Theses supervised by Prof. Dr. Yahya Kemal Baykal
19 theses · Çankaya University
Hava trafik hizmetlerinde VHF veri teknolojisi
ABSTRACTVHF DATA TECHNOLOGY IN AIR TRAFFIC SERVICESBELL KL , Ahmet ErenIn this thesis, we have introduced communication, navigation and surveillancesystem?s working principles and bottlenecks based on working performances used inAir Traffic Control systems. We investigated the possible system solution to meetcurrent bottlenecks, safety issues and Air Traffic growth handling for today and inthe future.Air Traffic Navigation continuation and communication quality regarding safetyissues are directly dependent on the chosen technology base. Choosing the righttechnology to meet requirements is what we have searched in this thesis.The baseline technology of Broadband -VHF project is as in the fourth generation(4G) mobile communications.ivB-VHF approaches communication in two different ways The one from groundstations to aircrafts (forward link) is based on combination of OFDM-CDMA calledMC-CDMA and the second link from aircraft to ground (reverse link) is based oncombination of OFDM-FDMA. We added Code Division Multiplexing into thereverse link to enhance the link robustness against interferences and data security. Inorder to realize this, we developed a Matlab code to simulate its performances toobserve whether this combination provides robustness against interferences. Usingthe simulation we have obtained BER results at different cyclic prefix, number ofOFDM symbols, code length size and channel settings. BER obtained with theinclusion of CDM are slightly favorable as compared to OFDM only reverse link,however, the performance improvement is not within the expected scale.v
Simulation of free space optical links under different atmospheric conditions
This thesis contains a feasibility study for the free space optical links, which would be installed in Turkey. In first chapters, some basic information and the background theory of the atmospheric channel are given. Predefined optical links are simulated with PCModWin-MODTRAN radiative transfer code to investigate the link availability under the influence of different weather conditions. In addition, numerical calculations according to some experimentally approved models are also performed and these results are compared with the results of simulations. For all these simulations and calculations, big amount of meteorological data was collected from the airport stations, which are in different cities in Turkey. The parameters used in calculations were supplied from the commercially available FSO systems.In conclusion, the effectiveness of FSO links in Turkey is discussed.
500MHz-2GHz broadband power amplifier design by non-linear modeling methods
This thesis presents the design methods of 500MHz-2GHz broadband RF poweramplifier. First of all, RF power transistor technologies are searched and the mostsuitable one is chosen according to its operation of frequency band, maximumoutput power, efficiency and cost features. The amplifier is designed as it has twostages, and in both stages LDMOS transistor technology is used as RF powertransistors. Large signal models for the LDMOS devices are used in simulation, andaccording to the measurement results, the circuitry in simulation is tried to model atnonlinear conditions. A broadband RF-Choke structure with a new technique isdeveloped to obtain high DC isolation and low RF loss over the desired bandwidth.Input and output matching networks and shunt feedback topology are introduced tofulfill the bandwidth requirements. Typical values of 20dB power gain, 37dBmoutput power, have been achieved at the most part of the frequency band of500MHz-2GHz.
Effects of beam types in the performance of free space optics systems
In this thesis, a general light source beam formula is developed which combines many beam types. Using different parameter sets in the general source beam formula, we obtained different beam?s source equations. Using Matlab, intensity distributions at the source plane for various beam types are plotted. Received average intensity in atmospheric turbulence is calculated for the general source beam and numerical evaluations are made and the received average intensities are plotted for certain specific beams such as Dark Hollow, Flat-topped, Bottle, Lorentz and Super Gaussian beams.
