Electrical & Electronics Engineering

Permanent URI for this collectionhttps://hdl.handle.net/10679/44

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Now showing 1 - 20 of 97

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3B kamera takibi için eylemsizlik algılayıcılarının birleştirilmesi
(IEEE, 2012) Özer, N.; Erdem, Tanju; Ercan, Ali Özer; Eroğlu Erdem, Ç.; Electrical & Electronics Engineering; Computer Science; ERDEM, Arif Tanju; ERCAN, Ali Özer
It is well known in a Bayesian filtering framework, the use of inertial sensors such as accelerometers and gyroscopes improves 3D tracking performance compared to using camera measurements only. The performance improvement is more evident when the camera undergoes a high degree of motion. However, it is not well known whether the inertial sensors should be used as control inputs or as measurements. In this paper, we present the results of an extensive set of simulations comparing different combinations of using inertial sensors as control inputs or as measurements. We show that it is better use a gyroscope as a control input while an accelerometer can be used as a measurement or control input. We also derive and present the extended Kalman filter (EKF) equations for a specific case of fusing accelerometer and gyroscope data that has not been reported before.
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Adaptive DCO-OFDM for underwater visible light communications
(IEEE, 2019-04) Elamassie, Mohammed; Karbalayghareh, Mehdi; Miramirkhani, Farshad; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Elamassie, Mohammed; Karbalayghareh, Mehdi; Miramirkhani, Farshad
Visible light communication (VLC) has been introduced as a complementary technology to acoustic communications for underwater applications. Underwater VLC can achieve much higher data rates sufficiently high for real-time image and video transmission. Such high data rates over underwater channels with frequency-selectivity necessitate the use of efficient multi-carrier techniques such as orthogonal frequency division multiplexing. In this paper, we consider an adaptive DC-biased optical OFDM (DCO-OFDM) underwater VLC system. The design of adaptive algorithm is formulated to maximize the throughput under error rate performance constraints. The receiver first calculates the signal-to-noise ratio (SNR) per each subcarrier. Then, based on SNR information, it determines which subcarrier should be loaded first and selects the maximum constellation size for each subcarrier while satisfying a predefined targeted bit error rate (BER). Our simulation results demonstrated that significant improvements in throughput can be obtained through link adaptation.
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An adaptive modulation scheme for coded free-space optical systems
(IEEE, 2014) Hariq, S. H.; Odabasioglu, N.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
For very slowly-varying fading channels as in the case of atmospheric turbulence-induced fading, it is possible to reliably estimate the channel state information and send it back to the transmitter. The transmitter can use this information to vary the transmission parameters such as power, modulation size, code rate etc according to the channel conditions. This is known as link adaptation. In this paper, we consider a turbo-coded free-space optical (FSO) system with M-ary pulse position modulation over log-normal turbulence channels and propose an adaptive modulation scheme under peak power constraints. Our simulation results demonstrate significant performance improvements of the proposed adaptive scheme over non-adaptive counterparts.
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Adaptive relay selection method for asynchronous amplify and forward cooperative communications
(IEEE, 2016) Celik, Y.; Odabasioglu, N.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we propose a new adaptive relay selection method named as Adaptive Best Relay Assessment (ABRA) for cooperative communication with amplify and forward (AF) relaying. ABRA is based on two relay selection criteria which are cascaded channel gain coefficient and cascaded time offset in source-relay-destination (S-R-D) channel. Our simulation results demonstrate that the channel gain coefficient is the best criteria at low signal-to-noise ratio (SNR) regimes and time offset at high SNR regimes. Therefore, we combine these two criteria to select best relay for all SNR values. Finally, ABRA achieves the best bit error rate (BER) performance in asynchronous AF cooperative communications for three different path gain ratios 30 dB, 0 dB, and -30 dB.
