UNIVERSITI PUTRA MALAYSIA EFFECT OF RAINFALL RATE …Kajian ini fokus kepada kesan hujan dan jerebu...

UNIVERSITI PUTRA MALAYSIA

EFFECT OF RAINFALL RATE AND VISIBILITY ON FREE SPACE OPTICAL COMMUNICATIONS IN MALAYSIAN ENVIRONMENT

BIBI SARPINAH SHEIKH NAIMULLAH

FK 2004 93


By


Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Partial Fulfilment of Requirements for the Degree of Master of Science

October 2004

In the name of God, Most Gracious, Most Merciful

Dedication to

My parents

ii

Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirements for the degree of Master of Science


By


October 2004

Chairman: Associate Professor Mohd. Khazani Abdullah, Ph.D.

Faculty: Engineering

Rare usage of Free Space Optical (FSO) communications in Malaysia might be

related to environmental factors. Unguided beam is also known as free space optics

technology or ‘optical wireless’ or ‘infrared broadband’. This project explores the

propagation of point-to-point FSO due to weather conditions. Weather severity has

detrimental impact on FSO transmission performance. The impact could result in

insufficient quality of transmission and communication failure. Therefore FSO

implementation requires thorough study of local weather patterns. By studying the

local weather pattern, scattering coefficient and atmospheric attenuation could be

derived to determine weather severity in this area. This information could help in

predicting possible impact on data transmission quality and transmission interference

system operation. In addition, FSO system design could be improved and altered to

overcome possible interference and optimize system operation.

iii

This study is focused on the effect of rain and haze in Subang Airport. The Climate

Division of Meteorological Department, Petaling Jaya branch, provided the data on

rain and haze, which were collected hourly throughout year 2000. The rain data,

which were collected in mm/hr, are categorized into three groups: heavy rainfall,

moderate rainfall and light rainfall. The haze data was collected based on visibility

distance in km. The visibility on hazy days is categorized into low visibility and

average visibility.

The non-selective scattering contributed dominant loss on rainy days and Mie

scattering on hazy days. The non-selective scattering is wavelength independent and

Mie scattering is wavelength dependent. The wavelength of 1550nm is selected

because it is not harmful to the human eyes, not aggressive to the environment and

contributes to better performances.

The scattering coefficient and atmospheric attenuation for rain and hazy days are

determined by using Stroke Law and Beer’s Law. The atmospheric attenuation due to

scattering coefficient has greater effect during hazy days than rainy days. From the

result analysis, using small beam divergence, small transmitter aperture, larger

receiver aperture and short link distance can optimize the FSO system transmission.

iv

Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi sebahagian keperluan untuk ijazah Master Sains

KESAN TABURAN HUJAN DAN JARAK PENGLIHATAN PADA OPTIKAL WAYARLES KOMUNIKASI DALAM PERSEKITARAN MALAYSIA

Oleh


Oktober 2004

Pengerusi: Profesor Madya Mohd. Khazani Abdullah, Ph.D. Fakulti: Kejuruteraan Penggunaan komunikasi Ruang Bebas Optik masih kurang mungkin disebabkan oleh

faktor persekitaraan. Projek ini mengkaji kaitan faktor persekitaraan dengan

mengkaji penyebaran titik ke titik Ruang Bebas Optik yang berpunca dari keadaan

cuaca. Kesan ini menyebabkan kualiti penghantaran kurang baik dan komunikasi

gagal. Oleh itu sebelum pemasangan Ruang Bebas Optik, kajian yang rapi perlu

dibuat ke atas keadaan cuaca tempatan. Dengan membuat kajian ke atas keadaan

cuaca, serakan koefisien dan gangguan di atmosfera diperolehi. Informasi ini boleh

dipeolehi dengan mengandaikan kesan yang mungkin terjadi pada kualiti

penghantaran data. Nilai andaian ini adalah untuk tujuan reka bentuk dan

memastikan minimum gangguan yang terjadi dalam operasi penghantaran.

