Elektrik-Elektronik Mühendisliği Bölümü / Department of Electrical and Electronics Engineering
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Publication A CNN based rotation invariant fingerprint recognition system(Istanbul Unıv, Fac Engineering, Elektrik-Elektronik Mühendisliği Bölümü, Avcılar Kampüsü, İstanbul, 34320, Turkey, 2017) Çelik Mayadağlı, Tuba; Saatçı, Ertuğrul; Rifat, Edizkan; 10488; 16117; 16117This paper presents a Cellular Neural Networks (CNN) based rotation invariant fingerprint recognition system by keeping the hardware implementability in mind. Core point was used as a reference point and detection of the core point was implemented in the CNN framework. Proposed system consists of four stages: preprocessing, feature extraction, false feature elimination and matching. Preprocessing enhances the input fingerprint image. Feature extraction creates rotation invariant features by using core point as a reference point. False feature elimination increases the system performance by removing the false minutiae points. Matching stage compares extracted features and creates a matching score. Recognition performance of the proposed system has been tested by using high resolution PolyU HRF DBII database. The results are very encouraging for implementing a CNN based fully automatic rotation invariant fingerprint recognition system.Publication A New Method for Doppler Centroid Estimation Based on Block Processing(IEEE, 345 E 47Th St, New York, Ny 10017 Usa, 2013) Kartal, Mesut; Tunçay, Pelin; 43246; 187162Doppler centroid frequency is an important parameter for Synthetic Aperture Radar signal processing, which is used to design a proper matched filter in azimuth domain. Doppler centroid is estimated from the received data. There are number of different algorithms for the Doppler centroid estimation presented in the literature. In all these algorithms, a general the Doppler centroid estimation is done for the whole data. Thus, some distortions occur in the final image away from the scene center for where the Doppler centroid is estimated. To overcome this problem, an alternative method for the Doppler centroid estimation, which is based on block processing, is presented. This method also takes advantage for saving time when the interested area is small.Publication A novel EOG-based wireless rapid communication device for people with motor neuron diseases(Taylor and Francis Online, 2018-11-22) Uşaklı, Ali Bülent; Gürkan, Serkan; GÜRKAN, GÜRAY; 118889; 244333; 113297In this study, a new electrooculography (EOG) based system that provides efficient communication for people suffered from motor neuron diseases is presented. The system consists of two distinct devices. The first device operates as a main unit that is activated by the subject’s eye movements. This unit is capable of transmitting 10 different command/state messages. These messages enable subject to choose his/her situation such as “I’m fine”, “I feel bad”, “I’m hungry” and “I’m thirsty”. Commands such as “Come”, “Go”. The number of messages can be increased. The main unit acquires the EOG signal from the subject. Newly developed analogue and digital signal conditioning interprets the eye movements as specific messages and transmits them to the second unit (receiver) using radio frequency transmitter. The messages related to the subject’s demands and situation can be heard from both main and receiver unit speakers. The wireless receiver unit is capable of notifying the patient’s command by auditory and visual indicators. The realised device was tested by 2 healthy and 2 ALS patients and confirmed to be successful with 100% performance for sending correct messages.Publication Accreditation for cademic quality(Int Scientific Conference SGEM, 14, Kilment Ohridsky BLVD, Sofia, 1797, Bulgaria, 2008) Şenel, Seçil; Yalçın, Dilek; 104470; 114377As it is well-known, the latest trend in academia has been the rapid growth of online or distance learning courses. Globalization makes mobility easy and possible. That is why a graduate has the opportunity to find not only a nationwide but also a worldwide occupation. In most countries in the world, the function of accreditation for educational institutions is conducted by a government ministry of education. The purpose of this study is presenting the goal of the accreditation. The goal of accreditation is to ensure that education provided by institutions of higher education meets acceptable levels of quality. In order to present the educational philosophy that monitors the international values and standards, ABET (Accreditation Board for Engineering and Technology) in engineering education and international standards in medical education are taken into consideration. Engineering departments of a few universities have been accredited with respect to the ABET criteria. In medical education a few universities have been initiating the accreditation process in Turkey. In this study, the accreditation and assessment methods in higher education are discussed.Publication Adaptive dual-mode OFDM with index modulation(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2018-10) Aldırmaz Çolak, Sultan; Başar, Ertuğrul; ACAR, YUSUF; 41633; 237377; 149116With the integration of the index modulation concept, the popular OFDM has gained an