In this thesis, optimization of the geometry of non-uniform arrays for direction finding yielding unambiguous results is studied. A measure of similarity between the array response vectors is defined. In this measure, the effects of antenna array geometry, source placements and antenna gains are included as variable parameters. Then, assuming that the antenna gains are known and constant, constraints on the similarity function are developed and described to result in unambiguous configurations and maximum resolution. The problem stated is solved with two different methods, the MATLAB optimization toolbox, and genetic algorithm in which different genetic codings are also studied. The performance of the MUSIC algorithm with the optimized array geometries are investigated through computer simulations. The direction of arrival estimates are obtained using the optimized array geometry on the MUSIC algorithm along with the effects of different parameters. Statistics of the true and probable erroneous arrival angles and the probability of gross error are obtained as a measure of performance. It is observed that the proposed optimization process for the array geometry gave rise to unambiguous results for direction finding.

Array processing involves manipulation of signals induced on various antenna elements. In an adaptive array system, the radiation pattern is formed according to the signal environment by using signal processing techniques. Adaptive arrays improve the capacity of mobile communication systems by placing nulls in the direction of interfering sources and by directing independent beams toward various users. Adaptive beamforming algorithms process signals induced on each array element that are assumed not to be affected by mutual coupling between the elements. The aim of this thesis is to investigate the effects of mutual coupling on the performance of various adaptive beamforming algorithms. The performance parameters such as signal to interference plus noise ratio and speed of convergence of the adaptive algorithms are studied and compared by both neglecting and considering the mutual coupling for the least mean squares, recursive least squares, conjugate gradient and constant modulus algorithms. Finally, it is concluded that the effect of mutual coupling is major in the performance of blind algorithms rather than non-blind algorithms. The results are obtained by simulations carried out on MATLAB.

In this thesis, two finalists of the AES (Advanced Encryption Standard) contest, RC6 developed by Rivest et al, Twofish proposed by Schneier et al, and preceding algorithm of RC6 cipher, RC5, are studied. The strength of ciphers to cryptanalytic attacks is measured according to different criteria. The studied evaluation criteria are the avalanche criterion and its derivations. After theimplementation of the algorithms and the test procedures, they are compared with each other. Different test criteria, including avalanche criterion, avalanche weight distribution (AWD) for randomness of RC5, RC6 and Twofish algorithms are applied / and the S-boxes of the Twofish algorithm are analyzed according to nonlinearity criterion. The avalanche criteria results of RC6 and Twofish are compared with NIST (National Institute of Standards and Technology) Statistical Test Suite results.

This document describes radar propagation modelling using split step parabolic wave equation (PWE) method. A computer program using Fourier split-step (FSS) marching technique is developed for predicting the electromagnetic wave propagation in troposphere. The program allows specification of frequency, polarization, antenna radiation pattern, antenna altitude, elevation angle and terrain profile. Both staircase terrain modelling and conformal mapping are used to model the irregular terrain. Mixed Fourier transform is used to implement the impedance boundary conditions. The conditions and the limits of different approximations are stated. The propagation code, RPPT (Radar Propagation Prediction Tool) is developed in Matlab 6.0 with a user friendly GUI. Different PWE methods can be selected in RPPT for different applications. The results are presented as one-way propagation factor and path loss in decibels versus range.Comparisons are made between different PWE techniques and other propagation models to demonstrate the ability and accuracy of the present model to accommodate various situations. It is assumed that the reader is familiar with the tropospheric propagation.

Automatic object detection is a challenging field which has been evolving over decades. The application areas span many domains such as robotics inspection, medical imaging, military targeting, and reconnaissance. Some of the most concentrated efforts in automatic object detection have been in the military domain, where most of the problems deal with automatic target detection and scene analysis in the outdoors using a variety of sensors. One of the critical problems in Automatic Target Detection (ATD) systems is multiscenario adaptation. Most of the ATD systems developed until today perform unpredictably i.e. perform well in certain scenarios, and poorly in others. Unless ATD systems can be made adaptable, their utility in battlefield missions remains questionable. This thesis describes a methodology that adapts parameterized ATD systems with image metrics as the scenario changes so that ATD system can maintain better performance. The methodology uses experimentally obtained performance models, which are functions of image metrics and system parameters, to optimize performance measures of the ATD system. Optimization is achieved by adapting system parameters with incoming image metrics based on performance models as the system works in field. A simple ATD system is also proposed in this work to describe and test the methodology.

Making a computer &lsquo / see&rsquo / is certainly one of the greatest challanges for today. Apart from possible applications, the solution may also shed light or at least give some idea on how, actually, the biological vision works. Many problems faced en route to successful algorithms require finding corresponding tokens in different views, which is termed the correspondence problem. For instance, given two images of the same scene from different views, if the camera positions and their internal parameters are known, it is possible to obtain the 3-Dimensional coordinates of a point in space, relative to the cameras, if the same point may be located in both images. Interestingly, the camera positions and internal parameters may be extracted solely from the images if a sufficient number of corresponding tokens can be found. In this sense, two subproblems, as the choice of the tokens and how to match these tokens, are examined. Due to the arbitrariness of the image pairs, invariant schemes for extracting and matching interest points, which were taken as the tokens to be matched, are utilised. In order to appreciate the ideas of the mentioned schemes, topics as scale-space, rotational and affine invariants are introduced. The geometry of the problem is briefly reviewed and the epipolar constraint is imposed using statistical outlier rejection methods. Despite the satisfactory matching performance of simple correlation-based matching schemes on small-baseline pairs, the simulation results show the improvements when the mentioned invariants are used on the cases for which they are strictly necessary.

