<<

. 4
( 87 .)



>>

copper cabling and leasing lines [3]. In addition, Wireless MANs can serve as back-
ups for wired networks should the primary leased lines for wired networks become
unavailable. Both radio waves and infrared light can be used in wireless MANs to
transmit data. Popular technologies include local multipoint distribution services
(LMDS) and multichannel multipoint distribution services (MMDS). IEEE has set
up a specific 802.16 Working Group on Broadband Wireless Access Standards that
develops standards and recommended practices to support the development and de-
ployment of broadband wireless metropolitan area networks [151].
3. Wireless Local Area Network (Wireless LANs). Wireless local area networks en-
able users to establish wireless connections within a local area, typically within a
corporate or campus building, or in a public space, such as an airport, usually with-
in a 100 m range. WLANs provide flexible data communication systems that can be
used in temporary offices or other spaces where the installation of extensive cabling
would be prohibitive, or to supplement an existing LAN so that users can work at
different locations within a building at different times [3, 7]. Offices, homes, coffee
shops, and airports represent the typical hotspots for wireless LAN installations.
Wireless LANs can operate in infrastructure-based or in ad hoc mode. In the in-
frastructure mode, wireless stations connect to wireless access points that function
as bridges between the stations and an existing network backbone. In the ad hoc
mode, several wireless stations within a limited area, such as a conference room,
can form a temporary network without using access points, if they do not require
access to network resources.
Typical wireless LAN implementations include 802.11 (Wi-Fi) and Hiperlan2.
Under 802.11a and 802.11b, data can reach transmission speeds between 11 Mbps
to 54 Mbps [13, 14].
4. Wireless Personal Area Networks (Wireless PANs). Wireless PAN technologies en-
able users to establish ad hoc, wireless communication among personal wireless de-
vices such as PDAs, cellular phones, or laptops that are used within a personal op-
erating space, typically up to a 10 meter range. Two key Wireless PAN technologies
are Bluetooth and infrared light. Bluetooth [10, 11] is a cable-replacement technol-
ogy that uses radio waves to transmit data to a distance of up to 9“10 m, whereas in-
frared can connect devices within a 1 m range. Wireless PAN is gaining momentum
because of its low complexity, low power consumption, and interoperability with
802.11 networks.

1.2.2.3. By Access Technology. Depending on the specific standard, frequency, and
spectrum usage, wireless networks can be categorized based on the access technology
used. These include:

GSM networks
TDMA networks
CDMA networks
6 MOBILE AD HOC NETWORKING WITH A VIEW OF 4G WIRELESS: IMPERATIVES AND CHALLENGES


Satellite networks
Wi-Fi (802.11) networks
Hiperlan2 networks
Bluetooth networks
Infrared networks

1.2.2.4. By Network Applications. Wireless networks can also be categorized based
on the specific usage and applications they support, for example,

1. Enterprise Networks
2. Home Networks
3. Tactical Networks
4. Sensor Networks
5. Pervasive Networks
6. Wearable Computing
7. Automated Vehicle Networks

1.2.3. Forces Driving Wireless Technology Evolution
To understand the wireless technology trends, and to see why noninfrastructure-based mo-
bile ad hoc networks are poised to play an important role in the evolution of future wire-
less networks, it helps to review the evolution path of different technology generations.
Table 1.1 summarizes the technologies, architectures, and applications for each of these
generations.
One can argue that the commercial history of wireless started with the first generation
or 1G in 1980s, which supported analog cell phones using FDMA and was relatively un-
sophisticated. Because different regions of the world pursued different mobile phone stan-
dards, 1G phones typically could only be used within one country. E Examples of 1G sys-
tems include NMT, TACS in Europe, and AMPS in North America.
The cellular industry began deployment of second-generation networks, 2G, a decade
or so ago. 2G digitizes the mobile system and adds fax, data, and messaging capabilities
on top of the traditional voice service. This evolution was triggered by the high demand
for low-speed data access required to enable popular mobile data services like email,
SMS, and so on. Again, different standards were deployed in different regions of the
world; for example, Europe and Asia use GSM, whereas North America uses a mix of
TDMA, CDMA, and GSM as 2G technologies. Recently, 2G has been extended to 2.5G to
provide better support for transmitting low-speed data up to 384 kbps.
Currently, efforts are under way to transition the wireless industry from 2G networks to
third-generation (3G) networks that would follow a common global standard based on
CDMA and provide worldwide roaming capabilities. 3G networks offer increased band-
width of 128 Kbps when mobile device is moving at higher speeds, for example, a car, up
to 384 Kbps for mobility at pedestrian speed, and 2 Mbps in stationary applications, mak-
ing it possible to deliver live video clips. There are still different flavors of the air inter-
faces though: Europe and Asia are promoting W-CDMA and EDGE, whereas North
America works on cdma2000, each developed by different standard bodies”3GPP for
Europe and Asia and 3GPP2 for North America.
7
1.2. REVIEW OF WIRELESS NETWORK EVOLUTION


