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Öğe ACO-OFDM Transmission over Underwater Pipeline for VLC-based Systems(Institute of Electrical and Electronics Engineers Inc., 2019) Tokgöz, Sezer Can; Boluda-Ruiz R.; Yarkan, Serkan; Qaraqe, Khalid A.Visible light communication (VLC) technology supports high-speed, reliable, flexible, and cost-effective designs which are demanded most of the underwater wireless communication (UWC) systems. Therefore, in this study, a comprehensive and completely adaptive asymmetrically clipped optical-OFDM based underwater VLC system is designed and demonstrated with widely used and commercially available light emitting diodes (LEDs) and photodiodes (PDs). The designed system is evaluated under twelve different test scenarios with varying fundamental system parameters such as sampling rate, modulation technique and order, and coding rates. In the light of experimental results, it is shown that the system is capable of transmitting and receiving the data supporting both QPSK and 16-QAM modulation techniques with sampling rates of 2 Mbps, 5 Mbps, and 10 Mbps. The experimental results also show that bit-error-rate (BER) could still be maintained on the order of 10-6 over 6.5 m long underwater pipeline channel. In addition, the performance analyses of cold white, blue and green LEDs at wavelengths of 430 nm, 470 nm, and 530 nm, respectively, are evaluated and compared. Their advantages and drawbacks are discussed in detail. © 2019 IEEE.Öğe The advances of fronthaul and backhaul communication for 5G and beyond(Elsevier B.V., 2019) Serpedin, Erchin; Ekti, Ali Rıza; Boyacı, Ali; Imran M.A.; Aydın, Muhammed Ali; Yarkan, Serkan[Abstract Not Available]Öğe Analysis and characterization of the impact of frequency-selective interference on reporting period for next-generation wireless networks(2012) Yarkan, Serkan; Qaraqe, Khalid A.In next-generation wireless networks (NGWNs), user equipment (UE) are required to send reports on their channel quality indicator (CQI) to maintain the overall service performance. In this regard, UE reports such as CQIs play a crucial role in interference management in NGWNs. Short reporting periods cause excessive amount of over-the-air signaling (overhead) in the network and negatively impact the battery life of UE, whereas long reporting periods cause interference management procedures not to instantaneously react to dynamically changing conditions. Therefore, in this study, a reporting mechanism that changes the reporting period in an adaptive manner is proposed. Interference is modeled as a composite stochastic process, which includes both shadowing and frequency-selective fading together. It is shown that the decorrelation distance of shadowing is the key parameter for such an adaptive reporting. Practical scenarios are considered in simulations, including different environmental and mobile speed classes. Performance evaluation is established by comparing the signaling overhead of the method proposed with those of traditional strategies such as deterministic/periodic and random reporting. Numerical and experimental results are presented, along with relevant discussions. © 2012 IEEE.Öğe Analysis of mobility impact on interference in cognitive radio networks(Elsevier B.V., 2013) Ekti, Ali Rıza; Yarkan, Serkan; Qaraqe, Khalid A.; Serpedin, Erchin; Dobre, O.A.Cognitive radio (CR) technology seems to be a promising candidate for solving the radio frequency (RF) spectrum occupancy problem. CRs strive to utilize the white holes in the RF spectrum in an opportunistic manner. Because interference is an inherent and a very critical design parameter for all sorts of wireless communication systems, many of the recently emerging wireless technologies prefer smaller size coverage with reduced transmit power in order to decrease interference. Prominent examples of short-range communication systems trying to achieve low interference power levels are CR relays in CR networks and femtocells in next generation wireless networks (NGWNs). It is clear that a comprehensive interference model including mobility is essential especially in elaborating the performance of such short-range communication scenarios. Therefore, in this study, a physical layer interference model in a mobile radio communication environment is investigated by taking into account all of the basic propagation mechanisms such as large- and small-scale fading under a generic single primary user (PU) and single secondary user (SU) scenario. Both one-dimensional (1D) and two-dimensional (2D) random walk models are incorporated into the physical layer signal model. The analysis and corresponding numerical results are given along with the relevant discussions. © 2012 Elsevier B.V.