The Vehicular Ad hoc Network (VANET) has emerged to offer solutions for Intelligent Transportation Systems (ITS) that aim at helping drivers on the roads by anticipating hazardous events or avoiding bad traffic areas, and it has received significant attention from industry, academia and national government agencies [1-2]. The Federal Communications Commission (FCC) allocated a 75 MHz band at the 5.9 GHz frequency (5.85–5.925 GHz) for the dedicated short range communications system (DSRC) in 1999, as a candidate for use in a VANET in North America. DSRC is defined as a short to medium range communications system that supports mainly safety applications in vehicle to vehicle (V2V) and vehicle to roadside (V2R) or vehicle to infrastructure (V2I) communication modes. Figure 1.1 depicts the overall components of VANET.
In 2009, the Vehicle Safety Communication (VSC) project sponsored by the US DoT (Department of Transportation) determined that the 5.9 GHz DSRC wireless technology is potentially best able to support vehicular communications requirements [3]. In 2010, the IEEE 802.11 Working Group (WG) published the IEEE 802.11p wireless access in vehicular environments (WAVE) amendment standards that provides a protocol suite solution to support DSRC vehicular communications in this licensed frequency band at 5.9 GHz [4].
The primary motivation beyond the IEEE 802.11p amendment [4] is to establish lightweight rules for accessing the medium in a highly mobile vehicular environment of which the opportunity to communicate may be fleeting and lasting only a few seconds. The upper DSRC layers are defined by IEEE 1609 standards. These standards define how applications will function in the WAVE environment.
The two units are defined in the WAVE environment: RoadSide Unit (RSU), and OnBoard Unit (OBU) which are essentially stationary and mobile devices respectively. The IEEE 802.11p MAC is based on the Enhanced Distributed Channel Access (EDCA) of IEEE 802.11e whereas the IEEE 802.11p PHY is based on the Orthogonal Frequency-Division Multiplexing (OFDM) technology of IEEE 802.11a standard. It is expected that the DRSC devices will commonly use 6Mb/s data rate from a 10MHz bandwidth since it seems to provide a good compromise between channel load and signal-to-noise requirement [5].
VANET can be utilized for many other applications beyond collision avoidance applications. For example, it can be used to facilitate navigation, make electronic payments (e.g., tolls, parking, and fuel), improve fuel efficiency, draw traffic probes, and disseminate traffic updates. Furthermore, the trend of ubiquitous availability of IP networks has also made internet access and multimedia content delivery possible in the vehicular environment. But, these applications require a wide range of restricted QoS levels that result in more difficulties and challenges to build them on top of the direct communication between vehicles. Undoubtedly, the capability to satisfy these applications’ requirements will open up great value-added services and will be a critical factor to the success of the vehicular networks deployment. Most of these applications involve unicast communication to and from the infrastructure.
Figure 1.1: General model of the vehicular network
VANETs are usually operated in two typical communications environments. In highway traffic scenarios, the environment is quite simple and straightforward, while, in city conditions, it becomes much more complex. Although several attempts are paid for solving the data dissemination on VANETs, the urban environment is largely considered as a subsidiary issue where the simulation experiments either did not include the urban scenario or an unrealistic radio propagation model is used that does not reflect the actual city conditions.
The problem of finding a unicast route under different surrounding scenarios is still a difficult problem in VANETs. Recently, several attempts have been proposed that explore the availability of RSUs to help in the unicast routing protocol from different points of view. After a comprehensive study of these infrastructure-assisted routing approaches highlighting the benefits behind RSUs’ usage, a novel Fast and Reliable hybrid Routing (FRHR) protocol is proposed that exploits RSUs to deliver lightweight, robust, and reliable urban vehicular communications [i].
Broadcasting transmission is an essential operational technique that serves a broad range of applications which demand different restrictive QoS provisioning levels. Although broadcast communication has been investigated widely in highway vehicular networks, it is undoubtedly still a challenge in the urban environment due to the obstacles such as high buildings. I proposed the Road-Topology based Broadcast Protocol (RTBP) [ii]: a distance and contention-based forwarding scheme suitable for both urban and highway vehicular environments.
Towards providing smooth multimedia services on VANETs, I am going to investigate the stability of the routes on the urban environment. Although there are novel routing algorithms attempt to provide stable routes between vehicles to enhance QoS, these routings are dedicated to working on highway scenario. Hence, my future work is to develop a new route selection policy to provide stable routes that can satisfy a wide range of the QoS levels required by different potential applications on the road grid keeping into consideration the importance of the capability of the new stable routing protocol to operate fairly on both urban and highway scenarios. After that, the integration of the new scheme with the delay-tolerant solution and the vehicle accessibility to other available wireless networks will be considered.
Finally, the routing protocols will be examined under realistic scenario to provide video streaming applications. In the V2V communication scenario, the fast selection, setup, and recovery of multi-hop paths to the destination vehicle are vital, for instance, to provide smoothness and quality to the video playout. Indeed, there is an urgent need to investigate and assist the multi-hop routing capability of the VANET, after that, to devise cross-layer routing algorithms considering the critical QoS and bandwidth requirements of multimedia transfer applications.
