RAIN ATTENUATION PREDICTION ON EARTH-

TO-SATELLITE MICROWAVE LINK IN LIBYA AS A

CASE STUDY

BY

ASMA ALI HUSSEIN BUDALAL

A dissertation submitted in fulfillment of the requirement for

the degree of Master of Science (Communication

Engineering)

Kulliyyah of Engineering

International Islamic University Malaysia

FEBRUARY 2017

i

ABSTRACT

Earth-to-satellite microwave links are revolutionary communication systems that

supports high-speed data rate. It can accommodate a large number of users with

increased spectral efficiency and high throughput. However, performances of those

links operating in Ku, Ka, and V-bands are degraded by the environment and strongly

attenuated by rain. Rain attenuation is the most significant consideration and challenge

for higher frequency bands. Hence, it is essential for the satellite link designer to take

into account rain fade margin accurately before system implementation. Rain rate is

the main measured parameter to predict of rain attenuation. Rainfall statistical data

measured and recorded in Libya with 3-hours integration time for the period of 30

years are collected. The prediction methods require one minute integration time rain

intensity. Therefore, collected data were analysed and processed to convert into one –

minute rain rate cumulative distribution in Libya. Several prediction models for

conversion of one –minute rain rate have been utilized by considering different

climatic conditions. A suitable prediction model is recommended to predict one-

minute rain rate distribution for microwave link design in Libyan environment.

Chieko and Yoshio is recommended in the calculation of one-minute rain rate

cumulative distribution under Libyan climatic conditions. The model proposed by

International Telecommunication Union-Radio wave Propagation (ITU-R) is used to

predict and investigate rain fade based on converted 1-minute rain rate data. C, Ku-

band downlink at 4-12 GHz rain fading is not a considerable factor in Libya. The

further result shows a fade marginal difference of about 15 dB between Ku- and Ka-

band frequencies for 99.99% availability of time in coastal regions. As well as the

results obtained at V-band downlink shows that 99.99% availability is possible in all

the southern part stations in Libya. It is observed that the ITU-R model seems to under

estimate the rain attenuation in northeast and northwest in Libyan costal line. Rain

fade predicted at five locations are used for performance analysis in terms of link

spectral efficiency and throughput. Taking into account of rain fade margin at

different outage probabilities. Findings will enable the earth-to-space link designer to

determine the optimum transmitting power to mitigate rain fade. Results and analysis

of this research will be a very useful resource to design highly reliable earth-to-

satellite communication links in Libya.

ii

خلاصة البحث

نطاقات تردديه التي تدعم اللاسلكيةظمه الساتلايت ثوره علميه في تقنيه الاتصالات أن باستخدامتصالات الادثت أح مثل ولكن هذه الاشارات ذات الترددات العاليه . الخدمات جوده وتحسين الاتصال قنواتوسرعه سعة لزيادةعاليه

Ku, V, Ka, والتشتت بسبب عوامل الطبيعه في الغلاف الجوي اثناء انتشارها.ولعل تعاني من التشويه والتوهينتصالات الساتلايت إانظمه فمن الضروري جدا لمصممي .هم هذه العوامل المؤثرهأمطار احد لأالتوهين بسبب ا

في وصلات الساتلايتبدقه متناهيه قبل تنفيد ثير الامطار أت حساب الفقد بسببباستخدام وصلات المايركويف لنماذج المعمول بها في حساب التوهين لاهم المدخلات منمعدل المطر المقاس بالمليمتر / الساعه يعتبر .الدراسه منطقه

في عام 03 لفتره مطار لأطول اله حصائيهإبيانات . في هذا البحث تم تجميع مطار لأبسبب ا اشارات الساتلايتفي وهذا فتره طويله جدا لايمكن التعامل .ساعات -0مقاسه كل 0313الى 1891ليبيا منطقه الدراسه من سنه

لايتعدى والتي تعتمد بشكل اساسي على معدل امطار مقدار الاضمحلال والتوهين لقياس الاتصالات لغرض معها معدل الامطار بالنسبه للدقيقه الواحده غير مقاس ويصعب وبما ان . minute rain rate-1الدقيقه الواحده

