A Survey of Codes for Optical Disk Recording
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paper_title: Optical Disc System for Digital Video Recording

paper_content:

We have developed a new error correction method (Picket: a combination of a long distance code (LDC) and a burst indicator subcode (BIS)), a new channel modulation scheme (17PP, or (1, 7) RLL parity preserve (PP)-prohibit repeated minimum transition runlength (RMTR) in full), and a new address format (zoned constant angular velocity (ZCAV) with headers and wobble, and practically constant linear density) for a digital video recording system (DVR) using a phase change disc with 9.2 GB capacity with the use of a red (λ=650 nm) laser and an objective lens with a numerical aperture (NA) of 0.85 in combination with a thin cover layer. Despite its high density, this new format is highly reliable and efficient. When extended for use with blue-violet (λ≈405 nm) diode lasers, the format is well suited to be the basis of a third-generation optical recording system with over 22 GB capacity on a single layer of a 12-cm-diameter disc.
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paper_title: Codes for zero spectral density at zero frequency

paper_content:

In pulse-amplitude modulation (PAM) digital transmission systems line encoding is used for shaping the spectrum of the encoded symbol sequence to suit the frequency characteristics of the transmission channel. In particular, it is often required that the encoded symbol sequence have a zero mean and spectral density vanishing at zero frequency. We show that the finite running digital sum condition is a necessary and sufficient condition for this to occur. The result holds in particular for alphabetic codes, which are the most widely used line codes.
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paper_title: Upper bound on the efficiency of dc-constrained codes

paper_content:

We derive the limiting efficiencies of dc-constrained codes. Given bounds on the running digital sum (RDS), the best possible coding efficiency η, for a K-ary transmission alphabet, is η = log 2 λ max /log 2 K, where λ max is the largest eigenvalue of a matrix which represents the transitions of the allowable states of RDS. Numerical results are presented for the three special cases of binary, ternary and quaternary alphabets.
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paper_title: Channel capacity of charge-constrained run-length limited codes

paper_content:

The methods of information theory are applied to run-length limited codes with charge constraints. These self-clocking codes are useful in several areas of information storage, including magnetic recording, where it may be desirable to eliminate the dc component of the frequency spectrum. The channel capacity of run-length limited codes, with and without charge constraints, is derived and tabulated. The channel capacity specifies the maximum ratio of data/message bits achievable in implementing these codes and gives insight into the choice of codes for a particular task. The well-known frequency modulation (FM) code provides a simple example of these techniques.
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paper_title: On modulation, coding and signal processing for optical and magnetic recording systems

paper_content:

A filter retaining device to prevent a unit filter from inadvertently falling out of a bottom access flow-through housing when the housing is opened to gain access to the interior. Bottom access flow-through filter housings typically include spaced apart elongated channels which slidably receive a unit filter. These channels serve to locate and hold a unit filter in a gas stream passing through the flow-through housing. The filter retaining means is removably attached to the bottom open end of each channel to support the unit filter in the flow-through housing when the bottom access is opened to gain access to the interior of the filter housing.
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paper_title: Optical Disc System for Digital Video Recording

paper_content:

We have developed a new error correction method (Picket: a combination of a long distance code (LDC) and a burst indicator subcode (BIS)), a new channel modulation scheme (17PP, or (1, 7) RLL parity preserve (PP)-prohibit repeated minimum transition runlength (RMTR) in full), and a new address format (zoned constant angular velocity (ZCAV) with headers and wobble, and practically constant linear density) for a digital video recording system (DVR) using a phase change disc with 9.2 GB capacity with the use of a red (λ=650 nm) laser and an objective lens with a numerical aperture (NA) of 0.85 in combination with a thin cover layer. Despite its high density, this new format is highly reliable and efficient. When extended for use with blue-violet (λ≈405 nm) diode lasers, the format is well suited to be the basis of a third-generation optical recording system with over 22 GB capacity on a single layer of a 12-cm-diameter disc.
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paper_title: Maximum Entropy Charge-Constrained Run-Length Codes

paper_content:

The authors present a study of run-length-limiting codes that have a null at zero frequency or DC. The class of codes or sequences considered is specified by three parameters: (d, k, c). The first two constraints, d and k, put lower and upper bounds on the run-lengths, while the charge constraint, c, is responsible for the spectral null. A description of the combined (d, k, c) constraints, in terms of a variable length graph, and its adjacency matrix, A(D), are presented. The maximum entropy description of the constraint described by a run-length graph is presented as well as the power spectral density. The results are used to study several examples of (d, k, c) constraints. The eigenvalues and eigenvectors of the classes of (d, k=2c-1, c) and (d, k=d+1, c) constraints for (c=1,2,. . .), are shown to satisfy certain second-order recursive equations. These equations are solved using the theory of Chebyshev polynomials. >
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paper_title: Upper bound on the efficiency of dc-constrained codes

paper_content:

