Roadside Units Deployment for Content
Downloading in Vehicular Networks
Yazhi Liu
∗
, Jian Ma
∗
, Jianwei Niu
†
, Yan Zhang
‡
, Wendong Wang
∗
∗
State Key Laboratory of Networking and Switching Technology, Beijing University of Posts and Telecommunications,
Beijing 100876, China, Email: liuyazhi991@gmail.com
†
State Key Laboratory of Software Development Environment, Beihang University,
Beijing 100191, China, Email: niujianwei@buaa.edu.cn
‡
Simula Research Laboratory and University of Oslo, Norway, Email: yanzhang@simula.no
Abstract—The Vehicular Ad hoc Networks (VANETs) have
been recently introduced to provide high-speed Internet access
to vehicles by deploying 802.11 enhanced Roadside Units (RSUs)
along roads. However, few content downloading oriented RSU
deployment strategies have been proposed. In this paper, we pro-
pose a new RSU deployment strategy for content downloading in
VANETs. The encounters between vehicles and RSUs are modeled
as a time continuous homogeneous Markov chain. The optimal
inter-meeting time between vehicles and RSUs is analyzed based
on the encounter model. Then, the road network is modeled as a
weighted undirected graph, and a RSU deployment algorithm is
designed based on the depth-first traversal algorithm for edges
of a graph. Simulation results show that the proposed RSU
deployment algorithm can satisfy the file downloading service
requirements with the lowest RSU deployment cost.
Index Terms—VANETs; RSU deployment; State transition
probability
I. INTRODUCTION
Due to the expansion of city scale and increasing traffic
congestion, people spend more time in vehicles. A recent
report shows that, in Europe, the average time spend is 274
hours a year per person, while it is up to 541 hours in America
[1]. On the other hand, with the advent of various mobile
Internet applications and social network services, people want
to access the rich-media contents on the Internet at any time
from any place. Although people can use GPRS or 3G to
access the Internet in mobile vehicles, these Internet access
techniques suffer from low bandwidth, high cost, and long
latency.
802.11 based Vehicular Ad hoc Networks (VANETs) can
provide mobile vehicles with high-speed, and low-cost Internet
access services [2]. VANET is a kind of mobile ad hoc
networks with infrastructures called Roadside Units (RSUs).
In VANETs, mobile vehicles and static RSUs are connected
by Dedicated Short Range Communication (DSRC) interfaces
(e.g., 802.11). Messages in VANETs are forwarded between
vehicles hop by hop or delivered between vehicles and RSUs.
J. ott et al. [2] proposed the drive through network infras-
tructure for VANETs based on 802.11, by which vehicles can
access the Internet with RSUs deployed along roads, and this
kind of network infrastructure is also recognized as the Vehicle
†
The correspondent author, tel: 8610-82317601
to Roadside Unit (V2R) communication infrastructure. V2R
communication is a highly potential technology to provide
low-cost and high-speed media file downloading service for
vehicles.
However, there are few VANET infrastructures deployed
recently which impedes the development of VANETs. How
to deploy VANET infrastructures with low cost to satisfy the
application required network quality of service is an important
issue to tackle in the further development of VANETs. Since
vehicles move fast, the connection between vehicles and RSUs
suffers from short period and frequent disconnections. As a
result, a mobile vehicle can hardly download a whole media
file from a single RSU. Therefore, in VANETs file are always
downloaded by means of file fragmentation. In other words,
when a mobile vehicle encounters a RSU, it downloads a piece
of the required file, until all of the pieces of the required file
are downloaded [3]–[5].
V2R based file downloading will be affected by the de-
ployment of RSUs, the travel path of vehicles, and the road
traffic conditions. Recently, some RSU deployment strategies
have been proposed for different purposes. Abdrabou et al. [6]
suggested a framework that aims at determining the minimum
number of RSUs required to cover a straight road while
satisfying the service requirement in terms of the transmission
delay. This RSU deployment algorithm is mainly designed for
message uploading scenarios. Lochert et al. [7] proposed a
genetic algorithm which is able to identify the proper positions
for static roadside units in order to cope with the highly
partitioned nature of a VANET in an early deployment stage.
Zheng et al. [8] introduced a new notion of intermittent cov-
erage for mobile vehicles, called α-coverage, which provides
worst-case guarantees on the interconnection gap while using
significantly fewer RSUs than needed for full coverage. Fiore
et al. [9] introduced a mixed-integer quadratic programming
based optimum RSU deployment scheme to provide Internet
access services for the maximum road traffic volumes with
limited number of RSUs. Zheng et al. [10] proposed the
contact opportunity in terms of distance or time as a new
metric for the characterization of VANETs and an efficient
deployment approach that maximizes the worst case contact
opportunity for a given budget.
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