## 3 System Overview
### Power Consumption  
Power consumption is very important, because the TMS has to be installed in a place without access to electricity mains. The system therefore relies entirely on a battery. Battery life determines the usefulness of the system. In addition, during the system modeling phase it is vital to select low power sensors and electronics components. Low powered components are selected for the design with minimal external components. In our work, the LDO regulator's quiescent current is 1.6 \(\upmu\)A, and the sensor's sleep current is typically 5 \(\upmu\)A.  
The typical SoC has many power modes, including deep sleep mode, sleep mode, standby mode, and transmission mode. The simplified plot in Figure 8 shows these different modes.  
Figure 8: Current profiles in different modes in IoT system’s operation.  
The maximum current consumption occurs during the transmission. There are dynamic variations in the current measurement, ranging from a few microamperes to hundreds of milliamperes. In addition, during the transmitting stage, a short current burst occurres, lasting between a microsecond and a millisecond. The battery life is estimated from the capture of the load current profile. However, in practice, the load current profile is not as simple as that shown in Figure 8. An accurate evaluation of this type of current profile requires a measuring instrument that has acceptable sensitivity, dynamic range, sampling speed, and bandwidth. Still our method is a cost-effective alternative that is also helpful for identifying problems and transient currents in electronic components. Such problems, once identified, can be later addressed by hardware modifications or firmware modifications to reduce the power consumption. There is no standardization of terms used in describing the power modes. In this paper, terminology derived from that of the ESPRESSIF ESP32 family SoC. In this application, we use deep sleep mode and active mode programmed through the open source ARDUINO IDE. In deep sleep mode, Wi-Fi connection data are stored in RTC memory. The SoC needs full initialization to exit from this mode. The SoC's active mode can turn on Wi-Fi and is able to transmit and receive data. This is the highest power consumption mode. The total energy consumption of the system including all the modes can be calculated as Equation (6), where \(E\), \(V_{cc}\), \(x\), \(n\), \(I_{x}\), \(T_{x}\) denote energy, supply voltage, number of power modes, and current consumption, respectively. The charge consumption of the battery in different modes can be denoted as in Equation (7) in amp-seconds. The battery can be selected based upon the system's targeted operating lifetime and the charge consumption of the application.  
\[E=\sum_{x=1}^{n}\ V_{cc}I_{x}T_{x}. \tag{6}\]  
\[C=\sum_{x=1}^{n}I_{x}T_{x}. \tag{7}\]  
An IoT device's use of standard network protocols mean each layer can affect the total energy consumption of the device. Figure 9 shows the energy parameters mapped onto each layer related to our research. The energy consumption profile illustrates the power consumption of different modes and the transition energy between modes. [PERSON] et al. [33] summarize the general power profile of low power IoT devices. The usual way of minimizing the application power is discussed. However, each system interfaces with at least one sensor with the SoC. In comparison with application-oriented research, it is necessary to consider the limitations of SoC boot up/wake up time, sensor boot up/wake up time and current, and communication power, depending on the application feature. The device programmer has no control over these factors since it is vendor specific. However, it is necessary to factor this into the power budget.  
Figure 9: The relationship between the conceptual OSI model and energy parameters through TMS.