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Some engineering considerations forover-the-horizon communication systems
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Authors El Hammali, Zakaria Ahmed
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Link to Item http://hdl.handle.net/10150/557674
- SOME ENGINEERING CONSIDERATIONS FOR "
' OX^ER-THE-HORIZON COMMDNICAf ION SYSTEMS
byZakaria Ahmed El Hammali
A Thesis Submitted to the Faculty of the DEPARTMENT of electrical engineering
In Partial Fulfillment of the Requirements For the Degree of
MASTER OF SCIENCE
In the Graduate College
THE UNIVERSITY OF ARIZONA
19 8 1
STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfillment of the requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.
Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
^ Z a r rIY CHARLES SCHOOLEY Associate Professor of Electrical Engineering
/Date
ACKNOWLEDGMENTS
I wish to thank the members of my thesis committee for their guidance, particularly Professor Larry Schooley, my thesis advisor,
and Professor Reagan.
I would like to thank my father, Ahmed, for his inspiration,
cooperation, patience and care.
TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS . . . . . . . . . . . . . . . . . . . . vii
LIST OF TABLES . . .............. .. i . . . xi
ABSTRACT . . ...................... . . . . . . . . . . . . . xii
OVER THE HORIZON COMMUNICATIONS— INTRODUCTION . . . . . . . . 1GENERAL ASPECTS OF OVER THE HORIZON COMMUNICATIONS . . . . . 3
Introduction . . . . . . . 32.1 General Properties of the Troposphere . . . . . . . . 32.2 Tropospheric Propagation Mechanism . . . . . . . . . 72.3 System Considerations ......... . . . . . . . . . . 82.4 Diversity Techniques . . ........... 102.5 Antennas and Transmission Lines . . . . . ... . . . . 122.6 Modulation and Detection Techniques . . . . . . . . 182.7 Bandwidth Capability ........... 212.8..Typical Tropo Equipment . . . . . . ............. . 22
2.8.1 High Power Transmitter . . . . .. . . .' . . 222.8.2 Receiving Equipment . 242.8.3 Low Noise Amplifier.................... 262.8.4 Threshold Extension Demodulator ........ 302.8.5 Combiner . . . . . . . . . . 34
2.9 Advantages of Tropo . . . . . . . ... . . . . . . . 38
OVERALL SYSTEM DESIGN OF TROPOSPHERIC SCATTERRADIO LINKS . . . . . . . . . . . . . . . . . . . . . . . . 39
Introduction . . . . . . . . . . ............ 393.1 Definition of Q u a l i t y ...................... 403.2 Calculation of the Quality Required
for a System .............. 423.2.1 Design Objective of a System
Having a Quality of Class I . . . . . . 423.2.2 Design Objectives of a System.
Having a Quality of Class II . . . . . . 433.3 System Design Procedure . . . . . ............ 46
TRANSMISSION LOSS . . . . . . 53
4.1 Surface Refractivity (NS) . . . . . . . . . . . . . 534.2 Scatter Angle (9) . . . .............. 584.3 Basic Median Transmission Loss (Lbms) . . . . . . . 62
iv
VTABLE OF CONTENTS— Continued
Page4,4 Antenna-to-medium Coupling Loss . . . . . . . . , . . 63"4«5 Feeder System Loss (Lt+Lr) . . . . . . . . . . . . . 704«6 Received Power (Pr) . , . . . . . . . . . . . * . , . 714.7 Fading Depth (F^) . . . . . 72 -
5. SIGNAL-TO-NOISE RATIO . . . . . . . . . . . . . 82
5.1 Diversity Improvement (U) . . . . . . . . . . . . . . 825.2 Signal-to-thermal Noise Ratio (S/N^) . . . . . . . . 825.3 Signal-to-path Intermodulation Noise
Ratio ( S / N x ) .............. ................... ... . 845.4 Signal-to-intermodulation Noise
Due to Feeder Echo (S/Np) . . . . . . . . . . . . . 865.5 Overall Signal-to-noise Ratio (S/N) . . . . . . . . . 87
6. DESIGN OF A LINK BETWEEN JALO AND KUFRAH IN LIBYA . . . . . . 92
6.1 Path and Equipment Parameters . , . . . . . . . . . . 92-6.2 Radio Frequency Arrangements . . . . . . . . . . . . . 986o3 Performance Objectives . . . . . . . . . . . . . . . 986.4 Noise Performance Calculation . . . . . . . . . . . . 98
7. PROPAGATION TEST BETWEEN JALO AND KUFRAH . . . ........ . . . . 114 -
7.1 Test Schedule . . . . . . . . . . . . . . . . . . . . 1147.2 Test Links . . . . . . . . . . . . . . . . . . . . . 1147.3 Testing Facilities . .............. 1157.4 Test Results and Considerations . . . . . . . . . . . 115
7.4.1 Basic Transmission Loss .. . . . . . . . . 1157.4.2 Daily Variations of Basic
Transmission Loss . 115.. 7,4.3 Signal-to-noise Ratio . . . . . . . . . . 115
7.5 Test Results and Propagation Characteristics . . . . 1267.5.1 Variation of the Receiving
/ Input Level . . . . . . . . . . . . . . 1267.5.2 Transmission Loss (Lbmg) . . . . . . . . . 1317.5.3 Comparison between Calculated and
Measured Values of the PropagationLoss . . . . . . . . . . . . . . . . . . 131
7.6 System Performance . . . . . . . . . . . . . . . . . 1337.6.1 General Description . . . . . . . . . . . 1337.6.2 S/N Throughout the Link . . . . . . . . . .133
viTABLE OF CONTENTS— Continued
Page7.6.3 Seasonal Variation of the S/N
Distribution . . . . . . . . . . . . . . 1347.6.4 TV Transmission ............ 134
8. SUMMARY AND CONCLUSIONS . .......... 136
APPENDIX A: DESIGN GRAPHS FOR DIFFERENT VALUES OFNg AND DIFFERENT C L I M A T E S .............. 138
APPENDIX B: PROPAGATION LOSS AND S/N CURVES FOR THEJALO-KUFRAH LINK . . .' . . . . . . . . . . . . . 149
APPENDIX C; SIGNAL-TO-NOISE RATIO IN OVERALL SYSTEM(BY STATISTICAL COMBINING METHOD) . . . . . . . 204
APPENDIX D: A COMPARISON OF SOME TROPOSCATTERPREDICTION METHODS . . ........ . . . . . . . . 210
LIST OF REFERENCES . . . . . . . . . ........... 214
LIST OF ILLUSTRATIONS
Figure Page2*1 Graphic Representation of a Tropospan . . . . . . . . . . 42.2 Quadruple Diversity Distributions . . .......... . . . 132.3 Dual Diversity Distributions . . . . . . . . . . . . . 14
2.4 Octuple Diversity Distributions . . . . . . . . . . . . . . 15
2.5 Correlation Coefficient (Frequency) Measured ......... 16
2.6 Correlation Coefficient (Space) Measured . . . . . . . . 17
2.7 Comparative Performance of FM and SSB . . . . . . . . . . 19
2.8 Relative Distribution of Energy in FM S i g n a l ......... 20
2.9 Curve of F(a/ac). . . . . . . . . . . . . . . . . . . . . 232.10 Block Diagram of 2 GHz Transmitter for Dual or
Quadruple Diversity ................ 252.11 Explanatory Circuit of Parametric Amplifier . . . . . . . 27
2.12 Block Diagram of 2 GHz Parametric Amplifier............ 29
2.13 Threshold* Extension Demodulator using FMNegative Feedback . . . . . .......... . . . . . . . . 31
2.14 Threshold Extension Demodulator using FM FeedbackPhase Detection System . . . . . . . . . . ........ . 33
2.15 Block Diagram of an IF Combiner for Frequency Diversity . 36
2.16 Block Diagram of a Quadruple Diversity Receiver . . . . . 37
3.1 Allowable Noise . . . . . . . . . . . . . . . . 44
3.2 Allowable Noise for 20% of Worst Month . . . . . . . . . 47
3.3 Allowable Noise 'for (a) 63,,000 PWP of Worst Month;and (b) 1,000,000 PW .................. 48
vii
viiiLIST OF ILLUSTRATIONS— •Continued
Figure Page3.4 Relation of Hop-distance vs. Overall Noise
Level (Worst Month) . . . . . . . . . . . . . . . . . . 514.1 Path Geometry of Troposcatter Radio System ............. 564.2 Minimum Monthly Surface Refractivity Values
Referred to Mean Sea Level . . . . . . . . . . . . . . 57
4.3 Ng Variations with Antenna Height.......... 594.4 Effective Earth's Radius 'a' vs. Surface
Refractivity 'Ng' .......... 61
4.5 The Attenuation Function, F(0d) . .............. 64
4.6 Estimate of Median Oxygen and Water Vapor Absorptionfrom August Data, Washington, D. C . . . ... ........ 65
4.7 The Function V(0.5,d^) for Eight Climatic Regions . . . . 66
4.8 Antenna to Medium Coupling Loss .......... 694.9 Composite Distribution Curve of Long-term Fading and
Short-term Fading for Non-diversity . . . .......... 75\ ■
4.10 Transmission Loss Variability . • * • • . • • . . . . . • 76
4.11 Parameter.dsl. . • •..™. . . . . • . ■ . « . * . . . . . . . • 774.12 Composite Distribution Curve of Long-term Fading and
Short-term Fading for Dual Diversity . . . . . . . . . 79
4.13 Composite Distribution Curve of Long-term Fading andShort-term Fading for Quadruple Diversity . . . . . . . 80
4.14 Composite Distribution Curve of Long-term Fading andShort-term Fading for Octuple Diversity . . . . . . . . 81
5.1 Diffusion Factor of Antenna Beam Width . . . . . . . . . 89
5.2 Feeder Echo Intermodulation Distortion . . . . . . . . . 90
5.3 Overall Noise Performance of Example Link(Weighted Value ) . . .............. 91
ixLIST OF ILLUSTRATIONS— Continued
Figure •' Page6c 1 Propagation Path Route M a p ............ 93
6c2 System Block Diagram . . . . . . . . . . . . . 94
6.3 Profile Map (4/3 Radius), Jalo-Zighan . . . . . . . . . 101
6.4 Profile Map (4/3 Radius), Zighan-Kufrah Mtn . . . . . . . 1026.5 Profile Map (4/3 Radius), Kufrah City-Kufrah Mtn . . . . . . 1036.6 Frequency Arrangement for Troposcatter Radio Link . . . . 104
6.7 Frequency Arrangement for L.O.S. Radio Link . . . . . ... 105
6.8 Noise Performance (TP): Jalo-Zighan Link . . . . . . . . . . 110
6.9 Noise Performance (TV): Jalo-Zighan Link . . . . . . . . Ill
6*10 Noise Performance (TV): Zighan-Kufrah Mtn. Link . . . . . . 112
6.11 Noise Performance (TP): Zighan-Kufrah Mtn. Link . . . . . 113
7.1 Block Diagram for Measurement of Propagation Characteristics, Jalo - Kufrah Mtn. Troposcatter Link . . . . . . . 117
7.2 Variation of Receiving Signal Level .............. 118
7.3 Cumulative Distribution of Transmission Loss(One Hour Median) . . . . . . . . . . . . . . . . . . . 119
7.4 Annual Transmission Loss Cumulative Distribution(One Hour M e d i a n ) ............ 120
7.5 Amplitude of Daily Variations in Hourly Median Value ofReceiving Signal Level: Jalo-Zighan Link . . . . . . . 121
7.6 Amplitude of Daily Variations in Hourly Median Values ofReceiving Level: Zighan-Kufrah Mtn. Link . ...........122
7.7 Variation of Signal-to-noise Ratio in dB . . . . . . . . . 123
7.8 Annual Signal-to-noise Cumulative Distribution(One Hour Median) . . . . . . . . . . . . . . . . . . . 124
X
Figure
7.9
7.10
7.117.12
7.13
LIST OF ILLUSTRATIONS— Continued
Signal-to-noise Cumulative Distribution (One Hour Median) for Jalo-Zighan and Zigham-Kufrah Mountain Links During the Months of August 1978 ............ .
Variation of Signal-to-noise Ratio for J-Z Hop . . . . . .
Variation of Signal-to-noise Ratio for K-Z Hop ..........Daily Variations of Receiving Input Level: May-August . .Daily Variations of Receiving Input Level: January-March . .........' ............. '.........
Page
125 .127
128
129
130
LIST OF TABLES
Table Page6.1 Path Parameters for Troposcatter Links . . . . . . . . , . 956.2 Path Parameters for Line of Sight Link . . . . . . . . . . 96
6©3 System Dnriensions• « @ • ■ .■ . . . * © © « © © © © © © © © © 97
6©4 System Parameters \ . . . , .. ......................... 99
6©5 Noise Performance Objectives © . © ©,© © © © © © © © © © © 100
6 © 6 Results of Noise Performance Calculations » • , ' . » . , © 107
7.1 Measurement of Propagation Characteristics forJalo-Kufrah Troposcatter Radio Link © , . . © » . © . © 116
7.2 Comparison between Calculated Value and MeasuredValue, of the Propagation Loss © © © ......... © © © © © 132
7.3 Measured Signal-to-noise Ratio of J-Z Link © © © © . -© © © 135
xi
ABSTRACT
This thesis describes the basic information, techniques' and practices used in the planning and engineering of over-the-horizon
communication systems. The communication channel used with these systems is the troposphere. The effect of the atmosphere and its refractive index on scatter propagation is investigated. Finally, a tropo
link for the Libyan Post and Telecommunication Corporation consisting
of four hops is analyzed and link performance is calculated. The propa
gation conditions of this link are discussed through its path loss variations and SNR performance. Theoretical calculations are compared with
experimental data and system quality is. evaluated.
CHAPTER 1
OVER THE HORIZON COMMI3NICATI ONS~ INTRODUCTI ON
Tropo-scatter radio-relay systems have reached a certain level
of maturity over the past years by the completion of solid state sys
tems* Howevers technical progress will still continue in the direction
of miniaturization9 high reliability, low power consumption and better receiving systems• This thesis attempts to bring to light some of the
recent methods in predicting the performance of such systems • The main
features of this thesis are:1* Overall design of troposcatter links provided by Nippon Electric
Company (NEC) standard design method, which is based on CCIR
Report 244-2 and NBS Report 101.
2 o Presentation of an actual link designed on the basis of the
above method.3. A propagation test carried out on that link. Evaluation of the
design and - system is achieved by comparison between theoretical estimates and experimental data.
The purpose of this thesis in general is to present an intro
ductory explanation of tropo-scatter systems with emphasis on system
design and international standards set for such kinds of systems.
Literature on tropo-spheric propagation is reviewed in Chapter 2,
with particular emphasis on propagation mechanism, diversity techniques,
. ' . 2- modulation and detection and a brief explanation of the advantages of
tropooMaterial in Chapters 3, 4» and 5 discusses the overall tropo-'
scatter system planning and design. The presentation begins with definitions of quality, CCIR recommendations and design objectives. It proceeds through design factors such as transmission loss, signal-to-
noise ratio, signal-to-thermal noise ratio, etc.
Chapter 6 describes a link that was designed by NEC for the
Libyan Post and Telecommunication Corporation. This tropo-scatter radio
system is a microwave communication link of 120 channels telephone arid one-way monochrome T.V, transmission which connects Jalo with Kufrah City across the Libyan desert. Path and equipment parameters are tabu
lated and noise performance is calculated.Chapter 7 discusses a propagation test carried out on the same
Jalo-Kufrah link. This test was to confirm the actual statistics of the
radio propagation It is discussed through its path loss variations ..and
S /N performance. Theoretical calculations are compared with the experi
mental data.
Finally, in Chapter 8, system quality is evaluated arid conclu^
sions are drawn.
CHAPTER 2
GENERAL ASPECTS OF OVER THE HORIZON COMMUNICATIONS
Introduction
Troposcatter communicatIons may be defined as a method or a sys
tem of transmitting, within the troposphere, microwaves in the IMF or
SHF bands to effect radio communication between two points. This method
of communication is now generally understood to embrace a radio system
that permits communication over wide distances, with.excellent reliabil
ity and good information capacity, using relatively high transmitted power, frequency modulation, anfl highly sensitive receiving apparatus.
Figure 2.1 is a conventional sketch of a tropo span. This
graphic representation is merely symbolic, and indicates in a general
way that the circuit utilizes high power and large directional antennas.
These may be duplexed, can surmount ground obstacles of considerable magnitude, and will span a relatively large distance over the earth’s sur
face.With accuracy, tropo can. be termed a ’’gap filler." It provides
a means of radio communication at distances not covered either by short range UHF and SHF Line-of-Sight systems, or by the HF and long range
LF systems.
2.1 General Properties of the Troposphere
The troposphere is the region of the atmosphere extending from
the surface of the earth up to a height of 8 to 10 kilometers at polar■ - 3 " ' ' ' '
Q J> o
Fig. 2.1. Graphic Representation of a Tropospan.
5. latitudes5 10 to 12 kilometers at the moderate latitudes s and up to 16 or 18 kilometers at the equator.
In the troposphere9 the percentage of the gas components com- .
prising the atmosphere does not vary with height, remaining practically
the same as it is at the surface. The only exception is the water-vapor
content which is strongly dependent on weather conditions and sharply
decreases with height.The most important property of the troposphere is that its tem
perature decreases with height. The average vertical temperature gra
dient is 6 degrees per kilometer (about 5 degrees per kilometer in the lower troposphere and 7 degrees per kilometer in the upper region).
The annual average temperature of the air in the upper part of the tropo
sphere is -55°C in the polar regions9 and -80°C at the equator. The upper boundary is usually termed the tropopause, which is a narrow re
gion of constant temperature.Although the troposphere extends to a relatively low height 9 it
accounts for four-fifths of the entire air mass. The.average pressure
at the earth’s surface is 1014 millibars (1 millibar = 1/1000th bar.51 bar = 10 Newtons per square meter = 1.019 kilograms per square cen
timeter, which is very close to one atmosphere). At an altitude of 5
kilometers, it is nearly halved, at 11 kilometers it is 225 millibars,
while at an altitude of 17 kilometers, the atmospheric pressure is a
mere 90 millibars.
The water vapor contained in the troposphere comes from the evaporation of water from the surface of oceans, lakes, and water res.er-
. voirs. This is the reason why the troposphere over an ocean contains
6more moisture than it does over a desert. The water-vapor content
rapidly decreases with height. At an altitude of 1.5 km, the water vapor content is about 1/2, and at the upper boundary it is a few thousandths of what it is at the earth’s surface.
The key characteristics of the troposphere are pressure P (in
millibars), absolute temperature T (in degrees Kelvin), and absolute
humidity e (in millibars). Sometimes, the water-vapor content of the air is expressed in terms of specific humidity S (which is the mass of water vapor in grams/kilograms of air) or relative humidity r, expressed
in percent.
