## 4 Performance Evaluation
### Results and Analysis
#### 4.4.2 V2V Channel Propagation Model
It can be seen that FPBR achieves a lower delay per hop than DDOR. This means that the next hop selection mechanism of FPBR made fewer erroneous selections than those made by the selection algorithm of DDOR. Furthermore, as previously mentioned DDOR's redundancy strategy needs at least 3 control packets while the redundancy strategy of FPBR implements an implicit acknowledgement mechanism. Therefore, when an erroneous selection is made, the redundancy strategy of DDOR generates higher medium access contention than that generated by FPBR's redundancy strategy. Figure 12: Average number of hops obtained with FPBR and DDOR when increasing the maximum acceleration, \(\alpha\). Four different vehicle densities, \(\lambda\), were considered for these plots. Each plot shows the number of hops _vs._\(\alpha\) for: (**a**) \(\lambda=133\); (**b**) \(\lambda=100\); (**c**) \(\lambda=66\) and (**d**) \(\lambda=33\). Figure 14 illustrates the EED metric behavior when increasing the maximum acceleration, \(\alpha\), for different vehicle densities, \(\lambda\). It can be seen in this figure that when using DDOR and increase in \(\alpha\) leads to an increase in the EED metric for \(\lambda=133\) and \(\lambda=100\) (_i.e._, medium and jam vehicular densities). In contrast, when using FPBR the changes in the acceleration rate do not lead to an increase in the EED for these vehicular densities. The FPBR protocol shows this behavior because of its particular next-hop selection algorithm, described in Section 3.3.2. Thus, it can be inferred that by using the dynamic factors \(\beta_{\alpha}\), \(\beta_{c}\) and \(\beta_{s}\) the probability of performing an erroneous next hop selection is decreased. Note that for the free flow vehicle density, \(\lambda=33\), the change in the acceleration, \(\alpha\), does not seem to have a significant effect in the EED metric. This behavior is observed because the location prediction mechanism of both protocols is more accurate for this vehicle density. Figure 13: Average delay per hop obtained with FPBR and DDOR when increasing the maximum acceleration, \(\alpha\). Four different vehicle densities, \(\lambda\), were considered for these plots. Each plot shows the delay per hop _vs._\(\alpha\) for: (**a**) \(\lambda=133\); (**b**) \(\lambda=100\); (**c**) \(\lambda=66\) and (**d**) \(\lambda=33\). Figure 15 shows the effects of increasing the maximum acceleration, \(\alpha\), on network overhead metric for different vehicle densities, \(\lambda\). As previously mentioned, the redundancy strategy of DDOR is performed at the MAC layer. Thus, the overhead introduced by DDOR at the network layer mainly consists of hello messages. Consequently, the network overhead for DDOR is lower than that introduced by FPBR (see Figure 15). Note that for \(\lambda=33\) both protocols show a higher network overhead (see Figure 15(d)). This is caused by the particular adaptive beacon rate mechanisms implemented in both protocols (see Sections 3.2 and 4.1). Figure 14: Average end-to-end delay (EED) obtained with FPBR and DDOR when increasing the maximum acceleration, \(\alpha\). Four different vehicle densities, \(\lambda\), were considered for these plots. Each plot shows the EED _vs._\(\alpha\) for: (**a**) \(\lambda=133\); (**b**) \(\lambda=100\); (**c**) \(\lambda=66\) and (**d**) \(\lambda=33\). Lastly, the Figure 16 shows the MAC overhead obtained when increasing the maximum acceleration, \(\alpha\), for different vehicle densities, \(\lambda\). As mentioned in Section 4.1, the RTS/CTS mechanism used in DDOR needs a minimum of three additional packets to transmit a single data packet. Consequently, this mechanism significantly increases the overhead introduced at the MAC layer. In contrast, FPBR provides a lower MAC overhead. This is because FPBR implements an implicit acknowledgement mechanism in the redundancy strategy for the location service, as explained in Section 3.4. Additionally, FPBR does not enable the RTS/CTS mechanism for the transmission of data packets.