We derive the limiting efficiencies of dc-constrained codes. Given bounds on the running digital sum (RDS), the best possible coding efficiency η, for a K-ary transmission alphabet, is η = log 2 λ max /log 2 K, where λ max is the largest eigenvalue of a matrix which represents the transitions of the allowable states of RDS. Numerical results are presented for the three special cases of binary, ternary and quaternary alphabets.
---
paper_title: Channel capacity of charge-constrained run-length limited codes

paper_content:

The methods of information theory are applied to run-length limited codes with charge constraints. These self-clocking codes are useful in several areas of information storage, including magnetic recording, where it may be desirable to eliminate the dc component of the frequency spectrum. The channel capacity of run-length limited codes, with and without charge constraints, is derived and tabulated. The channel capacity specifies the maximum ratio of data/message bits achievable in implementing these codes and gives insight into the choice of codes for a particular task. The well-known frequency modulation (FM) code provides a simple example of these techniques.
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paper_title: Optimization of low-frequency properties of eight-to-fourteen modulation

paper_content:

A description is given of the eight to fourteen modulation system (EFM) designed for the Compact Disc Digital Audio System with optical read-out. EFM combines high information density and immunity to tolerances in the light path with low power at the low-frequency end of the modulation bit stream spectrum. In this modulation scheme, blocks of eight data input bits are transformed into fourteen channel bits, which follow certain minimum and maximum run-length constraints by using a code book. To prevent violation of the minimum and maximum run-length constraints a certain number of merging bits are needed to concatenate the blocks. There are cases where the merging bits are not uniquely determined by the concatenation rules. This freedom of choice thus created is used for minimizing the power of the modulated bit sequence at low frequencies. The paper presents the results of algorithms that were used to minimize this low frequency content.
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paper_title: Method for encoding binary data

paper_content:

Hydraulically powered percussive apparatus for breaking rock, drilling etc. in which a combined spool valve and hammer reciprocates in the bore of a cylinder structure. A high pressure fluid inlet leads to the bore and a low pressure outlet leads from the bore. A fluid flow passage communicates with the bore at two axially spaced locations. As the hammer reciprocates, it cyclically connects, via the bore, the inlet to the passage and the outlet to the passage. Pressures in the inlet and outlet fluctuate between fairly narrow limits whereas the pressure in the passage fluctuates between a pressure approximating inlet pressure and a pressure approximating outlet pressure. The hammer has two operating faces. The first of these is exposed to the relatively steady inlet pressure and the second is subjected to the widely varying pressure in the passage. The direction of the resultant force on the hammer reverses at the pressure in the passage varies from approximately inlet pressure to approximately outlet pressure.
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paper_title: Method for encoding binary data

paper_content:

Hydraulically powered percussive apparatus for breaking rock, drilling etc. in which a combined spool valve and hammer reciprocates in the bore of a cylinder structure. A high pressure fluid inlet leads to the bore and a low pressure outlet leads from the bore. A fluid flow passage communicates with the bore at two axially spaced locations. As the hammer reciprocates, it cyclically connects, via the bore, the inlet to the passage and the outlet to the passage. Pressures in the inlet and outlet fluctuate between fairly narrow limits whereas the pressure in the passage fluctuates between a pressure approximating inlet pressure and a pressure approximating outlet pressure. The hammer has two operating faces. The first of these is exposed to the relatively steady inlet pressure and the second is subjected to the widely varying pressure in the passage. The direction of the resultant force on the hammer reverses at the pressure in the passage varies from approximately inlet pressure to approximately outlet pressure.
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paper_title: EFMplus: the coding format of the multimedia compact disc

paper_content:

Reports on an alternative to eight-to-fourteen modulation (EFM), called EFMPlus, which has been adopted as coding format of the multimedia compact disc proposal. The rate of the new code is 8/16, which means that a 6-7 % higher information density can be obtained. EFMPlus is the spitting image of EFM (same minimum and maximum runlength, clock content etc). Computer simulations have shown that the low-frequency content of the new code is only slightly larger than its conventional EFM counterpart. >
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paper_title: A new approach to constructing optimal block codes for runlength-limited channels

paper_content:

The paper describes a technique for constructing fixed-length block codes for (d, k)-constrained channels. The codes described are of the simplest variety-codes for which the encoder restricted to any particular channel state is a one-to-one mapping and which is not permitted to "look ahead" to future messages. Such codes can be decoded with no memory and no anticipation and are thus an example of what Schouhamer Immink (1992) has referred to as block-decodable. For a given blocklength n and given values of (d, k), the procedure constructs a code with the highest possible rate among all such block codes, and it does so without the iterative search that is typically used (i.e., Franaszek's recursive elimination algorithm). The technique used is similar to Beenker and Immink's (1983) "Construction 2" in that every message is associated with a (d, k, l, r) sequence of length n-d; however the values used in the present approach are l=k-d and r=k-1, as opposed to Beenker and Schouhamer Immink's values of l=r=k-d. Thus the present approach demonstrates that "Construction 2" is optimal for d=1 but is suboptimal for d>1. Furthermore, the structure of the present codes permits enumerative coding techniques to simplify encoding and decoding. >
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paper_title: Constructions of almost block-decodable runlength-limited codes

paper_content:

