ABSTRACT
Dust carry non-spherical particles which in the absence of turbulence or shear wind and hydrodynamic forces, tend to orient their major axis in the vertical plane, thus resulting in particles anisotropy which may contribute to Cross Polarization Discrimination (XPD) degradation due to differential phase shift. This research presents an improved model of harmattan dust effect on cross polarization of microwave access radio link operating between 15GHz and 38GHz. Meteorological data such as dust mass concentration, visibility, etc. for ten years (that is, 2003 to 2012) were obtained from Nigerian Meteorological Agency (NIMET) and the five months harmattan period data was sorted out. The sorted data were used to deduce important parameters like dielectric constant, relative particle volume and so on. Then, the complex propagation coefficients (attenuation and phase shift) were deduced as a function of wave frequency, media dielectric constant depolarization factor and fractional volume of dust storm using Maxwell’s electromagnetic equation for a random medium. Mathematical background for XPD was then established as a function of signal frequency, dielectric constant of dust storm, particle size probability distribution function and visibility. Finally, a link budget analysis was done for some selected frequency values of 18 GHz, 23 GHz, 27 GHz, 30 GHz and 35 GHZ to deduce a fade margin of 52.073dB, 50.5313dB, 41.2168dB, 43.1843dB, 41.6434dB and 41.3091dBrespectively due to the depolarization factor of harmattan period in Kano. A percentage time availability of 99.99 percent was obtained for the selected antenna thereby showing the validity of the developed model based on Rayleigh’s distribution Model for Link availability.
TABLE OF CONTENTS
DECLARATION i
CERTIFICATION ii
DEDICATION iii
ACKNOWLEDGEMENTS iv
TABLE OF CONTENTS vi
LIST OF FIGURES ix
LIST OF TABLES x
LIST OF ABBREVIATIONS xi
ABSTRACT xii
CHAPTER ONE: INTRODUCTION
1.1 Background of Study 1
1.2 Significance of Research 2
1.3 Statement of Problem 2
1.4 Aim and Objectives 2
1.5 Methodology 3
1.5 Dissertation Organization 4
CHAPTER TWO: LITERATURE REVIEW
2.1 Introduction 5
2.2 Review of Fundamental Concepts 5
2.3 Microwave Propagation Fundamentals 5
2.3.1 Microwave Radio Applications 7
2.3.2 Transmission Losses in Radio Communication 9
2.4 Dust Particle Geometry 9
2.4.1 Particle Size Distribution 10
2.4.2 Particle Size Measurement Methods 10
2.4.3 Dielectric Constant of Dust 11
2.4.3.1 Effect of Moisture Content on Dielectric Constant (Permittivity) 12
2.4.3.2 Dielectric Constant for Kano Region 13
2.4.4 Cross Polarization Discrimination Induced by the Atmosphere 14
2.4.4.1 Cross and Co-polarization 15
2.4.5 Analytical Methods to Single Particle Scattering 16
2.4.5.1 Rayleigh Approximation Method 16
2.4.5.2 Mie Theory 17
2.4.6 Dust Storm Depolarization 17
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2.4.6.1 Visibility 20
2.4.6.2 Dielectric Constant 22
2.4.6.3 Dusty Medium Permittivity 23
2.4.6.4 Wave Attenuation in a Lossy Medium 24
2.4.6.5 Dusty Media Depolarization Factor 27
2.4.6.6 Loss Due to Depolarization 28
2.4.7 Microwave Link Budget 29
2.4.8 Eclipse Radio Datasheet 31
2.5 Review of Similar Research Works 31
CHAPTER THREE:METHODOLOGY
3.1 Introduction 38
3.2 Methodology 38
3.3 Data Collection 39
3.4 Deduction of Complex Propagation Attenuation and Phase Constant 40
3.5 Mathematical Relationship between Visibility and Dust Mass Concentration for Kano Region 41
3.6 Mathematical Relationship for Fractional Volume of Dust Particle 43
3.7 Dielectric Constant for Harmattan Period in Kano Region 43
3.8 Particle Size Distribution Function for Kano 45
3.9 Computation of Cross Polarization Discrimination 46
3.10 Fade Margin Considering Loss Due to Depolarization 48
CHAPTER FOUR: RESULTS AND DISCUSSION
4.1 Introduction 50
4.2 Parameter Selection 50
4.3 Dielectric Constants 50
4.4 Result of Attenuation for Harmattan Period in Kano 52
4.5 Result of Cross Polarization Discrimination for Harmattan Period in Kano 53
CHAPTER FIVE: CONCLUSION AND RECOMMENDATION
5.1 Summary 56
5.2 Conclusion 56
5.3 Significant Contributions 57
5.4 Limitations 57
5.3 Recommendations 57
Appendix A1:Monthly Visibility Data for Kano Region (NIMET) 61
Appendix A2:Monthly Percentage Humidity Data for Kano Region (NIMET) 62
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Appendix B1:Dust Mass Concentration per Visibility Data for Kano Region (NIMET) 63
Appendix B2:Percentage Particle Size Distribution Data for Kano Region (NIMET) 64
Appendix C1:Standard Normal Distribution Table 65
Appendix D:MATLAB Codes 68
CHAPTER ONE
INTRODUCTION
1.1 Background of Study
