Mobile communication has gained significant importance in today’s society. As
of 2010, the number of mobile phone subscribers has surpassed 5 billion [ABI10],
and the global annual mobile revenue is soon expected to top $1 trillion [Inf10].
While these numbers appear promising for mobile operators at first sight, the
major game-changer that has come up recently is the fact that the market is
more and more driven by the demand for mobile data traffic [Cis10].
The rapid growth in mobile communications has led to an increasing demand for wide-
band high data rate communications services. In recent years, Distributed Antenna
Systems (DAS) has emerged as a promising candidate for future (beyond 3G or 4G)
mobile communications, as illustrated by projects such as FRAMES and FuTURE. The
architecture of DAS inherits and develops the concepts of pico- or micro-cell systems,
where multiple distributed antennas or access points (AP) are connected to and con-
trolled by a central unit.
Wireless metropolitan area networks (WirelessMANs) is emerging as a promising
broadband wireless access (BWA) technology to provide high-speed, high bandwidth
efficiency and high-capacity multimedia services for residential as well as enterprise
applications. It is observed that WirelessMAN (e.g., WiMAX) is even regarded as a 4G
technology. For the success of the WirelessMANs, international standardization organiza-
tions are very actively specifying the standards IEEE 802.16, ETSI HiperMAN and Korea
WiBro.
Rapid growth of wireless communication services in recent decades has created
a huge demand of radio spectrum. Spectrum scarcity and utilization inefficiency
limit the development of wireless networks. Cognitive radio is a promising tech-
nology that allows secondary users to reuse the underutilized licensed spectrum of
primary users. The major challenge for spectrum sharing is to achieve high spectrum
efficiency while making non-intrusive access to the licensed bands. This requires in-
formation of availability and quality of channel resources at secondary transmitters,
however, is difficult to be obtained perfectly in practice.
Radio frequency spectrum is a scarce and critical natural resource that is utilized for
many services including surveillance, navigation, communication, and broadcast-
ing. Recent years have seen tremendous growth in the use of spectrum especially by
commercial cellular operators. Ubiquitous use of smartphones and tablets is one
of the reasons behind an all-time high utilization of spectrum. As a result, cellular
operators are experiencing a shortage of radio spectrum to meet bandwidth
demands of users. On the other hand, spectrum measurements have shown that
much spectrum not held by cellular operators is underutilized even in dense urban
areas. This has motivated shared access to spectrum by secondary systems with no
or minimal impact on incumbent systems. Spectrum sharing is a promising
approach to solve the problem of spectrum congestion as it allows cellular operators
access to more spectrum in order to satisfy the ever-growing bandwidth demands of
commercial users.
Wireless Mesh Networks (WMN) are believed to be a highly promising
technology and will play an increasingly important role in future
generation wireless mobile networks. WMN is characterized by
dynamic self-organization, self-configuration and self-healing to
enable quick deployment, easy maintenance, low cost, high scalability
and reliable services, as well as enhancing network capacity, connect-
ivity and resilience.
Of the various applications that satellites have been used for, one of
the most promising is that of global positioning. Made possible by
Global Navigation Satellite Systems, global positioning enables any
user to know his or her exact position on Earth. Nowadays, the only
fully functioning system is the American Global Positioning System
(GPS). However, the European system, known as Galileo, is expected to
be operative in 2012.
