Elektronik ve Haberleşme Mühendisliği Bölümü Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/179

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Analysis and design broadband microwave distributed amplifiers
(Çankaya Üniversitesi, 2017) Yurt, Reyhan
In this thesis, microwave amplifier design techniques are analyzed and especially distributed technique is applied for broadband amplifier in L-S band according to the IEEE radar-frequency band. Conventional distributed amplifier (CDA) design topology is implied at 1-3 GHz frequency range. Available gain is obtained 14+2.5 dB with flatness. Optimum number of stages of amplifier is investigated and the result is evaluated as restriction of this topology so amplifier is designed with one stage. To increase gain performance cascaded single stage distributed amplifier (CSSDA) topology is analyzed and designed as 2-CSSDA at 1-3 GHz. In this design, almost 26 dB is obtained as peak value of available gain near 2.7 GHz and available gain is observed as 23.9+2 dB with simulations. CSSDA designed topology can be integrated with breakthrough circuit and approach so that more qualified distributed amplifier (DA) may be improved.
Analysis and performance measurements of MIMO OFDM techniques for LTE
(Çankaya Üniversitesi, 2018) İbişoğlu, İsmail
Nowadays, the demand towards mobile phones that require high data rates applications has rapidly increased. In mobile networks, the Third Generation Partnership Project (3GPP) to meet the increasing demand developed long-term evolution (LTE) standard. Today, on February 28th, 2017[1], 790 operators have commercially launched LTE in 201 countries, according to data released this week by GSA (Global mobile Suppliers Association) in its latest update of the Evolution to LTE report. This study has analyzed LTE network structure which is based 3GPP standards, Version 7, 8, 9, 10, 11 and 12, and defined LTE technology properties. Afterwards, information is offered about different methods for capacity and coverage area calculations. This study also tested whether Shannon Capacity Equality or using software (like ATOLL) tools are preferred by today operators on sample.
Analysis of lane changes for vehicle strings on highways: String stability, driving safety and comfort
(Çankaya Üniversitesi, 2017) Sağlam, Harun Buğra
An important aim of intelligent transportation systems (ITS) is the full or partial replacement of human driver functionality. Cooperative adaptive cruise control (CACC) is a recent technology for automating the longitudinal vehicle motion. Fulfilling the condition of string stability, CACC enables safe vehicle following at small inter-vehicle spacings and hence supports the formation of tight vehicle strings for improving the road capacity. In its classical realization, CACC is limited to the case where vehicle strings are already formed and all vehicles in a string follow each other on the same lane of a road. However, practical driving situations include the case of vehicles entering or leaving a string and performing maneuvers different from only vehicle following. This thesis is concerned with the effect of additional maneuvers due to lane changes (vehicles entering or leaving) on the safety of vehicle strings. Lane changes include gap opening and closing maneuvers and are subject to measurement inaccuracies and sensor errors due to changes of the vehicle locations. Accordingly, the effect of these maneuvers on the longitudinal vehicle motion has to be analyzed. As the first contribution, the thesis argues that the described measurement inaccuracies during lane changes can be modeled by input signal impulses of the respective vehicle. Moreover, opening/closing gap maneuvers can be realized by the generation of suitable feedforward input signals that are nonzero for a limited time. Respecting that multiple lane changes can occur in a vehicle string, the thesis proposes to study the effect of repeated input signals (impulses or time-limited input signals) on the output signal norm of LTI systems. The second contribution of the thesis is extending the definition of string stability to additional disturbances that can be applied to any vehicle in the string. Respecting the same idea, the third contribution of the thesis shows that a bound on the output signal norm of stable LTI systems exists if the repeated input signals (impulses or time-limited signals) are separated by a non-zero dwell-time. Additionally, an original computational procedure for finding a tight bound on the output signal norm is provided. The fourth contribution is the adaptation of these computational methods to the case of stable LTI systems with multiple inputs and outputs. The fifth contribution is the application of the obtained results to vehicle strings. It is shown that suitable analytical bounds for the relevant output signals such as distance error or acceleration can be determined and the results are validated by simulations. The last major contribution is the development of new numerical methods for bounding the matrix exponential function for large LTI systems based on the Jordan canonical form and the Schur decomposition. The evaluation of such norms is needed when computing the output signal norm of large LTI systems such as long vehicle strings.
