Investigation On Message Dissemination Technology Toward Vehicular Ad Hoc Network Applications

VANET (Vehicular Ad Hoc Network) is envisaged as a key component for reducing traffic accent, improving transport efficiency and providing comfort experience in Intelligent Trans-portation Systems (ITS). It is a remarkable embodiment of MANET (Mobile Ad Hoc Net-work) in transportation and receives much attention from the government, car manufactures and academic communities. High-efficiency message dissemination scheme is the key tech-nology in VANET. But it is different from that in MANET, due to the high mobility of vehicle, self-organization and multi hop in VANET. Furthermore, there are a plenty of applications relat-ed to vehicles, drivers, passengers and pedestrians. These different applications need different QoS (Quality of Service). Therefore, we investigate message dissemination techonlogy toward different applications which would promote the VANET development and provide better dis-semination performance.In this paper, we analyze and study message dissemination techonlogy based on the fact that different QOS needs between safety-related message and non-safety message, and furthermore consider the characteristics of VANET. The main contributions of this paper are summarized as follows:1. One hop successful transmission probability, multi-hop connectivity probability and average hop count are three important parameters that affect the system performance of VANET. In this paper, two new analytical model for those three parameters are proposed. It provides an effective way to analyze the performance and guide system design. In the successful transmission probability analytical model, we introduces a function to re-strain the selection probability of backoff counter initial value in MAC (Medium Access Control) layer and give the calculation formula. And then, a new analytical model for connectivity probability and average hop count is proposed for multi-hop broadcasting, which takes into account the following factors:propagation distance, one hop transmis-sion range, distribution of vehicles, vehicle density, average length of vehicles, and min-imum safety distance between vehicles. We give the calculation formula and analyze the constraint condition of connectivity. Furthermore, simulation results demonstrate that the proposed model can provide good performance in terms of connectivity probability and multi-hop count.2. In considering the latency time, propagation distance and easy implementation, we proposed a new distance-aware broadcasting scheme in safety-related message transmis-sion. We first use the relay node judgment scheme to reduce unnecessary flooding for-warding, and then we introduce a function to restrain the selection probability of backoff counter initial value in MAC layer and make the farthest forwarding station has the high-est probability to forward messages. This scheme is different from earlier location based works in searching the forwarding station. It does not need RTS/CTS and packet ac-knowledgment in broadcasting. This scheme is also different from probabilistic flooding algorithm based works in forwarding probability. It only distinguishes forwarding pri-ority for avoiding message covering problem. Furthermore, it does not need the priori information of the network and easy implementation in practice. Finally, analytical and simulation results demonstrate that the proposed algorithm can enhance the performance of safety-related message broadcasting.3. Most earlier studies focused on one-hop broadcasting while little attention has been paid to multi-hop delay and propagation distance. In this paper, a new model for analyzing the mutil-hop delay of safety-related message broadcasting in VANET is built, taking into account the following factors:propagation distance, one-hop transmission range, distribution of vehicles, vehicle density, average length of vehicles and minimum safe distance between vehicles. It provides an effective way to analyze the performance and guide system design. After that, A new scheme is proposed to track the optimal one-hop transmission range base on the analytical model. With this scheme, vehicles are allowed to adjust the one-hop transmission range based on vehicle density to reduce the multi-hop delay. Simulation results demonstrate that the proposed model can provide good performance in terms of analysing multihop delay and the new power based scheme could track the optimal one hop transmission range to minimize the multi-hop delay.4. In multi-channel system, channel coordination scheme is a key technology related to the utilization of channels, which limits the throughput of the system. In this paper, we s-tudy the multi-channel coordination scheme to enhance the throughput of non-safety mes-sage. First, we proposed a novel asynchronous RSU-coordinated multi-channel MAC for VANET to solve the multi-channel hidden terminal and missing receiver problem. And then, we proposed a novel synchronous RSU-coordinated multi-channel MAC for VANET to allow channel rendezvous on the CCH during the whole synchronization intervals and support simultaneous transmissions on different SCHs. It reducs the control channel con-gestion. Furthermore, we analyze the performance in the terms of multi-channel hidden terminal, missing receiver and control channel congestion problem. Simulation results demonstrate that the proposed scheme provide better performance in channel utilization, throughput and successful rendezvous than that of the same type of schemes.