## 6 Results
### Analysis of the Influence of Heights and Polarizations in Densely Wooded Environments
Furthermore, in all these situations, it is observed that RSSI exhibited a linear behavior, and SNR exhibited an exponential behavior for a distance over 250 m.  
Figure 8: (**a**) The collected GPS data corresponding to RSSI levels vs. distance in the studied environment. (**b**) The collected GPS data corresponding to SNR levels vs. distance in the studied environment. Figure 9: Distribution of the measured RSSI data with respect to distance for SF12 at all heights for HH and VV polarizations. Analysis of RSSI and SNR Values with Respect to Heights  
The results of RSSI and SNR for SF12 in densely wooded environments for IoT networks in the 915 MHz frequency band are presented and analyzed for each height. A new graph that condenses the information of RSSI, mean, and standard deviation values for fixed distance intervals is presented to make it easy to compare for different heights and polarizations. The mean and standard deviation are calculated considering all RSSI values contained within the distance interval covered by a sliding window. The RSSI and SNR values along the traveled path are displayed for the SF12 combination heights of 6, 12, and 18 m in Figures 11 and 12. First, while analyzing the horizontal antenna polarization (HH), for a height of 6 m, where the transmitter is located at the tree trunk level, it can observed that the RSSI values range from \(-131\) to \(-80\) dBm, while the SNR ranges from \(-8\) to 11 dB. Figure 11: Analysis of the mean and standard deviation values of RSSI for SF12 at all heights and for VV and HH polarizations. Figure 10: Distribution of the measured SNR data with respect to distance for SF12 at all heights for HH and VV polarizations. At a height of 12 m, corresponding to the beginning of the tree canopy, the RSSI values range from \(-133\) to \(-85\) dBm, while the SNR ranges from \(-11\) to \(8\) dB. Finally, at a height of 18 m, corresponding to the middle of the tree canopy, the RSSI values range from \(-132\) to \(-82\) dBm, while the SNR ranges from \(-12\) to \(8\) dB. Analyzing the vertical antenna polarization (VV), the RSSI and SNR values at a height of 6 m range from \(-131\) to \(-83\) dBm and from \(-7\) to \(12\) dB, respectively. At a height of 12 m, the RSSI values are in a range from \(-128\) to \(-81\) dBm, and the SNR values are in a range from \(-3\) to \(11\) dB. Finally, for a height of 18 m, the RSSI values are in a range from \(-129\) to \(-82\) dBm, and the SNR values are in a range from \(-5\) to \(10\) dB. From Figures 11 and 12, it is possible to observe that the VV polarization presents RSSI and SNR values similar to the HH polarization. However, the decay in the VV signal level over the distance is smaller compared to the HH signal. In addition, analyzing Table 4, it can also be verified that, on average, the lowest value of VV polarization (at a height of 18 m) shows a result practically equal to the highest value of HH polarization (at a height of 6 m). In summary, when placing the transmitter at heights of 12 and 18 m, corresponding to the beginning and middle of the leaves, respectively, a worse SNR is observed. Therefore, what most affects the signal quality in a wooded environment are the leaves. Furthermore, \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Height**} & \multicolumn{2}{c}{\(\sigma\)**-RSSI**} & \multicolumn{2}{c}{**Mean RSSI**} & \multicolumn{2}{c}{\(\sigma\)**-SNR**} & \multicolumn{2}{c}{**Mean SNR**} \\  & \multicolumn{2}{c}{**(dBm)**} & \multicolumn{2}{c}{**(dBm)**} & \multicolumn{2}{c}{**(dB)**} & \multicolumn{2}{c}{**(dB)**} \\  & **HH** & **VV** & **HH** & **VV** & **HH** & **VV** & **HH** & **VV** \\ \hline
6 m & 14.84 & 16.62 & \(-107.24\) & \(-105.76\) & 6.68 & 6.93 & 4.32 & 5.36 \\ \hline
12 m & 14.86 & 15.01 & \(-111.09\) & \(-106.24\) & 6.87 & 5.13 & 1.16 & 5.10 \\ \hline
18 m & 15.91 & 14.90 & \(-108.76\) & \(-107.31\) & 7.22 & 5.96 & 1.08 & 4.28 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Statistical metrics of the collected signal.