## 4 Results and Discussion
### Evaluation of Communication Range and Channel Attenuation Modeling
Measurements of received signal strength (RSSI) and noise impact on the signal (SNR) enabled conclusions about the transmission quality concerning the achieved packet delivery rate, as presented hereafter, with the highlighted combinations of communication parameters that produce the best results. The RSSI measures the incoming signal power at the RF input port, evaluated within the receiver bandwidth. This value is absolute in units of dBm and with a resolution of 0.5 dB. The RSSI value is usually used to determine the most significant possible distance between the transmitter and the receiver since the signal strength decreases as the distance between the transmitter and the receiver increases [52]. However, the signal strength also depends on the interference, i.e., the noise level. Therefore, the RSSI can sometimes indicate incorrect positioning of equipment [83]. In order to minimize the effects of obstacles on communication between the receiver and transmitter as much as possible, during all measurements, the gateway was placed at a height slightly above 60 m. Nevertheless, even then, direct visibility between the sensor node and the gateway was not enabled because the sensor node, considering its purpose, was placed too low to receive the most valuable results of the measurement. Moreover, the value of signal versus noise represents the comparison of the signal strength to the noise power. It is denoted as SNR, and its unit of expression is dB. SNR is the best indicator of obstacles in signal transmission. A positive SNR value means the signal is stronger than the noise, and a negative SNR means that the noise overpowers the signal [84]. For the listed combinations of communication parameter settings, measurements of RSSI and SNR values are carried out using the RFM95/96/97/98(W) LoRa module. For the signal strength at shorter distances, higher RSSI values are obtained. The obtained RSSI values are around \(-80\) dBm at distances less than 100 m, at distances of 500 m between \(-100\) and \(-110\) dBm, and at greater distances from \(-110\) to \(-130\) dBm. Moreover, with increasing distance between the transmitter and the receiver, the values of the SNR parameter decrease. In NLOS scenarios, the influence of obstacles on the SNR levels can be noted as well. The SNR values become negative at distances \(\geq\)2 km, which means that the received signal operates below the noise floor. In addition, the moderate success of the collected transmissions within each scenario is calculated for the measured range of RSSI and SNR values, and some unsuccessful transmissions are noted. Finally, as presented, the number of lost packets is recorded for the RSSI parameter values less than \(-110\) dBm and the negative SNR parameter values. According to the specifications of the transceiver used in the measurements [54], under an extended range mode of operation, and in the case of 125 kHz bandwidth, the following RF sensitivity levels can be realized: \(-118\) dBm for SF = 6, \(-123\) dBm for SF = 7, \(-126\) dBm for SF = 8, \(-129\) dBm for SF = 9, \(-132\) dBm for SF = 10, \(-133\) dBm for SF = 11, and \(-136\) dBm for SF = 12. A message is received if the signal strength is higher than the receiver's sensitivity. During the measurements, the LoRa signal's bandwidth was set to 125 kHz, and the transceiver was configured to use the different values of spreading factors. As presented in Figure 4, obtained from the analysis of the collected results, this enabled receiver sensitivity of up to approximately \(-130\) dBm. The results presented in Figures 4 and 5 were obtained from approximately five hundred conducted measurements of SNR and RSSI values, as described in more detail in [52]. Several spots with missing values were found in Figure 4, evident after analyzing the collected data from Figure 5 and from all additional sets of SNR and RSSI values with SF7-SF10 [52]. The spots were then filled and values were calibrated.