車車間アドホックネットワークにおける高効率高信頼性データ転送プロトコルについての研究

摘要

A Vehicular Ad hoc Network (VANET) is a form of mobile ad hoc network providing communications between vehicles in close proximity, and between vehicles and nearby fixed roadside equipment. Vehicular ad hoc networks attract a variety of applications which can be classified into two categories of point to point data transfer applications and broadcast data transfer applications according to their routing requirements. Point to point data transfer applications can provide point-to-point connectivity to vehicular nodes while on the move, so the users can download music, send emails, or playback-seat passenger games. On the other hands, broadcast applications can be used to disseminate messages such as traffic alert messages, nearby service information and real-time routes information.In case of point-to-point communications, general-purpose ad hoc routing protocols such as AODV cannot work efficiently due to frequent changes of network topology caused by vehicles’ movement. Thus, the routing problem of finding reliable paths from a traffic source to a traffic destination through a series of intermediate forwarding nodes is particularly challenging. As far as broadcast communications are concerned, the routing protocols should provide strict reliability, lower delay and should be lightweight and suitable for different traffic conditions. To provide efficient point-to-point data transfers in vehicular ad hoc networks, this thesis first proposes a VANET routing protocol QLAODV (Q-Learning AODV) which fits for unicast applications in high mobility scenarios. QLAODV is a distributed reinforcement learning routing protocol, which uses a Q-Learning algorithm to infer network state information and uses unicast control packets to check the path availability in areal time manner in order to allow Q-Learning to work efficiently in highly dynamic network environment. QLAODV is favored by its dynamic route change mechanism and therefore is capable of reacting quickly to network topology changes.To disseminate broadcast messages in vehicular ad hoc networks, this thesis also proposes a reliable and efficient multi-hop broadcast protocol for vehicular ad hoc networks.The proposed protocol provides the strict reliability in various traffic conditions.This protocol also performs low overhead by means of reducing rebroadcast redundancyin a high-density network environment. This thesis also proposes an enhanced multipoint relay (MPR) selection algorithm that considers vehicles’ mobility and then uses it for relay node selection.