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STUDIES OF PROPAGATION IMPAIRMENTS FOR FIXED SATELLITE COMMUNICATION LINKS AT THE MICROWAVE FREQUENCIES IN NIGERIA

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ABSTRACT
The study investigates the effect of propagation impairments such as rain, cloud, gases
and tropospheric scintillation on fixed satellite communication link on earth-space path for
frequencies between 10 and 50 GHz at Ku, Ka and V bands for 37 locations in Nigeria. Two
standard elevation angles of 50, 550 as well as some elevation angles for links to recently
launched Nigeria Communication Satellite, (NigComsat-1) were used in the computation of the
propagation impairments for the 37 locations. Linearly and circularly polarized waves were
considered. The International Telecommunication Union Radiowave Propagation models (ITURP) were used in the investigation of the propagation impairments. The study is divided into three parts; firstly, the collection and analysis of meteorological data from Tropical Rain
Measurement Mission (TRMM) and Atmospheric Infrared Sounder (AIRS) satellites such as rain accumulation, profiles of temperature, pressure, and relative humidity, surface temperature and pressure were validated with the available ground data in Nigeria to form statistics on monthly and annual basis. These are reprocessed to derive propagation parameters, such as; one-minute rainfall rate, water vapour density, total cloud liquid water content, and integrated water vapour content. Secondly, an appropriate ITU-RP propagation model was selected for each of the propagation impairment and was used to calculate each attenuation distribution for a percentage of time unavailability. Thirdly, the attenuation due to all impairments were combined based on the annual cumulative distribution and percentage of time unavailability between 0.01 to 10%. The calculation of the propagation parameters are based on the measured mean annual data in each location for the period of 4 to 9 years. Propagation impairments were also computed at Ku, Ka and V bands for links to NigComsat-1 at 0.01 to 10% of time unavailability in an average year. The results of all impairment were compared on regional basis by using a colour chart for all the 37 locations in Nigeria. The results of the predicted propagation impairments are as follows: rain attenuation is highly severe in Abakaliki the South-East (SE) region followed, in descending order, by Yenagoa the South-South (SS), Ibadan South-West (SW), Jos Middle-Belt (MB), Damaturu North-East (NE), and Kastina North-West (NW) regions. Cloud attenuation is highly severe in Abakaliki the SE region followed, in descending order, by Jos (MB), Gombe (NE), Dutse (NW), Ikeja (SW), and Calabar (SS) regions. Gaseous attenuation is highly severe in Calabar the (SS regions) followed, in descending order, by Ikeja (SW), Abakaliki (SE), Abuja(MB), Dutse the (NE) and Kastina (NW) regions. Tropospheric scintillation is very high in Calabar (the SS region) followed, in descending order, by Ikeja (SW), Owerri (SE), Abuja (MB), Dutse (NE) and Kastina (NW) regions. Combined impairments due to multiple sources of simultaneously occurring atmospheric attenuation is highly severe in Abakaliki the (SE region)
followed, in descending order, by Uyo (SS), Ikeja the (SW), Markudi (MB), Maiduguri (NE) and Katsina (NW) regions. For links to NigComsat-1 the combined impairments due to multiple sources of simultaneously occurring atmospheric attenuation is highly severe in Yenagoa the (SS region ) followed, in descending order, by Owerri (SE), Ibadan (SW), Jos (MB), Damaturu the (NE), and Katsina (NW) regions. Overall, Sokoto and Katsina appear as good locations to site fixed satellite earth stations (operating at Ku band and above) for deep space exploration as the results obtained showed consistently that the two locations are less affected by all propagation impairments investigated.
