Performance modeling and analysis of IEEE 802.11 DCF based
fair channel access for vehicle-to-roadside communication
in a non-saturated state
Qiong Wu
•
Jun Zheng
Springer Science+Business Media New York 2014
Abstract This paper considers the fair access problem in
vehicular ad hoc networks and develops analytical models
for analyzing the performance of an IEEE 802.11 distributed
coordination function based fair channel access protocol in a
non-saturated state. We first derive the relationship between
the transmission probability and the minimum contention
window size of a vehicle, and the relationship between the
velocity and the minimum contention window size of a
vehicle in a non-saturated state. Based on the analytical
model, the minimum contention window size of a vehicle for
a given velocity can be determined in order to achieve fair
access among different vehicles. Moreover, an analytical
model is also developed for analyzing the throughput per-
formance of the fair channel access protocol in a non-satu-
rated state. The effectiveness of the analytical models is
justified through simulation results.
Keywords MAC Fair access Non-saturated state
Performance modeling 802.11 DCF VANET
1 Introduction
In a vehicular ad hoc network (VANET), communication
may occur either between a couple of vehicles or between a
vehicle and a roadside unit or access point (AP). In many
cases, multiple vehicles need to access a single AP through
a common channel simultaneously, which would result in
data collision and the fair access problem. To address this
problem, it is necessary to employ an efficient medium
access control (MAC) protocol to coordinate the channel
access of multiple vehicles.
IEEE 802.11 is a classical MAC protocol standard that
has widely been used in wireless communication networks
[1]. The basic access mechanism in the IEEE 802.11
standard is the distributed coordination function (DCF),
which is a random access mechanism based on Carrier
Sense Multiple Access with Collision Avoidance (CSMA/
CA). Compared with traditional wireless networks, how-
ever, a VANET has some unique characteristics [2, 3]. For
example, a vehicle usually has only two moving directions
and changes its moving direction at a crossroad; a vehicle
usually moves at a velocity of 10–40 m/s, which results in
the topology of a network highly dynamic. These unique
characteristics make IEEE 802.11 DCF unable to coordi-
nate the channel access in a VANET efficiently and thus
present a new challenge in the design of MAC protocols for
VANETs.
A typical problem that arises with a VANET is the fair
access problem, i.e., a vehicle moving at a higher velocity
does not have the same opportunity to communicate with a
roadside AP as a vehicle moving at a lower velocity. This
problem was not considered in the design of most existing
MAC protocols proposed for VANETs [4]. To address this
problem, Karamad and Ashtiani proposed a modified IEEE
802.11 DCF based MAC protocol [5], which allows a
vehicle to dynamically adjust its transmission probability
by changing the size of its minimum contention widow in
order to achieve a fair access effect. This work assumes
that every node in the network is in a saturated state, i.e., a
node always has data to transmit to an AP. An analytical
model is developed to analyze the performance of the
Q. Wu J. Zheng (&)
National Mobile Communications Research Laboratory,
Southeast University, Nanjing 210096, Jiangsu, China
e-mail: junzheng@seu.edu.cn
Q. Wu
The State Key Laboratory of Integrated Services Networks,
Xidian University, Xi’an 710071, Shanxi, China
123
Wireless Netw
DOI 10.1007/s11276-014-0766-2