Regardless of the branch of science or engineering, theoreticians have always
been enamored with the notion of expressing their results in the form of
closed-form expressions. Quite often, the elegance of the closed-form solution
is overshadowed by the complexity of its form and the difficulty in evaluating
it numerically. In such instances, one becomes motivated to search instead for
a solution that is simple in form and simple to evaluate.
Regardless of the branch of science or engineering, theoreticians have always been
enamored with the notion of expressing their results in the form of closed-form
expressions. Quite often the elegance of the closed-form solution is overshadowed
by the complexity of its form and the difficulty in evaluating it numerically. In
such instances, one becomes motivated to search instead for a solution that is
simple in form and likewise simple to evaluate.
Multiuser multiple-input-multiple-output (MU-
MIMO) systems are known to be hindered by dimensionality
loss due to channel state information (CSI) acquisition overhead.
In this paper, we investigate user-scheduling in MU-MIMO
systems on account of CSI acquisition overhead, where a base
station dynamically acquires user Channels to avoid choking the
system with CSI overhead.
Communication today is not as easy as it was in the past. Protecting numerous com-
munication services, which are operating in the same or adjacent communication
Channels, has become increasingly challenging. Communication systems have to be
protected from both natural and manmade interference. Electromagnetic interfer-
ence can be radiated or conducted, intentional or unintentional.
The writing of this book was prompted by two main developments in wireless
communications in the past decade. First is the huge surge of research activities in
physical-layer wireless communication theory. While this has been a subject of study
since the 60’s, recent developments in the field, such as opportunistic and multi-input
multi-output (MIMO) communication techniques, have brought completely new per-
spectives on how to communicate over wireless Channels.
At the macroscopic level of system layout, the most important issue is path loss. In the
older mobile radio systems that are limited by receiver noise, path loss determines SNR and
the maximum coverage area. In cellular systems, where the limiting factor is cochannel
interference, path loss determines the degree to which transmitters in different cells interfere
with each other, and therefore the minimum separation before Channels can be reused.
Many wireless communications Channels consist of multiple signal paths from the
transmitter to receiver. This multiplicity of paths leads to a phenomenon known
as multipath fading. The multiple paths are caused by the presence of objects in the
physical environment that, through the mechanisms of propagation, alter the path of
radiated energy. These objects are referred to as scatterers. In the past, researchers
often looked at ways to mitigate multipath scattering, such as in diversity systems.
Multiple-input, multiple-output (MIMO) systems, on the other hand, use multipath
diversity to their advantage; a MIMO system has the ability to translate increased
spatial diversity into increased channel capacity.
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.
Orthogonal frequency division multiplexing (OFDM) has been shown to be
an effective technique to combat multipath fading in wireless Channels. It
has been and is going to be used in various wireless communication systems.
This book gives a comprehensive introduction on the theory and practice of
OFDM for wireless communications.
The investigation of the propagation channel is becoming more and more important in mod-
ern wireless communication. The demand for spectral efficiency motivates exploitation of
all Channels that can possibly be used for communications. Nowadays, a common trend for
designing physical layer algorithms is to adapt the transceiving strategy, either by maximizing
the diversity gains or by utilizing the coherence of the Channels to improve the signal-to-noise
power ratio.
