Electrical & Electronics Engineering

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

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Now showing 1 - 20 of 54

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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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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 In practice, feedback error or outdated selection due to temporal changes in the channel may result in selecting another source rather than the best one.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.
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Channel modelling and performance limits of vehicular visible light communication systems
(IEEE, 2020-07) Karbalayghareh, M.; Miramirkhani, F.; Eldeeb, Hossıen Badr; Kızılırmak, R. Ç.; Sait, S.Q.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; ELDEEB, Hossien Badr Hossien
Visible light communication (VLC) has been proposed as an alternative or complementary technology to radio frequency vehicular communications. Front and back vehicle lights can serve as wireless transmitters making VLC a natural vehicular connectivity solution. In this paper, we evaluate the performance limits of vehicular VLC systems. First, we use non-sequential ray tracing to obtain the channel impulse responses (CIRs) for vehicle-to-vehicle (V2V) link in various weather conditions. Based on these CIRs, we present a closed-form path loss expression which builds upon the summation of geometrical loss and attenuation loss and takes into account asymmetrical patterns of vehicle light sources and geometry of V2V transmission. The proposed expression is an explicit function of link distance, lateral shift between two vehicles, weather type (quantified by the extinction coefficient), transmitter beam divergence angle and receiver aperture diameter. Then, we utilize this expression to determine the maximum achievable link distance of V2V systems for clear, rainy and foggy weather conditions while ensuring a targeted bit error rate.
Open Access
Channel modelling for indoor visible light communications
(Royal Society Publishing, 2020-04-17) Miramirkhani, Farshad; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad
Visible light communication (VLC) allows the dual use of light-emitting diodes (LEDs) for wireless communication purposes in addition to their primary purpose of illumination. As in any other communication system, realistic channel modelling is a key for VLC system design, analysis and testing. In this paper, we present a comprehensive survey of indoor VLC channel models. In order to set the background, we start with an overview of infrared (IR) channel modelling, which has received much attention in the past, and highlight the differences between visible and IR optical bands. In the light of these, we present a comparative discussion of existing VLC channel modelling studies and point out the relevant advantages and disadvantages. Then, we provide a detailed description of a site-specific channel modelling approach based on non-sequential ray tracing that precisely captures the optical propagation characteristics of a given indoor environment. We further present channel models for representative deployment scenarios developed through this approach that were adopted by the Institute of Electrical and Electronics Engineering (IEEE) as reference channel models. Finally, we consider mobile VLC scenarios and investigate the effect of receiver location and rotation for a mobile indoor user.
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CoMP-based dynamic handover for vehicular VLC networks
(IEEE, 2020-09) Demir, Muhammet Selim; Eldeeb, Hossıen Badr; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; ELDEEB, Hossien Badr Hossien; Demir, Muhammet Selim
Visible light communication (VLC) has emerged as a potential wireless connectivity solution for infrastructure-to-vehicle networks where street lights can be configured to serve as access points. In this letter, we propose dynamic soft handover algorithm based on coordinated multipoint (CoMP) transmission. The proposed algorithm takes the rate of change in the received power as an input and accordingly revises the handover margin and time-to-trigger value without explicit information of the vehicle velocity. Our simulation results demonstrate that the proposed algorithm outperforms conventional CoMP and hard handover and maintains a stable signal quality regardless of vehicle velocity.
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Composite fading model for aerial MIMO FSO links in the presence of atmospheric turbulence and pointing errors
(IEEE, 2021-06) Khallaf, H. S.; Kato, K.; Mohamed, E. M.; Sait, S. M.; Yanikomeroglu, H.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this letter, we introduce accurate approximation expressions for composite fading channel model and outage probability of multiple-input multiple-output (MIMO) free space optical (FSO) link between two unmanned aerial vehicles (UAVs) in hovering state. In our derivations, we consider the effects of weather attenuation, random fluctuations in UAVs' positions and orientations, and atmospheric turbulence. Our proposed model is unified with respect to turbulence effect, which means it is valid for different atmospheric turbulence models. We show the accuracy of the proposed model through comparisons with Monte Carlo simulations under different channel conditions.
