## 5 Conclusions and Future Work  
In this paper a new routing protocol for VANETs called Freestanding Position-Based Routing (FPBR) protocol was introduced. The design of FPBR was aimed to the deployment of VANET's in highway scenarios. As such, the performance of FPBR was compared with the performance shown by the DDOR protocol, which is one of the few protocols explicitly developed for V2V communications in highway scenarios. When considering freespace propagation conditions, FPBR delivers performance metrics similar to those obtained when using the leading DDOR protocol. Nevertheless, when considering the V2V highway channel, the performance metrics obtained with both protocols for this scenario show that FPBR outperforms DDOR. The reason for this is because FPBR includes several mechanisms which help to overcome packet losses caused by the harsh conditions imposed by the highway radio channel. Particularly, FPBR's next hop selection and the implicit acknowledgment mechanisms proved to be vital when considering the highway channel, since these routines enabled the selection of suitable primary relay and backup nodes. Consequently, these mechanisms allowed FPBR  
Figure 16: Normalized MAC overhead 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 MAC overhead _vs._\(\alpha\) for: (**a**) \(\lambda=133\); (**b**) \(\lambda=100\); (**c**) \(\lambda=66\) and (**d**) \(\lambda=33\).  
to yield a high packet delivery ratio. Furthermore, the simulation results show that neither the redundancy strategy nor the location service of FPBR adds a significant overhead, even though the location service uses broadcast packets. Therefore, with the results presented in Section 4.4 it has been shown that in order to improve the performance of the routing protocols for highway scenarios, the constraints imposed by the radio channel must be considered when designing the routing strategy. In that sense, FPBR is a suitable protocol for VANETs deployment in highway scenarios, as it offers several advantages compared to traditional VANETs protocols (e.g., AODV and GPSR-L) and even outperforms the leading DDOR protocol for this kind of scenarios. In this paper the \(\beta\) parameters have been chosen based on overall performance for different densities. The performance of FPBR could be improved if the \(\beta\) parameters are customized for different network conditions. Thus, future work includes developing an adaptive method to set the \(\beta\) parameters values based on current network conditions. In order to adapt FPBR for city scenarios, future work will include obtaining specific \(\beta\) parameters for urban scenarios. Regarding the IEEE 802.11p standard, FPBR was evaluated considering one traffic class, delivering satisfactory performance metrics. Similarly, a single traffic class was considered in [35] for the performance analysis of AODV and DSR when using IEEE 802.11p transceivers (as previously mentioned the IEEE 802.11p implementation used in [35] was based in the IEEE 802.11a OPNET model). Therefore, future work will include obtaining performance metrics for FPBR, DDOR, AODV and DSR when considering concurrent traffic flows with different IEEE 802.11p traffic classes.