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发表于 2010-9-22 15:33:36
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Preface:
Mobile and wireless communications systems are becoming increasingly more
complex in an effort to cope with the growing demand for more supportable
peak data rates, coverage requirements, and capacity objectives, as well as exciting
new applications such as wireless multimedia and anywhere-anytime mobile
Internet access. Although new air interface standards and access technologies
such as code division multiple access (CDMA2000), wideband code division
multiple access (WCDMA), and their evolutions, including evolution data optimized
(EV-DO) and high-speed downlink packet access (HSDPA), promise to
meet these requirements with data rates up to several megabits per second, this is
often achievable only under ideal channel conditions—assumptions are rarely
encountered in real systems deployment. Smart antennas have great potential in
overcoming the impairments of these systems by exploiting the spatial domain
to reduce the effects of interference, extend the range and coverage of wireless
networks, increase system capacity, and achievable data throughout.
The area of smart antennas application in wireless communications has
received increased attention both in the wireless industry and academia for the
past few years. It is an interdisciplinary topic that requires knowledge and skills
in areas such as antenna arrays, signal processing, digital communications, radio
frequency (RF) engineering, and wave propagation. Today, a large body of literature
about the topic exists, although much of this is in the form of complex
research papers published across a multitude of technical journals, magazines,
and conference proceedings, making it very difficult for a practicing engineer to
develop the skills required for a successful design in a reasonable amount of
time. With that in mind, this book attempts to close the gap by consolidating
and presenting the principles of smart antennas along with the issues associated
with their application in modern communications systems in an easy-to-follow
format. The book’s purpose is to explain the principles and techniques of smart
antennas application in wireless and mobile communications systems. It presents
topics and issues in the design of advanced antennas systems in an
easy-to-follow methodology. The book is intended for graduate students in electrical
engineering, practicing communications engineers, engineering and product
managers, and wireless systems designers. It is intended to provide a useful
and needed reference in one place and cover a collection of topics necessary for
successful application of smart antennas in wireless systems.
The book begins in Chapter 1 with a brief history of wireless communications
systems and their drive to achieve increasing demands in terms of coverage
and capacity. In Chapter 2, the effects of cochannel interference, multiple access
interference, and other impairments affecting existing and future multiple access
techniques of 2.5 and third generation (3G) wireless systems are discussed to
show how they prevent these systems from achieving their full potential of range
and system capacity. Models for the mobile radio propagation channel are integral
tools that allow system designers to evaluate the benefits of different measures
for enhancing system performance. The coverage of smart antennas would
not be complete without addressing models that take the spatial domain into
account. In Chapter 3, shortcomings of conventional models will be outlined,
along with a description of spatial directional channel models adopted by the
industry’s standards bodies. Interference reduction with smart antennas offers
an efficient way to reduce the interference in mobile communications systems
through the use of narrow beams directed to a cluster of users or an individual
user while, at the same time, steering nulls toward interfering users. Smart
antennas could be divided into two major types, fixed multiple beams and adaptive
array (AA) systems. A detailed explanation of these two approaches, along
with their advantages and drawbacks, will be covered in Chapters 4 and 5. First,
we will provide an overview of the fundamentals of antenna arrays and then
show how these concepts tie into schemes like the Butler matrix and adaptive
beamforming. We will also discuss diversity techniques and other methods
applicable to both the uplink and downlink of wireless mobile communications
systems. A daunting task facing any smart antennas developer is selecting the
receiver structure and adaptive algorithms most suitable for the application in
hand. Today, a large number of proposed methods and technical solutions exist.
A comprehensive classification of smart antennas algorithms along with the
main implementation issues and trade-offs is presented in Chapter 6, as well as
some comparison between the different techniques. In Chapter 7, a section on
system performance improvements demonstrates the impact of using smart
antennas at the radio base station and potential improvements in terms of coverage
and capacity of mobile communications networks. In Chapter 8, we will
address the systems aspects of smart antennas and their interaction with various
network control algorithms such as admission control, power control, and radio
resource management. The application of antenna arrays in handsets is discussed
in Chapter 9. Finally, the book concludes with a brief overview of multiple
input multiple output (MIMO) systems, which combine antenna arrays at
both the receive and transmit side to create parallel spatial channels that dramatically
increase spectral efficiency and system capacity.
Although practicing engineers and designers as well as engineering and
product managers are the primary audience for this book, it can be easily
adopted as a graduate course textbook in smart antenna applications in mobile
communications systems. |
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