ABSTRACT
This study presents the performance improvement of signal over Ku-band satellite communication using fuzzy logic system. The satellite communication is an essential part of telecommunication systems which carries a large amount of data and telephone traffic in addition to television signals. At high frequency, satellite links are more sensitive to signal fades due to rain, especially in the tropical region. Rain attenuation can have a distorting effect on the quality of service (QoS) at higher frequencies that lead to excessive digital transmission error. This loss of signal is commonly referred to as signal attenuation. Rainfall data was obtained from the Nigerian Meteorological Agency for a period of ten (10) years for the purpose of estimating attenuation using ITU-R and DAH models. Umuahia geographical location was considered as the choice of environment. Data was also obtained from Modern Communications Limited which was used to calculate Bit-error-rate and Network throughput. A developed model was used to interact with the input parameters to improve the quality of signal. The fuzzy logic system was added to mitigate rain attenuation in order to guarantee a certain level of signal quality. The simulated results show the effectiveness of the developed model and its ability to improve QoS over Ku-band satellite communication in spite of rain attenuation. Netharn et al were able to improve the signal quality by 20.27% whereas the developed model in this Thesis was able to improve the quality of the satellite signal by 63.9%.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgements v
Table of contents vi
List of Tables x
List of Figures xi
List of Abbreviation xii
Abstract xiv
CHAPTER 1: INTRODUCTION
1.1 Background to the study 1
1.2 Problem Statement 4
1.3 Aim and Objectives 5
1.4 Scope of the study 6
1.5 Significance of the study 6
1.6 Organization of the research work 7
CHAPTER 2: LITERATURE REVIEW
2.1 Historical Background 8
2.2 Components of satellite system 9
2.3 Various satellite communication frequency bands 10
2.4 Satellite Orbits 12
2.5 Characteristics of satellite component 14
2.6 The benefits of satellite 15
2.7 Factors affecting satellite communication 16
2.8 Rain attenuation 19
2.9 Attenuation prediction models 21
2.10 Signal fading 24
2.11 Fuzzy logic 25
2.12 Review of related works 28
2.13 Identified knowledge gaps 40
CHAPTER 3: MATERIALS AND METHOD
3.1 Materials 41
3.2 Method of data collection 41
3.3 MCL satellite television 43
3.4 Block diagram of the system 43
3.5 ITU-R Model 48
3.6 DAH Model 51
3.7 Satellite Key Performance Indicators 53
3.7.1 Percentage Packet loss 54
3.7.2 Received Signal level 55
3.7.3 Determination of Bit-Error-rate 56
3.7.4 Determination of Network Throughput 57
3.8 Fuzzification 59
3.8.1 Fuzzy set associated with unit commitment 59
3.8.2 Fuzzy Inference System Editor 60
3.8.3 Membership Function Editor 61
3.8.4 Production Output Membership function 64
3.8.5 Rule Editor 64
3.8.6 Rule Viewer 66
3.9 Developed model for transmitted and received signal over satellite communication 69
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Simulated result for attenuation 71
4.1.1 Analysis of attenuation for conventional and fuzzy controller 72
4.1.2 Analysis of Received signal for conventional and fuzzy controller 73
4.1.3 Determination of Bit-error-Rate for conventional and fuzzy controller 75
4.1.4 Determination of Network throughput for conventional and fuzzy controller 77
4.2 MATLAB Simulation Code 77
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 78
5.2 Recommendations 79
5.3 Contribution to knowledge 79
References 80
Appendix 84
LIST OF TABLES
Table 2.1 Types of Frequency Bands 11
Table 3.1 Statistics of rainfall data in Umuahia for a period of ten years 45
Table 3.2 Average annual rainfall accumulation 46
Table 3.3 Average annual rainfall and rainfall rate 47
Table 3.4 Regression coefficients for estimating specific attenuation 49
Table 3.5 The annual attenuation and specific attenuation experienced each year 51
Table 3.6 The annual attenuation experienced each year using DAH model 53
Table 3.7 Average Percentage Packet loss experienced each year 54
Table 3.8 The received signal and packet loss experienced each year 55
Table 3.9 The Packet Error Rate experienced each year 56
Table 3.10 Computation of packet loss, received signal and BER 57
