Browsing by Subject "Control theory"

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Open Access
Çokyollu ortamda çapraz belirsizlik işlevi-yön bulma tekniğinin başarım analizi
(IEEE, 2008-04) Güldoǧan, Mehmet Burak; Arıkan, Orhan
Bu bildiride, Çapraz Belirsizlik İşlevi-Yön Bulma (CAFDF) tekniğinin çokyollu ortamlardaki sinyallerin zaman gecikmesi, Doppler kayması, geliş yönü(GY) ve genlik kestirimindeki başarımı ile yiiksek çözünürlüklü algoritmalar olan Uzay-Almaşan Genelleşmiş Beklenti-Enbüyüitme (SAGE) ve Çoklu Sinyal Sınıflandırılması(MUSIC)'in sentetik sinyaller iizerindeki başarımları kıyaslanmıştır. Algoritmalann performansları, kök Ortalama Karesel Hata (kOKH) cinsinden degişik işaret Gürültü Oranı (iGO) değerlerinde Monte Carlo denemelerine dayalı olarak sunulmuştur. Sentetik kanallarda istatiksel kıyaslama amaçlı Cramer-Rao alt sınırları eklenmiştir. Simülasyon sonuçları göstermektedir ki, orta ve düşük iGO değerlerinde CAF-DF diğer iki algoritmaya göre üstünlük sağlamaktadır.
Open Access
Comparison of the CAF-DF and sage algorithms in multipath channel parameter estimation
(IEEE, 2008-07) Güldoğan, M. Burak; Arıkan, Orhan
In this paper, performance of the recently proposed Cross Ambiguity Function - Direction Finding (CAF-DF) technique is compared with the Space Alternating Generalized Expectation Maximization (SAGE) technique. The CAF-DF, iteratively estimates direction of arrival (DOA), time-delay, Doppler shift and amplitude corresponding to each impinging signal onto an antenna array by utilizing the cross ambiguity function. On synthetic signals, based on Monte Carlo trials, performances of the algoritms are tested in terms of root Mean Squared Error (rMSE) at different Signal-to-Noise Ratios (SNR). Cramer-Rao lower bound is included for statistical comparisons. Simulation results indicate the superior performance of the CAF-DF technique over SAGE technique for low and medium SNR values. © 2008 IEEE.
Open Access
Decentralized blocking zeros in the control of large scale systems
(1992) Ünyelioğlu, Konur Alp
lu lliis lliesi.s, a luuiiber ot syiithe.sis problems i'or linear. ninc-invariauL, iiiiite-cliuieiiSioiial sysiems are adclres.se(l. It i.s sliown that tlie lu'w concejU of (l·.': m inili zed blocking zeros \s as fmidaineiital to controller .synthesis problems for large scale systems as the concept of decentralized fixed modes. The main problems considered are (i) decentralized stabilization problem, (ii) decentralized strong stabilization problem, and (iii) decentralized concurrent stabilization problem. 7'he dtcenIralized siabUizaiion problem is a fairly well-understood controller synthesis problem for which many synthesis methods exist. Here, we give a new .synthesis procedure via a proper stable fractional approach and focus our attention on the generic solvability and characitnzalion of all solutions. The decenlralized strong .stabilization problem is the problem of stabilizing a .systeni using stable local controllers. In this problem, the .set of decentralized blocking zeros play an essential role and it turns out that the problem has a solution in case tlie poles and the real nonnegative decentralized blocking zeros have parity interlacing property. In the more general problem of decentralized stabilization problem with minimum number of unstable controller poles, it is shown tliat this minimum number is determined by the nuiid.H-»r of odd distributions of plant poles among the real nonnegative decentralized blocking zeros. The decentralized concurrent stabilization problem is a special type of simultaneous stabilization problem using a decentralized controller. Tliis problem is of interest, since many large scale synthesis problems turn out to be its special cases. A complete solution to decentralized concurrent stabilization problem is obtained, where again the decentralized blocking zeros play a central role. Three problems that have receiviHİ wide atteiuion in tlie literature of large scale .systems: stabilization o f composite systems using locally :>tabilizing subsystem controllers, stabilization uf composite system.^ na the slabilization o f mam diagonal transfer matrices, and rcliablt decentralized siabilizaiion problem are solved by a specialization of oiir main result on decentralized concurrent stabilization problem.