Table 1.1. Wireless Technology Generations
Generation 1G 2G 2.5G 3G 4/5G
Time Frame 1980s 1990s Late1990s 2000s 2010s
(2010 full
deployment)
Signal Type Analog Digital Digital Digital Digital
Access
Multiple access FDMA/FDD TDMA/FDD EDGE, GPRS CDMA, W-CDMA, MC-CDMA, OFDM
CDMA/FDD TD-SCDMA
Frequency 824“894 MHz 1800“2400 MHZ Higher-frequency
spectrum 890“960 MHz (varies country bands 2“8 GHz
1850“1990 to country)
MHz (PCS)
Bandwidth 5“20 Mhz 100 MHz
Antenna Optimized antenna, Smarter antenna,
multiband adapter Multiband and
wide-band support
FEC Convolutional rate, Concatenated
1/2, 1/3 coding scheme
Network Architecture
Media type Voice Mostly voice Mostly Voice Voice Converged voice/
Low-speed Higher-speed High-speed data data/multimedia
data services data (10“384 (144 kbps“2 over IP; Ultra-high-
via modem kbps) Mbps) speed data (2“100
(10“70 kbps) Mbps)
Network type Cellular Cellular Cellular WWAN Integrated WWAN,
Cell based WMAN, WLAN
(Wi-Fi, Bluetooth)
and WPAN
(Bluetooth)
Structure Infrastructure Infrastructure Infrastructure Infrastructure- Hybrid of
based based based based network infrastucture-based
and ad hoc network
Switching Circuit Circuit Circuit Circuit switched Packet switched
switched switched switched and packet switched
IP support N/A N/A N/A Use several air All IP based (IP6.0)
link protocols,
including IP5.0
New Applications Emails, Ubiquitous
maps/directions, computing with
News, shopping, location intelligence
e-commerce,
interactive gaming,
etc.
Ex System AMPS, NMT, GSM, GPRS, UMTS
TACS DCS1900, EDGE IMT2000
IS-136, CDMA2000
CdmaOne W-CDMA
8 MOBILE AD HOC NETWORKING WITH A VIEW OF 4G WIRELESS: IMPERATIVES AND CHALLENGES


Despite the high expectations for 3G networks, 3G is facing difficulties getting de-
ployed and meeting its promised performance and throughput due to architecture and ca-
pability limitations. On the other hand, recent technology advancements enable new ser-
vices and thus impose new requirements on system capabilities that were not taken into
consideration in the original 3G system design. Let us take a closer look at some of
these.

1.2.3.1. The need to integrate various types of wireless networks. Today™s
wireless communication systems are primarily designed to provide cost-efficient wide-
area coverage for users with moderate bandwidth demands, and 3G is based on primarily
a wide-area concept. Many other types of wireless networks have since been designed and
are gaining popularity, including wireless LAN and PAN networks, but these are being de-
signed as logically separate networks. The various wireless networks need to be integrated
in order to provide seamless wireless services. Emerging technology trends indicate that
future-generation communication systems will consist of a high-speed wired backbone
and wireless local area networks attached to the periphery of the network. Wireless LANs
and PANs will extend the coverage of broadband services and provide ubiquitous network
access to mobile users [172].

1.2.3.2. The need to integrate wireless platforms with fixed network back-
bone infrastructures. The consumer of telecommunication services of tomorrow will
expect to receive the same services in a wireless fashion as he receives from a fixed net-
work. A wireless system should, therefore, be transparent to the user and thus highly inte-
grated with the fixed network backbone like Internet and PSTN networks.