Table 3.11 The Network throughput experienced each year 58
Table 3.12 Rules building and structuring 68
Table 4.1 Conventional and fuzzy controller attenuation 71
Table 4.2 Conventional and fuzzy controller received signal 73
Table 4.3 Conventional and fuzzy controller bit error rate 74
Table 4.4 Conventional and fuzzy controller Network throughput 76
LIST OF FIGURES
Figure 2.1: Satellite System Components 10
Figure 2.2: Various of satellite orbits 12
Figure 2.3: Schematic diagram for the attenuation prediction 23
Figure 2.4: Slant path geometry of Dissanayake-Allnutt-Haidara method 24
Figure 2.5: Fuzzy membership function 26
Figure 2.6: Fuzzy set operations 27
Figure 3.1: Equipment used for collecting rainfall data at Nigerian
Meteorological Agency, Umuahia 42
Figure 3.2: Block diagram of the system 43
Figure 3.3: Fuzzy Inference systems 60
Figure 3.4: Attenuation (input) Membership function 62
Figure 3.5: Network throughput (input) Membership function 63
Figure 3.6: Received signal level (input) Membership function 63
Figure 3.7: Bit-Error-Rate (input) Membership function 64
Figure 3.8: Membership function of the Production Output 66
Figure 3.9: Screenshot of rules defined in MATLAB 68
Figure 3.10: MATLAB views of fuzzy Rules 67
Figure 3.11: Developed model for transmitted and received signal 70
Figure 4.1: Graph of attenuation and number of years 72
Figure 4.2: Graph of received signal level and number of years 73
Figure 4.3: Graph of bit error rate and number of years 75
Figure 4.4: Graph of network throughput and Number of years 77
LIST OF ABBREVIATION
ACM Adaptive Coding and Modulation
BER Bit Error Rate
C/N Carrier-to-Noise Ratio
CAPEX Capital Expenditure
DAH Dissanayake, Allnutt, and Haidara
DSD Drop Size Distribution
DTH Direct to Home
DVB-S Digital Video Broadcasting – Satellite
DVB-S2 Digital Video Broadcasting – Satellite Second generation
EIRP Effective Isotropic Radiated Power
FDM Frequency Division Multiplexing
FLC Fuzzy Logic Controller
FRBS Fuzzy Rule Base System
FSS Fixed Satellite Service
GEO Geostationary Earth Orbit
GHz Gigahertz
GPS Global Positioning System
G/T Receiver Figure of Merit
HEO Highly Elliptical Orbit
ITU International Telecommunication Union
ITU-R International Telecommunications Union, Radio communications
Ka - band Kurtz above Band
Ku - band Kurtz under Band
LEO Low Earth Orbit
MATLAB Matrix Laboratory
MCL Modern Communications Limited
MEO Medium Earth Orbit
MPEG Moving Picture Experts Group
OBP On-Board Processor
PID Proportional Integral Derivative
PSN Public Switched Network
QAM Quadrature Amplitude Modulation
QoS Quality of Service
QPSK Quadrature Phase Shift Keying
SAAM Skillful Atmospheric Aware Model
SD Site Diversity
SLA Service Level Agreement
SNR Signal-to-Noise Ratio
TDM Time Division Multiplexing
UCP Unit Commitment Problem
UPC Uplink Power Control
VSAT Very Small Aperture Terminal
XPD Cross Polarization Discrimination
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND TO THE STUDY
Satellites are mainly space-based receiving and transmitting radios. They send electromagnetic waves which carry signals/information over long distances without using wires. Since its main work is to send signal from one place on Earth to another, it therefore works as a radio-frequency repeater. A satellite therefore receives radio-frequency signals, collected from a dish on the ground, called a ground Station or Antenna. It then magnifies the signals, modifies the frequency and resends the signals from the satellite to different Earth Stations, (Maval and Bousquet, 2002).
A satellite functions most effectively if the transmissions are directed to a desired area. When the desired area of coverage is focused, the emissions do not move away from the designated area and it minimizes the interference to the other systems. In designing a satellite, one of the major properties is on the ability to communicate with a ground station. Without a functioning communication link, most satellites are rendered useless. To ensure a proper satellite to ground link, one has to make estimations of the signal attenuation because of the distance to the satellite, atmospheric distortions and other system specific losses. An important aspect is noise originating in the system components and from general background radiation, (Vangli, 2010).