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Adaptive unipolar MIMO-OFDM for visible light communications
(IEEE, 2019) Al-Nahhal, Mohamed; Basar, E.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Al-Nahhal, Mohamed
Unipolar orthogonal frequency division multiplexing (U-OFDM) appears as an attractive optical OFDM solution for emerging visible light communication (VLC) systems. This paper proposes spectral efficiency improvement for U-OFDM systems by applying adaptive transmission over realistic VLC links. This adaptive transmission includes switching among a number of multiple-input multiple-output (MIMO) modes combined with appropriate modulation size selection. The considered MIMO modes are repetition coding, spatial modulation, and spatial multiplexing, where each mode supports different modulation sizes. The selection of the corresponding MIMO mode and its modulation size is based on the received signal-to-noise ratio and target bit error rate. The proposed U-OFDM system is applied over different VLC MIMO setups with realistic channel models for 8 x 8, 4 x 4 and 2 x 2 MIMO systems. Our simulation results show that the proposed adaptive system provides a significant spectral efficiency improvement over stand-alone U-OFDM MIMO modes/setups.
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Aerosol attenuation model for high altitude UAV-based FSO links
(IEEE, 2022) Elamassie, Mohammed; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
Free space optical (FSO) communication is well positioned to address connectivity needs in ground-UAV, inter-UAV and UAV-ground links. An accurate performance analysis of airborne FSO links requires the use of proper path loss models. While earlier studies have successfully modeled attenuation arising from rain, drizzle, fog, and snow, aerosols have received less attention. Aerosols are tiny particles suspended in the atmosphere. They can be found drifting in Earth's atmosphere from the stratosphere to the troposphere to the Earth's surface. In this paper, we conduct extensive simulations in MODTRAN to determine the extinction coefficient values for aerosol over the wavelength from 350 nm to 1550 nm including typical wavelengths (e.g., 690 nm, 780nm, 850nm, and 1550 nm) used in commercial FSO systems. Non-linear curve fitting is then used to obtain new closed-form expressions for extinction coefficients.
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Cantilever array oscillators with nonlinear optical readout
(IEEE, 2015) Lüleç, S. Z.; Adiyan, U.; Yaralıoğlu, Göksen Göksenin; Leblebici, Y.; Urey, H.; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
MEMS array oscillators typically require a separate detector and feedback loop for each oscillator. We show that grating-based-optical-readout induces nonlinearity, which enables simultaneous operation of an array-of-oscillators using only one detector and single electronic feedback-loop.
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Capacity of wireless ad-hoc broadcast networks under realistic channel models
(IEEE, 2009) Atıcı, Çağdaş; Sunay, Mehmet Oğuz; Computer Science; SUNAY, Mehmet Oğuz; Atıcı, Çağdaş
In a wireless broadcasting scenario, some of the nodes can help the source node by forwarding the received information. Due to the interference from multiple transmissions, selection of these nodes directly affects the performance of the system under a given total power and hop constraint. In this paper, we first analytically find the number and the positions of the rebroadcasting nodes that achieve the optimal broadcast capacity under the continuum model. Following the results of this part, we propose two heuristics, one centralized and another distributed, for relay selection in practical scenarios. Then, we discuss the broadcast capacity performances of these algorithms under different system settings. The results illustrate that using a distributed relay selection method brings significant gains to the broadcast capacity under a realistic system model.
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Channel estimation in underwater cooperative OFDM system with amplify-and-forward relaying
(IEEE, 2012) Şenol, H.; Panayırcı, E.; Erdoğan, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
This paper is concerned with a challenging problem of channel estimation for amplify-and-forward cooperative relay based orthogonal frequency division multiplexing (OFDM) systems in the resence of sparse underwater acoustic channels and of the correlative non-Gaussian noise. We exploit the sparse structure of the channel impulse response to improve the performance of the channel estimation algorithm, due to the reduced number of taps to be estimated. The resulting novel algorithm initially estimates the overall sparse channel taps from the source to the destination as well as their locations using the matching pursuit (MP) approach. The correlated non-Gaussian effective noise is modeled as a Gaussian mixture. Based on the aussian mixture model, an efficient and low complexity algorithm is developed based on the combinations of the MP and the space-alternating generalized improve the estimates of the channel taps and their location as well as the noise distribution parameters in an iterative way. The proposed SAGE algorithm is designed in such a way that, by choosing the admissible hidden data properly on which the SAGE algorithm relies, a subset of parameters is updated for analytical tractability and the remaining parameters for faster convergence Computer simulations show that underwater acoustic (UWA) channel is estimated very effectively and the proposed algorithm has excellent symbol error rate and channel estimation performance.