Öğe A detection and identification method based on signal power for different types of Electronic Jamming attacks on GPS signals(Institute of Electrical and Electronics Engineers Inc., 2019) Elezi, Esat; Çankaya, Göksel; Boyacı, Ali; Yarkan, SerkanIn this work, a detection method is proposed for Global Positioning System (GPS) jamming attacks. GPS signals despite being an indispensable part of our life, come with a great weakness which is having a weak signal. This makes it vulnerable to external attacks like jamming and spoofing. The purpose of this study is to properly be able to identify the type of jammer affecting the GPS signal so that proper defensive measures can be applied to ensure the safety of the signal. This work is the second phase of a study based on the effect of Electronic Jammers (EJ) on GPS signals. Four different EJ are studied and the purpose is to be able to identify which one of them is affecting the signal in order to apply the appropriate defensive measure. In order to achieve this, the power of the signal is analyzed in order to achieve a threshold/interval to be able to identify the type of jammer. All of the simulations and measurements are carried on MatLAB. © 2019 IEEE.Öğe Dynamic feature selection for spam detection in twitter(Springer Verlag, 2019) Karakaşlı M.S.; Aydın, Muhammed Ali; Yarkan, Serkan; Boyacı, AliSocial Networks continue to increase their popularity day by day. With the widespread availability of Internet access, interest of people in social networks has also increased significantly. The fact that, popularity of social media makes it tempting to use social media platforms for bad purposes. Malicious people are attempting to gain unfair profits by using fake accounts and various techniques. Among these initiatives, SPAM is one of the most frequently used methods. Today, SPAM attacks on social networks are increasing and many social network users are exposed to this and similar attacks. To identify SPAM users among billions of social network users, the examination of massive amounts of data requires a challenging large-scale data analysis. In this study, we group similar Twitter users and introduce a dynamic feature selection technique that use different features for each user groups instead of use static feature set and apply machine learning algorithms to classify spam users on Twitter. © 2019, Springer Nature Singapore Pte Ltd.Öğe The effect of Electronic Jammers on GPS Signals(Institute of Electrical and Electronics Engineers Inc., 2019) Elezi, Esat; Çankaya, Göksel; Boyacı, Ali; Yarkan, SerkanGlobal Positioning System (GPS) has found wide application in many areas of our daily life. However, it has a very week signal making it vulnerable to external attacks like blocking, jamming or spoofing. Jamming is a technique that blocks the GPS from receiving location signals making it nonfunctional. In this paper, several Electronic Jamming methods are introduced and a comparison is done between them to observe which of them has the most jamming effect on the GPS receiver. The methods that will be analyzed are Pulse Jamming (PJ), Spot Jamming (SJ), Barrage Noise Jamming (BNJ) and Sweep Jamming (SWJ). The Jamming signals are modelled using MATLAB and their effect on the GPS receiver is quantified by observing their Bit Error Rate (BER) for different Jamming to Signal ratio. © 2019 IEEE.Öğe Effects of mobility on uplink interference for short-range cognitive radio networks(2012) Ekti, Ali Rıza; Yarkan, Serkan; Qaraqe, Khalid A.; Serpedin, ErchinCognitive radio (CR) has attracted significant attention due to expected radio frequency (RF) spectrum scarcity with ever-increasing demands. CR networks, which strive to utilize opportunistically the RF spectrum, require new ways of looking at interference in wireless networks. Since a decrease in transmit power translates into an increase in energy efficiency and a decrease in RF interference, communication ranges have been shrinking dramatically in recently emerging wireless technologies. Prominent examples of decrease-in-transmit-power strategies are CR relays in CR networks and femtocells in next generation wireless networks (NGWNs). Therefore, the impact of mobility especially with respect to relatively small displacements needs to be investigated. In this study, a comprehensive interference model is considered and examined by taking into account all of the basic propagation mechanisms such as large- and small-scale fading under a generic single secondary user (SU) and single primary user (PU) scenario. The analysis and corresponding numerical results are given and discussed. © 2012 IEEE.