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% SPDX-License-Identifier: CC-BY-SA-4.0
%
% Copyright (c) 2020 Philipp Le
%
% Except where otherwise noted, this work is licensed under a
% Creative Commons Attribution-ShareAlike 4.0 License.
%
% Please find the full copy of the licence at:
% https://creativecommons.org/licenses/by-sa/4.0/legalcode
\phantomsection
\addcontentsline{toc}{section}{Exercise 5}
\section*{Exercise 5}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{question}[subtitle={Mixers}]
\begin{tasks}
\task
Is the mixer a linear device like filters and amplifiers?
\task
What is the difference between unbalanced and balanced mixers?
\task
Why do mixers need a non-linear component?
\end{tasks}
\end{question}
\begin{solution}
\begin{tasks}
\end{tasks}
\end{solution}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{question}[subtitle={Mirror frequencies}]
This is simplified block diagram of a receiver.
\begin{figure}[H]
\centering
\begin{adjustbox}{scale=0.8}
\begin{circuitikz}
\node[mixer](Mixer){};
\node[oscillator, below=1cm of Mixer](LO){};
\node[adcshape, right=2cm of Mixer](ADC){};
\node[block, draw, right=1cm of ADC](Baseband){Digital signal\\ processing};
\draw (LO.south) node[below,align=center,yshift=-5mm]{LO};
\draw (Mixer.north) node[above,align=center,yshift=3mm]{Mixer};
\draw (Mixer.west) -- ++(-1cm,0) node[rxantenna,xscale=-1]{};
\draw[-latex] (LO.north) -- (Mixer.south);
\draw[-latex] (Mixer.east) to[lowpass] (ADC.west);
\draw[-latex] (ADC.east) -- (Baseband.west);
\end{circuitikz}
\end{adjustbox}
\end{figure}
A signal of \SI{868}{MHz} should be received. The baseband is not zero-IF. The signal shall be mixed to \SI{1}{MHz} centre frequency.
\begin{tasks}
\task
How much is the minimum ADC sampling rate?
\task
To which frequencies can the LO be tuned to?
\task
The \SI{868}{MHz}-band is shared with lots of other users. Which important piece is missing in the receiver signal chain?
\task
An IQ demodulator is used instead of the single mixer. Sketch the spectrum of the complex-valued baseband signal for both possible LO frequencies!
\end{tasks}
\end{question}
\begin{solution}
\begin{tasks}
\end{tasks}
\end{solution}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{question}[subtitle={Constellation diagrams}]
Draw a constellation diagram of:
\begin{tasks}
\task
ASK (with 2 steps)
\task
BPSK
\task
QPSK
\task
16-QAM
\end{tasks}
\end{question}
\begin{solution}
\begin{tasks}
\end{tasks}
\end{solution}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{question}[subtitle={Constellation diagrams}]
A QPSK modulator has the following mapping and symbol constellation:
\begin{table}[H]
\centering
\begin{tabular}{|l|l|l|}
\hline
Data & Symbol & Phasor \\
\hline
\hline
$(00)_2$ & 0 & $\SI{2}{mV} \cdot e^{j 0}$ \\
\hline
$(01)_2$ & 1 & $\SI{2}{mV} \cdot e^{j \frac{\pi}{2}}$ \\
\hline
$(10)_2$ & 2 & $\SI{2}{mV} \cdot e^{j \pi}$ \\
\hline
$(11)_2$ & 3 & $\SI{2}{mV} \cdot e^{j \frac{3 \pi}{2}}$ \\
\hline
\end{tabular}
\end{table}
The carrier is:
\begin{equation}
x_C(t) = \SI{2}{mV} \cdot \cos\left(2\pi \cdot \SI{50}{MHz} \cdot t\right)
\end{equation}
The symbol rate is $\SI{25}{MHz}$. After the DAC, an ideal low-pass filter with $\SI{25}{MHz}$ cut-off frequency is applied.
\begin{tasks}
\task
How much is the transmission bandwidth?
\task
How many bits can be encoded per QPSK symbol? How many symbols are required to encode one byte (8 bits)?
\task
Draw the constellation diagram!
\task
The data byte $(2E)_{16}$ shall be transmitted. Give the sequence of phasors representing the data byte!
\task
Describe the problem with inter-symbol interference!
\task
Plot the I and Q baseband signals! Plot the RF signal after IQ modulation!
\task
The following phasors are received at the receiver:
\begin{equation}
[\SI{1.5}{mV} e^{j \SI{120}{\degree}}, \SI{1.5}{mV} e^{j \SI{300}{\degree}}, \SI{1.5}{mV} e^{j \SI{30}{\degree}}, \SI{1.5}{mV} e^{j \SI{210}{\degree}}]
\end{equation}
What would the decoded data be? What is the matter?
\end{tasks}
\end{question}
\begin{solution}
\begin{tasks}
\end{tasks}
\end{solution}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\begin{question}[subtitle={Decibel}]
% \begin{tasks}
% \end{tasks}
%\end{question}
%
%\begin{solution}
% \begin{tasks}
% \end{tasks}
%\end{solution}
|
