# Cross-Layer MAC/Routing Protocol for Reliability Improvement of the Internet of Things
## 4 Performance Evaluation  
We used the OMNeT++ simulator [73] to evaluate the performance of the TSMR. The common simulation parameters are summarized in Table 1, and we adopted the energy model of CC2630 [74]. The simulation model of the IEEE 802.15.4 in [75] is good since it provides several MAC layer service primitives, channel scan operations, beacon management functions, and WPAN management functions. Therefore, it has been used in several studies to evaluate the performance of the TSMR. In [75], it consisted of the following modules-- that is, an application layer implementing the traffic generator, battery module, network module, and physical layer module. The environmental parameter settings were determined by adjusting the variables in the omnetpp.ini configuration file of the model. The simulations were conducted in beacon-enabled mode, and all packets required an ACK frame. The devices were placed randomly on a 1000 \(\times\) 1000 m plane. The simulations were run for 1000 s, with the number of devices in the network being 400. For accuracy, the same configuration simulation was performed 20 times. In this simulation, we compared the TSMR with the IEEE 802.15.4 [1], RPL [54], and MeshMAC [61] schemes. For mesh networking using the IEEE 802.15.4 standard, we applied the AODV routing protocol in the IEEE 802.15.4 non-beacon enable mode. Figure 14 shows the energy consumption as a function of the number of source devices. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Value** \\ \hline Transmission power (dBm) & 3.5 \\ Bandwidth & 2.8 MHz \\ Synchronization mode & Beacon-enabled \\ Carrier sense sensitivity & \(-\)85 dBm \\ Channel number & 11 \\ IEEE 802.15.4 Header Length & 22 bytes \\ Packet Size & 50 bytes \\ RX current consumption & 5.9 mA \\ TX current consumption & 9.1 mA \\ IDLE current consumption & 0.550 mA \\ Sleep current consumption & 0.001 mA \\ BO & 10 \\ SO & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters. In this simulation, the transmission pair was randomly selected. For the IEEE 802.15.4 standard, devices participating in routing consume significant energy to establish and maintain routes. Therefore, the IEEE 802.15.4 standard provides the lowest energy performance. MeshMAC provides beacon scheduling techniques to reduce power consumption, and all devices operate in duty cycles. Therefore, the MeshMAC provides better energy performance than the IEEE 802.15.4 standard. However, since intermediate devices on the path simply forward data frames to the next hop device without a fixed path, even unnecessary devices participate in routing. Thus, many intermediate devices consume energy to relay the data frame to the destination. RPL transmits packets by bypassing the route, generating many control packets for flooding-based path discovery and topology maintenance, which can cause network congestion. Therefore, the RPL consumes more power than the TSMR. TSMR provides the best energy performance because it does not generate control packets for routing frames, and control packets for path maintenance do not occur except for packets for handover. Figure 15 shows the delivery success ratio as a function of the number of source devices. The delivery success ratio represents the ratio of the number of packets successfully arriving at the destination among data packets generated by the source node. Thus, this performance indicator implies the reliability of the data packet. As the number of source devices increases, many devices generate a large amount of control packets to set and maintain routing paths. In addition, because they participate in routing protocols and transmit data packets, the delivery success ratio of the IEEE 802.15.4 standard decreases and the collision probability increases significantly. Because packets in the RPL tend to bypass the route, they are concentrated on nodes close to the route, resulting in transmission failures around the route. Especially for IEEE 802.15.4 and RPL, the gap is much wider than the mesh topology.