Mobile Netw Appl
DOI 10.1007/s11036-010-0246-6
A-ADHOC: An Adaptive Real-time Distributed MAC
Protocol for Vehicular Ad Hoc Networks
Jia Liu · Fengyuan Ren · Limin Miao · Chuang Lin
© Springer Science+Business Media, LLC 2010
Abstract Vehicular Ad Hoc Networks (VANET) are
the foundation of Intelligent Traffic System (ITS), and
recently many MAC protocols for VANET are pro-
posed, among which a reliable MAC protocol called
ADHOC has aroused much attention. By investigating
the details of ADHOC protocol, we have discovered
several unsolved problems that might lead to network
failure. In this paper, we provide a quantitative analysis
of the success probability for contending nodes and
prove that an adaptive frame length is quite necessary.
We propose Adaptive-ADHOC (A-ADHOC) MAC
protocol, which implements a robust mechanism sup-
porting the adaptive frame length. Evaluation result
shows that A-ADHOC can maintain a high contending
success probability and obtain about 50% reduction of
response time over original ADHOC protocol, while
providing important enhancement on network scalabil-
ity and robustness.
Keywords VANET · MAC protocol · TDMA ·
adaptive frame length
J. Liu · F. Ren (
B
) · L. Miao · C. Lin
Department of Computer Science and Technology,
Tsinghua University, Beijing, China
e-mail: renfy@csnet1.cs.tsinghua.edu.cn,
renfy@tsinghua.edu.cn
J. Liu
e-mail: jliu@csnet1.cs.tsinghua.edu.cn
L. Miao
e-mail: mmpire@gmail.com
C. Lin
e-mail: clin@csnet1.cs.tsinghua.edu.cn
1 Introduction
The more and more growing traffic incurs a number
of congestions, accidents and other social issues which
have become serious problems of society. Over past
years, efforts have been made on vehicular equip-
ment, road environment as well as the communication
systems to mitigate these problems. For example, nav-
igation devices, compasses, parking radars and cam-
eras are the most common technologies employed in
vehicles now, providing the abilities of perceiving the
landscape, road and location to prevent accidents. For
another example, via the FM radio, daily broadcast in-
forms regularly or irregularly the drivers with the latest
information about traffic situations, hence facilitates
the route selection and smoothes the traffic flows.
In recent years, radio-communication-based solutions
exploiting the wireless communication, computing and
sensing capabilities, are used to overcome the the line-
of-sight constraints of radar and vision solutions. More
importantly, it enables cooperative communication
among vehicles rather than the traditional one-way mode
of broadcasts. Vehicular Ad Hoc Networks (VANET),
a most promising intelligent transportation systems
(ITS), enables the information to be exchanged in real
time in practical situations without any infrastructure.
By providing plenty of timely information, VANET
shall make driving much safer and more convenient.
Under the rapid development of this technology, peo-
ple could not help but envisage such a scene in the future:
while driving on the highway, vehicles can receive up-
to-date road information (electronic map, traffic con-
gestion, road maintenance and etc.), share entertainment
content with each other, and cooperate with nearby
ones to ensure the traffic safety at the same time.