Electrical & Electronics Engineering

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

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Now showing 1 - 20 of 158

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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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All-optical amplify-and-forward relaying system for atmospheric channels
(IEEE, 2012-10) Aminikashani, Mohammadreza; Rad, M. M.; Safari, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Aminikashani, Mohammadreza
In this letter, we investigate the performance of a dual-hop free space optical link with an all-optical amplify-and-forward relay. We employ photon counting methodology and derive closed form expressions for the end-to-end signal-to-noise ratio and the outage probability. In our derivations, we consider either full or partial channel state information (CSI) at the relay and take into account practical limitations such as amplifier noise and filtering effects. Our results indicate significant performance improvements over direct transmission and furthermore demonstrate that semi-blind relaying (which depends only on statistical CSI) provides nearly identical performance to its full-CSI counterpart.
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Analysis of asynchronous cognitive radio system with imperfect sensing and bursty primary user traffic
(Springer Science+Business Media, 2016-03) Ercan, Ali Özer; Electrical & Electronics Engineering; ERCAN, Ali Özer
This paper presents a theoretical analysis of the spectrum utilization levels in a cognitive radio system. We assume that the traffic of the primary network is bursty and asynchronous with the secondary network, which performs imperfect spectrum sensing. Collisions of the primary and the secondary packets are assumed to result in increased packet error probabilities. We present primary and secondary utilization levels under optimized secondary transmission periods for varying primary traffic characteristics and secondary sensing performance levels. The results are also validated by extensive Monte Carlo simulations. We find that an asynchronous cognitive radio network with imperfect spectrum sensing is feasible when optimized transmission periods are used. The effects of primary traffic’s burst pattern and secondary sensing performance are discussed.
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Analysis of vibratory gyroscopes: drive and sense mode resonance shift by coriolis force
(IEEE, 2017) Cetin, Hakan; Yaralıoğlu, Göksen Göksenin; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin; Cetin, Hakan
In this paper, we demonstrate the analysis of coupling between drive and sense systems of vibratory gyroscopes. Vibratory gyroscopes have attracted a lot of interest recently with the development of MEMS gyroscopes. These gyroscopes made their way through portable devices and smart phones. Novel gyroscope architectures have been proposed and analyzed in detail. However, in most of these analyses, coupling between the sense and drive systems was ignored. We analytically show that drive and sense systems are coupled together via Coriolis and centrifugal force. As a result, system resonances shift as the rotation rate increase for linear and torsional gyroscope systems. Starting from a simple gyro system, we calculated the sense and drive resonant frequency shifts in various configurations. Then, for more complex systems where analytical solution is difficult to obtain, we used commercially available FEM tools to determine corresponding frequency shift. In general, we found that the shift is small and can be ignored for linear vibratory gyroscopes where Q of the sense system is less than 2500 for mode matched gyros. But for higher Q systems, the frequency shift may affect the linearity of these gyroscopes. This sets a fundamental limit for the linearity of vibratory gyroscopes. Based on our calculations the non-linearity is above 1% for linear 2-DOF mode-matched vibratory gyroscopes where Q is above 3000 and for torsional 2-DOF vibratory gyroscopes where Q is above 600. Multi-DOF and ring vibratory gyroscopes are also examined. We find that the effect is less pronounced for Multi-DOF gyros, whereas there is a large effect on the linearity of ring gyroscopes.
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Aperture averaging in multiple-input single-output free-space optical systems
(SPIE, 2015-06) Gökçe, M. C.; Baykal, Y.; Kamacıoğlu, C.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
Multiple-input single-output systems are employed in free-space optical links to mitigate the degrading effects of atmospheric turbulence. We formulate the power scintillation as a function of transmitter and receiver coordinates in the presence of weak atmospheric turbulence by using the extended Huygens–Fresnel principle. Then the effect of the receiver–aperture averaging is quantified. To get consistent results, parameters are chosen within the range of validity of the wave structure functions. Radial array beams and a Gaussian weighting aperture function are used at the transmitter and the receiver, respectively. It is observed that the power scintillation decreases when the source size, the ring radius, the receiver–aperture radius, and the number of array beamlet increase. However, increasing the number of array beamlets to more than three seems to have negligible effect on the power scintillation. It is further observed that the aperture averaging effect is stronger when radial array beams are employed instead of a single Gaussian beam.
