LLM review
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@@ -55,7 +55,7 @@
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\DeclareAcronym{cn}{
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short=CN,
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long=chek node
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long=check node
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}
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\DeclareAcronym{ber}{
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@@ -4,7 +4,7 @@
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\Ac{qec} is a field of research combining ``classical''
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communications engineering and quantum information science.
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This chapter provides the relevant theoretical background on both of
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these topics and subsequently introduces the the fundamentals of \ac{qec}.
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these topics and subsequently introduces the fundamentals of \ac{qec}.
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% TODO: Is an explanation of BP with guided decimation needed in this chapter?
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% TODO: Is an explanation of OSD needed chapter?
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@@ -15,9 +15,8 @@ these topics and subsequently introduces the the fundamentals of \ac{qec}.
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% TODO: Maybe rephrase: The core concept is not the realization, its's the
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% thing itself
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The core concept underpinning error correcting codes is the
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realization that the introduction of a finite amount of redundancy
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to information before its transmission can leed to a considerably
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reduced error rate.
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realization that introducing a finite amount of redundancy to
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information before transmission can considerably reduce the error rate.
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Specifically, Shannon proved in 1948 that for any channel, a block
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code can be found that achieves arbitrarily small probability of
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error at any communication rate up to the capacity of the channel
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@@ -42,7 +41,7 @@ algorithm.
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% TODO: Do I need a specific reference for the expanded Hilbert space thing?
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One particularly important class of coding schemes is that of binary
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linear block codes.
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The information to be protected takes the form of a sequence of of
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The information to be protected takes the form of a sequence of
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binary symbols, which is split into separate blocks.
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Each block is encoded, transmitted, and decoded separately.
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The encoding step introduces redundancy by mapping input messages
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@@ -62,7 +61,7 @@ We call the set of all codewords $\mathcal{C}$ the \textit{code}
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During the encoding process, a mapping from $\mathbb{F}_2^k$
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onto $\mathcal{C} \subset \mathbb{F}_2^n$ takes place.
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The input messages are mapped onto an expanded vector space, where
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they are ``further appart'', giving rise to the error correcting
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they are ``further apart'', giving rise to the error correcting
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properties of the code.
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This notion of the distance between two codewords $\bm{x}_1$ and
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$\bm{x}_2$ can be expressed using the \textit{Hamming distance} $d(\bm{x}_1,
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@@ -77,7 +76,7 @@ We define the \textit{minimum distance} of a code $\mathcal{C}$ as
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%
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We can signify that a binary linear block code has information length
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$k$, block length $n$ and minimum distance $d_\text{min}$ using the
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notation $[n,k,d_\text{dmin}]$ \cite[Sec.~1.3]{macwilliams_theory_1977}.
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notation $[n,k,d_\text{min}]$ \cite[Sec.~1.3]{macwilliams_theory_1977}.
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%
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% Parity checks, H, and the syndrome
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@@ -201,7 +200,7 @@ whereas modern codes are suitable for iterative soft-decision
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decoding \cite[Preface]{ryan_channel_2009}. The iterative decoding algorithms
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in question are generally defined in terms of message passing on the
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\textit{Tanner graph} of the code. The Tanner graph is a bipartite
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graph that constitues an alternative representation of the \ac{pcm}.
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graph that constitutes an alternative representation of the \ac{pcm}.
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We define two types of nodes: \acp{vn}, corresponding to codeword
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bits, and \acp{cn}, corresponding to individual parity checks.
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We then construct the Tanner graph by connecting each \ac{cn} to
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@@ -282,11 +281,11 @@ Mathematically, we represent a \ac{vn} using the index $i \in
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1 : n \right]$ and a \ac{cn} using the index $j \in \mathcal{J}
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:= \left[ 1 : m \right]$.
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We can then encode the information contained in the graph by defining
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the neighborhood of a varialbe node $i$ as
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$\mathcal{N}_\text{V} (i) = \left\{ i \in \mathcal{I} : \bm{H}_{j,i}
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the neighborhood of a variable node $i$ as
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$\mathcal{N}_\text{V} (i) = \left\{ j \in \mathcal{J} : \bm{H}_{j,i}
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= 1 \right\}$
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and that of a check node $j$ as
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$\mathcal{N}_\text{C} (j) = \left\{ j \in \mathcal{J} : \bm{H}_{j,i}
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$\mathcal{N}_\text{C} (j) = \left\{ i \in \mathcal{I} : \bm{H}_{j,i}
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= 1 \right\}$.
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%
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@@ -385,12 +384,12 @@ Broadly, there are two kinds of \ac{ldpc} codes, \textit{regular} and
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Regular codes are characterized by the fact that the weights, i.e.,
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the numbers of ones, of their rows and columns are constant
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\cite[Sec.~5.1.1]{ryan_channel_2009}.
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Already during their introduction, regular \ac{ldpc} codes where shown to have
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Already during their introduction, regular \ac{ldpc} codes were shown to have
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a minimum distance scaling linearly with the block length $n$ for
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large values \cite[Ch.~2,~Theorem~1]{gallager_low_1960},
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which leads to them not exhibiting an error floor under \ac{ml} decoding.
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Irregular codes, on the other hand, generally do exhibit an error floor,
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their redeming quality being the ability to reach near-capacity
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their redeeming quality being the ability to reach near-capacity
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performance in the waterfall region \cite[Intro.]{costello_spatially_2014}.
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\subsection{Spatially-Coupled LDPC Codes}
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@@ -532,7 +531,7 @@ This is precisely the effect that leads to the good performance of
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% Introduction
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\ac{ldpc} codes are generally decoded using efficient iterative
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algorithms, something that is possilbe due to their sparsity
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algorithms, something that is possible due to their sparsity
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\cite[Sec.~5.3]{ryan_channel_2009}.
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The algorithm originally proposed alongside LDPC codes for this
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purpose by Gallager in 1960 is now known as the \ac{spa}
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@@ -544,7 +543,7 @@ The core idea of the resulting algorithm is to view \acp{cn} as
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representing single-parity check codes and \acp{vn} as representing
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repetition codes.
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The algorithm alternates between consolidating soft information about
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the \acp{vn} in the \acp{cn}, and consolidating soft information abou
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the \acp{vn} in the \acp{cn}, and consolidating soft information about
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the \acp{cn} in the \acp{vn}.
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To this end, messages are passed back and forth along the edges of
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the Tanner graph.
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