# Theses - Department of Electrical and Electronics Engineering

## Permanent URI for this community

Faculty of Engineering

## Browse

### Browsing Theses - Department of Electrical and Electronics Engineering by Issue Date

Filter results by year or month (Choose year) 2024 2023 2022 2021 2020 2019 2018 2017 2016 2015 2014 2013 2012 2011 2010 2005 2000 1995 1990 1980 (Choose month) January February March April May June July August September October November December Browse

Now showing 1 - 20 of 862

###### Results Per Page

###### Sort Options

Item Open Access Stabilization of multivariable systems with constrained control structure(Bilkent University, 1988) Ünyelioğlu, Konur AlpShow more The following problem is considered: Given a multivariable system with m inputs and r outputs and an m x r matrix whose nonnegative (i,j)’th element represents the cost of setting up a feedback link from the j ’th output to the i’th input, find a set of feedback links with minimum total cost, which does not give rise to fixed modes. Utilizing the graph-theoretic characterization of structurally fixed modes, the problem is decomposed into two subproblems, which are then solved by using concepts and results from network theory. The combination of the optimum solutions of the subproblems provides a suboptimal solution to the original problem.Show more Item Open Access Design and implementation of a general purpose median filter unit in VLSI(Bilkent University, 1988-10) Karaman, MustafaShow more The median of a group, containing an odd number of elements, is defined as the middle element, when the elements of the group are sorted. A median filter finds the median of a number of elements at its inputs. Median filters are frequently used in many signal and image processing applications for smoothing of the noisy signals and images while at the same time preserving the edge information. The required window size, speed, and the word length of the median filters vary depending on the applications. In order to meet these changing demands a general purpose median filter unit configuration is proposed. The unit consists of two single-chip median filters. One of the chips is designed for unlimited word-length and extensibility to larger window sizes whereas the other one is for real-time video applications. The networks of the chips are based on the odd/even transposition sorting. The chips are implemented in 3-mu m MsquareCMOS by using full-custom VLSI design techniques. For physical testing of the chips, the test vectors and the corresponding outputs of the chips are generated by using software tools written for this purpose. In this thesis, the algorithms, VLSI implementations, simulation results, testing, and applications of the chips are presented.Show more Item Open Access Structural analysis of pole assignment and stabilization in dynamic systems(Bilkent University, 1989) Şefik, AylaShow more Motivated by the need for qualitative investigation of general system properties such as controllability, obser\^bility, existence of fixed modes, etc. as the complement of the quantitative approach in analysis, especially of large-scale systems, the problems of pole assignability and stabilizability are considered from the structural point of view. The study is based on the definition of a generic property as a property that holds for almost all values of the nonzero system parameters. Structured matrices and digraphs are used for system description. Both problems are first formulated in an algebraic setting and then translated to a structural framework by means of several graph-theoretic results which give sufficient conditions for solvability, in terms of the existence of particular cycle families in the digraph. Following a similar approach, a graphical investigation of structural observability is presented. Lastly, genericity of several results are reconsidered in the light of these graphical characterizations.Show more Item Open Access Design and testing of a microprocessor compatible 128-bit correlator chip(Bilkent University, 1989) Topçu, SatılmışShow more In digital synchronous data transmission, synchronization (sync) words are used to mark the beginning of the incoming data stream. Detection of the sync word received from a noisy channel is a difficult problem. One of the optimum solutions to this problem is to use a correlator. A correlator could be implemented with SSI and MSI components on a printed circuit board with the disadvantage of bulkiness. To use it in light-weight equipment such as portable data terminals, it is designed to be implemented as a full custom single VLSI chip. It can be used for 128-bit sync word detection and PRBS generation. Two chips can be cascaded for 256-bit correlation as well as distributed sync words, and inverted or non-inverted sync words can be detected. It is fully programmable by a microprocessor to set the number of tolerable errors in detection and to select the bits of the 128-bit (or 256 bit) input data stream to be used in the correlation and hence, it can be directly connected to a microprocessor as a peripheral device. In designing the correlator chip some Design For Testability methods are used to improve the testability. Especially, scan design and partitioning techniques are applied resulting in a significant decrease in the number of test patterns although these techniques involve an overhead in the overall transistor count only by 1 percent. For functional and timing simulations ESIM and RNL simulators are used, respectively. Test patterns for the registers are generated manually and for testing of the combinational part two programs, gen and check, are written in C programming language. The