Open Access
An exponential stability result for the wave equation
(Elsevier, 2002) Morgül, Ö.
We consider a system described by the one-dimensional linear wave equation in a bounded domain with appropriate boundary conditions. To stabilize this system, we propose a dynamic boundary controller applied at the free end of the system. The transfer function of the proposed controller is a proper rational function which consists of a strictly positive real function and some poles on the imaginary axis. We then show that under some conditions the closed-loop system is exponentially stable. © 2002 Published by Elsevier Ltd.
Open Access
İçerik tabanlı görüntü erişimi için sahne sınıflandırması
(IEEE, 2008-04) Çavuş, Özge; Aksoy, Selim
Son yıllarda çok geniş veri tabanlarının kullanımıyla birlikte içerik tabanlı görüntü indekslemesi ve erişimi önemli bir araştırma konusu halini almıştır. Bu çalışmada, görüntü indekslemesi için sahne sınıflandırmasını baz alan bir görüntü erişim sistemi tanımlanmıştır. Görüntülerden çıkarılan alt düzey öznitelikler görüntü indekslemesinde doğrudan kullanılmak yerine, bu öznitelikler sahne sınıflandırması için kullanılmış ve görüntüler sınıflandırma sonucunda elde edilen anlamsal sınıf bilgileriyle indekslenmiştir. Sahne sınıflandırması için “kelime kümesi” (bag of words) dokuman analizi yöntemi olarak bilinen tekniğin bir uyarlaması kullanılmıştır. Görüntü erişim sistemini insan algısıyla desteklemek ve anlambilimsel uçurumu en aza indirgemek için erişim senaryosuna tek sınıf sınıflandırıcı bazlı ilgililik geri beslemesi eklenmiştir. Bunun için, ilgili görüntüleri çok iyi modelleyen, ilgili olmayan görüntülerden de bir o kadar uzak duran bir hiperkure oluşturan destek vektör veri tanımlaması kullanılmıştır. Önerilen yöntemler Corel veri kümesinde denenmiş ve başarılı sonuçlar elde edilmiştir. Content-based image indexing and retrieval have become important research problems with the use of large databases in a wide range of areas. In this study, a content-based image retrieval system that is based on scene classification for image indexing is proposed. Instead of using low-level features directly, semantic class information that is obtained as a result of scene classification is used during indexing. The traditional "bag of words" approach is modified for classifying the scenes. In order to minimize the semantic gap, a relevance feedback approach that is based on one-class classification is also integrated. The support vector data description is used for learning during feedback iterations. The experiments using the Corel data set show good results for both classification and retrieval. ©2008 IEEE.
Open Access
İnsansız hava araçları için eşanlı konumlandırma ve haritalama
(IEEE, 2008-04) Kök, Mehmet; Barshan, Billur
Sabit yükseklikte uçtuğu varsayılan insansız Hava Araçları ( İHA) için görü-tabanlı bir Eşanlı Konumlandırma ve Haritalama (EKVH) algoritması sunulmaktadır. Araç üzerindeki kameradan elde edilen görüntülerin öznitelikleri kullanılarak farklı yer işaretleri saptanmaktadır. Yer işaretlerine Genişletilmiş¸ Kalman Süzgeci (GKS) uygulanmış ve EKVH probleminin çözümü için bazı benzetim sonuçları sunulmuştur.
Open Access
Integral action based Dirichlet boundary control of Burgers equation
(IEEE, 2003) Efe, M. Ö.; Özbay, Hitay
Modeling and boundary control for Burgers Equation is studied in this paper. Modeling has been done via processing of numerical observations through singular value decomposition with Galerkin projection. This results in a set of spatial basis functions together with a set of Ordinary Differential Equations (ODEs) describing the temporal evolution. Since the dynamics described by Burgers equation is nonlinear, the corresponding reduced order dynamics turn out to be nonlinear. The presented analysis explains how boundary condition appears as a control input in the ODEs. The controller design is based on the linearization of the dynamic model. It has been demonstrated that an integral controller, whose gain is a function of the spatial variable, is sufficient to observe reasonably high tracking performance with a high degree of robustness.
