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organizing in networks. In ad hoc networks, the devices themselves are the network, and
this allows seamless communication, at low cost, in a self-organized fashion and with easy
deployment. The large degree of freedom and the self-organizing capabilities make mobile
ad hoc networks completely different from any other networking solution. For the first time,
users have the opportunity to create their own network, which can be deployed easily and
cheaply. However, a price for all those features is paid in terms of complex technology so-
lutions, which are needed at all layers and also across several layers.
For all those reasons, mobile ad hoc networking is one of the more innovative and chal-
lenging areas of wireless networking, and this technology promises to become increasing-
ly present in everybody™s life. Ad hoc networks are a key step in the evolution of wireless
networks. They inherit the traditional problems of wireless and mobile communications,
such as bandwidth optimization, power control and transmission quality enhancement. In
addition, the multihop nature and the lack of fixed infrastructure brings new research
problems such as network configuration, device discovery and topology maintenance, as
well as ad hoc addressing and self-routing. Many different approaches and protocols have
been proposed and there are multiple standardization efforts within the Internet Engineer-
ing Task Force and the Internet Research Task Force, as well as academic and industrial
projects.
This book is the result of our effort to put together a representative collection of chap-
ters covering the most advanced research and development in mobile ad hoc networks. It
is based on a number of stand-alone chapters that are deeply interconnected. It seeks to
provide an opportunity for readers to find advances on a specific topic, as well as to ex-
plore the whole field of rapidly emerging mobile ad hoc networks. In addition, the histor-
ical evolution and the role of mobile ad hoc networks in 4G mobile systems are discussed
in depth in the first chapter.

xv
xvi PREFACE


In most of the past research, mobile ad hoc networks are seen as part of the Internet,
with IP-centric layered architecture. This architecture has two main advantages: it simpli-
fies the interconnection to the Internet, and guarantees the independence from (heteroge-
neous) wireless technologies. The layered paradigm, which has significantly simplified
the Internet design and led to the robust scalable protocols, can result in poor perfor-
mances when applied to mobile ad hoc networks. In fact, in mobile ad hoc networks sev-
eral functions can hardly be isolated into a single layer. Energy management, security and
cooperation, quality of service, among the others, cannot be completely confined in a
unique layer. Rather, their implementation results are more effective by exploiting and in-
teracting with mechanisms at all layers. A more efficient and performing architecture for
mobile ad hoc networks thus should avoid a strict layering approach, but rather follow an
integrated and hierarchical framework to take advantage of the interdependencies among
layers. This book goes in this new direction by presenting cross-layering chapters. Most
of the chapters do not focus on single-layer mechanisms, rather they present and discuss
functions that are implemented by combining mechanisms that, in a strict layered archi-
tecture, belong to different layers.
Inside the ad hoc networking field, wireless sensor networks play a special role, as they
are used mainly for phenomena monitoring. The solutions for mobile ad hoc networks are
rarely suitable for sensor networks, as the latter are rarely mobile in a strict sense, and
prone to different constraints deriving by the sensing devices™ features and by application
requirements. This generated an extensive literature that could hardly be accommodated
in this book without being reductive.
This book is intended for developers, researchers, and graduate students in computer
science and electrical engineering, as well as researchers and developers in the telecom-
munication industry. The editors of this book first discussed the selection of problems and
topics to be covered and then discussed the choice of best authors for each of the selected
topics. We believe that we have achieved a balanced selection of chapters with top quality
experts selected for presenting the state of the art on each topic. The editors envision the
introduction of a number of computer science and electrical engineering graduate courses
in ad hoc networks, and believe that this book provides textbook quality for use in such
courses.
The editors are particularly grateful to the authors who have agreed to present their
work in this book. They would also like to express their sincere thanks to all the reviewers,
whose helpful remarks have contributed to the outstanding quality of this book. Special
thanks go to Stephen Olariu and Sergio Palazzo; we have benefited enormously from their
comments and suggestions. Finally, we are immensely grateful to Catherine Faduska and
Christina Kuhnen for their invaluable collaboration in putting this book together.

