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Thesis (Master)--Izmir Institute of Technology, Electronics and Communication Engineering, Izmir, 2013, Includes bibliographical references (leaves: 60-64), Text in English; Abstract: Turkish and English, x, 64 leaves, Chaos is an interesting nonlinear phenomena that occurs in wide variety of fields. A significant amount of research was devoted to understanding chaos and its properties. After that, researchers focused on searching for possible application areas for chaos to utilize its properties. The need to increase the security of a communication system is considered as a perfect match for chaos and its several properties, yielding chaotic communication. In this thesis, chaotic communication is approached from a control theory perspective. Specifically, three nonlinear observers are designed to extract message encrypted in a chaotic communication signal. The design and stability analysis is presented for the first observer, and the other observers are presented as modifications to the first one. Extensive numerical simulations are performed to demonstrate the viability of the proposed observers. Robustness of the observers to noise, additive disturbances, and parametric mismatch, and security of the observers are demonstrated numerically.

Thesis (Master)--Izmir Institute of Technology, Electronics and Communication Engineering, Izmir, 2014, Includes bibliographical references (leaves: 81-86), Text in English; Abstract: Turkish and English, xiii, 52 leaves, Twin rotor multi-input multi-output system (TRMS) is a laboratory setup resembling the dynamics of a helicopter. It is a complicated nonlinear system with high coupling effects between the propellers. In the literature, there is no commonly agreed dynamic model for these systems mainly due to the difficulties in modelling aerodynamic effects. As a result, numerical simulations of controllers performed on currently available dynamic models do not agree with experimental results obtained from a real system. The main motivations behind this thesis are to develop a TRMS in our laboratory and then apply different control algorithms on it. Firstly, the mechanical system is described briefly. The mechanical components are explained and the computer aided design model is given. The electronic system is then presented in detail. In the electronic system, hardware parts of the TRMS (mainboard, encoder reader circuits, and motor controller circuits) and the embedded algorithms are developed. The development of the user interface that is used both to observe the TRMS and to communicate with it, is then explained. Development of a mathematical model of the TRMS is described where its physical parameters are given. Finally, the performance of the TRMS is verified by conducting experiments for proportional, integral and derivative type controllers. The analysis of the experiments are discussed and compared in average maximum steady-state error, average root-mean-square error, error standard deviation, average root-mean-square control input and control input standard deviation.

Thesis (Doctoral)--Izmir Institute of Technology, Electronics and Communication Engineering, Izmir, 2013, Includes bibliographical references (leaves: 110-117), Text in English; Abstract: Turkish and English, xx, 144 leaves, In this dissertation, online identification of time delays is discussed. Specifically, a novel online time delay identification algorithm for nonlinear systems is presented. As a novel departure from the existing literature, in the design of the time delay identification algorithm, time delays are considered as nonlinear parameters effecting the system and nonlinear parameter estimation techniques are adopted. The presented time delay iden~ tification technique is based on a min-max optimization algorithm. The stability of the proposed time delay identification algorithm is investigated via Lyapunov-based stability analysis techniques. It is shown that the developed estimator identifies unknown time delays, upon satisfaction of a nonlinear persistent excitation condition, within a desireq precision that may be adjusted to be very small. The proposed time delay identification method is then modified to be applicable for sig~ nal processing applications. Afterwards, the control of nonlinear systems subject to state delays is considered. The control objective is to ensure output tracking of a time-varying reference trajectory while identifying unknown state delays. Two cases are considered~ First, only the state delays are assumed to be unknown in the nonlinear system dynamics, Second, linear parameters in the system dynamics are assumed to be unknown along witll unknown time delays. To meet the control objectives, the proposed time delay identifica~ tion technique is fused with a control algorithm, and in both cases, both identification anq control objectives are ensured.