## 7 Performance Evaluation  
In this section, our proposed models are evaluated and validated by using the OMNeT++ [28] simulator. We conduct the simulation to compare the performance of our proposed scheme with IEEE 802.15.4e. For the simulation, we consider the star topology and devices are located randomly in the area of 30 \(\times\) 20 m\({}^{2}\) with the PAN coordinator at the center. Again, we compare our work with the IEEE 802.15.4e standard for channel access failure, throughput, reliability, average MAC delay, energy consumption and packet drop rate over the Poisson arrival rate. We validate and compare our proposed mechanisms with the IEEE 802.15.4e standard. According to the standard, simulation parameters are set as shown in Table 2. Each simulation is performed for 50 rounds, and the results are produced by taking the average of those 50 rounds. As shown in Figure 9, the number of devices are taken along the \(X\) axis, and the corresponding channel access failure probability is obtained as shown along the \(Y\) axis. It is observed that the channel access failure probability increases as the number of devices attached to a coordinator increases. However, the channel access failure following our schemes during the retransmission is negligible. In our simulation, it is considered that all devices can assess the channel during the contention access period, i.e., in the transmission period of the superframe. However, the devices that fail to assess the channel during this transmission period can access the channel during the newly-allocated retransmission period. As shown in Figure 10, when our work is compared with the IEEE 802.15.4e scheme, it is found that the channel access failure probability of our work is significantly less during both the transmission and retransmission period. Again, as shown in Figure 9, it is observed that our simulation result matches the analytical one. The throughput corresponding to different numbers of devices is depicted in Figure 11, and it is observed that the throughput decreases as the number of devices attached to a PAN coordinator increases irrespective of their packet arrival rate. When the packet arrival rate is one packet per second and five devices are attached to the coordinator, the normalized throughput is 0.46. It is observed that the throughput of our work is higher during both transmission and retransmission, which is reflected in Figure 12, when we compare our work with the IEEE 802.15.4e standard. \begin{table}
\begin{tabular}{c c} \hline \hline
**Notation** & **Value** \\ \hline Radio band & 2.4 GHz \\ Data rate & 250 kbps \\ Carrier sensing sensitivity & \(-\)85 dBm \\ Communication channel number & 11 \\ Beacon interval & 15.6 \(\times\) 25 ms \\ Superframe duration & 15.6 \(\times\) 23 ms \\ Unit backoff duration & 20 symbols \\ PHY overhead & 6 bytes \\ MAC overhead & 3 bytes \\ Transmission energy consumption & 9.1 mA \\ Receiving energy consumption & 5.9 mA \\ Turnaround energy consumption & 7.5 mA \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters. Figure 10: Comparison of channel access failure for different numbers of devices. Figure 9: Validation of our proposed scheme for channel access failure for different numbers of devices. Figure 13 compares the reliability of data transmission with respect to different numbers of devices. When we consider the packet arrival rate as one packet per second, it is observed that the reliability decreases, along with the number of devices attached to a PAN coordinator increases. From Figure 14, it is observed that the reliability of our work is higher than the IEEE 802.15.4e scheme, and the simulation results of our scheme match with the analytical one. Figure 11: Validation of the throughput of our proposed scheme for different numbers of devices. Figure 12: Comparison of the throughput of our proposed scheme with the IEEE 802.15.4e standard. As shown in Figure 15, the number of devices is taken along the \(X\) axis, and the corresponding delay is obtained as shown along the \(Y\) axis.