المتعارف عليها من قبل بعض الباحثين تم الاعتماد علي بعض نماذج التحويل من هناتحديده في مختلف مناطق العالم نماذج لتغيير 6ختبارإوبالفعل قد تم .الواحدالى الدقيقه تغيير معدل الامطار في منطقه الدراسهلالمهتمين بهذا المجال

ومقارنتها مع القيمه المحسوبه لتوزيع معدل كميه الامطار من مليمتر الي مليمتر في الساعه بفارق زمني دقيقه واحده .ومن النتائج المتحصل عليها تبين ان .في ليبيا القيم المقاسه في مناطق جغرافيه مختلفه تحويل مطار المتحصل عليها منلأا

Chieko and Yoshio .باستخدام نموذج القيم المحتمله للتوهين تم حسابمن انسب النماذج للأستخدام في ليبيا outageوحساب احتماليه الخروج عن الخدمه ITU-RPتصالات موجة الانتشار الراديولأتحاد الدولي للأا

probabilities .حساب كفاءه الطيف عن طريق الساتلايت داء وصلات أتحليل تم وختاما عند ترددات مختلفهوحساب C,Ku,Ka,V المقترحةلمختلف مدى الترددات link spectral efficiency (bps/Hz) الترددي

GHz 12-4لترددات اتأثير لتوهين الامطار هناك ليس اظهرت النتائج ان .throughput Mbps الإنتاجية منطقه في الغربيلاشارات في الجزء الشمالي الشرقي والشمالي ا. وعند ترددات اعلى تسبب الامطار توهين في ليبيا

في المناطق الساحليه عند Ku- Ka-band بين fade marginal فرق dB 15 وهناك الدراسه 99.99% availability.كذلكV-band downlink يعمل في المناطق الجنوبيه فقط عند انيمكن

تعد مصدر مهم يمكن الرجوع إليه لرسم خرائط توزيع معدلات الامطار ث نتائج تحليل هذا البح . 99.99%التخطيط لتنفيذ و التصميم عن rain fade margin التوهين الامطار هامش وتحديد ،ليبيافي ج عنهااتوالتوهين الن

لتحديد قوة outage probabilitiesوحساب ستقباللإارسال والإوحساب تكلفه الوصلات وتصميم محطات ا .ليبيا في Kuعند استخدام مدى ترددات اعلى من الإرسال المثلى

iii

APPROVAL PAGE

I certify that I have supervised and read this study and that in my opinion, it conforms

to acceptable standards of scholarly presentation and is fully adequate, in scope and

quality, as a dissertation for the degree of Master of Master of Science

(Communication Engineering)

…………………………………..

Md. Rafiqul Islam

Supervisor

…………………………………..

Mohamed Hadi Habaebi

Co-Supervisor

I certify that I have read this study and that in my opinion it conforms to acceptable

standards of scholarly presentation and is fully adequate, in scope and quality, as a

dissertation for the degree of Master of Science (Communication Engineering)

…………………………………..

Internal Examiner

…………………………………..

Internal Examiner

This dissertation was submitted to the Department of Electrical And Computer

Engineering and is accepted as a fulfilment of the requirement for the degree of

Master of Science (Communication Engineering)

………………………………….

Anis Nurashikin Novdin.

Head, Department of Electrical and

Computer Engineering

This dissertation was submitted to the Kulliyyah of Engineering and is accepted as a

fulfilment of the requirement for the degree of Master of Science (Communication

Engineering)

…………………………………..

Erry Yulian Triblas.

Dean, Kulliyyah of Engineering

iv

DECLARATION

I hereby declare that this dissertation is the result of my own investigations, except

where otherwise stated. I also declare that it has not been previously or concurrently

submitted as a whole for any other degrees at IIUM or other institutions.

Asma Ali Hussein Budalal

Signature ........................................................... Date .........................................

v

INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA

DECLARATION OF COPYRIGHT AND AFFIRMATION OF FAIR

USE OF UNPUBLISHED RESEARCH

RAIN ATTENUATION PREDICTION ON EARTH-TO-SATELLITE

MICROWAVE LINK IN LIBYA AS A CASE STUDY

I declare that the copyright holders of this dissertation are jointly owned by the student

and IIUM.

Copyright © 2017 Asma Ali Hussein Budalal and International Islamic University Malaysia. All rights

reserved.