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Aperture averaging in multiple-input single-output free-space optical systems using partially coherent radial array beams
(The Optical Society, 2016-06) Gökçe, M. C.; Baykal, Y.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
Multiple-input single-output (MISO) techniques are employed in free-space optical (FSO) links to mitigate the degrading effects of atmospheric turbulence. In this paper, for the MISO FSO system, a partially coherent radial array and a finite-sized receiver aperture are used at the transmitter and the receiver, respectively. Using the extended Huygens–Fresnel principle, we formulate the average power and the power correlation at the finite-sized slow detector in weak atmospheric turbulence. System performance indicators such as the power scintillation index and the aperture averaging factor are determined. Effects of the source size, ring radius, receiver aperture radius, link distance, and structure constant and the degree of source coherence are analyzed on the performance of the MISO FSO system. In the limiting cases, the numerical results are found to be the same when compared to the existing coherent and partially coherent Gaussian beam scintillation indices.
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Asymptotic performance of generalized transmit laser selection over lognormal turbulence channels
(IEEE, 2020-08) Elamassie, Mohammed; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Elamassie, Mohammed
In free space optical communication systems, transmit laser selection (TLS) has been proposed as an efficient fading-mitigation technique over turbulence channels. In TLS, the transmitter is equipped with a number of laser sources and the best laser source is selected for transmission. In practice, feedback error or outdated selection due to temporal changes in the channel may result in selecting another source rather than the best one. In this letter, we consider a FSOC system with generalized TLS (GTLS) where the nth best laser is selected among the available N lasers. Under the assumption of lognormal turbulence channels in addition to pointing errors, we derive a closed-form expression for asymptotic bit error rate. We use our derived closed-form expression to determine the diversity gains. We finally present simulation results to corroborate our analytical findings.
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Attack to quantum cryptosystems through RF fingerprints from photon detectors
(IEEE, 2022-03) Durak, Kadir; Jam, Naser Chamani; Karamzadeh, S.; Electrical & Electronics Engineering; DURAK, Kadir; Jam, Naser Chamani
The well-known RF penetration method is implemented on the quantum cryptosystems. In this study, RF radiations from the single photon detectors in a quantum key distribution system are intercepted. It was found that the data contents of a quantum transmission system can be detected from the vicinity of the receiving parties by exploiting the radiations of avalanche effect of single photon detectors. We showed that any Geiger-mode avalanche photodetector acts like a downconverter that converts the optical-wavelength photons to radio-wavelength photons. In our experiment, the fingerprints of the avalanche radiations from commercial single photon detectors were fed to a trained deep learning neural network, and the bit content of quantum transmission was cloned with >99% accuracy up to a distance of 2 meters from the detectors. We also speculate on the enhancement of the key cloning accuracy and range of the eavesdropping.
Open Access
Automatic detection of attachment style in married couples through conversation analysis
(Springer, 2023-05-31) Koçak, Tuğçe Melike; Dibek, B. Ç.; Polat, Esma Nafiye; Kafesçioğlu, Nilüfer; Demiroğlu, Cenk; Electrical & Electronics Engineering; Psychology; KAFESCİOĞLU, Nilüfer; DEMİROĞLU, Cenk; Koçak, Tuğçe Melike; Polat, Esma Nafiye
Analysis of couple interactions using speech processing techniques is an increasingly active multi-disciplinary field that poses challenges such as automatic relationship quality assessment and behavioral coding. Here, we focused on the prediction of individuals’ attachment style using interactions of recently married (1–15 months) couples. For low-level acoustic feature extraction, in addition to the frame-based acoustic features such as mel-frequency cepstral coefficients (MFCCs) and pitch, we used the turn-based i-vector features that are the commonly used in speaker verification systems. Sentiments, positive and negative, of the dialog turns were also automatically generated from transcribed text and used as features. Feature and score fusion algorithms were used for low-level acoustic features and text features. Even though score and feature fusion algorithms performed similar, predictions with score fusion were more consistent when couples have known each other for a longer period of time.
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Bit error rate analysis of MISO FSO systems
(Informa Group Company, 2016-05-09) Gökçe, M. C.; Baykal, Y.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
Multiple-input single-output (MISO) systems are employed in free space optical (FSO) links to mitigate the degrading effects of atmospheric turbulence. In this paper, we consider a MISO FSO system with practical transmitter and receiver configuration that consists of radial laser array with Gaussian beams and a Gaussian receiver aperture function. We have employed our previously derived formulation of the power scintillation in which Huygens–Fresnel principle was employed. Therefore, we choose system parameters within the range of validity of the wave structure functions. Using the on-off keying modulation and the log-normal probability distribution function, we quantify the average bit error rate (〈BER〉) of laser array beams in weak turbulence. It is observed that the radial array beams at the transmitter are more advantageous than the single Gaussian beam. However, increasing the number of array beamlets to more than three seems to have negligible effects on 〈BER〉 . It is further observed that 〈BER〉 decreases when the source size, the ring radius and the receiver aperture radius increase.
