Electrical & Electronics Engineering

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

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Now showing 1 - 20 of 677

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A 130 nm CMOS receiver for visible light communication
(IEEE, 2022-06-15) Kısacık, Rıfat; Yagan, M. Y.; Uysal, Murat; Pusane, A. E.; Baykas, T.; Dundar, G.; Yalcinkaya, A. D.; Electrical & Electronics Engineering; UYSAL, Murat; Kısacık, Rıfat
Visible light communication (VLC) is an emerging technology that has been gaining attention over the last few years. Transmission of data at higher rates in a VLC system is mainly limited by the modulation bandwidth of the employed LED. To alleviate this limitation, equalization is frequently employed. This is usually achieved by either using discrete circuit elements or in digital form. In this paper, we present a power-efficient VLC receiver as a system-on-chip, implemented in 130 nm CMOS technology. The proposed receiver supports LEDs with different bandwidths thanks to the switchable equalizer. We tested the proposed receiver using phosphorescent white LEDs with different bandwidths on an experimental VLC link. For each tested LED, around 20 fold improvement in data rate was achieved compared to the original bandwidth of the LED. For the LED with a modulation bandwidth of 1.6 MHz, data rates of 32 Mbps and 50 Mbps at a BER of 102 were obtained at a distance of 2 meters without and with a blue filter, respectively.
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15-15-0747-00-007a-tg7r1-cirs-channel-model-document-for-high-rate-pd-communications
(IEEE, 2015-11-14) Uysal, Murat; Baykas, T.; Miramirkhani, Farshad; Serafimovski, N.; Jungnickel, V.; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad
The LiFi channels developed by Prof. Murat Uysal and Mr. Miramirkhani were selected as the "LiFi Reference Channel Models" by the IEEE 802.15.7r Task Group during the IEEE's latest meeting held in Bangkok, Thailand, in September. Accordingly, all companies, universities and research institutions are required to use these channel models as reference for their performance assessments and comparative analysis in the standardization proposals they will submit over the coming months. The channel models developed by them are the most realistic models available in the literature and pointed out the significance of recognition and adoption of these models by industry.
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16-elements helical antenna system integration with a solar cell powered IoT collector
(IEEE, 2019) Ullah, Naveed; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet; Ullah, Naveed
An 868MHz-915MHz 16-elements helical wire antenna array design with a solar-cell integration is presented. Each element is designed to be omni-directional with the corresponding tuning stubs and ground substrate. This is shared with distributed solar cell array, powering 16- Internet of Things (loT) transceivers operating at multiple Industrial Scientific and Medical (ISM) bands. 370mmx400mm design including the antennas, solar cells, and the tuning stubs can generate 8-watts solar power under direct sun, charging Lithium batteries. 1.6-mm thick planner design with horizontal radiation pattern resulted in average -15dB return loss at 868 MHz without using any external matching elements.
Open Access
A 1GS/s, 9-bits DAC interleaved (2+1)-bit then 2-bit per cycle SAR ADC
(Istanbul University, 2020-07) El-Sawy, Salma; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet; El-Sawy, Salma
This paper presents a high speed Successive Approximation Register Analog to Digital Converter (SAR ADC) for low-noise low-power satellite transceiver applications. The system is a (2+1) then 2-bit per cycle SAR ADC of 1GS/s sampling rate, 9-bits resolution designed in a 65nm standard CMOS technology. The system resolves 9 bits with a special switching scheme in a total of 4 cycles per sample. This is achieved by interleaving 4 Capacitive Digital to Analog Converter (C-DACs) of unit capacitance 1fF. Since the interleaving is limited to the DACs only which match well, the design does not suffer from the drawbacks of full interleaving. Hence, better power efficiency and performance metrics were obtained in comparison to regular interleaved ADCs. A special timing with an extra first bit comparator is optimized to leave proper timing margins for every step from a single 4-GHz low noise clock source which is readily available in the 8- GHz direct conversion front-end. This comparator is reused as all the other active comparators in the both interleaving phases. The proposed design achieved an effective number of bits (ENOB) of 8.2 bits at Nyquist with power consumption of 12mW, resulting in a Figure of Merit (FoM) of 38.37 fJ/conversion-step.
