diff --git a/latex/thesis/chapters/decoding_techniques.tex b/latex/thesis/chapters/decoding_techniques.tex index 68a5e7b..3211b0d 100644 --- a/latex/thesis/chapters/decoding_techniques.tex +++ b/latex/thesis/chapters/decoding_techniques.tex @@ -237,7 +237,7 @@ However, since the number of constraints needed to characterize the codeword polytope is exponential in the code length, this formulation is relaxed futher. By observing that each check-node defines its own local single parity-check code, and thus its own \textit{local codeword polytope}, -the \textit{relaxed codeword polytope} $Q$ is defined as the intersection of all +the \textit{relaxed codeword polytope} $\overline{Q}$ is defined as the intersection of all local codeword polytopes. This consideration leads to the following constraints:% % @@ -245,7 +245,7 @@ This consideration leads to the following constraints:% \ldots .\end{align*} -In figure \ref{fig:dec:poly} the two relaxations are compared based on an +In figure \ref{fig:dec:poly}, the two relaxations are compared based on an example code. Figure \ref{fig:dec:poly:exact} shows the codeword polytope $\text{poly}\left( \mathcal{C} \right) $, i.e. the constraints for the @@ -253,7 +253,7 @@ equivalent linear program to exact \ac{ML} decoding - only valid codewords are feasible solutions. Figures \ref{fig:dec:poly:local1} and \ref{fig:dec:poly:local2} show the local codeword polytopes of each check node. -Their intersection, the relaxed codeword polytope $Q$, is shown in figure +Their intersection, the relaxed codeword polytope $\overline{Q}$, is shown in figure \ref{fig:dec:poly:relaxed}. % @@ -537,7 +537,7 @@ Their intersection, the relaxed codeword polytope $Q$, is shown in figure {$\left( 1, \frac{1}{2}, \frac{1}{2} \right) $}; \end{tikzpicture} - \caption{Relaxed codeword polytope $Q$} + \caption{Relaxed codeword polytope $\overline{Q}$} \label{fig:dec:poly:relaxed} \end{subfigure} \end{subfigure} @@ -548,12 +548,12 @@ Their intersection, the relaxed codeword polytope $Q$, is shown in figure \end{figure} \noindent% -It can be seen, that the relaxed codeword polytope $Q$ introduces fractional -vertices; +It can be seen, that the relaxed codeword polytope $\overline{Q}$ introduces +vertices with fractional values; these represent erroneous non-codeword solutions to the linear program and correspond to the so-called \textit{pseudocodewords} introduced in \cite{feldman_paper}. -However, since for \ac{LDPC} codes $Q$ scales linearly with $n$ instead of +However, since for \ac{LDPC} codes $\overline{Q}$ scales linearly with $n$ instead of exponentially, it is a lot more tractable for practical applications. The resulting formulation of the relaxed optimization problem