BER and SNR performance analysis of 2-ASK & 4-ASK modulated truncated bessel beams on different receiver apertures in FSO communications links
(Çankaya Üniversitesi, 2017) Ağar, Tevfik
In this thesis, varying turbulent atmosphere environment are simulated random phase screen method. 2-ASK & 4-ASK modulated truncated Bessel beam are generated and propagated through turbulent atmosphere utilizing random phase screens. In MATLAB environment error counting method is applied then simulation results are obtained corresponding to BER and SNR. On the other hand, the contributions of enlargement receiver aperture on BER is examined. Also, to comprehend the free space optical (FSO) communication architecture in detail and to support the future experimental studies, FSO communication transmitter and receiver systems are designed.
Designing a patch antenna for 5G communication system
(Çankaya Üniversitesi, 2017) Yıldıran, Orçun
This thesis includes the design and analyzes of rectangular, circular and hexagonal type patch antennas for the next generation (5G) mobile networks. Both the microstrip feed line and coaxial feed techniques are used to feed the patch antenna. The best feed point location for both techniques is found to achieve the highest performance. The high frequency structural simulator (HFSS 12.1) is used to simulate the antenna and find out the characteristics. The antenna performance characteristics such as VSWR, return loss, radiation pattern are obtained. Moreover, a MATLAB Graphical User Interface (GUI) is designed to calculate the antenna parameters for rectangular and circular patch antennas with different feeding methods.
Digital implementation of trigonometric functions via FPGA devices
(Çankaya Üniversitesi, 2017) Ahmad, Shakir Salman
As the technology improves, the importance of dynamic hardware design gains more and more attention in the scientific world. FPGA devices are used for digital circuit design purposes, and recently a significant improvement has been observed in FPGA technology. Many communication systems employed in wireless and satellite systems employ FPGAs. Trigonometric functions, such as sine or cosine, are vital components of communication systems. With the invention of coordinate rotation digital computer, i.e., CORDIC in short, algorithm in 1956, it became possible to generate the trigonometric functions in digital devices, such as calculators, microcontrollers, and electronic chips etc. In this thesis work, we first implement the CORDIC algorithm in MATLAB environment, and analyze the iteration number of the algorithm considering the accuracy of the calculated sine or cosine value. Next, we implement the CORDIC algorithm in FPGA environment using the VHDL programming language. For this purpose, we used the FGPA board involving SPARTAN-3 FPGA chip produced by the XILINX company. Later, we followed an alternative approach for the generation of sine signal. For this purpose, we generated 1Hz sine signal in MATLAB and considering the ratio among sine samples, we generated an integer sequence keeping approximately the same ratio among samples, and using this integer sequence we generated sine signal in FPGA platform and using the D/A converter, we observed the generated sine signal on OSCILLOSCOPE screen. With this alternative approach, it became possible to generate sine signal with any frequency and much less hardware complexity. To generate different sine signals with different frequencies, we divide the clock of the FPGA device by a desired amount and use it while sending the sine samples to the output port.
Effect of sliding windows techniques over a performance of TCP/IP networks
(Çankaya Üniversitesi, 2018) Abedi, Abbas Fadhil Abdulabbas
The communication channels have a variety of features in the communication system and networks, particularly wireless channels. It is used in transmissions between two nodes and deals with high error rates. Such errors that occur frequently which are not easy to be avoided, have the greatest effect on the performance of a network. So, it must be concluded that error rates are for different network conditions with use of different types of sliding windows techniques. In this thesis, error correcting techniques have been investigated based on a retransmission technique they used. One of the famous retransmission techniques is sliding windows technique, which it has three sub-algorithms called: stop and wait, selective repeat, and go back N. In this work, selective repeat and go back N algorithms were taken into account, but a stop and wait algorithm was not considered since it doesn't use any window structure in their retransmissions. Also, it always has a high delay amount with less performance compared to the selective repeat and go back N techniques. For this purpose, sliding window techniques have been implemented on Multi-Protocol Label Switching (MPLS) network platform which is simulated in MATLAB with all its details. In the simulation, all nodes running over a TCP/IP on MPLS network and nodes randomly send a number of data packets to any random node over the same network, which uses a path determined by the shortest path routing algorithm. Finally, the sliding window techniques have been studied and analyzed for their performances on the MPLS for the different traffic conditions, in terms of delay, throughput and packet loss rates. Indeed, the best sliding window technique was determined and suggested for different traffic types of the MPLS networks.