TABLE OF CONTENTS
Title page i
Certification ii
Dedication iii
Acknowledgements iv
Table of contents v
List of Figures x
List of Tables xii
Abstract xvi
CHAPTER ONE
1.1 Introduction 1
1.2 Statement of the Problem 2
1.3 Rationale for the study 3
1.4 Aim and Objectives of the study 4
CHAPTER TWO
PROPAGATION IMPAIRMENTS AND MEASURING TECHNIQUES 6
2.1 Scattering and Absorption by Single Particles 6
2.1.1 Cross section and Scattering Amplitude 7
2.2 Propagation Impairment Mechanisms 8
2.3 Impairment by Rain 9
2.3.1 Characteristics of rainfall in tropical region 9
2.3.2 Types of Cloud 10
2.3.3 Stratiform and Convective Rain 12
2.3.4 Raindrop size and shape 13
2.3.5 Raindrop size distribution models 14
2.3.6 Models of Rain Attenuation Statistics 16
2.3.7 Methods of rain attenuation measurements 18
2.3.8 Rain Data Source 19
2.3.9 Processing of Rain Data 20
2.4.0 Computer program to compute one minute rainfall rate 21
2.4.1 Station height above mean sea Level 21
2.4.2 00C Isotherm height and Rain height 22
2.4.3 Calculation of long-term rain attenuation statistics from point rainfall rate 24
2.4.4 Empirical scaling formula 27
2.4.5 Some Geometrical Parameters Relevant to the Study of Rain Attenuation at
Selected 37 stations in Nigeria 27
2.5.1 Impairment by Clouds 29
2.5.2 Cloud Data sources 30
2.5.3 Cloud Data processing 31
2.5.4 Procedure for evaluation of SVD, TCC and IWVC 31
2.5.5 Surface Water Vapour Density, Ï (SVD) 31
2.5.6 Total columnar content of liquid water in clouds (TCC) 32
2.5.7 Integrated Water Vapour Content (IWVC) 33
2.5.8 Computer Program to Evaluate SVD, TCC and IWVC 34
2.5.9 Procedure for Evaluation of Cloud Attenuation 36
2.5.9.1 Specific Cloud attenuation coefficient 36
2.5.9.2 Computer Program for Attenuation due to Cloud 37
2.6 Impairment by Atmospheric Gases 38
2.6.1 Gaseous Specific Attenuation 39
2.6.2 Input Data sources for Gaseous Attenuation 39
2.6.3 Procedure for the Computation of Gaseous Attenuation 41
2.6.4 Gaseous Attenuation along Slant Paths 44
2.6.5 Computer program for evaluating evaluate gaseous attenuation 46
2.7 Tropospheric Scintillation 47
2.7.1 Amplitude Scintillation Prediction Models 47
2.7.2 Input Data Sources for Evaluation of Tropospheric Scintillation 48
2.7.3 Procedure for evaluating the input parameters 49
2.7.4 Calculation of monthly and long-term statistics of amplitude
Scintillations at elevation angles greater than 4° 49
2.7.5 Computer program for the Evaluation of Tropospheric Scintillation 51
2.8 Methods of Combining Propagation impairments 54
2.8.1 Combination of Different Attenuation Effects 54
2.8.2 Equiprobability Summing 54
2.8.3 Convolution method 54
2.8.4 Disjoint summing 55
2.8.5 Root-sum-square addition 55
2.8.6 Coherent summing 56
2.8.7 Prediction of Combined Propagation Effects 56
2.8.8 Estimation of Total Attenuation due to Multiple Sources of Simultaneously
Occurring Atmospheric Attenuation 57
CHAPTER THREE
RESULTS AND DISCUSSION
3.0 Validation of TRMM Data with Measured Rainguage data in Nigeria 59
3.1 Nine-year Results of Rain Events as Recorded by TRMM Satellite at
37-Locations in Nigeria 62
3.1.1 Year to Year Variation of the derived one-minute Rain rate from TRMM Data 65
3.1.2 Cumulative Distribution of Rainfall rates in Six regions 68
3.1.3 Comparison with Other Works 69
3.2 Results of Rain Attenuation 73
3.2.1 Rain Attenuation at Ku, Ka and V-Bands for Horizontally polarized Wave Unavailability
for 0.01% in an Average year at the 37-locations in Nigeria 76
3.2.2 Application of Rain Attenuation to NigComSat-1 at Ku and Ka for 0.01-1%
unavailability at the 37-Locations in Nigeria. 80
3.2.3 Rain Attenuation Results for Links to NigComSat-1 at Ku, Ka and V Downlink
Frequencies for a VSAT at 0.01 to 10% Unavailability of an Average at the 37-
locations in Nigeria 82
3.3 Results of Cloud attenuations for 1% Unavailability of an Average Year 87
3.3.1 Cloud Attenuations Results at Ku, Ka and V bands for 1% Unavailability of an