No part of this unpublished research may be reproduced, stored in a retrieval system,

or transmitted, in any form or by any means, electronic, mechanical, photocopying,

recording or otherwise without prior written permission of the copyright holder

except as provided below

1. Any material contained in or derived from this unpublished research may

be used by others in their writing with due acknowledgement.

2. IIUM or its library will have the right to make and transmit copies (print

or electronic) for institutional and academic purposes.

3. The IIUM library will have the right to make, store in a retrieved system

and supply copies of this unpublished research if requested by other

universities and research libraries.

By signing this form, I acknowledged that I have read and understand the IIUM

Intellectual Property Right and Commercialization policy.

Affirmed by Asma Ali Hussein Budalal

……..…………………….. ………………………..

Signature Date

vi

ACKNOWLEDGEMENTS

In the name of Allah, the most gracious and most merciful,

All praise is due to Allah (s w t) with the help of Allah the thesis would have reached

this stage. I would like to express my most sincere appreciation and gratitude to

Professor. Md. Rafiqul Islam for his advice, guidance, suggestions, critical comments

and supervision during the period of my study. He has added beneficial experience to

my life.

Additionally, I wish to express my appreciation and thanks to Libyan National

Meteorological Center (LNMC) for providing data used in rain fade estimation

Special thanks to Dr. Khalid Elfadli who provided their time, effort and support for

this project.

I wish to express my deep gratitude to my parents. To my mother Hameeda for her

endless support, love and patience.

Finally, special acknowledgment to my dear husband Abd Kareem, thank you for your

support and patience to accomplish this goal. I will be forever grateful to you.

vii

TABLE OF CONTENTS

Abstract .................................................................................................................... i

Abstract in Arabic .................................................................................................... ii

Approval Page .......................................................................................................... iii

Declaration ............................................................................................................... iv

Copyright Page......................................................................................................... v

Acknowledgements .................................................................................................. vi

Table of Contents ..................................................................................................... vii

List of Tables ........................................................................................................... ix

List of Figures .......................................................................................................... xi

List of Symbols ........................................................................................................ xiii

List of Abbreviations ............................................................................................... xv

CHAPTER ONE: INTRODUCTION .................................................................. 1

1.1 General Overview ................................................................................... 1

1.2 Problem Statement And Its Significance ................................................ 5

1.3 Purpose Of The Study............................................................................. 5

1.4 Research Objectives ............................................................................... 6

1.5 Research Scope ....................................................................................... 6

1.6 Rechearch Methodology ......................................................................... 7

1.7 Organization Of The Dissertation ........................................................... 8

CHAPTER TWO: LITERATURE REVIEW ..................................................... 11

2.1 Introduction ............................................................................................ 11

2.2 The Need Of Long Duration Rainfall Statistics ..................................... 11

2.3 Importance Of One- Minute Rain Rate Integration Time ...................... 11

2.4 Rain Rate Data ........................................................................................ 12

2.4.1 ITU-R Model ................................................................................ 12

2.4.2 Global Crane Model (Crane, 1996) .............................................. 13

2.4.3 Moupfouma Model ....................................................................... 13

2.4.4 Chebil’s Model .............................................................................. 14

2.4.5 Rice–Holmberg Model .................................................................. 15

2.4.6 Chieko Ito And Yoshio Hosoya .................................................... 16

2.5 Rain Attenuation Prediction ................................................................... 17

2.5.1 Rain Attenuation Prediction Measurements Methods .................. 17

2.5.2 Prediction Of Rain Attenuation .................................................... 18

2.5.3 Specific Attenuation Of Rain ....................................................... 19

2.6 Rain Attenuation Prediction Models ...................................................... 11

2.6.1 The ITU-R Model ......................................................................... 11

2.6.2 Crane’s Model ............................................................................... 24

2.6.3 Ajayi Model .................................................................................. 25

viii

2.6.4 Dissanayake- Allnutt Model ......................................................... 25

2.7 Satellite Links Budget Design ................................................................ 25

2.8 Link Performance And Availability ....................................................... 27

2.9 Link Margin ............................................................................................ 29

2.10 Link Budget Importance ....................................................................... 29

2.11 Summary ............................................................................................... 11

CHAPTER THEE: RAIN RATE DISTRIBUTION IN LIBYA ....................... 32

3.1 Introduction ............................................................................................ 32

3.1.1 Rainfall Patterns ............................................................................ 32

3.2 Data Collection And Data Processing .................................................... 33

3.3 Rain Rate Conversion ............................................................................. 37

3.4 Converted Rain Rate ............................................................................... 41

3.5 Type and the Characteristic of Intensity in Libya According to

Range of Rainfall Rate R .............................................................................. 43

