# I3 Mote: An Open Development Platform for the Intelligent Industrial Internet
## 6 Performance Evaluation
### System Considerations  
Low-energy systems spend most of their time sleeping. The I3 Mote has been specifically designed for minimal power in the sleep state. First, the two main cores (MSP432 and CC2650) are among the lowest energy consumption processors in the market. In their respective deep-sleep mode, the combined consumption is less than \(1\,\mathrm{\SIUnitSymbolMicro A}\). Second, special care has been taken in the selection of the components of the power supply (see Figure 4). With all DC sources in operation, the total quiescent consumption of the power subsystem is less than \(6\,\mathrm{\SIUnitSymbolMicro A}\). Finally, as we have seen in the previous section, the combined sleep current of the on-board sensors is approximately \(7.5\,\mathrm{\SIUnitSymbolMicro A}\). Taken together, the I3 Mote quiescent current has been measured below \(15\,\mathrm{\SIUnitSymbolMicro A}\) (with the microcontrollers in deep-sleep mode), a remarkable value for a system with almost 20 active components. In order to test the I3 Mote under actual operating conditions, a long-term experiment has been carried out. In this experimental configuration, an I3 Mote \"Engineering\" (see Figure 2), acting as a DagRoot node, is connected to a Linux gateway embedded into a BeagleBone Black board. The BBB acting as 6 LBR, handles all remaining 6 TiSCH management tasks (joining, provisioning, topology and scheduling), a CoAP Client Module and a simple web server. In turn, the I3 Mote \"Tiny\", acting as a child node, connects directly to the root (one-hop). The embedded application is configured so that each \(T=10\,\mathrm{s}\) reads all the on-board sensors, reporting the values acquired to the gateway. Figure 10(a) shows a record of \(10\,\mathrm{s}\) containing 7 slotframes (\(1.27\,\mathrm{s}\) each). Sensors are read and reported to the GW during the slotframe tagged as \"A\". In detail, Figure 10(b) shows a zoom of the slotframe \"A\". The slotframe is delimited by two Enhanced Beacons, labeled as \"\(1\)\" and \"\(4\)\"; the label \"\(2\)\" corresponds to the sensors reading (active state of the sensors) and the label \"\(3\)\" to the radio transmission of the acquired values. Figure 10: Power consumption of the I3 Mote on-board sensors vs sampling rate. The average current consumption reaches an asymptotic minimum (below \(10\,\mathrm{\SIUnitSymbolMicro A}\)) when the sampling interval is longer than \(30\,\mathrm{s}\). system from the super capacitor, (i.e., the system uses the super capacitor, not the primary battery), is given by  
\[\Delta t_{\text{discharging}}=\frac{C\Delta V}{V_{\text{system}}I_{\text{ system}}-V_{\text{solar}}I_{\text{solar}}}V_{\text{nominal}} \tag{4}\]  
where \(V_{\text{system}}\) and \(I_{\text{system}}\) are the system voltage and the system current consumption. Therefore, the effective time efficiency is defined by  
\[Eff\triangleq\max\left(\frac{\Delta t_{\text{discharging}}}{\Delta t_{\text{ charging}}+\Delta t_{\text{discharging}}},1\right)=\max\left(\frac{V_{\text{solar}}I_{\text{solar}}}{V_{ \text{system}}I_{\text{system}}},1\right) \tag{5}\]  
and the amount of the primary battery life extension is given by  
\[\frac{1}{1-Eff}= \begin{cases}\frac{V_{\text{system}}I_{\text{system}}-V_{ \text{solar}}I_{\text{solar}}}{\text{$\infty$}},&\text{if $V_{\text{system}}I_{\text{system}}>V_{\text{solar}}I_{\text{solar}}$}\\ \infty,&\text{otherwise}\end{cases}  \tag{6}\]  
where \(\infty\) means the system fully runs from the energy harvesting. Figure 13 shows the energy harvesting efficiency. In our indoor light environment under 300 lux light we can observe 92% of the efficiency, which corresponds to 13X battery life extension of the primary battery. For example, with two AAA batteries, our system can run for 1.36 years over a 6 TiSCH network with 10 s periodic duty cycling and with the energy harvesting under 300 lux indoor light, it can run for 17.54 years. Figure 14 shows the system life time for various battery types.