Average Year at the 37 Locations in Nigeria 90
3.3.2 Cloud Attenuation for Links to NigComSat-1 at Ku, Ka and V-band for
0.01-10% Unavailability of an Average Year 93
3.4 Gaseous Attenuation for 1% unavailability of an average year at the 37 Locations
In Nigeria 97
3.4.1 Gaseous Attenuations at Ku, Ka and V bands for 1% Unavailability of an Average
Year at the 37 Locations in Nigeria 100
3.4.2 Gaseous Attenuation for Links to NigComSat-1 at Ku Ka, and V-bands for
1% Unavailability of an Average at the 37-locations in Nigeria 103
3.5 Scintillation Fade depth for 0.01% unavailability at 50 and 550 for the 37-Locations in Nigeria 105
3.5.1 Scintillation Fade Depth for the 0.01% Unavailability at Ku, Ka and V-band at the 37 locations in Nigeria 108
3.5.2 Scintillation Fade Depth for Links to NigComSat-1 at Ku and Ka for 0.01 - 10% Unavailability of an Average at the 37-locations in Nigeria 111
3.6 Combined Attenuation for 0.01% Unavailability of an Average Year for Frequencies 10 to 50 GHz at the 37-Locations in Nigeria 115
3.6.1 Combined Attenuation at Ku, Ka and V-bands for 0.01% unavailability in an Average Year at the 37 Locations in Nigeria 118
3.6.2 Combined Attenuation at Ku, Ka and V-bands for Downlinks from NigComsat-1 at the 37 Locations in Nigeria from 0.01 to 10% Unavailability in an Average Year 121
CHAPTER FOUR
4 Summary and Conclusions 129
4.1.1 Rain Attenuation at frequencies between 10 to 50 GHz 129
4.1.2 Rain Attenuation Study at Links to NigComSat-1 at Ku and Ka from 0.01-1%
Unavailability of an Average Year 129
4.2. Cloud Attenuation at frequencies between 10 to 50 GHz 130
4.2.1 Cloud Attenuation Study for Links to NigComSat-1 at Ku and Ka from 0.01-1%
Unavailability of an Average Year 130
4.3 Gaseous Attenuation Study at 1% unavailability for frequencies between
10 to 50 GHz 130
4.3.1 Gaseous Attenuation Study for Links to NigComSat-1 at Ku and Ka for 1%
Unavailability of an Average year at the 37 locations 130
4.4 Tropospheric Scintillations Study at 0.01% unavailability of an Average
Year for Frequencies 10-50GHz at the 37 Locations in Nigeria 130
4.4.1 Scintillation fades depth Study for Links to NigComSat-1 at Ku and Ka for
0.01 to 10% Unavailability of an Average at the 37-locations 131
4.5 Combined Attenuation Study at 0.01% Unavailability of an
Average Year for Frequencies between 10 to 50 GHz 131
4.5.1 Results of Combined Attenuation Study at Ku, Ka and V-bands for Downlinks
from NigComsat-1 for 0.01 to 10% Unavailability in an Average Year at the
37-Locations in Nigeria 131
4.6 Conclusions and Recommendations 132
REFERENCES 134
Appendix 142 
LIST OF FIGURES
Figure                                                            Title Page
1.1 Map of Nigeria showing the 37 stations used in the study 5
2.1 Illustrating a single Scattering process 7
2.2 Types of Cloud 10
2.3 The Ten Basic Cloud Types 12
2.4 Raindrop size and shape 14
2.5 Schematic presentation of an Earth-space path giving the parameters to be input into the attenuation prediction process 24
2.6 Illustration of the A-Train Satellites 31
3.1 Cumulative Distribution of Rainfall rates for the 37-locations in Nigeria 68
3 .2 Rain Attenuation in Nigeria for 0.01% unavailability of an Average Year for Horizontal polarization at 50 elevation 74
3.3 Rain Attenuation in Nigeria for 0.01% unavailability of an Average Year for Horizontal polarization at 550 elevation 75
3.4 Rain Attenuation Cumulative distribution for links to NigComsat-1 at Ku"band (11GHz) 84
3.5 Rain Attenuation Cumulative distribution for links to NigComsat-1 at Ka"band (20GHz) 85
3.6 Rain Attenuation Cumulative distribution for links to NigComsat-1 At V"band (40GHz) 86
3.7 Cloud Attenuation at the 37 locations for 1% of an Average Year at 50 elevation 88
3.8 Cloud Attenuation at the 37 locations for 1% of an Average Year at 550 elevation 89