3.6 Summary ................................................................................................. 43

CHAPTER FOUR .................................................................................................. 45

RAIN ATTENUATION PREDICTION AND ITS EFFECTS .......................... 45

4.1 Introduction ............................................................................................ 45

4.2 Rain Attenuation Analysis ...................................................................... 45

4.2.1 Effects Of Polarization .................................................................. 50

4.2.2 Effects Of Frequency Band ........................................................... 52

4.2.3 Effects Of Percentage Of Time Of The Year ................................ 55

4.3 Comparison With ITU-R Predicted Attenuation .................................... 56

4.4 Satellite Communication Link Design ................................................... 61

4.4.1 Rain Effects On Uplink And Downlink ........................................ 61

4.5 Performance Analysisi Of Satellite To Earth Microwave Link ............. 62

4.6 Summary ................................................................................................. 67

CHAPTER FIVE: CONCLUSION AND RECOMMENDATION ................... 69

5.1 Conclusion .............................................................................................. 69

5.2 Recommendation And Futre Work......................................................... 72

REFERENCES ....................................................................................................... 73

LIST OF PUBLICATIONS .................................................................................. 77

ix

LIST OF TABLES

Table No. Page No.

2.1 Articles in term of findings and limitations 30

3.1 Locations of 20 meteorological stations from which rainfall

data are collected

35

3.2 Measured Precipitation Data from 20 Meteorological

Stations

35

3.3 Measured Precipitation Data of 5 Selected Sites in Libya.

With 100% Availability of Rainfall Data during the Time

Period from 1981-2010

38

3.4 Comparison of converted 1- Min Rain Rate at 0.01% of

time in a year, Predicted by 6 Models at 5 Locations using

measured Data

40

3.5 Predicted One- Minute Rain Rate based on Chieko and

Yoshio Model for 20 Metrological Stations in Libya using

rainfall data from January 1981, to December 2010

41

3.6 Range of Rain Intensity R in Function of the Type and the

Characteristic of Intensity (Gustavo -2015)

43

4.1 Local Geometry Parameters For Five Stations in Libya. 46

4.2 Frequency-Dependent Regression Coefficients for

Estimating Specific Rain Attenuation

47

4.3 Estimated Rain Fades A0.01 (dB) for C, Ku, Ka, V-band

Downlink Frequency at Horizontal Polarization

50

4.4 Rain fades A0.01% (dB) for Uplink and Downlink frequency

in Tripoli

53

4.5 Calculated Rain Fades A0.01% (dB) for C, Ku, Ka, V-band

Downlink at Different Polarization for Benina and Tripoli

airport stations

54

4.6 Rain Fades A0.01 (dB) at Tripoli and Benina based on

Measured R0.01 For Downlink Frequency Bands at

Different % of Time of the Year

55

x

4.7 Comparison of Rain Attenuation A0.01% (dB) Based on

ITU-R Recommended and Measured R0.01% at Different

Percentage of the Time of the Year in Tripoli

56

4.8 Comparison of Rain Attenuation, A0.01% (dB) at Shahat 57

4.9 Estimated Rain Fades Ap (dB) at Different Percentages of

Time for Down link frequency bands at Horizontal

Polarization for the Maximum R0.01

58

4.10 Spectral Efficiency and Throughput in Satellite- to- Earth

Microwave Links working at Tripoli

64

4.11 Spectral Efficiency and Throughput in Satellite- to- Earth

Microwave Links working at Shahat (Maximum R0.01)

65

4.12 Spectral Efficiency and Throughput in Satellite- to- Earth

Microwave Links working in Sebha (Minimum Measured

R0.01).

65

xi

LIST OF FIGURES

Figure No Page No.

1.1 Rain Attenuation at Microwaves and Millimetre- Wave

Frequencies

3

1.2 A small portion of the satellite path is affected by rain which may vary with elevation angles

4

2.1 Explain Rain Rate And Losses Vary Along The Path

18

2.2 Schematic presentation of an Earth–Space path

22

2.3 Example CCDF curve for rain rate 27

2.4 a

Performance Threshold Link’s Performance Above Target

28

2.4b

Availability Threshold Link Is Not Available Due To Bad

Performance

34

3.1

Locations of national weather network stations-Libya.