Absolute humidity e is related to S and r as follows:
623-0.377 ™ "" ‘
E -
6 - fjv :mb" , 2-2
where E'r ‘is the pressure of water vapor which will saturate the air at
a given temperature (usually found from charts).In summary5 the troposphere is an inhomogeneous dielectric.
The properties of this dielectric vary continually with time, so that the fluctuations related to the formation, movement, and disappearance
of local inhomogeneities in the troposphere are superimposed on the
slower variations caused by meteorological conditions.
72c2 Tropospheric Propagation Mechanism
The phrase "tropospheric scatter" describes a hypothesis that
explains the mechanism that enables the propagation of usable microwave radio signals well beyond line-of-sight distances,
It is generally known that the atmospheric conditions of the troposphere are not homogeneous and are constantly agitated by turbu-
lence* This turbulence is thought to produce "blobs" of atmosphere
whose refractive indices are sharply different from those of the sur
rounding atmosphere. When irradiated by a microwave signal5 these blobs
reradiate the signal, scattering it in all directions, Some of this
scattering is in the forward direction, which produces the field at a
receiving.location. The entire process is thought to occur in the region
between the stratosphere and the surface of the earth* that is, the .
troposphere. This hypothesis forms the basis for the National Bureau of
Standards (NBS) methods for predicting the strength and time availabilityTilof beyond the horizon fields,L J Although the hypothesis itself remains
unproved, the method has been widely accepted; the hypothesis combined
with massive empirical information ordinarily affords a1usable solution
to the problem of predicting performance.
Another promising hypothesis explains these fields as being the
products of mode propagation based on partial reflections, The gravi
tational stratification of the atmosphere, where the lowest layer is
the densest and each succeeding layer is less dense, with sharp boun
daries between the layers, is thought to be responsible. When an elec
tromagnetic wave is propagated through such an atmosphere, ray bending
8occurs and is accompanied by partial reflections„ This hypothesis has
f ?-51been advanced by Carroll and others/-' J
A third approach",, long a subject of speculation by many, has been formalized through a derivation by Bullington.^’ This concept is based primarily on the average value and the standard deviation of the index of refraction at the earth's surface, both of which decrease exponentially with height» The result is a quantitative explanation of tropospheric radio propagation, derived without the use of arbitrary
numerical factors.
All three hypothesis serve to explain the propagation mechanism
but the first one is adopted throughout the thesis due to the fact that
it is adopted by NBS and the huge amount of empirical formulas present
in the NBS reports that helps to predict and estimate the performance
of any tropo system.
2.3 System Considerations
Regardless of the true mechanism, much is known concerning the
characteristics of the microwave energy field propagated beyond the .
horizon. This knowledge has been obtained through observation of a large
mass of empirical data collected from operational tropo links.
First, it is known that the average amplitude of the field prop
agated beyond the horizon is greatly attenuated with respect to the
transmitted field. The amount of attenuation can be calculated as a
function of the angular distance between the transmitting and receiving sites. Angular distance is a parameter that takes into account
curvature of the earth, terrain configuration, and climatology« Usually it is closely related to the linear distance between the two sites.
Second, the amplitude of the received field varies substantially
with time over a given path. The NBS has gathered and analyzed a mass
of data on these variations, so that it is now possible to predict the amplitude-time distributions for most paths with a high degree of accu
racy . These amplitude variations are separated into short-term and longterm distributions. Short-term amplitude-time distributions are those
measured over periods shorter than a few minutes. During such periods the amplitude variations are described by a Rayleigh distribution. The
long-term distribution represents the variation of hourly median levels
over a longer period of time, usually a month, a season, or a year. If amplitude variations are sampled over a period of one hour, an hourly
median amplitude can be found, and if the hourly median amplitudes are observed over a longer period of time, the distribution becomes ,apparent. Since it has not yet been possible to derive exact theoretical expres
sions for these, long-term distributions, empirical relations9 based on
the large mass of available data, are used.. The short-term and long-term distributions of signal amplitude
vary considerably with the season.of the year and with geographical loca
tion. Therefore when a system is being designed these factors must be taken into consideration. Determination of parameters and design are
usually based on the worst propagations! month of the year.
Third, as was previously mentioned, the tropospheric scatter
signals are subject to amplitude time variations9 separated into shortterm and long-term distributions. In practice the two types of signal
10fading are not compensated individually * since the resultant fading is a combination of both types, usually referred to as a monthly median levele Methods known as diversity techniques have been developed to con.ter.act this fading and afford the desired propagational reliability«
Fourth9 all high qualitys long distance, multichannel communica
tion systems have two requirements: (1) reliability and (2) delivery
of a favorable SNR (signal-to-noise-ratio) to the customer. The signal
components usually are amplified, as required, to overcome the various
losses in the system. Every time the signal, is processed there is some addition of noise, which adds on a cumulative basis. The result is that
long-haul systems require careful attention to the details of noise
accumulation if the resulting SNR is to meet requirements.Much thought has been given to this general subject and Inter
national objectives of performance have been formulated. This work has
culminated in the C.C.I.R standards-,-fbf -.radio..:ptactlce'IT'""In addition, the Defense Communication Agency of the U.S. Department of Defense has formulated specialized versions of these standards to apply
to the Defense Communication System (Prescott, 1960).
2.4 Diversity Techniques
Diversity can be defined as the utilization of more than one
independent and uncorrelated transmission path over a single span of
tropo to afford greater reliability than that provided by a single trans
mitter and receiver at each end.
■ 11One of the most effective methods is known as space diversity,
in which two antennas, separated in space by 100 wavelengths or more, are used to receive the signals and reduce the effect of fading. Sig
nals separated in space by this distance show an almost complete absence of correlation. Another method in wide use is known as frequency diversity, wherein two frequencies, separated by about one to ten percent.
depending upon the frequency band in use, are transmitted over the span from the transmitting to the receiving station. Here again, there is a
minimum of correlation between the signals received on the two frequen
cies. Other types of diversity, which are little used at the present
time, include circular polarization and differences in azimuth orientation of antennas (angle diversity).
Although space and frequency diversity may be utilized indepen
dently (dual diversity), both may also be used simultaneously to afford quadruple diversity. For high reliability requirements and in applica
tions where the span length otherwise might produce marginal performance,
quadruple diversity is the preferred solution despite the additional
cost.To produce an optimum signal from a multiple receiver installation
utilizing either dual or quadruple diversity, a "combiner" is provided
for adding, and.effectively utilizing the received signals. The combiner, into which all the receivers are fed, may be operated at baseband fre
quencies (post detection combining) or at intermediate receiver frequen
cies (predetection combining).
12As shown in Figs. 2.2 to 2.4, diversity systems give remarkable
improvement in the short-term fading if the antenna spacing or the fre
quency spacing is sufficient. Figures 2.5 and 2.6 indicate the relation
between the correlations and the frequency spacing or the antenna spacing.
2.5 Antennas and Transmission LinesBecause of the high gain requirements encountered in troposcatter
transmission, highly directional antenna's are used. They usually take the form of large parabolic reflectors with horn feeds. The larger the
parabolic surface, the higher the gain. However, a point of diminishing
returns is reached. Above a certain gain, depending upon the particular
radio path, the increase of gain with increasing parabolic diameter proceeds at a slow rate. A'practical limit on. the .maximum gain capability
over that, path is reached. This effect occurs primarily because of the
medium-to-aperture coupling loss experienced in troposcatter systems.
This loss occurs only in the troposcatter mode; in the line-of-sight
applications, gain is not affected in this manner. The directly propor
tional relationship between gain and frequency limits the size of- antenna
that can be used for any particular frequency. Furthermore, since path
attenuation increases with increasing frequency, the optimum frequency
for a particular path is a compromise between path attenuation and net
antenna gain.The transmission lines used in troposcatter work are usually the
best available, since they represent only a small part of the total
equipment cost and contribute heavily to the performance of the system.
Out
put
of Si
gn a
I/Noi
se
Leve
l Re
lati
ve
to M
edia
n of
Sing
le
Sig
nal
.Ratio Sq uare r
.Linear Adder
Se lect ion-4
-8 Rayleigh Fading
-12
-16
Percent of Time Level E xceeded-20
90 95 98 99 99.80.01 99.99MFig. 2.2. Quadruple Diversity Distributions.
SeVscVton
Une°r
Se\©c " on
Fad'n9
Encee
OistriWOctupl-6
Cor
rela
tion
C
oe
ffic
ien
t0.6
FREQUENCY DISTANCE- • - 600 me 226 km
— ■— 0 2120 me 226 km(D 2120 me 326 km0 2120 me 345 km
300 km
<N s\ s = e x p r - (0.15 M n
_ _ \ \\\
2 i
3 = exp
8
Fig. 2.5. Correlation Coefficient (Frequency) Measured.
Cor
rela
tion
C
oef
fici
ent,
FREQUENCY DISTANCE __
3 4 9 km —
3 4 5 km—
343 km —
600 me eieo me0.8
4 + 4" + 4-+ 3000 me
0.6J3 = exp f- (0.0 > 5 —0.4
0.2
0.0 1009020 30 40 50 60 70 802i A n te n n a Spac in g , s/>
= exp
Fig. 2.6. Correlation Coefficient (Space) Measured.
18Large diameter, rigid coaxial cable is normally used for transmitting
power from the transmitter to antenna, particularly at powers of 10 KW and greater. It has high power-handling capability, low attenuation,
and low voltage standing-wave ratio (VSWR). In many instances, rectangular waveguide is used to provide even better performance in these
respects.
2.6 Modulation and Detection Techniques
Wideband. •Frequency: Modulation. (WBFM) is practically the only
method used in the transmission of. tropo signals today because of its• superior performance when..cbmpafed with-'singlevside. band suppressed-carrier amplitude modulation" (SSBSCvAH, -,or simply SSB) .
The reasons for the recognized superiority of FM over SSB arefrequently misunderstood, or overlooked. First is the fact that much
higher SNR performance is available from an FM system operating well
above threshold. The seldom-reproduced right-hand portion of Fig. 2.7
shows that the SNR values achievable at high signal strengths are farrgigreater with an FM system than with an SSB system, In both cases
the limiting factor is intermodulation noise caused by equipment non-
linearities.The second feature favoring FM can be seen when examining Fig.
2.8. It shows the distribution of energy about the carrier frequency.
It should be noted that these occur in balanced pairs and that the
process of detection produces a summation of all the individual compo
nents.
19
FM Threshold (o
otr<Dto
Ozoioco»J)
>
a©cr▲
T herm al Noise ( m s
R e la t ive Received S ig na l Power
Fig. 2.7. Comparative Performance of FM and SSB.
20
T h i r d O r d e r
S e c o n d O r d e r
B a l a n c e d 1st O rd e r C o m p o n e n ts
lL
Fig. 2.8. Relative Distribution of Energy in FM Signal.
21• These features are obtained at the cost of increased spectrum
space required9 but are unobtainable by any other presently known means of achieving the extremely high performance required for toll quality
of transmission. Current practice sets the FM index at about 3, requiring a bandwidth of about eight times the highest baseband frequency9 although in most systems optimization of deviation usually takes place
after installation to achieve best results.
2.7 Bandwidth Capability
The information bandwidth of a scatter system is limited by frequency sensitive fading and multipath effects. Because of these
effects 9 if a broadband signal is transmitted, frequency components in different paths of the band fade in...random manner. This is due to the
different time taken for components of the signal traveling by different paths between transmitter and receiver. In wideband communications
such as multiplex telephone communication, T. V. transmission, etc., the phase.and amplitude characteristics deteriorate with regard to the higher
baseband frequency, thus limiting the serviceable frequency bandwidth.Therefore, the longer the distance is, the larger the scatter
volume becomes, hence the bandwidth becomes narrow. To widen this band
width, the transmission and reception antenna beam width are narrowed
by using high gain antennas such that a radio wave passes only through
the central portion of the scatter volume. The path difference between
the longest and shortest path length is reduced, and thus a wideband transmission becomes possible.
22Available bandwidth:
bmc * f(a/^ < 2 - 3 )
where d = hop distance in km
a = half power antenna beam angle
= scattering angle
and f (a/a^) is shown in Fig. 2.9 . .
2.8 Typical Tropo Equipment
The development and subsequent experience with tropo throughout
the past years has tended to "standardize17 to a great extent the equipment used today on these circuits, regardless of point of manufacture..
As previously discussed, frequency modulation is used almost - exclusively on tropo circuits because of its. inherent capability to pro
duce a greater SNR. Almost all of the tropo circuits utilize, an output
power of one kilowatt or greater. In practically every case a Klystron
power tube is used. With the continual development of more efficient
and larger Klystrons, output powers up to 100 KW are now common. With
the advent of high-power traveling-wave tubes additional flexibility in
equipment design is forthcoming.
2.8.1 High Power Transmitter
The transmitter used in a tropo communications system requires
large radio frequency transmitting power. This power varies between
50 W and 50 KW up to 100 KW depending on the composition of the system.A Klystron is usually used in the final stage of such a high power
F(cx/cxc)
23
100
5 0
3 0
20
20 . 2 0 .3 0 .5 3 50.10 . 0 2 0 . 0 3 0 .0 5
OC/cXC
Fig. 2.9. Curve of F(a/ctc).
24transmitter, although there are cases where a TWT is utilized. Recent
trdpo transmitters are all solid state except for the final output tube. Figure 2.10 shows the block diagram of a transmitter which uses a
Klystron power amplifier, This transmitter is used in a dual orquadruple diversity system and is operated as described below.
Two modulators are installed in this transmitter for on-line
and standby use. The pilot signal detected at the modulator output is
used for on-line standby changeover„ The base band signal is pre- emphasized and then applied to a frequency modulator to obtain a 70 MHZ
IF signal. Automatic frequency control (AFC) is used in the modulator to ensure frequency stability.
The exciter converts the modulated IF signal to a signal in the
2 GHZ band. This signal is amplified by a transistor amplifier so that
approximately 1 watt of output power is obtained. The exciter also gene
rates the two frequencies to be used for frequency diversity. The dif
ference between these two frequencies is kept precisely constant by
means of the automatic phase control (AFC).
2,8.2 Receiving Equipment
The main differences between the receiver used in tropo systems
and the receiver used in line-of-sight radio systems are:
a. The transmission loss of the tropo system is great and according
ly the receiving input power is small, thus requiring that a
low-noise amplifier be used at the receiver head to improve the
noise figure.
Base,£ o n d _ j
S igna l Input
A F C
FM MOD1 ' iHYB
-FMMOC*70 M H i
J I FSignal
HYB
A F C
MIX H PA of,RF Output
OSC-I 111 PhaseAPC D E I
OSC-2I
M IX +-0SC-3 C=3
M IX HPA 0^2RF Output
A P C ! A u to m a t ic Phase Constant for Keeping Constant D if fe re n c e
A F C ! A u to m a t ic F req u en cy Control for Frequency S ta b i l i t y
Fig. 2.10. Block Diagram of 2 GHz Transmitter for Dual or Quadruple Diversity.
26b . A threshold extension demodulator is used to provide satisfac
tory demodulation and to recover the baseband signal from the
weak receiver input.
c,. A combiner is employed to provide a satisfactory signal from the
diverse receiver inputs whose levels are varying at all"times due to fading.
2.8,3 Low Noise Amplifier
A parametric amplifier or a transistor amplifier is generallyused as a low noise amplifier in tropo radio relay systems.
ricn -Parametric Amplifier.L The parametric amplifier is a type
of negative resistance amplifier. It has three tuned circuits* the
first one of which is tuned to the signal frequency, and the second to
the idler frequency (i.e., the lower side band frequency produced by
a pumping frequency and the signal frequency), and the third is tuned
to the pumping frequency. These three tuned circuits share a varactor
diode as shown in Fig. 2.11.When the pumping power is applied to the varactor diode through
the pumping circuit, a negative resistance is generated in the signal
circuit. A stable amplifier is acquired when a circulator, which is -
used for selection of an input signal and a reflected signal from the
diode is set in the input terminal of the signal circuit. In practice
the only noise in the amplifier is from thermal noise caused by the
series resistance of the varactor diode. This amplifier has the lowest
noise figure among microwave frequency amplifiers which do not require
refrigeration.
Fig. 2.11. Explanatory Circuit of Parametric Amplifier.
28Figure 2.12 shows the block diagram of a parametric amplifier
currently used for 2 GHZ tropo communications. The main performance features of the amplifier are as listed below:
Radio frequency band: 1700 to 2700 MHZNoise figure : - 1.5 db ;
Bandwidth - 29 dbPumping frequency : 18 GHZ
The amplifier consists of a parametric amplifier pumped by an IMPATT
(or GUNN) oscillator and a transistor amplifier. Both amplifier units are connected in series to obtain wide bandwidth, high gain, and
stability. All component parts of the equipment are solid state, pro
viding high reliability, low power consumption, and small size.
Transistor Amplifier. The power gain of a microwave tran
sistor generally decreases at a rate of 6 db per octave, the circuit design is made to compensate the falloff in gain so that a flat response is obtained.
The main performance characteristics of an amplifier suitable
for use in the 2 GHZ tropo systems are as follows:Frequency range : 1500 to 2700 MHZ
Noise figure : - 4 db
Small signal gain : ~ 20 db
29
Input
O utputTR AMP
2 S CA T TBias
SV 514 BPowerMonitor
I s o l a t o r
CUR STBI m p a t t i)sc
POWER SUPPLY
Fig. 2.12. Block Diagram of 2 GHz Parametric Amplifier.
2.8.4 Threshold Extension Demodulator
It is well known that there is a threshold phenomenon in fre
quency modulation systems. The baseband noise after demodulation is
inversely proportional to the receiving input power. However9 the noise increases abruptly when the receiving input power drops below a particular level. The input signal level at which an abrupt increase in noise
is produced is called the threshold level.
The threshold phenomenon takes place because the signal is de
pressed by noise when the peak value of noise at the input of the ampli
tude limiter is greater than that of the signal. The noise level at the
input of the amplitude limiter must be reduced to the greatest possible
extent to bring the threshold level down. The most effective method to
extend threshold level is to narrow the bandwidths since noise power is determined by the product of the noise spectral density multiplied by
the bandwidth. For this reason9 part of the demodulator output is applied to the local oscillator in a threshold extension demodulator, as shown
in Fig. 2.13.This process subjects it to frequency modulation so that the
local oscillator frequency may follow up the frequency deviation of the
receiving signal; i.e., FM negative feedback is utilized. Frequency deviation of the IF signal then becomes smaller than that of the receiv
ing signal. Distortion occurring in the feedback loop is also improved
by an amount, equivalent to the amount of feedback. As a result, the. bandwidth of the IF amplifier is narrowed)causing the threshold level
L.F. Signal —O Output
FM Signal
Input
FM Negative Feedback
NARROWBAND
FILTER
AMPLITUDE
LIMITERAMPLIFIER
WIDE BANCH LOWFREQUENCYAMPLIFIER
MODULATOR
FREQUENCY
FREQUENCY
CONVERTER DISCRIMINATOR
FREQUENCY
Fig. 2.13. Threshold Extension Demodulator using FM Negative Feedback.
