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EFM coding: Squeezing the last bits

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Abstract

Runlength-limited (RLL) codes have found widespread usage in optical and magnetic recording products. Specifically, the RLL codes EFM and its successor, EFMPlus, are used in the compact discs (CD) and the digital versatile discs (DVD), respectively. EFMPlus offers a 6% increase in storage capacity with respect to EFM. The work reports on the feasibility and limits of EFM like codes that offer an even larger capacity. To this end, we provide an overview of the various limiting factors, such as runlength constraint, dc-content, and code complexity, and outline their relative effect on the code rate. In the second part of the article we show how the performance predicted by the tenets of information theory can be realized in practice. A worked example of a code whose rate is 7.5% larger than EFMPlus, namely a rate 256/476, (d=2, k=15) code, showing a 13 dB attenuation at f<sub>b</sub>=10<sup>-3 </sup>, is given to illustrate the theory

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... The performance of the rate 8/15, code, EFM15 [17], listed in Table IV, is a far cry from the theoretical bound. Braun et al. [20] and Immink [21] presented coding schemes using long block codes with enumerative coding that are very close to the predicted maxentropic performance. The typical codeword length in their constructions is about 1000 bits, and the hardware required for encoding and decoding is about 5 kB. ...
Article
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Codes were designed for optical disk recording system and future options were explored. The designed code was a combination of dc-free and runlength limited (DCRLL) codes. The design increased minimum feature size for replication and sufficient rejection of low-frequency components enabling a simple noise free tracking. Error-burst correcting Reed-Solomon codes were suggested for the resolution of read error. The features of DCRLL and runlength limited (RLL) sequences was presented and practical codes were devised to satisfy the given channel constraints. The mechanism of RLL codes supressed the components of the genarated sequences. The construction and performance of alternative Eight to fourteen modulation (EFM)-like codes was studied.
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We report on the performance assessment of two methods for generating DC-free runlength-limited sequences. Redundant bits used to optimize the low-frequency properties are multiplexed with user data or encoded data. In the first method, the redundant bits are multiplexed with the channel bits generated by a (d,k) encoder. In the second method, on the other hand, the redundant bits are multiplexed with the user data. i.e. prior to application of the (d,k) encoder. The second method can only be used if the (d,k) encoder satisfies the parity preserving condition, i.e., data words and code words of that code must have the same parity. In the article we describe in detail an example of a parity preserving (1, 8) code.
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We will report on new dc-free runlength-limited codes (DCRLL) intended for the next generation of digital versatile disc (DVD). The efficiency of the newly developed DCRLL schemes is extremely close to the theoretical maximum, and as a result, significant density gains can be obtained with respect to prior art coding schemes. Prefer-red embodiments of the codes (footprints) and respective hardware realization will be considered.
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We report on new DC-free runlength-limited codes (DCRLL) intended for the next generation of DVD. The efficiency of the newly developed DCRLL schemes is extremely close to the theoretical maximum, and as a result, significant density gains can be obtained with respect to prior art coding schemes
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The digital versatile disc (DVD) is a new optical recording medium with a storage capacity seven times higher than the conventional compact disc (CD). The major part of the capacity increase is achieved by the use of optics, shorter laser wavelength, and larger numerical aperture, which reduces the spot diameter by a factor of 1.65. The track formed by the recorded pits and lands, as well as the track pitch, can be reduced by the same factor. The storage capacity is further increased by a complete redesign of the logical format of the disc, including a more powerful error correction and recording code. The system requirements of the DVD and the related channel coding are outlined in this paper.
