RAIN MODELS FOR THE PREDICTION OF FADE DURATION

AT MILLIMETER WAVELENGTHS

MOHD AFZAN BIN OTHMAN

UNIVERSITI TEKNOLOGI MALAYSIA

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“To my beloved mother, father, fiancé and family…”

Thank you.

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ACKNOWLEDGEMENTS

Alhamdulillah. First of all, I would like to express my gratitude to Allah S.W.T because of his blessing; I have managed to complete my master project successfully within the given time without any difficulties.

Here, I wish to take this opportunity to express my appreciation and gratitude of myself to my helpful and knowledgeable supervisor, Assoc. Prof. Dr Jafri Din from Wireless Communication Center, UTM, whom I deeply indebted, in the process of finishing this project. Without his brilliant suggestions and encouragement, I would never be able to write this thesis completely as I am right now. Thank you so much for your commitment and your very active participation in helping me doing this project, and again, I am very proud to have you as a supervisor. Thank you so much.

Also, a million thanks to all of the lecturers in Faculty of electrical Engineering who involves direct or indirectly in this project. I am really appreciate of your great assistances and would like to truly thank you for your magnificent teaching, and also for the wonderful and worthwhile experience I had during my course of study in UTM.

Last but not the least, I would like to say thank you to all of my friends for their

helps, support, and valuable hints.

Finally, my heartfelt thanks and appreciation goes to my beloved family, especially my Mum and Dad; and most important of all, to my fiancée. I am really grateful to have them in my life. Thanks for all of your helps and supports when I am trapped in a difficult time. Thanks for everything you have done for me.

To all, I wish you success in your future endeavors. Thank you

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ABSTRACT

The planning of radio communications system requires an estimate of the

average annual outage due to fading, which at millimeter wavelengths, is generally

dominated by the effects of rain attenuation. Current ITU-R recommendations provide

algorithm for estimating the exceedance static of rain-induced attenuation on terrestrial

links. Another factor of interest, not currently covered by ITU-R recommendations is

the distribution of the durations of rain fades. Hence this project involved an extensive

review on the available models describing annual rain fade distributions on line-of-sight

links. Also, analysis on the rain attenuation data conducted on an experimental 350m,

and 38GHz in frequency in UTM campus for 1 year will be used to obtain information

on the rain fade statistic. Previous researches pointed out that the distribution of the

durations of rain events at different intensities is more fundamental than distributions of

link fades. Thus, this project aim is to establish an expression for the average number of

events per year of rain intensity greater than a given threshold. This could be achieved

from the detail analysis of the 38GHz link signal level profile database. Thus, the rain

fade statistic describing annual rain fade distributions on line-of-sight could be

developed. To predict rain attenuation on complex multi hop or route diverse links, it is

necessary to have a statistical representative of rainfall in time and space, which is

accurate over wide ranges of spatial and temporal scales. Various available statistical

models will be used to demonstrate the influence of the developed rain fade statistic

when applied for more complex microwave links.

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ABSTRAK

Pada masa kini, perkembangan dalam bidang telekomunikasi adalah amat

memberangsangkan. Untuk menghasilkan system telekomunikasi radio, perkara penting

yang amat dititikberatkan ialah kesan isyarat radio terhadap hujan. Di mana seperti yang

kita sedia maklum, bagi isyarat yang lebih daripada 10 GHz, kesan hujan terhadap

isyarat ini adalah sangat tinggi. Dengan itu ITU-R telah memperkenalkan algorithm

bagi menganggarkan kesan hujan ini. Tetapi ada satu lagi faktor yang tidak kelaskan

oleh ITU-R, iaitu masa semasa isyarat ini menjadi lemah disebabkan oleh kesan hujan.

Oleh itu, projek ini akan merangkumi analisis terhadap data yang diamabil di UTM

kampus bagi tempoh 1 tahun iaitu pada 1999, 350m, 38GHz serta mengenal pasti model

kesan hujan terhadap isyarat yang telah dicadangkan oleh beberapa penyelidik. Model

hujan yang sesuai dengan data yang sedia ada akan diambil sebagai rujukan dan

pemalarnya akan diubah mengikut kesesuaian data hujan di Malaysia. Tujuan projek ini

dilaksanakan adalah untuk mencari nilai purata ‘event’ ini berlaku bagi tempoh setahun.