Kajian ini fokus kepada kesan hujan dan jerebu di Lapangan Terbang Subang. Data

hujan dan jerebu disediakan oleh Bahagian Cuaca, Jabatan Meterologi, cawangan

Petaling Jaya. Data tersebut berdasarkan bacaan untuk setiap satu jam. Data hujan

diambil dalam mm/jam dan boleh dikategorikan kepada tiga kumpulan: hujan lebat,

v

hujan sederhana dan hujan renyai. Jerebu pula dibaca mengikut jarak penglihatan

dalam km. Jarak penglihatan boleh dikategorikan kepada jarak penglihatan rendah

dan jarak penglihatan biasa. Serakan koefisien dan gangguan di atmosfera dipeolehi

dengan menggunakan persamaan matematik.

Penyelerakan bukan terpilih terjadi paling dominan pada hari hujan dan penyelerakan

Mie terjadi pada hari berjerebu. Penyelerakan bukan terpilih tidak bergantung dengan

panjang gelombang manakala penyelerakan Mie bergantung dengan panjang

gelombang. Panjang gelombang 1550nm dipilih kerana tidak mendatangkan kesan

bahaya pada mata, tidak berbahaya pada persekitaran dan perlaksanaan yang lebih

baik.

Kesan perlemahan atmosfera bergantung pada penyelerakan pemalar adalah lebih

besar pada hari berjerebu berbanding dengan hari hujan. Daripada keputusan analisis,

didapati penghantaran pada Ruang Bebas Optik boleh dioptimakan dengan

mengunakan sinaran sudut yang kecil, diameter apertur alat pemacar yang kecil ,

dimater apertur penerima yang luas dan jarak pendek antara pemancar dan penerima.

vi

ACKNOWLEDGEMENTS

First and foremost, all praise and thanksgiving to Allah the Almighty, for gracing me

with strength to complete of my thesis. Alhamdullilah.

I would like to express my deepest gratitude to my supervisor Dr Mohd Khazani

Abdulllah and the committee members, Dr Mohd Azhir Mahdi and Dr Kaharudin

Dimyati for their guidance, advice and encouragement throughout the completion of

my thesis.

To Pn Salasiah Hitam, Pn Nuriza, and Pn Rahmah, I would like to extend special

word of thanks for their support and guidance to provide valuable information during

my thesis completion.

I would like to express my appreciation to En. Azhar and all staff of Malaysian

Meteorological Department, Climate Division, Petaling Jaya for their assistance in

data collection.

My gratitude also goes to the members of Photonic Laboratory and staff of

Communications and Networking Department especially to Azura, for their

assistance and contribution of my thesis and to all of my friends for their moral

support throughout my study in UPM.

Last but not least I would like to express my sincere thanks to my family for being

patient and supported me throughout my study. Without their for being patient and

support I would not have made it till to the end.

vii

I certify that an Examination Committee met on 29 October 2004 to conduct the final examination of Bibi Sarpinah Sheikh Naimullah on her Master of Science thesis entitled “The Effect of Rainfall Rate and Visibility on Free Space Optical Communications in Malaysian Environment” in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulations 1981. The Committee recommends that the candidate be awarded the relevant degree. Members of the Examination Committee are as follows:

Abdul Rahman Ramli, Ph.D. Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman) Sabira Khatun, Ph.D. Faculty of Engineering Universiti Putra Malaysia (Member) Syed Javaid Iqbal, Ph.D. Faculty of Engineering, Universiti Putra Malaysia. (Member) Zainol Abidin Abdul Rashid, Ph.D. Associate Professor Faculty of Engineering Universiti Putra Malaysia (Independent Examiner)

GULAM RUSUL RAHMAT ALI, Ph.D. Professor / Deputy Dean School of Graduate Studies Universiti Putra Malaysia Date:

viii

This thesis submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfilment of the requirement for the degree of Master of Science. The members of the Supervisory Committee are as follows:

Mohammad Khazani Abdullah,Ph.D. Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman)

Mohd Adzir Mahdi,Ph.D. Associate Professor Faculty of Engineering Universiti Putra Malaysia (Member)

