Wireless protocols to support vehicular safety applications (2015)

In the last decades the number of vehicles travelling in European road has raised significantly. Unfortunately, this brought a very high number of road accidents and consequently various injuries and fatalities. Even after the introduction of passive safety systems, such as seat belts, airbags, and some active safety systems, such as electronic brake system (ABS) and electronic stabilization (ESP), the number of accidents is still too high. Approximately eight per cent of the fatal accidents occur in motorways, in the Portuguese case, the number of fatalities has remained constant in the first decade of the 21st century. The evolution of wireless communications, along with the north-American and European policies that reserve spectrum near the 5,9GHz band for safety applications in the vehicular environment, has lead to the development of several standards. Many of these applications are based on the possibility of using a wireless communication system to warn drivers and passengers of events occurring on the road that can put at risk their own safety. Some examples of safety applications are the hard-brake warning, the wrong-way warning and the accident warning. This work aims to contribute in defining a communication protocol that guarantees the timely dissemination of safety critical events, occurring in scenarios with a high number of vehicles or in the neighbourhood of so called motorway “blackspots”, to all vehicles in the zone of interest. To ensure information integrity and user trust, the proposed system is based on the motorway infrastructure, which will validate all events reported by the vehicles with the usage of several means, such as video surveillance or other sensors. The usage of motorway infrastructure that has full motorway coverage using fixed stations also known as road side units, allows to have a global vision of the interest zone, avoiding the problems associated to networks that depend solely on vehicle to vehicle communication, generally total ad-hoc networks. By using the infrastructure, it is possible to control medium access, avoiding possible badly intended intrusions and also avoiding the phenomenon known as alarm showers or broadcast storm that occur when all vehicles want to simultaneously access the medium to warn others of a safety event. The thesis presented in this document is that it is possible to guarantee in time information about safety events, using an architecture where the road side units are coordinated among themselves, and communicate with on board units (in vehicles) that dynamically register and deregister from the system. An exhaustive and systematic state of the art of safety applications and related research projects is done, followed by a study on the available wireless communications standards that are able to support them. The set of standards IEEE802.11p and ETSI-G5 was created for this purpose and is found to be the more adequate, but care is taken to define a scenario where WAVE enabled and non-enabled vehicles can coexist. The WAVE medium access control protocol suffers from collision problems that do not guarantee a bounded delay, therefore a new protocol (V-FTT) is proposed, based on the adaptation of the Flexible Time Triggered protocol to the vehicular field. A theoretical analysis of the V-FTT applied to WAVE and ETSI-G5 is done, including quantifying a real scenario based on the A5 motorway from Lisbon to Cascais, one of the busiest Portuguese motorways. We conclude the V-FTT protocol is feasible and guarantees a bounded delay.