# Energy Efficiency of IoT Networks for Environmental Parameters of Bulgarian Cities
## 3 Material and Methods
The average energy consumption (\(E_{A}\)) is determined on the basis of the arithmetic mean of the energies required for transmission, reception, sleep, and idle modes. It can be defined by the following formula:  
\[E_{A}=\frac{1}{N}\sum_{i=1}^{N}E_{i} \tag{2}\]  
where \(E_{i}\) is the energies required for transmission, reception, sleep, and idle modes of operation of the WSN; \(N\) is the number of reports for which this averaging is performed. In the present work, \(N\) is assumed to be 50 times as many as the number of rounds. The consumed energy for 50 rounds is determined. During the operation of the sensor network, each sensor node periodically sends data to the base station. One round of the transmitted data represents the length of time it takes to send a unit of data (4000 bits) to the base station. There is no description of all the functions of the used software product. Therefore, they are represented in the form \(\mathrm{y}=\mathrm{f}(\mathrm{x})\). The presented results of the work should be accepted within the described conditions and in those of the used software product. Figure 1: Location of measuring points by cities in Bulgaria. (**a**) T1 Burgas; (**b**) T2 Varma; (**c**) T3 Shumen; (**d**) T4 Yambol; (**e**) T5 Plovdiv; (**f**) T6 Pleven. Another factor that can increase the life of the network is the residual energy in each sensor node. It is calculated by a coefficient representing the current energy level of the individual sensor nodes. This remaining energy is calculated by the formula:  
\[E_{R}=f(E_{0},\ E_{m}) \tag{3}\]  
where \(E_{0}\) is the initial energies of each node; \(E_{m}\) is the energies required for the operation of the nodes in the WSN. The energy consumption of the whole network (\(E\)) through all rounds is determined. \[E=f(R) \tag{4}\]  
where \(R\) is the number of rounds. The number of received packets (\(N_{p}\)) for all rounds is determined. \[N_{p}=f(R) \tag{5}\]  
where \(R\) is the number of rounds. Data for the LoRa Wan module operating at 868 MHz were used. The data for the base station corresponds to LoRa WAN Gateway, 868 MHz (Shenzhen Dragino technology development Co., Ltd., Shenzhen, China). Table 3 shows the main characteristics of the LoRa WAN devices. The simulation study of the wireless sensor network was performed in the Matlab 2017 b software system (MathWorks Inc., Natick, MA, USA). A software tool was used to evaluate the energy efficiency of wireless sensor networks [22]. The performance of the six WSNs was evaluated under the following conditions: All sensor nodes have the same initial energy (E0). The location of the nodes is in accordance with the measurement points provided in the normative documents for each city. Each node transmits/receives packets when it has enough energy to do so. Receiving packets from all nodes to the base station is considered one round. A summary analysis of the obtained results was made with the method \"Principal component analysis\" (PCA) [23]. This is a method of reducing the amount of input data. The aim is to find and interpret the fundamental interdependencies between the characteristics in the data set. Features that are similar are combined and transformed into new features called principal components. Before being processed by this method, the data were normalized in the range [0, 1], depending on their minimum and maximum values.