Yenilenebilir enerji kaynaklarının avantaj, risk ve tehlikeleri
Nüfusun ve sanayileşme hızının artması ile birlikte enerji ihtiyacı ve tüketimi de giderek artmaktadır. Enerji sosyal gelişme,kalkınma ve büyüme için en önemli proses olarak karşımıza çıkmakta ve gelişmekte olan ülkeler için en önemli politika başlıklarındandır. Fosil yakıtlı kaynakların ilerleyen süreçte tükeneceği yada ihtiyacı tam karşılamayacağı göz önüne alındığında, yenilenebilir enerji kaynaklarına yönelmek zorunluluk haline gelmektedir. Ülkemiz fosil kaynakları açısından zengin olmasa da yenilenebilir enerji kaynakları olan güneş, rüzgar, hidroelektrik, jeotermal ve biyokütle enerjisinden jeopolitik yapısından kaynaklı şanslı bir coğrafyada yer almaktadır. Türkiye enerji talebini başka ülkelerden ithal ederek karşılamakta ve sonucunda en önemli problem olan dış ticaret açığı karşımıza çıkmaktadır. Türkiye sürdürülebilir ekonomik gelişme, istihdam ve küresel ısınma sonucu meydana gelen iklim değişikliğini önlemek için yenilenebilir enerji kaynaklarını etkin bir biçimde kullanması gerekmektedir. Fosil yakıtlı kaynaklarının kullanımıyla sera gazı ve asit yağmurları Dünya'yı tehdit etmekle birlikte insan sağlığını da olumsuz yönde etkilemektedir. Geçmişte yaşanan enerji krizleri sonucu ülkeler stratejilerini belirlemekte ve enerji arz güvenliğini sağlamak için yenilenebilir enerji kaynaklarına yönelik teşvik mekanizmaları sunmaktadır. Son zamanlarda kullanım oranı artan yenilenebilir enerji kaynakları çok tehlikeli sınıf kategorisinde yer aldıkları için iş sağlığı ve güvenliği anlamında iş kazası ve meslek hastalıkları sorunun yaşanmaması için gereken tüm tedbirler alınmalıdır. Yenilenebilir enerji kaynakları L Matris Analizi ile Fine Kinney Analizi risk değerlendirilmesi yapılmıştır. Elde edilen sonuçlar neticesinde Fine Kinney metodunun daha güvenilir ve hassas sonuçlar verdiği gözlemlenmiştir. Sonuç olarak iki farklı yöntem değerlendirilerek düzenleyici ve önleyici faaliyetler önerilmiştir.
Transmittance, scintillation and BER analysis in underwater optical wireless communication systems
Underwater Wireless Optical Communication (UWOC) has been more popular in recent years due to the need for high data rate transmission in underwater communication. In this thesis, UWOC system is considered to improve its performance by analyzing the effects of different beam types on the system in turbulent underwater medium. More specifically, the influences of oceanic turbulence on the link performance of UWOC such as the transmittance, beam spread, scintillation and BER are examined thoroughly for different optical sources beams. PCFT, cosine Gaussian, partially coherent cosine-Gaussian, cosine-hyperbolic Gaussian and partially coherent cosine-hyperbolic Gaussian beams are used as the source to benchmark the performance of the system. To investigate the oceanic turbulence effect on the UWOC system, the power spectrum of the ocean is assumed to be homogeneous and isotropic. Additionally, the extended Huygens Fresnel principle is employed to analyze the average transmittance. In particular, on-axis and off-axis average transmittance is examined for the PCFT, cosine-Gaussian, cosine-hyperbolic Gaussian, and their partially coherent cases as well. With the help of Carter's definition, beam spread is observed for the PCFT beam. The scintillation calculation is also benefited from the extended Huygens Fresnel principle. Apart from these, oceanic turbulence effects on BER, which is another performance criterion, in the UWOC link was also studied. Calculations were carried out by using the MATLAB program. All the system performance phenomena are examined against the important parameters of oceanic turbulence, such as the rate of dissipation of mean square temperature, ratio of the temperature and salinity contributions to the refractive index spectrum and the rate of dissipation of kinetic energy for the unit mass of fluid. Moreover, with these analyses, the degree of coherence and off-axis parameters are also studied. With this thesis, we aim at selecting suitable beams for the underwater turbulent environment and to examine the performance of UWOC links in different aspects under various excitations.
