Research On Distributed Slot Reservation MAC For Vehicular Ad-hoc Network

As the development of Intelligent Transport System (ITS) nowadays, VehicularAd-hoc Network (VANET) has become a hot research area of wireless ad-hocnetwork. Considering the requirements of applications in VANET and VANET’scharacteristics, the ideal features of VANET MAC protocols could be concluded asthe ability to support efficient broadcasting, Quality of Service (QoS) and theadaption to various node density and mobility. These ideal features severely challengethe MAC design in VANET.Basing on the survey of existing MAC protocols’ disadvantages as well asadvantages, the dissertation proposes MARR-ALOHA, a Mobility Adaptive varietyof RR-ALOHA for VANET, aiming to meet the requirements of VANET’sapplication and distinguishing features. MARR-ALOHA is a distributed slotreservation MAC protocol which enables nodes to precieve the accurate channel statewithin2hops and the statistic state within3hops. MARR-ALOHA also improves thechannel reservation process: it introduces the CSMA and backoff algorithm into slot,which reinforces the ability of collision detecting and avoidance. Furthermore,MARR-ALOHA introduces an algorithm to adjust the reserved slot to a new slotwhich is less likely to colid with other mobile nodes.Both static and dynamic NS-2simulation experiments have been done toevaluate the performance of MARR-ALOHA, which illustrates that, in mostproportion of simulation scenarioes with various node density, mobility and severityof reservation contention, MARR-ALOHA performs better than RR-ALOHA interms of the time used for channel reservation, the quality of slot allocation,broadcasting packet delivery ratio and the throughput of the network. In particular, ifthe parameters of the experiment are properly set, MARR-ALOHA could meet theVANET MAC’s requirements in QoS.In order to evaluate the algorithm in real world experiments, a SynchronousWireless Ad-hoc Network Testbed (SWANT) is developed and MARR-ALOHA is implemented in SWANT. During the implementation process, a synchronizationmechanism is added in SWANT to provide the basic synchronization service. Thecoopertation of softeware MAC layer and hardware MAC layer is solved to handlethe channel reservation.