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EEE00046 - REDUCTION OF INTERSYMBOL INTERFERENCE IN WIRELESS COMMUNICATION USING ZERO FORCING AND MINIMUM MEAN SQUARE ERROR EQUALIZATION TECHNIQUE


ABSTRACT

               In telecommunication, Inter-symbol interference (ISI) is a form of distortion of a signal in which one symbol interferes with another. The presence of ISI in the system introduces errors in the system and thereby causing undesirable result. Therefore, in the design of the transmitting and receiving filters, the objective is to minimize the effects of ISI, and thereby deliver the digital data to its destination with the smallest error rate possible. In this project, a zero forcing equalizer, which is a type of linear equalizer was designed to mitigate the effects of ISI (Inter-symbol Interference). The zero forcing equalizer does this by finding the inverse of the impulse response of the channel.                                                

              Channel equalizers based on minimum mean square error (MMSE) and zero forcing (ZF) technique have been developed for a general multiple input multiple output (MIMO) system and implemented for a 2x2 and 4x4 MIMO system with spatial multiplexing (SM) for channel associated with additive white Gaussian noise. The system model was developed using Minimum Mean Square Error (MMSE) and Zero Forcing (ZF) equalization technique. Binary data were randomly generated and modulated using Binary Phase Shift Keying (BPSK) modulation scheme.

            The modulated signal was made to pass through a Rayleigh fading channel, the received signal over the paths were combined using the hybrid ZF-MMSE technique. Bit Error Rate was used to evaluate the system and MATLAB 7.4 simulation software was used to simulate the developed model.

            The result showed that the hybrid ZF-MMSE gave a lower Bit Error Rate (BER) values when compared with conventional ZF and MMSE. Therefore, in this research, hardware complexity has been reduced and hybrid ZF-MMSE can be used in wireless communication.

 

CHAPTER ONE

INTRODUCTION

  • Background of the study

            Wireless communication has gone through a lot of improvements in the last few decades, it was first introduced in the 19th century and developed over the years. It is a very important medium of transmission of information from one point to another which maybe closer together or far apart in space. The medium of transmission in this system uses no wires, cables or any electrical conductors. Information is transmitted through space by using electromagnetic waves which may be IR, RF, Satellite etc.

             The first commercial mobile system was first launched by Bells in 1946. Early mobile systems use single higher power transmitter with analogue frequency modulation techniques to give coverage to about 50miles and hence only few users can get the services due to relatively small bandwidth. Recently, the wireless communication has become part of many devices like cordless telephones, GPS, Wi-Fi, wireless computer parts and satellite televisions just to mention a few. This technology may or may not use the line of site (LOS) system in such a channel as the old communication system, which require the transmitter and the receiver to face each other. The wireless channel is characterized by the presence of many paths between the transmitter and the receiver.

            Factors such as Reflection, Diffraction and scattering also increases the path of the Electromagnetic wave between communicators. Reflection: EM waves are reflected on collision with objects or surfaces in which they travel. A number of different surfaces can reflect EM waves. The sea provides the best reflection for EM waves in long distance transmission, it is observed that wet surfaces provide the best reflection compared with dry surfaces. Diffraction: give rise to bending of waves around obstacles. It usually occurs when path is blocked by a very large object with sharp edges. Scattering: it occurs when waves comes in contact with small objects, causing the reflected energy to spread out or scatter in many directions

 

  • Statement of The Problem

            Wireless communications are undergoing a strong expansion due to their immense applications in various economic sectors of every nation. As a result of this expansion, the demand for high data rate transmission is increasing rapidly. Multipath effects in wireless channels such as delay spread, signal fading and Doppler spread affect the performance of wireless communication system. This system suffers from extreme fading of the signal amplitude and delay spread due to the frequency selectivity of the channel at the receiver resulted in Inter-Symbol Interference (ISI). Inter-symbol interference (ISI) is a form of distortion caused by multipath, it occurs when one symbol interferes with subsequent symbols causing noise or a less desirable output signal, this is an undesirable result that should be reduced to the minimum amount possible. 

  • Aim and Objectives

            The aim of the project is to investigate the reduction of inter-symbol interference using Zero Forcing and Minimum Mean Square Error Equalization technique.

The objectives are to:

  1. To study the effect of inter-symbol interference on wireless communication systems.
  2. To develop a system model for Equalization technique.
  • To simulate the developed model using MATLAB 7.2 simulation software.
    • Justification

               Nowadays, the increase in the use of wireless communication has led to the creation of multiple channels which allow many subscribers to communicate simultaneously. The creation of these channels has led to a significant problem known as the Inter-symbol interference, which is a form of distortion caused by multipath. It occurs when one symbol interferes with another causing noise or a less reliable signal. This has the effect of blur which can reduce signal clarity. If Inter-symbol interference occur within a system, it introduces error at the decision device at the output. The objective of this project is to minimize the effect of ISI, and thereby to deliver the output signal to its destination with minimum error rate possible.

 

  • Scope of the study

          This project is limited to the study of Inter-symbol interference (ISI). Using Rayleign fading channel in the investigation.