Source

34

3.2 a

Cumulative Distribution Of Maximum Rain Rate

Variation At Shahat

38

3.2 b

Rain Rate Variation At Sebha In South Of Libya

38

3.2 c

Rain Rate Variation At Tripoli

39

3.2 d

Rain Rate Variation At Benina

39

3.2 e

Cumulative Distribution Graph Of Rain Rate Variation Of

Tripoli Airport

39

4.1

Rain Attenuation For C, Ku, Ka, V-Band Downlink At

Horizontal Polarization Using Minimum Measured Value

Of R 0.01

51

4.2

Rain Attenuation For C, Ku, Ka, And V-Band Downlink

At Horizontal Polarization Using Maximum Measured

Value Of R0.01%

51

4.3

Variation Of Rain Attenuation For C, Ku, Ka, And V-

Band Downlink At Horizontal Polarization In Tripoli At

Different Percentage Of Time Of The Year

54

xii

4.4

Comparative Of Rain Attenuation For Horizontal

Polarization In Tripoli At V Downlink Frequencies Band

57

4.5

Comparison Of Rain Attenuation For Horizontal

Polarization In Maximum At V Downlink Frequencies

Band

58

4.6

Comparative Plot Of Rain Attenuation For Horizontal

Polarization In Sebha At V- Downlink Frequencies Band.

59

4.7

Comparison of Rain Attenuation For Horizontal

Polarization In 5 Different Locations At V- Downlink

Frequencies Band

60

4.8

The relation between spectrum efficiency and SNR

63

xiii

LIST OF SYMBOLS

A Attenuation level in dB

A0.01 Attenuation exceed for 0.01% of the time in dB

d Path length

D Drop diameter

D0 Drop mean diameter

La Atmospheric losses

σ ζ Standard deviation of the conditional fade slope

Δh Altitude relative to the rain height in meters

γR Specific attenuation of rain in dB/km

E Expected value

f Frequency in Hz

Re Effective radius of the Earth (8 500 km)

hs Height above mean sea level of the earth station (km)

hR. Rain height as given in Recommendation ITU-R P.839

Ls Slant-path length, in km

LG Horizontal projection of the slant-path length in km

LE The effective path length through rain in Km

φ Altitude of the earth station

Θ Elevation angle (degrees)

r 0.01 Horizontal reduction factor for 0.01% of time

v0.01 Vertical adjustment factor, for 0.01% of time

β The thunderstorm ratio

k and α Frequency and polarization dependent coefficients

N(D) Drop size distribution

xiv

N0 Drop concentration at D = 0

Pr Received power

Pt Transmitted power

R Rain rate in mm/hr

R0.01% Rain rate exceeded for 0.01% of the time in mm/hr

R0.001% Rain rate exceeded for 0.001% of the time in mm/hr

T Number of hours in the year

Z Altitude

xv

LIST OF ABBREVIATIONS

ITU-R International Telecommunication Union- Radio Sector

DSD Drop Size Distribution

CD Cumulative Distribution

PDF Probability density function

CDF Cumulative Distribution Function

LNMC Libyan National Meteorological Center

BER Bit Error Rate

SNR Signal to Noise Ratio

FM Fade Margin

BW Band Width

FSPL Free Space Path Loss

EiRP Effective Radiated Power

1

CHAPTER ONE

INTRODUCTION

1.1 GENERAL OVERVIEW

Future satellite communication systems acutely require the use of higher frequency

bands in order to achieve larger bandwidths (Siles, Gustavo, et al, 2015). These bands

offer many advantages to satellite communication services and applications, in terms

of spectrum availability, reduced interference potential and minimized equipment size

(Owolawi,.2009 &Sujimol, et al,. 2015). However, rain attenuation is an important

challenge that limits the use of frequency above the 10 GHz and above in tropical and

sub-tropical regions. Atmospheric hydrometer affects the characteristic of the satellite

signals (Badron, et al. 2015). It causes considerable reduction in the density of an

electromagnetic wave as it propagates through the rain (Kamruzzaman et al, 2014).

