01-09-2016, 12:00 PM
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We propose a hybrid ITS safety architecture that combines vehicle-to-vehicle communication and
vehicle-to-roadside sensor communication. Opposed to dedicated roadside units, which require major
investments for purchase, installation and maintenance, roadside wireless sensor and networking
technology represents a cost-effective solution and can leverage the deployment of the system as
a whole. Among the various services of the hybrid communication system, the paper introduces
accident prevention and post-accident investigation. We present a system and protocol architecture
with a fully distributed concept for efficient and secure storage of sensor data. For deployment, this
architecture will likely be combined with an alternative approach using dedicated road-side units as
a centralized network element for communication and data storage. For the proposed system, we
describe the main components (radio, networking and services, security). Finally, we describe our
prototype implementation and experimental testbed featuring hardware and software platforms for
vehicle on-board units and sensor nodes.
Keywords: vehicular communication, wireless sensor networks, accident prevention, post-accident
investigation
I. INTRODUCTION
In order to make roads safer, cleaner and smarter, sensor and communication technologies
are increasingly considered in research, standardization and development. While today’s vehicles
are already able to sense the surrounding environment, we expect that future cars will
communicate with a roadside communication infrastructure and with each other. Connected
vehicles create a fundamental building block of intelligent transport systems (ITS) and can
provide numerous application services to improve safety and comfort of driving.
Among the various wireless technologies for vehicular communication, we can identify
a clear trend n the usage of Wireless LAN adapted to vehicular conditions in Europe and
North America [1], [2], [3]. The upcoming standard IEEE 802.11p [4] as well as the frequency
band allocations in the higher 5.8 GHz band for various public safety services clearly indicate
the next step towards deployment. For vehicle-to-infrastructure communications, the system
architecture assumes access points with IEEE 802.11p network interfaces to be set up at
least in dedicated locations (such as road intersections), whereas the system is still able to
deliver information even when no access point is available within the communication range of
a vehicle. A particular technology is vehicular ad hoc networking (VANET), which enables
communication over multiple wireless hops, potentially but not necessarily including roadside
access points.
While the development of vehicular communication technology based on IEEE 802.11p
has considerably progressed in the past years, the introduction and wide-scale deployment
of such a system has not been decided yet. In a purely vehicular communication system,
i.e. without roadside access points, a minimum market penetration of equipped vehicles is
required for applications to work. This can at best be achieved a few years after an initial
commercial roll-out. To accelerate the revenue of such investment, a roadside infrastructure
could be installed along major road across a country. However, costs for purchase, installation
and maintenance represent a major investment and in turn can be an obstacle for a successful
introduction.
A complementary solution to the deployment of road-side access points consists of roadside
wireless sensors. These devices represent a cost effective solution and allow to create
wireless sensor networks (WSN), but are subject to energy and processing constraints. For
battery-powered sensor nodes, IEEE 802.15.4 [5] is a well-established radio technology that
permits embedded systems to function up to years on a simple pair of AA batteries. WSN
islands could be rolled out along the road, such as on the road surface or at road boundaries
(curves, tunnels and bridges), and even on a much wider scale. They can be used to measure
physical data like temperature, humidity, light, or detect and track movements.
In this paper, we propose and analyze a hybrid architecture that combines vehicle-tovehicle
communication and vehicle-to-roadside sensor communication. From the wide range
of possible use cases, we have chosen accident prevention and post-accident investigation,
which we regard as important future services.
For accident prevention, roadside sensor nodes measure the road condition at several positions
on the surface, aggregate the measured values and communicate their aggregated value
to an approaching vehicle. The vehicle generates a warning message and distributes it to all
vehicles in a certain geographical region, potentially using wireless multi-hop communication.
For post-accident investigation, sensor nodes continuously measure the road condition and
store this information within the WSN itself. When a accident occurs, road condition data
stored over a sufficiently long duration can be used for forensic reconstruction of road
accidents. In contrast to the accident prevention service, such a liability service needs to
be restricted to a well specified group of end-users, e.g. insurance companies or the road
patrol. Information stored within the WSN can also be utilized to judge a driver’s driving
style according to the road condition at the moment of an accident.