## 4 Results and Discussion
### Evaluation of Communication Range and Channel Attenuation Modeling
Each of these channels has a bandwidth of 125 kHz, uses LoRa modulation, and must allow data rates from 0.3 kbps to 5 kbps (DR0 to DR5), depending on the SF value set. Considering the compromise between range and interference immunity, and energy consumption, two transmission power modes, a low-power (LP) mode and a high-power (HP) mode, are compared, and their impact on the communication range is analyzed. The LP mode with the transmission power of +14 dBm considers high efficiency and low current consumption (25 mW). The HP mode with the transmission power of +20 dBm considers a more extended range and robustness but has a higher current consumption (100 mW). The duty cycle of transmission at +20 dBm is limited to 1%. Although the transceiver supports transmit power of up to +20 dBm, according to frequency regulations, such power is permitted only for one frequency channel. However, any of the six channels can use +14 dBm. The LoRaWAN protocol is used for long-distance, low-power communication. A common problem that occurs in for instance, remote rural areas, as well as in some other specific deployments, such as in forests [82], is the lack of a seamless power source that allows the installation of gateways near an area that needs to be covered by the LoRa signal. Also, this causes the occasionally complex interconnection of gateways with the infrastructure of the core network. In these cases, it is necessary to use a more extended communication range. While communication over long distances of multiple kilometers is used for IoT, the narrow bandwidth can make it unreliable, and there may be significant losses in the delivery of sent packages. Moreover, since the line of sight is not always free of obstacles from vegetation or buildings, this imposes NLOS conditions that impair transmission quality. The performance metric used is packet delivery percentage. Therefore, the conclusions about the transmission quality, according to measured packet delivery percentage, and the combinations of communication parameters that give the best results are presented hereafter, as well as in Figures 2 and 3. Figure 3: Delivery rates of packets with a minimum size. Figure 2: Delivery rates of packets with the maximal size. As presented within the NLOS scenarios, some unsuccessful transmissions of packets are noted. The number of unsuccessful transmissions is more significant with a greater distance and less visibility between the transmitter and the receiver. During the measurement and data-collection process, the LoRa signal's bandwidth was set to 125 kHz. Moreover, the transceiver is configured to use different values of spreading factor, two of which are selected for more detailed analyses. These are SF = 7 (minimum value) and SF = 10 (optimal energy consumption if a more extended range needs to be ensured). Furthermore, the LP mode with the transmission power of +14 dBm for low current consumption (25 mW) and the HP mode with the transmission power of +20 dBm with higher current consumption (100 mW) are chosen. Table 8 shows the amount of delivered packets compared to packets sent with different configurations of SF and CR network parameters in different scenarios. Accordingly, 100% indicates that all sent data has been received. Circled values are those in which the most efficient data transfer was achieved in each of the scenarios, considering the combination of network parameters that represents a more energy efficient solution. The presented results indicate that, among all considered scenarios, the most critical packet deliveries are in remote suburban and rural areas with no direct optical visibility since NLOS conditions impair transmission quality. Therefore, data with the best values for a particular scenario were selected among the obtained data. In doing so, the differences in the obtained results should be considered with regard to the selected packet sizes. The selected packet size values were Pmax = 51 bytes and Pmin = 11 bytes.