3.9 Cloud Attenuation Cumulative distribution at Ku (11GHz) downlink Frequency from NigComsat-1 for the 37 locations 94
3.9.1 Cloud Attenuation Cumulative distribution at Ka (20GHz) downlink Frequency from NigComsat-1 for the 37 locations 95
3.9.2 Cloud Attenuation Cumulative distribution at V (40GHz) downlink Frequency from NigComsat-1 for the 37 locations 96
3.10 Gaseous Attenuation at the 37 location in Nigeria for 1% Unavailability at 50 Elevation 98
3.11 Gaseous Attenuation at the 37 location in Nigeria for 1% Unavailability at 550 Elevation 99
3.12 Tropospheric Scintillation in Nigeria for 0.01% Unavailability of an Average year at 50 Elevation 106
3.13 Tropospheric Scintillation in Nigeria for 0.01% Unavailability of an Average year at 550 Elevation 107
3.14 Tropospheric Scintillation Cumulative distribution at Ku (11GHz) downlink Frequency from NigComsat-1 for the 37 locations 112
3.15 Tropospheric Scintillation Cumulative distribution at Ka (20GHz) downlink Frequency from NigComsat-1 for the 37 locations 113
3.16 Tropospheric Scintillation Cumulative distribution at V (40GHz) downlink Frequency from NigComsat-1 for the 37 locations 114
3.17 Combined Attenuation due to Cloud, Gases, Scintillation and Rain in Nigeria for Horizontal Polarization at 50 elevation 116
3.18 Combined Attenuation due to Cloud, Gases, Scintillation and Rain in Nigeria
for Horizontal Polarization at 550 elevation 117
3.19 Combined Attenuation due to Rain, Cloud, Scintillation and Gases at Ku (11GHz) for links to NigComsat-1 122
3.20 Combined Attenuation due to Rain, Cloud, Scintillation and Gases at Ka (20GHz) for links to NigComsat-1 123
3.21 Combined Attenuation due to Rain, Cloud, Scintillation and Gases at V  (40GHz) for links to NigComsat-1 124
LIST OF TABLES
Table                                                                       Title Page
1.1 Frequency Bands used in Satellite Communication 2
2.0 Particles Responsible for Atmospheric Scattering 6
2.1 Approximate height ranges at which bases of cloud are found 11
2.2 List of the input parameters necessary for rain attenuation prediction models 17
2.3 Topographic data: Heights above Mean sea level (m), Zero degree Isotherm
Height (m) and Rain height (km) for the 37- locations in Nigeria 23
2.4 Some Geometrical Parameters Relevant to the Study of Rain Attenuation at
5 and 55 degrees elevations for the 37 locations 28
2.5 Summary of the input Climatic data for Cloud and Gaseous Attenuations
Derived from AIRS Satellite data from AUG 2002-JUL 2006 35
2.6 Summary of the input Climatic data for Computation of Gaseous Attenuations
Derived from AIRS Satellite data from AUG 2002-JUL 2006 40
2.7 Summary of Climatic Parameters Needed for the Computation of Tropospheric
Scintillation Derived from AIRS Satellite data, Average value from
Aug 2002- Jul 2006 52
2.8 Geometrical Parameters Relevant to Scintillation Fade Depth for Downlink
from NigSatcom-1 for the 37-locations 53
3.1 The Seasonal Variation of Mean Precipitation, Percentage Mean Bias Error and
Overall Correlation Coefficients 61
3.1b Comparison of the 3-yr mean seasonal rainfall (mm/month) of this work with
other climatic regions in Africa 62
3.2 Summary of Rain Events in Nigeria derived from TRMM 3B43V6 data
January 1998-December 2006 64
3.3 Year to Year Variations of One-minute Rainfall rates (in mm/h) Exceeded for
0.01% of an Average Year Derived from TRMM 3B43V6 Satellite Data:
January 1998 to December 2006 66
3.4 Statistical Summary of One-minute Derived Rainfall rates Exceeded for 0.01%
of an Average Year from TRMM 3B43V6 Data: Jan 1998-Dec 2006 67
3.5 Correlation of the Derived One-minute Rainfall rates with Other Works 70
3.5b Measured One-minute Rainfall rates for Tropical and Subtropical Locations
around the World Compared with some Tropical and Subtropical Stations in
Nigeria for the Present study 72
3.6 Calculated Attenuation due to Rain at 5 degrees Elevation for Ku, Ka and
V bands Uplink and Down link Frequencies for Horizontal Polarization for