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Comprehensive study on UAV-based FSO links for high-speed train backhauling
(The Optical Society, 2021-09-20) Khallaf, H. S.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we introduce the idea of using unmanned aerial vehicle (UAV)-based free-space optical communication systems to backhaul high-speed trains. We introduce a composite channel model that includes effects of both atmospheric turbulence and pointing errors due to position/orientation deviation. Based on the derived fading model, we present an approximation expression for the outage probability. The performances of the proposed air-relay and traditional ground-relay systems are compared under fair conditions. Pointing-acquisition-tracking (PAT) complexity and coverage distance under different weather conditions and different fading levels are considered as comparison metrics. Furthermore, we investigate the effect of several parameters such as beam divergence angle, displacement deviation variance, and UAV operation altitude on system performance. Our results reveal that air relay helps in mitigating the fog effect, can achieve longer coverage distance, and relaxes PAT system design.
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Cooperative MIMO-OFDM based inter-vehicular visible light communication using brake lights
(Elsevier, 2018-05) Narmanlıoğlu, Ömer; Turan, B.; Ergen, S. C.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlıoğlu, Ömer
Inter-vehicular connectivity to enhance road safety and support highly autonomous driving is increasingly becoming popular. Despite the prevalent works on radio-frequency (RF) based vehicular communication schemes, visible light communication (VLC) is considered to be a promising candidate for vehicular communications due to its low complexity and RF interference-free nature. Deployment of multiple light emitting diodes (LEDs) enables multiple-input multiple-output (MIMO) transmission in the context of vehicular VLC. This paper investigates applicability of both point-to-point (direct) vehicular VLC and decode-and-forward relaying based cooperative vehicular VLC including relay terminals between source and destination terminals to enhance road safety based on real world measurements. We consider direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) based MIMO transmission scheme and evaluate the performances of different MIMO modes including repetition code (RC) and spatial multiplexing (SM), different modulation orders with different transmitter–receiver selection mechanisms to support line-of-sight (LoS) and beyond LoS multi-hop vehicular VLC. The results reveal that the selection of the closest transmitters to the receivers provides better performance due to high signal-to-noise-ratio requirements for RC mode whereas SM suffers from channel correlation. Usage of all possible transmitters does not always yield better performance due to the power division at the transmitter side. On the other hand, the performance of RC shows more degradation on higher-order modulations that are required to yield the same throughput with SM. Therefore, considering the higher order modulation requirement for RC based VLC, SM is concluded to be a favorable MIMO scheme for cooperative vehicular VLC. We further demonstrate the benefits of multi-hop transmission over direct transmission with respect to different number of relay vehicles as a consequence of varying inter-vehicular distances between source and destination vehicles.
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Coriolis Effect on elastic waves propagating in rods
(Elsevier, 2020-10-27) Çetin, Hakan; Yaralıoğlu, Göksen Göksenin; Electrical & Electronics Engineering; YARALIOĞLU, Göksen Göksenin; Çetin, Hakan
Vibration analysis of rods that are subjected to rotation is presented. It is shown that flexural-flexural, longitudinal-flexural and torsional-flexural wave coupling occur due to the Coriolis Effect. First, we carried out our analysis for thin rods where the wavelength is much larger than the radius. It is shown that the wavenumbers change due to the Coriolis Effect. Then, we characterize the 3-D wave propagation in rotating rods by using the Finite Element Method (FEM) in order to determine the corresponding wavenumber shifts for each type of wave. We show that for different drive frequency (ω0) and rotation rate (Ω), wave couplings exhibit different characteristics. For flexural-flexural wave coupling, the wavenumber increases for the primary flexural wave whereas the wave number decreases for the coupled flexural wave where Ω < ω0. For the Coriolis coupling between flexural-longitudinal waves, the wavenumber increases for the flexural wave and decreases for the longitudinal wave where Ω < ω0. For the Coriolis coupling between flexural-torsional waves, the wavenumber increases for both flexural and torsional waves.
