## 5 Experimental Results and Analysis
### Comparison and Analysis of the Routing Control Strategy  
To perform the routing control comparison, different methods have been compared including the Shortest path routing strategy (SPRS) [25], the hybrid Congestion alleviation routing strategy (HCARS) [26], the online increasing fit first segment routing strategy (OI-SRS) [27], and the proposed minimum path selectivity routing control strategy (MPSRCS). Several parameters have been employed to evaluate the comparison performance including the packet loss rate, the network transmission delay and the average bandwidth occupancy rate of downlink routing. The network parameters are set up as follows: spreading factor = 7, number of gateways is 3, number of nodes is 20; \(CR_{\text{min}}\) = 25, which is the minimum number of links in the network; \(CR_{\text{max}}\) = 35, which is the maximum number of links in the network; \(RB_{\text{max}}\) = 40 Mbit/s, which is the maximum link bandwidth in the network; \(RB_{\text{min}}\) = 0.0625 Mbit/s, which is the minimum link bandwidth in the network; \(RT_{\text{max}}\) = 20 s, which is the maximum link delay in the network; and \(RT_{\text{min}}\) = 10 s, which is the minimum link delay in the network. The average request bandwidth is gradually increased, and the network performance parameters under different routing control strategies are analyzed. Then, the downlink load rate \(h_{m}\) is defined as follows:  
\[h_{m}=(\frac{h_{i}}{h_{\text{max}}})\times 100\% \tag{19}\]  
where, \(h_{i}\) is the current downlink traffic, and \(h_{\text{max}}\) is the downlink bandwidth value. Figure 15 shows the comparison of the packet loss rate under different downlink load rated. Figure 14: Model prediction comparisons. Figure 15: Comparison of the packet loss rate under different downlink load rates. In Figure 15, it is seen that when the downlink load rate is gradually increased, the packet loss rate of the MPSRCS is much less than those of the SPRS, HCARS and OI-SRS. The loss rate of SPRS is the largest since there is no link status detection in the process. When the load rate is relatively small, the loss rates of both the OI-SRS and HCARS are almost the same. When the load rate is further increased (exceeding 50%), the HCARS behaves relatively better than OI-SRS. It is known that the segment flow scheduling is used in the OI-SRS, and therefore the communication reliability can be ensured when the load rate is low. When the load rate exceeds 50%, it is seen that the communication reliability can be no longer guaranteed. In the HCARS, the dynamic process of route assigning is considered and therefore it is able to supply better reliability than those of the SPRS and OI-SRS. However, the bandwidth occupancy rate prediction is missing in this strategy and the dynamic response of the routing assigning in the dynamic process could be limited and this is the reason that the loss rate becomes larger when the load rate exceeds 70%. The proposed MPSRCS strategy fully considers the prediction of the link bandwidth occupancy rate. It is seen that the communication reliability of data transmission is better than the other three strategies. Transmission delay is also an important parameter to evaluate the routing control performance. By considering the difference in the data transmission delay requirements of different downlink services in the LoRaWAN network, it is assumed that the average transmission delay of the downlink communication of the LoRaWAN network with a stable transmission in period (\(t\), \(t+T\)) is \(T(X)\). The maximum value of the transmission delay is set as \(T_{\max}(X)\). The downlink data type of LoRaWAN is set as 3, and the average transmission delay \(T_{delay}\) can be described as follows:  
\[T_{delay}=\left[\sum_{X=1}^{3}T(X)/T_{\max}(X)\right]/3 \tag{20}\]  
Figure 16 shows the comparison of the average transmission delay of the downlink communication. It can be seen that different routing control policies demonstrate different delay regulation performances.