STEFANO BASAGNI
MARCO CONTI
SILVIA GIORDANO
IVAN STOJMENOVIC
April 2004
CHAPTER 1




MOBILE AD HOC NETWORKING
WITH A VIEW OF 4G WIRELESS:
IMPERATIVES AND CHALLENGES

JENNIFER J.-N. LIU and IMRICH CHLAMTAC




1.1 INTRODUCTION

The wireless arena has been experiencing exponential growth in the past decade. We have
seen great advances in network infrastructures, growing availability of wireless applica-
tions, and the emergence of omnipresent wireless devices such as portable or handheld
computers, PDAs, and cell phones, all getting more powerful in their capabilities. These
devices are now playing an ever-increasingly important role in our lives. To mention only
a few examples, mobile users can rely on their cellular phone to check e-mail and browse
the Internet; travelers with portable computers can surf the internet from airports, railway
stations, cafes, and other public locations; tourists can use GPS terminals installed inside
rental cars to view driving maps and locate tourist attractions; files or other information
can be exchanged by connecting portable computers via wireless LANs while attending
conferences; and at home, a family can synchronize data and transfer files between
portable devices and desktops.
Not only are mobile devices getting smaller, cheaper, more convenient, and more pow-
erful, they also run more applications and network services. All of these factors are fuel-
ing the explosive growth of the mobile computing equipment market seen today. Market
reports from independent sources show that the worldwide number of cellular users has
been doubling every 1½ years, with the total number growing from 23 million in 1992 to
860 million in June 2002. This growth is being fueled further by the exploding number of

1
Mobile Ad Hoc Networking. Edited by Basagni, Conti, Giordano, and Stojmenovic.
ISBN 0-471-37313-3 © 2004 Institute of Electrical and Electronics Engineers, Inc.
2 MOBILE AD HOC NETWORKING WITH A VIEW OF 4G WIRELESS: IMPERATIVES AND CHALLENGES


Internet and laptop users [6]. Projections show that in the next two years, the number of
mobile connections and the number of shipments of mobile and Internet terminals will
grow by yet by another 20“50% [6]. With this trend, we can expect the total number of
mobile Internet users soon to exceed that of fixed-line Internet users.
Among the myriad of applications and services run by mobile devices, network con-
nections and corresponding data services are without doubt in highest demand. According
to a recent study by Cahners In-Stat Group, the number of subscribers to wireless data
services will grow rapidly from 170 million worldwide in 2000 to more than 1.3 billion in
2004, and the number of wireless messages sent per month will rise dramatically from 3
billion in December 1999 to 244 billion by December 2004. Currently, most of the con-
nections among wireless devices occur over fixed-infrastructure-based service providers
or private networks; for example, connections between two cell phones set up by BSC and
MSC in cellular networks, or laptops connected to the Internet via wireless access points.
Although infrastructure-based networks provide a great way for mobile devices to get net-
work services, it takes time to set up the infrastructure network, and the costs associated
with installing infrastructure can be quite high. There are, furthermore, situations in
which user-required infrastructure is not available, cannot be installed, or cannot be in-
stalled in time in a given geographic area. Providing the needed connectivity and network
services in these situations requires a mobile ad hoc network.
For all of these reasons, combined with significant advances in technology and stan-
dardization, new alternative ways to deliver connectivity have been gaining increased at-
tention in recent years. These are focused around having mobile devices within the trans-
mission range connect to each other through automatic configuration, setting up an ad hoc
mobile network that is both flexible and powerful. In this way, not only can mobile nodes
communicate with each other, but also receive Internet services through an Internet gate-
way node, effectively extending both network and Internet services to noninfrastructure
areas. As the wireless network continues to evolve, this ad hoc capability will become
more important, and the technology solutions used to support it more critical, spurring a
host of research and development projects and activities in industry and academia alike.
This chapter dwells on the impetus behind the inevitable market adoption of the mobile
ad hoc network, and presents a representative collection of technology solutions that can
be used in different layers of the network, especially the algorithms and protocols needed
for its operation and configuration. In the following section, we review the wireless com-
munication technologies, the types of wireless networks and their evolution path, as well
as the problems and market demands for existing wireless systems. We then explain why
ad hoc networking is expected to form the essential piece in the 4G network architecture.
In Section 1.3, we look at the mobile ad hoc network in closer detail, covering its specific
characteristics, advantages, and design challenges. After that, we show the range of op-
portunities for MANET applications, both military and commercial, which also serve to
elaborate the market potential behind MANET technology advancement. Section 1.4
summarizes the current status and design challenges facing the research community. A
large number of protocols and algorithms have been developed for mobile ad hoc net-
works, which are presented, discussed and compared in Section 1.4. Although impressive
research and development results are demonstrated in this and the remaining detailed
chapters in this book, many open issues remain to clear the path for the successful ad hoc
network deployment and commercialization. Some of the open research problems in ad
hoc wireless networking are the subject of Section 1.5. Section 1.6 presents conclusions,
and introduces the rest of chapters in this book.
3
1.2. REVIEW OF WIRELESS NETWORK EVOLUTION


1.2 REVIEW OF WIRELESS NETWORK EVOLUTION

The wireless communication landscape has been changing dramatically, driven by the
rapid advances in wireless technologies and the greater selection of new wireless services
and applications. The emerging third-generation cellular networks have greatly improved
data transmission speed, which enables a variety of higher-speed mobile data services.
Meanwhile, new standards for short-range radio such as Bluetooth, 802.11, Hiperlan, and
infrared transmission are helping to create a wide range of new applications for enterprise
and home networking, enabling wireless broadband multimedia and data communication
in the office and home.
Before delving into these technologies and applications, we first examine some of the
main characteristics of wireless communication as related to specification and classifica-
tion of these networks, and then review the key capabilities exhibited by the various types
of wireless networks.


