Correct Introduction, round 1
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letter.tex
30
letter.tex
@ -102,7 +102,7 @@ attempted to be corrected.
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We suggesst an empirical rule with which the components most likely needing
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We suggesst an empirical rule with which the components most likely needing
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correction can be determined.
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correction can be determined.
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Using this insight and performing a subsequent ``ML-in-the-list'' decoding,
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Using this insight and performing a subsequent ``ML-in-the-list'' decoding,
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a gain of up to approximately 1 dB is achieved compared to conventional
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a gain of up to 1 dB is achieved compared to conventional
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proximal decoding, depending on the decoder parameters and the code.
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proximal decoding, depending on the decoder parameters and the code.
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\end{abstract}
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\end{abstract}
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@ -126,7 +126,7 @@ the reliability of data by detecting and correcting any errors that may occur
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during its transmission or storage.
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during its transmission or storage.
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One class of binary linear codes, \textit{low-density parity-check} (LDPC)
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One class of binary linear codes, \textit{low-density parity-check} (LDPC)
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codes, has become especially popular due to its ability to reach arbitrarily
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codes, has become especially popular due to its ability to reach arbitrarily
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small probabilities of error at code rates up to the capacity of the channel
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small error probabilities at code rates up to the capacity of the channel
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\cite{mackay99}, while retaining a structure that allows for very efficient
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\cite{mackay99}, while retaining a structure that allows for very efficient
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decoding.
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decoding.
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While the established decoders for LDPC codes, such as belief propagation (BP)
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While the established decoders for LDPC codes, such as belief propagation (BP)
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@ -139,37 +139,37 @@ Optimization based decoding algorithms are an entirely different way of
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approaching the decoding problem.
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approaching the decoding problem.
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A number of different such algorithms have been introduced.
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A number of different such algorithms have been introduced.
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The field of \textit{linear programming} (LP) decoding \cite{feldman_paper},
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The field of \textit{linear programming} (LP) decoding \cite{feldman_paper},
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for example, represents one class of such algorithms, based on a reformulation
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for example, represents one class of such algorithms, based on a relaxation
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of the \textit{maximum likelihood} (ML) decoding problem as a linear program.
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of the \textit{maximum likelihood} (ML) decoding problem as a linear program.
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Many different optimization algorithms can be used to solve the resulting
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Many different optimization algorithms can be used to solve the resulting
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problem \cite{interior_point_decoding, ADMM, adaptive_lp_decoding}.
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problem \cite{ADMM, adaptive_lp_decoding, interior_point_decoding}.
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Recently, proximal decoding for LDPC codes was presented by
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Recently, proximal decoding for LDPC codes was presented by
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Wadayama et al. \cite{proximal_paper}.
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Wadayama \textit{et al.} \cite{proximal_paper}.
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It is a novel approach and relies on a non-convex optimization formulation
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Proximal decoding relies on a non-convex optimization formulation
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of the \textit{maximum a posteriori} (MAP) decoding problem.
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of the \textit{maximum a posteriori} (MAP) decoding problem.
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The aim of this work is to improve upon the performance of proximal decoding by
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The aim of this work is to improve upon the performance of proximal decoding by
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first presenting an examination of the algorithm's behavior and then suggesting
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first presenting an examination of the algorithm's behavior and then suggesting
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an approach to mitigate some of its flaws.
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an approach to mitigate some of its flaws.
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This analysis is performed within the context of
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This analysis is performed for
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\textit{additive white Gaussian noise} (AWGN) channels.
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\textit{additive white Gaussian noise} (AWGN) channels.
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It is first observed that, while the algorithm initially moves the estimate in
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We first observe that the algorithm initially moves the estimate in
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the right direction, in the final steps of the decoding process convergence to
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the right direction, however, in the final steps of the decoding process,
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the correct codeword is often not achieved.
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convergence to the correct codeword is often not achieved.
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Furthermore, it is suggested that the reason for this behavior is the nature
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Furthermore, we suggest that the reason for this behavior is the nature
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of the decoding algorithm itself, comprising two separate gradient descent
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of the decoding algorithm itself, comprising two separate gradient descent
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steps working adversarially.
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steps working adversarially.
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A method to mitigate this effect is proposed by appending an additional step
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We propose a method mitigate this effect by appending an
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to the decoding process.
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additional step to the decoding process.
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In this additional step, the components of the estimate with the highest
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In this additional step, the components of the estimate with the highest
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probability of being erroneous are identified.
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probability of being erroneous are identified.
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New codewords are then generated, over which an ``ML-in-the-list''
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New codewords are then generated, over which an ``ML-in-the-list''
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\cite{ml_in_the_list} decoding is performed.
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\cite{ml_in_the_list} decoding is performed.
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A process to conduct this identification is proposed in this paper.
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A process to conduct this identification is proposed in this paper.
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Using the improved algorithm, a gain of up to
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Using the improved algorithm, a gain of up to
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approximately 1 dB can be achieved compared to proximal decoding, depending on
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1 dB can be achieved compared to conventional proximal decoding,
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the parameters chosen and the code considered.
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depending on the decoder parameters and the code.
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%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%%%%%%%%%%%%%%%%%%%%%%%%%%%
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