Encrypted optical communication
This thesis deeply tries to analyze log-normal fading effects, which happen because of atmospheric turbulence and damages reliability, integrity, and security of data transmission in FSO systems in many ways. FSO is known to be very advantageous because of high data bit rate. Atmosphere causes signal distortions at the receiver side, performance getting worse strongly and bit error rate (BER) with packet error rate (PER) values increasing noticeably. This situation is modeled with log-normal distribution mostly. To understand these impacts, experiments divided into two stages inside this study for making more organized structure. First stage investigates unencrypted data transmission. Clear weather, fog, dust, rain environments simulated inside channel and different sigma parameters applied for every condition especially. At the receiver side threshold decision method used to recover signals later. BER and PER are calculated. This part mainly focuses on the physical layer degradation effects, turbulence how damaging signal tried to be demonstrated carefully. In second stage same system was used but data transmitted with ASCON algorithm protection applied. It is the algorithm selected by NIST standards. It provides confidentiality and performs authentication process simultaneously. Encrypted data behavior tested under different turbulence intensities additionally, weak moderate and strong fading scenarios compared step by step. Encrypted and unencrypted transmissions are evaluated carefully. ASCON high entropy ciphertext structure impact over BE performance analyzed and corrupted packet rejection ability examined strongly with many comparisons. Some differences observed after these investigations. Results clearly showing log-normal fading significantly increase error rates, FSO links becoming vulnerable under these conditions strongly. ASCON authentication mechanism continuously blocks corrupted packets acceptance. Encrypted transmissions show slightly higher BER naturally. But communication integrity preserved end-to-end. ASCON does not perform error correction actually, it only detects errors and discards invalid packets without trying to repair them. Overall, this thesis demonstrates that integrating ASCON into FSO systems improves security performance strongly. Proposed hybrid optical cryptographic structure seems promising for future communication architectures. Especially important expected for 6G based next generation networks.
Fiber coupling efficiency of vortex beam in underwater turbulent medium
Underwater optical wireless communication is a encouriging technology for high-bandwidth data transmission in oceanic environments. Nevertheless, the performance of underwater optical wireless communication (UOWC) systems is typically hampered by oceanic turbulence, which causes signal degradation and reduces link reliability. This thesis investigates the potential of vortex beams, a special class of laser beams carrying orbital angular momentum, to enhance the efficiency and robustness of UOWC systems. In turbulent underwater channels, conventional Gaussian beams are vulnerable to beam spreading and scattering. Vortex beams, due to their unique phase structure, offer potential advantages in mitigating turbulenceinduced impairments. Moreover, since its great capacity, resistance to turbulence, and ability to work with sophisticated multiplexing techniques, vortex beams are an essential component of optical communication systems of the future. These benefits are especially helpful in settings like undersea communication, where conventional optical beams encounter several difficulties. This research focuses on analyzing the FCE of vortex beams propagating through underwater turbulent channels. The concept of vortex beam propagation in oceanic turbulence is based on the extended Huygens-Fresnel principle. The analysis considers the effects of key turbulence parameters, including the rate of dissipation of kinetic energy, the rate of dissipation of mean squared temperature, and the temperature-salinity gradient. Numerical simulations are guided in MATLAB to evaluate the FCE under varying environmental conditions and vortex beam parameters. The simulations take into account a variety of source sizes, receiver aperture diameters, wavelengths, and link distances. Additionally, the effect of the vortex beam's topological charge on the coupling efficiency is examined. The results of the simulations reveal that higher topological charges in vortex beams lead to better resistance to turbulence-induced beam spreading. Furthermore, the study quantifies the relationship between the FCE and key environmental parameters, such as temperature and salinity. The design and implementation of UOWC systems that use vortex beams can be optimized with the help of these discoveries. The study highlights the potential of vortex beams to strengthen the performance and accuracy of underwater optical communication links. Finally, this thesis aims to improve the performance of UWOC employing vortex beams and to provide the best conditions for FCE in underwater turbulent environments.
