# Security Challenges of Location Privacy in VANETs and State-of-the-Art Solutions: A Survey
## 3 Related Work
### Location Privacy Preserving Schemes
#### 3.2.2 Mixed Group Authentication  
A simple mixed group scheme establishes mixed areas in various parts of the town where vehicles can join it and quit. Vehicles change their pseudonyms at the same time as they enter the mixed zone, and their Identities change as they leave the same mixed zone. As a result, trackers cannot track vehicles entering the mixing zone under a given pseudonym and leaving under another pseudonym, as suggested by [46]. Nevertheless, issues occur when the amount of traffic is small. In this case, building several mixed zones in different parts of the city can solve the issue of privacy. One similar strategy was proposed by [47], called the Urban Pseudonym Strategy (UPCS). This approach produces silent mixed zones (SM) at different signalized intersections in the area. This method needs a high bulk of traffic. The drawback of this scheme is that targets remain traceable between mixed areas, which expose them to privacy attacks. One more variant of the traditional mix-group approach is the Velocity-Based pseudonym Change (VBPG) approach [48]. This approach implies a change in the nickname depending on the velocity classes. Here, classes are formed based on the speed of each vehicle. Vehicles that have similar speed and are identical to the same RSU have been collected together and consequently validated by TA using the same username. This makes it impossible for an attacker to recognize and trace specific automobiles in a particular community. The UPCS and VBPG approaches are identical as they both have the essential features of the mixing groups. UPCS can be called a subclass of VBPG. Because Basically VPGB approach is followed. In other terms, you change the user ID by joining and exiting the Mix-group. Nevertheless, in addition to its location, VBPG also integrates a variable for user speed, ensuring the sharing of pseudonyms between nodes with identical patterns of activity and increasing resistance to malicious pseudonym monitoring. In the latest study proposed by [49], the writers introduced privacy security via modifying pseudonyms based on the number of nearby vehicles and their location. Many other similar efforts have also been made via mixed group-based, Pseudonym-Driven Dynamic ID assignment to authenticate authenticate VANET knobs while hiding position information have adopted an anonymous approach. Uncertainty (or entropy) is the power to maintain the position protection pseudonym scheme. The Mix-group scheme focuses on connecting hotspots near transport to the extended Kana evolution domain. Increasing the storage area of the vehicle increases confusion and improves the security of privacy. Mix-Group provides excellent confrontation to Brute Force crypto attacks through authentication and encryption techniques. Timestamps avoid replay attacks as well as guard against spoofing such as legitimate RSUs or forging RSU messages. When local traffic is low (to remove pseudonyms), the attacker will listen to the safety message of the OBU and then record the probabilities and frequencies to chart the probability distribution and track the target vehicle. However, the Mix-Group operates with several pseudonyms, enabling vehicles to pass vehicles and swap pseudonyms with new areas. If this change occurs in a very huge group, it will be very tough for an invader to keep track of a particular vehicle. For unauthorized traffic in a mixed party, fake data transmission within the party is possible. However, the same can be avoided from the spoofed malicious code. In addition, by introducing digital certificates in OBU, you can prevent forgery. It also addresses a related approach. Mixing-Group schemes that focus on a wider variety of benefits and are easy to implement. Nevertheless, frequent adjustments to Kana require strong OBU and RSU computational resources. Low-traffic areas, the probability of monitoring is high due to the limited number of participants involved in the pseudonym exchange. The scheme can work well in urban models.