**3.2. V2V based clustering**

V2V based clustering is a decentralized clustering where clusters are formed based on communication between vehicles. Additionally, the CH election will be based on V2V communication. There are several advantages of using V2V-centric clustering as compared with the infrastructure-centric VANETs. V2V-centric clustering can avoid the short commu‐ nication link period, high frequent hand-offs, fast channel fading, etc., that are caused by the high relative-speed difference between the fixed infrastructure and the fast-moving vehicles. Finally, the V2V-centric clustering performs better in active safety applications, which only requires exchanging messages among one hop vehicles within their transmission range.

V2V communications are expected to significantly improve transportation safety and mobility on the road. Several applications of V2V communications have been identified, from safety and warning applications, up to traffic control and driver assistance applications. In infra‐ structure centric clustering, all the communications is done via the infrastructure which causes a lot of control overhead and additional delay. Furthermore, it would be very cost intensive to build an infrastructure based communication all along the road structure. The V2V based clustering technique avoids the use of stationary base stations by building up VANETs, where all vehicles in a common transmission radius can exchange messages. However, CH selection carried out through V2V communications has some shortcomings, e.g., highly complex protocols, large computation and communication cost, need of additional devices and so on. Another important issue is that the connection between two adjacent CHs may be lost due to vehicles high speed, which drastically reduces the link quality. The hidden terminal problem where two vehicles are outside of each other's transmission radius, but both attempt to transmit to a vehicle that is within the radius of both. This issue is likely in pure V2V scenarios where there is no centralized communication system. The result of the hidden terminal problem is data collisions. By enabling vehicles to transmit/receive messages with each other via V2V as well as with infrastructure communications, VANETs could contribute to more safer and congestion free roads by providing correct and timely message to neighboring vehicles and other related departments.