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A cross-layer design for dynamic resource management of VLC networks
(IEEE, 2021-03) Demir, Muhammet Selim; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Demir, Muhammet Selim
In this article, we propose a cross-layer resource management mechanism for an indoor multiuser visible light communication (VLC) access network. The physical layer builds upon DC-biased orthogonal frequency division multiple access. Channel state information at the physical layer serves as a performance indicator for better data rate opportunity while queue state information at medium access control layer provides the information about packet urgency. A packet based traffic arrival model is considered such that incoming packets with random inter arrival times join a separate queue dedicated to each user if the admission control accepts them, otherwise packets are dropped. We formulate and solve a stochastic cross-layer optimization problem to optimize the network resources under the constraints of queue stability and power to maximize the average system throughput. By using the Lyapunov optimization technique, we convert the long term time-Average optimization problem into series of single time slot online problem. Then, we decompose the problem into independent sub problems and propose packet admission, resource (access point and subcarrier) allocation and power control solutions. We present simulation results to demonstrate the superiority of proposed scheme over existing solutions in the literature.
Open Access
Crucial topics in computer architecture education and a survey of textbooks and papers
(International Association of Engineers, 2020) Yıldız, A.; Gören, S.; Uğurdağ, Hasan Fatih; Aktemur, B.; Akdoğan, Taylan; Natural and Mathematical Sciences; Electrical & Electronics Engineering; UĞURDAĞ, Hasan Fatih; AKDOĞAN, Taylan
We have been teaching undergraduate computer architecture since 2012 in an unconventional way. Most undergraduate computer architecture courses are based on microprocessors, and they quickly move into advanced topics such as instruction pipelining, forwarding, branch prediction, cache, and even memory management unit. We instead spend only the last one-third of our course on these topics. The first two thirds of the course is devoted to microcontrollers, i.e., simple-minded processors with no memory hierarchy, no branch prediction, sometimes even no pipelining. Our claim is that it is very hard to truly grasp the advanced topics without full grasp of the basics. Equipped with the above approach, this article comes up with an all-inclusive list of crucial topics for computer architecture education, and it surveys 25 computer architecture textbooks as well as 38 computer architecture education papers to see how much they cover these topics. In addition to that, the article contains a concise description of the perspective of our course. One of the pillars of our course is a working CPU on FPGA. We have so far had around 600 students design their own unique CPUs using Verilog given a complete instruction set, close to 70% of them with complete success.
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Cryptographic security concerns on timestamp sharing via a public channel in quantum-key-distribution systems
(American Physical Society, 2022-07) Pahalı, Melis; Durak, Kadir; Tefek, U.; Electrical & Electronics Engineering; DURAK, Kadir; Pahalı, Melis
Quantum-key-distribution protocols are known to be vulnerable against a side channel attack that exploits the time difference in detectors' responses used to obtain key bits. The recommended solution against this timing side channel attack is to use a large time bin width instead of high-resolution timing information. A common notion is that using a large bin width reduces the resolution of detectors' responses, hence supposedly minimizes the information leakage to an eavesdropper. We challenge this conventional wisdom and demonstrate that increasing the bin width does not monotonically reduce the mutual information between the key bits and the eavesdropper's observation of detectors' responses. Instead of randomly increasing the bin width, it should be carefully chosen because the mutual information fluctuates with respect to the bin width. We also examine the effect of full width half maximums (FWHMs) of the detectors' responses on the mutual information and show that decreasing the FWHM increases the mutual information. Lastly, the start time of binning is also shown to be important in the binning process and the mutual information fluctuates periodically with respect to it.
