path: root/text/labina.tex

\chapter{Laboratory testing}

This chapter will evaluate selected \ac{IoT} modules in laboratory setting based on their two critical performance indicators: their wireless data transmission capabilities and their associated power consumption depending on signal quality.

Here is an overview of the main aspects considered in the chosen measurement method:

The goal fo this chapter is to evaluate the nRF916x performance parameters in different operating conditions. For each of these conditions \ac{RF} parameters are gathered directly from the modem and information of power consumption using external ampere meter.

Chosen simulated conditions are payload size, signal strength and operating mode.

To include most of potential use-cases the outlined parameters will be measured for three different payload sizes:
\begin{itemize}
    \item 0 B - empty transmission for reference on protocols overhead 
    \item 64 B - usual amount of data for simpler IoT devices
    \item 1024 B - larger continuous data block transfer
\end{itemize}

This is done for ever increasing signal attenuation until communicating can be no longer established.
Decline of signal strength is simulated using addition attenuators between \ac{RF} output and antenna. Additional shielding was necessary for prevention of \ac{RF} leaking. EMC champer is sufficient for this case.

This procedure is done for both NB-IoT and LTE-M.

\section{RF parameters - nRF modem}

The radio parameters can be measured with specialized measurement equipment to evaluate objective characteristics or directly on the specific RF chip/modem.
Usage of "on-chip" statistics has lower resolution compared to specialized measurement equipment such as spectrum analyzer but their integration into existing \ac{RF} circuits can introduce even more variability and thus lower the accuracy of measuring and still without getting the real signal that decoded by the modem.
Another key point for consideration of "on-chip measurement" is the fact that these are the values that the modem considers for its signal quality evaluation and for subsequent setting of radio output parameters regardless on the opinion of more accurate measuring instrument.

As described in chapter \ref{chap:nrfdesc} Nordic \ac{SiP}s consist of application core and modem core. The modem is responsible for all radio and communication related tasks. Among other it is a evaluation of signal quality based on which it select different \ac{BTS}s and optimal communication parameters. Communication with application core is done using the AT commands. As a form of human-machine abstraction layer \ac{NCS} includes a \ac{MoSh}. \ac{MoSh} is an application that runs in application core and encapsulates AT commands in unix-like commands. \cite{ncsmosh}

First used command for communication evaluation is \texttt{ping}. This command establishes a \ac{ICMP} connection and outputs packet drop and transfer duration both are gathered for later analysis.

The destination of these pings i a Cloudflare DNS service 1.1.1.1. It was chosen for their massive network infrastructure and according to them the fastest connection \cite{oneoneoneone}.

%Ping command has this signature: \texttt{ ping -d DESTINATION -c COUNT -t TIMEOUT -i INTERVAL -L PAYLOAD_LENGTH }.

Example from testing of NB-IoT on nRF9161 with 10 dB additional attenuation:
{ \tiny
\begin{lstlisting}
mosh:~$ ping -d 1.1.1.1 -c 10 -t 10000 -i 100 -l 1024
Initiating ping to: 1.1.1.1
Source IP addr: 100.97.68.179
Destination IP addr: 1.1.1.1
Pinging 1.1.1.1 results: time=1.448secs, payload sent: 1024, payload received 1024
Pinging 1.1.1.1 results: time=2.082secs, payload sent: 1024, payload received 1024
Pinging 1.1.1.1 results: time=1.490secs, payload sent: 1024, payload received 1024
Pinging 1.1.1.1 results: time=3.103secs, payload sent: 1024, payload received 1024
Pinging 1.1.1.1 results: time=1.089secs, payload sent: 1024, payload received 1024
Pinging 1.1.1.1 results: time=1.171secs, payload sent: 1024, payload received 1024
Pinging 1.1.1.1 results: time=1.364secs, payload sent: 1024, payload received 1024
Pinging 1.1.1.1 results: time=1.891secs, payload sent: 1024, payload received 1024
Pinging 1.1.1.1 results: time=1.581secs, payload sent: 1024, payload received 1024
Pinging 1.1.1.1 results: time=1.124secs, payload sent: 1024, payload received 1024
Ping statistics for 1.1.1.1:
    Packets: Sent = 10, Received = 10, Lost = 0 (0% loss)
Approximate round trip times in milli-seconds:
    Minimum = 1089ms, Maximum = 3103ms, Average = 1634ms
Pinging DONE
\end{lstlisting}

}

Second command for communication evaluation is \texttt{link status}. This command prints out last done report of \ac{BTS} connection. For it to be accurate it is done after all \texttt{ping} commands. Items saved for analysis are \ac{RSRP} and \ac{SNR}.