32In this case5 the group delay of the FM signal will become un
stable if the bandwidths of all stages of the IF amplifier are narrowed= It is necessary to narrow the bandwidth of only one IF stage to stabilize
the FM feedback, while the frequency bands of the other stages are kept wide.
Another method is the so-called FM feedback phase detection sys^ tem (or phase locked loop) which is often used as a means of extending
the threshold level as shown in Fig. 2.14. The input FM signal
enters the phase detector where the phase difference between this signal .
and the output of the voltage controlled oscillator (VCO) is detected.
The threshold phenomenon does not occur if the amplitude of the VCO out
put is kept sufficiently high and constant since the. phase detector is
a kind of synchronous detector. The'linear characteristic range of.the
phase detector is restricted within approximately ± 60° which is insuf
ficient for demodulation of the wideband FM signal. Therefore, the
phase detector output is amplified by the low frequency amplifier and applied to the VCO. A negative feedback loop is formed causing the out
put phase of the VCO to follow the phase of the incoming FM signal and
also reduce distortion. Demodulation of the wideband FM signal is then
possible.Noise in the demodulator output increases when the receiving
input level becomes smaller. This noise modulates the VCO output when
passing through the feedback loop. Modulation by means of noise in
creases deviation and also causes an increase in the phase difference
between the input signal to the phase detector and the VCO output.
L.F . S igna l— K)
Output
FM SignalO ----Input
N e g a t iv e F e e d b a c k
LO WFREQUENCYA M P L IF IE R
V C. 0.
P H A S E
DETECTOR
N TER M E D IA T EFREQ U ENC YA M P L IF IE R
Fig. 2.14. Threshold Extension Demodulator using FM Feedback Phase Detection System.u>u>
34When the phase difference exceeds a certain value5 an abrupt increase in distortion takes place and the threshold phenomenon occurs. The
above shows that the threshold level of this system is determined by
the bandwidth of the feedback loop (so-called equivalent noise band
width).
2.8.5 CombinerA diversity system is always used to minimize the effects of
fading in tropo communication systems. As a result of diversity reception, not only fading depth.but also transmission bandwidth and inter-
modulation noise are improved.
Diversity reception requires combiner equipment to combine the
receiving signals. The combiner used in tropo circuits is designed to, • ■ ' /follow the fading which varies more often and more rapidly than that in
line-of-sight radio relay systems.
. The combiners are classified from two standpoints, One of these
is the combining point of the signals. Among the combiners classified
in this way are the radio frequency combiner, the IF combiner (both
so-called predetection combiner), and the baseband combiner (so-called
post detection combiner). Predetection combiners require precise phase control of the RF or IF signals which are to be combined. However, the combining is accomplished prior to demodulation.. Therefore, the carrier-
to-noise ratio of the combined signal is improved and normal demodula
tion is performed even when each input signal is. below the threshold
level.
35The other classification of combiners is by combining function.
Among combiners classified according to function are the selector type, the linear adder type and the ratio squarer type. A selector type combiner selects the signal having the most satisfactory S/N from among
two or more received signals. The linear adder type combiner performs
signal combination by adding two or more received signals just as they are. On the other hand, the ratio squarer type combiner combines the
signals by emphasizing the stronger signal and by de-emphasizing the
weaker signal.The former two types of combiners are simple in circuitry, but
the latter has the best S./N improvement. Therefore, the ratio squarer
type is widely used.
Figure 2.15 shows an example of an IF combiner. Two input
signals must be of the same frequency and phase at the combiner. For
this reason, the phase difference between the two IF signals is detectedby a phase detector. Two receiving local oscillators are controlled by
this phase detector output. In addition, a common AGC output voltageis simultaneously applied to the main IF amplifiers since the gains of
the two receivers must always be the same.r 101.Figure 2,16 shows a quadruple diversity system using IF and
baseband combiners. These combiners have ratio squarer characteristics'.
The receiver low noise pre-amplifier performs common amplification of two signals having different frequencies in order to minimize the over
all deviation. : Therefore, the IF combiner provides frequency diversity.
RF InputM I X I F AMP
B P F
L O C A L M I X
V C 0B P F DETECTOR
I F AMPM I XRF Output
VARIABLE ATTENUATOR
FOR RATIO SQUARER
C O M BIN ER
V A R IA B L E A TENUATORFOR RATIO SQUARER
-*oIF Output
Fig. 2.15. Block Diagram of an IF Combiner for Frequency Diversity.
DUAL L .N d lS EAMPLIE1EBB.RF.
BRANCHINGF IL T E R ,
DUALB.P.F
TTNTOTST"AMELlElEfi
BRANCHING _ F ILTER
DOWN CONVERTER
ARC
DOWN
DOWN
IFCOMBINER
.
IFCOMBINER
DOWN CONVERTS
THRESHOLDEXTENSION
DEMOD
BASE BAND COMBINER
THRESHOLD EXTENSION
DEMOD
BoseBond
SignalOutput
Fig. 2.16. Block Diagram of a Quadruple Diversity Receiver.
w
332.9 Advantages of Tropo
Tropo has been developed over the past years into a highly
successful method of radio communications which offers certain advan
tages not .possessed by other modes:1. It provides a high-grade multichannel service over distances
between 112 and 960 kilometers in a single span, thus reducing
the number of stations or terminals required in a line-of-
sight system.2.. With a properly designed system,, it will offer, a circuit of high
propagational reliability on a year-round basis. This reliabil
ity compares very favorably with that of line-of-sight circuits.
3. It can be utilized in rugged or otherwise inhospitable.terrain
where it is impractical or impossible to provide other means of
communication..4. It provides a high degree of spectrum utilization while simul
taneously minimizing frequency allocation problems incident to
radio interference in a high density location.
Under many conditions, tropo offers certain overriding advan
tages. When the cost of a tropo system is considered, these advantages
must be weighed against the cost of other systems that may lack the •
advantages peculiar to tropo.
CHAPTER 3
OVERALL SYSTEM DESIGN OF TROPOSPHERIC SCATTER RADIO LINKS
Introduction
This is a standard design method that is adopted by Nippon
Electric Company (NEC). It is based on CCIR Report 244-2 and NBS
Report 101,The most important factors for designing a tropo-scatter radio
system in general are the following:1. To predict the transmission loss and its time variations due
to the variations of atmospheric conditions,2. To predict the total noise power consisting of path thermal
noise9 path intermodulation noise, etc,.3. The thermal noise and the intermodulation noise of the radio
path vary with geographical and meteorological conditions of
the radio path. Thus, a detailed field survey or some assump
tions for path conditions are necessary for the system design.
4. Allowable cost, where there is a tradeoff between the required
performance and the cost of the system.
Since communication system installations are of national and
international importance, there has to be a certain minimum of require
ments in order for the system to be part of an international link. The
. 39
AOInternational Consultive Committee for Telephone and International Con
sultive Committee for Radio (CCIT, CCIR) specify in their recommendations the minimum required performance of a hypothetical reference
circuit as well as the minimum required performance,of a system to be part of an international connection.
3.1 Definition of Quality
In defining the performance of any communication system, two
features are of paramount importance, the quality of the communication
channels, and the reliability with which this quality is achieved.
In voice communications, channel quality is measured in terms
of the signal-1o-noise ratio (SNR) . In teleprinter and data channels,
it is measured in terms of binary error rate. The reliability of microwave communication systems has two factors, i.e., propagation reliabil
ity, and equipment reliability. The quality and reliability required is generally determined in accordance with the purpose of the system.
The following CCIR recommendations are applied toward the system
quality required for tropo—scatter radio systems.
Allowable Noise Power in the Hypothetical Reference Circuit (CCIR Rec. 397-2, New Delhi, 1970) Recommends:
1. That, from the point of view of performance, trans-horizon radio-relay systems be divided into two classes;
2. that, when a trans-horizon system is intended to operate between two points for which other transmission systems could be used without excessive difficulty, e.g., line-of-sight radiorelay, underground cable, etc., the hypothetical reference circuit should be established in accordance with Recommendation 296-1. The noise power at the end of this hypothetical reference circuit will be calculated by statistical combination of
41-the noise power in each of its radio sections.. The statistical distribution curve of the one-minute mean psophometric power*,during the most unfavorable month, should then pass below the points defined in Recommendation 393-1 §§1.2 and 1.3. The requirements of Recommendation 393-1, §1.1 need not necessarily be satisfied;
3. that, if a trans-horizon system is to be used between points, for which other transmission systems cannot be used without excessive difficulty, and if the condition laid down in Recommendation 393-1 cannot be met without excessive difficulty, the following conditions will apply, once the statistical noise power distribution at the end of the hypothetical reference circuit has been calculated by the method set out in §2;
3.1 The mean psophometric power during one minute must not exceed 25,000 EW for more than 20% of any month;3.2 The mean psophometric power during, one minute must not exceed 63,000 PW for more than 0.5% of any month; .
4. that, for the two classes of system defined above, the unweighted noise power (with an integration time of 5 ms) must meet Recommendation 393-1, §1.4, but with the percentage of the most unfavorable month changed to 0.05% for the systems referred to in 3 of the present Recommendation;
5. that, the conditions given in §§3 and 4 are provisional and should be considered later.
The required quality has been defined by the CCIR for a 2500 km route
length as described above. Taking the hypothetical circuit as a refer
ence, we have to consider the one-minute noise power which is not
attained during 20% and 0.5% (or 0.1%) of any month, also the instan
taneous noise power (measured with a 5 ms time constant) which is not attained during 0.005% of the most unfavorable month. However, the
actual troposcatter radio system is usually designed for a route length
*PW0P = psophmetrically weighted power, in pico-watts (10 watts) at a point of zero relative level.
42.
shorter than 2500 km. This calls, therefore,- for the ability to adjust the required" system quality from a 2500 km circuit to any system of a given length.
3.2 Calculation of the Quality -Required for a System
Recommendation 397-2 states that the noise power at the terminal of a hypothetical reference circuit must be calculated by statistical
combination of the noise power of each of its links. Accordingly, when
predicting the overall noise power of a given system, the calculations have been made on the basis of statistical combining methods. Also,
allowable noise power for the given system to be designed should be
determined by use of the same method, when Class II spedification (i.e.,
CCIR Red. 397-2, para. 3) is applied as a quality required for that sys
tem.
When. Class I specification (i.e., CCIR Rec. 397-1, para. 1) is
applied as a quality required for the system to be.designed, it is
recommended that the allowable noise power be determined in accordance
with CCIR Rec. 395-1, using the same philosophy adopted by "line-of-
sight" radio systems, with the exception of the specification for the
hourly mean noise power.
3.2.1: Design Objective of a System Having a Quality of Class I
CCIR Recommendation 395-1 prescribes as follows:That circuit to be established over real links., the composition of which, for planning reasons, differs substantially
. from the hypothetical reference circuit, should be planned in such a way that the psophotnetrically weighted noise power
• ,at a point of zero relative level in a telephone channel of
43
Length L» where L is between 50 and 2500 km, carried in one or more baseband sections of frequertcy-division multiplex (FDM) radio links, should not exceed:i) for 50 km < L < 840 km:
- 3 LpW + 200 pW one-minute mean power for more than 20% of any month,- 47500 pW one-minute power for more than (280/2500)x0.1% of any month when L is less than 280 km, or more than (L/2500)x0.1% of any month when L is greater than 280 km;
ii)for 840 km < L < 1670 km: _- 3 LpW + 400 pW one-minute mean power for more than 20% of any month,- 47500 pW one-minute mean power for more than (L/2500)x0.1% of any month;
iii)for 1670 km < L < 2500 km:- 3 LpW + 600 pW one-minute mean power for more than 20% of any month,- 47500 pW one-minute mean power for more than (L/2500) x0.1% of any month;
On the basis of each of the above statements, the allowable noise of the given system is determined by the use of Fig. 3.1.
3.2.2 Desigp Objeetiyes- of a System Having a; Quality of Class II
As regards the noise caused by tropo-scatter radio path, it is
known that the mean level of received signal follows a distribution law
which can be approximated by a log-normal law. It follows that the same
law applies to determine the allowable noise of the system to be de
signed.
As the system, in the case of a tropo-scatter system, has no .
fixed length, the CCIR Rec. 396-1 para. 3 states that, if a radio sec
tion under study is L km long, the hypothetical reference circuit should
be composed of 2500/L sections of this type in tandem, the value 2500/L being taken to the nearest whole number.
Wei
ghte
d No
ise
Leve
l (-
dB
m)
44
743 L - 2 0 0 PW P ( f o r 5 0 k m < L 4 8 4 0 k m )
3 L - 4 0 0 P W P ( f o r 8 4 0 km < L < 1 6 7 0 km)
3 L - 6 0 0 PW P ( f o r 1 6 7 0 km < L 4 2 5 0 0 km)
7 2
7 0
68R e fe ren ce C i rcu i t66R e a l C i rcu i t
6 4
6 2
6 0
5 8
5 6
5 4
52
D is ta n c e in K i l o m e t e r s5 0
1000 200010 20 5 0 100 200 5 0 0
Fig. 3.1. Allowable Noise.(a) Hourly mean and 20% of worst month
(CCIR Rec-393-1 and 395-1).
Allo
wab
le
Perc
ent
(in
any
mon
th)
O.l 4 7 , 5 0 0 PWP
2802 5 q q x 0 . 1 % ( for 5 0 k m < L < 2 8 0 k m )0 . 0 5
(for 2 8 0 k m < L 4 2500km)2 5 0 0
0.02
0 . 0 1 -
0 . 0 0 5
0.0021 , 0 0 0 , 0 0 0 PWP
0 .0 0 1x 0 . 0 1 %2 5 0 0
( N o t e ) 1 , 0 0 0 , 0 0 0 PW unweighted
0 . 0 0 0 5
1000 20005 0 05 0 100 2 0 0
D i s t a n c e ( L ) i n K i l o m e t e r s
20
Fig. 3.1— Continued
(b) Percent for 47,500 PWP and 1,000,000 PW (CCIR Rec. 393-1 and 395-1).
46
With the help of this statement and a log-normal law, allowable noise on a system (or a link) of a given length, can be computed in relation to the one permissible on the whole 2500 km hypothetical circuit for the time percentage 20% indicated in the CCIR Recommendations„ Figure 3.2 has been made on the basis of the above statements.
The log-normal law statistical combining method is made on the
basis of the assumption that the correlation among the noise distribution (noise variation) of each section is equal. However, it is gen
erally understood that "the small percentage of a month in which one
minute mean power may exceed 47500 pW or more is proportional to the number of homogeneous sections" as is done with line—of-sight radio links
(Rec. 393-1, para. 3). By applying this point of view, as regards the
small percentage specification, an allowable percent for 63000 pW is
calculated as follows:
L ' -Allowable percent = 2506 x 0«5% (for 63000 pW)
Figure 3.3 has been made on the basis of the above formula.
3.3 System Design Procedure
For designing a tropo-scatter radio system, the following pro
cedure is usually applied:
A. Preparation for System Design .
(1) Determine the channel plan of the telephone or telegraph system.
(2) Determine the requirements of the transmission quality.
Noi
se
Leve
l (-
dBm
) fo
r 20
%
(Wei
gh
ted
)47
60
5 5
2 0 % value50
4 510 12 14 16 18 20 22 244 6 8
Fig. 3.2. Allowable Noise for 20% of Worst Month.
(CCIR Rec. 397-2).
Allo
wab
le
Perc
ent
for
63,0
00
PWP
48
0.80.6
0 .4
0.2
0-08
0 .0 6
0 .04
0.02
0.0
20 22 24
(a)
Fig. 3.3. Allowable Noise for (a) 63,000 PWP of Worst Month; and (b) 1,000,000 PW.
(CCIR Rec. 397-1)
Allo
wab
le
Per
cen
t
49
0 . 0 5 -
0.02
0.01
0 . 0 0 5 x 0 .0 5 %2 5 0 0
0.002
(Note) 1,000,000 PW: unweighed
0.001
0 .0 0 0 5
10 20 5 0 050 100 200 1000 2000D i s t a n c e ( L ) in K i l o m e t e r s
Fig. 3.3— Continued
50
(3) Select a route for the system, taking into consideration convenient and economical maintenance as well as easy installation-
(4) Study the path profiles.(5) Confirm the path parameters and equipment parameters.
B. System Design(1) Calculate the allowable noise of the overall system and
each link to be designed.
(2) Determine the provisional system dimensionstaking: into
consideration the link distance. .
a. Transmitter power
b. antenna diameter
c. low-noise amplifier
d. feeder type
e. order of diversity
(For reference to determine the provisional dimensions.Fig. 3.4 gives the typical system dimensions in accordance
with various hop distances.)
(3) Calculate the received powers of each link, and the long
term fading distribution of the received powers.
(4) Confirm the threshold margins. Generally, median receiving
power at 99.9% of the long-term fading distribution is necessary to maintain a higher level than the receiver
threshold level to avoid system interruption due to propa
gation.
No
ise
Le
ve
l in
-dB
m
(P =
20
%)
dual\ d i v e r s i t y
6 0Allowable^^V Noise of \ CCIR Rec 397-
5 0
4 04 0 0 5 0 0 6 0 0200 3 0 0
Hop D i s t a n c e in K i l o m e t e r s
100
Fig. 3.4. Relation of Hop-distance vs. Overall Noise Level (Worst Month).
in
"Threshold Margin" '
= "99.9% of the Median Receiving Power"- "Threshold level" > 0
(5) If the threshold margins of some of the links cannot satisfy the above figures, change the provisional system dimen
sions of their links.
(6) Calculate the signal-to-noise ratio of each link.
(7) Calculate the overall signal-to-nbise ratio of the system.
(8) Compare the overall signal-to-noise ratio of the system
with the allowable noise.
(9) If the overall noise is greater than the allowable noise,
change the provisional system dimensions of the links
having the most noise.
(10) Determine the final system dimensions.
CHAPTER 4
TRANSMISSION LOSS
The receiver input power of a radio communication link isf Ill-obtained, by the following equation
P.. = p.. + Gt + Gr - - (Lt+Lr) - L=t (4.1)
where 9 P.
h ms
t t t + y
mediaii input power level of the receiver system, in dBm
transmitter output power in dBm
gain of the transmitting antenna in dB
gain of. the receiving antenna in dB
basic median transmission loss in dB
losses of the'feeder system including, filters in dB
antenna-1o-medium coupling loss in dB
Among these parameters which determine the receiving input
power9 ail<3 "1 " are decided by the propagation path.