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Deep learning-based blind image super-resolution with iterative kernel reconstruction and noise estimation
(Elsevier, 2023-08) Ateş, Hasan Fehmi; Yildirim, S.; Gunturk, B. K.; Electrical & Electronics Engineering; ATEŞ, Hasan Fehmi
Blind single image super-resolution (SISR) is a challenging task in image processing due to the ill-posed nature of the inverse problem. Complex degradations present in real life images make it difficult to solve this problem using naïve deep learning approaches, where models are often trained on synthetically generated image pairs. Most of the effort so far has been focused on solving the inverse problem under some constraints, such as for a limited space of blur kernels and/or assuming noise-free input images. Yet, there is a gap in the literature to provide a well-generalized deep learning-based solution that performs well on images with unknown and highly complex degradations. In this paper, we propose IKR-Net (Iterative Kernel Reconstruction Network) for blind SISR. In the proposed approach, kernel and noise estimation and high-resolution image reconstruction are carried out iteratively using dedicated deep models. The iterative refinement provides significant improvement in both the reconstructed image and the estimated blur kernel even for noisy inputs. IKR-Net provides a generalized solution that can handle any type of blur and level of noise in the input low-resolution image. IKR-Net achieves state-of-the-art results in blind SISR, especially for noisy images with motion blur.
Open Access
Design and implementation of dual band microstrip patch antenna for WLAN energy harvesting system
(2018-07) Amjad, Osama; Munir, Syeda Wajiha; Imeci, S. T.; Ercan, Ali Özer; Electrical & Electronics Engineering; ERCAN, Ali Özer; Amjad, Osama; Munir, Syeda Wajiha
Since the demand for self-sustained wireless systems is increasing, there is a trend towards RF energy harvesting. It is a key solution to energize the low power systems such as the Internet of Things (IoT) devices without replacing the batteries periodically. This paper presents the design and analysis of RF energy harvesting system that consists of dual-band microstrip patch antenna operating at 2.4 GHz and 5.8 GHz, an impedance matching network, 4-stage voltage doubler and a storing circuit. The antenna is designed using ADS Agilent and sonnet suites software that provides a directivity of 5.5 dBi and 6.3 dBi at 2.4 GHz and 5.8 GHz respectively. The measured results of the fabricated antenna are well agreement with the simulated results. Simulated results show that for an input received power of 10 mW, the proposed system can provide 4.5 mW power at the output of 4-stage voltage rectifier with an overall efficiency of 45%.
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Design and implementation of VLC-based smart barrier gate systems
(Elsevier, 2021-07) Rasti-Meymandi, A.; Madahian, A.; Abouei, J.; Mirvakili, A.; HajiAkhondi-Meybodi, Z.; Mohammadi, A.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, an innovative and smart Visible Light Communication (VLC)-based Intelligent Transportation System (ITS) is designed. The proposed system uses vehicle LED headlamps as a remote controller. Differential Pulse Position Modulation (DPPM) is utilized for the sake of its asynchronicity. The system features an innovative optical interference cancellation mechanism to address the unwanted variable DC component and AC line noise in the received signal. The feasibility of the proposed system is demonstrated experimentally in day and night conditions using an off-the-shelf LED headlights. The Bit Error Rate (BER) performance of the system in terms of angular position of the vehicle with respect to the VLC receiver at different link ranges is evaluated. The prototype successfully demonstrates the smart control over the barrier gate using the ATmega microcontrollers family for the outdoor environment. BER of lower than 10(-3) is achieved for a maximum link range of 4.4 meters.