Rain is therefore, directly responsible for link outages and causes link performance

degradation. Rain attenuates the signal, disturbs the polarization and increases system

temperature (Panchal& Joshi, 2016). In order to avoid these ramifications, an accurate

prediction of rain attenuation is of utmost significance while designing a reliable

microwave link at higher frequencies. The prediction methods require rain intensity at

one-minute integration time. In this study, one-minute integration time rain-rate

cumulative distribution (CD) has been derived from the total monthly rainfall

measured at 20 different meteorological stations in Libya over a span of 30 years.

Both converted as well as ITU-R proposed rain rates have been used to predict rain

fades at C, Ku, Ka and V-bands with Vertical, Horizontal and Circular polarized

2

waves for five stations in Libya. The performance of links has also been analyzed with

and without rains.

The Rainfall rate R (mm/h) is the most significant parameter to predict rain

attenuation in radio waves propagation. Rain fade is directly responsible for link

outages at Ku, Ka and future V-bands. Variations of rain fade with microwave

frequencies and rain intensities are shown in Fig. 1.1. The quality of services for

wireless communication depends strongly on it, especially at higher frequencies.

Signal attenuates because of absorption of the energy or by scattering of the energy

through raindrops. Attenuation depends on the frequency, wavelength of the signal

shape and size of raindrops as well as the effective path and rain rate (Siles, Gustavo

et al, 2015) as shown in Fig 1.2.

It is mentioned that in Tamosiunas, (2006) absorption causes attenuation more

than scattering if the wavelength is small compared to the drop size. On the other

hand, the attenuation caused by scattering is larger than absorption if the wavelength

is large compared to drop size. As well as rain attenuation higher at lower elevation

angle as the effective path passes the rain layer will be longer.

3

Figure 1.1 Rain attenuation at microwaves and millimetre- wave frequencies (E-Band

Technology, 2011)

Satellite link’s reliability depends mostly on convective rain. (Abdulrahman, et

al., 2015). In ŞEN & Eljadid, (1999) represents a Mediterranean climate region such

as Libya, whereas the temperate rain is mostly stratiform and widespread. Rain‐Rate

which vary in time and space randomly. Therefore the statistics of, Rain‐Rate and

related propagation effects are of major attention (Karagianni, et al., 2016). Hence, the

conditions of the electromagnetic wave propagation absolutely different in Libya

because of rain intensities vary significantly over large areas in the country. Thus,

rainfall rate cumulative distribution was derived in this work using long-term

statistical data. The highest and the lowest prediction of rain rate in the study of

interested locations are considered and analyzed.

4

Figure 1.2 A portion of the satellite path is affected by rain which varies with

elevation angles and rain characteristics

Satellite signals propagate long distance and decades exponentially as a

function of distance. As rain is not in the constant rate it fluctuates when the signals

propagate for the longer rainfall duration.

This dissertation aims at highlighting the importance of rain rate distribution and one-

minute rain rate data collection. Rain rate prediction models proposed by ITU-R,

Crane and Moupfouma have also been elaborated here. Additionally, to elucidate the

subject for better understanding, few prediction models, which convert rainfall data

from hourly/daily/ annual rainfall to rain rate with 1-minute integration time have

been presented in this dissertation. Apart from these, this dissertation also includes

conversion models proposed by Chebil, Rice Holmberg, Chieko Ito and Yoshio

Hosoya. Finally rain attenuation prediction proposed by ITU-R has been elaborated

step-by-step.

The following rainfall data has been collected from 20 meteorological stations

in Libya over a span of 30 years. This rainfall statistical data has been subsequently

recorded with 3-hours integration time and then eventually analyzed to be converted

Earth-station

Satellite

5

into one–minute rain rate cumulative distribution in Libya. Six conversion models

Chebil, modified-Chebil, Rice-Holmberg, Chieko and Yoshio, Crane global model,

and ITU-R have also been used in the process.

1.2 PROBLEM STATEMENT AND ITS SIGNIFICANCE

Rain attenuation is the most significant consideration to design an earth-to-satellite

links at higher frequencies. The consequences of this rain attenuation are degradation

of microwave link performance and increase link outage probability. The Problem

statement of this study is stated in the following points:

1. The lack of satellite propagation impairments studies in Libya and

consequently feasibility of future Ka and V-bands applications has not been

investigated thoroughly integration time is very long to assess the fluctuation

of rain attenuation.

