## 4 Performance Evaluation
### Simulation Results
Additional data cells cannot be allocated to the WPT slotframe, and thus the end-to-end delay is no longer increased. In the legacy TSCH MAC, data cells are randomly allocated to a TSCH slotframe of fixed length. Accordingly, the HAP may wait for the next TSCH slotframe to transmit because, in the TSCH slotframe, the data cells used for inter-cluster traffic transmission may be allocated to an earlier timeslot compared with the data cells used for intra-cluster traffic transmission. The average end-to-end delay of TMSS is similar to that of the legacy TSCH MAC but slightly longer. The lengths of the TMSS slotframe and TSCH slotframe are equal to 100 timeslots; thus, in both cases, the same number of power and data cells for inter-cluster traffic and intra-cluster traffic transmissions are allocated in one slotframe. However, in TMSS, due to the use of a separate EB slotframe, overlap between cells may cause the delay of data packets. Quantitatively, when the numbers of data packets transmitted per second are one, two, and four, the average end-to-end delays of MCSS are 94.09% and 94.15%, 80.40% and 80.60%, and 37.41% and 38.03% shorter than those of the legacy TSCH MAC and TMSS, respectively. Figure 7: Average end-to-end delay. Figure 8a-c illustrates the variations in the WPT slotframe length for each HAP according to the change in the number of cluster members for one, two, and four data packets transmitted per second, respectively. Commonly in each figure, the WPT slotframe length of HAP 1 equals two because HAP 1 is the root and does not have any cluster members. When the number of data packets transmitted per second is one, the WPT slotframe length of HAPs (except HAP 1) increases as the number of cluster members increases because the WPT slotframe length is determined to accommodate the increased power and data traffic in the HAP cluster. In contrast, when the number of data packets transmitted per second is two or four, it increases and is limited to 101, the maximum value. Figure 8: WPT slotframe lengths of HAPs: (**a**) one, (**b**) two, and (**c**) four packets/s. Figure 9 displays the change in the aggregate throughput as the number of data packets transmitted per second varies. In MCSS, only the data and power cells are allocated to the WPT slotframe; however, in the existing TSCH, all types of cells are allocated to one TSCH slotframe. Similarly, in TMSS, all power and data cells except for EB frames and CMs are allocated to the same TMSS slotframe. In other words, the WPT slotframe of the MCSS can accommodate more data cells of sensor nodes than the slotframe of the legacy TSCH MAC. Therefore, in the figure, MCSS obtains a higher aggregate throughput than the legacy TSCH MAC and TMSS when the number of sensor nodes is larger than a certain number and the number of data packets transmitted per second is fixed. If the number of sensor nodes is less than a certain number, the aggregate throughput of all protocols is the same because their slotframe accommodates all network traffic. Quantitatively, when one, two, and four data packets are transmitted per second, the aggregate throughputs of MCSS are 26.82% and 26.60%, 18.63% and 18.37%, and 8.21% and 7.87% higher than those of the legacy TSCH MAC and TMSS, respectively. Figure 10 depicts the average harvested energy for varying numbers of data packets transmitted per second. When the number of data packets transmitted per second is one, MCSS exhibits higher average harvested energy than legacy TSCH MAC and TMSS regardless of the number of sensor nodes because the WPT slotframe length is always shorter than the slotframe lengths of legacy TSCH MAC and TMSS.