A Vehicle Collision Warning System Employing
Vehicle-to-infrastructure Communications
Shie-Yuan Wang
Department of Computer Science
National Chiao Tung University
Hsinchu, Taiwan
Email: shieyuan@csie.nctu.edu.tw
Yow-Wei Cheng, Chih-Che Lin, Wei-Jyun Hong, Ting-Wei He
Department of Computer Science
National Chiao Tung University
Hsinchu, Taiwan
Email: {welljeng, linjc, hungwc, anton}@cs.nctu.edu.tw
Abstract—Road safety has become an important issue and
gained much attention for many years. To avoid vehicle collisions
on the roads, researchers have proposed various collision warning
systems (CWS) using different technologies. Compared with CWS
using other technologies, a radio-based CWS is more capable of
avoiding collisions in off-sight scenarios (such as the four corners
of an intersection). Most existing radio-based CWSs operate using
vehicle-to-vehicle communications. However, in such CWSs, high
mobility of moving vehicles easily results in message collisions
and link breakage, impairing the reliability of these CWSs.
An alternative is employing vehicle-to-infrastructure commu-
nication to build CWSs. In this paper, we propose a radio-based
CWS employing vehicle-to-infrastructure communications. Our
simulation results show that the proposed CWS can effectively
reduce the number of vehicle collisions without degrading the
traffic throughput of a road network.
I. INTRODUCTION
Road safety has become an important issue and gained much
attention for many years. Since 1994, each year there have
been over 40,000 fatalities and 2,788,000 non-fatal injuries
due to traffic accidents in the United States [1], resulting
in considerable economic losses and life threats to people.
To reduce traffic accidents, researchers have proposed several
vehicle-to-vehicle (v2v) collision warning systems (CWS) to
avoid vehicle collisions. The v2v collision warning system
can be categorized into three classes based on the employed
technologies: radar-based, camera-based, and radio-based. The
radar-based and camera-based collision warning systems are
mainly designed to avoid forward collisions of vehicles on the
same lane due to the line-of-sight limitation resulting from the
radar and camera technologies. In contrast, the radio-based
collision warning system is more capable of avoiding vehicle
collisions in off-sight scenarios, such as the four corners of an
intersection.
A radio-based v2v collision warning system operates by
using either periodic or emergent-event-driven v2v communi-
cations. Each vehicle on the roads is assumed to be equipped
with a radio (such as an IEEE 802.11(b)-based or DSRC-based
radio). Vehicles on the roads form a mobile ad-hoc network.
Exchanging messages in such a network is not reliable because
message collisions and link breakage are likely to occur
due to high mobility of moving vehicles. Using such an
unreliable message exchanging mechanism greatly degrades
the performances of v2v-communication-based CWSs.
On the other hand, in recent years WLANs are getting
popular and widely available in public metropolitan areas.
Many large-scale deployments of WLAN infrastructure nodes
on the roadsides already exist (e.g., the WiFly project has
deployed over 4,000 access points in Taipei city in Taiwan
[2]). This trend makes collision warning systems that employs
vehicle-to-infrastructure (v2i) communications feasible and
low-cost.
To the best of the authors’ knowledge, no paper in the
literature has studied the performances of radio-based collision
warning systems that employs v2i communications. This mo-
tivates the authors to study the performances of such systems.
In this paper we propose a radio-based collision warning
system that utilizes periodic v2i communication (referred to
as V2I-CWS in this paper for brevity). The proposed V2I-
CWS adopts a TDMA-based scheme that is built on top of the
IEEE 802.11(b) ad-hoc mode MAC layer to access wireless
channels. Under this scheme, roadside units and vehicles
use different time slots to transmit messages. The details of
the adopted scheme are explained in Section III-B. Such a
design effectively reduces the number of message collisions
in a vehicular network, thus increasing the reliability of the
operation of V2I-CWS. Our simulation results show that the
proposed V2I-CWS can effectively reduce the number vehicle
collisions in off-sight scenarios. As such, it greatly improves
the driving safety on the roads.
The rest of this paper is organized as follows. In Section II,
we present related work. In Section III, we present the
proposed V2I-CWS. We then evaluate its performances in
Section IV and finally conclude the paper in Section V.
II. R
ELATED WORK
Radio-based collision warning systems have been pro-
posed for years. Most of the work, however, focuses on
v2v communication-based collision warning systems. In [3],
the authors propose a cooperative collision avoidance (CCA)
system to enhance driving safety on highways. In the CCA
system, each vehicle employs a DSRC-based v2v protocol
to distribute emergent warning messages in a TDMA-based
manner upon encountering emergency events on the roads.
In [4], the authors propose the time-to-collision (TTC)
metric to estimate the expected collision timing for a pair of
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This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the WCNC 2008 proceedings.
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