4o1 Surface Refractivity (NS)Much work has been done on the quantitative study of the influ
ence of radio-meteorological phenomena on propagation. It has been
found that a consistent correlation exists between the gradient of the
radio refractivity of the atmosphere in the first kilometer above the[inearth’s surface and.the transmission loss.1 J
54;
Furthermore.9 the variations of the refractive index are important not only from the view of variation in the field strength or transmission loss9 but also from the viewpoint of total bending of radio waves passing through the troposphere. Thus, the atmospheric refractive index is one of the most important parameters to be taken into consideration
as well as such characteristics of the radio transmission path such as itslengths the antenna heights andv-roughness; of terrain.
The radio refractivity of the atmosphere (N) is given by the following equation.reported in the CCIR Recommendation 453.
N = (n-1) xlO6 = ^ (4.2)
where, ns refractive index of the atmosphere
P: atmospheric pressure in millibars
T: temperature in degree Kelvin
es: saturation vapor pressure in millibars forthe temperature T
Rh: relative humidity in percent
To simplify the problem in the radio propagation application of
the radio refractivity, it is pertinent to represent the atmosphere by
means of the refractivity gradient (AN), which is defined as the simple
difference between the value of the refractivity at the earth's surface (NS) and at one kilometer above the earth s surface (Nl).
AN = Nl - NS (4.3)
55
The transmission loss is a function of AN. value. Accordingly,
the AN value is a very important factor in calculating the transmission loss. Moreover, AN is in general correlated with the surface value
Ng, and the relation between both values is approximated as follows:
AN/Km = -7.32 exp(0.005577 NS) (4.4)
The above formula may be used for estimating AN in the usualnncase where only surface meteorological data are available.L
However, the estimation of AN and Ng values is impossible in
places where meteorological data are not available. For this purpose,
the use of the data of the refractive index at sea level (Nq) reported
in the CCIR Report No. 233-2 (refer to Fig. 4.2.) is the best way to
estimate N and NS of any place with the aid of the following formula and Fig. 4.3;
„s „ Ho e-0.1057h (4.5)
where h is the elevation of the surface above mean sea level
in kilometers.Most of the refraction of a radio ray takes place at low ele
vations, so it is appropriate to determine N and h for locations corre-- • • . ° V -
spending to the lowest elevation of. the radio rays most important to the
geometry of a propagation path. As a practical matter for within-the-
horizon paths, h is defined as the ground elevation immediately below
the lower antenna terminal, and N is determined at the same location.
56
S c a t t e r V o lu m e
Fig. 4.1. Path Geometry of Troposcatter Radio System.
AO'80 80*
310
60* 60*
320
40*
20* 20*
17020' 20*370
■350
33040'
60*
00"
Fig. 4.2. Minimum Monthly Surface Refractivity Values Referred to Mean Sea Level.
For beyond-the-horizon paths5 h and Nq are determined at the radio horizons along the great circle path between the antennas 5 and Ng is the average of the two values calculated from Eq. (4.5) or Fig. 4.3.An exception to this latter rule occurs if an antenna is more than 150meters below its radio horizon; in such a case, h and N should be
determined at the antenna location. .
Considering the worst case9 Ng is generally computed as follows:
.. Nq(ht) + Nq (hr) + Nq (hLt) 4- Nq(hLr)Ns ■ -5-------- S----_ _ J --------- — ---- (4.6)
where ht and hr are. the elevations of the antenna location above
mean sea level and hLt and hLr are the elevations of the transmitter and
receiver radio horizons, respectively.
4.2 Scatter Angle (8)The scatter angle is the angle between the radio horizon rays
from the transmitting and receiving antennas in the great circle plane. The value of the scatter angle is an important factor.: in determining
propagation loss and fading depth. The scatter angle for the path shown
in Fig. 4.1 can be obtained by using the following procedure.
The horizon rays are elevated above (or below) the horizonal
by angles 0i and 02 5 0% and ©2 are given by the following equations;
4 0 0
3 8
3 6
3 4 0
3 2 0
3 0 0
2 8 0
2 6 0
60
(4.8)
where, ht and hr: the elevations of the antenna locationsabove mean sea level in meters.
hit and hLr: the elevation of the radio horizons above mean sea level in meters.
dLt and dLr: the distances from the antenna locations to the radio horizons in kilometers
a: effective earth's radius in kilometers.
"a" is given by the following formula:
a = aQ [1-O.04665 exp(0.00577 Ng)] *where: a is the actual radius of the
earth (6370 km). Figure 4.4 shows the effective earth's radius, a, plotted versus Ng.
For irregular terrain, angles a and g defined in Fig. 4.1 are
calculated as follows:
a = 2a x^lb-3 + 01 + (m rad) (4.9)
% = 2a rVo-S + 0% + — 'J-h“ (m rad) (4.10)
The scatter angle (0) is then calculated as follows:
0 = a + g (m rad) (4.11)
hLr - hr dLr
dLr2a x 10— j (m rad)
To allow for the effect of a nonlinear.refractivity gradient $
a and g are. modified by the corrections AaQ and Ag • However9 these corrections are generally very small: so that they can be safely neglected•
Eff
ecti
ve
Eart
h R
adiu
s a
in km
e61
11600
11200
10800
10400
10000
9 6 0 0
9 2 0 0
8 8 0 0
8 4 0 0
8 0 0 0
7 6 0 03 8 0 4 0 03602 8 0 3 0 0 3 2 0 3 4 02 6 0
Fig. 4.4. Effective Earth's Radius 'a' vs. Surface Refractivity 'N^'.
62 -
4.3 Basic Median Transmission Loss (Lbms)The basic path loss in tropo-scatter propagation varies with
such geographical and meteorological parameters as path length, antennaelevationss roughness of the intervening terrain, atmospheric conditions»
and the radio frequency to be used. The most general formula for the
prediction of a median basic transmission loss, Lbms, which agreesrnfairly well with actual measured values, is given as follows:1
Lbms = F(d6) + 30 log f - 20 log d + A - V(0.5»de) (4.12)
where the distance, d, is expressed in kilometers, the scatter
angle, 0, in radians and the frequency, f, in MHZ.The first three terms of the above formula are the most signifi
cant terms. The first one is called the attenuation function. It
depends on the path distance (d), angular distance (8), path symmetry(S) and surface refractivity (Ng). The second is a frequency attenuation •
term. The third is a distance correction term to F(d6), the fourth represents atmospheric absorption and the fifth is a correction term to the
median of the worst hourly median according to CCIR Report 244-1.
Transmission loss of each tropo-scatter link can be estimated by
using this expression. The detailed calculation method for determiningFillF(d0) and A are expressed as follows:
F(d0)The attenuation function F(d0) depends upon the most important
features of the propagation path and upon the surface refractivity, Ng.
63
Figure 4.5 gives an example of the kind of graphs that are used gene- .
rally to obtain F(d0). Other figures for different values of Ng and d6 are found in Appendix A. In Fig. 4.5, F(d8) is plotted versus the product d0.
For values of d8 < 10 the curves of Fig. 4.5 are valid for all values of the symmetry parameter S = a/0. For values of 0 greater than
10 the curves may be used for values of S from 0.7 to unity.
For highly asymmetrical path with 0 > 10, Figs. A1 to-A4 in
Appendix A are used to obtain F(d6). For S greater than 1, 1/S is used
in reading the graph. .
AAtmospheric absorbtion due to oxygen and water vapor for trans-
horizpn paths with the frequency range 0.1 ~ 10 GHZ is shown in Fig.
4.6.[111
V(0.5,de)
The correction term is obtained from Fig, 4,7 with the functionr hiof effective distance (de) and climate regions. J Effective distance
is calculated from Eqs. (4.36) ~ (4.39).
4,4. Antenna-1o-medium Coupling Loss Another important system parameter.to be estimated in a tropo-
scatter system is the antenna-to-medium coupling loss,. In a troposcat- ter link9 high gain antennas are usually employed. In that case the
total path antenna gain is often unequal to the sum of the free space
F(0d
) in
Dec
ibel
s
6470
8 0 2209 0 2 3 0
100 2 4 0N«= 301
2 5 0
120 2 6 0
130 2 7 0N = 2 5 0
140 2 8 0
150100 2 0 0 5 0 0
160
170
180
190
200( 0 . 7 5 4 S < I )
210220
5 0 1000 .5 20
6d
Fig. 4.5. The Attenuation Function, F(6d).d is in kilometers and 9 is in radians.
Oxy
gen
and
Wat
er
Vapo
r A
bsor
btio
n i F requency in M H z 10.000
7000
3000
2000
4 0 0 5 0 0 6 0 0 7 0 0
Distance in Kilometers8 0 0 9 0 0 1000 HOO
Fig. 4.6. Estimate of Median Oxygen and Water Vapor Absorption from August Data, Washington, D. C.
(TLn
V(0
.5,d
e) in
Dec
ibel
s
L (0 .5 )= Lcr - V (0 .5 ,d e ) dB30
CLIMATESEquatorial ---------------------------------Continental S u b t r o p i c a l ---------------Mari t ime Subtropical (Over Land)Desert ----------------------------------------------Cont inental T e m p e r a t e ------------------M ar i t im e Tem perate (Over Land) • M ar it im e Tempera te (Over Sea) -
20
7b
-10
d. in Ki lometers
-207 0 06 0 0 8 0 0200 4 0 0 5 0 03 0 0 9 0 00 100
Fig. 4.7. The Function V(0.5,d^) for Eight Climatic Regions. o\
67
antenna gains of transmitting and receiving antennas. Generally, tropo-
scatter antenna gain is smaller, than the sum of free space antenna gain
due to losses. This loss is called the antenna-to-medium coupling loss.
It is estimated by the following formula which gives the best agreementwith practical experimental data, {U]
Lc = Lch + Lev (4.17)
where Lch: the partial antenna-to-medium coupling lossassociated with the horizontal antenna pattern.
Lev:, the partial antenna-to-medium coupling lossassociated with the vertical antenna pattern.
The above values are calculated from the following formulas:
Lch = *(*)‘S T • (4.18)
Lev = exp <9 \2rm \w
(4.19)
where 9^: optimum elevation of angle of beam axis of transmitting antenna
rm
thrhtv
that of the receiving antenna
0.6X (horizontal beam width of transmitting antenna)0.6X (that of receiving antenna)
0.6X (vertical beam width of the transmitting antenna
68ip : 0»6X (that, of the receiving antenna)rvKl: Meteorological constant for mean value
estimation K = 0o4for worst value estimation K = 1/1,3
NOTE: When a is larger than g9 replace ip with ip inEq. (4,18) 9 (4.19), (4.20), (4.21) and (4,22)
In practice, Lch and Lev are calculated using the following
procedures:
Lch = 5 log 1 += t e ) + f c
(dB).
The parameters to obtain —^ and — are:tv rrv
(4.20)
Xt \|> ' S(nrK).5 • T • ho) (4.21)
Xn S0ip (m+0.5 • F « ho)rv
(4.22)
ho = S d8 (1+S)" (Km)
m = 2.5 for mean value estimation
m = 1.3 for worst value estimation-1r = 3 (Km ) for mean value estimation
I = 0 for worst case estimation
(4,23)
And, by the use of Fig. 4.8;
Then Lev and Lc are obtained as follows:
j and ( ■ — ) are obtained.* t J \ w
69
0.86 t m "y t v r
0.6
0 . 4Q r m
0.2
0 2 3 5 74 6
* x 2= (V tv '(rv ') = 0 .6Y tv (rv )j
1.4
8 r m
8 10 20 3 0 4 0
Fig. 4.8. Antenna to Medium Coupling Loss.
70
LCT ' exp ^ . f e ) + f e )
_ . . . _ . 11Lev = 4•H(te)+fe) f (dB) (4-24)
Lc — Lch + Lev (dB) (4,25)
4.5 : Feeder System Loss (L^+Lr)
Feeder system loss includes the insertion losses of all mate
rials composing the feeder system. When the NEC method is applied,
feeder system loss is calculated, as follows:
Lt+Lr = LTXBF + a (l1+l2) + LrxBP + Liso (4.26)
where, ^mXBF’ insertion loss of bandpass filter or branchingfilter used in the transmitting side in db
a: Insertion loss of waveguide feeder per meterin db
L-i: Feeder length of transmitting side in meters
L2: that of the receiving side in meters
Lr x bF “ Insertion loss of the dual bandpass filter or.branching filter used for receiving side in db
Liso; Insertion loss of isolator in db
4.6 Received Power (F )
F12TThe median received power of a link is calculated as follows:
Pr - Pt + <Gt+ep - ^ - t t t+ V - Lc (dbm) (4.27)
Each parameter mentioned in the above equation has already been
■ explained in the previous paragraphs.When obtaining the distribution curve of the received power, the
following equation is applied:
Pr(P%) = Pr - F d(P) (dbm) (4.28)
where P^(P%): Receiver input level of P% in dbm.
P^: Median receiver input, level
Fd(P): Long-term fading depth of P% in db
The threshold margin of the system is considered by using the
following relation:
M =. Pr(99.9) - Pth > 0(dbm) (4.29)where, M
Pr(99.9)
Pth
Threshold margin in db
99.9% of the median receiver input level in db
threshold level in dbm
72 -4.7 Fading Depth (F^)
Two types of fading, long-term and short-term fading, must be considered for the system design of a tropo-scatter link.
The long-term fading is caused by the variations of meteorolog
ical conditions. Its distribution has been experimentally found to be
a log-normal distribution. The standard deviation of the long-normal distribution is determined by the scatter angle and/or meteorological
conditions.
distribution, which has been verified theoretically and experimentally.
Therefore to estimate the fading, both long-term and short-term fadings
must be combined into a composite distribution.
The probability density function of the Rayleigh distribution,
P(y ), is given by:
The short-term fading is produced by the multipath effect of
incoming radio waves. Its distribution can be .taken as- a. Rayleigh
(4.30)
where, y: the input levela: the standard deviation
y- : median value
The median value (yQ) is given by
Yo = /2a2 log 2 (4.31)
73Now, assuming. that the log-normal distribution is e.entered at the
median value y of the Rayleigh distribution, the,density function isO ' ;given by* the following equation;
2
q(V ‘ ■ 2it □ r0 exp V 2 O?' " ' /X <4-32)
where R: mean value of y- oK: the transfer coefficient from true value to db value.
Hence9 supposing that the median value in Eq„ (4.30) is such a function as in Eq, (4.32), Eq. (4,30) can be rewritten as follows:
P(y;Y0) = (2y/y02) Log 2 » exp j- (y2/yq2) log 2j (4.33)
The density, P(y)» of the composite distribution to be found is
therefore given by:
f (y ) - P(Y‘Y0) q (Y 0) d y0 (4.34)
The distribution function, P(y) is given byY . ,
f (y ) = f(Y) dY ' (4.35)o .
The cumulative distribution of fading for about one month in a tropo-scatter link can be estimated-from Eq, (4,35), The
result of calculating this distribution from Eq. (4,35) 9 .-with the standard deviation of the log-normal distribution used:as a parameter.
74
is shown in Fig. 4.9. The long-term fading is estimated, by the methodwhich is presented in CCIR Rep. 244—2 (see Fig. 4.3,0).
The standard deviation (a) of the log-normal distribution is
obtained from Fig. 4.10 by. use of the following effective distance (de)[111as a parameter.
for d < dL + dSl de = 130 d/dL + dSl (Km) (4.36)
for d > dL + dSl de = 130 + d - (dL+dSl) (4.37)
where: dSl = 65(100/f)1/3 (Km) (4.38)
dL = 3 /2hte + 3/2hre (Km) (4.39)
hte,hre: effective antenna height in meters
f: radio frequency in MHZ
Parameter dSl can also be obtained from Fig. 4.11.
When a diversity system is applied in a link,., the diversity
improvement is considered in accordance with the order of the diversity
configuration. This is true for the noise distribution and also the
receiving level distribution.
By properly setting the antenna and frequency spacing, the cor
relation coefficient of the short-term Rayleigh fading can be made
satisfactorily small. But that of the log-normal distribution may be
regarded as nearly one.
In this case, the resultant short-term distribution of n signals
with equal median value in several diversity systems will be as follows
Rel
ativ
e Le
vel
in d
B
1-------1----- 1------ T T
cr= 10 dB
.01 0 .0 5 0 2 I 2 5 10 20 30 40 50 60 70 80 90 95 98 99
T i m e ( P e r c e n t )
99.8 99.95 99.99
Fig. 4.9. Composite Distribution Curve of Long-term Fading and Short-term Fading for Non-diversity.
-~iUi
V(P
,de
)
76
D e s e r t C l im a te ( S a h a ra )
99.99
-20 —
100 200 300 400 500 600 700 800 900 km
E f fec t ive D is ta n c e
Fig. 4.10. Transmission Loss Variability.
dsl (
KM)
77
70
6 0
50
4 0
30
20d s l = 3 (K M )
0.1 0.2 0 .5 2 105
F(GHz)
Fig. 4.11. Parameter dsl.
78
a. Selector Combining System:
- {i- 2F(L) = <1 - exp(-C2L2) > (4.40)
!
b . Linear adder combining, system:
F(L) = 12n/(2n)! | (CL)2n (4.41)
c. Ratio squarer combining type:
F(L) = ||(CL)2n/n!^ + (CL) (n+1) /(n+1) ! (4.42)
where, L: S/N
C: 1/L0Lg: mean value of L.
Accordingly, by use of this short-term distribution, the compo
site distribution of the Rayleigh and the log-normal distribution for
each order of a diversity system, can be calculated.
The calculated composite distribution curves for dual diversity,
quadruple diversity, and octuple diversity systems are illustrated in
Figs. 4.12, 4.13, and 4.14.
Rel
ativ
e Le
vel
in d
B
i— i— i
10 dB
II II I I I I I I I I I>.01 0.03 0.2 20 30 40 50 60 70 80
T i m e ( P e r c e n t )
90 95 98 99 99.8 99.95 99.99
Fig. 4.12. Composite Distribution Curve of Long-term Fading and Short termFading for Dual Diversity. <o
Rel
ativ
e Le
vel
in dB
4 0
30
20
-10
-20
-3 0
- 4 0
98 99 99.8 99.95 999920 30 40 50 60 70 80 90 95100.01 0.05 0.2 I 2 5
T i m e ( P e r c e n t )
Fig. 4.13. Composite Distribution Curve of Long-term Fading and Short-term Fadingfor Quadruple Diversity.
o
4 0
3 0
20
10
0
-10
-20
-3 0
4 0
o.
ig.
i— i--- n — i— i— |— ,— |— p-,---- 1— r
I i I i i i i j 1— 1 1 . . . 1 i i i l i 1 101 0.03 0.2 1 2 5 10 20 30 40 50 60 70 60 90 95 96 99 99.6 99.93
T i m e (P erc en t )
4.14. Composite Distribution Curve of Long-term Fading and Short termFading for Octuple Diversity.
CHAPTER 5
SIGNAL-TOtNOISE RATIO - -
5.1 Diversity Improvement (U)The diversity improvements against fading were explained in
paragraph 4.7, the median improvement (U) by a diversity system which
is provided by the ratio square combiner is as follows t
Dual diversity system 3 db
Quadruple diversity system 6 db
Octuple diversity system 9 db
« When angular diversity is applied in each of the above,
improvement is decreased by 3 db because antenna deflection
loss (3 db) is added to the transmission loss.
