2.3

chapter_02.tex

@@ -81,8 +81,19 @@ Figure \ref{fig:fig_iir} visualizes a simple IIR-filter with one feedforward coe
 \end{figure}
 
 \subsection{Introduction to Adaptive Nose Reduction}
-
+As already mentioned in the introduction, environmental noise severely degrades cochlear implant user's speech understanding and listening comfort. The traditional concept of static noise reduction, such as fixed filters, are not a feasible solution due to dynamic acoustic conditions where the type, intensity, and spectral composition of noise can change rapidly. Adaptive Noise Reduction addresses this problem by using adaptive filters that can automatically adjust their parameters in real time, continuously optimizing the system's response to changing environments.\\ \\
+In the beginnings of the 20th century, filter techniques were limited to the use of static filters like low- or highpass filters. The fundamental techniques allow to limit the frequency sprectrum, by cutting out certain frequency like high-pitched noises. In the 1930's, the first real concept of active noise cancellation was proposed  by the German Physician Paul Lueg. Lueg patented the idea of two speakers emitting antiphase signals which cancel each other out. Though his patent was granted in 1936, back at the time, there was no technical possibility detect and process audio signals in a way, to make his noise cancellation actually work in a technical environment.\\ \\
+20 years after Luegs patent, Lawrence Fogel patented a practical concept of noise cancellation, intended for noise supression in aviation - this time, the technical cirumstances of the 1950's enabled the development of an aviation headset, lowering the overall noise experienced by pilots in the cockpit of a helicopter or an airplane \ref{fig:fig_patent}.  
+\begin{figure}[H]
+    \centering
+    \includegraphics[width=0.8\linewidth]{Bilder/fig_patent.jpg}
+    \caption{Patent of a device for lowering ambient noise to improve intelligence by Lawrence Fogel in 1960 \cite{soure_patent}}
+    \label{fig:fig_patent}
+\end{figure}
+Until this point in time, the realised concepts were analog noise surpression, were a microphone measures the noise and a fixed circuit generates the antiphase signal - this means, the system only works in a specified environment and there is no real adatpiveness.\\ \\
+The final step to real adaptive noise cancellation was made with the introduction of the fundamental Least-Mean-Square (LMS) algorithm in 1960 by Widrow & Hoff.
 \subsection{Introduction to the Least Mean Square algorithm for adaptive filtering}
+, allowing an automatic adaption of the filter coefficients depending on the surrounding by stepwise minimization of the squared error \\ \\
 \subsection{Signal flow diagram showing the origin of the useful signal,
 noise signal, and their coupling}
 \subsection{Derivation of the system’s transfer function based on the problem setup}