Efficient phase rotation techniques in PAPR reduction of OFDM symbols
(Çankaya Üniversitesi, 2017) Ali, Wisam Hasan
Orthogonal frequency division multiplexing (OFDM) is an efficient digital multi-carrier wireless communication method that offers high-speed data rate, high spectral capability, and robustness to multipath fading. In spite of their enormous features, OFDM systems have high peak to average power ratios (PAPRs) which create serious problems for their use in practical communication systems. In this thesis we inspect multiple signaling PAPR reduction methods for OFDM communication systems. Multiple signaling PAPR reduction techniques include the partial transmit sequence (PTS), the tone injection (TI) and the tone reservation (TR) which has two implementation algorithms; the clipping based (TR-C) and the Kernel-based (TR-K) methods. We also tried a new PAPR reduction approach. The new method is based on the rotation of the information symbols before inverse fast Fourier transform (IFFT) processing. Via computer simulations, we compared the performances of classical multiple signaling and new optimum phase rotation tone PAPR reduction methods to each other.
Improvements in the finite element method and method of moments for the solution of electromagnetic problems
(Çankaya Üniversitesi, 2017) Albayaty, Abdullah Omran Ali
In this thesis, two numerical techniques, the finite element method (FEM) and the method of moments (MoM) are improved for solving electromagnetic boundary value problems governed by differential and integral equations. The FEM is a numerical technique used to solve differential equations. The solution domain is divided into small intervals (elements), and the unknown function is calculated by finding an approximate solution by a truncated series of different shape functions. This approximate solution can be replaced with the original function in the differential equation. As a result, we get the matrix of equations that can be solved to obtain separate solution to the problem. In this thesis, we used the sigmoid function as a novel application, and compare the accuracy of FEM with the sigmoid function against the well-known linear and the step functions. Two examples of electromagnetic problems are presented. It is concluded that the sigmoid function under specific conditions yields the most accurate results. For MoM, this thesis presents a new mathematical algorithm for the solution of electromagnetic problems. This algorithm is schemed to be suitable for solving the singularity that exists in the solution matrix. This adaptive integration algorithm aims to avoid the singularity in the evaluation of the integral so called the Cauchy Principal Value integral. An example electrostatic problem is presented and it is proved that the novel method is accurate.
Lane keeping control for self-driving vehicles
(Çankaya Üniversitesi, 2018) Saraçoğlu, Kıvanç
Intelligent Transportation Systems including Lane Keeping Systems (LKS) aim at providing comfort to drivers, preventing congestion, decreasing gas and CO2 emissions and the number of traffic accidents. LKSs will be widely employed in the automobile industry in the near future as an essential part of modern vehicles including cars, buses and trucks. When realizing a LKS, it is necessary to decide about the required signal measurements and to implement control algorithms that are suitable for different vehicle speeds, road curvatures and can be adapted to different types of vehicles such as passenger vehicles, buses and trucks. The main aim of this thesis is to evaluate and compare different lane keeping algorithms. These lane keeping algorithms are applied to a vehicle model, whose longitudinal motion is decoupled from the lateral motion. Four lane keeping control algorithms are investigated. The first two control algorithms measure the yaw rate and the displacement error at a pre-view distance to compute the necessary rate of change of the steering angle for following a road. The first control algorithms uses a linear controller transfer function, whereas the second control algorithm uses sliding mode control. The third control algorithm also measures the yaw rate and the displacement error at a pre-view distance but directly computes the required steering angle for lane keeping. The fourth control algorithm measures the yaw rate, the heading error and the displacement of the center of gravity (COG). These algorithms are evaluated using simulation experiments with given displacement errors and road profiles. The main outcomes of the thesis are as follows. As the first contribution, the thesis shows that the measurement of the displacement error at a pre-view distance increases the robustness of lane keeping control algorithms. On the downside, since the displacement error at the pre-view distance is controlled, the displacement error at the COG can become large at high velocities. As the second contribution, the thesis concludes that it is beneficial to combine measurements of the yaw rate, the displacement errors at the preview-distance and the COG as well as a prediction of the road curvature to obtain an efficient control algorithm. Such control algorithm is proposed in the thesis and its superior performance is shown by simulation experiments.
