# Energy Efficiency of IoT Networks for Environmental Parameters of Bulgarian Cities
## 4 Results and Discussion  
Figure 2 shows simulation diagrams of the WSN's access to the measuring points for the six cities in Bulgaria. A star topology was used. Most nodes that are close to the base station (up to 2 km) are in cities T1, T2, T4 and T5. The nodes are presented with blue points \begin{table}
\begin{tabular}{c c c} \hline \hline
**Characteristic** & **LoRa WAN Gateway** & **LoRa Wan Module** \\ \hline Max Output Power, dBm & 27 & 20 \\ \hline Sensitivity, dBm & \(-\)140 & \(-\)148 \\ \hline Power Input, V & 12 & 5 \\ \hline bit rate up to, kbps & 300 & 300 \\ \hline Transmitting power, mW & 100 & 100 \\ \hline Antenna gain (Transmit), dBm & 168 & 168 \\ \hline Antenna gain (Receive), dBm & 27 & 27 \\ \hline Frequency, MHz & 868 & 868 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Data on LoRa WAN devices. and green lines show the two-way communication with the base station. Some of the green lines are not visualized by the used software, but there are calculations for the nodes. Figure 3 shows a graph of maximum energy consumption in wireless sensor networks for different cities in Bulgaria. The maximum energy consumption for the entire WSN in every city is presented. The highest energy consumption is observed in the cities T1 and T3. In T1, this is due to the many nodes that are located near the base station. In T3, the characteristics of the geographical location of the sensor nodes with network communication have a significant impact and increase the energy consumption in the network. Similar conditions are observed for the T6 network. Although T2 and T5 are significantly larger cities than the others, their average energy consumption is significantly lower compared to the networks in other cities. Figure 3: Maximum energy consumption for WSN by cities. Figure 2: Simulation schemes for cities in Bulgaria. (**a**) T1 Burgas; (**b**) T2 Varma; (**c**) T3 Shumen; (**d**) T4 Yambol; (**e**) T5 Plovdiv; (**f**) T6 Pleven. Joules are used as the measurement unit because Watts measure the rate of using energy, which is not useful for reporting the amount of energy that WSNs use. We must consider that Watts were used for such a long time, which would give a figure and was a convenient way to obtain measurements; however, the actual unit for an amount of consumed energy is the Coulomb, which is a small unit, so for WSN energy consumption measurement, we need of a bigger unit. That is why Joules is the preferred measurement unit in WSN. Figure 4 shows the average level of power consumption in wireless sensor networks, depending on the number of rounds. The results obtained during the continuous operation of the network show that in the city of T2, the distribution of nodes has a significant impact on average energy consumption. With T6, the lowest power consumption is observed, compared to other networks; this is because the nodes located close to the base station are significantly fewer and this generally reduces the energy consumption during the operation of the network. In other cases, for T1, T3, T4 and T5 networks, the average energy consumption is similar in value. Only in T1, due to the presence of a number of nodes near the base station, when transmitting more than 30 rounds, there is an increase in energy consumption. The nodes that are near the base station (less than 1 km) have greater energy consumption because they communicate more often with the station in comparison with other notes at greater distances. Figure 5 shows the remaining energy level in the wireless sensor networks, depending on the number of rounds. The highest levels of residual energy are observed in the T2 and T5 networks. As can be seen from the previous graphs, in these networks, the maximum and average levels of energy consumption are maintained during operation of the network. For this reason, these two networks operate more energy efficiently than the others. The lowest residual energy levels are observed in T4. Although there are fewer nodes, the distances in the city are not great (up to 4 km).