Öğe Energy-Per-Bit Performance Analysis of Relay-Assisted Power Line Communication Systems(Institute of Electrical and Electronics Engineers Inc., 2018) Rabie K.M.; Adebisi, Bamidele; Gacanin H.; Yarkan, SerkanThis paper provides a comprehensive analysis of the energy efficiency performance for different relaying schemes over the non-Gaussian power line communication (PLC) channel. Specifically, amplify-and-forward (AF), decode-and-forward (DF), selective DF (SDF) and incremental DF (IDF) relaying systems are investigated. For a more realistic scenario, the power consumption profile of the PLC modems is assumed to consist of both dynamic and static power. For each system, we derive accurate analytical expressions for the outage probability and the minimum energy-per-bit performance. For the sake of comparison and completeness as well as to quantify the achievable gains, we also analyze the performance of a single-hop PLC system. Monte Carlo simulations are provided throughout this paper to validate the theoretical analysis. Results reveal that AF relaying over the non-Gaussian PLC channel does not always enhance the performance and that the IDF PLC system offers the best performance compared to all other schemes considered. It is also shown that increasing the channel variance, which is related to the PLC network branching, and impulsive noise probability can considerably deteriorate the system performance. Furthermore, when the end-to-end distance is relatively small, it is found that the single-hop PLC approach can perform better than AF relaying. © 2018 IEEE.Öğe A generic measurement setup for implementation and performance evaluation of spectrum sensing techniques: Indoor environments(Institute of Electrical and Electronics Engineers Inc., 2015) Yarkan, SerkanSpectrum sensing is the preeminent task of both cognitive radios and next generation wireless networks. There are various spectrum sensing techniques and methods presented in the literature. Performance evaluation of these techniques and methods is an important issue from the perspective of both the receiver and system design. In this regard, experimental studies that involve implementation, measurement, and performance evaluation of these methods under realistic conditions are of paramount importance, along with the relevant theoretical work. Therefore, in this paper, a generic measurement methodology is proposed to implement various spectrum sensing techniques and evaluate their performances. Mobile and immobile scenarios; line-of-sight and non-line-of-sight conditions; and presence/absence of perfect spectral knowledge cases are all investigated for both energy detector (first-) and second-order statistical receivers. Results are presented along with relevant discussions. Future directions are outlined as well. © 2014 IEEE.Öğe Identification of shadowed fast fading interference in celullar mobile radio systems(2013) Boyacı, Ali; Yarkan, Serkan; Zaim, Abdül HalimIn this study, a method that identifies shadowed fast fading interference is proposed on downlink transmission for frequency division duplexing (FDD)-based cellular mobile radio communications systems. The method proposed exploits the independence of shadowing and fast-fading processes along with the difference between their occurrence scales in spatial dimension and provides an analytical approach to identify the interference with the aid of a metric defined. © 2013 IEEE.Öğe An IEEE 802.11x implementation for V2X communications towards IoT and big data(Springer Verlag, 2019) Serin, Dilara Albayrak; Boyacı, Ali; Özpınar, Alper; Yarkan, SerkanGreen transportation is an integral part of green environment concept. Next generation transportation systems are desired to achieve high performances with reduced fuel consumption and carbon emission. In this regard, vehicle maintenance status along with some other critical diagnostic data should steadily be checked and tracked. It is known that vehicles that are poorly maintained or not maintained in a timely manner lead to both emissions exceeding the standards and low performance. Vehicle telematics along with some other conveniences such as infotainment systems, location–based services and applications are expected to improve safety, availability, and reliability of next generation transportation systems. From this perspective, intelligent transport systems (ITS) seems to be a promising solution candidate which encompasses all of the aforementioned topics as well as vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), and vehicle-to-cloud (V2C) opportunities. Therefore, in this study, a conceptual model that links vehicle telematics to the cloud along with V2V communications facility is proposed and a prototype based on IEEE 802.11x protocol suite is implemented. Mobile data collection and measurements are obtained. Results are presented along with relevant discussions as well as the end point storage and usage of the data are introduced. In the proposed model, the mobile data are transferred to cloud computing platform to create the big data for further research opportunities for car manufacturers, policy makers, and researchers with the concern of ethics and security issues. © 2019, Springer Nature Singapore Pte Ltd.