Kaharuddin Dimyati,Ph.D. Associate Professor Faculty of Engineering Universiti Malaya (Member)

__________________ AINI IDERIS, Ph.D. Professor/Dean School of Graduate Studies Universiti Putra Malaysia

Date:

ix

DECLARATION

I hereby declare that the thesis is based on my original work except for the quotations and citations which have been duly acknowledged. I also declare that it has not been previously or currently submitted for any other degree at UPM or other institutions. __________________________ BIBI SARPINAH SHEIKH NAIMULLAH Date:

x

TABLE OF CONTENTS

Page

DEDICATION ii ABSTRACT iii ABSTRAK v ACKNOWLEDGMENTS viii APPROVAL ix DECLARATION x LIST OF TABLES xiii LIST OF FIGURES xiv LIST OF ABBREVIATION xvi CHAPTER 1 INTRODUCTION

1

1.1 Introduction 1.2 Background

1.3 Statements of Problems and Motivation 1.4 Objectives 1.5 Scope of Works

1.5.1 Study Model Description 1.5.2 Assumptions

1 1 3 4 4 4 7

1.6 Thesis Organization 1.7 Conclusions

9 10

2 LITERATURE REVIEW 11 2.1 Introduction 11

2.2 Optical Communications 2.2.1 FSO Architecture

11 13

2.2.2 FSO Applications 16 2.2.3 FSO Advantages 2.2.4 Disadvantages

2.3 Comparison of Broadband Access Technologies 2.4 FSO System

2.4.1 Wavelength 2.4.2 Beam Angle 2.4.3 Diameter Aperture 2.4.4 Range

2.5 Atmospheric Effect

19 20 22 22 24 27 30 31 32

2.5.1 Absorption 2.5.2 Scattering 2.5.3 Atmospheric Turbulence

32 36 39

xi

2.6 Rainfall Rate 2.6.1 Effect of Rainfall Rate on FSO System

40 42

2.7 Haze Visibility 2.7.1 Effect of Haze Visibility on FSO System

2.8 Attenuation 2.8.1 Atmospheric Attenuation 2.8.2 Total Attenuation

2.9 Conclusions

3 METHODOLOGY 3.1 Introduction

3.2 Data Analysis 3.2.1 Rain 3.2.2 Reading Data 3.2.3 Haze Visibility

3.3 Scattering Coefficient in Rainy Days 3.4 Atmospheric Attenuation in Rainy Days 3.5 Scattering Coefficient in Hazy Days 3.6 Atmospheric Attenuation in Hazy Days 3.7 Total Attenuation

3.7.1 Total Attenuation in Rainy Days 3.7.2 Total Attenuation in Hazy Days

3.8 Conclusions

4 RESULTS AND DISCUSSION 4.1 Introduction 4.2 Results

4.2.1 Scattering Coefficient in Rainy Days 4.2.2 Atmospheric Attenuation in Rainy Days

4.2.3 Scattering Coefficient in Hazy Days

44 45 47 47 50 51

52 52 52 52 52 54 59 61 62 63 64 65 66 67

68 68 68 69 73 75

4.2.4 Atmospheric Attenuation in Hazy Days 4.3 Geometric Loss 4.4 Total Attenuation in Rainy Days 4.5 Total Attenuation in Hazy Days 4.6 Discussions

4.6.1 Rain Effect on FSO System 4.6.2 Haze Effect on FSO System 4.6.3 Geometric Loss on FSO System 4.6.4 Total Attenuation Effect in Rain and Haze Days