5.2 Signa1-to-therma1 Noise Ratio (S/N^)
is given by
The unweighted signal to EM thermal noise ratio without emphasis[ii]
V so2S/N'T ~ 10 LoS KTF Af X f^2 C5 «l)
wheres Receiver input power
K: Boltzman’s constant
T: Absolute temperature in KelvinF: Noise figure
82\
83
Sq : r em 0s».' frequency deviation for test tonefm: the highest frequency of the baseband f: Bandwidth of a voice channel (3.1 x 10^ Hz)
However $ the f requency deviation of troposcatter systems is
usually determined in terms of the optimum frequency deviation by
studying the relation between thermal noise and intermodulation noise.
The signal to thermal noise ratio at the input of the receiver is
proportional to the square of the frequency deviation while the signal-
to-intermodulation noise ratio due to propagation is inversely propor
tional to the square of the frequency deviation.
Accordingly9 NEC generally uses the following formula for cal
culating the S/N , keeping in mind that an improvement of about 4 db due
to preemphasis is included.p
S/Nt = 10 Log 2KTFAf X ^ (5.2)
where, m: modulation index per channel in radians
AFm = —fm
where, AF: Peak frequency deviation of the highest baseband frequency per channel.
Considering the diversity improvement and fading depth, the
signal-to-noise ratio is calculated as follows:
Sx anti-log (5.3)
pS/Njff) ' 10 2KiF ' A • “2 • M • D ' fdfe)
84
= -10 Log 2KT - 10 log Af - F + 20 Log. m
+ W + U + Pr - Fd(P) (5.4)
where, S/N^(P): Signal-to-noise ratio of P%
F: Noise figure of the receiver3Af: Bandwidth of voice channel (3.1 x 10 Hz)
m: Modulation index per channelW: Weighting factor
U: Diversity improvement
5.3 Signal-to-path Intermodulation 'Noise Ratio (S/N^)
Tropo-scatter propagation is strongly influenced by multipath
propagation. For this reason, the relative delay of arrival time at
each propagation path is different. A sort of delay distortion occurs
causing a distortion noise. A number of theories in the field are
advocated but no definite theory has been established yet.
All the theories so far established agree on the following
relation:
. S/Nj « t-4 M™2
where, t : Relative delay timeM: Deviation (modulation index)
85
The difference among the above mentioned theories is found in the calculation formula of t .
Concerning the distortion noise5 NEC found through experimenta
tion that the formula stated above9 which was formulated on the basis of[13]Y. Okumura's theory, agrees best with practical measured values.
Thus, the median signal-to-path intermodulation noise ratio
is given by:^^"^
S/N -(P). = K - 40 Log fm t - 20 Log M
+ Z + W + UT - FdT(P) (db) (5.5)n i 1
where, Znv= 6 Log N 4- 1 = 13.5. db. for 120 ch
K: = constant (110.3 db) .
= diversity improvement (0,7U)‘W = Weighting.factor
Fd . (P) = P% fading depth of intermodulation noise fm^ = Baseband top frequency index
r = delay time (ys) •
The delay time (t) and modulation index (M) are defined asfollows:
~ (ag+Qm) (6+ag + 9m) (ys) (5.6)
where, d: Link distance in Km
C: Light velocity 3 x 10^ (Km/sec)
as Half of the antenna beamwidth
866: Diffusion factor of the antenna beaiwidth
(Refer to Fig. 5,1)6m: Optimum elevation angle (mrad)
e m > 1 . * (5.7)Yrt yrv
(Bm is obtained by using the result of the antenna-1o-medium
coupling loss calculations. See para. 4.4).
The total modulation index is given by:
M = 0.4 m Lf rad (5.8)
where$ M: Modulation index: Loading factor = 2-3 db for 120 ch
The radio path intermodulation noise varies with time . Its
distribution differs slightly from that of the thermal noise. Assuming that the standard deviation of the thermal noise long-term distribution
is ai, and that of the intermodulation noise to be 0 2 , then the follow
ing relation exists between a 1 and a2 1
02 = 0.7 a1 (db) (5.9)
This relationship has been verified by many experiments and by NEC's own research department as well. Accordingly9 by the use of 02, fading depths-of intermodulation noise. (EdL) can-be obtained from Figs. 4.12, 4.13, 4.14.
5.4 Signal-to-intermodulation Noise Due to Feeder Echo (S/Np)
■ The feeder echo distortion is generated when any mismatching
exists at each end.of the feeder, that is, between antenna and output/
87output of the transmitter/receiver.' In practice, the feeder^echo dis
tortion is determined hy, further. , taking:, into consideration . the number of channels, the delay time of the transmission loss between two reflecting
points, etc. The signal-to-echo distortion noise per channel is given
by:. [Ill
S/Nt " j - 20 Log yA ° yB + 2 j™
+ L + W n (db) (5.10)
where, YA, yB: Reflection coefficient at two reflecting points
yA, yB =
nW
r
v
A, B - 1 A, B + 1,
r
A:
channel conversion value (13•5 db for 120 ch)
Weighted value (2*5 db)
Feeder loss between two reflecting points
Noise value improved by the delay time (refer to Fig* 5,2)
0,4 m L.c2L2itfmr: 2ir fm ° — g
feeder length8
8 wave velocity (2.7 x 10 m/sec)
5.5 Overall Signal-to-noise Ratio (S/N)
Overall signal-to-noise ratio is obtained by summing up the
noise powers of thermal noise, intermodulation noise, and equipment
noise.
88N = NT + NI + NE + Nf
wheres Thermal noise power in pwp
N^: Intermodulation noise power in pwpNp: Feed.echo noise power in pwpNp: Basic noise power of equipment in pwp
Basic noise of equipment means . that the residual noise of the
equipment includes intermodulation noise. In case of 120 ch using NEC
equipment residual noise is 100 pwp (S/N = 70 db) for 120.channels» Figure 5.3 gives an example of the summation of' the noise powers of the
thermal noise, intermodulation noise and equipment noise. .
3.02.82.62 . 4
2.22.0.8.6
.4
.2
.0' 0 0 . 2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
9m/cx v
Fig. 5.1. Diffusion Factor of Antenna Beam Width.
Dis
tort
ion
/Sig
no
l Ro
tio
in To
p C
ho
nn
el
Echo
A
mp
litu
de
F EEDER EC H O
IN T E R M O D U L A TIO N DISTORTION
A=l .0 A » 0.4
. 0.6=1.2
* 0.2=1.4 < 0.8
0.1=1.6
30 =1.8 1.4
=2.0 A = 0.14 0 2 0A = 0 . 2
= 0 . 4
= 0.65 0
= 0.86 0 200 . 0 3
2 n f mT; IN R A D I A N S / S E C
Fig. 5.2. Feeder Echo Intermodulation Distortion.
A= r.m e. freq. deviat ion
Pm = maximum modulating frequency.
o
9 0
8 0
70
6 0
5 0
4 0
30
20
10
0o.
5.:
i— i— n — i— i— n t i i i i— i— i— rr
Feeder Echo Noise
Basic _Nj>iseThermol N oi se
Path Intermod. Noi&e
Total Noise
Speci f ied Va lu e —
01 0.05 02
T i m e (Percent)
j...... ..................................... i_i i i10 20 30 40 50 60 70 60 90 95 98 99 99.8 99.95 99.
Overall Noise Performance of Example Link (Weighted Value).
CHAPTER 6
DESIGN.OF A LINK BETWEEN JALO AND KUFRAH IN LIBYA
This tropospheric radio system is a communication link of
120 telephone channels and one-way monochrome television transmission.It connects Jalo with Kufrah across the Libyan Desert .
The system comprises three radio links; two troposcatter radio
systems using the frequency band of 1.8 GHZ and one approach line-of- sight radio system using the frequency band of 7 GHZ, • The system is
composed of four stations, Jalo, Zighan, Kufrah mountain and Kufrah
city as shown in Fig. 6.1.
In addition to the normal traffic operation (120 ch TP + one
way monochrome T.V. transmission), the system can transmit a monochrome •
T.V. signal in the opposite direction from Kufrah to Jalo occasionally.
This operation is performed using one of the power amplifiers of the telephony system.
The overall system block diagram is. shown in Fig. 6.2.
6.1 Path and. Equipment Parameters
Path, equipment parameters and system dimensions used in this
system design are shown in the following tables and figures:
Table 6.1, Path parameters for the tropo links.
Table 6.2, Path parameters for L.O.S. link.
Table 6.3, System dimensions.
93
d
BENGHAZI
JALO28" 59* 31" N 21" 32" 45" E 170" 07'
Existing Line - o f-S ight Link
Troposcotter Link
Line - of * Sight Link
ZtGHAN25° 47' 51" N 22* 10' 03" E
154° 20'
KUFftAH MOUNTAIN 24* 13' 49" N 22* 5 9 '3 1" E
KUFRAH CITY
Fig. 6.1. Propagation Path Route Map.
Table 6.1. Path Parameters for Troposcatter Links.
Symbol Jalo - Zighan Zighan ~ Kufrah Mt.
D 358.5 km 198.9 kmhts 49 m 215 mhrs 220 m 487 m
hLt 43.9 m 220.3 mhLr 197.3 m 524.5 mhte 5 m 0 m
hre 22.7 m 25 m
dLt 10 km 12.1 km
dLr 19.6 km 22 km
NS 301 (MU)a 8,493 km
Climate Region Desert C.C.I.R. Rep. 244, type 4
96Table 6.2. Path parameters for Line of Sight Link.
LinkKufrah Mt. ~ Kufrah CitySymbol Notes
29.1 kmKufrah Mt. Station512 mhts
412 m Kufrah City StationhrsSee Fig. 6.5Path Profile
D: Path distancehts, hrs: Altitude of transmitting and receiving antenna
hte, hre: Effective height of antenna
hLt, hLr: Elevation of the radio horizon beyond mean sea level
dLt, dLr: Distance from antenna location to radio horizon
Ng: Surface refractivity
a: Effective earth’s radius
Table 6.3. System Dimensions.
Link System
DescriptionJalo - Zighan Zighan - Kufrah Mt. Kufrah Mt - Kufrah City
0/H TV System 0/H TP System 0/H TV System 0/H TP System L.O.S. TP SystemOperating freq band 2 GHZ band (1,700 - 2,000 MHZ)
Transmission capacity 1 CH • TV monochrome 120 CH • TP 1 CH • TV
monochrome 120 CH • TP 300 CH • TPTransmission Output power 20 KW 10 KW 2 KW 1 KW 400 mW
Antenna diameter 27 m, common vse 10 m<f>, common use 2 mij)Low noise amplifier transistor
amplifiertransistoramplifier
transistoramplifier
transistoramplifier -
Diversity system octuple octuple quadruple quadruple single
Combining method Maximum ratio (Ratio square)
Combining stage IF IF £ baseband IF IF I basebandFeeder type Elliptical type waveguide
98
Table 6.4, System parameters.
Table 6.5, Noise performance objectives.
Figure 6.1, Route map and site locations and directions.
Figure 6.2, Overall system block diagram.
Figure 6.3, Profile map of Jalo-Zighan (J-Z) linkFigure 6.4, Profile map of Zighan-Kufrah mountain linkFigure 6.5, Profile map of Kufrah mountain-Kufrah link.
6.2 Radio Frequency Arrangements
The radio frequency arrangements used for the system are illus
trated in the following figures:Figure 6.6, Frequency arrangement for the tropo link.
Figure 6.7, Frequency arrangement for the approach L.O.S link.
These frequency arrangements were determined according to CCIR Recom
mendations 382 and 385.
6.3 Performance Objectives
Refer to Table 6.5.
6.4 Noise Performance Calculation
The noise performance estimations were carried out in accor
dance with the overall design method for troposcatter links as dis
cussed in Chapter 5. This approach as previously stated is based onri2iCCIR Recommendations and NBS Reports-.1- J The calculations of the
overall noise of the radio link has been made with the following assumptions:
99Table 6.4. System Parameters.
0/H Link
Jalon - Zlghan
TV TP
Zlghan - Kufrah Mt.
TV TP
L.O.S. Link Kufrah ~ Kufrah Mt. City
TP
RF center freq, fo
1800 MHZ 1800 MHZ 7575 MHZ
Transmission Output Power (Pt)
20 KW (73 dbm)
10 KW (70 dbm)
1 KW (60 dbm)
2 KW (63 dbm)
400 mW (25 dbm)
Antenna gain at fo (G,)
Antenna beam width
Feeder system loss (Lf)Noise figure of receiver (NF)
Diversity improvement (Y)
51.1 db
7.32 mrad
- 4.0 db
2.5 db
6.0 db
42.5 db
19.78 mrad
- 4.0 db
2.5 db
6.0 db
41.0 db
23.5 mrad
- 11.3 db
8.0 db
0 db
Baseband top freq. (video band)
Freq. deviation
Modulation index
Equipment basic noise
4 MHZ
4 MHZ p-p
-61.2 dbir
552 KHZ
0.5 rad/ CH
-70 dbm
4 MHZ
4 MHZp-p
-61.2dbm
552 KHZ
1.0 rad/ CH
-70 dbm
1300 KHZ
200 KHZ rms
Table 6.5. Noise Performance Objectives.
Noise Performance S/N
System 99.9%95%80%
Jalo-Zighan Link34 db45 dbTelephone route
37 dbTelevision route
Kufrah-Zighan Link34 db45 dbTelephone route
37 dbTelevision route
me
te
r s
A L TI T U D E S C A L E M U L T I P L I E D BY 1 / 4 OR 4
D I S T A N C E P L O T T E D IN 1 / 2 OR 2 X S C A L E
e l e v a t i o n : e s o 1000m
i T x . d i s t a n c e : i e o 240k m
3 9 . 3 mrod
4 0 0 0
2003 0 0 0 30a100
358.2kmd i s t a n c e
Z i g h o n
e l e v . 210 m4 01000
Fig. 6.3. Profile Map (4/3 Radius), Jalo-Zighan.
TOT
met
e r
s
A L T I T U D E S C A L E M U L T I P L I E D BY 1 / 4 OR 4 D I S T A N C E P L O T T E D IN l / E OR EX S C A L E
e l e v a t i o n : tso 1000m d i s t a n c e : i e o B 4 0 kmiOOO
2 3 . 6 mrad1500
1000
1005 0 0
19 8 .9 km 20D I S T A N C E
Kufrah Mtn.ZighanE L E V . 210 m A N T . 5
E L E V . 4 8 2 m ANT. 5
Fig. 6.4. Profile Map (4/3 Radius), Zighan-Kufrah Mtn.
o
A L T I T U D E S C A L E M U L T I P L I E D BY l / 4 OR 4
D I S T A N C E P L O T T E D IN 1/2 OR 2 X S C A L E
e l e v a t i o n : eso 1000m
DI S T A N C E * . 1 2 0 2 4 0 k m
5 5
10005 0 0
9 0 0
8 0 04 5 0
7 0 0
6 0 04 0 0
5 0 0
4 0 03 5 0
3 0 0
200 2030.23;lhm
D I S T A N C E100 Kufroh City
E L EV . 3 8 2 m
A N T . 3 0
Kufroh Mtn.
E L E V . 4 8 2 m
A N T . 3 0
Fig. 6.5. Profile Map (4/3 Radius)» Kufrah City-Kufrah Mtn.
104
1 9 7 5 . 5 -
1 9 4 7 . 5 -
1 9 1 9 .5 -
1 9 0 2 . 5
1 8 7 4 . 5
1 8 4 6 . 5
1 7 8 3 . 5
1 7 5 5 . 5
1 7 2 7 .5
C.C. I. F 6 0
Fig. 6.
TP R o u t e I
t v R o u t e
OCC. T V R o u t e VZZZZfy Future T V C : : ^ >
M H z
• 1961 .5
. 1 9 3 3 .5
1 9 0 5 . 5
• 1 8 8 8 . 5
— 18 6 0 . 5
• 1 8 3 2 . 5
1 8 0 8 . 0
• 1 7 6 9 . 5
• 1 7 4 1 . 5
• 1713.5
M H z
' ' 9 5 1 5 ( H i
M H z
J 9 6 5 .5 jm
1 9 3 7 . 5 (hO
^ 9 2 3 .5 iH ]
I9 0 9 .5 M ,/16 95,5 (VI
--------- /
1981- 5 {.Vk\i--------------. I 8 6 7 . 5 ( V )
--------- /ki--------------
I 7 6 9 . 5 ( H 1
w l 8 l l . 5 (H)_
^ 1 7 8 3 .5(H)
, 1 7 5 5 . 5 M1 7 4 1 . 5 ( V k 'm--------------
, 1 7 2 7 . 5 (V)---------/
1713.5 ( V k <N----------------------------1/
t. Rec, 382 K u f r a h Mtn. Z i g h a n Jo Io
to 3 0 0 CH
6. Frequency Arrangement'for Troposcatter Radio Link.
105
Fig.
7 7 2 2
7 6 8 7
— 7 6 3 8
7 5 8 97 5 7 5
— 7 5 2 6
- 7 4 7 7
- 7 4 2 8
C.C.I.R. Rec. 3 8 5 6 0 to .3 0 0 ch
MHz
ISM-ttibx— — — — — —y/
7 5 8 9 (H )
/ 7 4 7 7 ( H )
7 4 2 8 (H )
ST-BY
TP ROUTE
S T -B Y
TP ROUTE
Kufroh Kufroh City Mountain
6.7. Frequency Arrangement for L.O.S. Radio Link.
106
i. Surface Refractivity, Ng = 301.
ii. Climate Region, Desert (CCIR Rep.. 244-2, type A) Refer to Table 6.6 and Figs. 6.8 to 6.11.
Table 6.6. Results of Noise Performance Calculations.
