## 7 Performance Evaluation
It is observed that the delay increases slowly as the number of devices increases when we consider the packet rate as one packet per second. When the data payload is 100 bytes and five devices are considered, the delay is nearly 0.056 s during the transmission and 0.059 s during retransmission, if the packet arrival rate is one packet per second. From Figure 16, it is also observed that the packet transmission delay in our work is significantly less as compared to the IEEE 802.15.4e scheme for different arrival rates, and our simulation result coincides with the analytical one. Figure 14: Comparison of the reliability of our proposed scheme with the IEEE 802.15.4e standard. Figure 13: Validation of the reliability of our proposed scheme for different numbers of devices. Figure 17 shows the packet drop rate with the variable number of devices. It is observed that the packet drop rate increases as the of number of devices increases considering one packet per second. When the data payload is 100 bytes and five devices are considered, the packet drop rate is nearly 0.22 during the transmission. However, the packet drop rate is negligible during the retransmission. As shown in Figure 18, the packet drop rate of our work is significantly less as compared to the IEEE 802.15.4e scheme. Figure 16: Comparison of the delay of our proposed scheme with the IEEE 802.15.4e standard. Figure 15: Validation of delay of our proposed scheme for different numbers of devices. The energy consumption in joules/byte with different numbers of devices when one packet per second arrives at a device is shown in Figure 19. The energy consumption increases as the number device increases. When we consider only five devices and the data payload is 100 bytes, the average energy consumption for successful packet transmission is nearly \(2.38466\times 10^{-5}\) Joule during the transmission and \(1.81308\times 10^{-5}\) Joule during the retransmission. The energy consumption of our work is significantly less than the IEEE 802.15.4e scheme and is shown in Figure 10:0 We achieve this improved result through our proposed separate retransmission period and single CCA operation rather than two times consecutive CCA operations as suggested in the IEEE 802.15.4e standard and by allowing only collided devices to contend during the retransmission period. Figure 10:1 Validation of the packet drop rate of our proposed scheme for different numbers of devices. Figure 10:2 Comparison of the packet drop of our proposed scheme with the IEEE 802.15.4e standard. As shown in Figure 21, the number of devices is taken along the \(X\) axis, and the corresponding energy consumption in joules is obtained as given along the \(Y\) axis. It is observed that the energy consumption increases as the numbers of devices attached to a coordinator increase. However, the energy consumption in our schemes is significantly less for different interference levels of WiFi as compared to the IEEE 802.15.4e. Figure 22 shows the delay with a variable number of devices under WiFi interferences. It is observed that the delay increases as the numbers of devices increase considering one packet per second. However, the delay of our mechanism is significantly less as compared to the IEEE 802.15.4e scheme. Figure 10:3 Validation of the energy consumption of our proposed scheme for different numbers of devices. Figure 10:4 Comparison of the energy consumption of our proposed scheme with the IEEE 802.15.4e standard. Figure 23 compares the reliability of data transmission with respect to different numbers of devices under WiFi interferences. It is observed that the reliability of our work is significantly higher than the IEEE 802.15.4e scheme. The throughput corresponding to different numbers of devices is depicted in Figure 24, and it is observed that the throughput decreases as the number of devices attached to a PAN coordinator increases irrespective of the interference level. It is observed that the throughput of our work is marginally higher than the IEEE 802.15.4e scheme.