simulation programs and test pattern generation programs are run on SUN workstations under 4.3 BSD UNIX operating system.Show more Item Open Access Exact and approximate decoupling and noninteracting control problems(Bilkent University, 1989) Akar, NailShow more In this thesis, we consider “exact” and “approximate” versions of the disturbance decoupling problem and the noninteracting control problem for linear, time-invariant systems. In the exact versions of these problems, we obtain necessary and sufficient conditions for the existence of an internally stabilizing dynamic output feedback controller such that prespecified interactions between certain sets of inputs and certain sets of outputs are annihilated in the closed-loop system. In the approximate version of these problems we require these interactions to be quenched in the ‘Hoo sense, up to any degree of accuracy. The solvability of the noninteracting control problems are shown to be equivalent to the existence of a common solution to two linear matrix equations over a principal ideal domain. A common solution to these equations exists if and only if the equations each have a solution and a bilateral matrix equation is solvable. This yields a system theoretical interpretation for the solvability of the original noninteracting control problem.Show more Item Open Access VLSI implementation of a microprocessor compatible 128-bit programmable correlator(Bilkent University, 1989) Ungan, İsmail EnisShow more A single chip microprocessor compatible digital 128-bit correlator design is implemented in 3 ¡im M^CMOS process. Full-custom design techniques are applied to achieve the best trade off among chip size, speed and power consumption. The chip is to be placed in a microprocessor based radio communication system. It marks the beginning of a synchronous data stream received from a very noisy channel by detecting the synchronization (sync) word. Two chips can be cascaded to make a 256-bit correlator. It is fully programmable by a microprocessor to set the number of tolerable errors in detection and to select the bits of the 128-bit (or 256-bit) data stream to be used in the correlation. The latter feature makes the correlator capable for use in detection of distributed sync words and PRBS generation. The silicon area of the chip and hence the chip cost is minimized by reducing the gate count in the logic design, by keeping the transistor sizes minimum without avoiding the timing specifications of the design and by a proper placement (floor plan) of the transistors on the silicon. The layouts are laid in a hierarchical manner. Unused areas are minimized and the layouts are designed in compact forms. During the layout design, charge sharing, body effect, latch-up, metal migration, noise and clock skew problems are considered. Mainly, the softwares. M agic, Spice, E sim and R nl are used for layout editing, timing and function simulations. These programs are run on SUN workstations under 4.3 BSD UNIX^ operating system.Show more Item Open Access Cutoff rate for fixed-composition coding over energy constrained AWGN channels(Bilkent University, 1990) Oğuz, Nihat CemShow more Shannon showed that, under an energy constraint, the ensemble of shell constrained codes optimizes the cutoff rate for AVVGN channels. Unfortunately, this ensemble is not very practical since its input alphabet is the entire real line. In this thesis, we consider the ensemble of fixed-composition codes which satisfy the shell constraint and have a finite input alphabet. For a certain four-letter symrnetric input alphabet, the cutoff rates for ensembles of fixed-composition codes of blocklengths ii]) to 10 are compnti'd for tlie AVVGN channel at various signal-to-noise ratios. Also an asymptotic analysis of these cutoff rates is carried out a.s blocklenghth tends to infinity. These results are compared with the cutoff rates optimized over the independentletters code ensemble, which is the ensemble ordinarily used in [>ractice. The results of this comparison show that, for relatively moderate signal-to-noise ratios, it is possible to achieve cutoff rates within 1-2% of the optimum value by using fixed-composition codes; whereas, with iudepeiideiit-letters codes, one can get at most within 9-10% of the optimum value. Thus, fixed-composition codes can provide significant improvements in cutoff rate in practice, cispiicially for moderate to high signal-to-noise ratios.Show more Item Open Access Simulation of a holographic 3-D television display(Bilkent University, 1990) Bozdağı, GözdeShow more The theory and the computer simulations of an acousto-optical holographic 3-D television display are presented in this dissertation. The technique used is based on the reproduction of the desired pattern, in our case the hologram, using traveling surface waves. The crystal that will be used as the medium of display is assumed to have a number of electrodes attached to it on one side. If signals are applied to all of the electrodes, propagating waves from the electrodes will superpose to form a time-varying surface field pattern on the crystal. It is possible to find out the signals to be applied to the electrodes through an inversion relationship from the original holographic pattern. The proposed method is simpler and more efficient than the methods available in the literature and it solves the display resolution problem completely.Show more Item Open Access Capacity of noisy, discrete memoryless channels under input constraints(Bilkent University, 1990) Karaşan, EzhanShow more In this thesis work, we examine the capacity of discrete memoryless channels under input constraints. We consider a certain class of input-restricted