## 5 Results
### Proposed LR Models  
Figure 4 and Equations (18) and (19) present the empirical propagation models with the separated distances for the short grass environment.  
\[RSSI_{1}(d)=-53.79-19.42\log(d);\ \mathrm{d}\ \leq\ \mathrm{d}_{\mathrm{bp}} \tag{18}\]  
\[RSSI_{2}(d)=-49.31-25.87\log(d);\ \mathrm{d}\ >\ \mathrm{d}_{\mathrm{bp}} \tag{19}\]  
where \(\mathrm{d}\) is the distance between the two nodes. The RSSI models were the CI (close in free space) and dual-slope models. The PLEs before the breakpoint distance were approximately 20, while those after were more than 20. These values confirmed the wave propagation theory for the LOS condition. We used the breakpoint distance at 15 m (log (15) = 1.18) (Figure 4) calculated from Equation (11) with a 1.2 m antenna height to determine the overall separated parts of communication. Similarly, the proposed models for the tall grass and weed environments are presented as follows:  
\[RSSI_{1}(d)=-56.04-18.37\log(d);\ \mathrm{d}\ \leq\ \mathrm{d}_{\mathrm{bp}} \tag{20}\]  
\[RSSI_{2}(d)=-43.76-26.95\log(d);\ \mathrm{d}\ >\ \mathrm{d}_{\mathrm{bp}} \tag{21}\]  
Equation (20) shows that the PLE is mostly unchanged compared to Equation (18). This follows from the theory that the PLE is still approximately 20 in the first Fresnel zone region for the incomplete blocking case in tall grass and weed. However, this effect occurs after the breakpoint and makes the PLE increase as shown in Figure 5 and Equation (21).  
For the case of people moving, the experiment was performed in two scenarios: (1) random blocking, and (2) full blocking. For the first scenario, one farmer walks forward and reverse between the communication nodes for all antenna heights as shown in Figure 6a. The propagation result is shown in Figure 6b and expressed in Equations (22) and (23),  
\[RSSI_{1}(d)=-65.00-8.95\log(d);\ \mathrm{d}\ \leq\ \mathrm{d}_{\mathrm{bp}} \tag{22}\]  
\[RSSI_{2}(d)=-43.76-23.52\log(d);\ \mathrm{d}\ >\ \mathrm{d}_{\mathrm{bp}} \tag{23}\]  
Equation (22) shows that the PLE before the breakpoint was less than 20 since the random movements make the RSSIs fall, especially at the reference distance (1 m) as shown in Figure 7. In the case of distance before breakpoint, the maximum radius of the firstFresnel zone is small compared with the obstruction side. This makes the path loss slope decrease greatly. In the case of distance after breakpoint, the radius is very large compared with the obstruction side; therefore, the path loss slope shows almost no change. Thus, breakpoint distance optimization makes the prediction accurate, especially in the case of the distance after breakpoint. Thus, the PLE in Equation (23) was still more than 20. In the case of the second scenario, two farmers fully blocked the radio wave at each node (see Figure 6b). Figure 8 depicts the propagation result expressed in Equations (24) and (25),  
\[RSSI_{1}(d)=-70.47-10.14\log(d);\ \mathrm{d}\ \leq\ \mathrm{d}_{\mathrm{bp}} \tag{24}\]  
\[RSSI_{2}(d)=-59.67-21.84\log(d);\ \mathrm{d}\ >\ \mathrm{d}_{\mathrm{bp}} \tag{25}\]  
In Figure 8, the RSSI in each distance was collected in the lower bound because the radio paths were blocked from obstructions. This caused a small effect from the multi-path fading. Equation (24) shows that the PLE before the breakpoint was mostly equal to that in Equation (22) with one moving person and that with the PLE of Equation (25), which was also more than 20.