Example from testing of NB-IoT on nRF9161 with 10 dB additional attenuation:

{ \tiny
\begin{lstlisting}
mosh:~$ link status
Modem functional mode: normal
Network registration status: Connected - roaming
Modem config for system mode: NB-IoT
Modem config for LTE preference: No preference, automatically selected by the modem
Currently active system mode: NB-IoT
Battery voltage:       5054 mV
Modem temperature:     28 C
Device ID:             nrf-358299840012328
Operator full name:   "Vodafone"
Operator short name:  "VF"
Operator PLMN:        "23003"
Current cell id:       269600 (0x00041D20)
Current phy cell id:   400
Current band:          20
Current TAC:           48024 (0xBB98)
Current rsrp:          57: -84dBm
Current snr:           26: 2dB
Mobile network time and date: 25/05/19,13:08:15+08
PDP context info 1:
  CID:                0
  PDN ID:             0
  PDP context active: yes
  PDP type:           IP
  APN:                lpwa.vodafone.com
  IPv4 MTU:           1430
  IPv4 address:       100.97.68.179
  IPv6 address:       ::
  IPv4 DNS address:   217.14.160.130, 217.14.164.35
  IPv6 DNS address:   ::, ::
}
\end{lstlisting}

}

Another two commands are \texttt{link sysmode} for switching between NB-IoT and LTE-M and \texttt{link funmode} for turning the modem to and from flight-mode for save antenna and attenuators reconfiguration.

\section{Power consumption - ampere meter}

Power consumption can be accurately measured with negligible influenced by introduction of additional measurement equipment so measurement with external meter was chosen over the modem estimates or table values. For the power consumption evaluation of \ac{IoT} devices there are two different factors to consider. First is standby or sleep power that is usually long (orders of minutes or hours) and very small (orders of miliamps) and second are short rapid transmission spikes in orders of amperes. This requires ampere meter with very high sampling speed and very high dynamic range.

For measuring of power consumption was done using Nordic \ac{PPK II}, seen in picture \ref{fig:ppk}. \ac{PPK II} was chosen for its high sampling rate, large dynamic range and its good integration with other Nordic applications and development kits.

\begin{figure}[H]
	\begin{center}
		\includegraphics[width=0.4\textwidth]{obrazky/ppk2foto.png}
	\end{center}
	\caption[Nordic Power Profiler Kit II]{Nordic Power Profiler Kit II\cite{ppkdatasheet}}
	\label{fig:ppk}
\end{figure}


Its key features are \cite{ppkdatasheet}:
\begin{itemize}
    \item 200nA to 1A current measurement range with a resolution that varies between 100nA and 1mA
    \item Source mode and ampere meter mode
    \item 100 ksps sampling rate
    \item 8 digital inputs for logic analyzer support
    \item Supported through nRF Connect for Desktop's Power Profiler app
\end{itemize}

The measurement setup of nRF9161 DK with PPK II in EMC chamber and addition attenuators can be seen in figure \ref{fig:ppkmeas}. These development kits from Nordic enable a direct connection of serial ampere meter using special pins. This is them main reason why both boards were chosen for this measurement. 

\begin{figure}[H]
	\begin{center}
		\includegraphics[width=0.6\textwidth]{obrazky/nrfppkemc.jpg}
	\end{center}
	\caption[Nordic PPK II measuring setup]{Nordic Power Profiler Kit II measuring setup with nRF9161 in EMC chamber\cite{ppkdatasheet}}
	\label{fig:ppkmeas}
\end{figure}

The output of PPK II can be seen in figure \ref{fig:ltemcurr} for LTE-M and and in figure \ref{fig:nbiotcurr}.