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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 practical wireless multihop broadcast networks
(Springer Science+Business Media, 2013-04) Atıcı, Çağdaş; Sunay, Mehmet Oğuz; Computer Science; SUNAY, Mehmet Oğuz; Atıcı, Çağdaş
In a wireless multihop broadcasting scenario, a number of relay nodes may cooperate the source node in order to improve the capacity of the network. However, the imposition of total energy and maximum hop constraints to this system in a practical setting. In this paper, we study an ad-hoc network with infinitely many nodes and analytically find the number and positions of rebroadcasting relay nodes to achieve the optimal broadcast capacity. The interference due to multiple transmissions in the same geographical area is taken into account. According to the results of this theoretical model, we propose two heuristics, one distributed and one centralized, as suboptimal but practical solutions to the relay selection problem in wireless multihop broadcasting. We discuss the broadcast capacity performances and CSI (channel state information) requirements of these algorithms. The results illustrate that the benefits of peer-assisted broadcasting are more pronounced in the centralized relay selection algorithm when compared to the fully randomized and distributed selection under a realistic system model.
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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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A cartridge based sensor array platform for multiple coagulation measurements from plasma
(Royal Society of Chemistry, 2015) Cakmak, O.; Ermek, E.; Kilinc, N.; Bulut, S.; Baris, I.; Kavakli, I. H.; Yaralıoğlu, Göksen Göksenin; Urey, H.; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin
This paper proposes a MEMS-based sensor array enabling multiple clot-time tests for plasma in one disposable microfluidic cartridge. The versatile LoC (Lab-on-Chip) platform technology is demonstrated here for real-time coagulation tests (activated Partial Thromboplastin Time (aPTT) and Prothrombin Time (PT)). The system has a reader unit and a disposable cartridge. The reader has no electrical connections to the cartridge. This enables simple and low-cost cartridge designs and avoids reliability problems associated with electrical connections. The cartridge consists of microfluidic channels and MEMS microcantilevers placed in each channel. The microcantilevers are made of electroplated nickel. They are actuated remotely using an external electro-coil and the read-out is also conducted remotely using a laser. The phase difference between the cantilever oscillation and the coil drive is monitored in real time. During coagulation, the viscosity of the blood plasma increases resulting in a change in the phase read-out. The proposed assay was tested on human and control plasma samples for PT and aPTT measurements. PT and aPTT measurements from control plasma samples are comparable with the manufacturer's datasheet and the commercial reference device. The measurement system has an overall 7.28% and 6.33% CV for PT and aPTT, respectively. For further implementation, the microfluidic channels of the cartridge were functionalized for PT and aPTT tests by drying specific reagents in each channel. Since simultaneous PT and aPTT measurements are needed in order to properly evaluate the coagulation system, one of the most prominent features of the proposed assay is enabling parallel measurement of different coagulation parameters. Additionally, the design of the cartridge and the read-out system as well as the obtained reproducible results with 10 μl of the plasma samples suggest an opportunity for a possible point-of-care application.
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Centralized light access network (C-LiAN): a novel paradigm for next generation indoor VLC networks
(IEEE, 2017) Kizilirmak, R. Ç.; Narmanlıoğlu, Ömer; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlıoğlu, Ömer
Visible light communication (VLC) builds upon the idea of using existing lighting infrastructure for wireless data transmission. In a conventional VLC network, each light fixture acts as an access point (AP) which are connected to each other through electrical grid as well as data backbone. These VLC-enabled fixtures consist baseband unit (BBU) followed by the optical front-end (OFE). In this paper, we propose the so-called centralized light access network (C-LiAN) which aggregates all AP computational resources into a central pool that is managed by a centralized controller. Unlike the distributed architecture where each light fixture performs both baseband processing and optical transmission/reception, the centralized architecture employs “dummy”fixtures with a VLC OFE. Moving the baseband processing to a central pool reduces the associated cost and complexity of each VLC-enabled LED luminary. It further enables joint processing of signals from different APs making possible an efficient implementation of joint processing, offloading, handover, interference management, scheduling, and resource management algorithms. As an example to demonstrate the virtues of C-LiAN, we further present the performance of coordinated multipoint transmission and enhanced inter-cell interference coordination with almost blank subframe techniques originally proposed for Long Term Evolution-Advanced in the context of indoor VLC networks.
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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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