## 6 Performance Evaluation
### Sensitivity to MPMF's Factors of \(W_{0}\), \(\alpha\), \(L\), and \(\epsilon\)  
This section inspects the performance sensitivity of the delivery rate and transmission overhead ratio against three MPMF-specific coefficients, including the \(\alpha\) parameter in (7), the threshold of the weight value \(W_{0}\), the threshold of the sum of the geometric angles at one- and two-hop distances \(\epsilon\) in (8), and each message's initial copy number \(L\). A smaller value of \(\epsilon\) indicates that one- and two-hop nodes closer to the destination node are considered as candidate nodes. A larger value of \(W_{0}\) implies that one-hop relay frequently contacting the destination and two-hop relay closer to and frequently contacting the destination are selected as candidate nodes. A larger value of \(L\) indicates that an original message will be replicated at most \(L\) times. After extensive simulation under TVCM and NCCU, we obtain the appropriate values of \(\epsilon\), \(W_{0}\), \(L\), and \(\alpha\) used for the performance comparison among Epidemic, PRoPHETv2, GSaR, TC, and TCCB. Figures 3 and 4 depict the influence of \(\epsilon\) and \(W_{0}\) on the performance of the MPMF under TVCM and NCCU. In TVCM, the threshold \(\epsilon\) affects the delivery rate and overhead ratio, while the change in \(W_{0}\) has a minor effect on the overhead ratio. In NCCU, the threshold \(W_{0}\) affects the delivery rate and overhead ratio, while the change in \(\epsilon\) has a minor effect on the delivery rate. In TVCM, with the incremental values of \(\epsilon\) from 40 to 60, the delivery ratio decreases while the overhead ratio increases. The delivery rate and overhead ratio remain almost the same for \(\epsilon\geq 70\). When \(\epsilon\) is smaller than 60 in TVCM, the nodes moving closer to the destination node are selected as the candidate nodes, then the possibility of delivering messages earlier increases, which considerably effects the delivery rate and overhead ratio. Compared with TVCM, NCCU has a higher node population distributed in a large area. Thus, the variation of \(\epsilon\) shows little effect on the delivery rate and overhead ratio. In Figure 4, as \(W_{0}\) increases from 0.5 to 0.6, the delivery rate decreases while the overhead ratio increases. However, as \(W_{0}\) increases from 0.6 to 0.8, the delivery rate and the overhead ratio remain the same. Figure 3: Results by MPMF with different values of \(\epsilon\) and \(W_{0}\) under TVCM trace (TTL = 5 h and buffer size = 10 MB). Figures 5 and 6 depict the influence of \(\alpha\) and \(\epsilon\) on the performance of the MPMF under TVCM and NCCU. Given the buffer size of 10 MB on each node and message TTL 5 h, Figure 5 exhibits that the delivery rate decreases and the overhead ratio increases as \(\epsilon\) increases from 50 to 70. However, the variation of \(\alpha\) does not affect the results of either delivery rate or overhead ratio. In Figure 6, as \(\alpha\) increases from 0.6 to 0.9, the delivery rate decreases while the overhead ratio increases. Figure 4: Results by MPMF with different values of \(\epsilon\) and \(W_{0}\) under NCCU trace (TTL = 5 h and buffer size = 10 MB). Figure 5: Results by MPMF with different values of \(\alpha\) and \(\epsilon\) under TVCM trace (TTL = 5 h and buffer size = 10 MB). Figures 7 and 8 display the influence of \(L\) with respect to the variance of the TTL values in the range of [2, 6] h under TVCM and NCCU. Given the buffer size of 10 MB on each node, the results in Figure 7 exhibit that both the delivery rate and overhead ratio increase as \(L\) increases from 5 to 15 regardless of the TTL values. The overhead ratio increases as \(L\) increases from 5 to 15 in Figure 8, whereas the delivery rate increases as \(L\) increases from 5 to 10. However, for \(L=15\), the delivery rate decreases for the TTL from 3 to 6. A buffer overflow possibly occurs more times with the limited buffer and higher node population in NCCU. It is noted that the overhead ratio is more sensitive to the incremental TTL values.