# Virtual Pseudonym-Changing and Dynamic Grouping Policy for Privacy Preservation in VANETs
## 7 Performance Comparison  
In this section, we compare the simulation results of our proposed scheme DGVP with Context-based Location Privacy Scheme (CLPS) [18] and Coupling Privacy with Safety (CPS) [10] in terms of anonymity, entropy, and location traceability. The average anonymity set size versus simulation time result is shown in Figure 15. The proposed scheme DGVP improves the anonymization of vehicles in the group compared to CPS and CLPS. The enhanced results of vehicle anonymization is due to the efficient management of vehicles in the group for the pseudonym update process. The non-linearity in the results arises because some vehicles may leave the group's transmission range or join the group dynamically, reducing or increasing the vehicle anonymization process. Similarly, anonymity versus a different number of vehicles is shown in Figure 16. Here, DGVP increases the anonymity of vehicles to improve the location privacy in the vicinity compared with existing schemes CPS and CLPS. The reason for the lower average anonymity of CLPS is the use of a short pseudonym life, which changes individually by a vehicle before the trigger for collaborative pseudonym change. The reduced level of vehicles' anonymity in CPS is the lack of cooperation among vehicles for pseudonym change. CPS only considers delay for beacon broadcast but does not ensure the cooperative pseudonym update process in the vicinity, reducing vehicles' anonymity and privacy. Figure 15: Vehicle anonymization at various time periods. Mean maximum entropy in terms of different periods is shown in Figure 17. DGVP achieves better results than existing schemes CPS [10] and CLPS [18]. The entropy measures an adversary's confusion level about the target vehicle's identity in the region of interest. DGVP increases confusion for the adversary to identify a vehicle. This is because of the efficient management of anonymization of vehicles in the groups. Similarly, in Figure 18, the results of mean maximum entropy with varying number of vehicles in the vicinity are presented. Our proposed scheme achieves higher confusion for an adversary in extracting the target vehicle in a group than existing CPS and CLPS. It hides the private information of a vehicle from the adversary. The achieved results of a higher level of location privacy is due to the cooperative pseudonym-changing process. The lack of cooperation for pseudonym-changing among vehicles reduces the entropy of CPS. In CLPS, pseudonyms are changed by a smaller number of vehicles in silent mode, ultimately decreasing the mean maximum entropy value. Figure 16: The anonymity of vehicles at different traffic densities. Figure 17: The entropy of vehicles at different periods on the road network. Figure 19 shows the vehicle location traceability at different periods. At the start of simulations, the traceability probability is higher; after some time, traceability is reduced with the increasing anonymization of vehicles. The proposed scheme DGVP has a lower traceability probability than existing schemes CPS [10] and CLPS [18]. The location traceability percentage with different vehicle traffic conditions is shown in Figure 20. Here also, DGVP has improved results reducing the vehicle location traceability than CPS and CLPS. The efficient results of DGVP are due to the higher value of anonymization of vehicles on the road network. The anonymization process of DGVP increases the difficulty for an adversary to track the vehicle's various locations during a journey. CLPS has a lower traceability probability than CPS because of the efficient management of silent periods for hiding actual vehicle identity. While in the CPS scheme, the reduced number of beacon broadcasts and use of a pseudonym for a long period provides more chance for an adversary to track a vehicle. Figure 19: Location traceability at different periods. Figure 18: Vehicle entropy at various traffic densities.