LinkDescription Jalo - Zighan Zighan-Kufrah Mt. Kufrah Mt. - Kufrah City
System TV TP TV TP TP
hop distance 358.5 KM 198.9 KM 29.1 KM
propagating mode scatter scatter L.O.S.
operating radio freq. 1,700 MHZ ' 2,000 MHZ 1,700 ~ 2,000 MHZ 7,425 MHZ - 7,725 MHZ
antenna diameter 27 m 10 m 2 m
order of diversity octuple quadruple route standby
transmission capacity 1 CH monochrome 120 CH 1 CH mono 120 CH 300 CHchrome
transmitting output power 73 dbm 70 dbm 63 dbm 60 dbm 26 dbm
antenna gain 51 db 51 db 42.5 db 42.5 db 41 db
total gain 175 dbm 173 dbm 148 dbm 145 dbm 108 dbm
propagation loss 231. 9 db 217. 1 db 139.3 db
antenna coupling loss 16. 3 db 3. 4 db -
feeder circuit loss 4, 0 db 4.0 db 8.8 db
Total loss 252. 2 db 224. 5 db 148.1 db
Table 6.6— Continued."— '— Link
Description ~~~~---_
System TV TP TV TP TP
Receiving input level -77.2 dbm -80.2 dbm -76.5 dbm -79.5 dbm -40.1 dbmUpper limit of video band 4 MHZ 552 KHZ 4 MHZ 552 KHZ 1300 KHZFreq. deviation (modulation
index) 4 MHZ p—p 0.5 rad/CH 4 MHZ p-p 1.0 rad/CH 200 KHZ r.m.s.noise figure of receiver 2.5 db 2.5 db 2.5 db 2.5 db 7.0 dbS/N for triangle or thermal noise 50% 52.3 db ' 55.8 db 53. db 62.6 db 82.3 db
80% 47.8 db 51.3 db 46.2 db 55.8 db 79.1 db99.9% (95%) 43.4 db 38.8 db (95%) 39.4 db 36.4 db -
S/N for path intermod. noise 50% 55.8 db 50.4 db
80% - 52.4 db - 55.6 db -
99.9% - 43.0 db - 40.6 db -
S/N for equip, noise 68.1 db 70.0 db 68.1 db 70.0 db 75.5 db
S/N for feeder echo noise - 68.2 db - 68.2 db 77 db
Table 6.6— Continued.
TPTPTVTPTV
S/N Total69.4 db57.5 db52.9 db52.6 db52.2 db50%69.1 db52.5 db46.2 db48.7 db47.8 db80%
(95%) 39.4 db 35.0 db37.4 db(95%) 43.4 db99.9%
ovo
Sig
nal
- to
- N
oise
R
atio
in
d B
110
8 0
7 0
6 0
5 0
4 0
3 0
9 0 95 9 8 99 9 9 j8 9 9 . 9 9
T i m e Percentage
Fig. 6.8. Noise Performance (TP): Jalo-Zighan Link.
*Refer to Table 6.5.
Ill
8 0
N o i s e O b jec t ive
7 0
6 0
5 0
4 0
30
209 0 95 9 8 9 98 0 9 9 .8 9 9 . 9 9
T i m e Percentage
Fig. 6.9. Noise Performance (TV): Jalo-Zighan Link.
Sig
nal
-to
- N
oise
R
atio
in
dB
112
8 0
. Noise O b je c t i v e
7 0
6 0
5 0
4 0
30
209 0 9 5 9 8 9 9 9 9 . 8 9 9 . 9 9
T i m e P e r c e n t a g e
Fig. 6.10. Noise Performance (TV): Zighan-Kufrah Mtn. Link.
Sig
nal
- to
- N
oise
R
atio
in
dB113
8 0
NoiseO b je c t iv e
70
6 0
5 0
4 0
30
9 9 . 9 99 9 . 89 8 9 99 0 956 0 7 0 8 0
Time Percentage
Fig. 6.11. Noise Performance (TP): Zighan-Kufrah Mtn. Link.
CHAPTER 7
PROPAGATION TEST BETWEEN JALO AND KUFRAH
The propagation test for the Jalo-Kufrah troposcatter radiosystem was carried out during the 11 months following the completion
of the system in April 1978, The purpose of the test was to confirm
the actual statistics of the radio propagation.
The radio propagation path of the Jalo-Kufrah system is across
desert. Propagation conditions in the desert are comparatively more
unstable than other areas.' *However, with the results of the propagation test it could be
confirmed that satisfactory system quality for practical use would be
accomplished.
7.1 Test Schedule
The propagation test was carried out for nearly a whole year,
from April 1978 to March 1979, with a few interruptions in between due
to adjustments arid maintenance.
7.2 Test Links
Two hops were involved in the. testing, and those were Jalo-
Zighan (J-Z), and Zighan-Kufrah (K-Z).
A route map of the propagation path was already illustrated
in Fig. 6.1. The propagation path parameters were also summarized in
114 ■
115
Table 6.1. Figure 7.1 shows the block diagram of the measurement
test.
7.3. Testing Facilities The main characteristics of the testing facilities are tabu
lated in Table 7.1.
7.4 Test Results and Considerations
7.4.1 Basic Transmission LossFigure 7,2 shows samples of the strip recording of the received
signal level. Figures 7.3 and 7.4 show the cumulative distributions of
the basic median transmission loss for the month of August 1978 and for
the whole period of 11 months. It was computed, from the strip record
ings of the received signal level.
Cumulative distributions for. each month specifically during the
whole period are illustrated in Appendix B,
7.4.2 Daily Variations of Basic Transmission Loss
Figures 7.5 and 7.6 show the variations of the basic transmis
sion loss, in both hops. The variations of the basic transmission loss are exactly corresponding to the variation of the hourly median value of the recorded received signal level.
7.4.3 Signal-to-noise Ratio
Figure 7.7 shows samples of the strip recording of the signal
to noise ratio. Figures 7.8 and 7.9 show the cumulative distributions
116Table 7.1. Measurement of Propagation Characteristics for
Jalo-Kufrah Xroposcatter Radio Link.
1. Block diagram for the measurement Refer to Fig. 7.1
2. Measurement condition
2.1 Receiving Signal Level (RSL)Signal-to-noise Ratio (S/N)
2.2 Calibration Period
2.3 Measurement Period
3. System Parameter3.1 Transmitter End Jalo-Zighan Kufrah-Zighan
output power (Pt) 73.0 dbm 60.0 dbmBPF loss (L^pP 0.3 db 0.3 dbfeeder loss (L^^) 0.7 db ■ 0.7 dbcircuit loss (Lct) 0.3 db 0.3 dbgain of antenna (G^) 51.0 db 42.5 db
Receiving Enggain of antenna (G^) 51.0 db 42.5 dbantenna coupling loss (L^) 16.3 db 3.4 dbfeeder loss (L^ ) 0.7 db 0.7 dbBPF loss 0.5 db 0.3 dbcircuit loss (L ) 1.5 db 1.5 dbcr-gain of diversity (G^) 3.0 db 3.0 db
Relation between Receiving Signal Level (RSL) and Basic Transmission Loss (L, ) is as follows;DtilS
RSL = pt " S p t " Lft " Lct + Gt ' H m s " Lc + Gr " Lfr " H p r
—-- . TP-1 , .
—TP—1/TP—2 Comb
—— Monthly From April 78
to March 1979
A N T - 2
frorn^MUX
MON
ANT-1AGO OUT
Terminal No. 9
RSL
S/N
DEMLNA-2
D E ML N A - ICONV
FREQ
FREQ
CONV
MAIN
AMP
MAIN
AMP
MODEX-2
EX-
PA-I
HPA
PA-2
HPA
COMB
B B
2 - P E NRECORDER
(E R P -200 )
Fig. 7.1. Block Diagram for Measurement of Propagation Characteristics Jalo - Kufrah Mtn. Troposcatter Link.
i
toMUX
117
Rec
eivi
ng
Sign
al
Leve
l (-
dBm
) R
ecei
ving
Si
gnal
Le
vel
HB
m)
118
M OK» L ie * # " Lo ca l Time
2 3 M a y»o80
50
40M e i le n H o u r l y V a l u e s
V a r ia t io n of Receiving Signal LevelU a lo — Zighan Link)
CHART SPEED: 20mm/hour TIME CONSTANT: I min.
L ib ya n Lo c a l T im e3 Aug
50
60
70
80
90
100M edian H o u r l y Va l u e s
V a ria t io n of Receiving Signal Level(Zlghan — Kufrah Min. Link)
CHART SPEED: 20mm/hour TIME CONSTANT: | min.
Fig. 7.2. Variation of Receiving Signal Level.
Tra
nsm
issi
on
Loss
in
dB
(One Hour M e d i a n )J-Z*. Jo lo —Z ig h a n K-Z* Z ig h a n - Kufrah M t n .
170
180Duration: August 1978
190 k - z
j - z
200
210
220
230
2 4 0
2 5 0 90 95 98 99 99.5 99.90.1
Time Percentage
Fig. 7.3. Cumulative Distribution of Transmission Loss (One Hour Median).
Tran
smis
sion
Lo
ss
in d
B
170
180 —
190 —
200 —
210
220
23 0 —
240
I I I I I I I I I I I I I I I IJ-Z*. J a lo - Z i g h a n K-Z*. Z i g h a n - Kuf rah Mtn.
2501o.i i 111111 ii iii0 .5 I 2 5 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 9 5 9 8 99 99 .5 9 9 .9
Time Percentage
Fig. 7.4. Annual Transmission Loss Cumulative Distribution (One Hour Median). 120
Rec
eivi
ng
Sig
nal
L
evel
(-
dB
m)
August 1 9 7 8
M a x V a r ia t i o n
5 0
M i n V a r i a t i o n
7 0
8 0
9 0
100302 5
DateFig. 7.5. Amplitude of Daily Variations in Hourly Median Value of Receiving Signal
Level: Jalo-Zighan Link.
121
Rec
eivi
ng
Sig
na
l L
evel
(-
dB
m)
4 0 August 1 978
Max V a r i a t i o n
5 0Min V a r i a t i o n
6 0 GT
7 0
( W
8 0
9 0
Dat e
10020 353 02 55 10 15
Fig. 7.6. Amplitude of Daily Variations in Hourly Median Values of Receiving Signal Level: Zighan-Kufrah Mtn. Link.
Slgn
al-t
o-N
oise
Ra
tio
in dB
Si
qnal
-to-
Noi
se
Ratio
in
dB
123
70
60
50
40
30
§ oOo o o o o o oo oo
a o O O o o <*1 1 1 1 1 r i i i i r i r i " r i t 1 1 1 1 1 I 1
L ib y a n L o ca l Tim a/ — "
-
2 3 May ~
1 1 l I i 1M e d i a n H o u r l y V a l u a e
_ . i .1 l... .1 1 1 1 l l 1 1 1 1 1 ! 1 1 1 ~
V ariat ion of S ig n a l-to -N o ise Ratio in dB(Jolo -Z lg h a * Link)
CHART SPEED*. 20 mm/hour TIME CONSTANT: I
70
60
60 —
40 —
I I I I I I I I I I IL ib y a n Lo c a l T im a
oo
t i r3 Aug
so — I I IM e d i a n H o u r l y V a l u e *i i i i i i i ' i i
V a r ia t io n of Signal-to-Noise Ratio in dB(Zlghon - Ku f r oh Min. Link)
CHART SPEED-. 20 mm/hour TIME CONSTANT: I mie.
Fig. 7.7. Variation of Signal-to-noise Ratio in dB.
Sig
nal-
to-N
oise
Ra
tio
in dB
J-Z'. Jalo - Z ighan K-Z*. Zighan - Kufrah Mjn.
90
Des ig n Ob je c t ives .8 0
7 0
6 0
5 0 J -Z
K-Z4 0
80 9 0 95 9 8 99 99.5 9 9.9 9 9 .9 9
Time Percentage
Fig. 7.8. Annual Signal-to-noise Cumulative Distribution (One Hour Median).
Sig
na
l-to
-No
ise
R
atio
in
d8
80
D uration : August 1978
Design ObjectivesK-Z J -Z70
60
50
4 0
3 0
9 0 9 5 9 8 99 99.8 99.
Time Percentage
Fig. 7.9. Signal-to-noise Cumulative Distribution (One Hour Median) for Jalo-Zighan and Zighan-Kufrah Mountain Links During the Months of August 1978.
126of the SNR for the month of August 1978 and for the whole period of 11 months.
7.4.4 Daily Variations of the SNR
Figures 7.10 and 7.11 show the variations of the SNR in both
hops. The variations of the SNR correspond to the variations of the
hourly median value of the recorded signal to noise.
7.5 Test Results and Propagation Characteristics
7.5.1 Variation of the Receiving Input LevelIn this area, the general trend in the variation of the re
ceived input level (basic transmission loss) is that it is high at nights beginning to decrease sometime at dawn. It decreases gradually
in the daytime, becomes very low in the afternoon and increases rapidly
in the evening.The variations in one day seem not to be affected by the season
and is somewhat similar throughout most of the year. Typical examples
are shown in Figs. 7.12 and 7.13 respectively.
The amplitude of the daily variations for each month are illus
trated in Appendix B, for both (j-Z) and (Z-K) links. The difference
between the maximum and the minimum level of the daily variations is
55 db maximum for (J-Z) link, and 60 db maximum for (Z-K) link.
There are two types of fading, low level and fast fading and
high level and slow fading. The latter may be caused by refractive layers at the tropo region, that is, a duct type mode. It appears that,
the duct mode in the Northern Sahara desert area occurs more frequently
Sig
nal-
to
- N
oise
R
atio
in
d B
A u g u s t 1 9 7 8
7 0
6 0
5 0
Ai M a x im u m H o u r ly M e d i a n L eve l
B! M e d ia n H o u r l y M e d i a n L eve l
C: M i n i m u m H o u r ly M e d i a n L eve l4 0
D a t e
30 20 25 3 0
Fig. 7.10. Variation of Signal-to-*noise Ratio for J-Z Hop.
Sig
na
l-to
- N
oise
R
atio
in
dB
80A u g u s t 1 9 7 8
70
6 0
50
A*. M ax im um Hourly M e d i a n Leve l
B ‘. M e d ia n H o u r l y M e d i a n L eve l
C: M i n im u m H o u r ly M e d i a n L eve l4 0
Da t e3 0
20 3 0
Fig. 7.11. Variation of Signal-to-noise Ratio for K-Z Hop.
128
Rec
eivi
ng
S
ign
al
Lev
el
(-d
Bm
)
4 0
5 0J - Z 31 M a y 7 8 J - Z I A u g u s t 7 8
6 0
70
8 0
9 0
1005 10 15 20 250
E l a p s e d T im e in H o u r s
Fig. 7.12. Daily Variations of Receiving Input Level: May-August. 129
Rec
eivi
ng
S
ign
al
Lev
el
(-d
Bm
)4 0 Y ;
J - Z 10 Feb 7 9
• A
6 0 J - Z 17 M a r 7 9
7 0
8 0
9 0
10020 255 10 150
E l a p s e d T im e in H o u r s
Fig. 7.13. Daily Variations of Receiving Input Level: January-March.
130
131at night. Also,, in the daytime, when the ground receives the direct rays of the sun, strong air disturbances occur, At night, the air disturbances become weak, since there is no heat caused by the sunshine.
The temperature drops considerably, and an elevated layer can be formed.
This causes duct propagation to be increased. Occurrence of the ducts then increases the possibility of higher receiving inputs.
7.5.2 Transmission Loss (L, )omsCumulative distribution of the basic transmission loss obtained
from the hourly median received level for the whole period are illus
trated in Appendix B.Fading range of the transmission loss ) of each link is
16 to 29 db for 5.0% to 99.9%. Its average value is 21 db, a normal distribution with a standard deviation of 5 to 9 db.
7.5.3 Comparison between Calculated and Measured Values of the Propagation Loss
The transmission loss of the troposcatter propagation were cal
culated by the design method stated in Chapter 4. This design method
as previously stated is in accordance with CCIR Report 244-2 and NBS
Reports. The results are shown in Table 7.2. Comparison with the test
data show that: ,1. Calculated value of the transmission loss is larger than that
of the measured value by 15 db for the (J-Z) link and by 3 db
for (K-Z) link. The difference is presumably caused by the
following:
132
Table 7,2* Comparison between Calculated Value and Measured Value of the Propagation Loss,
. Hop J-Z K-ZDistance KM 358.5 KM. 198.9 KMAntenna diameter 27 m<}> 10 m<j>
Scatter angle 38.801 23.554
Propagation loss calculated
231.9 db 217.1 db
Propagation loss measured
217 db 214 db
133a. The value of the correction term to the median for the Northern
Sahara area, V(de, 0,5), is not that accurate for the climatic
region of this district.
b . The propagation characteristics markedly affected duct type mode
propagation, i.e., the probability occurrence of duct type mode propagation in these two links was high during the whole period.
7.6 ' System Performance
7.6.1 General Description
Performance of the system is intended to satisfy CCIR Rec.
397-2. Noise loading tests were carried out at each hop for one day
or two and S/N was recorded continuously. From those tests and as a
design factor for the system, the optimum S/N was obtained at 0.5
radians of the modulation index for (J-Z) link and at 1 radian for (K-Z) link.
7.6.2 S/N Throughout the Link
S/N was recorded for eleven months between the two hops (J-Z)
and (K-Z). The result is arranged in accumulative distribution curves
as shown in Figs. 7.7 and 7.8 and the figures present in Appendix B,These figures indicate that:
1. The noise performance objectives were met throughout the whole period.
2. Variations of the hourly median value of the S/N within a day
was about 10 to 20 db. Amplitude of the daily variations for
most of the months is present in Appendix B and Figs. 7.12 and
7.13.
134
7.6.3 Seasonal Variation of the S/N Distribution
• An obvious difference caused by the nature of fading phenomena can be observed between the S/N distributions in the summer (April- October) and in winter (November-March) seasons.
In the summer season the 50% value is less than that in the winter (refer to Tables 7.3 and 7,4). The shape of the lower percen
tage of the distributions tends to show that the S/N is greater in the
summer than it is in winter. This leads to the conclusion that severe fading occurs more frequently in the summer.
7.6.4 TV Transmission
No special test for TV transmission was carried out. As far as S/N considerations are concerned9 the- system appears to satisfy the noise
performance objectives recommended by the CCIR,'which is 37 db for 95%
of the time.
135
Table 7.3. Measured Signal-to-noise Ratio of J-Z Link.X A M J -'A - S 0 N D J F M
20% 70 69 68 70 70 69 69 69 70 70 68.5 68
50% 65.5 64 64 68 68 66 65.5 68 69.5 68 65 65
80% 60 58 58.5 64 64 62 59 65.5 67.5 65.5 60 60
95% 54 52.5 53 59.5 59.5 57 53 61 65 62 55.5 55
99% 49 -p- oo In 49 54 55 53 49.5 57 62 59 52.5 52
99.9% 42 46 46 43 51 48 46 54 60 58 50 50
Table 7.4. Measured signal-to-noise ratio of K-Z link.X A M J J A S 0 N D J F
20% 67 67 66 69 65 63 66 67 70 70 68.5
50% 62 60 60 65 61.5 59.5 61 65 68.5 67 65
80% 56 52.5 53 59.5 55.5 55 53 61 65 63 60
95% 49 54 47 53.5 50 50 45 56 61.5 60 54.5
99% 42.5 39 43 46 45 46 40 51 59 58 51
99.9% 35 34 40.5 38 38 42 36 48 58 56 48
CHAPTER 8
SUMMARY AND CONCLUSIONS
The main purpose of this thesis was to describe the basic
information, techniques, and practices used in planning and engineering
over-the-horizon communication systems.The design method discussed and presented in Chapters 3, 4 and 5
was provided by Nippon Electric Company, which is based on CCIR Report
244-2 and NBS Report 101,
Literature on tropospheric.propagation was outlined with emphasis
on propagation mechanisms, diversity techniques and modulation systems
such as the extension demodulator which helps to extend the threshold
point of the receiving system to a low point, thus enabling it to receive
incoming weak signals,A troposcatter radio link between Jalo and Kufra across the
Northern Sahara desert was presented in Chapter 6. It was designed by NEC using the design procedure discussed in the proceeding chapters.
