European Research Framework Programs are a public policy instrument to
strengthen European competitiveness through cooperation. Although they have a
fixed timeframe, determined research themes, and specific expected impact, the
achievements in research and Development (R&D) made by the funded projects
pave the way for a research continuum.
All wireless communication standards, existing and under Development, adopt or
consider adopting orthogonal frequency-division multiplexing (OFDM) as the
modulation technique. It is clear that OFDM has become the definitive modulation
scheme in current and future wireless communication systems.
Before delving into the details of orthogonal frequency division multiplexing (OFDM), relevant
background material must be presented first. The purpose of this chapter is to provide the necessary
building blocks for the Development of OFDM principles. Included in this chapter are reviews of stochastic
and random process, discrete-time signals and systems, and the Discrete Fourier Transform (DFT). Tooled
with the necessary mathematical foundation, we proceed with an overview of digital communication
systems and OFDM communication systems. We conclude the chapter with summaries of the OFDM
wireless LAN standards currently in existence and a high-level comparison of single carrier systems versus
OFDM.
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.
Optical wireless communication is an emerging and dynamic research and Development
area that has generated a vast number of interesting solutions to very complicated
communication challenges. For example, high data rate, high capacity and minimum
interference links for short-range communication for inter-building communication,
computer-to-computer communication, or sensor networks. At the opposite extreme is
a long-range link in the order of millions of kilometers in the new mission to Mars
and other solar system planets.
Since the advent of optical communications, a great technological effort has
been devoted to the exploitation of the huge bandwidth of optical fibers. Start-
ing from a few Mb/s single channel systems, a fast and constant technological
Development has led to the actual 10 Gb/s per channel dense wavelength di-
vision multiplexing (DWDM) systems, with dozens of channels on a single
fiber. Transmitters and receivers are now ready for 40 Gb/s, whereas hundreds
of channels can be simultaneously amplified by optical amplifiers.
This book focuses on the study and Development of one of the most
advanced topics in broadband wireless communications systems:
power efficiency and power consumption in wireless communications
systems, especially of mobile devices. Hence, the main focus of this
book is on the most recent techniques for the conservation of power
and increase in power efficiency.
One of the prerequisites for the Development of telecommunication services is the
understanding of the propagation of the waves, either acoustic, electromagnetic,
radio or light waves, which are used for the transmission of information.
In this work, we shall limit ourselves to the study of radio waves: this term
apply to the electromagnetic waves used in radio communications. Their
frequency spectrum is very broad, and is divided into the following frequency
bands : ELF waves (f < 3 kHz), VLF (3-30 kHz), LF waves (30-300 kHz), MF
waves (300-3000 kHz), HF (3-30 MHz), VHF waves (30-300 MHz), UHF waves
(300-3000 MHz), SHF waves (3-30 GHz), EHF waves (30-300 GHz) and sub-
EHF waves (300-3000 GHz).
Wireless communications and networking technology are advancing at a very rapid
pace. Newer technologies and standards are evolving to serve the ever-increasing num-
ber of users demanding different types of mobile applications and services. Research
and Development activities on wireless technology constitute one of the most impor-
tant segments of research and Development in the telecommunications area today.
This book was born from the perception that there is much more to spectrum use
and sharing than one sees reflected in publications, whether academic, commercial
or political. the former – in good research style – tend towards reductionism and
concentrate on specific, detailed aspects. commercial publications tend to empha-
size the positive aspects and they tend to put promise above practice. Given the ever
increasing pace of technology Development and recent successes of new wireless
technologies, some pundits predict large-scale spectrum scarcity, potentially lead-
ing to economic catastrophe. Although economic theory has a hard time explaining
recent events that shook the world economy, the notion of spectrum scarcity is intui-
tively acceptable, even if not correct or immediately relevant.