Book
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Since the early 1980s we have witnessed the digital audio and video revolution: the Compact Disc (CD) has become a commodity audio system. CD-ROM and DVD-ROM have become the de facto standard for the storage of large computer programs and files. Growing fast in popularity are the digital audio and video recording systems called DVD and BluRay Disc. The above mass storage products, which form the backbone of modern electronic entertainment industry, would have been impossible without the usage of advanced coding systems. Pulse Code Modulation (PCM) is a process in which an analogue, audio or video, signal is encoded into a digital bit stream. The analogue signal is sampled, quantized and finally encoded into a bit stream. The origins of digital audio can be traced as far back as 1937, when Alec H. Reeves, a British scientist, invented pulse code modulation \cite{Ree}. The advantages of digital audio and video recording have been known and appreciated for a long time. The principal advantage that digital implementation confers over analog systems is that in a well-engineered digital recording system the sole significant degradation takes place at the initial digitization, and the quality lasts until the point of ultimate failure. In an analog system, quality is diminished at each stage of signal processing and the number of recording generations is limited. The quality of analog recordings, like the proverbial 'old soldier', just fades away. The advent of ever-cheaper and faster digital circuitry has made feasible the creation of high-end digital video and audio recorders, an impracticable possibility using previous generations of conventional analog hardware. The general subject of coding for digital recorders is very broad, with its roots deep set in history. In digital recording (and transmission) systems, channel encoding is employed to improve the efficiency and reliability of the channel. Channel coding is commonly accomplished in two successive steps: (a) error-correction code followed by (b) recording (or modulation) code. Error-correction control is realized by adding extra symbols to the conveyed message. These extra symbols make it possible for the receiver to correct errors that may occur in the received message. In the second coding step, the input data are translated into a sequence with special properties that comply with the given "physical nature" of the recorder. Of course, it is very difficult to define precisely the area of recording codes and it is even more difficult to be in any sense comprehensive. The special attributes that the recorded sequences should have to render it compatible with the physical characteristics of the available transmission channel are called channel constraints. For instance, in optical recording a '1' is recorded as pit and a '0' is recorded as land. For physical reasons, the pits or lands should neither be too long or too short. Thus, one records only those messages that satisfy a run-length-limited constraint. This requires the construction of a code which translates arbitrary source data into sequences that obey the given constraints. Many commercial recorder products, such as Compact Disc and DVD, use an RLL code. The main part of this book is concerned with the theoretical and practical aspects of coding techniques intended to improve the reliability and efficiency of mass recording systems as a whole. The successful operation of any recording code is crucially dependent upon specific properties of the various subsystems of the recorder. There are no techniques, other than experimental ones, available to assess the suitability of a specific coding technique. It is therefore not possible to provide a cookbook approach for the selection of the 'best' recording code. In this book, theory has been blended with practice to show how theoretical principles are applied to design encoders and decoders. The practitioner's view will predominate: we shall not be content with proving that a particular code exists and ignore the practical detail that the decoder complexity is only a billion times more complex than the largest existing computer. The ultimate goal of all work, application, is never once lost from sight. Much effort has been gone into the presentation of advanced topics such as in-depth treatments of code design techniques, hardware consequences, and applications. The list of references (including many US Patents) has been made as complete as possible and suggestions for 'further reading' have been included for those who wish to pursue specific topics in more detail. The decision to update Coding Techniques for Digital Recorders, published by Prentice-Hall (UK) in 1991, was made in Singapore during my stay in the winter of 1998. The principal reason for this decision was that during the last ten years or so, we have witnessed a success story of coding for constrained channels. The topic of this book, once the province of industrial research, has become an active research field in academia as well. During the IEEE International Symposia on Information Theory (ISIT and the IEEE International Conference on Communications (ICC), for example, there are now usually three sessions entirely devoted to aspects of constrained coding. As a result, very exciting new material, in the form of (conference) articles and theses, has become available, and an update became a necessity. The author is indebted to the Institute for Experimental Mathematics, University of Duisburg-Essen, Germany, the Data Storage Institute (DSI) and National University of Singapore (NUS), both in Singapore, and Princeton University, US, for the opportunity offered to write this book. Among the many people who helped me with this project, I like to thank Dr. Ludo Tolhuizen, Philips Research Eindhoven, for reading and providing useful comments and additions to the manuscript. Preface to the Second Edition About five years after the publication of the first edition, it was felt that an update of this text would be inescapable as so many relevant publications, including patents and survey papers, have been published. The author's principal aim in writing the second edition is to add the newly published coding methods, and discuss them in the context of the prior art. As a result about 150 new references, including many patents and patent applications, most of them younger than five years old, have been added to the former list of references. Fortunately, the US Patent Office now follows the European Patent Office in publishing a patent application after eighteen months of its first application, and this policy clearly adds to the rapid access to this important part of the technical literature. I am grateful to many readers who have helped me to correct (clerical) errors in the first edition and also to those who brought new and exciting material to my attention. I have tried to correct every error that I found or was brought to my attention by attentive readers, and seriously tried to avoid introducing new errors in the Second Edition. China is becoming a major player in the art of constructing, designing, and basic research of electronic storage systems. A Chinese translation of the first edition has been published early 2004. The author is indebted to prof. Xu, Tsinghua University, Beijing, for taking the initiative for this Chinese version, and also to Mr. Zhijun Lei, Tsinghua University, for undertaking the arduous task of translating this book from English to Chinese. Clearly, this translation makes it possible that a billion more people will now have access to it. Kees A. Schouhamer Immink, Rotterdam, November 2004
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Full-text available
Basic trade-offs between the rate of combined DC-free runlength-limited (DCRLL) modulation codes and the amount of suppression of low-frequency components are presented. The main results are obtained by means of a numerical study of dependencies between statistical properties of ideal, “maxentropic” DCRLL sequences. The numerical results are mathematically founded by proving the observed behavior of the Shannon capacity of the DCRLL constraints for asymptotically large values of digital sum variation. Presented characteristics of maxentropic DCRLL sequences comply with the corresponding properties of maxentropic pure DC-free sequences, as previously considered by Justesen (1982) and Immink (1991). Knowledge of the maxentropic bounds enables us to evaluate the performances of implemented DCRLL codes with respect to their low-frequency suppression capability. Among the considered codes are the EFM code as applied in the compact disc system, and the EFMPlus code which has been adopted as the coding format of the DVD system
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A new configuration of codes is proposed for translating user information into a constrained channel sequence. The new configuration makes it possible to practically apply constrained channel codes whose efficiency approaches the channel capacity
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This paper describes a modulation method suitable for high-density recording on an optical disc. This method, called 8-15 modulation method, is based on an 8-15 channel coding with longer minimum interval between transitions and an efficient DC component suppressing method. The maximum and minimum intervals between transitions of the 8-15 channel code achieve the theoretical limits for conversion of an 8-bit data word to a 15-bit codeword. The DC component suppressing method which adds several redundant bits to the 8-15 channel code, can suppress the low-frequency components of the channel bit stream. These features allow this method to extend the minimum interval between transitions and window margin by 5%, compared with EFMPlus. Additionally, this paper proposes a data format suitable for using the 8-15 modulation method and RS product code as the modulation method and error correcting code, respectively
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The technique introduced has relatively simple encoding and decoding procedures which can be implemented at the high bit rates used in optical fiber communication systems. Because it is similar to the established technique of self-synchronizing scrambling but is also capable of guiding the scrambling process to produce a balanced encoded bit stream, the technique is called guided scrambling, (GS). The concept of GS coding is explained, and design parameters which ensure good line code characteristics are discussed. The performance of a number of guided scrambling configurations is reported in terms of maximum consecutive like-encoded bits, encoded stream disparity, decoder error extension, and power spectral density of the encoded signal. Comparison of guided scrambling with conventional line code techniques indicates a performance which approaches that of alphabetic lookup table codes with an implementation complexity similar to that of current nonalphabetic coding techniques.