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25th IFIP/IEEE conference on very large scale integration (VLSI-SoC 2017)
(IEEE, 2018-02) Elfadel, I. A. M.; Uğurdağ, Hasan Fatih; Electrical & Electronics Engineering; UĞURDAĞ, Hasan Fatih
The 25th IFIP/IEEE Conference on Very Large Scale Integration (VLSI-SoC 2017) was held between 23 and 25 October in the landmark Yas Viceroy Hotel, overlooking the Formula 1 Yas Marina racetrack in Yas Island, Abu Dhabi, United Arab Emirates (UAE). The conference was held under the overarching theme: “The Internet of Things: SoC Challenges and Opportunities,” and featured four keynote addresses on this topic by renowned leaders from industry and academia, including Dr. Yervant Zorian, Synopsys Fellow and President of Synopsys Armenia, Dr. Rafic Makki, Executive Fellow, GLOBALFOUNDRIES, Dr. Leon Stok, VP EDA, IBM, and Prof. Simha Sethumadhavan, Columbia University. Prof. Tod A. Laursen, President of Khalifa University of Science and Technology gave the Welcome Address at the Opening Session.
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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.
Open Access
3D neuromorphic wireless power transfer and energy transmission based synaptic plasticity
(IEEE, 2019) Gülbahar, Burhan; Electrical & Electronics Engineering; GÜLBAHAR, Burhan Cahit
Energy consumption combined with scalability and 3D architecture is a fundamental constraint for brain-inspired computing. Neuromorphic architectures including memristive, spintronic, and floating gate metal-oxide-semiconductors achieve energy efficiency while having challenges of 3D design and integration, wiring and energy consumption problems for architectures with massive numbers of neurons and synapses. There are bottlenecks due to the integration of communication, memory, and computation tasks while keeping ultra-low energy consumption. In this paper, wireless power transmission (WPT)-based neuromorphic design and theoretical modeling are proposed to solve bottlenecks and challenges. Neuron functionalities with nonlinear activation functions and spiking, synaptic channels, and plasticity rules are designed with magneto-inductive WPT systems. Tasks of communication, computation, memory, and WPT are combined as an all-in-one solution. Numerical analysis is provided for microscale graphene coils in sub-terahertz frequencies with unique neuron design of coils on 2D circular and 3D Goldberg polyhedron substrates as a proof-of-concept satisfying nonlinear activation mechanisms and synaptic weight adaptation. Layered neuromorphic WPT network is utilized to theoretically model and numerically simulate pattern recognition solutions as a simple application of the proposed system design. Finally, open issues and challenges for realizing WPT-based neuromorphic system design are presented including experimental implementations.
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Achievable data rates and power allocation for frequency-selective fading relay channels with imperfect channel estimation
(Springer Science+Business Media, 2012-12) Ding, Y.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this article, we investigate the information-theoretical performance of a cooperative orthogonal frequency division multiplexing (OFDM) system with imperfect channel estimation. Assuming the deployment of training-aided channel estimators, we derive a lower bound on the achievable rate for the cooperative OFDM system with amplify-and-forward relaying over frequency-selective Rayleigh fading channels. The bound is later utilized to allocate power among the training and data transmission phases. Numerical results demonstrate that the proposed power allocation scheme brings between 5 and 19% improvement depending on the level of signal-to-noise ratio and relay locations.
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Adaptive 6.78-MHz ISM band wireless charging for small form factor receivers
(IEEE, 2017) Abouzeid, Mohamed Osama Hussein Soliman; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet; Abouzeid, Mohamed Osama Hussein Soliman
This paper presents a low cost wireless power transfer system tailored particularly for size limited insulation sealed wearable devices. The 5-V USB input system features a crystal oscillator as reference signal source, a class-E power stage, a transmit coil with tunable series resonance and a feedback path to tune the resonance for peak power transmission. Regardless of the receive coil, load, component variations or any external blockers, the system continuously targets peak power at the strict center frequency of 6.78 MHz for compliance with international frequency regulations. Design choices and experimental measurement results were presented along with detailed circuit diagrams. The design can transfer around 50mW power to a 15mm × 17mm × 1mm 40-turn receive coil in a charging pad area of as wide as 9cm × 9cm.
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Adaptive bit loading for multi-relay cooperative orthogonal frequency division multiple with imperfect channel estimation
(IEEE, 2012-08-14) Amin, O.; Ikki, S. S.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this study, the authors introduce an adaptive bit loading scheme for an amplify-and-forward orthogonal frequency division multiple cooperative system with relay selection. The proposed bit loading scheme maximises the throughput for a target error rate taking into account the quality of imperfect channel estimation. It relies on estimated channel state information (CSI) at the destination node and partial CSI (which involves the number of loaded bits) at the source node. The authors provide extensive Monte Carlo simulation results to demonstrate the throughput and the no-transmission probability performance of the proposed scheme and discuss the effect of various system and channel parameters on the performance.