appealing new dimension. However, OFDM with index modulation (OFDM-IM) causes a decrease in data rate for higher order modulations due to its unused subcarriers. Recently, dual-mode OFDM with index modulation (DM-OFDM-IM) has been proposed to prevent this decrease in data rate. The spectral efficiency (SE) of both techniques depends on the selection of different parameters, such as modulation types and number of active subcarriers. However, the quality of the wireless channel has not been taken into account yet to increase the data rate. In this paper, we propose a new adaptive DM-OFDM-IM (A-DM-OFDM-IM) system to enhance the bit error probability (BER) performance considering the channel conditions and obtain a substantial increase in SE. Unlike the previous DM-OFDM-IM and the classical OFDM-IM schemes, our proposed system enables the use of different types of modulations for different subblocks in one OFDM signal. We demonstrate that the SE of the proposed system is comparable with that of its OFDM-IM and DM-OFDM-IM counterpart under frequency selective Rayleigh channels. Moreover, computer simulations corroborate that the derived theoretical results are considerably accurate for the SE of A-DM-OFDM-IM systems. (C) 2018 Elsevier B.V. All rights reserved.Publication Adjective Check List and Psychological Stress: Evidence From Turkey(Int Scientific Conference SGEM, 14, Kilment Ohridsky BLVD, Sofia, 1797, Bulgaria, 2008) Erkoç, Tuba; Kurt, Doğuş; Bayramoğlu, Oya; Yıldırım, Halil; Yıldırım, OsmanIt is called stress when an individual begins to act different physically and mentally as a result of the fact that he or she is affected by the environment lie or she lived and worked in. To block or balance the process of adaptation to stressful circumstances of people can be in different ways. However, it may not be possible to get rid of stress completely. So that, an individual who is overstressed can suffer aggressiveness, non-confidence, difficulties in focusing, chronic tiredness, tension, sadness, anxiety, anger, poor health, depression, etc. Naturally, this causes the individual, who is overstressed, to have mental, physical, and psychological illnesses. As a result, it becomes more difficult for the individual to adapt his or her social environment. In this research, the stress levels of the parents having disabled students was assessed using Abidin's (1990) Parenting Stress Index (PSI) on a sample of 190 parents. According to the results, it has been achieved that parents who has low socio-economic status, are exposed to more stress to the extent of parenting distress.Publication Aircraft sensor fault detection based on unknown input observers(Emerald Group Publishing Limited, Howard House, Wagon Lane, Bingley Bd16 1Wa, W Yorkshire, England, 2008) Çetin, Ömer; Kıyak, Emre; Kahvecioğlu, Ayşe; 288107; 19395; 199397Purpose - The purpose of this paper is to generate residuals which can be used to detect fault and isolate on a vertical takeoff and landing (VIOL) aircraft dynamic model. Design/methodology/approach - In the proposed approach, a generalized observer scheme method based on an unknown input observer is used for residual generation and applied to detect and isolate a faulty sensor. A bank of robust unknown input observers estimates the state variables of the system and gathers necessary information for fault detection and isolation purposes. Findings - A sinus signal is considered as a non-linear disturbance in simulations. A failure simulation was prepared in different times. In this situation an unknown input observer should be designed which could predict the states of the system against the disturbances or unknown inputs. In the real world, there exist unknown inputs such as system non-linearities, noise and disturbances. The paper shows that the system based on UIO is robust for unknown inputs mentioned above. Originality/value - It is simulated on a VTOL dynamic model using MATLAB/Simulink. Any single sensor fault could be detected and isolated correctly. This kind of observer is also robust and flexible.Publication An FPGA implementation of 2-D CNN Gabor-type filter(IEEE, 345 E 47TH ST, NEW YORK, NY 10017 USA, 2007) Saatçı, Ertuğrul; Cesur, Evren; Tavşanoğlu, Vedat; Kale, İzzet; TR10488; TR36339A field programmable gate array (FPGA) implementation of the Gabor-type filter is presented. The implementation uses the forward Euler approximation with optimal step size to solve the CNN cell-state equation. The FPGA is implemented on Xilinx Spartan XC3S400 device using 219 slices. An image of dimension 60 x 60 can be processed without using any external RAM only with the block RAM.Publication Analysis of brain connectivity changes after propofol injection by generalized partial directed coherence(Academic Press Inc Elsevier Science, 525 B St, Ste 1900, San Diego, Ca 92101-4495 Usa, 2014) Akan, Aydın; Özkan Seyhan, Tülay; GÜRKAN, GÜRAY; 113297; 2918; 25235In this paper we present a method for the analysis of multichannel EEG by using Generalized Partial Directed Coherence (gPDC) to extract cortical connectivity changes under anesthesia. 