부산대학교 도서관

Recent technological developments have resulted in the extensive usage of Vehicular Ad‐hoc Networks (VANET) for Intelligent Transport Systems (ITS) and road safety applications. With a road safety application, vehicles in a VANET are required to consistently communicate with its neighbours and exchange the information about their position and other specific road safety data. Realising this service of road safety from VANET requires the need of reliable delivery of the emergency information about road accidents in timely manner. However, supporting both timely and reliable delivery of the data messages (emergency information) to the receiver has become highly challenging in VANET because of the factors like vehicle mobility, dynamic mobility pattern of the vehicles, dynamic network topology, and error‐prone wireless communication channel. Moreover, practical application of VANETs in the road safety applications requires the need of sharing the channel media so that reliable and timely delivery of the data can be supported. In this research, the effectiveness of the error control method is explored and a novel approach of Adaptive Byte‐level HARQ (Hybrid Automatic Repeat Request) (AB‐HARQ) was developed to guarantee reliable delivery of the messages to the destination. Despite the evaluations showing is high probability of success in delivering the safety messages, the extent of overhead involved in this method is found to be high. Identifying this room of improvement available for the proposed approach, a novel MACscheme called Broadcasting Relayed‐based Cross‐layer Medium Access Control (BRC‐MAC) is developed in this research. This BRC‐MAC explores the effectiveness of Network Coding (NC) method in assuring reliable delivery of the safety messages without any extra overhead. Analytical model of this BRC‐MAC showed the error recoverability and the high probability of delivering the safety messages within the deadline to the destination. From this analytical model of BRC‐MAC, a criteria function F_rv(i) was developed to help in selecting the relay vehicle to support both reliable and timely communication of the safety messages. In addition to this analytical model, the effectiveness of the proposed BRC‐MAC method is also evaluated in this research through simulation studies. The simulation results of BRC‐MAC showed the ability of this novel MAC method in terms of the probability of successful packet delivery, packet delay and the network throughput. Finally, considering the high extent of the occurrence of hidden node problem in the wireless networks, an improved three‐way handshake method to exchange data is given in this report and then evaluated by combining with 3 the BRC‐MAC method. Therefore, both theoretical analysis and simulation studies were used in this thesis to evaluate the performance of the proposed MAC scheme.