Öğe Monitoring, surveillance, and management of the electromagnetic spectrum: Current issues in electromagnetic spectrum monitoring(Istanbul University, 2018) Boyacı, Ali; Ekti, Ali Rıza; Yarkan, Serkan; Aydın, Muhammed AliThis paper discusses the current aspects of the surveillance and management of the electromagnetic spectrum under various topics that are vital to wireless communications. On the basis of the recent technological advancements in conjunction with the discussions on the global approaches toward electromagnetic spectrum monitoring, the paper addresses short-, medium-, and long-term strategies in wireless communications for monitoring, governing, and managing the electromagnetic spectrum of leading countries and multinational organizations. Furthermore, it proposes a novel spectrum monitoring strategy for next-generation wireless systems and outlines the implications of the proposed strategy. © Copyright 2018 by Electrica.Öğe On error variance for autoregressive process-based spectrum occupancy prediction with energy detector for cognitive networks(Institute of Electrical and Electronics Engineers Inc., 2015) Boyacı, Ali; Akı, Fatma Nur; Yarkan, SerkanSpectrum sensing is considered to be the most important task for both cognitive radio (CR) networks and next generation wireless networks (NGWNs). Spectrum sensing operation allows wireless nodes to identify vacant bands so that radio frequency (RF) spectrum could be used more efficiently. It is clear that a powerful spectrum sensing method equipped with an effective prediction strategy will carry utilization of the RF spectrum to the utmost level. Analysis of the performances of prediction strategies plays a critical role in quantifying the efficiency of the overall spectrum sensing operation. Therefore, in this study, autoregressive process-based prediction strategy for energy detection is investigated. It is shown that prediction error variance relies heavily on both the intercept of the autoregressive model and the threshold value selected. Theoretical findings are validated and verified by measurement data which are obtained by capturing the complete Global System for Mobile (GSM) downlink band at Nyquist rate of in-phase/quadrature (I/Q) level. Results and relevant discussions are provided along with future research directions as well. © 2015 IEEE.Öğe On the Investigation of Bandwidth Allocation for Short-Range and Long-Range Heterogeneous Wireless Networks(Institute of Electrical and Electronics Engineers Inc., 2019) Kazda?, C.; Alaca, Özgür; Ekti, Ali Rıza; Yarkan, SerkanIt is clear that heterogeneous wireless network (HetNet) will be an essential deployment mode of next generation wireless networks. There are various HetNet layouts present in the literature such as coexistences of mid-range networks and long-range networks. With the recent advances in digital technology, mobile terminals (MTs), which are the integral part of HetNet, have multiple radio interfaces which brings the concept of multi-homing capabilities. As a result, MTs are able to establish connections to multiple wireless networks. MTs also can increase the bandwidth by benefiting from all these available networks around to meet the requirements of demanding applications such as high definition multimedia stream. Such a diverse set of scenarios brings about a critical challenge regarding how MT assignment and bandwidth allocation could be carried out jointly in HetNet. In contrast to the traditional layouts present in the literature, in this study, a more realistic scenario is investigated by considering the coexistence of mid- and long-range networks with an extension of the presence of short-range networks. Therefore, as a solution mixed integer non-linear program (MINLP) approach is proposed by incorporating the connection interfaces of Bluetooth, wireless-fidelity (WiFi) and cellular systems. It is shown with both the aid of mathematical analysis and the support of numerical results that the method proposed attains suboptimal MT assignment and bandwidth allocation jointly with significantly reduced computational complexity. © 2019 IEEE.Öğe An online adaptive cooperation scheme for spectrum sensing based on a second-order statistical method(2012) Yarkan, Serkan; Töreyin, Behçet Uğur; Qaraqe, Khalid A.; Çetin, A. EnisSpectrum sensing is one of the most important features of cognitive radio (CR) systems. Although spectrum sensing can be performed by a single CR, it is shown in the literature that cooperative techniques, including multiple CRs/sensors, improve the performance and reliability of spectrum sensing. Existing cooperation techniques usually assume a static communication scenario between the unknown source and sensors along with a fixed propagation environment class. In this paper, an online adaptive cooperation scheme is proposed for spectrum sensing to maintain the level of sensing reliability and performance under changing channel and environmental conditions. Each cooperating sensor analyzes second-order statistics of the received signal, which undergoes both correlated fast and slow fading. Autocorrelation estimation data from sensors are fused together by an adaptive weighted linear combination at the fusion center. Weight update operation is performed online through the use of orthogonal projection onto convex sets. Numerical results show that the performance of the proposed scheme is maintained for dynamically changing characteristics of the channel between an unknown source and sensors, even under different physical propagation environments. In addition, it is shown that the proposed cooperative scheme, which is based on second-order detectors, yields better results compared with the same fusion mechanism that is based on conventional energy detectors. © 2012 IEEE.