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.

2.        To investigate the interference and noise reduction capabilities of an adaptive antenna array.

3.        Comparative analysis of omni-directional antenna and adaptive antenna array based on SINR maximization.

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