2. No measurement for 1- minute rain rate in Libya is available in order to predict

rain fade on earth-to-satellite path operating at higher frequencies.

3. Suitable conversion model is required to convert annual and seasonal rainfall

data with longer integration time measured by meteorological department of

Libya for 30 years at more than 20 locations to 1-minute data.

1.3 PURPOSE OF THE STUDY

The purpose of this study is to help earth-to-space link designers for fixed satellite

communication services at Ku, Ka and V-bands for 20 stations in Libya by investigating

the effect of rain on microwave links. In order to predict the largest additional losses on

6

the free space that link will experience in the given reliability threshold of the satellite

links.

1.4 RESEARCH OBJECTIVES

The study is aimed to achieve the following objectives:

1. To convert available measured long term monthly rainfall data, collected from

different meteorological stations in Libya into one- minute integration time rain

rate

2. To predict rain attenuation in different frequency bands with different

polarizations and percentages of time of the year.

3. To analysis estimated rain fade margins and evaluate the earth-to satellite link

performances at different locations in Libya.

1.5 RESEARCH SCOPE

In this research only the rain attenuation prediction over Libya is considered. Monthly

rainfall data measured and recorded with 3- hours’ integration time in the Libyan

National Meteorological Center (LNMC) have been collected and processed. Data

were available at 20 stations in Libya over the 30 years-period from 1981 to 2010. In

this study, monthly total in (mm) are used from daily rainfall data. Since most of daily

rainfall records are zeros in arid regions. In addition to the 30 years commutative

rainfall data, the other parameters which are average annual total rainfall M (mm/yr),

the highest monthly precipitation Mm (mm/month), the average number of rainy days

in a year are utilized to estimate ratio of maximum monthly rainfall to the total

average rainfall accumulation (β). Predicted attenuation using ITU-R-618P-11 is used

7

to evaluate system performance for 0.01% exceedance attenuation value which gives

the 99.99% availability on a radio link .To elaborate attenuation variation

characteristics frequencies of C, Ku, Ka and V bands with different polarizations, and

various percentage of times are considered. ARABSAT-5A satellite located at 30.5E◦

would be used for reference. Predicted values of rain fade margin would be utilized to

analyses of satellite to earth microwave link performance.

1.6 RECHEARCH METHODOLOGY

In respect of the objectives outlined above, the following approaches are used in the

present study:

Step 1. Collecting and processing of rainfall data from Libyan nation metrological

center.

Step 2. Processing of rainfall data for 20 stations

Step 3. Conversion of long- term rainfall statistical data into 1-minute rain rate using

Matlab 7.0, which can be called in Microsoft Excel as a function. The parameters used

are:

Annual rainfall accumulation M in mm

Number of rainy days

Thunderstorm ratio β

Percentage of time unavailability Pin %.

Step 4. Selection of suitable conversion model ITU-R, Crane, Chebil, Rice-Holmberg

and Chieko-Yoshio models are investigated with 3 hourly measured data from 5

locations .Suitable conversion model is recommended for Libya.

8

Step 5. Conversion of 30 years measurement for 20 locations to 1-minute rain rate

using recommended conversion model.

Step 6. Prediction of rain attenuation at C, Ku, Ka and V-bands with horizontal,

vertical and circular polarization for 0.01% outages. MATLAB program has been

written for conversion

Step 7. Performance is analyzed based on link efficiency in bps/Hz and throughput in

Mbps. Performance parameters:

7 dB SNR

BER = 10-6 at clear air condition

Particular reliability to evaluate earth –to satellite microwave link in different

cities in Libya

1.7 ORGANIZATION OF THE DISSERTATION

This thesis presents five chapters. The first chapter provides an overall background of

the thesis, including research motivations, problem statement, research objectives,

research scope, and research methodology. The second chapter considers literature

review of the previous works done in the area. Strength and limits of each work are

critically reviewed in order to evaluate the performance of rain rate and rain

attenuation prediction models by considering the weather peculiarity in the study area

of interest. The research methodology procedure of this work is described in chapter

three. This chapter will describe data analysis and processing. The method of how to

convert the raw long term rainfall data to rain rate mm/h. Then the capability of some

working model of converting of annual rainfall data into 1-minute rain rate is

highlighted in this chapter.