This book is
divided into the following chapters...
1.- Introduction to Wireless Propagation
We
present a brief introduction to the basic concepts and
mechanisms driving the wireless propagation channel. Then, we present
very simple time-series analysis techniques which cover the basics
previously introduced. These include the fast variations due to
multipath and the combined effects of shadowing and multipath. Finally,
we have a look into the signal's complex envelope, and we plot its
magnitude and phase. We also present the Rayleigh and Rice cases which
correspond to harsh and benign propagation conditions.
2. - Shadowing
Effects
We
present
several techniques for quantifying the shadowing effects caused by
totally absorbing screens. Even though the formulations presented are
somehow more involved than those in other chapters, we have thought it
helpful to provide the reader with tools to reproduce the effect of the
presence of buildings and other large obstacles. In this way, the
reader will be able to replicate the effects of the terrain or the
signal variations while driving along a street. We also wanted to point
out that, through fairly simple physical models, it is possible to
reproduce the inherent cross-correlation properties observed between
wanted or interfering signals converging on a given mobile terminal.
3.- Coverage
and Interference
Looks into the shadowing
phenomenon
from a statistical point of view. In Chapter 2 we looked at it from a
deterministic point of view. We provide a number of simulation cases
where the various aspects of shadowing are presented, thus, we first
look at the normal distribution describing the variability of shadowing
effects when expressed in dB, and we link the mean of the distribution
to the path loss. We define two additional concepts, the location
variability and the correlation length. We present alternative ways of
reproducing such variations. We then present the effect of
cross-correlation, and how to introduce it in simulated series using a
statistical approach. Finally, we introduce the multiple interference
case. We also use the generated series in hard- and soft-handover
examples.
4. - Introduction
to Multipath
After
studying the shadowing effects, we start the analysis of
the multipath phenomenon. This is introduced by presenting first, very
simple geometries, and continuing with more intricate ones. We point
out how multipath is a time-selective phenomenon,
i.e., it
gives rise to fades. In addition, the movement of at least one of the
terminals causes Doppler effects. We see how the Doppler
shift
and the angle of arrival of a given echo are interrelated, and that
there is a limit to the maximum rate of change possible, if it is only
the terminal that is moving. Throughout, we assume that multipath gives
rise to a spatial standing wave, sensed by the terminal antenna as it
moves. We also show a possible way of generating time variations when
the mobile terminal is stationary. Finally, we briefly introduce the
case where both terminals, and even the scatterers, are moving. In this
chapter, and throughout this book, we use a very simple approach for
the multipath channel based on the so-called multiple
point-scatterer model.
5.- Multipath: Narrowband Channel
We
continue our discussion on the narrowband multipath channel.
In this case, we go one step further and use normalized levels so that
we are able to introduce our synthetic time series in actual link-level
simulators, where the working point (the average signal-to-noise ratio)
is extremely important. We continue our discussion using the multiple
point-scatterer model to simulate second-order statistics, and other
parameters. We then introduce in the model a direct ray, thus
generating a Rice series. Afterward, we present alternative ways for
generating Rayleigh and Rice series, one consisting in an array of low
frequency sinusoidal generators, and the other consisting on the
combination in quadrature of two random Gaussian, noise-like signals,
which are also filtered to force the wanted Doppler characteristics.
Finally, we look into the issue of space diversity, both at the mobile
and the base station sides. The concept of diversity gain/improvement
is introduced.
6.- Shadowing
and Multipath
We
conclude our analysis of the narrowband
channel by modeling
together the slow and fast variations due to shadowing and multipath,
respectively. We present two mixed distributions: Suzuki and Loo. We
also simulate a very simple power control technique.
7.- Wideband
Channel
Completes
our picture of the channel. When the time spreading is
significant with respect to the duration of the transmitted symbols,
selective fading starts to be important. We introduce techniques for
characterizing wideband channels, starting with deterministic
time-varying channels, and then going on to introduce the stochastic
characterization. The main functions and parameters necessary are
discussed. We put the wideband channel in the frame of the multiple
point-scatterer model, which has been used for presenting illustrative
channel simulations. Finally, a statistical model, that of COST 207, is
implemented.
8.- Propagation
in Microcells and Picocells:
We review several issues of relevance for the
microcell and
picocell scenarios. We also consider the outdoor-to-indoor propagation
case. In addition to reviewing some basic theoretical and empirical
techniques, we propose and implement simulations which deal with the
modeling of these scenarios using simple, image-theory ray-tracing
techniques, which reproduce what empirical models forecast. Moreover,
we introduce the consideration of diffraction effects in these
scenarios. Finally, we also present a widespread statistical model due
to Saleh and Valenzuela for describing the wideband indoor channel,
where we present the concept of ray clustering.
9.- The
Land Mobile Satellite Channel
We become
acquainted with some of the issues specific to this
channel, and its more common modeling techniques. We present
alternative ways for generating time series, i.e., using a fully
statistical approach based on Markov chains, and a mixed
statistical-deterministic approach, called here the virtual
city
approach. Additionally, we become familiar with simple techniques for
assessing multiple satellite availability by making use of constellation
simulator data, together with urban masks.
Finally, we quantify the Doppler shift caused by non-GEO
satellites.
10.- The
Directional Wireless Channel
Concludes
our study on the wireless channel.
Here we study the
spatial properties of the multipath channel. We first learn how
scatterer contributions tend to be clustered in terms of excess delays,
which indicate that they can belong to the same obstacle. We also see
that these clustered contributions are spread out in angle of arrival
and departure. We also simulate the multiple antenna channel (MIMO, multiple-input
multiple-output)
using our point-scatterer approach and we show how the capacity can be
increased substantially. Finally, we present another approach, a
statistical one, for simulating the MIMO channel.