Ini membolehkan kita membuat ramalan berapa lama isyarat akan menjadi lemah

bergantung kepada jumlah hujan yang turun. Maka dengan itu sebuah model yang baru

akan dihasilkan untuk meramalkan kesan hujan terhadap isyarat radio ini.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF ABBREVIATIONS xiii

LIST OF SYMBOLS xiv

LIST OF APPENDICES xv

CHAPTER I INTRODUCTIONS 1

1.1 Project Background 1

1.2 Problem Statement 3

1.3 Objective 4

1.4 Scopes of Project 4

1.5 Importance of the Project 5

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CHAPTER II LITERATURE REVIEW 7

2.1 Rain Attenuation on Satellite Communication 7

2.2 Fade Mitigation Techniques 9

2.2.1 Power Control 10

2.2.2 Signal Processing 11

2.2.3 Diversity 11

2.3 Available Prediction Models 12

2.3.1 ITU-R Model 12

2.3.2 Chris J. Gibbins/ Kevin S. Paulson 17

2.3.3 Kormayos/ Lena Pedersen/ Cyril Sagot/ 19

Janos Bito

2.4 Summary 21

CHAPTER III METHODOLOGY 22

3.1 Methodologies 22

3.2 Data Collection 24

3.3 Data Extractions 26

3.4 Existing Rain Models Programming 29

3.4.1 ITU-R Model Programming 30

3.4.2 Chris J. Gibbins/ Kevin S. Paulson 32

Programming

4.4.3 Kormayos/ Lena Pedersen/ Cyril Sagot/ 33

Janos Bito Programming

3.5 Comparison 33

CHAPTER IV RESULTS 35

4.1 Introduction 35

4.2 Measured Data Interpretations 35

4.2.1 Power Received 35

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4.2.2 Measured Data Analysis 37

4.3 Result and Analysis 41

4.3.1 Obtain Rain Fade Statistics 41

4.3.2 Comparison 45

CHAPTER V CONCLUSIONS 49

5.1 Conclusions 49

5.2 Future Works 50

REFERENCES 51

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LIST OF TABLES

TABLE NO TITLE PAGE

4.1 Convert AGC (V) to decibel (dBm) 38

4.2 Analysis on fade duration 40

4.3 Number of events which duration exceeds abscissa 42

at 1, 3, 6, 9, 12, 15, 18 and 21 dB levels

4.4 Number of events for each month over one year 44

4.5 Fade duration statistics information 46

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LIST OF FIGURES

FIGURE NO TITLE PAGE

1.1 Features characterizing the dynamic of fade 2

Events[1]

3.1 Research methodology flow chart 23

3.2 Path profile for Ericson Microwave Link at 25

38GHz in WCC, UTM

3.3 Rain rate contour map in Peninsular Malaysia 26

3.4 Read data form text file 27

3.5 Converts AGC (volts) values to dBm 27

3.6 Compile fade duration statistic for attenuation 28

exceeding threshold

3.7 Save fade duration statistics data to corresponding 29

files

3.8 Set parameters with correct values 30

3.9 Matlab programming for corresponding equations 31

3.10 Matlab programming for total numbers of fade 31

durations

3.11 Matlab programming for number of fades NA 32

3.12 Matlab programming for probability numbers of fades 33

durations

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3.13 Matlab programming for comparison among measure 34

data and studied rain fade models

4.1 Received power level time series on clear weather 36

4.2 Received power level time series on rainy weather 37

4.3 Power received signal attenuation 39

4.4 Analysis on fade duration 40

4.5 Fade duration grouping by attenuation levels 43

4.6 Fade duration grouping by months 45

4.7 Comparison among existed rain models with 47

measured data

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LIST OF ABBREVIATIONS

DTH - Direct To Home

FMT - Fade Mitigation Technique

MEASAT - Malaysia East Asia Satellite

WCC - Wireless Communication Centre

AGC - Automatic Gain Control

UTM - Universiti Teknologi Malaysia

CD - Cumulative Distribution

ITU-R - International Telecommunications Union - Radiocommunications

sec - seconds

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LIST OF SYMBOLS

f - frequency

φ - elevation angle

A - attenuation

σ - standard deviation

γ - power law distribution

Dt - boundary time

k - fraction time

Q - standard cumulative distribution function

N - number of fade events

R - rain rate

r - path reduction factor

L - path length

V - AGC value (volt)

