Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/11
Browse
26 results
Search Results
Research Project Bağımsız bileşen analizinin iletişim, imge işleme ve jeofizikteki uygulamaları(TÜBİTAK - Türkiye Bilimsel ve Teknolojik Araştırma Kurumu, 2006) Sankur, Bülent; Gençağa, Deniz; Kalkan, Olcay; Altınkaya, Mustafa AzizBu projede literatürde kaynak ayrıştırma olarak bilinen istatistiksel işaret işleme yöntemleri hem kuramsal açıdan, hem de uygulamaları açısından ele alınmıştır. Kuramsal çalışmalarda, kaynakların uzamda ve zamanda birbirlerinden bağımsız olmadıkları düşüncesiyle parçacık süzgeçleri yöntemi ele alınmıştır. Bu yaklaşımda süreç hakkında elimizde varolan önsel bilgilerin algoritmaya ağdırılması mümkün olmuştur. Ayrıca durağan olmayan süreçlerin de ayrıştırılma problemi ele alınmış, farklı yeniden örnekleme ve önem fonksiyonları seçerek literatürdeki teknikleri aşan sonuçlar bulunmuştur. Uygulamaya dönük çalışmalarda ise, jeofizik işaret işlemede klimatolojik verilere bakılmış ve gerek Kuzey Atlantik Salınımı diye adlandırılan olgu irdelenmiştir. Ancak topografık etkiler istenen sonuca ulaşılmasına engel olmuştur. Öte yandan sıcaklık verileri faktör analizi ile incelenmiş ve volkanik hareketlerin etkisi ortaya çıkarılmaya çalışılmıştır. Beyin-işaretleri konusunda özellikle prefrontal korteks bölgesinden bilişsel süreçlerle ilgili araştırmalar yapılmıştır. Deneklerin biliş esnasında beyindeki kan dengesinin, oksi- ve deoksi hemoglobinin değişimleri yakalanmaya çalışılmıştır. Bağımsız bileşen analizinin bu türlü dalga biçimlerini ortaya çıkarmakta çok etkili bir araç olduğu gösterilmiştir. Biyometri alanında, bağımsız bileşenler analizi hem yüz imgelerine hem de el imgelerine uygulanmıştır. Bağımsız-bileşenlerin deneklerin kimlik bilgilerini taşıyan ve bozucu etkilere karşı en dayanıklı öznitelikler olduğu görülmüştür. Nihayet bağımsız bileşen analizi CDMA: kod bölüşümlü çoklu erişim işaretlerine uygulanmış ve sönümlü kanallardaki alıcının performansını iyileştirici tasarımlar irdelenmiştir.Conference Object Citation - Scopus: 1Kod Bölüşümlü Çoklu Erişim (cdma) İletişiminde Gauss Olmayan Sönümlü Kanal Kestirimi için Pearson Sistemi'ne Dayalı Gözü Kapalı Kaynak Ayrıştırma Yöntemi(Institute of Electrical and Electronics Engineers Inc., 2004) Kalkan, Olcay; Altınkaya, Mustafa AzizIn this work, a Pearson System based-blind source separation method is used for detecting the signal coming to a mobile user which is subject to multiple access interference in a CDMA downlink communication. Considering some fading channel measurements showing that the fading channel coefficients may have an impulsive nature, these coefficients are modeled with an a-stable distribution whose shape parameter a takes values between 1.8 and 1.9. These a values show that the distribution resembles a Gaussian distribution but has a more impulsive nature. Simulation studies show that the conventional MMSE receiver fails in this impulsive fading scenario. Both the independent component analysis (ICA) method using the conventional hyperbolic tangent score function and the Pearson System-based ICA are successful in estimating the channel coefficients and the proposed Pearson System-based ICA method performs faster.Conference Object Citation - WoS: 3Citation - Scopus: 4Düşük Maliyetli Serbest-uzay Optik İletişim Sistemi Tasarımı(Institute of Electrical and Electronics Engineers Inc., 2004) Karatay, Okan; Dinleyici, Mehmet Salihhi recent years commercial and military interest in free-space optical communication (FSO) is growing due to the high bandwidths, portability and high security. Although the numerous advantages, atmospheric events such as attenuation and scintillation severely effects the link quality. Novel methods of mitigating atmospheric events were applied. Usage of large aperture lenses and high transmitted power according to decrease scintillation effects increases the system cost. Fresnel lenses, as an alternative to the classical optic system for mitigating scintillation effects would be a low-cost solution. As a result of the technological improvements on the output power and divergence angles of VSCEL (Vertical Cavity Surface Emitting Laser) enables high-speed cost effective FSO communication system design. In this research current applied FSO systems are analysed and fresnel lens optical system of alternative low-cost system designed.Conference Object Citation - WoS: 2Citation - Scopus: 4Tek Kamera ve Aynalar Kullanan Bir Görsel Denetleme Sistemi(Institute of Electrical and Electronics Engineers Inc., 2004) Gümüştekin, ŞevketIn this paper the geometrical properties of an imaging system are investigated. This system uses mirrors to simulate additional cameras. The geometry developed here helps us to capture the images of an object from meaningful viewpoint locations. The imaging system with the desired geometry is realized by adjusting the positions and orientations of mirrors. A special calibration pattern is used for the process of camera calibration which finds the unknown camera parameters and gives feedback about the degree of compliance with the desired geometry. The calibrated camera and its mirror images are used to create a 2D image of an object surface with a uniform geometry. After a pre-defined inner or outer surface of a test object is imaged from different view angles using mirrors, these images are warped and blended in a single image which is used for visual inspection. Hence, the vaguely defined process of