Machine learning based anomaly detection technique for in-vehicle networks
(Çankaya Üniversitesi, 2017) Akar, Arif
The automotive industry faces a revolution by connecting vehicles to the communication infrastructure in the scope of intelligent transportation systems (ITS). The idea of internet of things (IoT) entering the automotive domain raises much skepticism about security and privacy issues. The information received from and sent to vehicles bears considerable risks for all components in the transportation system. Commonly, the IT industry uses firewall devices to filter communication in both receiving and transmitting directions that require heavy maintenance personnel support and instant configuration changes. Considering the mobility of vehicles and the light-weight nature of in-vehicle networks, firewalls require too many resources and miss automated decision making. Intrusion detection systems (IDS) are widely used in traditional IT networks and try to close gaps resulting from stateful firewalls. This thesis proposes the In-Vehicle Anomaly Detection Engine (IVADE) as an anomaly based intrusion detection algorithm for in-vehicle controller area network (CAN) applications using machine learning methods. The algorithm aims at detecting malicious manipulations of vehicle mobility data (such as position, speed, direction) which are exchanged in the form of Cooperative Awareness Messages on vehicle to vehicle (V2V) and vehicle to infrastructure (V2I) networks. The functionality of IVADE is validated by simulations of a Lane Keeping Assistance system that is implemented on a CAN bus together with the electronic control units (ECUs) for signal measurement and control computations. The relevant features for applying machine learning in IVADE are derived from received CAN message fields, supported with automotive domain-specific knowledge of the dynamic system behavior and trained with Decision Trees. The obtained simulation results indicate that IVADE successfully detects anomalies in in-vehicle applications and hence supports safety-critical functions.
PAPR reduction of OFDM system symbole via optimal rotation of information symbols
(Çankaya Üniversitesi, 2018) Jassim, Alaa Hussein
Orthogonal frequency division multiplexing (OFDM) is an effective multicarrier transmission for wireless communication systems. The demand for high data rate for multimedia applications made OFDM widely used in wireless communication. The main drawback of OFDM communication systems is their high peak-to-average power ratios (PAPRs) which limit their use in practical applications. There are two well-known PAPR reduction techniques known in the literature, partial transmit sequence (PTS), and selective mapping which are closely related to each other. In this thesis work, we propose a new PAPR reduction approach. Our method is based on rotation of the information symbols before inverse fast Fourier transform (IFFT) operation. The selection of the information symbols is performed inspecting their combinations in OFDM symbols, and this is achieved detailing decimation in frequency IFFT algorithm, i.e., inspecting the combination of information symbols while performing decimation in frequency IFFT algorithm. The proposed reduction method has better performance than that of the PTS method, and has much less complexity when compared to that of the PTS technique.
Radiation from parabolic type radio link antennas
(Çankaya Üniversitesi, 2016) Kılıç, Gamze
In this thesis, the fields scattering from parabolic reflectors with perfectly electric surface (PEC) have been investigated. The parabolic reflector surface illuminated by a point source located at focus. In order to find the surface integral, the modified theory of physical optics (MTPO) method was used and analyzed. The reflected geometrical optics (GO), transmitted fields and edge diffracted fields were evaluated by using asymptotic methods. One of these asymptotic methods was the stationary phase method (SPM), which was used to find the reflected geometrical optics and transmitted fields; and the other one was the edge point method which was used for edge diffracted fields. The scattered fields were plotted by MATLAB numerically and compared by various parameters such as angle of incidence and the distance between the sources.
