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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 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 and Compensation of Tx and Rx IQ Imbalances in Uplink IM-OFDMA Systems(Institute of Electrical and Electronics Engineers Inc., 2023) Alaca, Ozgur; Althunibat, Saud; Yarkan, Serhan; Miller, Scott L.; Qaraqe, Khalid A.Index modulation-based orthogonal division multiple access (IM-OFDMA) has recently been proposed as a potential technique for future wireless communication systems due to its su perior spectral efficiency and error performance over conventional multiple access schemes. However, its performance is still under investigation by researchers in light of a variety of scenarios and assumptions. Following this direction, in this Article, the individual and joint effects of the transmitter (Tx) and receiver (Rx) in-phase and quadrature imbalances (IQI) on the bit-error-rate (BER) per formance of the uplink IM-OFDMA scheme are investigated by considering whether each user’s RF front-end is identical or not. Moreover, to reduce the detrimental effect of IQI, a preamble-based estimation and compensation method is proposed for IM-OFDMA. Closed-form expressions for the average BER of IM-OFDMA are obtained by considering the physical effect of the Tx and Rx IQI. Also, using Monte Carlo simulations, the derived expressions are verified under different system configurations. Analytical and sim ulation results reveal that Tx and Rx IQI cause an error floor in the BER performance of IM-OFDMA schemes. However, the proposed estimation and compensation method not only reduces the impact of IQI but also leads to a better BER performance compared to the case of no IQI, which mainly refers to the frequency diversity caused by the IQI.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 CNN-Based Signal Detector for IM-OFDMA(Institute of Electrical and Electronics Engineers Inc., 2022) Alaca, Ozgur; Althunibat, Saud; Yarkan, Serhan; Miller, Scott L.; Qaraqe, Khalid A.The recently proposed index modulation-based up-link orthogonal frequency division multiple access (IM-OFDMA) scheme has outperformed the conventional schemes in terms of spectral efficiency and error performance. However, the induced computational complexity at the receiver forms a bottleneck in real-time implementation due to the joint detection of all users. In this paper, based on deep learning principles, a convolutional neural network (CNN)-based signal detector is proposed for data detection in IM-OFDMA systems instead of the optimum Maximum Likelihood (ML) detector. A CNN-based detector is constructed with the created dataset of the IM-OFDMA transmission by offline training. Then, the convolutional neural network (CNN)-based detector is directly applied to the IM-OFMDA communication scheme to detect the transmitted signal by treating the received signal and channel state information (CSI) as inputs. The proposed CNN-based detector is able to reduce the order of the computational complexity from O(n2n) to O(n2) as compared to the ML detector with a slight impact on the error performance.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 Experimental Evaluation of OFDM-Based Underwater Visible Light Communication System(Institute of Electrical and Electronics Engineers Inc., 2018) Hessien, Salah; Tokgöz, Sezer Can; Anous, Noha; Boyacı, Ali; Abdallah, Mohamed; Qaraqe, Khalid A.High-speed, reliable, flexible, and cost-effective underwater wireless communication systems have a wide variety of use in scientific, civilian, and commercial domains. Visible light communication (VLC) seems to be a promising candidate in satisfying majority of the requirements listed above. From this perspective, VLC could easily be deployed in heterogeneous wireless networking scenarios with high quality of service. Therefore, in this paper, an adapted LTE frame structure is implemented for underwater VLC (UVLC) system. The performance of UVLC system employing asymmetrically clipped optical orthogonal frequency division multiplexing modulation technique is practically tested by taking channel estimation and synchronization into account. Also, the effects of varying orthogonal frequency division multiplexing parameters on the system's signal-to-noise ratio and the bit-error-rate (BER) performances are studied. The implementation is tested for quadrature phase shift keying and 16-quadrature amplitude modulation techniques supporting both 128-and 1024-points fast Fourier transform configurations, which correspond to data rates of 1.92 and 15.36 Mbps, respectively. Experimental results