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FA GW/AP
FA
MH

WLAN
Built
150BC




WPAN


Figure 1.1. 4G wireless network architecture.


1.2.4.1. Network Integration. 4G networks are touted as the hybrid broadband
networks that integrate different network topologies and platforms. In Figure 1.1, the inte-
gration of various types of networks in 4G is represented by the overlapping of different
network boundaries. There are two levels of integration: the first is the integration of het-
erogeneous wireless networks with varying transmission characteristics such as wireless
LAN, WAN, and PAN as well as mobile ad hoc networks; the second level includes the in-
tegration of wireless networks and fixed network-backbone infrastructure, the Internet
and PSTN.

1.2.4.2. All-IP Networks. 4G starts with the assumption that future networks will
be entirely packet-switched using protocols evolved from those in use in today™s Internet.
An all-IP-based 4G wireless network has intrinsic advantages over its predecessors. IP is
compatible with, and independent of, the actual radio access technology. This means that
the core 4G network can be designed and can evolve independently from access networks.
Using an IP-based core network also means the immediate tapping of the rich protocol
11
1.2. REVIEW OF WIRELESS NETWORK EVOLUTION


suites and services already available, for example, voice and data convergence, can be
supported by using a readily available VoIP set of protocols such as MEGACOP, MGCP,
SIP, H.323, and SCTP. Finally, the converged all-IP wireless core networks will be packet
based and support packetized voice and multimedia on top of data. This evolution is ex-
pected to greatly simplify the networks and reduce cost for maintaining separate networks
for different traffic types.

1.2.4.3. Lower Cost and Higher Efficiency. 4G IP-based systems are expected
to be cheaper and more efficient. First, equipment costs are four to ten times lower than
equivalent circuit-switched equipment for 2G and 3G wireless infrastructures. An open
converged IP wireless environment further reduces costs for network buildout and mainte-
nance. There will be no need to purchase extra spectrum, as 2G/3G spectrum can be
reused in 4G and much of the spectrum needed by WLAN and WPAN is public and does
not require a license.

1.2.4.4. Ultrahigh Speed and Multimedia Applications. 4G systems aim to
provide ultrahigh transmission speeds of up to 100 Mbps, 50 times faster than those in 3G
networks. This leap in transmission speed will enable high-bandwidth wireless services,
allowing users to watch TV, listen to music, browse the Internet, access business pro-
grams, perform real-time video streaming, and other multimedia-oriented applications,
such as E-Commerce, as if they were sitting at home or in the office.

1.2.4.5. Ubiquitous Computing. A major goal toward the 4G Wireless evolution
is the provision of pervasive computing environments that can seamlessly and ubiquitous-
ly support users in accomplishing their tasks, in accessing information or communicating
with other users at any time, anywhere, and from any device. In this environment [172],
computers get pushed further into the background; computing power and network connec-
tivity are embedded in virtually every device to bring computation to us, no matter where
we are or under what circumstances we work. These devices will personalize themselves
in our presence to find the information or software needed.

1.2.4.6. Support of Ad Hoc Networking. Noninfrastructure-based mobile ad hoc
networks (MANETs) are expected to become an important part of the 4G architecture. An
ad hoc mobile network is a transient network formed dynamically by a collection of arbi-
trarily located wireless mobile nodes without the use of existing network infrastructure or
centralized administration. Mobile ad hoc networks are gaining momentum because they
help realize network services for mobile users in areas with no preexisting communica-
tions infrastructure [8]. Ad hoc Networking enables independent wireless nodes, each
limited in transmission and processing power, to be “chained” together to provide wider
networking coverage and processing capabilities. The nodes can also be connected to a
fixed-backbone network through a dedicated gateway device, enabling IP networking ser-
vices in areas where Internet services are not available due to lack of preinstalled infra-
structure. All these advantages make ad hoc networking an attractive option in the future
wireless networks arena.

1.2.4.7. Location Intelligence. To support ubiquitous computing requirements,
4G terminals need to be more intelligent in terms of user™s locations and service needs,
including recognizing and being adaptive to user™s changing geographical positions, as
12 MOBILE AD HOC NETWORKING WITH A VIEW OF 4G WIRELESS: IMPERATIVES AND CHALLENGES