Spectral analysis of ECG signals for pre-diagnosis of heart diseases
(Çankaya Üniversitesi, 2018) Al-Jada, Omar Saad Abdulqader
In this thesis we used the three cases for diagnosis of the heart attacks. The first case is healthy persons, second case is non healthy persons and the last one is unknown persons. For detection of them we used the correlation and auto correlation between the cases. For the simulation results we used the MATLAB programming languages. For diagnosis we used two statistical method. The first one is to take only one dice (assuming that this selected dice is a perfect representative of the remaining dice) and throw it many times (multiplying the time axis, to get time average). The second is to throw all dice or some of the dice at the same time (multiplying the event axis, to get ensemble average). The question is how many times should the experiment be repeated along time axis in the first case and how many dice thrown at a time in the second case so that we arrive at a result well approximated to the ones to get a result within 98 % confidence interval the minimum number that an experiment should be performed
String stability analysis of Cooperative Adaptive Cruise Control (CACC) with actuator saturation
(Çankaya Üniversitesi, 2017) Bingöl, Hilal
Intelligent transportation systems aim at improving the efficiency and safety of transportation. In dense traffic, vehicles are aggregated to vehicle strings that travel on the same lane, whereby it is desired to maintain a small but safe distance between the vehicles. In the literature, this task is captured by the notion of string stability: fluctuations that are introduced by maneuvers of the leader vehicle should be attenuated by the follower vehicles. The literature provides various methods for achieving string stability under the assumption that the vehicles are modeled as linear systems. In this thesis, we study the case where vehicles are modeled as nonlinear systems and hence face actuation constraints as well as state constraints. Different methods are employed. First, a reachability analysis based on the level-set method determines the states that are reachable under limitations on the engine force of vehicles. It turns out in the thesis that, although the reachability analysis is the proper method to analytically address the problem of saturation, it is computationally not feasible due to the large state space of the vehicle model. As a remedy, a further analysis of the model is carried out for the special case of maneuvers. Based on the realistic assumption that the impulse response of the vehicle following model is positive, several sufficient conditions for the input signal of the leader vehicle are derived in order to preserve string stability under actuator saturation. The first set of condition is concerned with the computation of maximum/minimum input signal that generated based on optimal control solution. These maximum/minimum input signals depend on the initial velocity of the vehicle string. The second set of conditions allows computing suitable input signals of the leader vehicle analytically and is hence highly beneficial in practice. The obtained results are illustrated by extensive simulation experiments.
Trajectory generation for open/close gap maneuvers in vehicle strings
(Çankaya Üniversitesi, 2017) Çankaya, Erkam
Cooperative adaptive cruise control (CACC) is an advanced technology allowing vehicle following at a small inter-vehicle spacing. In its classical usage, CACC assumes that vehicles are arranged in the form of a vehicle string and follow each other at a velocity-dependent distance. Nonetheless, practical driving situations include the case of lane changes, where vehicles can join or leave a vehicle string. In such case, it is required that gaps for joining vehicles are provided or gaps after leaving vehicles are closed in order to ensure safe and efficient driving. This thesis is concerned with gap opening and closing maneuvers in vehicle strings. Introducing a suitable control architecture, gap opening and closing maneuvers can be realized by the generation of feedforward input signals. To this end, the first contribution of the thesis is the development of five methods for the computation and representation of gap opening and closing trajectories that fulfill additional safety and comfort constraints. The first method is based on the solution of an optimal control problem, the second method uses a polynomial trajectory and plant inversion, the third method concatenates three polynomials and uses nonlinear programming to determine the polynomial coefficients, the fourth method uses a high-order polynomial and the fifth method uses concatenated polynomials in order to approximate the optimal control solution. A simulation study shows that the fifth method is particularly useful in practical applications since it computes trajectories that approximate the optimal control solution in real-time. The second contribution of the thesis is the implementation of a vehicle model that realizes CACC and additional feedforward signals in the form of a Matlab S-function.

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