalizer coefficients but also any parameters inside the detector. This thesis proposes two new tuning strategies: one is to minimize the bit-error rate after detection, and the other is to minimize the frame-error rate after error-control decoding. Furthermore, this thesis designs a neural network read channel architecture and compares the performance and complexity with these traditional signal processing techniques.Ph.D

Timing recovery for low signal to noise ratio recording channels

Master'sMASTER OF ENGINEERIN

Soft-decision decoding of MTR codes over magnetic recording channels

U radu su predstavljene nove tehnike dekodovanja maximum transition run (MTR) kodova na principu finog odlučivanja. Analizirane su performanse ovih tehnika u kombinaciji sa zaštitnim LDPC kodom na kanalima za magnetsko memorisanje informacija, sa posebnim osvrtom na model kanala sa dve staze za zapisivanje i dve glave za čitanje. U modelu kanala je korišćena idealna E2PR4 ekvalizacija staza adekvatna za sisteme sa visokom gustinom magnetskog zapisa.This thesis presents the novel soft-decision decoding techniques for decoding of the maximum transition run (MTR) codes. Performances of such techniques have been analyzed in combination with error correcting LDPC code over magnetic recording channels, especially the two-track two-head channel model. Ideal E2PR4 track equalization suitable for high density magnetic recording has been used

Contributions to adaptive equalization and timing recovery for optical storage systems

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