4.7 Comparison Result with ITU-R Model 4.8 Conclusions

78 83 85 91 99 99 101 102 102 103 105

5 CONCLUSION AND RECOMMENDATIONS

5.1 Introduction 5.2 Conclusion 5.3 Recommendations For Future Research

106 106 107 108

REFERENCES APPENDICES

93

BIODATA OF THE AUTHOR 98

109 113 116

xii

LIST OF TABLES

Table Page

2.1 Subdivisions of the infrared 13

2.2 Comparison of Broadband Access Technologies 22

2.3 Maximum Permissible Exposure limit for ‘unaided viewing’ 26

2.4 Diameter of transmitter and receiver aperture of FSO 30

2.5 Radius range of different types of particles 38

2.6 International Visibility Code for Weather Conditions 46

3.1 Sample Data Records of Hourly Weather Conditions 55

3.2 Data of Rainfall 56

3.3 Data of Haze Visibility 59

3.4 Uncontrollable Parameters and Performance Parameter (Rain) 60

3.5 Uncontrollable Parameters and Performance Parameter (Rain) 61

3.6 Design Parameters and Performance Parameter (Rain) 61

3.7 Uncontrollable Parameters and Performance Parameter (Haze) 62

3.8 Design Parameters and Performance Parameter (Haze) 62

3.9 Uncontrollable Parameters and Performance Parameter (Haze) 63

3.10 Design Parameters and Performance Parameter (Haze) 63

3.11 Design Parameters and Performance Parameter (Rain) 66

3.12 Design Parameters and Performance parameter (Haze) 66

4.1 Comparison Result in Rainy Days 103

4.2 Comparison Result in Hazy Days 104

xiii

LIST OF FIGURES

Figure Page 1.1 Study Model Showing the Scope of Study 6

2.1 Point to Point Architecture 14

2.2 Point to Multipoint Connections 14

2.3 Multipoint to Multipoint Connections 15

2.4 Metro Network Extensions 17

2.5 FSO Redundancy Link 18

2.6 Personal Cellular Service (PCS) Backhaul 18

2.7 Schematic showing FSO transmitter and receiver mounted on top of

two building 24

2.8 Wavelength > 1400nm; Light absorbed in cornea and lens 26

2.9 Spread of the central maximum in the far field diffraction pattern 28

2.10 A 1mrad beam divergence produces a spot size of 1m in diameter at a

range of 1km 28

2.11 Absorption curve for CO2 34

2.12 Absorption curve for water vapor 34

2.13 Atmosphere absorption for solar energy 35

2.14 Patterns of Rayleigh, Mie and Non-selective scattering 38 2.15 The process of scattering 38

2.16 Laser beam wander due to turbulence cells that are larger than the

beam diameter 39

2.17 Scintillation or fluctuations in beam intensity at the receiver due to

turbulence cells that are smaller than the beam diameter 40

2.18 Several rain droplets process 41

2.19 Scattering Efficiency, Q(x) versus Ratio of Raindrop radius to

wavelength (a/λ) 43

xiv

2.20 FSO losses 48 2.21 Factors that effect on the link performance 48 3.1 Rain recorder 53 3.2 Inside part of Rain recorder 53 3.3 Rain gauge 54 3.4 A θ mrad with diameter of transmitter aperture d1(m) produces

spot size of d3(m) 65

4.1 Scattering coefficient as a function of rainfall rate 69

4.2 Velocity versus Radius of Raindrop 71 4.3 Scattering Coefficient versus Radius of Raindrop 72 4.4 Atmospheric Attenuation versus Rainfall Rate 73 4.5 Atmospheric Attenuation Versus Range 74 4.6 Scattering Coefficient versus Average Visibility 75

4.7 Scattering Coefficient versus Low Visibility 77 4.8 Atmospheric Attenuation versus Average Visibility 78 4.9 Atmospheric Attenuation versus Low Visibility 79

4.10 Atmospheric Attenuation versus Link Range 81

4.11 Geometric Loss versus Diameter Transmitter Aperture 83

4.12 Geometric Loss versus Diameter Receiver Aperture 84

4.13 Total Attenuation versus Rainfall rate 85

4.14 Total Attenuation versus Link Range in Heavy Rain 87

4.15 Total Attenuation versus Beam Divergence 89 4.16 Total Attenuation versus Average Visibility 91 4.17 Total Attenuation versus Low Visibility 93

