ABSTRACT
This thesis presents the uniform Linear Array model of a simple
adaptive antenna array based on signal-to-interference plus noise ratio (SINR)
maximization.
The SINR was investigated for a conventional narrow band beam
former by varying the number of antenna array elements and number of
interfering signals or users. The results were compared with that of
omni-directional antenna. The graph obtained showed significant improvement in
SINR as the number of antenna elements increases in the presence of large
interferers for odd numbered array.
CHAPTER ONE
INTRODUCTION
1.1 Background
Smart antennas have emerged as one
of the leading innovations for achieving highly efficient networks that
maximize capacity and improve quality and coverage. Smart antennas provide
greater capacity and performance benefits than conventional antennas because
they can be used to customize and fine-tune antenna coverage pattern to the
changing traffic or radio frequency (RF) conditions in a wireless communication
system like the WCDMA network.
Beam forming (BF)
which is a key technology in smart antenna system is a process in which each
user’s signals is multiplied by complex weight vectors that adjust the
magnitude and phase of the signal from each antenna element [1]. A beam forming
appropriately combines the signals received by different elements of an antenna
array to form a single output. Many adaptive algorithms have been
developed to determine the optimal weight vectors of array antenna elements
dynamically, based on different performance criteria. The weight vectors
produce the desired radiation pattern that can be changed dynamically, by
considering the position of users and interferers to optimize the
signal-to-interference and noise ratio (SINR).
1.2 Problem statement
The mobile radio propagation
environment places fundamental limitations on the performance of wireless
communication systems. Signals arrive at a receiver (usually the base station,
BS) via a scattering mechanism and the existence of multipath with different
time delays; attenuations and phases give rise to a highly complex, time-varying
transmission channel. The radio channel in a wireless communication system is
often characterized by multipath propagation [3]. A fading signal results from
interference between multipath components at the receiver.
The
conventional antenna systems; the omni-directional antenna and the sectorized
systems cannot overcome these limitations. Omni-directional antenna radiates
and receives equally in all directions. This will result in wastage of power as
antenna patterns are radiated in the direction of undesired users. While
sectorized antenna systems multiply the use of channels which results in many
handoffs between sectors [4], they do not overcome the major limitations of
omni-directional antennas such as filtering of unwanted signals from adjacent
cells. Therefore, the need for an antenna system that will minimize or overcome
these limitations arises.
1.7 Objective
of the work
The
specific objectives of this thesis are:
1.
Modeling and evaluation of a simple
adaptive antenna array that can form part of a WCDMA BS structure for improving
link capacity.
3.
Comparative analysis of
omni-directional antenna and adaptive antenna array based on SINR maximization.
1.8 Justification
There is an ever – increasing
demand on mobile wireless operators to provide voice and high speed data
services. At the same time, these operators want to support more users per BS
to reduce overall network cost and make services available to subscribers.
Unfortunately, because the available broadcast spectrum is limited, attempts to
increase traffic within a fixed bandwidth create more interference in the
system and degrade the signal quality. To overcome this problem, adaptive
antenna array is proposed for BS transceivers. This work will encourage mobile
wireless operators in Nigeria to consider the option of adopting adaptive antennas
at BSs due to its numerous benefits.
1.9 Scope
of the work
This work will look at adaptive
filtering technique which is the principle of an adaptive antenna array. A cell
model deploying adaptive antenna array at BS was proposed and a mathematical
model for received signal at the antenna array derived based on uniform linear
array model. The SINR of an adaptive antenna array was investigated for
different antenna arrays for a conventional narrow band beam former using fixed
angles of arrival considering different scenarios. Real time measurement was
carried out at a test bed to obtain the signal strength and distance of mobile
users from BS used in the evaluation of pathloss model described in chapter two
for a typical WCDMA carrier deploying sectorized antenna at base station. The
angles of arrivals (AOA) obtained from same measurement are also useful in the
evaluation of SINR for adaptive antenna. Channel model was
considered as Rayleigh flat fading and antenna noise as additive white Gaussian
(AWGN). The simulations are done in Matlab environment.
1.5
Thesis organization
This thesis is organized into five chapters. Chapter one deals
with the introduction to the research work which includes research background,
research objectives, justification and scope of the work.
In chapter two, past
related works were reviewed; evolution, principles and technologies of smart
antenna were explained. Channel model and the CDMA system model were
illustrated. Adaptive filtering was discussed also as the basis of beam
forming.
Chapter three
contains methods adopted in the research. Cell model and signal model for an
adaptive antenna array deployed at BS were provided. The array factor and array
response vector at each element of the array were derived.
Chapter
four deals with system analysis. Here, the SINR was investigated for different
antenna arrays at d=0.5 and 0.75 by varying the number of array elements and
the number of interfering signals for a fixed weight beam former. The
comparative analysis of omni-direction antenna and adaptive antenna was done in
this chapter.
Chapter 5 is Summary
and conclusion. It contains summary of achievements, problems encountered and
solutions, recommendations and suggestion for future research and conclusion.
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