1.2.1 Wireless Communication Characteristics
In general, wireless networking refers to the use of infrared or radio frequency signals to
share information and resources between devices. Many types of wireless devices are
available today; for example, mobile terminals, pocket size PCs, hand-held PCs, laptops,
cellular phone, PDAs, wireless sensors, and satellite receivers, among others.
Due to the differences found in the physical layer of these systems, wireless devices
and networks show distinct characteristics from their wireline counterparts, specifically,

Higher interference results in lower reliability.
”Infrared signals suffer interference from sunlight and heat sources, and can be
shielded/absorbed by various objects and materials. Radio signals usually are less
prone to being blocked; however, they can be interfered with by other electrical
devices.
”The broadcast nature of transmission means all devices are potentially interfering
with each other.
”Self-interference due to multipath.
Low bandwidth availability and much lower transmission rates, typically much
slower-speed compared to wireline networks, causing degraded quality of service,
including higher jitter, delays, and longer connection setup times.
Highly variable network conditions:
”Higher data loss rates due to interference
”User movement causes frequent disconnection
”Channel changes as users move around
”Received power diminishes with distance
Limited computing and energy resources: limited computing power, memory, and
disk size due to limited battery capacity, as well as limitation on device size, weight,
and cost.
Limited service coverage. Due to device, distance, and network condition limita-
tions, service implementation for wireless devices and networks faces many con-
straints and is more challenging compared to wired networks and elements.
4 MOBILE AD HOC NETWORKING WITH A VIEW OF 4G WIRELESS: IMPERATIVES AND CHALLENGES


Limited transmission resources:
”Medium sharing
”Limited availability of frequencies with restrictive regulations
”Spectrum scarce and expensive
Device size limitation due to portability requirements results in limited user inter-
faces and displays.
Weaker security: because the radio interface is accessible to everyone, network se-
curity is more difficult to implement, as attackers can interface more easily.

1.2.2. Types of Wireless Networks
Many types of wireless networks exist, and can be categorized in various ways set out in
the following subsections depending on the criteria chosen for their classification.

1.2.2.1. By Network Formation and Architecture. Wireless networks can be di-
vided into two broad categories based on how the network is constructed and the underlin-
ing network architecture:

1. Infrastructure-based network. A network with preconstructed infrastructure that is
made of fixed and wired network nodes and gateways, with, typically, network ser-
vices delivered via these preconfigured infrastructures. For example, cellular net-
works are infrastructure-based networks built from PSTN backbone switches,
MSCs, base stations, and mobile hosts. Each node has its specific responsibility in
the network, and connection establishment follows a strict signaling sequence
among the nodes [2]. WLANs typically also fall into this category.
2. Infrastructureless (ad hoc) network. In this case a network is formed dynamically
through the cooperation of an arbitrary set of independent nodes. There is no
prearrangement regarding the specific role each node should assume. Instead,
each node makes its decision independently, based on the network situation, with-
out using a preexisting network infrastructure. For example, two PCs equipped
with wireless adapter cards can set up an independent network whenever they are
within range of one another. In mobile ad hoc networks, nodes are expected to be-
have as routers and take part in discovery and maintenance of routes to other
nodes.

1.2.2.2. By Communication Coverage Area. As with wired networks, wireless
networks can be classified into different types based on the distances over which data is
transmitted:

1. Wireless Wide Area Networks (Wireless WANs). Wireless WANs are infrastruc-
ture-based networks that rely on networking infrastructures like MSCs and base sta-
tions to enable mobile users to establish wireless connections over remote public or
private networks [3]. These connections can be made over large geographical areas,
across cities or even countries, through the use of multiple antenna sites or satellite
systems maintained by wireless service providers. Cellular networks (like GSM
networks or CDMA networks) and satellite networks are good examples of wireless
WAN networks.
5
1.2. REVIEW OF WIRELESS NETWORK EVOLUTION


2. Wireless Metropolitan Area Networks (Wireless MANs). Wireless MAN networks
are sometimes referred to as fixed wireless. These are also infrastructure-based net-
works that enable users to establish broadband wireless connections among multi-
ple locations within a metropolitan area, for example, among multiple office build-
ings in a city or on a university campus, without the high cost of laying fiber or

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