15 channel EEG data were recorded from female subjects undergoing general anesthesia for gynecological surgery. Multivariate Autoregressive (MAR) modeling was applied to multichannel, bipolar EEG segments of awake and anesthetized states. gPDCs were calculated using the derived MAR model and averaged through EEG alpha frequency band (8-14 Hz) and through a number of data segments. The gPDC calculation was performed for three different sets of bipolar EEG channel pairs each of which mainly represent a specific scalp area. To derive consistency levels of gPDC values, surrogate analysis is also performed. Using paired t-test for 12 patients, we extracted significant gPDC changes between. awake and anesthetized stages for each set. Analysis revealed that during transition from awake to anesthetized stage, gPDCs of central. to parietal directions were suppressed whereas gPDCs of parietal to central directions were increased. The results indicate that the proposed gPDC analysis method can be used to track the changes in brain connectivity and hence to estimate the depth of anesthesia. (C) 2013 Elsevier Inc. All rights reserved.Publication Analysis of linear lung models based on state-space models(Elsevier Ireland Ltd., 2020-01) Saatçi, Ertuğrul; Akan, Aydın; SAATÇI, ESRABackground and Objectives: Linear parametric respiratory system models have been used in the model-based analysis of the respiratory system. Although there are studies exploring the physiological correctness and fitting accuracy of the models, they are not analysed in terms of interaction between parameters and dynamics of the model. In this study we propose to use state-space modelling to yield the time-varying nature of the system incorporated by the parameters. Methods: We tested controllability, observability and stability characteristics of the equation of motion, 2-comp. parallel, 2-comp. series, viscoelastic, 6-element and mead models while using the parameters given in the literature. In the sensitivity analysis we proposed to use dual Desensitized Linear Kalman Filter (DKF) and Extended Kalman Filter (EKF) method. In this method, state error covariance revealed the parameter sensitivities for each model. Results: Results showed that all models, except 2-comp. parallel and mead models, are both controllable and observable models. On the other hand all models, except mead model, are stable models. Regarding to the sensitivity analysis, dual DKF - EKF method estimated states of the models successfully with a low estimation error. Sensitivity analysis results showed that airway parameters have higher effects on the state estimation than the other parameters have. Conclusion: We proved that state-space evaluation of the previously proposed parametric models of the respiratory system led us to quantitative and qualitative assessments of the respiratory models. Moreover parameter values found in the literature have different effects on the models. (C) 2019 Elsevier B.V. All rights reserved.Publication Application of Stockwell Coherence To Prediction Of Alertness Under Anaesthesia(Brno Univ Technology Vut Press, Purkynova 118, Brno 61200, Czech Republic, 2010) Akan, Aydın; Demiralp, Tamer; GÜRKAN, GÜRAY; TR113297; TR2918; TR6916In this paper, we represent an application of Stockwell Coherence to scalp EEG signals under anesthesia. By the analysis of overlapping, stationary data segments, we obtained the time-varying Stockwell coherence, which reveals the time evolution of coherence changes between any selected channel pair. After the injection and release of the anesthetic agent, time-varying Stockwell coherence analyses demonstrate similar characteristics for different patients.Publication Bandpass sampling of multiband signals by using geometric approach(IEEE, 345 E 47th St, New York, Ny 10017 USA, 2017) Saatçı, Ertuğrul; Akan, Aydın; SAATÇI, ESRA; 112197; 10488; 2918This paper presents a simple and fast approach to f nd a minimum sampling frequency for multi-band signals. Instead of neighbor and boundary conditions, constraints on the sampling frequency were derived by using the geometric approach. Reformulation of the minimum sampling determination problem by using geometric approach enables to represent the problem as a basic inequality problem. Recursive algorithm was proposed to solve the constraints on the minimum sampling frequency. The proposed method was verif ed through numerical simulations in terms of the minimum sampling frequency and the computational eff ciency by using 2-band and 3-band signals. Although the results illustrated the valid minimum sampling frequencies for the multi-band signals, due to the increase in the number of iterations, optimization approaches were recommended in the solution of the constraints on the minimum sampling frequency.Publication Bayesian Compressive Sensing for Ultra-Wideband Channel Models(Ieee, 345 E 47Th St, New York, Ny 10017 Usa, 2012-07-03) Özgör, Mehmet; Erküçük, Serhat; Çırpan, Hakan Ali; 173126; 38099; 36844Considering the sparse structure of ultra-wideband (UWB) channels, compressive sensing (CS) is suitable for UWB channel estimation. Among various implementations of CS, the inclusion of Bayesian framework has shown potential to improve signal recovery as statistical information related to signal parameters is considered. In this paper, we study the channel estimation performance of Bayesian CS (BCS) for various UWB channel models and noise conditions. Specifically, we investigate the effects of (i) sparse structure of standardized IEEE 802.15.4a channel models, (ii) signal-to-noise ratio (SNR) regions, and (iii) number of measurements on the BCS channel estimation performance, and compare them to the results of l(1)-norm minimization based estimation, which is widely used for sparse channel estimation. The study shows that BCS exhibits superior performance at higher SNR regions only for adequate number of measurements and sparser channel models (e. g., CM1 and CM2). Based on the results of this study, BCS method or the l(1)-norm minimization method can be preferred over the other for different system implementation conditions.Publication A Broadband, Polarization Insensitive, Wide Incidence-Angle-Slotted Ring/Lumped Resistor-Based Metamaterial Absorber for K-u-Band Applications(Istanbul University - Cerrahpaşa, 2021) AKŞİMŞEK, HÜSEYİN SİNANA broadband-slotted ring/lumped resistor-based metamaterial absorber (MA) is presented in this study for K-u-band microwave applications. Numerical results of the MA indicate that it can achieve a broadband absorption ratio of more than 85% in the frequency range of 12.4-17.6 GHz and has active polarization insensitivity and wide incidence-angle response over the entire operation band between 12.4-17.6 GHz. The designed MA is ultrathin around lambda/14.7 in terms of wavelength at its lowest operation frequency, corresponding to 1.7 mm. The proposed unit-cell structure of the MA is novel, consisting of a slotted ring with eight symmetrically-located lumped resistors, FR-4 material, and a metallic ground, which is compatible with low-cost PCB fabrication; therefore, the MA is suitable for practical microwave applications in the K-u-band.Publication Capacitor coupled converter (C3) for high power DC conversion(IEEE, 1995) Ehsani, Morteza; Bilgiç, Mehmet Oruç; Khan, S.; Laskai, L.; Jeong, Seung-Gi; 1616The bang-bang controlled capacitor coupled converter (C3) is described in this paper. Due to the converter's inherent commutating property, the C3 can accommodate thyristors as well as high-power gate turn-off switches, due to zero-current switching transitions. The zero-current switching is achieved at no current stress increase, therefore, the topology is considered appropriate for high-power processing. DC and small signal AC models are derived for the bang-bang controlled C3, a design procedure is proposed, and simulation results are discussed. Finally, oscillograms from a proof of principle prototype circuit are presentedPublication Channel estimation for OFDM-IM systems(2019) Aldırmaz Çolak, sultan; Başar, Ertuğrul; ACAR, YUSUFOrthogonal frequency division multiplexing with index modulation (OFDM-IM) has been recently proposed to increase the spectral efficiency and improve the error performance of multicarrier communication systems. However, all the OFDM-IM systems assume that the perfect channel state information is available at the receiver. Nevertheless, channel estimation is a challenging problem in practical wireless communication systems for coherent detection at the receiver. In this paper, a novel method based on the pilot symbol-aided channel estimation technique is proposed and evaluated for OFDM-IM systems. Pilot symbols, which are placed equidistantly, allow the regeneration of the response of the channel so that pilot symbol spacing can fulfill the sampling theorem criterion. Our results shows that the low-pass interpolation and SPLINE techniques perform the best among all the channel estimation algorithms in terms of bit error rate and mean square error performance.Publication Channel Estimation for SM Systems over Time-Varying Rayleigh Fading Channels(IEEE, 345 E 47Th St, New York, Ny 10017 Usa, 2014) Doğan, Hakan; Panayırcı, Erdal; ACAR, YUSUF; 237377; 41066; 10331This paper is concerned with the challenging and timely problem of channel estimation for spatial modulated systems in the presence of time varying channels. Recently, estimation of channel state information for SM systems is investigated by the recursive least square (RLS) algorithm for slow fading channels. However, it is clear that the RLS based receiver will have a performance degradation for fast fading channels. Therefore, we developed iterative channel estimation based on detected symbols and curve fitting to track the channel variations for SM systems. Simulation results have demonstrated that the proposed iterative channel estimation offer substantial performance gains over the RLS channel estimation. In particular, a savings of about 4dB is obtained at BER = 10(-7), as compared with RLS based receiver at 150km/h for 2 x 4 single carrier SM systems.Publication Channel estimation for spatial modulation orthogonal frequency division multiplexing systems(IEEE, 345 E 47th St, New York, Ny 10017 USA, 2015-10-14) Doğan, Hakan; Panayırcı, Erdal; ACAR, YUSUF; 237377; 10331A combination of spatial modulation and orthogonal frequency division multiplexing (SM-OFDM) has been recently proposed for multicarrier systems while assuming the perfect channel state information (P-CSI) available at the receiver. But, in practical scenarios, the estimation of CSI is crucial in order to detect the transmitted data coherently. In this work(1), a new frame structure and pilot symbol aided channel estimation (PSA-CE) technique