The link performance was calculated and estimates for path loss arid S/N
were laid out.A propagation test for the mentioned link was carried out for
nearly a whole year, from April 1979 to March 1979, The propagation
conditions were investigated through path loss variations and S/N per
formance. Theoretical calculations were compared with experimental
data and the following conclusions were drawn out: .
136
The measured propagation loss is smaller by 15 db and 3. db for (J-Z) and (K-Z) . links than the estimated values..Noise performance was met throughout the months of testing,
indicating the suitability for the design choice of having a 0.5 radian as a modulation index for (J-Z) link and 1 radian
for (K-Z) link.
Severe fading was existent and evident throught most of the year especially during the summer months, indicating the need
for further studies of the meteorological effects in the area.
The diversity techniques employed in the system did not seem to
be completely effective against the severe fading existing in the link. This indicates the need for more propagation testing
for longer periods of time.With the nature of fading existing in the area, future data
transmission on this link would be out of the question without
a very effective form of error control coding. This would
greatly reduce the effective data transmission rate.
APPENDIX A
DESIGN.GRAPHS FOR DIFFERENT VALUES OF Ng AND DIFFERENT CLIMATES
(From N.E.C,, Ltd. Tokyo, Japan, System design of tropospheric scatter radio links, SB534R-006 (issue-3) 1969.^^)
138
150
160
170
180
190
200
210
220
2 3 0
2 4 0
2 5 0
Path D is ta n c e ' d ' in K i l o m e t e r s
A n g u l a r D i s t a n c e ' 9 ' in R a d i a n s
S = 0 . 2 0 S = 0 .3 0" S = 0 . 5 0 S = 0 . 7 0 S= 1 .00 -
2 5 10 2 0 5 0 100 2 0 0 5 0 0
THE FUNCTION F (8 d ) FOR N s = 301
Fig. A-l
150
160
170
180
190
200
210
220
2 3 0
2 4 0
2 5 0
2 6 0
2 7 0
2 8 0
14iI I
S = 0.0l = 0.02
S = 0 . 0 5 = 0.10
Path D is ta n ce ' d ' in K i l o m e t e r s
A n g u l a r D is ta n c e ' 0 ' in R a d i a n s
S = 0* 2 0 S = 0 . 3 5 = 0 5 0 5 = 0 7 0 5= 1.00
100 , 2 0 0 5 0 0 10
THE FUNCTION F (6d ) FOR N s = 2 5 0
Fig. A-2
150
160
170
180
190
200
210
220
2 3 0
2 4 0
2 5 0
2 6 0
2 7 0
2 8 0
2 9 0
3 0 0
14
S=00l = 002
S= 0 - 0 5 = 010
P a t h D is tance ' d ' in K i l o m e t e r s
A n g u l a r D is tan ce ' 6 # in R a d i a n s
S = 0 . 2 0 ' S = 0 . 3 0 ' S = 0 . 5 0
S = 0 . 7 0 ' S= 1 .0 0 '
100 200 10
THE FUNCTION F (6 d ) FOR N s = 3 5 0Fig. A-3
150
160
170
180
190
200
210
220
2 3 0
2 4 0P a t h D is t a n c e ' d ' in K i l o m e t e r s
A n g u la r D is t a n c e '9 ' in R a d i a n s
S = 0 . 2 0 ' S = 0 . 3 0 "
S = 0 . 5 0 ' S = 0 . 7 0 S=1.00
THE FUNCTION F(6d) FOR N s = 4 0 0Fig. A-4
9 0
80
70
6 0
5 0
4 0
30
20
10
0
-10
20
-30
Maritime Subtropical Climate Over Land
100 2 0 0 3 0 0 4 0 0 5 0 0
E f f e c t i v e D i s t a n c e
TRANSMISSION LOSS VARIABILITY
Fig. A-5
V(P
,de
)
144
Equatoria l C limate
9 9 . 99 9 . 9 9
0 0 2 0 0 3 00 4 0 0 500 600 700 800
E f f e c t iv e Distance
9 0 0 km
T R A N S M IS S IO N LOSS V A R IA B IL ITY
Fig. A-6
V(P
,de
)
145
Continental Te m p era te Climate50
4 0
3 0
0.010.120
5 09 09 9
9 : 9 9-10
-20
- 3 0
- 4 0 7 0 0 8 0 0 9 0 0 km
E f f e c t i v e D is tance
T R A N S M IS S IO N LOSS VARIABILITY
Fig. A-7
V(R
,de
)
146
Maritime Temperate Climate Over Land70 0.0
6 0
5 0
4 0
3 0
20
5 0
9 0-109 9
-20 99 .9
99 .99
- 3 0
-40
E f fe c t iv e Distance
TRANSMISSION LOSS VARIABILITY
Fig. A-8
V(P
,de
)
147
Continental Subtropical C l im ate (Sudan)50
4 0
3 0
20
5 09 09 99 9 . 99 9 . 9 9-10
-20
- 3 0
- 4 08 0 0 9 0 0 km100 2 0 0 3 0 0 4 0 0
Ef fec t ive D is tance
Fig. A-9
V(P
,de
)
148
Maritime Temperate Climate Over SeasP %
o.oi70
600.1
50
4 0
30
20
50
-10 90
99-2099.9
- 3 0 99.99
- 4 0100 200 3 00 4 0 0 500 600 700 800 900 km
E f fe c t iv e D is tan ce
TRANSMISSION LOSS VARIABILITY
Fig. A-10
APPENDIX B
PROPAGATION LOSS -AND S /N" CURVES FOR THE JALO-KUFRAH LINK
The following is an explanation of the groups of figures
represented in this Appendix:
a. Propagation loss and S/N cumulative distribution curves for
the period between April 78 and March 79; Figs, B-l through
B-22.
b . Amplitude of daily variations of hourly median values of R.S.L. for different months of the period between April 78
to March 79; Figs. B-23 through B—42.
c. Variations of signal-to-noise ratio for different months of
the per dbetween April 78 to March 79; Figs. B-43 through
B-46.d. Daily variations of receiving input level for different months
during the period between April 78 and March 79; Figs. B-47
through Br-51.
The following figures (B-l through B-22 show the propagation
loss and S/N cumulative distribution curves for the period between
April 78 and March 79.
149
SIGN
AL
TO
NOIS
E RA
TIO
IN db
80J-Z
Duration: April, 1978
Design ObjectivesK-Z70
60
50
4 0
30
200.1 0.2 0.5 I 2 5 10 2 0 30 4 0 50 60 70 8 0 90 95 98 99 99.9
TIME PERCENTAGE
Fig. B-l.
SIGN
AL
TO
NOIS
E RA
TIO
IN db
80
J-ZDurotion: May, 1978
Design Objectives70 K-Z
60
50
4 0
30
2020 30 4 0 50 6 0 70 80 90 950.102 0.5 I 2 105 98 99 999
TIME PERCENTAGEFig. B-2.
SIGN
AL
TO
NOIS
E RA
TIO
IN db
80
Duration: June, 1978
Design Objectives
J-Z70 K-Z
6 0
50
4 0
30
2098 99 99990
TIME PERCENTAGEFig. B-3.
SIGN
AL
TO
NOIS
E RA
TIO
IN db
80
Duration: Jul% 1978
'^ 0 Design ObjectivesJ-Z-K-Z70
60
50
4 0
3 0
20 90 95 98 99 99.90.1 0.2 0.5 K 2TIME PERCENTAGE
Fig. B-4.
SIGN
AL
TO
NOIS
E RA
TIO
IN db
80
Duration: September, 1978
’’ D Design Objectives7 0 J-ZK-Z
60
50
40
3 0
2090 98 99 99.9
TIME PERCENTAGEFig. B-5.
SIGN
AL
TO
NOIS
E RA
TIO
IN db
80
Duration: October, 1978
Design ObjectivesJ-Z70K-Z
60
50
40
30
2080 90 98 990.1 0.2 05 99.9
TIME PERCENTAGEFig. B-6.
SIGN
AL
TO
NOIS
E RA
TIO
IN db
80
Duration: November, 1978
^ 0 Design ObjectivesJ-Z70
60
50
4 0
3 0
2098 999 0 99.90.1 0.2 0.5
TIME PERCENTAGEFig. B-7.
80|
TO
601
50
40'
30'
20 1------- 1---1----- 1----- L0.1 02 03 I 2 5
Duration: December, t9™^ D e s i g n Objectives
98 99999
20 30 40 50t i m e PERCENTAGE
70 80
Fig. B'8*
i_n
SIGN
AL
TO
NOIS
E RA
TIO
IN db
80
Duration: January, 1979
^Design Objectives70 J -ZK-Z
60
50
4 0
30
2090 98 99 99.9
TIME PERCENTAGE
Fig. B-9.
SIGN
AL
TO
NOIS
E RA
TIO
IN db
80
Durotiore February, 1979
^ 0 3 Design Objectives70
60
J-Z
5 0K -Z
40
30
2090 98 99 9 9 3
TIME PERCENTAGE
Fig. B-10.
159
SIGN
AL
TO
NOIS
E RA
TIO
IN db
80
Duration: March, 1979
Design ObjectivesJ-Z
7 0
6 0
50
4 0
30
209 0 95 9 8 99 99.90.50.1
TIME PERCENTAGE
Fig. B-ll.
Tra
nsm
issi
on
Lo
ss
in d
B
170
180 Duration: A p r i l 197 8
190
200
210
220
2 3 0
2 4 0
2 5 0 90 98 99 99.5 99l9OT
T im e Percentage
Fig. B-12.
Tran
smis
sion
Lo
ss
in dB
170
180
190
200
210
220
2 3 0
2 4 0
1 ! I T T m i" I I I
Duration: May 1 978
2 5 0 4o 30 Jo 36 60 Jo 05 sL 95 9§ 99 is.3 99-90.1 0 .5 I 2 10
T im e Percentage
Fig. B-13.
170
CDTJ
«/)UtOco
200 —
0.5 I
220 —
2 3 0 —
2 4 0 —
250,
Duration: June 1978
5 8 0 9 0 95 98 9.9
T im e Percentage
Fig. B-14. 163
Tra
nsm
issi
on
Lo
ss
in d
B
170
180Durat ion! July 1 9 7 8
K-z190
J - Z
200
210
220
2 3 0
2 4 0
2 5 09 0 9 5 98 9 9 99 .5 9 9 .9
Time Percentage
Fig. B-15. 164
170
180
190
200
210
220
2 3 0
2 4 0
2 5 00
m — n — i tt tt i i m tttDur a t i on ! S e p t e m b e r 1978
k - z \ j - z
I o .5 I 2 5 10 2 0 3 0 4 0 5 0 6 0 70 8 0 9 0 9 5 98 99 9 9 .5 9 9 .9
Time P e r c e n t ag e
Fig. B-16. 165
Tra
nsm
issi
on
Lo
ss
in d
B
170
180Durat ion! Oct ober 1978
K-z190
200
210
220
230
2 4 0
2 5 09 0 9 5 98 9 9 9 9 .5 9 9 .9
T i me P e r c e n t ag e
Fig. B-17. 166
Tra
nsm
issi
on
Lo
ss
in d
B
170
180Duration*. November 1978
190j-z
200
210
220
2 3 0
2 4 0
2 5 09 0 95
T i me P e r c e n t a g e
Fig. B-18. 167
Tra
nsm
issi
on
Lo
ss
in d
B
170
180
190
200
210
220
2 3 0
2 4 0
2 5 0
I
Durat ion: D e c e m b e r 1978
U0.1 0 .5 I 2 5 10 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 9 5 98 9 9 9 9 .5 9 9 .9
Ti me Per c e n t a ge
Fig. B-19. 168
170
180
190
200
210
220
2 3 0
2 4 0
2 5 00
i i T ~ n — i t i n i i— i i iDurat ion: J a n u a r y 1 9 7 9
10 20 30 40 50 60 70 80
T i m e P e r c e n t a g e
Fig. B-20.
1_J__111 .90 95 98 99 99.5 99.90.5 I
169
00*o
170
180
190
200
210
| 220 o
2 3 0
2 4 0
2 5 0o.i
m n
0.5 I 10
Durat i on: F e b r u a r y 1 9 7 9
CD*o
c0toto
1COcoL.H
170
180
190
200 —
210
220
2 3 0
2 4 0
2 5 0o.i
J -Z
0.3 I 10
D u r a t i o n : Ma r c h 1 9 7 9
I I I I I I I_LJ_1_L20 30 40 50 60 70 80 90 95 98 99 99.5 99.9
T i m e P e r c e n t a g e
Fig. B-22. 171
172The following figures (Figs. B-23 through 33-42) show amplitude
of daily variations of hourly median values of R.S.L. for different months of the period between April 78 to March 79.
Rec
eivi
ng
Sig
na
l L
evel
(-
dB
m)
4 0 A p r i l 1 9 7 8
Max V a r i a t i o n ---------------
Mi n V a r i a t i o n
60gr-r
M
D a t e100
10 15 2 0 2 5 3 0 3 5
Fig. b-23. Amplitude of Daily Variation in Hourly Median Valueof Receiving Signal Level: Zighan - Kufrah Mtn. Link
Rec
eivi
ng
Sig
na
l L
evel
(-
dB
m)
40
5 0
6 0 —
7 0
8 0
A p r i l 1 9 7 8
Max V a r i a t i o n ----------------
Mi n V a r i a t i o n
9 0 A mp l i t u de of D a i l y Va r i a t ion in Hour ly M e d i a n V a l u e
of Receiv ing S i g n a l Le ve l : J a l o - Z i g h a n Link
1001
10 15 20Date
2 5
Fig. B-24.
30 35
Rec
eivi
ng
S
ign
al
Lev
el
(-d
Bm
)
4 0May 1 9 7 8
Max V a r i a t i o n5 0
M i n V a r i a t i o n
7 0
8 0
Ampl i tude of Dai ly V a r i a t ion in Hour ly Med i an V a l u e of Rece iv i ng S i g n a l L e v e l : J a l o - Z i g ha n Link
9 0 —
10035302520
Date Fig. B-25.
Rec
eivi
ng
S
ign
al
Lev
el
(-d
Bm
)
4 0 M a y 1 9 7 8
M a x V a r i a t i o n5 0
M i n V a r i a t i o n
6 0
7 0
9 0
1003 0 3 52 5
Fig. b-26. Ampli tude of Daily Variat ion in Hourly Median Valueof Receiving Signal Level! Zighan - Kufrah Mtn. Link
176
Rec
eivi
ng
S
ign
al
Lev
el
(-d
Bm
)
4 0J u n e 1 9 7 8
M a x V a r i a t i o n5 0
Mi n V a r i a t i o n
6 0
7 0 — 6
8 0
9 0
D a t e
1003 0 3520 2 5
Fig. b-27. Amplitude of Daily Variation in Hourly Median Valueof Receiving Signal Level* J a l o -Z ighan Link
Rec
eivi
ng
S
ign
al
Le
ve
l (-
dB
m)
40 <?n J u n e 1 9 7 8
5 0
6 0
7 0
8 0
9 0
100
X3%\
a
$>-Ql % /
Date
Max V a r i a t i o n
Mi n V a r i a t i o n
10 15 20 25 30 35Fig. B-28. Amplitude of Daily Variation in Hourly Median Value
of Receiving Signal Level: Zighan - Kufrah Mtn.
Rec
eivi
ng
S
ign
al
Lev
el
(-d
Bm
)
4 0 J u l y 1 9 7 8
M a x V a r i a t i o n
5 0M i n V a r i a t i o n
6 0
8 0
9 0 Ampli tude of Dai ly Var iat ion in Hourly Median Value
of Receiving Signal Level : Z igha n - Kufrah Mtn. Link
10020 25 30 35
DateFig. B-29.
Rec
eivi
ng
S
ign
al
Lev
el
(-d
Bm
)(p"0-O“© J u l y 1 9 7 8
b oM a x V a r i a t i o n
Mi n V a r i a t i o n
100 —
Ampl i tude of Dai ly V a r i a t i o n in Hour ly M ed i an V a l u e
of Rec e i v i ng S i g n a l Level : Ja Io - Z i g h a n L ink
i i I___________15 20
Date25
Fig. B-30.
3 0
Re
ce
ivin
g
Sig
na
l L
evel
(-
dB
m)
T
9 0 —
100 —
I \ I \ P-&Qf113
y W ® \ k ' \ p
S e p t e m b e r I 9 7 8
M a x V a r i a t i o n
Min V a r i a t i o n
Amp l i tu de of Da i ly V a r i a t i o n in Hour ly M e d i a n Value of Receiving S i g n a l Level : J a l o - Z i g h a n L i nk
10 15 20Date
25 30 35
Fig. B-31.
Rec
eivi
ng
Sig
na
l L
evel
(-
dB
m)
4 0 — S e p t e m b e r 1 9 7 8
M a x V a r i a t i o n - -50
Min V a r i a t i o n
6 0 — 4 1
V-X I7 0
80
9 0A mpl i t ude of D a i l y V a r i a t i on in H o ur ly M e d i a n V a l u e
of R ece iv i ng Signal Level : Z i g ha n - K u f r a h Mtn. Link
10030 352520
DateFig. B-32.
Rec
eivi
ng
S
ign
al
Lev
el
(-d
Bm
)40 October I 978
, Max V a r i a t i o n
Min V a r i a t i o n
D a t e
10 15 2 0 25 3 0 3 5
Fig. b-33. Amplitude of Dai ly Variation in Hourly Median Valueof Receiving Signal Level: Zighan - Kufrah Mtn. Link
Rec
eivi
ng
Sig
na
l Le
vel
(-d
Bm
)4 0
N o v e mb e r 1 9 7 8
Max V a r i a t i o n
0-0 Mi n V a r i a t i o n
6 0
8 0
A mp l i t u de of Dai ly Va r i a t ion in Hour ly M e d i a n Va lue
of Receiving S i g n a l Level*. J a l o - Z i g h a n L i nk
9 0
10030 3520 2 5
DateFig. B-34.