R0.01 - rain intensity at 0.01% of time

dBm - decibel meter

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LIST OF APPENDICES

APPENDIX TITLE PAGE

A FLOW CHART 53

B PROGRAMMING CODES 57

CHAPTER I

INTRODUCTIONS

1.1 Project Background

The planning of radio annual outage due to fading at millimeter wavelengths is

generally dominated by the effects of rain attenuation. This is usually determined from

long-term statistic of annual rainfall rates, applying the procedures in ITU-R

Recommendation P.530 for terrestrial links.

In the design of a variety of telecommunication systems, the dynamic

characteristics of fading due to atmospheric propagation are of concern to optimize

system capacity and meet quality and reliability criteria. Examples are fixed networks

that include a space segment and systems that apply fade mitigation or resource sharing

techniques.

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Several temporal scales can be defined, and it is useful to have information on

fade slope, fade duration and interfade duration statistics for a given attenuation level

(Figure 1.1).

Figure 1.1: Features characterizing the dynamic of fade events [1]

Fade duration is defined as the time interval between two crossings above the

same attenuation threshold whereas interfade duration is defined as the time interval

between two crossings below the same attenuation threshold. Fade slope is defined as

the rate of change of attenuation with time. Of particular interest in the context of

availability criteria is the distinction between fades of shorter and longer duration than

10 s. Knowledge of the distribution of fade duration as a function of fade depth is also a

prerequisite for the application of risk concepts in the provision of telecommunication

services.

In addition, information about the expected fade slope is essential to assess the

required minimum tracking rate of a fade mitigation system.

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1.2 Problem Statement

Nowadays, the advancement in microwave communication technologies

especially in telecommunication and broadcasting has resulted in congestion for

frequencies below 10GHz. This has forced microwave designers to look for higher

frequencies. Unfortunately for the frequencies that greater than 10GHz, rain become the

main factor of attenuation especially for tropical and equatorial countries that

experience high rainfall rate throughout the year such as in Malaysia. Where is for the

frequencies above 10GHz, it will lead to outages that compromise the availability and

quality of service, making this one of the most critical factors in satellite link design.

Thus, in some cases the use of suitable compensation techniques to counter excessive

attenuation will be needed to maintain reliable system operation. The proper design of

fade mitigation techniques on satellite links requires not only knowledge of long-term

statistics, but also of second-order statistics describing the dynamic behavior of

attenuation, such as duration of fades, duration between fades and fade rate. So due to

this circumstance it is important to have a predication of fade duration.

Usually, fade duration statistics are presented as conditional distributions of the

number of fades exceeding certain durations, given that specified fade threshold has

been exceeded. This representation provides information on the number of outages and

system availability due to propagation on a link, given a fade margin and an availability

specification.

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1.3 Objective

The main objective of this project is to estimate of the average number of events

per year of rain attenuation greater than a given threshold. As we know, the cumulative

probability distribution of the system (take Astro as an example) will down for one year

is about 0.01%. This downtime is equal to 52mins/year that the signal will drop due to

the attenuation of rain. In this case we don’t know the exact number of events occur per

year, how much the signal drop and also the duration for one event occurs. Hence, this

project is expected to answer all of the questions stated previously.