with a piecewise linear interpolation is proposed for the SM-OFDM systems operating in the presence of frequency selective channel. Bit error rate (BER) performance of the proposed channel estimation technique is then investigated with different channel models such as Typical Urban ( TU) and Rural Urban (RU) for 4-quadrature amplitude modulation (QAM). In particular, it is shown that the performance with estimated channel came close to that with known channel within 2.3 dB in SNR for BER = 10(-4) for TU channels.Publication Correlation analysis of respiratory signals by using parallel coordinate plots(Elsevier Ireland Ltd, Elsevier House, Brookvale Plaza, East Park Shannon, Co, Clare, 00000, Ireland, 2018-01) SAATÇI, ESRA; 112197Background and objectives: The understanding of the bonds and the relationships between the respiratory signals, i.e. the airflow, the mouth pressure, the relative temperature and the relative humidity during breathing may provide the improvement on the measurement methods of respiratory mechanics and sensor designs or the exploration of the several possible applications in the analysis of respiratory disorders. Therefore, the main objective of this study was to propose a new combination of methods in order to determine the relationship between respiratory signals as a multidimensional data. Methods: In order to reveal the coupling between the processes two very different methods were used: the well-known statistical correlation analysis (i.e. Pearson's correlation and cross-correlation coefficient) and parallel coordinate plots (PCPs). Curve bundling with the number intersections for the correlation analysis, Least Mean Square Time Delay Estimator (LMS-TDE) for the point delay detection and visual metrics for the recognition of the visual structures were proposed and utilized in PCP. Results: The number of intersections was increased when the correlation coefficient changed from high positive to high negative correlation between the respiratory signals, especially if whole breath was processed. LMS-TDE coefficients plotted in PCP indicated well-matched point delay results to the findings in the correlation analysis. Visual inspection of PCB by visual metrics showed range, dispersions, entropy comparisons and linear and sinusoidal-like relationships between the respiratory signals. Conclusion: It is demonstrated that the basic correlation analysis together with the parallel coordinate plots perceptually motivates the visual metrics in the display and thus can be considered as an aid to the user analysis by providing meaningful views of the data. (C) 2017 Elsevier B.V. All rights reserved. Methods: In order to reveal the coupling between the processes two very different methods were used: the well-known statistical correlation analysis (i.e. Pearson's correlation and cross-correlation coefficient) and parallel coordinate plots (PCPs). Curve bundling with the number intersections for the correlation analysis, Least Mean Square Time Delay Estimator (LMS-TDE) for the point delay detection and visual metrics for the recognition of the visual structures were proposed and utilized in PCP. Results: The number of intersections was increased when the correlation coefficient changed from high positive to high negative correlation between the respiratory signals, especially if whole breath was processed. LMS-TDE coefficients plotted in PCP indicated well-matched point delay results to the findings in the correlation analysis. Visual inspection of PCB by visual metrics showed range, dispersions, entropy comparisons and linear and sinusoidal-like relationships between the respiratory signals. Conclusion: It is demonstrated that the basic correlation analysis together with the parallel coordinate plots perceptually motivates the visual metrics in the display and thus can be considered as an aid to the user analysis by providing meaningful views of the data. (C) 2017 Elsevier B.V. All rights reserved.Publication Data detection based iterative channel estimation for coded SM-OFDM systems(IEEE, 345 E 47Th St, New York, Ny 10017 USA, 2016) Leblebici, Mehmet Merih; Doğan, Hakan; Panayırcı, Erdal; ACAR, YUSUF; 237377; 249850; 10331The combination of spatial modulation (SM) and orthogonal frequency division multiplexing (OFDM) as SM-OFDM is a recently proposed efficient modulation scheme with exploiting the index of transmit antenna to convey information bits for multiple-input multiple-output (MIMO) wireless communication systems due to its low complexity feature. The pioneering works assume that the perfect channel state information (P-CSI) or pilot symbols aided channel estimation (PSA-CE) is available at the receiver. The open question is whether the accuracy of pilot based channel estimation is satisfactory to accomplish high data rate transmission in SM-OFDM systems. This paper explores the iterative channel estimation (ICE) problem for the coded SM-OFDM systems. We showed that the quality of the channel estimation can be further enhanced by the detection of symbols at the receiver. Through comparative simulations, we show that the proposed ICE method has notable bit error rate (BER) performance compared with the PSA-CE method for the binary phase shift keying (BPSK) modulation over the typical urban (TU) channel model.