Research On Reliability And Real-time Performance Of Safety Messages In Vehicular Ad Hoc Networks

Vehicular Ad-hoc Network car Networking(VANET)is a large-scale interactive network which consists of vehicle location,speed and route information.As a new type of wireless communication technology,VANET has attracted wide attention of scholars as well as research institutions and carmakers.With the development of the economy,the increasing traffic accidents have brought serious threat to the social property and the safety of life.How to reduce the traffic accidents and enrich the functions of vehicles with VANET has become the main research direction for scholars and institutions.The dissemination of security information is very important for security application,facing the rapidly changing traffic environment,transmission of safety message with low latency and high reliability is the focus of this paper.Based on the analysis of the Wireless Access for Vehicular Environments(WAVE),this paper analyzes the inadequacy of CSMA/CA mechanism for MAC layer in VANET environment.The main problem is in the environment of the high traffic density,“collision” can easily occur during the information transimission,and quickly changing topology expense a lot.Therefore we proposes a MAC protocol based on TDMA which is suitable for single-hop broadcasting,the protocol ensures the reliability of message transmission through the independent occupancy of time slot.Based on the unified management and allocation of the time slot by the roadside unit(RSU),we achieved the dynamic recovery of time slot and dynamically adjust the frame length that greatly improves the transmission efficiency.In the following simulation experiments,the protocol proposed in this paper outperforms the IEEE 802.11 p MAC in terms of message transmission delay and packet loss rate under the condition of large vehicle density,Based on the Reliable Reservation ALOHA(RR-ALOHA),this paper also designs a MAC protocol for multi-hop broadcasting.We devide the vehicle connectivity into several adjacent virtual regions through the vehicle absolute distance.Each frame in the virtual area chose a vehicle as the temporary management node in the current region,so we can avoid the independent maintenance of two-hop neighbor message which caused huge extra payout with unified maintenance in the virtual region.In the virtual area,we can not only solove the hidden node/exposed node problem in traditional WAVE MAC,avoid the decline performance caused by the rapidly changing topology,but also effectively disseminate the multi-hop broadcast that chose the farest relay node in a simple way.The following simulation experiments show that the multi-hop protocol designed in this paper has a great improvement on the transmission delay and packet loss rate compared with RR-ALOHA protocol.