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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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Adaptive density control in heterogeneous wireless sensor networks with and without power management
(IEEE, 2010-04-30) Machado, R.; Ansari, N.; Wang, G.; Tekinay, Şirin; Electrical & Electronics Engineering; TEKİNAY, Şirin
The authors study the design of heterogeneous two-tier wireless sensor networks (WSNs), where one tier of nodes is more robust and computationally intensive than the other tier. The authors find the ratios of densities of nodes in each tier to maximise coverage and network lifetime. By employing coverage processes and optimisation theory, the authors show that any topology of WSN derived from random deployments can result in maximum coverage for the given node density and power constraints by satisfying a set of conditions. The authors show that network design in heterogeneous WSNs plays a key role in determining key network performance parameters such as network lifetime. The authors discover a functional relationship between the redundancy, density of nodes in each tier for active coverage and the network lifetime. This relationship is much less pronounced in the absence of heterogeneity. The results of this work can be applied to network design of multi-tier networks and for studying the optimal duty cycles for power saving states for nodes in each tier.
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Adaptive free space optical communication system with multiple apertures
(2016) Nouri, Hatef; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Nouri, Hatef
In the current literature on free space optical (FSO) communication, typically open-loop designs are considered where the knowledge of channel state information is only available at the receiver. This is mostly favorable in the context of time-varying channels where the feedback implementation becomes problematic. Atmospheric turbulence channels in FSO systems exhibit quasi-static nature. The feedback information can be reliably transmitted, therefore makes possible the use of channel state information at the transmitter side. Such close-loop systems where transmission parameters are adaptively adjusted according to the channel conditions are widely used in radio frequency wireless communications. In this work, we consider adaptive transmission techniques in the context of FSO systems with multiple apertures and investigate their performance.
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Adaptive MIMO FSO communication systems with spatial mode switching
(IEEE, 2018-08) Nouri, Hatef; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Nouri, Hatef
In this paper, we propose an adaptive multiple-input multiple-output (MIMO) free-space optical (FSO) system with dynamic adaptation between spatial modes of operation. The proposed adaptive system supports three MIMO modes. In the spatial multiplexing mode, the system transmits independent parallel data streams over multiple apertures to increase data rate. In diversity mode, the system transmits coded streams through multiple apertures to extract diversity gains. In hybrid mode, a trade-off between diversity and multiplexing gains is targeted. For each operation mode, we first derive the outage probability for the MIMO FSO system over log-normal turbulence channels. Then, we formulate the design of an adaptive FSO system to select the MIMO mode that yields the highest throughput while satisfying a predefined target outage probability. Extensive numerical results are provided to demonstrate the performance of the proposed adaptive scheme.
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Adaptive modulation for FSO IM/DD systems with multiple transmitters and receivers
(IEEE, 2023-02) Nouri, Hatef; Sait, S. M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Nouri, Hatef
Atmospheric turbulence is a major impairment in free space optical (FSO) communication systems. Since turbulence induced fading exhibits quasi-static characteristics, reliable feedback of channel state information is possible allowing the implementation of adaptive transmission. In this letter, we consider multiple-input single-output (MISO) and single-input multiple-output (SIMO) FSO systems with pulse position modulation (PPM) and pulse amplitude modulation (PAM). We propose an adaptive algorithm where the modulation size/type is adjusted according to the channel fading conditions. We formulate the design of adaptive algorithm to maximize the spectral efficiency under peak and average power constraints while maintaining a targeted value of outage probability. We present extensive Monte Carlo simulations to demonstrate the performance of proposed adaptive scheme over turbulence channels.
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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.
Open Access
Adaptive OFDM-based acoustic underwater transmission: system design and experimental verification
(IEEE, 2017) Sadeghi, Mohammad; Elamassie, Mohammed; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Sadeghi, Mohammad; Elamassie, Mohammed
In this paper, we present the design and implementation of a software defined orthogonal frequency division multiplexing (OFDM)-based underwater acoustic (UWA) communication system with link adaptation. Our system implementation is based on the customized versions of National Instruments Universal Software Radio Peripheral (USRP). The modified USRPs are interfaced with hydrophone front-ends for acoustic transmission. We investigate the performance of various adaptive algorithms where both modulation order/type and power on each subcarrier are selected based on channel conditions in order to maximize throughput. The experimental in-pool test results verify the superiority of adaptive transmission.
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Adaptive power loading for multi-relay OFDM regenerative networks with relay selection
(IEEE, 2012-03) Amin, O.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we propose an adaptive power loading algorithm for an OFDM (orthogonal frequency division multiplexing)-based multi-relay regenerative network with relay selection. The proposed scheme is based on selecting the "best" relay(s) according to different strategies and distributing the power adaptively among the subcarriers of source and selected relay(s) as to minimize an upper bound on the bit error rate (BER). Our Monte Carlo simulation results demonstrate superior performance gains through power loading with respect to conventional equal power loading schemes. The effects of imperfect channel estimation and relay location on the BER performance are further discussed.
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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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