diff --git a/correction.tex b/correction.tex index 536180a..14de523 100644 --- a/correction.tex +++ b/correction.tex @@ -30,6 +30,8 @@ \maketitle \section{Introduction} When messages are transmitted over real media, errors are inevitably introduced. +Examples range from mundane sources of errors like scratches on CDs and capacitive coupling of conductors +to geomagnetic storms. Though the source of errors are manifold, they are ubiquitous and need to be accounted for if we want any real chance of reading a correct message at the end. On a basic level, we can understand that a channel with a lower \textit{\acrfull{snr}}, @@ -49,7 +51,60 @@ If the noise level is small on average, most transmissions will be interpreted c However, there generally remains a chance that an intended 1 will be received as .47 volts and hence interpreted incorrectly as a 0. \cite{enwiki:signal-to-noise} + In this digital system, we can improve communication reliability by using a coding scheme that is tolerant of errors. +As a naive approach, we will simply transmit our message multiple times. +This is called a \textit{repetition code}, where the receiver will perform a majority vote over the received bits, +resulting in the following + +\begin{figure}[H] +\begin{minipage}{.5\textwidth} + \begin{tabular}{c|ccc} + recieved & 0 & \textcolor{red}{1} & 2 \\ + \hline + read & 0 & ERR & 1 \\ + \end{tabular} + + \begin{tabular}{c|cccccccc} + recieved & 0 & \textcolor{red}{1} & \textcolor{red}{2} & 3 \\ + \hline + read & 0 & 0 & 1 & 1 \\ + \end{tabular} + + \begin{tabular}{c|cccccccc} + recieved & 0 & \textcolor{red}{1} & \textcolor{red}{2} & \textcolor{red}{3} & 4 \\ + \hline + read & 0 & 0 & ERR & 1 & 1 \\ + \end{tabular} +\caption{Error detection and detection for 2,3 and 4 bits used per symbol in a repetition code} +\label{tab:detection-correction} +\end{minipage} +\begin{minipage}{.5\textwidth} +\begin{tikzpicture} + \begin{axis}[ + domain=0:1, + samples=100, + axis lines=middle, + xlabel={$p$}, + ylabel={Channel Capacity $C$}, + xmin=0, xmax=1, + ymin=0, ymax=1.1, + xtick={0,0.25,0.5,0.75,1}, + grid=both, + width=8cm, + height=6cm, + every axis x label/.style={at={(current axis.right of origin)}, anchor=west}, + every axis y label/.style={at={(current axis.above origin)}, anchor=south}, + ] + \addplot[thick, blue] {1-(-x * log2(x) - (1-x) * log2(1-x))}; + \end{axis} +\end{tikzpicture} +\caption{Capacity of a binary channel with crossover probability $p$} +\label{fig:graph-errorrate} +\end{minipage} +\end{figure} + + \section{Hamming Condition} theorems: Hamming condition, Varsham-Gilbert