well as offering location-based services [94]. Anytime, anywhere requires the intelligent
use of location information and the embedding of this information in various applica-
tions.
Outdoor wireless applications can use the Global Positioning System (GPS) to obtain
location information. GPS is a satellite-based system that can provide easy and relatively
accurate positioning information almost anywhere on earth. Many GPS implementations
are available, including integrating a GPS receiver into a mobile phone (GPS/DGPS), or
adding fixed GPS receivers at regular intervals to obtain data to complement readings on
a phone (A-GPS), or by using help from fixed base stations (E-OTD). These implementa-
tions provide different fix times and accuracies ranging from 50 m to 125 m. For indoor
applications, since GPS signals cannot be received well inside buildings, alternative tech-
nologies like infrared, ultrasound, or radio have to be used.
Possible location-based services include finding nearest service providers, e.g., restau-
rants and cinemas; searching for special offers within an area; warning of traffic or weath-
er situations; sending advertisements to a specific area; searching for other collocated
users; active badge systems, and so on.
Location information can also be used to help enhance other 4G network services; for
example, by using location information to aid and optimize routing in mobile ad hoc net-
works. Geocasting is another new application that involves broadcasting messages to re-
ceivers within a user-defined geographical area.


1.3. MOBILE AD HOC NETWORKS

As mentioned in Section 1.2.4, mobile ad hoc networks (MANETs) are envisioned to
become key components in the 4G architecture, and ad hoc networking capabilities are
expected to become an important part of overall next-generation wireless network func-
tionalities. In general, mobile ad hoc networks are formed dynamically by an au-
tonomous system of mobile nodes that are connected via wireless links without using an
existing network infrastructure or centralized administration. The nodes are free to move
randomly and organize themselves arbitrarily; thus, the network™s wireless topology may
change rapidly and unpredictably. Such a network may operate in a standalone fashion,
or may be connected to the larger Internet. Mobile ad hoc networks are infrastructure-
less networks since they do not require any fixed infrastructure such as a base station for
their operation. In general, routes between nodes in an ad hoc network may include mul-
tiple hops and, hence, it is appropriate to call such networks “multihop wireless ad hoc
networks.” Figure 1.2 shows an example mobile ad hoc network and its communication
topology.
As shown in Figure 1.2, an ad hoc network might consist of several home-computing
devices, including notebooks, handheld PCs, and so on. Each node will be able to com-
municate directly with other nodes that reside within its transmission range. For commu-
nicating with nodes that reside beyond this range, the node needs to use intermediate
nodes to relay messages hop by hop.

1.3.1. Characteristics and Advantages
MANETs inherit common characteristics found in wireless networks in general, and add
characteristics specific to ad hoc networking:
13
1.3. MOBILE AD HOC NETWORKS




MANET

D
A

B F



C E




Figure 1.2. Mobile ad hoc network.



Wireless. Nodes communicate wirelessly and share the same media (radio, infrared,
etc.).
Ad-hoc-based. A mobile ad hoc network is a temporary network formed dynamical-
ly in an arbitrary manner by a collection of nodes as need arises.
Autonomous and infrastructureless. MANET does not depend on any established
infrastructure or centralized administration. Each node operates in distributed peer-
to-peer mode, acts as an independent router, and generates independent data.
Multihop routing. No dedicated routers are necessary; every node acts as a router
and forwards each others™ packets to enable information sharing between mobile
hosts.
Mobility. Each node is free to move about while communicating with other nodes.
The topology of such an ad hoc network is dynamic in nature due to constant move-
ment of the participating nodes, causing the intercommunication patterns among
nodes to change continuously.

Ad hoc wireless networks eliminate the constraints of infrastructure and enable devices
to create and join networks on the fly”any time, anywhere”for virtually any applica-
tion.


1.3.2. MANET Applications
Because ad hoc networks are flexible networks that can be set up anywhere at any time,
without infrastructure, including preconfiguration or administration, people have come to
realize the commercial potential and advantages that mobile ad hoc networking can bring.
Next we will look at the range of mobile ad hoc network applications, how they evolved
historically, and will evolve in the future.
Historically, mobile ad hoc networks have primarily been used for tactical network-re-
lated applications to improve battlefield communications and survivability. The dynamic
nature of military operations means it is not possible to rely on access to a fixed preplaced
communication infrastructure on the battlefield. Pure wireless communication also has
14 MOBILE AD HOC NETWORKING WITH A VIEW OF 4G WIRELESS: IMPERATIVES AND CHALLENGES