Effect of spatial diversity on underwater optical wireless communication
Underwater optical wireless communication systems have recently increased in use due to their high data rate transmission feature. However, turbulence is the compelling factor in the propagation of optical waves in underwater environments. Intensity fluctuations and performance degradation due to turbulence are observed. In this thesis, a spatial diversity model designed to reduce the effects of ocean turbulence is used and performance improvements are investigated. In our designed model, a point detector is used on the receiver side and annular array beam is used on the transmitter side. The average received intensity and the mean square of the intensity are found by using the Huygens-Fresnel principle. Later, the scintillation index and bit error rate are found for the model created with the found parameters. The scintillation index and bit error rate (BER) were compared and evaluated according to the values of the rate of dissipation of kinetic energy per unit mass of fluid, ratio of temperature to salinity contributions to the refractive index spectrum, source size, ring radius, field amplitude, the rate of dissipation of the mean-squared temperature, Kolmogorov inner scale, propagation distance and wavelength. Calculations were made using the MATLAB program and graphics were created. In this thesis, it is aimed to observe the decreases in scintillation and BER calculation for beam propagation in underwater turbulent environment.
Effects of modulation types on the performance of FSO communication systems
In this thesis, the Bit Error Rate (BER) performance of Binary Phase Shift Keying (BPSK) modulation used in Free Space Optics (FSO) communication systems under marine atmospheric conditions is investigated. Marine atmospheres have a more complex structure than land atmospheres with effects such as high humidity, temperature differences and aerosol particles. These atmospheric factors cause turbulence in the propagation of optical signals, which directly affects the system performance. In this study, the BER performance of BPSK modulation is analyzed by MATLAB simulations considering weak and strong turbulence conditions. Within the scope of the study, parameters such as wavelengths, source field sizes, internal scale and atmospheric structural constant are varied and their effects on BER are evaluated. The results show that low BER values are obtained at short distances, but the effect of turbulence becomes dominant as the distance increases. It is also found that physical parameters such as higher photodetector sensitivity, favorable load resistance and low noise factor improve the system performance. This thesis presents a detailed analysis of the performance of BPSK modulation in marine atmospheres, which is limited in the literature, and aims to develop optimization recommendations for future FSO system designs
Effect of atmosphere on power attenuation in free space optical communication systems
This thesis aims to investigate the power attenuation due to atmospheric absorption, scattering [1] and turbulence faced at the receiver of Free Space Optics (FSO) communication systems. Power losses will be characterized in FSO systems due to atmospheric conditions and the impact of these losses on the system performance will be evaluated [2]. Based on the attenuation levels and the characteristics of the detectors used, power levels needed at the transmitter will be estimated for the required link availability. The thesis will search theoretical methods to understand the critical effects of atmospheric absorption and scattering on the reliability and efficiency of FSO systems and solutions will be proposed [3] The results of the research can make an important contribution to guide new strategies for FSO technology to be resilient to power losses in the atmosphere.
Performance of satellite optical links that use Cosh-Gaussian beams
This thesis investigates the performance of satellite optical communication links that utilize cosh-Gaussian beams, presenting an innovative approach to enhancing the efficiency and reliability of high-speed data transmission. Cosh-Gaussian beams distinguish themselves from other beam profiles due to their unique non-uniform intensity distribution, which enhances resilience to atmospheric turbulence and enables superior energy focusing in free-space optical channels, outperforming conventional Gaussian beams. A detailed theoretical model is developed to examine the propagation characteristics of cosh-Gaussian beams under turbulent atmospheric conditions. Performance metrics of bit error rate (BER) is evaluated across different configurations. Comparative analyses with traditional Gaussian beams highlight the benefits of cosh-Gaussian beams in preserving signal integrity and mitigating turbulence effects. Validated through simulations, the findings demonstrate the significant potential of cosh-Gaussian beams for improving satellite optical link performance and advancing optical communication technologies.
