## 3 Results and Discussion
### Model Selection and Application for Short-Range Propagation in a Corn Field
Also, Figure 10 shows that the COST-235 model is appropriate for \(\rm h_{Tx}\)\(\lambda/3\) m to \(\rm h_{Rx}\) 2 m and 3.4 m scenarios with co-polarized V-V antennas. Figure 10: Comparison between losses for co-polarized V-V antennas at transmitting antenna height \(\lambda/3\) m with existing models: (**a**) 0.9 GHz, \(\rm h_{Rx}\) = 2.0 m; (**b**) 0.9 GHz, \(\rm h_{Rx}\) = 3.4 m; (**c**) 2.4 GHz, \(\rm h_{Rx}\) = 2.0 m; (**d**) 2.4 GHz, \(\rm h_{Rx}\) = 3.4 m.  
Figures 11 and 12 illustrate the comparison between predictions of the Weissberger, COST-235, and Multi-slope models and measured losses at the above-ground installation of the sensor node in the corn field, i.e., for a transmitting antenna height of 0.5 m at two frequencies (0.9 GHz and 2.4 GHz) and two receiving antenna heights (2.0 m and 3.4 m) for H-H (Figure 11) and V-V (Figure 12) polarized antennas. We can observe from Figure 11 and Tables 5 and 6 that the Weissberger model provides the best results in scenarios of above-ground installation of a sensor node in the cornfield at co-polarized H-H antennas, giving MAPE values of 6.4% and 12.7% for \(\rm{h_{Rx}}\) = 2 m at 0.9 GHz and 2.4 GHz (Table 5) and of 6.2% and 7.5% for \(\rm{h_{Rx}}\) = 3.4 m at 0. Figure 12: Comparison between losses for co-polarized V-V antennas at transmitting antenna height 0.5 m with existing models: (**a**) 0.9 GHz, h\({}_{\text{Rx}}\) = 2.0 m; (**b**) 0.9 GHz, h\({}_{\text{Rx}}\) = 3.4 m; (**c**) 2.4 GHz, h\({}_{\text{Rx}}\) = 2.0 m; (**d**) 2.4 GHz, h\({}_{\text{Rx}}\) = 3.4 m. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{\(\mathbf{h_{Rx}}\) *} & \multirow{2}{*}{\(\mathbf{h_{Tx}}\) *} & \multirow{2}{*}{**Frequency **} & \multirow{2}{*}{**Polarization ***} & \multicolumn{4}{c}{**Mean Absolute Percentage Error**} \\ \cline{5-8}  & & & & **Basic Free-Space Loss** & **Multi-Slope Model** & **Weissberger Model** & **COST-235 Model** \\ \hline \multirow{4}{*}{2} & & 0.9 & H & 26.7 & 6.7 & 14.4 & 16.8 \\  & & 2.4 & H & 24.3 & 9.8 & 14.4 & 12.3 \\  & & 0.9 & V & 36.7 & 15.3 & 25.8 & 3.9 \\  & & 2.4 & V & 33.1 & 17.8 & 24.3 & 5.9 \\ \cline{1-1} \cline{2-8}  & & 0.9 & H & 20.9 & 7.2 & 6.4 & 28.6 \\  & & 2.4 & H & 23.4 & 22.9 & 12.7 & 12.8 \\  & & 0.9 & V & 33.6 & 20.9 & 19.4 & 10.2 \\  & & 2.4 & V & 31.6 & 31.6 & 24.9 & 7.62 \\ \hline \hline \end{tabular}  
* \(\mathbf{h_{Rx}}\) and h\({}_{\text{Tx}}\) are receiving and transmitting antenna heights in meters. ** The frequency indicated in the table is in GHz. *** H—horizontal and V—vertical polarization.  
\end{table} 
Table 5: A comparison of the mean absolute percentage error of Weissberger, COST-235, and Multi-slope models when they are used to predict the loss-versus-distance trend in several scenarios in a corn field at a receiving antenna height of 2 m.  
We can conclude that the COST-235 model provides a reasonable estimate of the path loss of vertically polarized signals in corn fields, with MAPE values of 3.9% to 14.0% between the prediction and the actual path loss value. Hence, it is appropriate to recommend using the COST-235 model for omnidirectional, in-azimuth-plane vertical polarized antennas of nodes and base stations in both scenarios: near- and above-ground installation of sensor nodes in corn fields for smart agriculture. Also, concerning smart agriculture applications in the corn fields, the Multi-slope model performed well in the near-ground application scenarios at omnidirectional in-elevation-plane antennas with horizontal polarization. In addition, we identify the Weissberger model as suitable for planning radio coverage in the cornfield for the above-ground node connectivity scenario with omnidirectional in-elevation plane and horizontal polarization.