1.2.3.3. The need to support high-speed multimedia services. Growth in In-
ternet information services and the emergence of new multimedia applications including
music, video streaming, or videoconferencing make multimedia services highly attractive
to wireless users. In 3G systems, the maximum data speed supported is 2 Mbit/s, band-
width that is not sufficient to meet the needs of these high-performance applications
[143]. Very high-speed data transmission speed has to be supported in order to enable
multimedia services on mobile devices.

1.2.3.4. The need for convergence in network infrastructure. Today, wireless
communications are heavily biased toward voice. With data traffic growing at almost ex-
ponential speed and IP becoming prevalent, maintaining two separate backbone infra-
structure for voice and data traffic becomes untenable. Converged IP-based digital packet
networks that can support voice, data, as well as multimedia applications at the same time
provide the ideal platform to lower network operating cost and enable new breeds of net-
work services [15].

1.2.3.5. The need to support high mobility and device portability. High mo-
bility and device portability enable wireless users to connect to networks and communi-
cate with other users or devices anytime, anywhere [12]. 3G systems cannot yet fully sup-
port this transparency, such as dynamically changing network addresses and device
locations. Progress is needed to eliminate the shortcomings of wireless systems so that the
inherent convenience of mobility will no longer cause deterioration of system functionali-
ties.
9
1.2. REVIEW OF WIRELESS NETWORK EVOLUTION


Another aspect of portability relates to the need to make the mobile device more us-
able, to extend the battery power, make devices smaller, and create better user interfaces
that match the conventional environment.

1.2.3.6. The need to support noninfrastructure-based networks. Current
wireless systems rely on preconfigured infrastructure (routers, MSCs, base stations) to
deliver wireless services. This limits the service availability in established areas. However,
in many situations networking services are required where infrastructure is not available
or not deliverable in a short period of time, for example, in combat or emergency situa-
tions. Support and integration of noninfrastructure-based networks becomes important in
these situations.

1.2.3.7. The need to add location intelligence. As adoption of mobile wireless
systems continues to grow, wireless users will demand services that utilize the conve-
nience stemming from mobility. Among these services, location-based information ser-
vices, such as getting driving or service directions, location-dependent query support, and
system configuration are becoming commonplace and need to be gradually added to sys-
tem capabilities.

1.2.3.8. The need to lower the cost of wireless services. Cost is one of the key
nontechnical issues that need to be dealt with in 3G systems. For example, the cost is ex-
ceedingly high for deployment. 3G spectrum licenses are auctioned at very high prices of
more than $100 billion. Being able to lower these costs while providing better services is a
key requirement for future network success. One of the ways to lower the infrastructure
cost is, for example, by successfully implementing convergence of voice and multimedia
into IP networks.

1.2.3.9. The need for greater standard interoperability. Multiple air interface
standards in 3G are making it difficult for devices to roam and interoperate across net-
works. Furthermore, global mobility and service portability cannot be fully achieved
without universal network standardization. Areas needing additional standardization start
from lower-layer issues such as modulation techniques, spectrum allocation, and signal-
ing, and continue all the way up to protocols and enabling architectures discussed in the
remainder of this chapter.
To meet these new requirements and overcome the limitations and problems of current
3G systems, new architectures and capabilities need to be incorporated into the next-gen-
eration wireless systems to provide the much needed improvements.

1.2.4. 4G Wireless Architecture and Capabilities
4G is all about an integrated global network based on an open-systems approach. Integrat-
ing different types of wireless networks with wireline backbone networks seamlessly and
the convergence of voice, multimedia, and data traffic over a single IP-based core network
will be the main focus of 4G. With the availability of ultrahigh bandwidth of up to 100
Mbps, multimedia services can be supported efficiently. Ubiquitous computing is enabled
with enhanced system mobility and portability support, and location-based services and
support of ad hoc networking are expected. Figure 1.1 illustrates the networks and compo-
nents within the 4G network architecture.
10 MOBILE AD HOC NETWORKING WITH A VIEW OF 4G WIRELESS: IMPERATIVES AND CHALLENGES


4GW Architecture

Satellite Network
Cellular


MANET
PSTN
Cellular Network


CH HA

DFA
GW
CH HA
Internet
FA
Backbone
FA
DFA
router
MH

<<

. 4
( 87 .)



>>