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Channel measurements and ray tracing simulations for MIMO light communication at 200 MHz
(IEEE, 2020-09) Eldeeb, Hossıen Badr; Uysal, Murat; Mana, S. M.; Hellwig, P.; Hilt, J.; Jungnickel, V.; Electrical & Electronics Engineering; UYSAL, Murat; ELDEEB, Hossien Badr Hossien
In this paper, we investigate 2 × 2 MIMO light communication channels using non-sequential ray tracing simulations, and measurements over 200 MHz bandwidth using a MIMO channel sounder. Results indicate good agreement between simulations and measurements validating the accuracy of ray-tracing.
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Channel modeling and performance characterization of underwater visible light communications
(IEEE, 2018-07-03) Elamassie, Mohammed; Miramirkhani, Farshad; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Elamassie, Mohammed; Miramirkhani, Farshad
Underwater visible light communication (UVLC) has emerged as an attractive complementary solution to long-range acoustic communication and is able to achieve much higher data speeds. In this paper, we investigate the transmission range limits of UVLC systems. We first develop a closed-form path loss expression as a function of transceiver parameters and the water type. We then utilize this new expression to determine the maximum achievable link distance for UVLC systems while satisfying a specified bit error rate. Finally, we provide extensive numerical results to demonstrate the achievable distances in pure sea, clear ocean, coastal water and harbor water.
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Channel modeling for visible light communications
(Springer Science+Business Media, 2016) Miramirkhani, Farshad; Uysal, Murat; Panayirci, E.; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad
In this chapter, we present a novel and realistic channel modeling approach for visible light communications that overcomes to the limitations of previous works. In our work, we consider wavelength dependency, effect of realistic light sources as well as different types of reflections such as specular and mixed cases of diffuse and specular. We use non-sequential ray tracing algorithms to calculate the detected power and path lengths from source to detector for each ray. These are then processed to yield the channel impulse responses for various indoor environments. We further present a channel characterization study where channel parameters such as channel DC gain, root mean square delay spread, coherence bandwidth, mean excess delay are calculated for different environments.
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Characterization of orbital angular momentum-multiplexed FSO channel in the presence of pointing errors
(IEEE, 2023) Elamassie, Mohammed; Tadayyoni, Hamed; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat; Tadayyoni, Hamed
Free space optical communication (FSO) uses laser transmitters at near-infrared wavelengths for line-of-sight wireless communication. Through the use of advanced laser beams instead of the conventional Gaussian-shaped beam, orbital angular momentum (OAM) allows taking advantage of higher degrees of freedom in the FSO link design. OAM enables the simultaneous transmission of multiple data streams due to the orthogonality between beams of different spatial modes. However, in practice, atmospheric turbulence and pointing errors may destroy the orthogonality. Pointing errors may result in crosstalk between modes and power disparities as a result of shifting the received beam. In this paper, we consider Laguerre-Gaussian beams and investigate the effect of random pointing errors on crosstalk coefficients.