Satellite communications are essentially used for providing communication links between different areas on the Earth by receiving information from a transmitting earth station. Satellite communications play an important role globally in the telecommunications system. About 3,000 satellites are orbiting the Earth relaying continuous and discrete information bearing data, video and audio from one area/location to another in the world.
Satellite based communication networks at high frequencies are rapidly expanding. These high frequency operations have enabled a large number of available applications and services including communications, navigation, telemedicine, remote sensing, network sensors distribution, and access to internet without the use of wires. However, high frequency applications can generally result to large transmission problems because of atmospheric attenuations, (Harb at al, 2012).
Satellites send signal using frequency bands. The most profitable bands presently used are C and Ku-bands. The application of a new band called Ka-band is expected to emerge in the nearest future. Generally C-band uses frequency bands of 4-6 GHz which is usually applied for constant services like mobile feeder links, Internet Trunking and Public Switched Network. Ku-band uses frequencies of 12-18 GHz range which is widely applied in constant services like VSAT, serving small businesses and corporate networks that use a small transceiver which is directly connected to the satellite in star system topology. Ku-band serves video distribution applications and Internet trunking, (Kota and Marchese, 2003).
Application of larger bands like the Ku band for satellite services offers so many advantages which include congestion reduction in the lower bands that are been distributed within terrestrial connections; it propagates larger available bandwidths at higher bands, and offers lower cost application of spectrum conservation methods and a better utilization of the geostationary arc. (Sarat et al, 2008) posited that the increase in radiowave propagation increases frequency due to severity of atmospheric impairments. It therefore implies that in depth idea of the propagation study influencing availability of the system and quality of signal in different bands are required.
Kurtz-Under band (Ku band) is a microwave frequency band which is used for satellite broadcasting and communication using frequencies of about 12GHz for terrestrial reception and 18GHz for transmission. Ku-band is mostly adopted for satellite services, mostly satellite to ground station applied in direct broadcast satellite television. Ku-band handles the challenge encountered in terrestrial microwave backhaul connections. Furthermore, it is known for its increase in power signals. Ku-band radio transmitter needs lesser power. Mostly, 0.9, 1.2, or 1.8m dish is applied for Ku-band operations. This is economical and could save much Capital Expenditure (CAPEX) and makes Ku-band best applicable for small networks, (Wikipedia, 2018).
However, Ku-band is very much prone to rain fade and the attenuation caused by rain can be up to 10dB. Ku-band works better in small area for installation due to small size of dish is required and it is simple and easy to install. Moreover, Ku-band is suitable for satellite services which require a little bandwidth, as the device is cheaper. Ku-band can provide acceptable quality of service and communication speed, (Link Communications, 2018).
The effect of atmosphere is a primary issue when designing satellite-to-earth links operating at frequencies beyond 10GHz. Droplets of rain absorb and scatter radio waves, leading to signal attenuation and decrease in the system reliability and availability. It also causes one of the major fundamental problems on the communication satellite links performance, resulting to large variations in the signal power at the receiver end. Moreso, satellite services using 10GHz frequencies and beyond are influenced by different propagation impairments like attenuation caused by rain, attenuation caused by cloud, rain and ice depolarization, (Osahenvemwen, 2013).
Rainfall causes attenuation of radio waves by absorption and by scattering of signal obtained from the wave and facilitate increase in the frequency that reduces the reliability and efficiency of the communication satellite link. Rain effects are dependent on frequency, rain rate, drop size distribution and drop shape, which are determined by the type of rain being witnessed in a particular region, (Nethern et al, 2013).
Attenuation caused by rain is a primary source of impairment to information propagation at millimeter and microwave wavebands. These impairments become particularly severe at higher frequencies, especially beyond Ku-band. Because of this, it is very difficult to maximally utilize satellite based network resources which are affected by weather attenuations. Therefore, there is need to adequately study important attenuation factors which influence quality of service and the application of fuzzy logic can be deployed over the system to enhance received signal over satellite broadcasting.