Describes a new technique for constructing fixed-length (d,k) runlength-limited block codes. The new codes are very close to block-decodable codes, as decoding of the retrieved sequence can be accomplished by observing (part of) the received codeword plus a very small part (usually only a single bit) of the previous codeword. The basic idea of the new construction is to uniquely represent each source word by a (d,k) sequence with specific predefined properties, and to construct a bridge of /spl beta/, 1/spl les//spl beta//spl les/d, merging bits between every pair of adjacent words. An essential element of the new coding principle is look ahead. The merging bits are governed by the state of the encoder (the history), the present source word to be translated, and by the upcoming source word. The new constructions have the virtue that only one look-up table is required for encoding and decoding. >
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paper_title: On runlength-limited coding with DC control

paper_content:

Constructions are presented of finite-state encoders for certain (d,k) runlength-limited (RLL) constraints with direct current control. In particular, an example is provided for a rate 8:16 encoder for the (2,10)-RLL constraint that requires no look-ahead in decoding, thus, performing favorably compared to the EFMPlus code used in the DVD standard.
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paper_title: EFM coding: squeezing the last bits

paper_content:

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/=10/sup -3/, is given to illustrate the theory.
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paper_title: An Enumerative Coding Technique for DC-Free Runlength-Limited Sequences

paper_content:

We present an enumerative technique for encoding and decoding DC-free runlength-limited sequences. This technique enables the encoding and decoding of sequences approaching the maxentropic performance bounds very closely in terms of the code rate and low-frequency suppression capability. Use of finite-precision floating-point notation to express the weight coefficients results in channel encoders and decoders of moderate complexity. For channel constraints of practical interest, the hardware required for implementing such a quasi-maxentropic coding scheme consists mainly of a ROM of at most 5 kB.
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paper_title: DC-free run-length-limited codes for magnetic recording

paper_content:

In this paper, a method to design high-efficiency codes with combined run-length and dc-null constraints is presented. Using the new method, two new dc-free (1,7) codes, with rates of 12/20 and 16/26 were developed. The code efficiencies are 89.31 and 91.6%, respectively. The proposed approach is more general than the technique used to design the existing dc-free d=1 code. The performances of the new codes are also compared with that of the rate 8/10 dc-free (0,4) code. The minimum distance analysis and the bit error rate simulation both show that while at low densities the proposed codes exhibit performance degradation compared to the higher rate (0,4) code, they perform better than the latter as density increases, despite the code rate disadvantage.
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paper_title: Binary two-thirds rate code with full word look-ahead

paper_content:

A new 2/3-rate run-length limited code with d = 1 and k = 7 is described in this paper. It is a state dependent, look-ahead code that has advantages over the MFM and 3PM
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Title: A Survey of Codes for Optical Disk Recording

Section 1: Properties of RLL and DCRLL Sequences
Description 1: Explain the basic characteristics of RLL and DCRLL sequences, their importance in optical disk recording, and their capacity and spectral properties.

Section 2: Capacity and Spectral Properties of DCRLL Sequences
Description 2: Discuss the capacity and spectral properties of DCRLL sequences in detail, including their power density functions and the impact of different parameters on the spectral performance.

Section 3: EFM
Description 3: Describe the EFM coding scheme, including its parameters, operation, and techniques used for minimizing low-frequency content.

Section 4: EFMPlus
Description 4: Outline the design and characteristics of EFMPlus, its advantages over EFM, and its application in DVD systems.

Section 5: Alternatives to EFM Schemes
Description 5: Explore the possibilities of redesigning EFM and EFMPlus codes, comparing their performance and complexity, and propose alternative code designs.

Section 6: Performance of EFM-Like Coding Schemes
Description 6: Assess the spectral performance of various EFM-like coding schemes through computer simulation results and theoretical bounds.

Section 7: Other Examples of DCRLL Codes
Description 7: Present other examples of DCRLL codes, their systematic design approaches, and methods for enhancing dc-control.

Section 8: Dc-Control on Data Level versus Coded Level
Description 8: Compare the effectiveness of dc-control strategies performed at the source data level versus the channel data level, illustrating their impacts on low-frequency content suppression.

Section 9: Codes with Parity Preserving Word Assignment
Description 9: Describe the design and advantages of parity preserving codes, providing examples and performance comparisons with standard codes.

Section 10: Conclusion
Description 10: Summarize the survey, highlighting the key insights about channel codes for optical disk recording systems and their proximity to theoretical bounds.