Öğe Performance Evaluation of White LED-based OFDM-VLC Systems with Blue Filters: Experimental Study(Institute of Electrical and Electronics Engineers Inc., 2019) Tokgöz, Sezer Can; Anous, Noha; Yarkan, Serkan; Boyacı, Ali; Qaraqe, Khalid A.This paper experimentally evaluates the performance of visible light communications (VLC) systems employing phosphor-coated white light emitting diodes (LEDs). Phosphor-coated white LEDs though widely used commercially, are known to limit the system's maximum data rate. Such a limitation is conventionally treated by two methods: either adding a blue filter at the receiver or using orthogonal frequency multiplexing (OFDM) digital modulation technique. Adding a blue filter at the receiver is controversial in current literature and claimed to decrease the signal-to-noise-ratio (SNR) or to be inefficient if OFDM is employed. Hence, in this work, we experimentally evaluate the above OFDM based VLC system with and without a blue filter. Results are compared to prove that adding a blue filter at the receiver boosts SNR and bit-error-rate (BER) values. This, in turn, helps maximize the data rates supported by such systems. The addition of a blue filter is tested with different modulation techniques. Results in this work remove the controversy around employing a blue filter in OFDM based VLC systems with phosphor-coated white LEDs. Improved BERs and SNRs at high data rates are observed. Specifically, this experimental work demonstrates a BER enhancement of ?40% and ?15% for data rates up to 12 Mbps when a blue filter is added. © 2019 IEEE.Öğe Performance improvement of white led-based vlc systems using blue and flattening filters(Institute of Electrical and Electronics Engineers Inc., 2019) Tokgöz, Sezer Can; Anous, Noha; Yarkan, Serkan; Khalil D.; Qaraqe, Khalid A.This paper proposes a means to maximize the data rate supported by a visible light communication (VLC) system. The investigated VLC system uses phosphor-coated white light emitting diodes (LEDs), which are common in existing illumination systems but are also known to limit the communication system's data rate. In this paper, we propose a remedy to such a limitation by adding a response-flattening filter at the receiver's end to mitigate the effect of the slow yellow phosphor spectral component. An experimental study is conducted to evaluate the validity of the proposed remedy. The resulting performance is compared with an existing remedy that involves adding a blue filter at the receiver. Off-the-shelf commercial filters are used in the experiment. Enhanced bit-error-rates (BERs) and signal-to-noise ratios (SNRs) at high data rates are observed. Specifically, our experimental work demonstrates that BER is enhanced by 40% and 15% for data rates up to 12 Mbps when responseflattenina filter and blue filter are adopted, respectively. © 2019 IEEE.Öğe Preface(Springer Verlag, 2019) Boyacı, Ali; Ekti, Ali Rıza; Aydın, Muhammed Ali; Yarkan, Serkan[Abstract Not Available]Öğe Real-Time Data Transmission over PSTNs on Physical Layer(Institute of Electrical and Electronics Engineers Inc., 2019) Tokgöz, Sezer Can; Yarkan, Serkan; Miller S.; Qaraqe, Khalid A.Widespread use of data communications applications along with recently emerging high-performance telecommunication techniques enforce people, organizations, and even countries to rely on the infrastructures with which these communication services are provided. It is clear that dependence on infrastructure leads to critical concerns about security, reliability, authenticity, and integrity of the data carried over the same infrastructure. Therefore, a prototype based on digital signal processor (DSP) is implemented, which operates on public switched telephone network (PSTN) lines in accordance with the regional (ITU-R, European) standards, supports steganographic information exchange, and allows both analog and digital data transfer in several security levels. In addition, statistical characteristics of the physical layer channel are identified via measurements and communication between two end nodes is established with the use of DSPs by taking into account the behaviors of the switching center. Future directions are provided in light of the results and relevant discussions as well. © 2019 IEEE.