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Traditional schemes for encoding and decoding runlength-constrained sequences using the enumeration principle require two sets of weighting coefficients. A new enumeration is presented requiring only one set of coefficients
Coding Techniques for Digital Recorders, Prentice-Hall International (UK) Ltd., Englewood CliffsThe Digital Versatile Disc (DVD): System Requirements and Channel CodingOn the Low-frequency Suppression Per-formance of DC-free Runlength-limited Modulation Codes
  • K A S K A S Immink
  • Immink
[1]K.A.S. Immink, Coding Techniques for Digital Recorders, Prentice-Hall International (UK) Ltd., Englewood Cliffs, New Jersey, 1991. K.A.S.Immink, ’The Digital Versatile Disc (DVD): System Requirements and Channel Coding’, SMPTE Journal, vol. 105, pp. 483-489, no. 8, Aug. 1996. V. Braun and A.J.E.M. Janssen, ’On the Low-frequency Suppression Per-formance of DC-free Runlength-limited Modulation Codes’, IEEE Trans. Consumer Electr., vol. CE-42, pp. 939-945, no. 4, Nov. 1996
Code configuration foravoiding error propagation Elec-tronics LettersEncoding of weight set IT-42Guided Scrambling: A New Line Coding Technique for High Bit Rate Fiber Optic Transmission Systems
  • K A S L Immink
  • K A S Patrovics
  • I J Immink
  • W D Fair
  • W A Gover
  • R I Krzymien
  • Macdonald
[2] [3] [4]K.A.S.Immink,’Code configuration foravoiding error propagation’, Elec-tronics Letters, vol. 32, No. 24, pp. 2191-2192, Nov. 1996. L. Patrovics and K.A.S. Immink, ’Encoding of weight set’, IEEE Trans. Inform. Theory, vol. IT-42, no. 5, pp. 1553-1554, Sept. 1996. I.J. Fair, W.D. Gover, W.A. Krzymien, and R.I. MacDonald, ’Guided Scrambling: A New Line Coding Technique for High Bit Rate Fiber Optic Transmission Systems’, IEEE Trans. Commun., vol. COM-39, no. 2, pp. 289-297, Feb. 1991. A. Kunisa, S. Takahashi, and N. Itoh, ’Digital Modulation Method for Re-cordable Digital Video Disc’, IEEE Trans. Consumer Electr., vol. 42, pp. 820-825, Aug. 1996
The Digital Versatile Disc (DVD): System Requirements and Channel CodingOn the Low-frequency Suppression Per-formance of DC-free Runlength-limited Modulation Codes
  • K A S Immink Rraun
  • A J E M Janssen
K.A.S. Immink, 'The Digital Versatile Disc (DVD): System Requirements and Channel Coding', SMPTE Journal, vol. 105, pp. 483-489, no. 8, Aug. 1996. V. Rraun and A.J.E.M. Janssen, 'On the Low-frequency Suppression Per-formance of DC-free Runlength-limited Modulation Codes', IEEE Trans. Consumer Electr, vol. CE-42, pp. 939-945, no. 4, Nov. 1996.
Guided Scrambling: A New Line Coding Technique for High Bit Rate Fiber Optic Transmission Systems
  • I J Fair
  • W D Gover
  • W A Krzymien
  • R I Macdonald
I.J. Fair, W.D. Gover, W.A. Krzymien, and R.I. MacDonald, 'Guided Scrambling: A New Line Coding Technique for High Bit Rate Fiber Optic Transmission Systems', IEEE Trans. Commun., vol. COM-39, no. 2, pp. 289-297, Feb. 1991.