| Vehicular ad hoc networks (VANET) have been envisioned to be useful in road safety and many commercial applications. Although VANET is a kind of mobile ad hoc network, many unique characteristics of VANET bring out new research challenges. For example, due to fast vehicle movement, the link topology changes rapidly. As a result, many well studied structures for efficient data dissemination such as tree, cluster and grid, are extremely hard to be set up and maintained. Also, the network density is highly dynamic. The traffic density is low in rural areas and during night, which may result in frequent disconnections and network partitions. Thus, data dissemination techniques should address these unique characteristics of VANET.;The specific goal of this dissertation is to provide cohesive solutions for data dissemination in VANETs. Different algorithms and protocols are applied based on where the vehicles are and how far they are from the roadside units. First, we design and evaluate schemes for vehicles far away from the roadside units. To deal with the frequent disconnection problem in sparsely connected VANET, we adopt the idea of carry and forward. Different from existing works, we make use of the predictable mobility in VANET, which is limited by the traffic pattern and the road layout. Second, we design and evaluate pushed-based solutions for vehicles near the roadside units. To reduce the bandwidth consumption, data poured from the source are buffered and rebroadcasted at the intersections. Analytical models are developed to provide guidelines to maximize the dissemination capacity. Third, we propose a relay-based solution for vehicles approaching the one-hop range of a roadside unit. With relay from vehicles close to the roadside unit, vehicles faraway can still access the roadside unit with high rate rate. Finally, we study the benefit of using the vehicular infrastructure mesh network to disseminate data. We design and implement a cooperative cache based scheme which allows mesh stations to cooperatively cache data for vehicles within the mesh network coverage. |