Open Access
CL-FedFR: Curriculum learning for federated face recognition
(SciTePress , 2024-02-29) Dube, D. C.; Eroğlu Erdem, Ciğdem ; Korcak, Ö.; Electrical & Electronics Engineering; ERDEM, Çiğdem Eroğlu
Face recognition (FR) has been significantly enhanced by the advent and continuous improvement of deep learning algorithms and accessibility of large datasets. However, privacy concerns raised by using and distributing face image datasets have emerged as a significant barrier to the deployment of centralized machine learning algorithms. Recently, federated learning (FL) has gained popularity since the private data at edge devices (clients) does not need to be shared to train a model. FL also continues to drive FR research toward decentralization. In this paper, we propose novel data-based and client-based curriculum learning (CL) approaches for federated FR intending to improve the performance of generic and client-specific personalized models. The data-based curriculum utilizes head pose angles as the difficulty measure and feeds the images from “easy” to “difficult” during training, which resembles the way humans learn. Client-based curriculum chooses “easy clients” based on performance during the initial rounds of training and includes more “difficult clients” at later rounds. To the best of our knowledge, this is the first paper to explore CL for FR in a FL setting. We evaluate the proposed algorithm on MS-Celeb-1M and IJB-C datasets and the results show an improved performance when CL is utilized during training.
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Class E resonant converter design for LED drivers
(IEEE, 2019-06) Zengin, Ö. Ö.; Boztepe, M.; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet
The LED (Light Emitting Diode) lighting technology has been becoming widespread rapidly due to having advantages such as extremely long lifetime, compact structure and very low energy consumption. In the literature, various LED driver topologies are proposed for controlling the LED's current and voltage. However, most of them require a large capacitor and inductor values due to low switching frequency operation. On the other hand, high capacitance with low volume can be achieved by using the electrolytic type capacitors which limits the lifetime and reliability of LED driver. By the help of high switching frequency, converter size can be reduced significantly. In addition, the capacitor size decreases and therefore electrolytic capacitors can be eliminated. In this study, isolated Class E resonant topology operating at 1 MHz is analysed and designed for 48 V/60 W offline LED driver. The design methodology is presented and verified by PSIM simulation.
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Design and simulation of an optimal energy management strategy for plug-In electric vehicles
(IEEE, 2018) Gözüküçük, M. A.; Akdoğan, Taylan; Hussain, Waqas; Tasooji, Tohid Kargar; Şahin, Mert; Çelik, M.; Uğurdağ, Hasan Fatih; Natural and Mathematical Sciences; Electrical & Electronics Engineering; AKDOĞAN, Taylan; UĞURDAĞ, Hasan Fatih; Hussain, Waqas; Tasooji, Tohid Kargar; Şahin, Mert
Energy management algorithms play a critical role in improving the energy efficiency of modern electric vehicles. In order to be desirable for the customer, electric vehicles should be capable of long distance driving on a single battery charge with a range which must be comparable to the values of their conventional counterparts. To achieve this goal, both the use of large-capacity battery and the development of a custom energy management algorithm are necessary. Thus, one must solve equations of vehicle dynamics, which is a part of conventional methods used in generalized energy management problems. In this paper, a Monte Carlo method is proposed for probabilistic prediction of the optimum energy to attain a given route. The route in question is obtained from the Google Maps and includes locations and road topologies. First, optimum speed set-points are generated for each state of the journey, and this generated speed array is imported into the vehicle control system to generate the required torque for vehicle propulsion. Then, this process is repeated with a constant average speed for comparison purposes. The simulation results show that an electric vehicle gains significant energy efficiency over a Hardware in the Loop (HIL) emulation, when it is being controlled with the proposed speed set-points generated by the Monte Carlo method.
