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\chapter{Field testing of mobile capabilities of NB-IoT and LTE-M} \label{chap:mobil}
Standard notion on selecting between LTE-M and NB-IoT when one has a choice is to choose LTE-M when one needs higher speed or needs for the device to be mobile while not having not so extreme requirements for continual communication or environment with extreme attenuation and to choose NB-IoT for smaller payload applications with potential of very weak signal.
To test this hypothesis an experiment was created where the created demonstrator from chapter \ref{chap:demo} was placed inside a personal car as can be seen in figure \ref{fig:demofelda}. One way to test LTE-M on road from north Moravia to Brno and to test NB-IoT on return path.
Because of large intervals (orders of minutes) needed for switch between GNSS and LTE connection on nRF916x, it was chosen to perform only reading from the meteo sensor, reading of connection quality report and periodical sending of these data to MQTT server. On the same server there was running Python script that saved all data in json format to the server storage.
Location data were collected by smartphone with GNSS logging application and later these two datasets were joined by time.
\begin{figure}[H]
\begin{center}
\includegraphics[width=1\textwidth]{obrazky/demofelda.jpg}
\end{center}
\caption[Demonstrator secured in car for mobile measurement]{Demonstrator secured in car for mobile measurement}
\label{fig:demofelda}
\end{figure}
Gathered data included from GPS tracker included latitude, longitude, accuracy of position, smartphone battery, computed elevation, number of visible satellites, and speed.
Evaluation data from LTE modem were LTE band, down link path loss, LTE mode (1 is LTE-M 2 is NB-IoT), Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), Signal to Noise Ratio (SNR) and TX power.
Lastly to demonstrate transfer of useful data the values form sensor BME680 were also included. These were atmospheric pressure, inside car temperature,
car humidity, resistance of gas sensor representing amount of for example volatile organic compounds in the air.
All of these data joined by Python script were than used to create interactive maps for better data visualization.
An example of such map of reported signal power can be seen in figure \ref{fig:mapaltem} for LTE-M and \ref{fig:mapanbiot} for LTE-M.
\begin{figure}[h]
\begin{center}
\includegraphics[width=1\textwidth]{obrazky/mapltem.png}
\end{center}
\caption[Map RSRP reported by demonstrator operating using LTE-M]{Map RSRP reported by demonstrator operating using LTE-M}
\label{fig:mapaltem}
\end{figure}
\begin{figure}[h]
\begin{center}
\includegraphics[width=1\textwidth]{obrazky/mapnbiot.png}
\end{center}
\caption[Map RSRP reported by demonstrator operating using NB-IoT]{Map RSRP reported by demonstrator operating using NB-IoT}
\label{fig:mapanbiot}
\end{figure}
Findings from thise sdata are:
\begin{itemize}
\item LTE-M provided stable connection for transmission of packet about 0.5 kB in size every second in speeds lesser than 130 km/h. Higher speed of due to highway laws and technical state of used car. With exception near Lipník na Bečvou where most likely due to change in network operating LTE band demonstrator lost connection for 1.5 minutes. This transition from band 8 to band 20 can be clearly seen in figure \ref{fig:mapaltemband}.
\item NB-IoT also provided fairly stable connection for at least 130 km/h with 2 minute connection loss near Brno airport and nearly 2 minute loss between Nový Jičín and Hranice na Moravě at borderline of Olomouc and Moravian-Silesian region (whenever is this detail significant is not clear but the band change as in the LTE-M did not happened here). Last understandable signal loss was in tunnels in west Brno (different route than LTE-M due to traffic situation in Brno).
\end{itemize}
\begin{figure}[h]
\begin{center}
\includegraphics[width=1\textwidth]{obrazky/maplteband.png}
\end{center}
\caption[Map of LTE band used by demonstrator when using LTE-M]{Map of LTE band used by demonstrator when using LTE-M}
\label{fig:mapaltemband}
\end{figure}
Better visualization of these data with interactive maps can be found in this GitHub page: \url{https://mikehanus.github.io/bcthesis-datavisualisation/}
Including them in attachments were not possible due to large size of these maps but it should be possible to generate them using python scripts and data in the attachments.
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