Open Access
A Mathematical Model for Cholesterol Biosynthesis under Nicotine Exposure
(Elsevier B.V., 2016) Gölgeli, M.; Özbay, Hitay
In this paper, a mathematical model is considered for analyzing the impact of nicotine exposure to cholesterol biosynthesis. The dynamical model is nonlinear. Its equilibrium points are computed and conditions are provided under which a unique locally stable positive equilibrium exists. Moreover, effect of internal time delays on local stability is also investigated.
Open Access
On the boundary control of a flexible robot arm
(IEEE, 2001) Morgül, Ömer
We consider a flexible robot arm modeled as a single flexible link clamped to a rigid body. We assume that the system performs only planar motion. For this system, we pose two control problems; namely, the orientation and stabilization of the system. We propose a class of controllers to solve these problems.
Open Access
On the control of chaotic systems in Lur'e form by using dither
(Institute of Electrical and Electronics Engineers, 1999-10) Morgül, Ö.
In this paper we propose the application of dither for controlling chaotic systems in the Lur'e form. Dither is a high-frequency periodic signal and has the effect of modifying the nonlinearity for some nonlinear systems. We use piecewise constant dither signals and propose three different methods for the selection of dither parameters. We also present some experimental results.
Open Access
On the performance of linear least-squares estimation in wireless positioning systems
(IEEE, 2008-05) Gezici, Sinan; Güvenç, İ.; Sahinoğlu, Z.
A common technique for wireless positioning is to estimate time-of-arrivals (TOAs) of signals traveling between a target node and a number of reference nodes, and then to determine the position of the target node based on those TOA parameters. In determining the position of the target node from TOA parameters, linear or nonlinear least-squares (LS) estimation techniques can be employed. Although the linear LS techniques are suboptimal in general, they facilitate low-complexity position estimation. In this paper, performance of various linear LS techniques are compared, and suboptimality of the linear approach is quantified in terms of the Cramer-Rao lower bound (CRLB). Simulations are performed to compare the performance of the linear LS approaches versus the CRLBs for linear and nonlinear techniques. ©2008 IEEE.
Open Access
On the S-procedure and some variants
(Springer, 2006) Derinkuyu, K.; Pınar, M. Ç.
We give a concise review and extension of S-procedure that is an instrumental tool in control theory and robust optimization analysis. We also discuss the approximate S-Lemma as well as its applications in robust optimization.
Open Access
On the stabilization and stability robustness against small delays of some damped wave equations
(IEEE, 1995) Morgül, O.
In this note we consider a system which can be modeled by two different one-dimensional damped wave equations in a bounded domain, both parameterized by a nonnegative damping constant. We assume that the system is fixed at one end and is controlled by a boundary controller at the other end. We consider two problems, namely the stabilization and the stability robustness of the closed-loop system against arbitrary small time delays in the feedback loop. We propose a class of dynamic boundary controllers and show that these controllers solve the stabilization problem when the damping coefficient is nonnegative and stability robustness problem when the damping coefficient is strictly positive.
Open Access
On the stabilization of a cable with a tip mass
(IEEE, 1994) Morgül, Ö.; Rao, B. P.; Conrad, F.
In this note, we consider a vertical cable which is pinched at the upper end. A mass is attached at the lower end where a control force is also applied. We show that this hybrid system is uniformly stabilized by choosing a suitable control law for the control force depending on the velocity and angular velocity at the free end. Moreover for specific values of the feedback coefficients, we obtain the rate of decay of the energy of the system.
Open Access
Online balancing two independent criteria
(Springer, 2008-10) Tse, Savio S.H.
We study the online bicriteria load balancing problem in this paper. We choose a system of distributed homogeneous file servers located in a cluster as the scenario and propose two online approximate algorithms for balancing their loads and required storage spaces. We first revisit the best existing solution for document placement, and rewrite it in our first algorithm by imposing some flexibilities. The second algorithm bounds the load and storage space of each server by less than three times of their trivial lower bounds, respectively; and more importantly, for each server, the value of at least one parameter is far from its worst case. The time complexities for both algorithm are O(logM). © 2008 Springer Berlin Heidelberg.