Rec
eivi
ng
Sig
nal
L
evel
(-
dB
m)
4 0N o v e m b e r 19 7 8
Max V a r i a t i o n
5 0Min V a r i a t i o n
6 0
8 0
9 0 Ampl i tude of Dai ly V a r i a t i o n in Hour ly M e d i a n V a l u e
of Receiv ing S i g n a l L ev e l : Z i g h a n - Kuf rah Mtn. Link
1003 0 3520
D a t e Fig. B-35.
Rec
eivi
ng
Sig
na
l Le
vel
(-d
Bm
)4 0 D e c e m b e r 1 9 7 8
Max V a r i a t i o n
5 0Mi n V a r i a t i o n
7 0
8 0
A mp l i t u de of Da i ly Va r ia t ion in Hour ly M e d i a n V a l u e
of Rec e i v i ng S i g n a l Level : J a l o - Z i g h a n Li nk9 0
100353020 25
Dat e Fig. B-36.
Rec
eivi
ng
Sig
na
l L
evel
(-
dB
m)
4 0 9-0 December 1 9 7 8
M a x V o r l a t i o n -5 0
Min V a r i a t i o n
_ 0-0
70
8 0
Ampl i tude of D ai l y Var ia t ion in Hour ly M e d i a n V a l u e of Receiving S i g n a l Level : Z i ghan - Kuf rah Mtn. Link
9 0
1003525 3 020
D a t e Fig. B-37.
187
Rec
eivi
ng
Sig
na
l L
evel
(-
dB
m)
J a n u a r y 1 9 7 9
Max V a r i a t i o n
5 0 —Mi n V a r i a t i o n
6 0
7 0
8 0
Ampl i t ude of D a i l y V ar ia t i on in Hour ly M e d ia n V a l u e
of Receiving S i g n a l Level : J a l o - Z i g h a n L i n k9 0
10030 3520
DateFig. B-38.
Rec
eivi
ng
S
ign
al
Leve
l (-
dB
m)
J a n u a r y 1 9 7 9
— \
Max V a r i a t i o n
so — ;/Min V a r i a t i o n
6 0
7 0
8 0
Ampli tude of Dai ly V a r i a t i o n in Hourly Median Value
of Receiving S ig na l Level: Zighan - K uf r ah Mtn. Link9 0
100 —
3 02 520Date Fig. B-39.
Rec
eivi
ng
Sig
nal
L
evel
(-
dB
m)
4 0 — F e b r u a r y 19 7 9
Max V a r i a t i o n
M i n V a r i a t i o n
6 0
7 0
00
9 0
100353 02520
Fig. b-40. Amplitude of Daily Variation in Hourly Median Valueof Receiving Signal Level: Zighan - Kufrah Mtn. Link
Rec
eivi
ng
Sig
nal
L
evel
(-
dB
m)
40& — p-gF e b r u a r y 1 9 7 9
M a x V a r i a t i o n -----------------
Mi n V a r i a t i o n
9 0 — A m p l i t u d e of Da i ly V ar ia t i on in Hour ly M e d i a n V a l u e of Receiv ing S i g n a l Level: J a l o - Z i g h a n L i n k
100 —10 15 20
I25 35" 35Date Fig. B-41.
Rec
eivi
ng
S
ign
al
Le
ve
l (-
dB
m)
4 0 M a r c h 1 9 7 9
M a x V a r i a t i o n
5 0
M i n V a r i a t i o n_ i
7 0
8 0
9 0Ampl i tude of Dai ly Var ia t ion in Hourly M e d i a n V a l u e
of Receiv ing S i gna l Le ve l : J a l o - Z i g h a n Link
10015 2520 30 355 10
Date Fig. B-42.
193The following figures (Figs. B-43 through B-46 show variations
of signal-1o-noise ratio for different months of the period between April 78 to March 79.
4 0 —
3 0 _______IFig. B-
A: M a x i m u m H o u r l y M e d i a n L e v e l
B*. M e d i a n H o u r ly M e d i a n L e v e l
C: M i n i m u m H o u r l y M e d i a n L e v e l
Date
5 10 15 2 0 25 30
43. V a r i a t i o n of S i g n a l - t o - N o i s e Rat io for J - Z Hop
Sig
na
l-to
-No
ise
R
atio
in
d B
80S e p t e m b e r 1 9 7 8
4 0 —
A: M a x im u m H o u r l y M e d i a n L e v e l
B: M e d i a n H o u r ly M e d i a n Level
C: M in im u m H o u r ly M e d i a n L e v e l
30
Date
5 10 15 2 0 2 5 3 0
Fig. b-44. V a r i a t io n of S i g n a l - t o - N o i s e Rat io for J - Z Hop
195
Sig
na
l-to
-
Noi
se
Rati
o in
dB
80O c t o b e r 1 9 7 8
4 0 —
30
A! M a x im u m H o u r ly M e d i a n L eve l
B: M e d i a n H o u r l y M e d i a n L e v e l
(X Min im um H o u r ly M e d i a n L e v e l
. D a t e5 10 15 2 0 2 5
Fig. b-45. V a r i a t i o n of S i g n a l - t o - N o i s e Rat io for K-Z Hop
30
SIGN
AL
TO NO
ISE
RATIO
IN
db
80F e b r u a r y 19 7 9
7 0
6 0
5 0
A: M ax im um H our ly M e d ia n Level
B: M e d i a n H o u r l y M e d i a n L eve l
0= M in im um H o u r l y M e d i a n L e v e l4 0
D a t e
3 05 10 15 2 0 25
Fig. b-46. V a r i a t i o n of S i g n a l - t o - N o i s e Rat io for K-Z Hop
3 0
197
198
The following figures (B—47 through B-51) show the daily variations of receiving input level for different months during the period
April 78 and March 79.
Rec
eivi
ng
Sig
na
l L
evel
(-
dB
m)
4 0
5 0
K - Z 2 J a n u a r y 7 96 0 /— \
/ K - Z 2 6 F e b r u a r y 7 970 /
— /
80
Dai ly V ar ia t ions of Receiving Input Level: January and February9 0
10010 15 2 0
E l a p s e d T i m e in H o u r s25
Fig. B-A7.
199
Rec
eivi
ng
Sig
na
l L
evel
(-
dB
m)
4 0
Dai ly Va r i a t ion s of Rec e i v i ng I n pu t Leve l : Apr i l — June5 0
6 0
• K-Z 9 A p r i l 7 8
\\7 0
K - Z 8 Ju n e 7 8
K - Z 4 M ay 7 8\._8 0
9 0
1005 10 15 20 250Elapsed Time in Hours 200
Rec
eivi
ng
Sig
na
l L
evel
(-
dB
m)
4 0
5 0
6 0
K - Z 2 6 Ju ly 7 8
. K - Z 15 August 7 8 ' K - Z 14 S e p t e m b e r 7 8
8 0
Dai ly V a r i a t i on s of Receiving Input Level : Ju ly - S e pt e m be r9 0
1002 515 205 100
E l a p s e d T i m e in H o u r s ^Fig. B-49
201
Rec
eivi
ng
Sig
na
l L
evel
(-
dB
m)
4 0
5 0
6 0
\ / «-K-Z 7 N o v e m b e r 7 8 Z X ^ K - Z 31 O c to b e r 7 8
V ' X / K - Z 5 D e c e m b e r 7 8
7 0
8 0
Daily Var ia t ions of Receiving Input Level: October - December9 0
1002515 20105
Elapsed Time in Hours 202
Rec
eivi
ng
S
ign
al
Le
ve
l (-
dB
m)
4 0
5 0J - Z 3 0 September 7 8 J —Z 2 8 November 7 8
6 0
J - Z 5 D e cem b er 7 87 0
80
Daily Variation of Receiving Input Level*. September — December9 0
10050 10 15 20 2 5Elapsed Time in Hours 203
APPENDIX C
SIGNAL-TO-NOI.SE RATIO IN OVERALL SYSTEM (BY STATISTICAL COMBINING METHOD)v
As a general rule, it is very difficult to find the correct
value of the distribution of noise power at the terminals of a tele
phone circuit when trans-horizon links are connected in tandem, but
the cumulative noise power of the telephone channel is found by then i lfollowing approximation method. The values are relatively close
to actual measured values.If, therefore, the mean value and variance of the noise distri
bution of each link is known, the mean value and variance of the dis
tribution at the end of a circuit can be calculated.
long, period of approximately one month shows a distribution very similar
to the dB-normal distribution. Noise distribution at the terminal is,
therefore, calculated on the basis of the dB-normal distribution.
The probability density function P(x) of the db-normal distribution is
The long-term noise distribution at n-relay terminals over a
(C.l)
where, M: mean value
a2: variancea: 10 Log^Q e = 4.343*
204
205
Thus, the true value of means value (M^) and variance (S^2) of each link are given by the following formula:
/m. a.2 \Mi = + I I 2 J ( c - 2 )
S ^ - e x p ^ + ^ - | - ll (C.3)
where9 mean noise value of each link in dBm
a.: standard deviation of each link in dB1
From Equations (C.2) and (C,3), we find the mean value and vari
ance of the noise distribution of each link9 and then their sum total;
nM = Y M. (Co4)
" i
nS2 = 2 S^2 (C.5)
iAs a"result, mQ and aQ of the overall system are found from
the following equations.
mo = 10 Log10 M - 5 Log10 | 1 + ( | ) | ' (dbm) (C,6)
% = A / 43,43 Logio j 1 + > (dB) (C.7)
Therefore overall noise distribution curves for thermal noise
and path intermodulation noise are obtained from the respective mQ and
Cg by applying the log-normal law. The above obtained noise distributions, which are log-normal distributions, are assumed to have a correlation of one among the noise variations of each link
Detailed procedures for obtaining the overall noise distribution
curve are explained as follows:
i. confirm the median signal-to-noise ratio (S/N^, S/N^) and
standard deviations of each link.
Link S/Nt 1 s/%i 2
A S/Nt (A) 01 (A) S/N]. (A) a 2 (A)B s7 n t (b ) Ol(B) S/N].(B) 02(B)c; S/Nt (C) cri(C) S/Nr(C) 02(C)D s /n t (d ) ai(D)
b
S/N]. (D) 02(D)
• • 0 • e
ii. Convert each signal-to-noise ratio to noise level
M. = - (S/N)
iii. Calculate the true values of mean value (M.) and variance: 1 , .
(S^2) for each noise distribution of the link
207iv. Calculate the total 1L and S^2
nM = ^
in
S2 = } si2
v. Calculate the median noise level (mQ) and standard deviation(ao) of the overall noise distribution.
mQ = 10 Log M - 5 Log 1 +( — ) (dBm)l)2
(I) )CT0 = x / 4 3 * 43 L°s U + Im J i db
vi. Calculate the noise levels of various time percents.
m(50%) = mo dBm
. m(20%) = m + 1.84 an dBm0 °
m(5%) = m + 1.64 aQ dBm
m(l%) = mQ + 2.32 aQ dBm
m(0.5%) - m0 + 2.58 oQ dBm
' m(0.1%) = mo + 3.1 q-Q dBm
vii. Draw the noise distribution curve in the distribution chart. See Line 1 of Fig. 1.
viii. Correct the above distribution curve as shown in Line 2 of
, Fig. 1.ix. Draw the curve (Line 3) smoothly connecting Line 1 and Line 2,
208
This curve is the overall noise distribution curve. Two
distribution curves have to be prepared, one is for the thermal
noise and the other for intermodulation noise.
The calculations from procedure ’i’ to 'v* are generally calculated by the use of computer.
Sig
na
l-to
-No
ise
R
atio
in
dB70
4 0
TTherm al Noise or Roth In termodulat ion Noise Dist r ibut ion Curve of Eac h L ia k U
C a l c u la t e d D is t r ibu t io n Curve (L ine-1)
Corrected Curve ( L i n e - 2 ) —
Overal l Noise D is t r ibut ion C urve (Line-3|L in k -
L i n k - D
Line - 2
.Reference. LevelsLine - 1 (assumed 0 3 d b )
L i n e -
1_J L J L0.01 0.1 0 . 2 0 .5 I 10 2 0 3 0 4 0 5 0 60 7 0 8 0 9 0 95 98 99 9 9 . 8 9 9 . 9 9
Fig. c-i. Drawing Method of the Distr ibut ion Curve of the
Overal l Noise in M u l t i - S e c t i o n Rad io Link
209
APPENDIX D
A COMPARISON OF SOME. TROPOSCATTER PREDICTION METHODS
In the design of tropospheric scatter links it is useful to have some prior knowledge of the magnitude of the path loss to.be
expected. There are a number of prediction methods in current use.
The prediction methods are that of MBS Technical Note 1 0 1 , ^ ‘a simplified version of this contained in the COR Report of 1966, a
method proposed by Yeh, a modification of Norton’s method, by RiderF171and Collin’s method. J The formulas for the various methods are as
follows:NBS, 101 '
L = 30 Log f - 20 Log d + F(<j>d) + L^ (D.l)
- V(de) - Fq + Hq + Aa
f: frequency in MHZ
d : distance in KM
: scattering angle in radiance
de: effective distanceF (<j>d) : attenuation function
Lc: aperture to medium coupling loss
V(de): climate variation factor which accommodates the applicationof the formula to areas of differing meteorological conditions
F : scattering efficiency correction term to allow for the reduction of scattering efficiency at great heights in theatmosphere -
: 210
211
Hg: frequency gain function term to allow for the variationwith frequency of ground reflection effects
CCIR
L = 30 Log f - 20 Log d + F(*d) + Lc (D.2)
- V(de) -f, d, <j>, de are defined as for BBS 101. The functions F and V
are plotted in the CCIR Report and are almost identical with the graphs
in the NBS. The coupling loss term is estimated using the formula.:
, Lc = 0.07 exp {0.055 (G^+Gp} (D.3)
: where and Gr are the free space gains of the transmitting
and receiving antenna.
Yeh
L = 30 Log f + 20 Log d + 10cj> - 0.2(3^-310) (D.4)
+ L + S—7 cff r e q u e n c y in MHZ
d: distance in miles
<p: scattering angle in degrees
1SL: surface refractivitys
The coupling loss in this case is estimated from a graph given by Yeh
in his paper, based on experimental data.
Rider[181This is a modification of Norton’s method : , which leads to the
formula:
212L = 30 Log f + 30 Log d + 50 Log <j> (D.5)
- 0 . 4 3 (N g -3 3 0 ) + L c + 49
f . d cj), Ng are defined as for Yeh’s method. This formula does
not include an estimate of aperture to medium coupling loss. Usually the coupling loss figure from the CCIR method is used in order to give
a complete estimate of propagation loss.
Collins
This is a method contained in an instruction manual for the
U.S. Army. It was prepared by the Collins Radio Cbmpany. The method
is entirely graphical, the four graphs being:1. Loss against distance for 1 GHZ, which appears to be an empirical
curve.2. Frequency correction curve to allow for frequencies other than
1 GHZ. This is simply a graph of 30 Log f with the origin
suitably placed.3. Loss due to elevated.horizon angles— a set of curves for varying
distances to allow for loss variations when the horizon angles
are non-zero.4. A nomograph to determine aperture-to-medium coupling loss.
The values from the four graphs are added together to give an
estimate of troposcatter propagation loss. The method contains no terms
dependent on Ng, or any other climatic factor.
213
Conclusion; '
The conclusion drawn by many scientists and working engineers is
that the NBS and CCIR are almost equal in performance, although GCIR is much more convenient to use. The CCIR method provides important estimates
of fading ranges, and a combination of CClR and Teh gives good estimates
of median path loss. The Collins method suffers from having a restricted range of parameters, but gives good results when used inside this range. All calculation methods show remarkable failure to account satisfactorily
for climate variations.
LIST OF REFERENCES
1. Rice, P. L., Longely, A. G., Norton, K. A., and Baris, A. "Transmission loss predictions for tropospheric communication circuits," Tech. Note 101, Vol.. 5, 1 and 2, National Bureau of Standards, May 7, 1965.
2. Carrol, T. J., Lebatich, J. L., and Vergara, W. C., "VHF and groundpropagation for beyond the horizon," Bendix Radio Report, Feb.1961.
3. Carrol, T. J.* "Mode theory as proof of partial interreflections fromthe normal air," International Scientific Radio Union Program,May 1961, pp. 52-53.
4. Carroll, T. J., "Interpretation of Tukizi's calculations in twilightpropagations," International Scientific Radio Union Program,Oct. 1961, p. 34.
5. Armand, N. A., Vrdenskii, B. A., "Long range characteristics of ultrashort radio waves," Radiotekh'na Electro (U.S.S.R), Vol. 6,June 1961, pp. 867-885.
6. Bullington, K., "Reflections from an exponential atmosphere," BellSystem Tech. J., Vol. 42, pp. 2849—2868, Nov. 1963.
7. CCIR, Volume II, Part 1, Propagation in Non-ionized Media, New Delhi,1970.
8. Prescott, H., "A method for predicting the statistical distribution ofB. W. in troposcatter links," Proc, 7, National Conv. on Military Electronics, Washington, D. C., 1960, pp. 281-285.
9. Gunther, F. A., "Tropospheric scatter communications past, present,and future," IEEE Spectrum, September 1966.
10. "Yonezaw, S., and N. Tanaka, Microwave Communications, Second Edition,Manizen Company, Ltd., Tokyo, 1965.
11. N.E.C., Ltd. Tokyo, Japan, System design of tropospheric scatter radiolinks, SB534R-006 (issue-3) 1969.
12. N.B.S. Technical Notes, N. 101, Revised Jan. 1, 1967..
214
21513. Okumura, Y. "Estimation method of propagation quasi crosstalk
noise in tropospheric scatter circuits," Electrical Communication Laboratory, NTT Result Report, Oct. 1964.
14. CCIR Documents of XI Plenary Assembly, Oslo, Volume II, Propagation, p. 143, 1966.
15. Yeh, L. P. "Simple methods for designing troposcatter circuits,"IRE Transactions on Communications Systems, September 1960.
16. Rider, G. C. "Median signal level prediction for troposphericscatter," Marconi Review, 25(146, pp. 203-210, 1962.
17. "Instruction Manual for Tropospheric Scatter— Principles andApplications," USAEPG-SIG960-67. U. S. Army Electronic Proving Ground, Fort Huachuca, Arizona, March 1960.
18. Norton, K. A. "Point-to-point radio relaying via the scatter mode of tropospheric propagation," Trans. IRE CS-4, 1, p. 39, March 1956.
VDF
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EXC - Exciter ( )kW PA - ( )kW Power Amplifier
MOD - Modulator REC - Receiver BBC - Baseboard Combiner I FC - IF Combiner
DEM - Demodulator PRO - Process Amplifier
SVSC - Sound Vision Separator and Combiner
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