channels for which constrained sequences can be modeled as outputs of a finite-state machine(FSM). No efficient algorithm is known for computing the capacity of such a channel. For the noiseless case, i.e., when the channel input letter and the corresponding output letter are identical, it is shown that [1] the channel capacity is the logarithm of the largest eigenvalue of the adjacency matrix of the state-transition diagram of the FSM generating the allowed channel input sequences. Furthermore, the probability distribution on the input sequences achieving the channel capacity is first-order markovian. Here, we discuss the noisy case. For a specific input-restricted channel, we show that unlike the noiseless case, the capacity is no longer achieved by a first-order distribution. We derive upper and lower bounds on the maximum rate achievable by a K-th order markovian distribution on the allowed input sequences. The computational results show that the second-order distribution does strictly better than the first-order distribution for this particular channel. A sequence of upper bounds on the capacity of an input-restricted channel is also given. We show that this sequence converges to the channel capacity. The numerical results clarify that markovian distribution may achieve rates close to the capacity for the channel considered in this work.Show more Item Open Access 3-dimensional median-based algorithms in image sequence processing(Bilkent University, 1990) Alp, Münire BilgeShow more This thesis introduces new 3-dimensional median-based algorithms to be used in two of the main research areas in image sequence proc(',ssi,ng; image sequence enhancement and image sequence coding. Two new nonlinear filters are developed in the field of image sequence enhancement. The motion performances and the output statistics of these filters are evaluated. The simulations show that the filters improve the image quality to a large extent compared to other examples from the literature. The second field addressed is image sequence coding. A new 3-dimensional median-based coding and decoding method is developed for stationary images with the aim of good slow motion performance. All the algorithms developed are simulated on real image sequences using a video sequencer.Show more Item Open Access Generation and parameter estimation of Markov random field textures and a parallel network for texture generation(Bilkent University, 1990) Gürelli, Mehmet İzzetShow more In this thesis, a special class of Markov random fields (MRF), which is defined on two dimensional pixel arrays and represented by a few numbers called the MRF parameters, is studied as a texture model. Specifically, the generation of sample MRF textures and estimation of MRF texture parameters are considered. For the generation of sample MRF textures, an algorithm that can be implemented in a parallel manner is developed together with a parallel network which implements the algorithm. A mathematical description of the algorithm, based on finite state Markov chains is given and the structure of the network is explained. For the estimation of MRF texture parameters, a method based on histogramming of a sample MRF texture is studied cind a mathematical justification of the. method is given. Generation and parameter estimation methods studied in this thesis are tested by some computer programs and the results are observed to be satisfactory for many purposes.Show more Item Open Access Cutoff rate for fixed-composition on-off keying over direct detection photon channels(Bilkent University, 1990) Toygar, M. Şenol.Show more In this thesis, we consider direct detection photon channel with peak and average power constraints. This channel is modelled as a binary input discrete memoryless channel. We study the cutoff rate for different modulation formats on this channel since it is a measure of decoding complexity when sequential decoding is used and also, it gives an upper bound for the probability of error which decreases exponentially with the constraint length of convolutional code. Cutoff rates for the ensembles of fixed-composition and independent-letters codes along with ON-OFF keying are computed numerically and also some bounds are given. Cutoff rates versus signal-to-noise ratio or peak power are plotted for blocklengths of N=40,100 and for both ensembles. Comparison of cutoff rates for these two ensembles shows that for the direct detection photon channel the cutoff rate of fixed-composition ensemble is significantly greater than that of independent-letters ensemble for small values of signal-to-noise ratio and when the average power is a small fraction of peak power, say, 5-30%. In an uncoded system, for achieving a probability of error P(E)=(10 to the power -9), we should send 10 photons/slot with rate R=1 bit/slot, resulting in an efficiency of 0.1 bits/photon.However, using coding we can make probability of error arbitrarily small achieving an efficiency of 1 bit/photon. Also, some remarks on the implementation of fixed-composition trellis codes and on multi-level signalling instead of ON-OFF keying are given in conclusions.Show more Item Open Access BUSTLE: a new circuit simulation tool using asymptotic waveform evaluation and piece-wise linear approach(Bilkent University, 1990) Dikmen, Cemal TamerShow more BUSTLE, a new general purpose circuit simulation program is developed especially for the analysis of VLSI circuits. BUSTLE uses Asymptotic Waveform Evaluation (AWE), which is a new method to analyze linear(ized) circuits, and PWL approach for the I'epresentation of nonlinear devices. AWE employs a form of Fade approximation rather than numerical integration to approximate