show that BER could be reduced down to a level on the order of 10-6. © 2009-2012 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 Analysis of Uplink IM-OFDMA Systems in the Presence of CFO and Rx-IQI(IEEE Computer Society, 2023) Alaca, Ozgur; Althunibat, Saud; Yarkan, Serhan; Miller, Scott L.; Qaraqe, Khalid A.Index modulation-based orthogonal frequency divi sion multiple access (IM-OFDMA) has been recently proposed as a promising candidate for future wireless communication systems due to its superior spectral efficiency and error performance compared to conventional multiple access schemes. Therefore, it has been under investigation by researchers analyzing its performance considering different scenarios and assumptions. Following this direction, this paper presents the error perfor mance of the uplink IM-OFDMA in the presence of carrier fre quency offset (CFO) and receiver (Rx) in-phase and quadrature imbalance (IQI). In particular, the individual and joint effects of the CFO and Rx-IQI on the bit-error-rate (BER) performance of the uplink IM-OFDMA scheme are investigated, and then the IM-OFDMA is compared with the conventional OFDMA scheme by considering the detrimental effect of CFO and Rx IQI. Accordingly, this paper shows that IM-OFDMA achieves better BER performance results than the OFDMA scheme in the presence of CFO and Rx-IQI. However, the obtained results also reveal that the IM-OFDMA scheme is very sensitive to RF impairments even though it performs better than conventional OFDMA.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 Physical Layer Authentication for Uplink IM-OFDMA System(Institute of Electrical and Electronics Engineers Inc., 2023) Alaca, Ozgur; Althunibat, Saud; Yarkan, Serhan; Miller, Scott L.; Qaraqe, Khalid A.This study investigates the physical layer authentica tion (PLA) for the index modulation-based orthogonal frequency division multiple access (IM-OFDMA) systems by considering users’ in-phase and quadrature imbalances (IQI). Specifically, the PLA scheme is created for the uplink IM-OFDMA systems exploiting the IQI, forming at each user’s RF front-end as an identity. In a malicious user’s presence, the uplink IM-OFDMA scheme is examined, and the mathematical model for the proposed authentication scheme is established. Through the Monte Carlo simulation method, the performance of the proposed scheme is presented by employing two well-known performance metrics: authentication false rate and detection of malicious/authenticated users rate. The results for the proposed PLA scheme are demon strated under the different parameters of IM-OFDMA and IQI. The first-time implementation of a PLA scheme for the uplink IM-OFDMA system has shown promising results.Öğe Physical layer security of hybrid FSO-mmWave communications in presence of correlated wiretap channels(IEEE, 2021) Tokgoz, Sezer C.; Althunibat, Saud; Yarkan, Serhan; Qaraqe, Khalid A.Hybrid Free-Space Optical (FSO) and millimeter Wave (mmWave) systems have emerged as a promising candidate for high data rate wireless transmissions due to the unique complementary properties against the different channel and environment conditions. Consequently, in this study, we investigate the hybrid FSO-mmWave systems from a physical-layer security point of view in the presence of a hybrid type eavesdropper, where the communication between two legitimate peers takes place over both FSO and RF links simultaneously. We examine practical scenarios to eavesdrop the legitimate communication and discuss the effects of random radio power of mmWave link and optical irradiance of FSO link on the probability of achieving a secure transmission. The impact of the fundamental physical layer parameters on the secrecy performance of the hybrid system is analyzed by obtaining closed-form derivations of the probability of strictly positive secrecy capacity (SPSC) for correlated wiretap channels.Öğe Propeller Effects on mmWave UAV Channels: A Statistical and Empirical Modeling Study(IEEE, 2022) Cankurtaran, Halil Said; Kachroo, Amit; Choi, Wooyeol; O'Hara, John; Yarkan, Serhan; Qaraqe, Khalid A.; Hasna, Mazen Omar; Ekin, SabitIn this study, a statistical analysis of the simplest drone-to-drone millimeter waves (mmWave) communication channel is presented along with the field measurement results. The statistical analysis reveals that propeller blade rotation for the simplest transmission scenario could be modeled with angle modulation accompanied with an on-off process whose characteristics are determined by several factors including blade shape and material, vibrating body due to propeller thrust, antenna position and its possible wobble. The results are presented along with discussion and future directions.