inspecting 3D objects and their surface textures is converted to an efficient and well defined process of inspecting 2D images.Conference Object Citation - Scopus: 1Özilinti Matrisinin Oluşturulma Yönteminin Modele Dayalı Sinüzoidal Parametre Kestirimindeki Etkileri(Institute of Electrical and Electronics Engineers Inc., 2004) Altınkaya, Mustafa AzizAlthough the maximum likelihood method gives the optimum solutions for the parameter estimation problem of the sinusoids embedded in noise, it is computationally difficult since it generally requires to solve nonlinear optimization problems. So some model-based parameter estimators with high frequency resolution property are preferred quite often. In order to find these estimates the first step is usually forming the autocorrelation (AC) matrix. In this work the effects of the method utilized in the generation of the AC matrix on the performances of sinusoidal parameter estimators are investigated. One way of forming the AC matrix is to use a Toeplitz structure with either the biased or the unbiased AC lag estimates as the matrix elements. Another way is to use the socalled "covariance method" in the AC matrix generation. In this method the matrix formed is no longer Toeplitz; but it is still symmetric. We can think of that the Toeplitz AC matrix is a perturbed version of the non-Toeplitz AC matrix. The differences in the performances of the MUSIC spectral estimator with Toeplitz; and non-Toeplitz AC matrix usage is related to the perturbation in the AC matrix estimate. For this purpose the 3 x 3 AC matrix is is utilized in the estimation of the frequency of a single sinusoid using the MUSIC frequency estimator. The accuracy of the perturbation analysis is checked with the simulation results. Additionally, the fact that the performance of an estimator with data windowing and Toeplitz AC matrix generation becomes near to the performance of the same estimator with non-Toeplitz AC matrix is shown with simulation studies.Conference Object Citation - Scopus: 1Hava Fotoğraflarından Deniz Kıyılarının Belirlenmesi(Institute of Electrical and Electronics Engineers Inc., 2006) Kahraman, Metin; Gümüştekin, ŞevketThe unique structures of different coastline segments provide distinctive image features for several applications such as oceanography, georeferencing, cartography and autonomous navigation. In this paper, a procedure involving automatic multiresolution coastline extraction is described. Using this method, sea and land textures are segmented utilizing cooccurrence and histogram features of wavelet image representation. The coastlines are identified as the boundaries of the sea regions.Conference Object Citation - Scopus: 1Asimetrik Alfa-kararlı Kaynakların Enküçük Saçılım Kriteri Kullalınarak Ayrıştırılması(Institute of Electrical and Electronics Engineers Inc., 2006) Altınkaya, Mustafa AzizIn this work, we extend the method which separates symmetric alpha-stable sources using minimum dispersion criterion to the case of skewed alpha-stable mixtures. Thus, a more robust method based on fractional lower order statistics is developed which is capable of separating general alpha-stable sources.Conference Object Citation - Scopus: 1Kaotik İ̇şaretlerde Wiener ve Kalman Yöntemleri Kullanarak Gürültü Süzgeçleme(Institute of Electrical and Electronics Engineers Inc., 2007) Çek, Emre; Oral, Ömer; Akay, OlcayIn this paper, the additive white noise was filtered from chaotic signals obtained by Logistic map by using Wiener, Extended and Unscented Kalman filters, respectively. Performances of each method were compared by finding mean square error versus signal to noise ratio (SNR) and correlation dimension which is one of the invariants of the chaotic dynamical systems. It was observed that, each method exhibits different MSE performances depending on the particular signal to noise ratio.Conference Object H264/avc ile Sıkıştırılmış Videoda Sahne Değişimi Kestirimi için Bir Yaklaşım(Institute of Electrical and Electronics Engineers Inc., 2007) Şimşek, Gökhan; Gümüştekin, ŞevketIn this paper, we provide methods to detect abrupt and gradual scene changes on ISO/ITU H264/AVC coded video sequence using macro-block type information. The analysis is realized in compressed domain without the need of full decompression to pixel domain. In order to realize the proposed methods, several video test sequences are constructed in QCIF resolution. The syntax and semantics, parsing, decoding processes of ISO/ITU H264/AVC is followed to realize such analysis and proposed methods are realized using reference software. The application addresses emerging standard ISO/ITU H264/AVC coded video databases as low level tools to realize a video summarization, abstraction or segmentation system.Conference Object Citation - WoS: 1Citation - Scopus: 2Dalgacık Tepeleri Kullanarak İ̇şaretlerin Bileşenlerine Ayrılması(Institute of Electrical and Electronics Engineers Inc., 2007) Özkurt, Nalan; Savacı, Ferit AcarÇok bileşenli durağan olmayan bir işaretin enerjisi tüm zaman-frekans alanına yayılır. Kaynak ayrıştırma gibi bazı uygulamalarda, işaretin farklı zaman-frekans özelliklerine sahip bileşenlerini ayırmak gerekli olabilir. Bu çalışmada, çok bileşenli durağan olmayan bir işaretin dalgacık tepeleri bulunarak bu tepeleri oluşturan doğrular Hough dönüşümünü kullanılarak saptanmış ve analitik olarak modellenmiştir. Her bir doğru parçasına ait işaret bileşeni ayrı ayrı yeniden elde edilmiştir.
- «
- 1 (current)
- 2
- 3
- »