Yellow vertical lines mark a start of ping set and red vertical it end. These boundaries were set due to noise manually.
Green horizontal line indicates average draw in idle state where the modem does not communicate in cellular network. Red horizontal line indicates average draw in ready state where communication is established without need for active communication. Both "horizontal" values are calculated using Python script from the measured data.

\begin{figure}[H]
	\begin{center}
		\includegraphics[width=1\textwidth]{mereni/komora2/nrf9161_nb-iot_measured_current_20dB.png}
	\end{center}
	\caption[PPK II current plot of NB-IoT]{Current plot of nRF9161 communicating using NB-IoT}
	\label{fig:nbiotcurr}
\end{figure}

\begin{figure}[H]
	\begin{center}
		\includegraphics[width=1\textwidth]{mereni/komora2/nrf9161_lte-m_measured_current_20dB.png}
	\end{center}
	\caption[PPK II current plot of LTE-M]{Current plot of nRF9161 communicating using LTE-M}
	\label{fig:ltemcurr}
\end{figure}

Another value that is calculated from these data and cannot be depicted in the chart is the raw charge needed for transmission of one packet. This is calculated by integration of the current over time set by the boundaries. This value expressed in coulombs or more commonly in mAh.

\section{Results}



\input{mereni/ltem61_1024_table}

This is 

Complete data are for their large extent placed in Appendix \ref{appendix:ltetables}.



%\chapter{Labina osnova}


%\textit{Každá section jak protokol, Co chci změřit, Fyzika - princip toho co měřím, čím to měřím, zapojení měřící techniky, tabulky, graf}

%\section{Communication range}

%One of main consideration when choosing a IoT platform is communication range. Main source of attenuation of radio energy caused by electric field dispersion/diffusion of electric field. This effect if best described by \ac{FSPL}:

%\begin{equation}
	%FSPL=\left( \frac{4 \pi d}{\lambda} \right) ^2
%\end{equation}

%Signal attenuation is also dependent on directivity of antennas and loss on connectors and \textbf{electrical wiring}. When antenna and transmission total \textbf{gain} is constant and can be added to equation like this:

%\begin{equation}
	%A = D_{ANT} \cdot A_{RX} \cdot \left( \frac{4 \pi d}{\lambda} \right) ^2
%\end{equation}

%Where $D_{ANT}$ is directivity of antenna and $A_{RX}$ is total loss from \ac{RF} connector to \ac{LTE} modem. These must be accounted to only when measuring on directly on LTE modem.

%This can be converted to simplify calculation to decibel form:

%\begin{equation}
	%A = D_{ANT}^{[dB]} + A_{RX}^{[dB]} + 10 \cdot \log_{10} \left( \frac{4 \pi d}{\lambda} \right) ^2
%\end{equation}

%From this a maximal range can be simulated using \ac{RF} attenuators in laboratory environment by converting

%\begin{equation}
	%d = A_{max}
%\end{equation}

%\subsection{Antennas}

%For ability to add additional attenuators external antennas had to be made. For this a $\lambda / 4$ monopole antenna design has been chosen.


%O2 on 800 MHz


%Dosah zásvisí na vzdálenosti, v ideálních podmínkách line of sight Free-space path loss

%Popis Free-space path loss, teorie, vzorečky

%Technika - variable attenuator,

%Tabulka utlum , km ve free-space , teoreticka sila signalu , signal na vstupu podle FW , packet drop / BER

%\section{Noise immunity - reliability}

%Noise makes signal bad, reciver much sad.

%Teorie, vzorecky, Bit error rate, Added white gausian noise

%Teoreticke vypocty pro NB-IoT, LTE-M, DECT NR+

%Technika zdroj šumu, směšovač,

%Pro jednotlivé AWGN a CNR carier noise ratio
%Tabulka utlum , km ve free-space , teoreticka sila signalu , signal na vstupu podle FW , packet drop / BER , spotřeba

%\section{Power consumption}

%\colorbox{orange}{Toto asi bude chujovina}
%With wireless communication often comes an incentive for power source without need for external wires and power transmission network. Significant research has been made to alternative power sources for IoT devices from prevalent energy sources like light, vibration, temperature gradient and similar. Use of small solar panels with potential large capacitor seems to be the most viable out of these but there [tuzdroj].

