Research Of Message Broadcast And Handover Scheme In VANETs

In recent years, VANETs (Vehicular Ad hoc Networks) gradually go from academia into people’s daily life, affecting people’s travel safety. It has two goal:1) providing road safety messages to drivers, to prevent traffic accidents; 2) providing multimedia messages which include commercial messages and entertainment etc. for drivers, allowing users to obtain a satisfactory travel experience. The communication patterns of VANET include vehicle- to-vehicle (V2V) and vehicle-to-roadside unit (V2R). Due to high-speed mobility of nodes and network topology changing frequently in VANETs, stable and real-time transmission of messages is facing serious challenges. In this paper, messages broadcast mechanism and handover mechanism based on IEEE 802.11p protocol are studied.In V2V communication pattern, For message broadcasting, we improve messages transport mechanism in VANETs MAC layer, to reduce transmission delay of safety messages and to improve fluency of multimedia messages. For safety messages, we propose DVO-SB mechanism, which selected relay vehicle considering speed, distance and direction of vehicle. For multimedia messages, we use RTB/CTB mechanism to select relay vehicle. In addition, we propose ARC-SMB mechanism, which reduce loss ratio by adjusting data transmission rate based on channel transmission data frame. To further enhance the user experience, we propose a idea that users need to manually adjust multimedia quality. Finally, simulation demonstrate effectiveness of the proposed mechanism.In V2R communication pattern, due to the traffic load of RSU is limited, it will cause handover congestion when the number of vehicles execute the handover operation is large at the same time. In order to realize the seamless handover between RSUs of vehicles, we need to reduce the handover congestion probability of vehicle. We present ST-BSB scheme. First, we consider the factors, such as the current number of the handover of vehicles, vehicle speed, the received signal strength of vehicles and packet emergency degree, when executing the handover of vehicles was analyzed. Second, we use Stackelberg game to determine the handover of vehicles, use binary exponential back off algorithm (BEB) to disperse vehicles handover time as far as possible and to reduce the congestion probability when vehicles have an unsuccessful attempt for handover, so that vehicles can realize the seamless handover and get higher throughout. Finally, we demonstrate the effectiveness of ST-BSB mechanism by simulation. In this paper, we proposed messages broadcast mechanism and handover mechanism, which greatly enhanced stability and real-time of messages transmission in VANETs. Although it is not perfect, it provides a reference value for further development of VANETs.