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Effect of sea waves on vertical underwater visible light communication links
(IEEE, 2023-04) Elamassie, Mohammed; Sait, S. M.; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
Underwater visible light communication (VLC) has been proposed to deal with emerging high bandwidth underwater applications. Initial research works on underwater VLC are based on the assumption that both transmitter and receiver are submerged, creating a horizontal link. In most of the vertical communication links, one of the transceiver nodes takes the form of a buoy and requires taking into the effect of the sea surface, which is inherently unsteady due to wind and waves. In this article, we consider a vertical underwater VLC link where the transmitter is in the form of a buoy at the sea surface, and the receiver is a submerged node at a certain depth. We assume sinusoidal waves and consider the fact that the buoy will fluctuate and oscillate, during drifting up and down, around its vertical axis. This effectively results in a 3-D displacement at the suspended transmitter. Building upon these assumptions of practical relevance, we propose an aggregate channel model, which includes a random path loss due to periodic changes of the transmission distance and a fading term induced by pointing errors with periodic changes of relative movement. Based on the proposed statistical model, we derive closed-form expressions for the exact and asymptotic bit error ratio and investigate the achievable diversity orders. We further present numerical results to confirm the analytical findings.
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Efficient coupling of down-converted photon pairs into single mode fiber
(Elsevier, 2021-08-15) Kuniyil, Hashir Puthiyapurayil; Durak, Kadir; Electrical & Electronics Engineering; DURAK, Kadir; Kuniyil, Hashir Puthiyapurayil
We present the analysis of the down-conversion emission profile from a critically phase-matched type-I nonlinear crystal. The emission profile of the down-conversion modes shows asymmetry in cylindrical coordinate system due to the birefringent effects of the nonlinear crystal, i.e. pump walk-off. This effect leads to reduced collection of the pairs from the source to the single mode fiber, which limits the brightness as a function of the crystal length. We propose a method to improve the symmetry of the down-conversion modes by inserting a lens off-centered with respect to the optical axis. Our theoretical and experimental results show that the asymmetry of the system increases with the crystal length by L0.5, and the brightness is proportional to crystal length by L0.72 and L0.91 for uncorrected and corrected down conversion mode profiles, respectively. The proposed method allows more efficient use of photon pair sources in terms of brightness which is to be used in quantum optics applications.
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Finite-SNR diversity gain analysis of FSO systems over gamma-gamma fading channels with pointing errors
(IEEE, 2021-06) Elamassie, Mohammed; Sait, S. M.; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, Murat
Free space optical (FSO) communication systems are subject to turbulence-induced fading as a result of fluctuations in the refractive index. Gamma-Gamma (GG) distribution is commonly used in the literature to characterize moderate-to-strong turbulence conditions. The performance of FSO systems is further degraded by pointing error-induced fading as a result of building sways. While the asymptotic analysis presented in earlier works is important to understand the maximum diversity gains of FSO systems attainable over fading channels, such gains might not be available in practical range of signal-to-noise ratio (SNR). Furthermore, different systems with the same asymptotic slope may have different slopes in the range of finite SNR values. In this paper, we consider a multiple-input multiple-output (MIMO) FSO system with intensity modulation and direct detection (IM/DD). We derive approximate expression for the finite-SNR diversity order over GG turbulence channels in the presence of pointing errors. We also investigate convergence speed to full diversity. We provide numerical results to demonstrate the accuracy of our derivations and corroborate on our analytical findings.
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Flexible generalized spatial modulation for visible light communications
(IEEE, 2021-01) Al-Nahhal, Mohamed; Başar, E.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Al-Nahhal, Mohamed
Adaptive spatial modulation (ASM) varies the modulation size across the transmit light-emitting diodes (LEDs) to improve the overall spectral efficiency of visible light communication (VLC) systems. This article proposes a novel ASM scheme, referred to as flexible generalized spatial modulation (FGSM), for VLC systems. The proposed FGSM system changes the modulation sizes over the LEDs and the number of active LEDs, to improve the average symbol error rate (SER) and spectral efficiency compared to ASM with a fixed overall number of LEDs. The modulation sizes are selected in order to optimize the average SER under a predefined spectral efficiency value. A closed-form expression of approximate SER is derived along with decoding complexity calculations for the proposed system. Numerical results are provided to confirm the superiority of the proposed system and to support theoretical derivations.

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