4.18 Total Attenuation versus Link Range 95

4.19 Total Attenuation versus Beam Divergence 97

xv

LIST OF ABBREVIATIONS

CLEC - Competitive Local Exchange Carrier

CO2 - Ground State Absorption

FCC - Federal Communications Commission

FIR - Far Infrared

FSO - Free Space Optical

GL - Geometric Loss

H2O - Water

IEC - International Electrotechnical Commission

IR - Infrared

IP - Internetworking Protocol

ITU-R - International Telecommunications Union – Radio

Communications

LASER - Light Amplified Spontaneous Emission

LAN - Local Area Network

LOS - Line Of Sight

MIR - Middle Infrared

MPE - Maximum Permissible Exposure

MST - Malaysian Station Time

NIR - Near Infrared

OSI - Open System Interconnect

PCS - Personal Cellular Service

RF - Radio Frequency

SONET - Synchronous Optical NETwork

ST - Station Time

xvi

xvii

US - United State

WDM - Wavelength Division Multiplexing

XIR - Extreme Infrared

CHAPTER 1

INTRODUCTION

1.1 Introduction

Transmission through light has been developed since the nineteenth century. In 1880,

Alexander Graham Bell expanded optical communications with his ‘photo-phone’

that modulated sunlight for communication. In the early 1960’s, scientists have

successfully developed Light Amplification by Stimulated Emission of Radiation

(LASER) technology. Finally, optical communication was shortly discovered after

the development of LASER technology (FSO, 2003 & Johnson, 2002).

1.2 Background

There are several options for data communication in the existing technology today.

First is fiber optic cable technology. It is the best choice in the telecommunications

industry. Fiber is the most reliable for many applications in various areas in

communication connectivity. However, using fiber optic is extremely uneconomical.

This is because the costs of trenching street to lay fibers are excessively high.

Another option is radio frequency (RF) technology. RF is a mature technology, but is

limited in data rate, requires FCC licensing and is costly relative to other access. RF

technology cannot scale to 2.5Gbps. The current RF bandwidth ceiling is 622

Megabits. When compared to Free Space Optical, RF does not make economic sense

for service providers looking to extend optical networks (Rockwell, 2001).

1

The third alternative is wire and copper based technologies. The percentage of

copper technology use is higher than fiber, but it does not solve the bottleneck of

connectivity problem and bandwidth capability limitation. Losses in copper cables

increase with the frequency, the more information carried in copper conductors, the

higher the losses.

The fourth and often most popular alternative is Free Space Optical (FSO). FSO

provides higher bandwidth to the end user at a faster speed. Because of high

bandwidth availability (currently capable of up to 2.5Gbps), a large amount of data

can be transmitted through a narrow laser beam. FSO is also portable, quickly

deployable and cost effective, costing on average one-fifth the cost of installing fiber

optic cable (Willebrand, 2001).

2

1.3 Statement Of Problems And Motivation

FSO systems are sensitive to poor weather conditions such as fog, haze and rain.

All of these conditions act to attenuate light and could block the light path in the

atmosphere. As a result, interruption and disturbance could occur in the

communication process.

Before the installation process of FSO on tall buildings, detailed investigation of

weather conditions have to be carried out. This is to ensure FSO will operate with

sufficient transmission power and minimal losses, even during bad weather

conditions.

This project is a FSO system propagation study on atmospheric effect in the

Malaysian weather environment. The study focused more on rain and haze effects,

on the FSO system. The selection of wavelengths, divergence angle, receiver area,

transmitter area and distance between transmitter and receiver can be adjusted to

minimize the attenuation effect on FSO. Further discussion will be elaborated later

in this project.

3

1.4 Objectives

The main limitation in FSO is proper understanding of weather effects on its signal

propagation. The analysis based on weather statistics should be conducted at a

specific location to estimate the link availability. Therefore the main objectives of

this project are stated below:

a) To study the propagation of infrared signals in rain and haze conditions.

b) To determine the scattering coefficient, atmospheric attenuation and total

attenuation due to rainy and hazy days by using Stroke Law and Beer’s Law

c) To study the performance of FSO under different wavelengths, beam angles,

diameters of receiver and transmitter apertures and link range.