the behavior of linear(ized) circuits in either the time or the frequency domain. AWE is extended to match both derivative and integral moments to overcome the unstability problem.Show more Item Open Access BUSTLE, a new circuit simulation tool(Bilkent University, 1990) Alaybeyi, M. MuratShow more A new circuit simulation tool, BUSTLE, using Asymptotic Waveform Evaluation (AWE) technique and Piece-wise Linear (PW L) models, is implemented. The results are very promising, especially for large circuits. This piece of work, in cooperation with [1], explains the techniques used in the simulator BUSTLE, such as • efficient LU decomposition of the sparse matrices, • using derivative and integral moments in order to get rid of the instability problem, • combining the PWL approach with AWE in transient analysis, and illustrates some simulation results.Show more Item Open Access A method for extracting object related information from in-line holograms using Wigner distribution(Bilkent University, 1990) Özgen, Mehmet TankutShow more In this thesis, a method based on Wigner distribution is developed to find the three-dimensional coordinates of particles directly from their in-line hologram without reconstruction. If a one-dimensional discrete hologram signed is subtracted from unity and the discrete-time Wigner distribution of the resulting signal is computed then a two-dimensional real sequence is obtained which can be displayed as an image carrying coordinate information about the objects encoded in the hologram. In order to analyze three-dimensional object distributions, the idea described above is adapted to the case of twodimensional holograms in the following way. A two-dimensional hologrcim is digitized in an image processing system, then, one of its rows or columns is selected and a DC level shift is given to thcit row or column. The discrete-time Wigner distribution of the resulting one-dimensional signal is computed and displayed as a two-dimensional image. If this is done for a sufficient number of rows and columns of the hologram then a set of images is obtained which contaixas the total information about the coordinates of particles encoded in the hologram.Show more Item Open Access Robust sampled data control(Bilkent University, 1990) Ocalı, OganShow more Robust control of uncertain plants is a major area of interest in control theory. In this thesis, robust stabilization of plants under a class of structural perturbations using sampled-data controllers is considered. It is shown that a controllable system under bounded perturbations that satisfy matching conditions can be stabilized using high-gain sampled-data control, provided that the sampling period is sufficiently small. This result is then applied to robust stabilization of interconnected systems using decentralized sampled-data control, where both single-rate and multi-rate sampling schemes are considered.Show more Item Open Access Ripple-free deadbeat control of sampled-data systems(Bilkent University, 1990) Mumcuoğlu, Erkan ÜnalShow more In this thesis, we consider the ripple-free deadbeat control problem for linear, multivariable sampled-data systems represented by state-space models. Existing results concerning the deadbeat/ripple-free deadbeat regulation and tracking problems are based on controller configurations of either constant state-feedback or discrete dynamic output feedback. In the thesis, the problem is analyzed for two new sampled-data controllers, namely, generalized sampled-data hold functions and multirate-output controllers. Some necessary and sufficient solvability conditions for the problem are stated by theorems in time-domain and frequency domain in terms of the open-loop system parameters. Several special cases are also considered as corollaries.Show more Item Open Access Implementation of a state-space Kalman filter on a digital signal processing microprocessor(Bilkent University, 1990) Islam, M. KhaledulShow more Item Open Access Sequential decoding on intersymbol interference channels with application to magnetic recording(Bilkent University, 1990) Alanyalı, MuratShow more In this work we treat sequential decoding in the problem of sequence estimation on intersymbol interference ( ISI ) channels. We consider the magnetic recording channel as the particular ISI channel and investigate the coding gains that can be achieved with sequential decoding for different information densities. Since the cutoff rate determines this quantity , we find lower bounds to the cutoff rate. The symmetric cutoff rate is computed as a theoretical lower bound and practical lower bounds are found through simulations. Since the optimum decoding metric is impractical, a sub-optimum metric has been used in the simulations. The results show that this metric can not achieve the cutoff rate in general, but still its performance is not far from that of the optimum metric. We compare the results to those of Immink[9] and see that one can achieve positive coding gains at information densities of practical interest where other practical codes used in magnetic recording show coding loss.Show more Item Open Access The Examination of the effect of polarization on the radiation losses of bent optical fibers(Bilkent University, 1990) Tanyer, Süleyman GökhunShow more It has long been recognized that the bending losses in weakly guiding optical fibers, is independent of the polarization for large bend radius. We showed this fact using the volume equivalent current method. The procedure is then applied to a helically bent fiber, and it is shown that the radiation from the helical fiber is also independent of the polarization as long as the fiber is weakly guiding.Show more