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Introduction
It is widely acknowledged that the k-factor plays a key role in radiowave propagation, and therefore in all radio applications such as, for example, radio coverage planning, engineering of microwave links, interference estimates, etcetera. Because of this, a knowledge of the statistical distribution of the k-factor is of paramount importance from the radio spectrum conservation point of view. As the value of the k-factor is determined by radio meteorological conditions, it is important for this to be known locally as it mainly affects local conditions, which will naturally change from place to place.
It is a popular misconception that the traditional 4/3rds value for the k-factor is sufficient for radiocommunications planning. In areas of high usage of the radio spectrum there is acute frequency congestion across all planned frequency bands. The fundamental shift from fixed to mobile radio services, as exemplified by the ubiquitous cellphone, and thus in the use of the radio spectrum, as well as the higher complexity of such communications demands in mobile services because of dynamic frequency allocations, requires more accurate values of the k-factor for coverage and interference planning.
The present research is mainly focused on extending current expertise in radio refraction studies, developed in South Africa, by reviewing and confirming values of the k-factor around the country as well as taking such work further by modelling the k-factor distribution along terrain elevation.
This first chapter serves as an introduction to describe the research reported in this thesis. It places the work in perspective from the conception of the original topic, through its early development and further research in South Africa to date. The latest results reported in this work are intended to address present requirements of the radio community, and to bring the general application of the model in communications systems design a step closer.
The k-factor’s importance and motivation for the study
From experience in radio engineering practice, it became evident that it was necessary to study and develop the knowledge of the k-factor together with its properties further. This need was dictated by more demanding practical requirements for new complex radio planning of modern radio systems than has been the case until quite recently. It became apparent that the existing k-factor tables in common use would soon be inadequate for more sophisticated radio planning applications. New more refined models leading to a better understanding of the distribution of k-factor values would be urgently required.
The context of the k-factor study has not been simple, involving not only a practical study, but also empirical and theoretical studies to decide how relevant the topic was. It has been enlightening to see from the literature survey how scarce theoretical knowledge of the subject is. Apart from the fact that the concept is relatively young, and as far as can be established, first introduced by Baker (1927), there is no exclusive theoretical study devoted to the k-factor alone, despite the fact that it was acknowledged as a valid concept Wait (1960).
Initially, indeed, practical aspects prevailed in recognising the importance of the k-factor concept. Further work involving a search for a suitable function expressing the k-factor in terms of the refractivity gradient and the percentage of time for events, led to the theoretical study, further complemented by the literature survey to determine the status quo.
Chapter 1 INTRODUCTION AND BACKGROUND
1.1 Introduction
1.2 The k-factor’s importance and motivation for the study
1.3 Preliminary reading provides focus for the study of the k-facto
1.4 Identification of the research problem, questions and hypothese
1.5 Methodology, research design, structure of the study
1.6 Remainder of the thesis
Chapter 2 LITERATURE REVIEW
2.1 Introduction
2.2 Definitive References of the k-factor by background, history, concept, applications
2.3 Definitive references organised according to the k-factor and percentage of time for event
2.4 References directly supporting the hypotheses in this thesis
2.5 Indefinite references, supporting the current line of inquiry indirectly by examples
2.5.1 Terrestrial Microwave Radio-Network Applications
2.5.2 Examples of the use of the k-factor in airborne radar
2.5.3 Discussions of the ducting mode
2.5.4 Examples in Broadcasting
2.5.5 Review of Appropriate Engineering Models
2.5.5.1 The Okumura-Hata Model
2.5.5.2 Longley-Rice and Johnson-Gierhart Models
2.5.5.3 Jenkinson and Van Dijk
2.5.5.4 Harvey’s work
2.5.5.5 The EHF Telecommunication System Engineering Model (ETSEM)
2.5.5.6 Ground wave propagation over an irregular earth surface
2.5.5.7 Parabolic Equation Method
2.5.5.8 Ray Tracing method
2.5.6 Historic background where propagation development is validated
2.5.7 Other Southern African Studies
2.6 Conclusion
Chapter 3 THE AVAILABLE SOUTH AFRICAN DATA SOURCES AND THE FIRST HYPOTHESIS
3.1 Introduction
3.2 THE SOUTH AFRICAN DATA SOURCES
3.2.1 The SABC Data
3.2.2 The CSIR Data
3.2.3 The Comprehensive Set of Monthly Averaged Dat
3.4 Regression Analysis of Nel’s Data
3.5 Discussion of the combined model dry & wet – inclusion of the climatic term
3.6 Analysis of the Annual Average Data
3.7 Comparison of Predicted and Observed Cumulative Distributions for the Inland Stations
3.8 Discussion and Conclusion
3.9 Discussion of the First Hypothesis and its Consequences
3.10 New data from the SA Weather Service
3.11 New Data Processing & Results
3.12 Comparison between different models
3.13 Discussion of the empirical model based on Nel’s results
3.14 Comments on the New Model Derived from SA Weather Service Dat
3.15 Discussion of Results and Conclusion
Chapter 4 GEOGRAPHIC EXTENSION OF THE DATA ACROSS SOUTH AFRICA
4.1 Introduction
4.2 Analysis of the SABC and the CSIR Recommended Data
4.3 Algorithm Selection and Implementation
4.4 Geographic Data Extension by means of the Elliptic Model
4.5 Conclusions
Chapter 5 THE SEARCH FOR SUITABLE MODELS OF THE K-FACTOR FOR USE IN SOUTHERN AFRICA
5.1 Introduction
5.2 Features of the new model
5.3 Characteristics of the tropopause, scale height and the derivation of the Elliptic Model
5.4 Linear model from the experimental data and an analytic model as an extension to the empirical one
5.5 Non-linear Model obtained from a theoretical study
5.6 The Exponential Model
5.7 The Digital Terrain Model and Its Use in the Visualisation of k-factor contours
5.8 Distribution of the refractivity gradient on the DTM
5.9 Range of the normalised refractivity gradient used for map productions
5.10 Conclusion
Chapter 6 GENERAL DISCUSSION AND CONCLUSIONS
7 References
Appendix