1.5 Scope of Works

1.5.1 Study Model Description

FSO is an independent protocol that can be fixed to any network topology. The Open

System Interconnect (OSI) for FSO is under physical layer. The scope of this project

is shown clearly under study model in Figure 1.1. Generally, FSO system is divided

into two categories: indoor system and outdoor system. This study concentrated on

propagation study of FSO under Malaysian weather environment for outdoor system,

especially dealing with atmospheric effect and total attenuation.

The atmospheric effect can be divided into 2 categories: atmospheric attenuation and

atmospheric turbulence. Scattering due to water droplets (rainfall) effect is called

non-selective scattering. This scattering is a wavelength independent process. Mie

scattering dominates total scattering coefficients on haze days. Attenuation due to

4

5

Mie scattering is a function of the visibility and laser wavelength. Mie scattering

effect depends on wavelength.

In examining FSO performance, it is important to take several system parameters

into consideration. This project concentrated on rain and haze conditions. The

parameters can be divided into 3 categories: design, uncontrollable performance

parameters. Design parameters are related to design of the FSO system such as

wavelength, aperture size, beam divergence and link range. Uncontrollable

parameters are related to weather conditions. Uncontrollable parameters on rain

conditions include rainfall rate and radius of raindrop. The uncontrollable parameters

of hazy conditions are related to visibility. Performance of rain and haze conditions

can be evaluated from scattering coefficient effect, atmospheric attenuation and total

attenuation.

Free Space Optical

Outdoor Indoor

Propagation study onWeather

Atmospheric Effect

AtmosphericAttenuation

AtmosphericTurbulence

Scattering Absorption

Rayleigh MieNon Selective /

Geometric

Rain

Haze

Total Attenuation

UncontrollableParameters

DesignParameters Performance

ParametersUncontrollable

Parameters DesignParameters

PerformanceParameters

Haze Rain

DesignParameters




DesignParameters


a) Visibility a) Wavelengthb) Link Range a) Rainfall Rate

b) Radius of Raindrop

a) Link Range

a) Velocityb) Scattering Coefficientc) Atmospheric Attenuation

a) Scattering Coefficientb) Atmospheric Attenuation

a) Visibility a) Aperture Sizeb) Link Rangec) Beam Divergence

a) Total Attenuation

a) Aperture Sizeb) Link Rangec) Beam Divergence

a) Rainfall Rateb) Radius of Raindrop

a) Total Attenuation

Scintillation

Figure 1.1: Study Model Showing the Scope of Study

6

1.5.2 Assumptions

There are a few assumptions made in this project. The effect of aerosol absorption,

Rayleigh scattering, scintillation fluctuation and background noises are assumed to be

negligible. There are some reasons of ignoring these effects as stated below. The

detailed explanation is given in Chapter 2.

The laser wavelengths of 780nm, 850nm and 1550nm fall inside the transmission

windows within the absorption spectra and the contributions of absorption to the total

attenuation coefficient are very small; thus absorption effect is negligible (as shown in

Figure 2.13). FSO systems are operated in the longer wavelength near infrared

wavelength range so the impact of Rayleigh scattering on the transmission signal can be

ignored (Chu, 2002).

Using either multiple beams or larger receiver apertures could reduce scintillation

fluctuations. However, the large receiver aperture approach is more effective for

scintillation reduction than multiple smaller apertures. Besides that, the longer

wavelength is less susceptible to scintillation. At ranges less than 1km, most FSO

systems have enough dynamic range or margin to compensate for scintillation effects

(Kim, 2001, Achour, 2001 & Bloom, 2003). In this project a larger receiver aperture is

used, wavelength of 1550nm is considered and link range is only 1km. Therefore effect

of scintillation is ignored.

7

UNIVERSITI PUTRA MALAYSIA EFFECT OF RAINFALL RATE …Kajian ini fokus kepada kesan hujan dan jerebu...

Documents

Transcript of UNIVERSITI PUTRA MALAYSIA EFFECT OF RAINFALL RATE …Kajian ini fokus kepada kesan hujan dan jerebu...