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.Öğe Secrecy Analysis of Uplink IM-OFDMA Systems in the Presence of IQ Imbalance(Institute of Electrical and Electronics Engineers Inc., 2023) Alaca, Ozgur; Althunibat, Saud; Yarkan, Serhan; Miller, Scott L.; Qaraqe, Khalid A.This paper introduces the secrecy analysis of the index modulation-based orthogonal frequency division multiple access (IM-OFDMA) schemes by considering the in-phase and quadrature imbalance (IQI) presence at the users’ RF front ends. In particular, by assuming the existence of an eavesdropper, the secrecy performance of the considered uplink multiple-access sys tem is investigated through the strictly positive secrecy capacity and secrecy outage probability, and closed-form expressions are derived for both quantities. Moreover, the secrecy performance is conducted regarding IQI compensation based on a preamble based estimation method. Further, analysis of the impact of the different parameters of IM-OFDMA, IQI, and estimation method is included via analytical and simulation-based results. The results reveal that IM-OFDMA is more reliable in secrecy performance than OFDMA, regardless of whether IQI is present. Also, IQI compensation can lead to a better secrecy performance compared to the case of no IQI.Öğe Secure Uplink IM-OFDMA With Artificial IQ Imbalance(Institute of Electrical and Electronics Engineers Inc., 2023) Alaca, Ozgur; Althunibat, Saud; Yarkan, Serhan; Miller, Scott L.; Qaraqe, Khalid A.This study proposes a novel secure uplink index modulation-based orthogonal frequency division multiple access (IM-OFDMA) systems using artificial in-phase and quadrature imbalance (A-IQI). The fact of the distinct A-IQI induced at the users’ end and the unpredictable allocation of users based on confidential data brings a different perspective on physical layer security. Accordingly, in this study, the non-identical effect of A-IQI is exploited to provide a physical-layer security scheme for the IM-OFDMA systems. Specifically, the estimation method is created with preamble data in order to achieve each user’s unique A-IQI information from a legitimate receiver. The A-IQI will help to secure the transmitted data against a potential eavesdropper, and hence, improving data confidentiality. The proposed scheme’s performance is analytically evaluated by deriving closed-form expressions of the average bit error rate (BER) at both the base station and the eavesdropper. The image rejection ratios of A-IQI and practical IQI are provided for IM-OFDMA to indicate the region of intentionally generated A-IQI. Under the different system model specifications of IM-OFDMA, the analytical results are provided with simulation results obtained using the Monte Carlo simulation method. Further, the proposed secure scheme is compared with the state of-the-art artificial noise method. Results reveal a significant improvement in the BER at the base station, accompanied by severe degradation in the BER at the eavesdropper.Öğe Statistical modeling of sand and dust storm attenuation(IEEE, 2022) Cankurtaran, Halil Said; Yarkan, Serhan; Hasna, Mazen Omar; Qaraqe, Khalid A.Propagation characteristics of electromagnetic (EM) waves such as amplitude, wavelength, and polarization can be altered by the medium that they travel. Such changes can decrease performance, and even lead to complete failures in communication networks. Hence, studies focusing on the propagation of EM waves under different atmospheric conditions such as rain, fog and snow have attracted researchers for decades. However, it is evident in both literature and standards that effects of sand and dust storms (SDS) on EM waves have not been understood well. Although proposed models consider randomness in the estimation of parameters, they end up with a deterministic solution without any uncertainty. However, uncertainty in the measurements makes the use of statistical models obligatory. In this study, a statistical model of attenuation is proposed solely based on frequency, and visibility. Moreover, in the proposed model, a region of uncertainty in estimations is provided by considering randomness in visibility measurements, whose characteristics are determined by the World Meteorological Organization and offthe-shelf measurement devices. Additionally, visibility and SDS statistics of Gulf area has been obtained by the analysis of NASA Hourly Global – Integrated Surface Database (ISD). Also, SDS attenuation is compared with rain and gaseous attenuation according to ITU recommendations.