%\colorbox{orange}{Konec chujoviny}

%All power sources expect the ones connected directly to energy power grid have some sort of limited capacity. In the case of primary batteries and rechargeable batteries this limit is absolute and usually has to be guarantied in terms of




%%Globální oteplování bad, small battery good

%\subsection{Nordic Power Profiler Kit II}

%\section{Latency}

%Pro jednotlivé AWGN a CNR carier noise ratio
%Tabulka utlum , km ve free-space , teoreticka sila signalu , signal na vstupu podle FW , packet drop / BER , spotřeba , latence

%Experimentální ověření NB-IoT, LTC-M, DECT NR+:
%\begin{itemize}
    %\item dosah - popis cesty šíření ve volném prostoru, odkaz na teoretický výpočet útlumi vzdáleností ve volném prostředí ve vzduchu. Popis atenuátoru.
    %\item spotřeba - variabilní snižování síly signálu, popis Power Profiler Kit II
	%\item přenosová rychlost - primárně pro DECT, praktická superhurbá přenosová rychlost UDP Byty/(čas od konce do začátku sleep)
	%\item odolnost vůči šumu - VF generátor šumu, teorie
%\end{itemize}

%Experimentální ověření DECT NR+ navíc:
%\begin{itemize}
    %\item spolehlivost -
    %\item latence -
%\end{itemize}

%Teorie mereni - Náhradní modely prostředí. Degradace signálu.

%Popis experimentální instrumentace a sestav.

%Spotřeba, packet drop, rychlost, latence závislá na útlumu (popř. intenzita bílého šumu) (vsechny protokoly)

%\section{Measurement}

%\begin{sidewaystable}
    %\centering

  %\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|c|c|c|}
    %\hline
      %\multicolumn{2}{|c|}{Nominal} &
      %\multicolumn{3}{c|}{nRF modem} &
	  %\multicolumn{2}{c|}{nRF FW} &
	  %\multicolumn{6}{c|}{Power Kit II} \\
	  %\hline
	  %$K_U$ & CL & $P_I$ & $Q_I$ & $SNR$ & $T_{lat}$ & $PD$ & $P_{TX}$ & $P_{RX}$ & W & $T_{TX}$ & $T_{RX}$ & $R_B$ \\

	  %[dB] & [dB] & [dBm] & [dBm] & [dB] & [ms] & [\%] & [mA] & [mA] & [J/msg] & [$\mu$ s] & [$\mu$ s] & [kB/s] \\\hline
	  %0  & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %3  & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %6  & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %10 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %13 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %16 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %20 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %23 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %26 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %30 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %33 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %36 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %40 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %43 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %46 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %50 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %53 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %56 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %60 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
  %\end{tabular}
%\caption{NB-IoT / LTE-M measurements for message length = X B and added noise = X dBm}
%\end{sidewaystable}




%\begin{sidewaystable}
    %\centering

  %\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|c|c|c|}
    %\hline
      %\multicolumn{2}{|c|}{Nominal} &
      %\multicolumn{5}{c|}{nRF modem} &
	  %\multicolumn{6}{c|}{Power Kit II} \\
	  %\hline
	  %$K_U$ & CL & $RSSI$ & $RSSI-2$ & $SNR$ & $T_{lat}$ & $PD$ & $P_{TX}$ & $P_{RX}$ & W & $T_{TX}$ & $T_{RX}$ & $R_B$ \\

	  %[dB] & [dB] & [dBm] & [dBm] & [dB] & [ms] & [\%] & [mA] & [mA] & [J/msg] & [$\mu$ s] & [$\mu$ s] & [kB/s] \\\hline
	  %0  & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %3  & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %6  & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %10 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %13 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %16 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %20 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %23 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %26 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %30 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %33 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %36 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
	  %40 & -140 & -80 & 10 & 40 & 0.5 & 0.1 & 98 & 10 & 0.1 & 400 & 400 & 1 \\ \hline
  %\end{tabular}
%\caption{DECT-NR+ measurements for message length = X B and added noise = X dBm}
%\end{sidewaystable}