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Article Citation - WoS: 11Citation - Scopus: 15A Study on the Performance Evaluation of Wavelet Decomposition in Transient-Based Radio Frequency Fingerprinting of Bluetooth Devices(Wiley, 2022) Almashaqbeh, Hemam; Dalveren, Yaser; Kara, AliRadio frequency fingerprinting (RFF) is used as a physical-layer security method to provide security in wireless networks. Basically, it exploits the distinctive features (fingerprints) extracted from the physical waveforms emitted from radio devices in the network. One of the major challenges in RFF is to create robust features forming the fingerprints of radio devices. Here, dual-tree complex wavelet transform (DT-CWT) provides an accurate way of extracting those robust features. However, its performance on the RFF of Bluetooth transients which fall into narrowband signaling has not been reported yet. Therefore, this study examines the performance of DT-CWT features on the use of transient-based RFF of Bluetooth devices. Initially, experimentally collected Bluetooth transients from different smartphones are decomposed by DT-CWT. Then, the characteristics and statistics of the wavelet domain signal are exploited to create robust features. Next, the support vector machine (SVM) is used to classify the smartphones. The classification accuracy is demonstrated by varying channel signal-to-noise ratio (SNR) and the size of transient duration. Results show that reasonable accuracy can be achieved (lower bound of 88%) even with short transient duration (1024 samples) at low SNRs (0-5 dB).Master Thesis Doğrusal Kablosuz Algılayıcı Ağlar için Bir Eşzamanlama Algoritması ve Link Katmanı Protokolün Gerçeklenmesi(2020) Imran, Md Abdullah Al; Kara, AliEşzamanlama, Kablosuz Algılayıcı Ağlar (KAA) gibi dağıtılmış ağ sistemlerinde büyük önem taşımaktadır. KAA'lar dağıtılmış varlıkların ve olayların koordinasyonu ve korelasyonu için eşzamanlamayı yaygın olarak kullanır. Tipik olarak, enerji, depolama, hesaplama ve bant genişliği gibi sınırlı kaynaklar, ortam koşulları ve uygulamaya özel gereksinimlerle birleştirilmiş sınırlı özellikleri nedeniyle, geleneksel eşzamanlama yöntemlerini olanaksız kılabilir. Bu nedenle, form faktörü, hassasiyet, işlem süresi ve gücü, bellek, trafik, verimlilik ve ölçeklenebilirlik gibi çok sayıda tasarım parametresi, KAA'ların eşzamanlanmasında çalışılmaktadır. Bu tez çalışmasında, doğrusal KAA'larda eşzamanlanma çalışılmış ve buna yönelik bütünsel bir protokol geliştirilerek deneysel sonuçlar irdelenmektedir. Geliştirilen protokol, düğümler üzerinden veri toplama ve basit hata işleme özellikleri ile donatılmıştır. Deneysel çalışmalar sonucunda, geliştirilen protokol ve eşzamanlama yönteminin etkinliği irdelenmiş ve ağ ömrünün optimizasyonlar ile arttırılabildiği gösterilmiştir. Bu kapsamda, eşzamanlamadaki kritik parametreler olan ofset ve zamanda kaymaların eşzamanlama doğruluğuna etkisi incelenmiştir. Yapılan testlerde, daha küçük eşzamanlama pencereleri ile daha yüksek bir eşzamanlama doğruluğu sağlanmaktadır. Buna bağlı olarak enerji tüketimi de optimize edilebilmektedir.Master Thesis Milimetre Dalga Bandında Bina İçi İnsan Yoğun Ortamlarda Sinyal Seviyesi Değişkenliğinin Ölçümü ve Modellenmesi(2021) Benzaghta, Mohamed; Kara, AliMilimetre dalga spektrumu, beşinci nesil (5G) kablosuz teknoloji için en temel bileşendir. Milimetre dalga bandındaki radyo kanallarında insan vücudu önemli kesinti sebebi ve sinyal değişkenliği nedenidir. Bu tez çalışmasında, 28 GHz bandında 3 farklı insan modeli ile insan vücudunun sinyal kesintisine ve zayıflamasına etkisine yönelik ölçümler sunulmaktadır. Ayrıca farklı alıcı-verici anten yüksekliklerine göre insan vücudu yerleşiminin etkisi de incelenmektedir. Farklı boyutlarda insan vücutları ve yerleşimleri ile anten yükseklikleri dikkate alınarak Fresnel kırınım modelinin en iyi çalışan model olduğu gösterilmektedir. Ayrıca Fresnel kırınım modeli ile Geometrik Kırınım Teorisi (GKT) modellerini de kıyaslanmakta, öncekinin daha doğru ve gerçeklenmesi basit olduğu gösterilmektedir. İlave olarak tez çalışmasında, insan yoğunluğunun milimetre dalga yayılımında kesinti süresi ve derinliğine yönelik istatistiklerde ölçümler yoluyla