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Disposable cartridge biosensor platform for portable diagnostics
(SPIE , 2017) Yaras, Y. S.; Cakmak, O.; Gunduz, A. B.; Saglam, G.; Olcer, S.; Mostafazadeh, A.; Baris, I.; Civitci, F.; Yaralıoğlu, Göksen Göksenin; Urey, H.; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
We developed two types of cantilever-based biosensors for portable diagnostics applications. One sensor is based on MEMS cantilever chip mounted in a microfluidic channel and the other sensor is based on a movable optical fiber placed across a microfluidic channel. Both types of sensors were aimed at direct mechanical measurement of coagulation time in a disposable cartridge using plasma or whole blood samples. There are several similarities and also some important differences between the MEMS based and the optical fiber based solutions. The aim of this paper is to provide a comparison between the two solutions and the results. For both types of sensors, actuation of the cantilever or the moving fiber is achieved using an electro coil and the readout is optical. Since both the actuation and sensing are remote, no electrical connections are required for the cartridge. Therefore it is possible to build low cost disposable cartridges. The reader unit for the cartridge contains light sources, photodetectors, the electro coil, a heater, analog electronics, and a microprocessor. The reader unit has different optical interfaces for the cartridges that have MEMS cantilevers and moving fibers. MEMS based platform has better sensitivity but optomechanical alignment is a challenge and measurements with whole blood were not possible due to high scattering of light by the red blood cells. Fiber sensor based platform has relaxed optomechanical tolerances, ease of manufacturing, and it allows measurements in whole blood. Both sensors were tested using control plasma samples for activated-Partial-Thromboplastin-Time (aPTT) measurements. Control plasma test results matched with the manufacturer’s datasheet. Optical fiber based system was tested for aPTT tests with human whole blood samples and the proposed platform provided repeatable test results making the system method of choice for portable diagnostics.
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Distributed MIMO for Li-Fi: Channel measurements, ray tracing and throughput analysis
(IEEE, 2021-08-15) Eldeeb, Hossıen Badr; Mana, S. M.; Jungnickel, V.; Hellwig, P.; Hilt, J.; Uysal, Murat; Electrical & Electronics Engineering; ELDEEB, Hossien Badr Hossien; UYSAL, Murat
LiFi has been considered as a promising candidate for future wireless indoor networks. The IEEE P802.15.13 and P802.11bb standardization groups agreed upon channel models generated using the non-sequential ray tracing approach of OpticStudio. In this paper, in order to validate the channel modelling approach, at first 2 × 2 multiple-input multiple-output (MIMO) channel measurements are carried out over 200 MHz bandwidth using a channel sounder. The experimental scenario is also modeled in 3D by applying ray tracing. The obtained results indicate good agreement between simulations and measured channel impulse responses, from which parameters such as path loss and delay spread are derived. After validating the channel modeling approach, we investigate the singular values and the effect of user mobility onto the performance in a 4× 4 distributed multi-user MIMO scenario.
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Diversity gain analysis of underwater vertical MIMO VLC links in the presence of turbulence
(IEEE, 2019) Yılmaz, Anıl; Elamassie, Mohammed; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Yılmaz, Anıl; Elamassie, Mohammed
To satisfy the demands of high data rate underwater applications such as image and real-time video transmission, underwater visible light communication (UVLC) has emerged as an alternative to acoustic signaling. One of the major impairments in UVLC systems is turbulence-induced fading as a result of temporal variations in temperature and salinity. Furthermore, unlike the horizontal links modeled with fixed turbulence strength, vertical links experience varying turbulence strength based on the depth-dependent temperature and salinity profiles. In this paper, we consider a multiple-input multiple-output (MIMO) UVLC link over a vertical turbulence channel which is modeled as the concatenation of multiple non-mixing layers. Under the assumption of cascaded log-normal channel model, we derive the outage probability of vertical MIMO UVLC links and quantify the diversity gain in terms of the number of transmitter/receivers.
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Diversity-multiplexing tradeoff for network coded cooperative OFDMA systems
(IEEE, 2015) Heidarpour, Ali Reza; Kurt, G. K.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Heidarpour, Ali Reza
Network coded cooperation (NCC) is an effective method to improve the throughput efficiency in cooperative wireless networks. In an effort to have further gains over the initial works, which build upon the assumption of time division multiple access, the combined use of orthogonal frequency division multiplexing (OFDM) with NCC has been proposed in the literature. In this paper, we consider orthogonal frequency division multiple access (OFDMA), an extension of the OFDM to a multiuser system where subsets of carriers are assigned to different users. We derive a closed-form expression for the outage probability of the system under consideration and present the diversity-multiplexing tradeoff (DMT) analysis. Our results demonstrate that NCC-OFDMA system is able to fully exploit both frequency and spatial diversity. Simulation results are presented to verify our theoretical analysis.

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