Wireless Vehicular Communications

Wireless vehicular communication systems, including Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communications, have been identified as a promising technology to improve traffic safety and efficiency through the constant exchange of messages among nearby vehicles. To overcome the vehicular limitations of current mobile and wireless technologies, the IEEE 802.11p or WAVE (Wireless Access for Vehicular Environment) standard is being developed. This standard is based on seven channels, six service channels and one control channel, on the 5.9GHz band. While the service channels can be used for public or private applications, the control channel is used to detect any nearby vehicles and initiate all communication transmissions. Consequently, it is of paramount importance to adequately dimension the communications protocols to ensure the reliable transmission of safety and traffic messages while ensuring the system's scalability as wireless vehicular communication technologies are gradually introduced. In this context, Uwicore has been working on various important aspects to ensure the transmissions reliability and the system's scalability:

1. Communications system design. To adequately design and optimise wireless vehicular communication protocols, Uwicore has been working on identifying the communication parameters that most strongly influence the wireless vehicular communications performance under various operating conditions and scenarios.

2. Wireless channel modelling. Wireless communications performance is heavily influenced by the experienced radio propagation conditions. This will also be the case for future wireless vehicular communication systems operating at the 5.9GHz band, in particular for V2V communications where transmitting and receiving antennas are at the same height. In this context, Uwicore has worked at identifying the impact that limited wireless channel modelling has on the estimated wireless vehicular communications system performance through computer simulations.

3. Opportunistic and adaptive transmission policies. The important traffic safety and efficiency QoS demands require maximum wireless vehicular transmission reliability. In addition, the potential benefits of future wireless vehicular communication systems will depend on its mass market introduction. While such mass market introduction will benefit the technology's adoption, it can cause scalability problems that need to be considered when defining communication protocols. In this context, Uwicore has developed adaptive and opportunistic transmission policies that dynamically modify the transmission power and rate to achieve the required application QoS levels while efficiently using the radio channel. Such efficient use results in lower channel congestion and better system scalability.

4. Contextual inter-vehicle communications. Currently, the majority of wireless vehicular communications studies are user or system focused, neglecting the potential impact that the use of wireless vehicular communications could have on nearby vehicles. Such impact can be easily illustrated with the case of an intersection, where an approaching vehicle is informed of a potential collision thanks to the use of wireless vehicular communication technologies. While this vehicle might be informed with sufficient time to avoid the accident, the intersection's proximity might cause a driver's sudden reaction that can result in rear-end collisions. To avoid such collisions, Uwicore has proposed, designed and evaluated a communications protocol dimensioning procedure that considers the vehicular context (presence of surrounding vehicles and vehicle's density).

The operation of wireless vehicular communication systems will strongly rely on ad-hoc networking protocols to route and forward information among vehicles. The definition of vehicular routing and data dissemination policies is particularly challenging due to the high node's mobility and the decentralized nature of wireless vehicular communications. To address these challenges, Uwicore has been working on the following aspects:

1. Effect of wireless channel modelling on the operation and performance of wireless vehicular routing protocols. Following the research conducted on the impact of the wireless channel modelling on the wireless vehicular system's performance, Uwicore has also investigated its effect on the actual performance of broadcast and unicast vehicular routing protocols. The research conducted highlights the strong dependence of the routing protocol's performance and actual route selection on the wireless channel modelling.

2. Robust wireless vehicular routing protocols. Based on the observed routing protocol's operation under realistic wireless channel propagation conditions, Uwicore has proposed a robust route selection policy that guarantees a wireless channel reliable origin-destination transmission. The performance of routing protocols also strongly depends on the presence of surrounding vehicles over which to relay the required information. To increase the probability of finding a nearby relaying vehicle, Uwicore has also developed a very simple routing policy based on the estimated traffic density. This unicast routing mechanism, combined with the wireless channel reliable route selection policy developed at Uwicore, achieves a performance similar to that of broadcast routing schemes while significantly reducing the communications channel load. Such reduction reduces the system interference and improves the system's scalability.

3. Data dissemination techniques. The implementation of real-time traffic management policies using wireless vehicular communication technologies is based on traffic information propagation through geocast routing/broadcast policies. To ensure that the propagated message stays 'alive' in the geographical destination area for the required period of time, Uwicore is currently analysing and developing radio efficient and reliable data dissemination techniques.

An approach generally employed to evaluate wireless vehicular communication technologies is to use, as an input to a communications/networking research platform, vehicular mobility traces obtained from microscopic traffic simulators. Although this approach allows working with realistic mobility patterns when evaluating wireless vehicular communication protocols, it is not capable of capturing the effect that the exchange of traffic messages through wireless vehicular communication systems will have on traffic mobility. Such effect should not be neglected since the exchange of traffic messages could result in real-time traffic re-direction following possible traffic congestion situations. To overcome this limitation, Uwicore has developed a software interface between the open-source communications/networking ns2 and the microscopic traffic SUMO platforms. Through this software interface, Uwicore is currently capable to modify traffic mobility based on traffic re-routing policies derived from the real-time vehicular exchange of traffic messages. This capability allows Uwicore to realistically investigate the effect that wireless vehicular communication technologies will have on traffic management.

In addition to these research activities, Uwicore is currently working to extend its research in wireless vehicular communications to real-time hardware prototyping. Uwicore's target is to implement, evaluate and optimise its resource management and networking protocol solutions in real testbeds, to gain additional insight into their operating characteristics and potential additional improvements.