Add image captions

paper/safety-reset-paper.tex

@@ -197,6 +197,10 @@ traditional PLC, any large industrial load that allows for fast computer control
     \includegraphics[width=0.4\textwidth]{flowchart}
     \caption{Structural overview of our concept. 1 - Government authority or utility operations center. 2 - Emergency
     radio link. 3 - Aluminium smelter. 4 - Electrical grid. 5 - Target smart meter.}
+    \Description{A schematic overview of the safety reset system with its parts represented by icons. A signal is sent
+    from a radio tower next to a government building to a radio tower next to a factory. The factory forwards this
+    signal to the electrical grid, where it is transmitted through a series of transformers to a smart meter at a
+    residential building.}
     \label{fig_intro_flowchart}
 \end{figure}
 
@@ -560,6 +564,14 @@ measurement literature~\cite{borkowski01}.
     smoothed spectrum is shown in red. The blue line is inversely proportional to frequency and illustrates the $1/f$
     nature of the spectrum. Distinctive peaks in the spectrum are marked with red crosses, and their locations
     are given on the bottom of the diagram.}
+    \Description{A plot of power spectral density in Hertz squared per Hertz versus period in seconds. The plot shows
+    the measured spectrum, a smoothed fit of the measured spectrum, and an one over f line for comparison. The measured
+    spectrum is very noisy. The smoothed signal looks much cleaner, and roughly follows the one over f line. The
+    smoothed data contains several notable features. At a period of about 80 seconds, its slope suddenly starts falling
+    off faster than one over f to form a through shape towards higher frequencies. There are several narrow bumps at
+    round number periods such as 10 seconds, 60 seconds, 300 seconds and 900 seconds. There are three wider bumps
+    visible. Two, a larger and a smaller one, next to each other centered on 4.7 seconds for the larger one and 7.0
+    seconds for the smaller one. The last wider bump is below 0.5 seconds.}
     \label{fig_freq_spec}
 \end{figure}
 
@@ -700,6 +712,14 @@ durations move our signals' bandwidth into the lower-noise region from $\SI{0.2}
     \centering
     \includegraphics[width=0.45\textwidth]{../notebooks/fig_out/dsss_gold_nbits_overview}
     \caption{Symbol Error Rate as a function of modulation amplitude for Gold sequences of several lengths.}
+    \Description{A plot of symbol error rate versus amplitude in millihertz. The plot shows four lines, one each for 5
+    bit, 6 bit, 7 bit and 8 bit. All four lines form smooth step functions, plateauing at a symbol error rate of 1.0 for
+    low amplitudes and falliing to a symbol error rate of 0.0 for high amplitudes. The low-amplitude plateau is widest
+    for 5 bit and narrowest for 8 bit. The falloff is steepest for 8 bit, and slowest for 5 bit. For 8 bit, a symbol
+    error rate of 0.5 is crossed at about 0.4 millihertz. For 7 bit at about 0.6 millihertz, for 6 bit at 0.8 millihertz
+    and for 5 bit at 1.3 millihertz. For 7 and 8 bit, symbol error rate settles at zero above 1.0 millihertz. For 5 bit
+    above 2.0 millihertz and for 8 bit at about 3.0 millihertz.
+    }
     \label{fig_ser_nbits}
 \end{figure}
 
@@ -709,6 +729,19 @@ durations move our signals' bandwidth into the lower-noise region from $\SI{0.2}
     \vspace*{-5mm}
     \caption{SER vs.\ Amplitude and detection threshold. Detection threshold is set as a factor of background noise
     level.}
+    \Description{This figure shows four plots that are similar to the previous figure. Each plot shows symbol error rate
+    plotted against signal amplitude in millihertz. Each of the four plots shows a different gold sequence length, from
+    5 bit up to 8 bit. Each plot contains more than ten traces that are color-coded for a different detection threshold
+    factor. All plots show that a high threshold factor going towards 10 shifts the symbol error rate curve towards
+    higher amplitudes, implying a less sensitive receiver. For lower threshold factors the sensitivity improves,
+    however, for very low threshold factors performance deterioates and the plotted curves suddenly become completely
+    erratic, with several curves for low threshold factors around 2 at all bit lengths never reaching symbol error rates
+    below 0.2. The middle ground between the two seems to be a threshold factor of around 5. The four plots show a clear
+    dependency between receiver sensitivity and gold code length. For a 5 bit gold code, only a few graphs settle at all
+    and those that do settle towards zero symbol error rate only between 3 and 4 millihertz in amplitude. For a 6 bit
+    gold sequence, most graphs settle, and for the best threshold factor the graph settles to zero symbol error rate
+    below 2 millihertz amplitude. For the 7 bit gold code, the best graph settles at approximately 1.2 millihertz, and
+    for the 8 bit gold code at approximately 0.8 millihertz.}
     \label{fig_ser_thf}
 \end{figure}
 
@@ -717,6 +750,19 @@ durations move our signals' bandwidth into the lower-noise region from $\SI{0.2}
     \hspace*{-5mm}\includegraphics[width=0.5\textwidth]{../notebooks/fig_out/chip_duration_sensitivity_6}
     \vspace*{-5mm}
     \caption{SER vs.\ DSSS chip duration.}
+    \Description{The figure shows two plots. The first plot shows symbol error rate against signal amplitude in
+    millihertz, but this time it shows a cohort of curves for different chip durations. The general amplitude behavior
+    is similar to the previous figure showing threshold factor instead, with a plateau at a 1.0 symbol error rate for
+    low amplitudes, and a smooth step settling to a 0.0 symbol error rate for large signal amplitude. The plot shows
+    chip durations between 0.1 seconds, equivalent to 6.4 seconds symbol duration and 5.0 seconds, equivalent to 320
+    seconds symbol duration. Most curves settle within the plotted range of 0 to 5 millihertz. Larger chip durations
+    settle only at higher amplitudes, and the fastest settling chip durations are also the shortest. There is a cluster
+    of fast-settling curves settling around 1.0 millihertz amplitude for chip durations below 1.0 seconds. A clear best
+    candidate is hard to distinguish from this cluster.
+    The second plot in the figure shows the minimum amplitude necessary for a symbol error rate of 0.5 plotted in
+    millihertz against chip duration in seconds. The graph shows a nicely round curve bottoming out at approximately
+    0.75 millihertz for a chip duration of 0.3 seconds. For lower chip durations, the curve slightly rises, while for
+    longer chip durations it rises by a lot, reaching 4.0 millihertz for a chip duration of 5.0 seconds.}
     \label{fig_ser_chip}
 \end{figure}
 
@@ -818,6 +864,13 @@ the meter's display after boot-up.
     \centering
     \includegraphics[width=0.45\textwidth]{prototype_schema}
     \caption{The signal processing chain of our demonstrator.}
+    \Description{A photo of the safety reset prototype. Visible is a stand made from plywood to which a smart meter is
+    mounted in the middle. To one side of the smart meter a light switch and a socket are connected. To the other side,
+    an orange power cable exits towards the back of the stand. The smart meter is connected to a prototype circuit board
+    with colorful wires. The prototype circuit board is in turn connected to a microcontroller development board. The
+    development board is connected to a USB hub with both an SWD programming adapter and a USB to serial converter. A
+    usb cable from the USB hub as well as a 3.5 millimeter audio cable from the prototype circuit board are neatly
+    coiled up and hang down from the stand.}
     \label{fig_demo_sig_schema}
 \end{figure}