Open Access
Online bicriteria load balancing using object reallocation
(Institute of Electrical and Electronics Engineers, 2009-03) Tse, S. S. H.
We study the bicriteria load balancing problem on two independent parameters under the allowance of object reallocation. The scenario is a system of $M$ distributed file servers located in a cluster, and we propose three online approximate algorithms for balancing their loads and required storage spaces during document placement. The first algorithm is for heterogeneous servers. Each server has its individual tradeoff of load and storage space under the same rule of selection. The other two algorithms are for homogeneous servers. The second algorithm combines the idea of the first one and the best existing solution for homogeneous servers. Using document reallocation, we obtain a smooth tradeoff curve of the upper bounds of load and storage space. The last one bounds the load and storage space of each server by less than three times of their trivial lower bounds, respectively; and more importantly, for each server, the value of at least one parameter is far from its worst case. The time complexities of these three algorithms are O(\log M) plus the cost of document reallocation. © 2009 IEEE.
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Optimal hybrid control of a two-stage manufacturing system
(IEEE, 2006) Gökbayrak, Kağan; Selvi, Ömer
We consider a two-stage serial hybrid system for which the arrival times are known and the service times are controllable. We derive some optimal sample path characteristics, in particular, we show that no buffering is observed between stages. The original non-smooth optimal control problem is first transformed into a convex optimization problem which is then simplified by the no buffer property. Further simplifications are possible for the bulk arrival case.
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Smart composites with tunable stress–strain curves
(Springer, 2020) Özcan, Mert; Çakmakçı, Melih; Temizer, İlker
Smart composites with tunable stress–strain curves are explored in a numerical setting. The macroscopic response of the composite is endowed with tunable characteristics through microscopic constituents which respond to external stimuli by varying their elastic response in a continuous and controllable manner. This dynamic constitutive behavior enables the composite to display characteristics that cannot be attained by any combination of traditional materials. Microscopic adaptation is driven through a repetitive controller which naturally suits the class of applications sought for such composites where loading is cyclic. Performance demonstrations are presented for the overall numerical framework over complex paths in macroscopic stress–strain space. Finally, representative two- and three-dimensional tunable microstructures are addressed by integrating the control approach within a computational environment that is based on the finite element method, thereby demonstrating the viability of designing and analyzing smart composites for realistic applications.
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Stride-to-stride energy regulation for robust self-stability of a torque-actuated dissipative spring-mass hopper
(A I P Publishing LLC, 2010) Ankarali, M. M.; Saranli, U.
In this paper, we analyze the self-stability properties of planar running with a dissipative spring-mass model driven by torque actuation at the hip. We first show that a two-dimensional, approximate analytic return map for uncontrolled locomotion with this system under a fixed touchdown leg angle policy and an open-loop ramp torque profile exhibits only marginal self-stability that does not always persist for the exact system. We then propose a per-stride feedback strategy for the hip torque that explicitly compensates for damping losses, reducing the return map to a single dimension and substantially improving the robust stability of fixed points. Subsequent presentation of simulation evidence establishes that the predictions of this approximate model are consistent with the behavior of the exact plant model. We illustrate the relevance and utility of our model both through the qualitative correspondence of its predictions to biological data as well as its use in the design of a task-level running controller. © 2010 American Institute of Physics.
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Theoretical limits on time delay estimation for ultra-wideband cognitive radios
(IEEE, 2008-09) Gezici, Sinan; Celebi, H.; Arslan, H.; Poor, H. V.
In this paper, theoretical limits on time delay estimation are studied for ultra-wideband (UWB) cognitive radio systems. For a generic UWB spectrum with dispersed bands, the Cramer-Rao lower bound (CRLB) is derived for unknown channel coefficients and carrier-frequency offsets (CFOs). Then, the effects of unknown channel coefficients and CFOs are investigated for linearly and non-linearly modulated training signals by obtaining specific CRLB expressions. It is shown that for linear modulations with a constant envelope, the effects of the unknown parameters can be mitigated. Finally, numerical results, which support the theoretical analysis, are presented. © 2008 IEEE.