Turguy Goker

MDS Product Code Performance Estimations Under Header CRC Check Failures and Missing Syncs

Data storage systems that use removable media heavily rely on strong concatenated error correction coding (ECC) architectures in order to guarantee very low target data loss rates. Particularly, tape drives and optical disk drives (e.g., CD, DVD, and BD) employ powerful ECC schemes based on a concatenation of an outer maximum distance separable (MDS) code called C2 and an inner MDS code called C1 in order to achieve this performance. In addition to data, these storage systems employ header and synchronization appends (i.e., sync patterns) for appropriate allocation of user information on the physical storage medium. Since headers and sync patterns are subject to channel errors as well, accurately retrieved data may be regarded useless if an error occurs in either of these fields. In order to predict very low target C2 failure rates (which is typically on the order of 10-17) in the presence of header and synchronization errors, we propose a semianalytical method in this paper that incorporates the effects of the header and synchronization errors in the output error rate expressions. We use our proposed model with linear tape open (LTO) data examples to both show the effectiveness of the estimation results and draw some interesting conclusions.

Error Event Corrections Using List-NPML Decoding and Error Detection Codes

A List-Noise Predictive Maximum Likelihood (List-NPML) decoding algorithm based on a periodic error detection mechanism is proposed for magnetic recording systems to minimize the number of error events. The proposed detector keeps a list of candidate paths ( candidates per state of a trellis) based on the observation that most of the error events can be recovered by finding a set of most likely paths. A periodic decision making process is utilized for every bits based on error detection codes. With this approach, a tradeoff between performance and complexity is studied with various combinations of and . The proposed structure is robust to miscorrections and time-varying error events, eliminating the need for knowing the error event distributions prior to its operation. We also introduced a novel design of parity bits that meets the run length constraints of the channel and a trellis update architecture for improved performance. Simulation results show that the proposed List-NPMLD gives us significant BER performance and post-ECC gains at the expense of some increase in complexity.

A joint dedupe-fountain coded archival storage

An erasure-coded archival file storage system is presented using a chunk-based deduplication mechanism and fountain codes for space/time efficient operation. Unlike traditional archival storage, this proposal considers the deduplication operation together with correction coding in order to provide a reliable storage solution. The building blocks of deduplication and fountain coding processes are judiciously interleaved to present two novel ideas, reducing memory footprint with weaker hashing and dealing with the increased collisions using correction coding, and applying unequal error protection to deduplicated chunks for increased availability. The combination of these two novel ideas made the performance of the proposed system stand out. For example, it is shown to outperform one of the replication-based as well as RAID data protection schemes. The proposed system also addresses some of the fundamental challenges of todays low-cost deduplicated data storage systems such as hash collisions, disk bottleneck and RAM overflow problems, securing savings up to 90% regular RAM use.

Cycle Slip Detection and Correction Through Classification of Modulation Code Failures

In high-density recording systems, synchronization might be lost due to increased noise and/or inaccurate sampling/filtering. In such, long bursts of errors occur due to bits either erased from or inserted into the bit stream. At low signal-to-noise ratios, such bit slips (also known as cycle slips) lead to excessive post-error correction code (post-ECC) failures. In order to reduce the rate of the post-ECC failures, cycle slips should be detected and corrected. In the past, the majority of the research was concentrated on iterative joint timing recovery and error decoding methodologies. In this study, we propose to detect and correct cycle slips using a decoding failure analysis of maximum transition run (MTR) codeword sequences in conjunction with a general-purpose classification algorithm. First, noncyclic properties of constrained coding are identified by realizing that MTR codewords render invalid more often if bit shifts happen. Later, we present a method to use such invalid codewords to help detect and correct cycle slips. Finally, some numerical results are presented to show the effectiveness of the proposed detection/correction scheme using MTR codes and the support vector machines. It is demonstrated that such a combination has the potential for BER and post-ECC failure rate performance improvements by eliminating cycle slips for the generalized partial response channels.

Tape Mechanics Over a Grooved Roller: Experiments and Theory

In the case of an axially translating tape, supported by a roller, the effects of air entrainment can be reduced by a grooved roller. Use of grooves on the roller surface substantially improves the traction capacity, relative to a non-grooved roller surface [1,2,3,4]. In our previous work, a mechanics model of the tape interacting with a grooved roller was presented [5]. In this work, a comparison of the experimental and modeling studies of the tape-to-grooved-roller spacing is reported.Copyright

EMBEDDING NOISE PREDICTION INTO LIST-VITERBI DECODING USING ERROR DETECTION CODES FOR MAGNETIC TAPE SYSTEMS

A List Viterbi detector produces a rank ordered list of the N globally best candidates in a trellis search. A List Viterbi detector structure is proposed that incorporates the noise prediction with periodic state-metric updates based on outer error detection codes (EDCs). More specifically, a periodic decision making process is utilized for a non-overlapping sliding windows of P bits based on the use of outer EDCs. In a number of magnetic recording applications, Error Correction Coding (ECC) is adversely effected by the presence of long and dominant error events. Unlike the conventional post processing methods that are usually tailored to a specific set of dominant error events or the joint modulation code trellis architectures that are operating on larger state spaces at the expense of increased implementation complexity, the proposed detector does not use any a priori information about the error event distributions and operates at reduced state trellis. We present pre ECC bit error rate performance as well as the post ECC codeword failure rates of the proposed detector using perfect detection scenario as well as practical detection codes as the EDCs are not essential to the overall design. Furthermore, it is observed that proposed algorithm does not introduce new error events. Simulation results show that the proposed algorithm gives improved bit error and post ECC codeword failure rates at the expense of some increase in complexity.

Generalized sensitivity decoupling for dual-stage servo systems

In this paper, we present a new method for designing a dual-stage compensator. Sensitivity decoupling, decoupling the output sensitivity into the product of two sensitivities, is used as the starting point. This paper extends the idea of sensitivity decoupling so that optimization methods can be used to adjust the closed loop responses of the system while maintaining a pre-specified output sensitivity function. The set of all sensitivity decoupling controllers is derived by using the Youla parameterization and this set is used to formulate an optimization problem to shape the closed loop response of the system. A design example shows how decoupling can be maintained while changing the other system responses.