the limitation that radio signals are subject to interference and radio frequencies higher
than 100 MHz rarely propagate beyond line of sight (LOS) [16]. A mobile ad hoc network
creates a suitable framework to address these issues, provides a mobile wireless distrib-
uted multihop wireless network without preplaced infrastructure, and provides connectiv-
ity beyond LOS.
Early ad hoc networking applications can be traced back to the DARPA Packet Radio
Network (PRNet) project in 1972 [16]. This was primarily inspired by the efficiency of
packet switching technology, such as bandwidth sharing and store-and-forward routing,
and its possible application in mobile wireless environments. PRNet featured a distributed
architecture consisting of networks of broadcast radios with minimal central control, and
a combination of Aloha and CSMA channel access protocols used to support the dynamic
sharing of the broadcast radio channel. In addition, by using multihop store-and-forward
routing techniques, the radio coverage limitation is removed, which effectively enables
multiuser communication within a very large geographic area.
Survivable Radio Networks (SURANs) were developed by DARPA in1983 to address
open issues in PRNet, in the areas of network scalability, security, processing capability,
and energy management. The main objectives of this effort were to develop network algo-
rithms to support networks that can scale to tens of thousands of nodes and withstand se-
curity attacks, as well as use small, low-cost, low-power radio that could support sophisti-
cated packet radio protocols [16]. This effort resulted in the design of Low-cost Packet
Radio (LPR) technology in 1987 [17], which featured a digitally controlled DS spread-
spectrum radio with an integrated Intel 8086 microprocessor-based packet switch. In ad-
dition, a family of advanced network management protocols was developed, and hierar-
chical network topology based on dynamic clustering was used to support network
scalability. Other improvements in radio adaptivity, security and increased capacity were
achieved through management of spreading keys [18].
Toward the late 1980s and early 1990s, the growth of the Internet infrastructure and the
microcomputer revolution created a feasible environment for the implementation of the
initial packet radio network ideas [16]. To leverage the global information infrastructure
in the mobile wireless environment, the U.S. Department of Defense initiated the DARPA
Global Mobile (GloMo) Information Systems program in 1994 [20], which aimed to sup-
port Ethernet-type multimedia connectivity any time, anywhere, among wireless devices.
Several networking designs were explored; for example, Wireless Internet Gateways
(WINGs) at UCSC deploys a flat peer-to-peer network architecture, whereas the Multime-
dia Mobile Wireless Network (MMWN) project from GTE Internetworking uses a hierar-
chical network architecture that is based on clustering techniques.
Tactical Internet (TI), implemented by U.S. Army in 1997, is by far the largest-scale
implementation of mobile wireless multihop packet radio network [16]. TI uses direct-se-
quence, spread-spectrum, time division multiple access radio with data rates in the tens of
kilobits per second ranges, whereas modified commercial Internet protocols are used for
networking among nodes.
Extending the Littoral Battle-space Advanced Concept Technology Demonstration
(ELB ACTD) in 1999 is another MANET deployment exploration to demonstrate the fea-
sibility of Marine Corps war fighting concepts that require over-the-horizon (OTH) com-
munications from ships at sea to Marines on land via an aerial relay. Approximately two
dozen nodes were configured for the network, Lucent™s WaveLAN and VRC-99A were
used to build the access and backbone network connections. The ELB ACTD was success-
ful in demonstrating the use of aerial relays for connecting users beyond LOS.
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1.3. MOBILE AD HOC NETWORKS


Although early MANET applications and deployments were military oriented, nonmil-
itary applications have grown substantially since then and have become the main focus to-
day. Especially in the last few years, with the rapid advances in mobile ad hoc networking
research, mobile ad hoc networks have attracted considerable attention and interest from
the commercial sector as well as the standards community. The introduction of new tech-
nologies such as Bluetooth, IEEE 802.11, and Hyperlan greatly facilitate the deployment
of ad hoc technology outside of the military domain. As a result, many new ad hoc net-
working applications have since been conceived to help enable new commercial and per-
sonal communications beyond the tactical networks domain, including personal area net-
working, home networking, law enforcement operations, search-and-rescue operations,
commercial and educational applications, sensor networks, and so on. Table 1.2 shows the
classification of present and future applications as well as the example services they pro-
vide.

1.3.3. Design Issues and Constraints
As described in the previous section, the ad hoc architecture has many benefits, such as
self-reconfiguration, ease of deployment, and so on. However, this flexibility and conve-
nience come at a price. Ad hoc wireless networks inherit the traditional problems of wire-
less communications, such as bandwidth optimization, power control, and transmission
quality enhancement [8], while, in addition, their mobility, multihop nature, and the lack
of fixed infrastructure create a number of complexities and design constraints that are
new to mobile ad hoc networks, as discussed in the following subsections.

1.3.3.1. They are Infrastructureless. Mobile ad hoc networks are multihop infra-
structureless wireless networks. This lack of fixed infrastructure in addition to being wire-
less, generate new design issues compared with fixed networks. Also, lack of a centralized

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