Formal verification for I2C communication protocol in aerospace and aviation industries
Aerospace Industry has many aviation applications that involve vast number of subsystems. Therefore, the need of reliable data communication between devices and components is a critical subject. In this context, I2C communication protocol is widely preferred over other protocols in terms of high speed, flexibility, low power consumption and reliability. However, issues such as data corruption, data loss, slow data transmission may occur in I2C data transmission. These problems can lead to serious consequences in the aviation industry, such as safety risks at multiple levels, electronic problems, air traffic management issues, and incorrect navigation information. Therefore, it is an important requirement that the I2C RTL design be written completely and without errors and also verified. The I2C master design in this thesis was downloaded from OpenCores. There are several verification methods for digital design verification. Formal Verification, which will be used for this thesis, is one of the most precise and reliable methods, especially in critical systems. This method is a significant method that mathematically proves that the design complies with certain features and requirements by saving time. This method checks and proves that the design meets specific features and requirements, providing a mathematical proof while saving time and costs. Yosys, an open source, easily integrated, flexible, synthesis framework that offers comprehensive Verilog support, and the Yosys-based Symbiyosys tool were used to implement this method. In this thesis, using the SystemVerilog Hardware Verification Language and SystemVerilog Assertion supported by Symbiyosys, design errors have been detected according to the design requirements. Thanks to Formal Verification, it prevents problems by ensuring that avionic operations with I2C designs continue smoothly.
Target detection and tracking from unmanned aerial vehicle cameras using embedded GPU
In surveillance, camera aerial vehicles are a common tool. The majority of these surveillance systems follow things in two phases: they identify and detect their targets first, and then they follow them in the live video feed. However, modern object identification methods often use deep learning models trained on massive picture datasets and operate on GPU powered platforms with tremendous processing capacity. Additionally, managing feature matching and association in object tracking introduces additional activities into the system, hence impacting the system's real-time performance. For wide area surveillance (WAS) applications, vision-based object recognition and target tracking is crucial for identifying and following things on ground targets. But since these unmanned aerial vehicles (UAVs) fly so far above the ground, they distort the size of things on the ground. Consequently, it is necessary to have a sensitive object detection detector that can identify these minute ground objects and thoroughly scan characteristics. Furthermore, since CNN based object detectors use deep learning and need a lot of computing and mathematical modeling, they might be difficult to use on embedded devices. The before mentioned issues that may impact object identification and tracking system performance were thoroughly investigated in this thesis. The absence of extensive UAV datasets including object size, brightness, and diversity in form and texture details in the photos captured from airplanes is one of the issues with target identification. Accuracy in object tracking is impacted by performance problems brought on by deep learning approaches' high computational complexity. This thesis uses the RNN model for target tracking and the YOLOV4 target detection model in embedded devices like the NVIDIA JETSON AGX XAVIER to design an efficient, quick, daytime, and real-time target detection and tracking system that can operate quickly and efficiently with the model optimization approach in embedded systems.
Wireless optical systems for aircraft
Aircraft is one of the most preferred transportation and military mission vehicles that contain many subsystems and can perform tasks with the coordinated operation of these systems. Since the emergence of the fly-by-wire concept, many systems such as flight control, navigation, communication, identification, propulsion and landing system have been coordinated with electronic communication infrastructures and many electro-mechanical parts are controlled with digital data. Current communication techniques in aircraft are provided either with wired infrastructures or with wireless radio frequencies. These technologies have reached a saturation level that cannot meet the increasing data demand and it has become increasingly difficult to provide new capabilities to aircraft. In this study, optical wireless communication infrastructures that have gained momentum in recent years have been examined, radio frequency infrastructures used by aircraft and infrastructures in the communication of avionics equipment with each other have been scanned, and accordingly, the gains that can be obtained with optical wireless communication systems that can replace current systems in avionic communication in aircraft have been evaluated.