ABSTRACT SIMULATION BASED INVESTIGATION OF AN IMPROVEMENT FOR FASTER SIP RE-REGISTRATION TANRIVERDi, Eda M.Sc., Department of Electrical and Electronics Engineering Supervisor: Prof. Dr. Semih BiLGEN July 2004, 78 pages In this thesis, the Session Initiation Protocol (SIP) is studied and an improvement for faster re-registration is proposed. This proposal, namely the &ldquo / registration &ndash / activation&rdquo / , is investigated with a simulation prepared using OPNET. The literature about wireless mobile networks and SIP mobility is reviewed. Conditions for an effective mobile SIP network simulation are designed using message sequence charts. The testbed in [1] formed by Dutta et. al. that has been used to observe SIP handover performance is simulated and validated. The mobile nodes, SIP Proxy v servers, DHCP servers and network topology are simulated on &ldquo / OPNET Modeler Radio&rdquo / . Once the simulation is proven to be valid, the &ldquo / registration &ndash / activation&rdquo / is implemented. Different simulation scenarios are set up and run, with different mobile node speeds and different numbers of mobile nodes. The results show that the re-registration delay is improved by applying the &ldquo / registration &ndash / activation&rdquo / but the percentage of improvement depends on the improvement in the database access delay in the SIP Proxy server.

Phase control in microwave circuits is an impotant process. Especially, in certain applications such as phase array antennas, it is the main principle of opeation. In antenna arrays, each array element is fed by an individual oscillator. By controlling the phase of each oscillator, the radiation pattern and the RF power can be combined in space in certain directions. For such applications, phase shifters have been utilized extensively. However, their high costs, difficulties in design and efficiency are impotant disadvantages. More recently, another technique, &quot / Injection Locking&quot / or &quot / Phase Locking&quot / suggests to use a single reference signal injected into each oscilator element. Through this signal, the phase of the individual oscillators can be controlled and set to a desired value. Therefore, power combining in space or known as &quot / Spaial Power Combining&quot / is possible by using &quot / Phase Locking&quot / of individual oscillator elements. In this thesis, this new phase control technique is examined in theory and in application of a 1GHz oscillator system. A reference signal is injected into a voltage controlled oscillator, and the phase progression is obtained by tuning the oscilator&#039 / s free running frequency.

iv ABSTRACT DESIGN AND CONSTRUCTION OF REDUCED SIZE PLANAR SPIRAL ANTENNA IN THE 0.5-18 GHz FREQUENCY RANGE YILDIZ, 5nan&ccedil / M.S., Department of Electrical and Electronics Engineering Supervisor: Prof. Dr. Altunkan HIZAL October 2004, 106 pages In this thesis, theoretical and practical evaluation of usual spiral antenna is revised. Working principles of both types of planar spiral antennas as Equiangular and Archimedean are introduced. A predesigned microstrip tapered balun used for feeding section of a spiral antenna is simulated on Ansoft HFSS software. Successful simulation results are obtained and measurements of implemented balun structure are made by using an HP 8722 D vector network analyzer. Antenna measurement techniques used in this study are introduced. Measurement set-ups are defined and some preliminary knowledge is given on these. As the main matter of thesis, reduced size planar spiral antennas are designed and implemented. Return loss, gain / radiation and polarization patterns of antennas are measured. Datasets of measurements are compared with each other and with reference spiral antenna. Quite promising results are obtained and size reduction of spiral antenna is achieved in many aspects.

In this dissertation, new approaches in the design of a voice transformation (VT) system for Turkish are proposed. Objectives in this thesis are two-fold. The first objective is to develop standard speech corpora and segmentation tools for Turkish speech research. The second objective is to consider new approaches for VT. A triphone-balanced set of 2462 Turkish sentences is prepared for analysis. An audio corpus of 100 speakers, each uttering 40 sentences out of the 2462-sentence set, is used to train a speech recognition system designed for English. This system is ported to Turkish to obtain a phonetic aligner and a phoneme recognizer. The triphone-balanced sentence set and the phonetic aligner are used to develop a speech corpus for VT. A new voice transformation approach based on Mixed Excitation Linear Prediction (MELP) speech coding framework is proposed. Multi-stage vector quantization of MELP is used to obtain speaker-specific line-spectral frequency (LSF) codebooks for source and target speakers. Histograms mapping the LSF spaces of source and target speakers are used for transformation in the baseline system. The baseline system is improved by a dynamic programming approach to estimate the target LSFs. As a second approach to the VT problem, quantizing the LSFs using k-means clustering algorithm is applied with dimension reduction of LSFs using principle component analysis. This approach provides speaker-specific codebooks out of the speech corpus instead of using MELP&#039 / s pre-trained LSF codebook. Evaluations show that both dimension reduction and dynamic programming improve the transformation performance.