# A Hybrid Scheme for Disaster-Monitoring Applications in Wireless Sensor Networks
## 6 Performance Evaluation
### Data Transmission Performance  
After clustering, the nodes transmitted sensing data at the steady-state stage in each cluster. The mean queue length, mean cycle time, and mean upper bound of the frame delay were obtained for the HT-MAC scheme. We verified the results of the theoretical analysis and studied the system performance as shown in Figures 10-17. Figure 10: Mean queue length of superior Node 1. Figure 9: Total amount of data received at the base station over time. Figure 11: Mean queue length of superior Node 2. Figure 12: Mean queue length of the ordinary node. Figure 13: Mean cycle time. Figure 16: Alert data delay. Figure 14: Superior data delay. Figure 15: Mean queue length of superior data in superior node. The simulations used the same parameters as in the theoretical analysis, and the system was assumed to have 5, 10, and 20 ordinary nodes in a cluster. Each cluster consists of two superior nodes. We compared the simulation and theoretical results with the change in total traffic intensity under different conditions. The total traffic intensity is the ratio of all node loads (both ordinary and superior nodes) to the link rate. The total traffic intensity range is from 0.1 to 0.95 in theoretical calculations and simulations, with a step of 0.05. Ordinary nodes have symmetrical inputs, the traffic intensity proportion of the superior node to the ordinary node is denoted by \(L\), and the values are 1 and 2. Figure 10 presents the mean queue length of superior Node 1, and shows that the simulation results agree with the theoretical results under different degrees of total traffic intensity. As shown in Figure 10, when the total traffic intensity increases, the mean queue length of superior node 1 also increases. When the load proportion \(L\) is the same, more nodes in the cluster lead to a smaller mean queue length for the superior node. In fact, more nodes in the cluster cause a lower traffic intensity for superior node 1 under the same total traffic intensity. When the number of nodes is the same (\(N=5\)) and \(L\) is larger, the mean length of the superior node increases. Figure 11 presents the mean queue length of superior Node 2 and shows that the simulation results conform to the theoretical results under different degrees of total traffic intensity. Figure 11 is similar to Figure 10; however, the mean queue length of superior Node 2 is less than that of superior Node 1 under the same configuration. Figure 12 shows the mean queue length of ordinary nodes, which agrees with the theoretical results under different degrees of total traffic intensity. This verified the accuracy of the theoretical analysis. In Figure 12, when the total traffic intensity exceeds 0.8, the mean queue length of ordinary nodes increases substantially. Figure 13 shows the mean cycle times for the different situations. The simulation and theoretical results were in agreement under various conditions. Figure 13 shows that the mean cycle time is similar when the number of nodes and total traffic intensity are the same. With \(N=5\), the mean cycle time increases when the total traffic intensity exceeds 0.8. When \(N=20\) and the total traffic intensity exceeds 0.7, the mean cycle time increases rapidly. Frame delays are vital in disaster-monitoring applications. As part of the WirelessHART simulation scenario, alert data were added to WirelessHART. Contention-free period slots were used for alert data, whereas contention access period slots were used for ordinary data. In the WirelessHART simulation, superior data were based on a contention-free period. We created a DRX simulation scenario and set the alert and superior data delay thresholds to 0.4 s. The traffic intensity proportion of the superior node to that of the  
Figure 17: Ordinary data delay. ordinary node is 2. The queue buffers of the superior, ordinary, and alert data were 1 kB each. As shown in Figures 14-17, the performance of HT-MAC is presented and compared with those of the WirelessHART and DRX protocols.