1.4 Scope Of Project

This project will involve an extensive review on the available models describing

annual rain fade distribution on line-of-sight links. There are many fade duration

models that was published in order to predict the rain fade duration. The examples of

the published prediction models of fade duration are;

• ITU-R Model [1]

• Chris J Gibbins and Kevin S Paulson [2]

• Zsolt Kormanyos/ Lena Pedersen/ Cyril Sagot/ Janos Bito [3]

• Mopfouma [4]

• A two component rain model [5]

Details on ITU-R Model [1], Chris J Gibbins and Kevin S Paulson [2] and Zsolt

Kormanyos/ Lena Pedersen/ Cyril Sagot/ Janos Bito [3] will be discussed in the next

chapter.

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Secondly, do analysis on the available rain attenuation data in UTM. This data

was conducted on an experimental 350m, 38GHz by Wireless Communication Center

(WCC) [6]. At first, the purpose of these rain attenuation data is to produce cumulative

distribution (CD) of rain attenuation data. And for the purpose of this project, these data

will be used to obtain information on the rain fade statistics.

This rain fade statistics will be developed by using Matlab software. The result

from this rain fade statistics will be used to compare with the available empirical

models. The best empirical models that suit to the obtained rain fade statistic will be

adopted as rain fade model in Malaysia.

1.5 Importance Of The Project

Fade duration is an important parameter to be taken into account in system design for

several reasons;

• System outage and unavailability: fade duration statistics provide information on

number and duration of outages and system unavailability due to propagation on

a given link and service;

• Sharing of the system resource: it is important from the operator’s point-of-view

to have an insight into the statistical duration of an event in order to assign the

resource for other users. For example, nowadays most of the telecommunication

systems are based on bandwidth on demand. In this case, when signal is dropped

then we must assign small bandwidth to users in order to make sure that C/N

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(Carrier to Noise ratio) is high. If not, user will no longer receive any signal

during that event;

• FMT (Fade Mitigation Technique): fade duration is of concern to define

statistical duration for the system to stay in a compensation configuration before

coming back to its nominal mode. This FMT will be discussed in more detail

later;

• System coding and modulation: fade duration is a key element in the process of

choosing forward error correction codes and best modulation schemes; for

satellite communication systems, the propagation channel does not produce

independent errors but blocks of errors. Fade duration impacts directly on the

choice of the coding scheme (size of the coding word in block codes,

interleaving in concatenated codes, etc.).

REFERENCES

[1] ITU-R P.1623-1, “Prediction method of fade dynamics on Earth-space paths”,

ITU, Geneva, 2005

[2] Paulson, K.S.; Gibbins, C.J.; “Rain models for the prediction of fade duration at

milimetre wavelengths”, IEEE Journal, Volume 147, Issue 6, Dec. 2000

Page(s):431 – 436

[3] Zsolt Kormayos, Lena Pedersen, Cyril Sagot, Janos Bito; “Rain attenuation and

fade duration statistic at 38 GHz derived from long term radio link measurement

in Hungary, Norway and Ireland”, AP2000, Davos, 13 April 2000

[4] F. Moupfouma and L. Martin, “Point rainfall rate cumulative distribution

function valid at various locations,” Electronic Letters, vol. 29, no. 17, pp. 1503-

1505, 1993

[5] M.M.J.L. van de Kamp; “Short-term prediction of rain attenuation using two

samples”, Electronic Letters, vol. 38, no. 23, pp. 1476-1477, 7th November 2002

[6] R. Singliar, J. Din, L. Csurgai, A.R. Tharek, P. Horvath and J. Bito,

“Comparison of 38 GHz rain fade dynamics between Malaysia and Hungary”,

15th IST Mobile & Wireless Communication Summit Myconos 4-8 June 2006

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[7] ITU-R P.618-6, “Propagation data and prediction methods required for the

design of earth-space telecommunication systems”, ITU, 1999

[8] ITU-R P.838-6, “Specific attenuation model for rain for use in prediction

methods”, ITU, 1999

[9] ITU-R P.530-8, “Propagation data and prediction method required for the design

of terrestrial line of sight systems”, ITU, 1999

[10] J.W.F. Goddard and M. Thurai, “Radar derived path reduction factors for

terrestrial systems,” Proc. Tenth International Conference on Antenna and

Propagation, ICAP’ 97, 14-17 April 1997, Edinburg UK, pp. 2.218-2.221