Transmittance of optical beams in biological tissues
The propagation of Gaussian beams across different biological tissues is investigated. The extended Huygens-Fresnel technique that uses the turbulent power spectrum of biological tissues is employed to get an optical intensity profile and average transmittance at the observation site. Modeling variations in the beam profile and beam broadening involves considerations of source size and wavelength of the beam. Changes in the source size and wavelength of the Gaussian beam lead to diverse beam profiles and variations in beam spot radius when interacting with biological tissue. This variability in the propagating optical beam serves as a means to identify cancer tumors and other anomalies within biological tissues. A comparative analysis of these differences against established test cases aids in the recognition of abnormalities during optical beam propagation through biological tissues. In our evaluations of transmittance, the effects of turbulence, scattering and absorption are included.
Wireless optical wave propagation in underwater medium
In this thesis, the effects of the turbulence on the average transmittance are examined when the lowest order collimated Gaussian optical beam wave propagates in a wireless underwater medium. To observe the oceanic turbulence effect, the power spectrum of homogeneous and isotropic oceanic water combining the effects of salinity and temperature is used. Employing the Rytov method and the numeric integration, the effects of the parameters of power spectrum on the average transmittance are analyzed. Obtaining results with the help of Matlab program indicates that the rate of dissipation of the kinetic energy per unit mass of fluid is directly proportional to the average transmittance while the rate of dissipation of the mean-squared temperature is inversely proportional to the average transmittance. Increase in the link distance and decrease in the wavelength reduce the average transmittance. When the temperature-induced optical turbulence is dominant in the ratio of the salinity and temperature contributions to the refractive index spectrum, the average transmittance almost never decreases. However, the salinity-induced optical turbulence reduces the average transmittance sharply. Increasing the Kolmogorov microscale length, first the turbulence effect increases and the average transmittance decreases, but when the value of Kolmogorov microscale is further increased, the turbulence effect starts to decrease and the average transmittance increases, eventually a saturation is observed.
Adaptive optics corrections in improving the beam spread in underwater turbulent medium
The popularity of the underwater wireless optical communication has increased recently because optical systems have the advantage of providing transmission at high data rates with low latency. However, UWOC is challenging due to harsh environmental conditions and one of the main effects of in oceanic medium is the turbulence. Turbulence causes increase in the beam spread which reduces the performance of the UWOC. In this thesis, the effectiveness of adaptive optics correction for Gaussian beams in oceanic turbulence is studied. The beam size and beam spread were examined with adaptive optics method. The reductions in beam size and beam spread indicate that the adaptive optics correction is a very effective method for reducing the turbulence-caused signal degradations. When investigating the effect of underwater turbulence, the power spectrum in the oceanic medium is supposed to be isotropic and homogeneous. Using the extended Huygens Fresnel principle, average intensity is found. The beam size and beam spread were observed utilizing Carter's definition. Piston, focus, tilt and astigmatism components of adaptive optics corrections were utilized to find the beam size and the beam spread in turbulent oceanic medium. The reduction in the beam size and beam spread was investigated against the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of mean squared temperature, rate of dissipation of kinetic energy per unit mass of fluid, inner scale, receiver aperture diameter, link length, source size and the wavelength. This reduction was compared with and without the adaptive optics method. Using the MATLAB program, graphs were presented and calculations were performed. In this thesis, it is aimed to provide the most suitable conditions for beam propagation in underwater turbulent environment and to increase the UWOC performance.
Performance of channel coding on free space optical (FSO) communication link
The average loss power and the channel fading are among the major challenges of the free-space optical (FSO) communications through the turbulent atmosphere, resulting in the bit-error-rate (BER) performance degradation, or even communication link outage. For the same average received optical signal power, the degradation in BER performance is strongly dependent on the fading statistics. This thesis investigates the performance of channel coding to improve the FSO communication system performance and the communication distance by mitigating atmospheric turbulence. We derive a pairwise error probability (PEP) expression considering the recently introduced gamma-gamma turbulence model and then we drive the upper bounds for the bit-error probability for block codes through atmospheric turbulence channels, considering the gamma-gamma model. Also we present numerical results for the BER performance of different codes such as the Reed-Solomon (RS), Bose, Chaudhuri, and Hocquenghem (BCH) and Hamming codes under different turbulence conditions (weak, moderate, strong).