the State Capitals in Nigeria 78
3.7 Calculated Attenuation due to Rain at 55 degree Elevations for Ku, Ka and
V bands Uplink and Down link Frequencies for Horizontal Polarization in
the State Capitals in Nigeria 79
3.8 Some Geometrical Parameters Relevant to NigComSat-1 at Downlink
Frequencies at Ku, Ka, and Extended to V Bands for Future Communication
 Satellite at 0.01%Unavailability 81
3.9 Calculated Attenuation due to Cloud at 50 Elevations for Ku, Ka and V Bands
Uplink and Downlink frequency for the State Capitals in Nigeria 91
3.9.1 Calculated Attenuation due to cloud at 55
0 Elevations for Ku, Ka and V Bands
Uplink and Downlink frequency for the State Capitals in Nigeria 92
3.10 Results of Gaseous Attenuation at 5 degree Elevations for Ku, Ka and V Bands
Uplink and Downlink Frequencies for the 37-Locations in Nigeria 101
3.11 Results of Gaseous Attenuation at 55 degree Elevations for Ku, Ka and V Bands
Uplink and Downlink frequencies for the 37-Locations in Nigeria 102
3.12 Gaseous Attenuation relevant to link to NigComSat-1 at 1% unavailability at Ku,
Ka and V Satellite Bands 104
3.13 Results of Tropospheric Scintillation at 5 Degree Elevation for 0.01%
Unavailability at Ku, Ka and V Bands, Uplink and Downlink, Frequencies, for
the State Capitals in Nigeria. 
3.14 Results of Tropospheric Scintillation at 55 Degree Elevation for 0.01%
Unavailability at Ku, Ka and V Bands, Uplink and Downlink, Frequencies, for the State Capitals in Nigeria. 110
3.15 Combined Attenuations due to Cloud, Gas, Rain and Scintillation at 50 Elevations for Ku, Ka and V bands Uplink and Downlink Frequencies for Horizontal Polarization in the State capitals in Nigeria 119
3.16 Combined Attenuations due to Cloud, Gas, Rain and Scintillation at 55
0 Elevations for Ku, Ka and V bands Uplink and Downlink Frequencies for
Horizontal Polarization in the State capitals in Nigeria 120
3.17 Combined Attenuations due to Cloud, Gas, Rain and Scintillation at Ku-bands
Downlink from NigComsat-1 for Horizontal Polarization for the State capitals in Nigeria 126
3.18 Combined Attenuations due to Cloud, Gas, Rain and Scintillation at Ka-bands
Downlink from NigComsat-1 for Horizontal Polarization for the State capitals in Nigeria 127
3.19 Combined Attenuations due to Cloud, Gas, Rain and Scintillation at V-bands Downlink from NigComsat-1 for Horizontal Polarization for the State capitals in Nigeria 128
4.1 Summary of all propagation impairments in Nigeria by region from 10-50GHz 132
A1 Results of Rain Attenuation (in dB) for 0.01 % Unavailability for Vertical Polarization at 5 degree elevation 143
A2 Results of Rain Attenuation (in dB) for 0.01 % Unavailability for Circular Polarization at 5 degree elevation 144
A3 Results of Rain Attenuation (in dB) for 0.01 % Unavailability for Vertical Polarization at 55 degree elevation 145
A4 Results of Rain Attenuation (in dB) for 0.01 % Unavailability for Circular Polarization at 55 degree elevation 146
A5 Results of Rain Attenuation (in dB) for links to NigComsat-1 at 0.01 % Unavailability for Horizontal Polarization 147
A6 Results of Rain Attenuation (in dB) for links to NigComsat-1 at 0.01 % Unavailability for Vertical Polarization 148
A7 Results of Rain Attenuation (in dB) for links to NigComsat-1 at 0.01 % Unavailability for Circular Polarization 149
A8 Matlab 7.0 Functions for the Computation of Climatic input Parameters Needed for Propagation Studies 150
A9 Matlab 7.0 Functions for the Computation of Attenuations Due to Rain, Gas, Cloud, Tropospheric Scintillation 151
A10 Matlab 7.0 Programs for the Computation of Climatic input Parameters Needed for Propagation Studies 152
A11 Matlab 7.0 Programs for the Computation of Attenuations Due to Rain, Gas, Cloud, Tropospheric Scintillation 155
A12 TRMM Instruments and Flight Characteristics 167
A13 NigComsat-1 Characteristics 170

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