Context-aware MAC Protocol For VANETs

VANET (Vehicular Ad hoc Network) is a new kind of wireless network formed byvehicular nodes and wireless devices. As one of the most crucial parts of IntelligentTransport Systems (ITS), VANET has been widely used for driving assistance, trafficaccident warning, entertainments and so on.Defined by IEEE802.11p MAC protocol, VANET is used to alert emergency andcontrol traffic congestion by broadcasting messages which is also known the contextinformation, including beacon messages which represent the nodes’ statuses and thesafety-related messages. However, the increase of the node density will raise a series ofproblems such as higher channel access collisions and lower message trustworthyprobability. Based on the characteristics of IEEE802.11p and the context information, anear collision-free MAC protocol based on historical beacons and a trustworthy MACmechanism for safety-related messages are proposed and simulations are implementedto validate their effectiveness. The main contributions are shown as follows:Firstly, based on the historical beacons and in order to solve the increasing channelaccess collisions, a near collision-free MAC protocol is proposed. In this protocol all thecontention nodes are mapped into neuron nodes of a hamming competing network andthe hamming competing weight of each node is set as the priority which can be got byanalyzing historical beacons using fuzzy logic. The winner of the hamming networkswill gain the opportunity to access the channel. The simulation results show that theproposed protocol has a considerably low collision probability and high transmissionreliability while keeping a low access delay even in high dense scenario.Secondly, a trustworthy MAC mechanism is proposed for safety-related messagewhich is also a kind of context information so as to solve the problem caused bymalicious nodes which may broadcast false messages. The mechanism raises thetrustworthy probability when a very message is broadcasted multiple times and anadapted algorithm based on node density is also used to adjust the trustworthy threshold,therefore, the number of nodes involved in broadcasting varies directly as the actualnumber of neighbor nodes. Simulation and analysis indicate that this mechanism canimprove the broadcasting trustworthy probability effectively.Finally, the above MAC mechanisms are both designed and implemented based onNS-3, and their correctness, reliability and effectiveness are verified in thecorresponding vehicular environment.