1.2 PROBLEM STATEMENT
There are some basic effects of propagation abnormalities which affect the communication satellite systems performance. In a satellite communication, weather losses result from degradation of the satellite signals by hydrometers as they cross the earth’s atmosphere. One of the losses encountered by satellite communication systems is rain attenuation.
When higher frequencies are transmitted and received under heavy rain fall, signal degradation which is proportionate to the intensity of rain fall occurs, (Singam, 2018).
Rain leads to reduction of the transmitted signals with different degrees of severity, depending on the rain rate, size of raindrop, intensity of rain and the frequency of operation. Excessive rainfall rates at frequencies beyond 10 GHz have significant adverse effect on radio communication links and most often causes complete signal outages.
Attenuation due to rain is the primary cause of attenuation over Ku-band communication satellite; this is because the frequency of Ku-band is influenced in rhythm of rain attenuation. If there is a synchronization of both of them, the signal will be attenuated or lost. This is a major limitation that occurs in Ku-band when a high frequency is deployed, (Amruta and Patane, 2015).
Satellite communications that suffer attenuation problems at high frequency sometimes could not be able to receive down link signal which conveys picture and sound. Therefore for signals to be properly received and transmitted during rain, attenuation and bit-error-rate should be reduced to the barest minimum so as to increase the received signal level and the network throughput thereby improving the quality of the satellite signal.
1.3 AIM AND OBJECTIVES OF THE THESIS
The aim of the study is to improve the performance of signal over Ku-band satellite communications using fuzzy logic system.
The main objectives of the research work are;
i. To review the current state of art in improving signal strength in satellite communication.
ii. To employ different methods for estimating rain attenuation.
iii. To develop a model for transmitted and received signal over Ku band satellite communication.
iv. To simulate the developed model appyling fuzzy logic system.
v. To compare the degree of signal improvement in received signal over Ku-band satellite communication with and without fuzzy logic system.
1.4 SCOPE OF THE THESIS
The scope of this study is limited to the performance improvement of signal over Ku-band satellite communications applying fuzzy logic system. Umuahia metropolis is chosen as the choice of environment and rainfall data was obtained for a period of ten years for the estimation of rain attenuation.
A model will be developed which will be implemented using MATLAB simulation to increase the signal quality.
1.5 SIGNIFICANCE OF THE STUDY
The application of the satellite systems are generally important in Nigeria and where areas are geographically diversified. With the advent of satellite technology, the services become widespread where lower frequency band like Ku band becomes imperative. It is becoming an inevitable alternative to adopt higher frequency band for satellite services. Therefore Ku band and above are attractive bands, because they offer wider bandwidth, higher data rate, and smaller component size, like very small aperture terminals.
In line with these recent achievements, sharp increase in Internet traffic around the globe is causing a geometrical growth in the demand of transmission bandwidth allocated for multimedia services. These services include high-speed data, high-resolution imaging, and desktop videoconferencing, all of which require large transmission bandwidths.
Rain fade can impair signal transmission and reception and also causes temporary reduction in radio frequency communications. The term rain fade generally shows how atmospheric conditions like snow, sleet and rain can absorb microwave signals in both terrestrial point-to-point and satellite communications and result to path loss.
Satellites are broadly applied for mobile services like communication to ships, vehicles, planes, hand-held terminals and for radio and TV broadcasting. They are specifically adopted for telecommunication purpose. They provide services to specified location on the earth. The bandwidth and power of the satellites is dependent on the cost of ground stations, desired footprint size, and traffic control protocol schemes complexity.
1.6 ORGANIZATION OF THE RESEARCH WORK
This research work is arranged in five chapters;
Chapter 1 presents the introduction and background information of the study.
Chapter 2 presents the literature review of Ku-band frequency satellite communication and fuzzy logic concepts. Reviewing of related work and fuzzy logic system is also presented.
In chapter 3, the methodology and processes leading to the development of fuzzy inference system are presented. It also describes the simulation carried out in fuzzy logic toolbox in MATLAB.
Chapter 4 presents the results and discussion obtained from the conventional/analytical and fuzzy logic method.
Finally, in chapter 5, conclusion and recommendations for future work is presented.
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