Article

Code configuration for avoiding error propagation

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Abstract

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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... The encoding arrange ment is shown in figure 5.2. Immink [45,46] proposes a scheme th a t employs an added lossless compression stage before the error control encoding to improve the tolerance to burst errors. A comprehensive overview of such schemes with emphasis to applications in magnetic recording is presented in [47]. ...
Thesis
Channel coding is an important consideration influencing the design of a communications system. In particular, error control coding is used to detect and/or correct errors and line coding to modify the characteristics of the transmitted signal to suit other constraints of the channel, such as restricted frequency response. This thesis explores aspects of channel coding for such constrained channels with emphasis given to error control coding. Specifically, the hrst chapter of this thesis presents a general overview of channel coding, presents the organisation of the thesis and details the main contributions. The second chapter gives an overview of the principles of error control coding and line coding and explains a few terms that are connnonly used in the remainder of the thesis. One kind of constrained channel investigated here is the binary asymmetric error channel, where error transitions from one to zero occur with different probability than from zero to one. Error correcting codes for this channel and their properties are investigated in the third chapter. The fourth chapter introduces disparity control coding, and proposes a new error control coding structure that satisfies disparity constraints for both binary asymmetric and symmetric error channels. Run length limited channels are the subject of the hfth chapter. A new coding structure is proposed that offers advantages in performance over the one conventionally used for error control in such channels. The sixth chapter introduces peak power constraints present in multi-carrier systems. Codes that can be used limit the peak to average power ratio of such systems are presented and the application of the coding structure of the fifth chapter is also discussed. The final chapter brings the thesis to a conclusion by summarising the main results and proposing areas where further work may be fruitful.
... Certainly the error channel in such a system must be well understood, and the choice between low overall packet loss, or "even" packet loss regardless of data, must be carefully made for the given application. If error correcting codes are to be used in conjunction with line codes, it is vital that they are selected to interoperate correctly; Immink [174] discusses the order in which channel and error-correcting coding schemes are applied, in terms of error propagation reduction. ...
Thesis
Full-text available
Optical fibre communications are now widely used in many applications, including local area computer networks. I postulate that many future optical LANs will be required to operate with limited optical power budgets for a variety of reasons, including increased system complexity and link speed, low cost components and minimal increases in transmit power. Some developers will wish to run links with reduced power budget margins, and the received data in these systems will be more susceptible to errors than has been the case previously. The errors observed in optical systems are investigated using the particular case of Gigabit Ethernet on fibre as an example. Gigabit Ethernet is one of three popular optical local area interconnects which use 8B/10B line coding, along with Fibre Channel and Infiniband, and is widely deployed. This line encoding is also used by packet switched optical LANs currently under development. A probabilistic analysis follows the effects of a single channel error in a frame, through the line coding scheme and the MAC layer frame error detection mechanisms. Empirical data is used to enhance this original analysis, making it directly relevant to deployed systems. Experiments using Gigabit Ethernet on fibre with reduced power levels at the receiver to simulate the effect of limited power margins are described. It is found that channel bit error rate and packet loss rate have only a weakly deterministic relationship, due to interactions between a number of non-uniform error characteristics at various network sub-layers. Some data payloads suffer from high bit error rates and low packet loss rates, compared to others with lower bit error rates and yet higher packet losses. Experiments using real Internet traffic contribute to the development of a novel model linking packet loss, the payload damage rate, and channel bit error rate. The observed error behaviours at various points in the physical and data link layers are detailed. These include data-dependent channel errors; this error hot- spotting is in contrast to the failure modes observed in a copper-based system. It is also found that both multiple channel errors within a single code-group, and multiple error instances within a frame, occur more frequently than might be expected. The overall effects of these error characteristics on the ability of cyclic redundancy checks (CRCs) to detect errors, and on the performance of higher layers in the network, is considered. This dissertation contributes to the discussion of layer interactions, which may lead to un-foreseen performance issues at higher levels of the network stack, and extends it by considering the physical and data link layers for a common form of optical link. The increased risk of errors in future optical networks, and my findings for 8B/10B encoded optical links, demonstrate the need for a cross-layer understanding of error characteristics in such systems. The development of these new networks should take error performance into account in light of the particular requirements of the application in question.
... Certainly the error channel in such a system must be well understood, and the choice between low overall packet loss, or "even" packet loss regardless of data, must be carefully made for the given application. If error correcting codes are to be used in conjunction with line codes, it is vital that they are selected to interoperate correctly; Immink [174] discusses the order in which channel and error-correcting coding schemes are applied, in terms of error propagation reduction. ...
... The condition (6) ensures that the error propagation in the decoder always remains finite [15]. Further improvement can be reached in error propagation if we diminish the error probability at the bit stuff decoder's input by the application of an outer error correcting code with a Bliss scheme [16], [17]. Keeping the WRDS high by applying the coding rule ...
Article
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By generalizing the accumulated charge concept, we introduce a new class of constraints, the generalized charge constraint to control the spectral properties of a binary sequence. The new constraint limits the level at the output of a digital filter, diminishing those spectral components of the channel sequence being enhanced by the filter. A suitable coder structure, a feedback controlled bit stuff encoder is suggested to implement the new constraint. We demonstrate the spectral shaping property of the new coder structure and derive an approximate formula for the spectrum of the output binary signal. We also show that the coder performs a sigma-delta-like operation and the method is capable of implementing spectral and run-length constraints simultaneously. As a demonstration, we present a few particular spectral characteristics shaped by different examples of loop filters. Full text available: http://regi.hte.hu/HXT4805DG225R7EC7896G9ED545133D0S/InfocomJ2012_I_komplett.pdf
... Single channel bit errors may result in error propagation which could corrupt the entire data in the decoded word, and, of course, the longer the codeword the greater the number of data symbols affected. With a new technique massiv error propagation is avoided by reversing the conventional hierarchy of the error control code and the constrained code [4]. Before dealing with the techniques for suppressing the low-frequency components of RLL codes, we will describe in the next section how encoding and decoding of these very long codes can be done in a practical manner. ...
Article
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
Conference Paper
In this paper we present a new method of integrating constrained sequence (CS) and error control (EC) codes for digital communication systems. In our technique, encoded sequences are constructed such that they contain the required redundancy for error control while also exhibiting the characteristics required of constrained sequences. These sequences are constructed by distributing the EC parity bits throughout the CS coded sequence so that decoding can be performed with standard error control decoding techniques followed by constrained sequence decoding. This decoding structure avoids the problem of CS error propagation when CS decoding is performed prior to EC decoding
Conference Paper
Full-text available
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 Disc (CD) and the Digital Versatile Disc (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 will 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 will 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 b =10 ;3 , will be given to illustrate the theory. I.
Article
A method for constructing constrained sequences with embedded redundancy for error control is reported. These sequences are constructed such that the first stage of decoding can be performed with standard error control decoding techniques, avoiding the problem of error propagation with prior constrained-sequence decoding