Wireless communications service providers are currently facing challenges due to the congested radio spectrum which has imposed the use of higher frequencies. However, higher frequency bands are more sensitive to weather conditions and microwave signal degradation due to rapid increase in atmospheric particles.(Elsheikh et al., 2010). The termgeographical dust usually refers to solid inorganic particles that are derived from the weathering of rocks. In the geological sciences, dust is defined as particles with diameters smaller than 62.5 μm. In the atmospheric sciences, dust is usually defined as the material that can be readily suspended by wind (Shao, 2008). Increase in frequency of occurrence of dust storm has made the study of wind-blown dust particles as well as their effects on human activities an important topic for research. Appreciable interest has been expressed in the problem associated with influence of dust storm on microwave link performance(Kok et al., 2012). This has been largely attributed to the continuous growth of satellite and terrestrial microwave systems and the use of higher frequencies. There is now spectral congestion of microwave radio frequency range owing to the emergence of new technologies and high demand of telecommunication applications, such as mobile video traffic and other multimedia applications over the past decade. This has given rise to a steady move towards higher carrier frequencies for increased information transfer rates and to further miniaturize equipment for portability. However, a range of meteorological phenomena such as dust storm make microwave propagation a serious problem as operations can be hampered by attenuation due to dust storm particles (Musa et al., 2014a)
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1.2 Significance of Research
The research is important to discover the effect of dust on microwave access links operating in regions prone to harmattan dust. The results can then be used to deduce the depolarization loss and then effectively calculate link budgets in these regions to reduce link outages during the harmattan season.
1.3 Statement of Problem
The reliability of microwave signals operating in areas that have high rainfall, a lot of obstacles,where dust and other particles are abundant in air is limited. The effect of dust on microwave signals have attracted interest of researchers because dust is associated with poor visibility which causes high attenuation in the long run. Therefore, there is a need to consider the effect of dust (for areas having abundant dust quantity in air)when developing models for cross polarization of microwave access radio links and when designing a link budget to ensure precision in the fade margin calculation. Thus, the motivation was to investigate the phenomenon of depolarization of microwave signal, propagating through atmosphere having dust particles. The factors of dust size parameter, frequency of incident wave, the angle of incident, and dust permittivity, dust storm visibility and water content analysis was taken into consideration to obtain cross-pole discrimination of electromagnetic wave propagation in the dust storm. Finally, a loss margin due to depolarization was computed from XPD results. This loss margin was added to the traditional link margin calculation for microwave line of sight path planning within the telecommunication radio access frequency range of 15 to 38 GHz.
1.4 Aim and Objectives
The aim of this research work was to examine the effect of dust storm on the cross polarization of a microwave access radio link operating between 15GHz to 38GHz in order to establish an improved mathematical model which includes loss margin due to XPD
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degradation for fade margin calculation. This loss margin was added to the traditional fade margin calculation for microwave line of sight link at the microwave radio access network. The objectives of this research were as follows:
i. Establish a mathematical relationship between XPD and the variables (particle size density, visibility, propagation frequency and permittivity).
ii. Establish a loss margin due to XPD degradation using deduced XPD values and a line of sight fade margin due to XPD degradation.
iii. Design link budget template to account for losses due to dust depolarization.
1.5 Methodology
The following steps were taken to achieve the objectives:
i. Solving Maxwell’s electromagnetic equation in the random medium (dust storm medium) to deduce complex propagation coefficients (attenuation and phase constant) as functions of variables including wave frequency, media dielectric constant, depolarization factor and fractional volume of dust particles.
ii. Deduction ofthe mathematical relationship between visibility and fractional volume of dust particle.
iii. Using meteorological data in Kano to deduce dielectric constant.
iv. Establishing:
a. Probability distribution function from particle size distribution data.
b. Mathematical relationship between XPD as a function of signal frequency, dielectric constant of dust storm, particle size probability distribution function, and visibility at foremost.
v. Deduction of the fade Margin due to wave depolarization of a co-channel dual polarized microwave transmission link
vi. Modelling and programming using MATLAB R2015b and validation of results.
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1.5 Dissertation Organization
The organization of this dissertation report is as follows: Chapter one presents the general background of the study. In Chapter two, review of fundamental concepts pertinent to this research work and detailed review of similar works were presented. Chapter three covers detailed explanation of methods and materials used in this work and Chapter fourcentres onthe results and discussions. In Chapter five, conclusions, significant contributions, limitations and recommendations are presented.The references quoted in this dissertation report as well as appendices have also been provided.
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