Enstitüler - Tezler

Permanent URI for this communityhttps://hdl.handle.net/20.500.12416/6

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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 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.
Design of high performance low latency rateless codes
(Çankaya Üniversitesi, 2017) Abdulkhaleg, Nadhir Ibrahim
Luby Transform (LT) codes are one of the best rateless codes mainly designed for binary erasure channel. The characteristics of such codes perfectly performing when used with bulk data files, however a performance degradation has been observed when using them with short length messages. In this thesis, we present a new design for rateless codes, particularly an efficient LT codes using robust soliton distribution (RSD) as a degree generation method and tested in both binary erasure channel (BEC) and noisy channels like the additive white Gaussian noise (AWGN) channel. First, a new proposed decoding technique is defined as belief propagation-pattern recognition (BP-PR) is implemented to enhance the decoding ability of the conventional (BP) algorithm to overcome the problem of losing degree-one coded symbols which caused early decoding termination. The simulation results approve the improvement of the BP-PR when used with LT-RSD and outperforms the bit error rate (BER) records for the state of art techniques like memory-based robust Soliton distribution using conventional BP (LT-MBRSD-BP) or the Gaussian elimination assisted belief propagation (LT-RSD-BP-GE) and improve the records for the BER when used with MBRSD, ISD and optimal degree distribution (ODD), to form the new code called (LT-MBRSD-BP-PR),(LT-ISD-BP-PR) and (LT-ODD-BP-PR) respectively. Second, a new efficient deterministic encoding technique using deterministic degree generator with random data selection (LT-DE) is applied for extremely short data lengths. The degree generation method is based on creating the degrees in a repeated frame with a limited upper value called repetition period (𝑅𝑝) and the data symbols are chosen sequentially from a truncated data file. The data file is truncated to segments of length (𝑅𝑝) and each segment is chosen based on a random sequence. Testing this (LT-DE) against (LT-RSD-BP-PR), (LT-MBRSD-BP-PR) and (LT-ODD-BP-PR) in a BEC environment had approved the superiority of such code over all the other mentioned techniques. It has the lower error floor and higher successful decoding rate with minimum overhead and computational cost. The formation of this (LT-DE) associates a mutual relation between the successive coded symbols which motivate us to present a new sequential decoding technique mainly used over (AWGN) channel. With such new encoding-decoding technique LT codes can approach the decoding complexity cost of Raptor codes with smaller overhead and less encoding complexity as well.
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.
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.
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.
Scattering of evanescent waves by reflectors
(Çankaya Üniversitesi, 2017) Kara, Mustafa
In this thesis, the scattering integral of electromagnetic incident waves scattered by a cylindrical parabolic perfectly electric conducting reflector is evaluated asymptotically. For the determination of the reflected fields the method of stationary phase, and for the diffracted fields the edge point method, whose details are given in appendix, are employed. A plane wave with an arbitrary angle is assumed as incident on the reflector. The evaluated reflected and diffracted fields are examined numerically for any observation point. In the evaluation of diffracted fields, the non-uniform diffracted field expression encountered is overcome by means of Fresnel function. For the numerical analysis, basically two cases are taken into consideration. One of them is the incident angle being real, and the other is the complex value of it. For these values, the effects of all possible combinations including the complex conjugates are examined and plotted numerically.
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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