# Efficient Cluster Tree Topology Operation and Routing for IEEE 802.15.4-Based Smart Grid Networks
## 5 Performance Evaluations
It is defined as follows:  
\[R_{S}=\frac{N_{E}}{N_{C}}\times 100(\%)\]  
where \(N_{E}\) is the number of data frames received by the end device and \(N_{C}\) is the number of data frames received by the coordinator device. Packet loss is the ratio of packets dropped owing to interference to the total number of packets received. In this simulation, the delivery success rate of the proposed scheme was 98.19% when the packet loss was 0%, and 77.14% when the packet loss was 20%. When considering the beacon loss owing to transmission errors, a device adopting the proposed scheme loses 2.86% of the data frames. Meanwhile, the delivery success rate of the IEEE 802.15.4 standard and IEEE 802.15.4 mesh protocol was 47.13% when the packet loss was 0%. As the packet loss probability increases, the performance of the legacy protocol degrades significantly, and the difference in its performance from that of the proposed scheme increases further. This is because the IEEE 802.15.4 standard and IEEE 802.15.4 mesh protocol cannot prevent interference from other networks, and a larger interference causes more packet losses. Figure 21: Number of received frames vs. time. Figure 22: Comparison of the delivery success rate. Figure 23 shows the dissipated power consumption of the device located in the overlapping region of the transmission ranges. The dissipated power consumption of the device that used the proposed scheme was equal to that of both a device that used the IEEE 802.15.4 standard and one that used the IEEE 802.15.4 Mesh protocol before data frames collide, as observed in this figure. At 253.19 s, the beacon frames first collided. Then, the devices that used the IEEE 802.15.4 standard and IEEE 802.15.4 mesh protocol performed an orphan scan after 253.19 s. In the simulation, the device that used the IEEE 802.15.4 standard and IEEE 802.15.4 mesh protocol attempted to synchronize with its cluster head. However, this device could not receive beacon frames and failed to synchronize because of beacon frame collisions. This legacy device restarted and attempted to associate with the cluster head but failed again because of beacon frame collisions. Finally, the device was switched off. Hence, the device using the legacy protocol did not consume energy after 270.58886 s.  
The next scenario considered a network environment with the presence of WLAN. Figures 24 and 25 show the throughput of the interfered network when the traffic loads of the WLAN were 2 and 8 Mbps, respectively. In the simulation, the WLAN device was switched on for 50 s. It can be observed that the IEEE 802.15.4 standard and IEEE 802.15.4 mesh protocols were highly susceptible to the presence of the interferer. The network performance of the two protocols was degraded severely by the presence of the interferer because these do not provide an interference avoidance scheme. However, the proposed scheme could maintain the network performance, regardless of the presence of an interferer. This is because it can modify its network channel into an idle channel when it detects interference. Additionally, the proposed scheme provides a significantly faster recovery time. This is primarily because it can rapidly prevent channel interference by migrating the network channel to a predetermined idle channel. Figure 26 depicts the packet error rate (PER) for different frame sizes of the IEEE 802.15.4 protocol. As the traffic load of the WLAN and size of the frame increased, the PER of the IEEE 802.15.4 standard and IEEE 802.15.4 mesh protocols increased significantly because the WLAN device could not circumvent interference. However, the PER of the proposed scheme did not vary regardless of the WLAN traffic load. This is because it can prevent interference by the WLAN. Figure 23: Energy consumption of a device that detects interference. Figure 24: The throughput comparison when WLAN traffic load is low. Figure 26: PER as a function of WLAN traffic load for different frame sizes. Figure 25: The throughput comparison when WLAN traffic load is high.