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

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.

Certification ii

Dedication iii

Acknowledgements iv

Table of contents v

List of Figures x

List of Tables xii

Abstract xvi

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

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, ÏÂ� (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.