Resumen:
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In the age of the Communications, when everybody needs to stay connected, to their
mobile phone operator, or internet, the lack of coverage in indoor environments is one
of the main worries. People needs to stay always ...[+]
In the age of the Communications, when everybody needs to stay connected, to their
mobile phone operator, or internet, the lack of coverage in indoor environments is one
of the main worries. People needs to stay always connected, does not care if it is a
shopping mall, an underground station or an airport.
In the last years many mobile phone operators and wireless networks installers, started
to research the phenomena of the propagation of signals in indoor systems attending to
the needs of the population.
When designing a communications system, one of the critical points is modelling the
channel of radio communication. Once we have an appropriate model of propagation we
can predict the behaviour of the signals when propagating in our environment. The
propagation models allow us to predict the power (And thus the loss) of a signal
received at a certain distance of the transmitter, what allows us to plan wireless
networks with more accuracy.
The principles of radio transmission in indoor environments are the same than in
outdoors environments, reflection, refraction, dispersion, but the conditions vary a lot
from one environment to another. The lack of line of sight between transmitter and the
point of measurement is a disadvantage that makes harder to determine the bandwidth
of the channels and the quality of the transmission, because of the presence of obstacles
like walls. We have to take in account the distribution of the floors, the height of the
walls, the materials they are made of and even the furniture.
The actual system for modelling indoor propagation is by mean of measurements taken
in the area where we want to know the coverage. With those measures make a
simulation and determine the coverage. This system involves having to send workers to
the place of study, what means a waste of money, human resources, and time.
This led them to the development and study of various propagation models that could be
implemented in simulation tools that could predict the coverage without needing to take
those in-the-field measurements.
Many indoor propagation models have been developed, both empirical and
deterministic, each one with its own advantages and disadvantages. Some work better in
some environments and circumstances than others.
There are many propagation models and we will discuss them in the chapter 1 of this
document, basically we can divide them in two groups, the deterministic ones and the
empirical ones.
The deterministic ones are base on Maxwell equations and the empirical ones are based
on experimental measurements.
There are many simulation tools based in those propagation models, but there is another
model to take in account. In 1998 three researchers, Kwok-Wai Cheung, Jonathan H-M
Sau and R.D Murch developed a new indoor propagation model [1]. This model is an empirical model that provides accuracy similar to the ray-tracing techniques, like the
uniform theory of diffraction (UTD), requiring lower computation times. Because of
that, it was selected as base for the tool developed in this project. This model will be
explained deeply in chapter 2.
The objective of this project was to develop a simulation tool based on that empirical
model keeping the low computation times and accuracy of the model, offering a user
friendly interface with commercial purposes.
The platform chosen for developing this tool has been Matlab® from MathworksTM.
The reason for selecting this option was because the programming language used in
Matlab® is very similar to C, is compatible with other programming languages, it
provides many graphic tools and has its own mathematical libraries.
The result has been a tool able to predict the looses of a wireless system in an indoor
environment, taking in account the number of floors, the angle of incidence of the signal
with the floors and walls, the material of the walls, the looses due to the distance
between transmitter and point of measurement and the influence of the diffraction in the
corners of the walls. How this tool works will be explained deeply in chapter 3.
After comparing our tool with other ray-tracing based tools, and some experimental
measurements, the accuracy of the empirical model has been proved to be pretty good
and with low computation times. The comparison between both tools will be explained
deeply in chapter 4.
So, is this the best propagation model? Is this tool finished or needs improvement? In
chapter 5 you will find all the conclusions obtained from this project and what I think
are the next work lines to take in account.
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