çıkarılmaktadır. Bu kapsamda, 3 ve 6 kişinin bir ofis ortamında olağan günlük hareket rotaları dikkate alınarak radyo linkini kesmesine yönelik istatistikler ilk defa bu tez çalışmasında sunulmaktadır.Article Citation - WoS: 17Citation - Scopus: 31Deep Learning-Based Vehicle Classification for Low Quality Images(Mdpi, 2022) Tas, Sumeyra; Sari, Ozgen; Dalveren, Yaser; Pazar, Senol; Kara, Ali; Derawi, MohammadThis study proposes a simple convolutional neural network (CNN)-based model for vehicle classification in low resolution surveillance images collected by a standard security camera installed distant from a traffic scene. In order to evaluate its effectiveness, the proposed model is tested on a new dataset containing tiny (100 x 100 pixels) and low resolution (96 dpi) vehicle images. The proposed model is then compared with well-known VGG16-based CNN models in terms of accuracy and complexity. Results indicate that although the well-known models provide higher accuracy, the proposed method offers an acceptable accuracy (92.9%) as well as a simple and lightweight solution for vehicle classification in low quality images. Thus, it is believed that this study might provide useful perception and understanding for further research on the use of standard low-cost cameras to enhance the ability of the intelligent systems such as intelligent transportation system applications.Article Citation - WoS: 5Citation - Scopus: 6On the Design and Effectiveness of Simulink-Based Educational Material for a Communication Systems Course(Wiley, 2020) Coruk, R. Busra; Yalcinkaya, Bengisu; Kara, AliThe methods used in engineering education have gained diversity in parallel with rapidly evolving technology. New technological methods along with the traditional methods have been adopted for undergraduate education. Today, Simulink-based educational materials are used in many fields in engineering education. However, in the literature, the contribution of such educational materials to the learning process has not been measured thoroughly. This study presents a comprehensive measurement method to improve the created course material and show the effectiveness of developed course material in students' success. First, educational material was developed for an undergraduate electrical engineering course: communication systems. A feedback group made up of diverse student learners was employed extensively in the material development phase. Next, the impact of the developed material on the success of the students was examined using both qualitative and quantitative measurement tools including questionnaires, one-to-one interviews, and class and university level anonymous surveys. This also included students' performance regarding laboratory quizzes and achievement of course learning outcomes. Overall, the measurement results show that the course material increased students' success in the course. Moreover, students' general perception of the course material was positive.Article Citation - WoS: 5Citation - Scopus: 7On the Classification of Modulation Schemes Using Higher Order Statistics and Support Vector Machines(Springer, 2022) Coruk, Remziye Busra; Gokdogan, Bengisu Yalcinkaya; Benzaghta, Mohamed; Kara, AliThe recognition of modulation schemes in military and civilian applications is a major task for intelligent receiving systems. Various Automatic Modulation Classification (AMC) algorithms have been developed for this purpose in the literature. However, classification with low computational complexity as well as reasonable processing time is still a challenge. In this paper, a feature-based approach along with various classifiers is employed based on statistical features as well as higher-order moments and cumulants. An over-the-air (OTA) recorded dataset consisting of four analog and ten digital modulation schemes are used for testing the proposed method at 0-20 dB SNR. The overall accuracy for quadratic Support Vector Machine (SVM) is found to be as high as 98% at 10 dB. The comparison of the results with other AMC papers published in the literature indicates that the proposed method present higher accuracy, especially for realistic channel induced OTA dataset.Article Citation - WoS: 14Citation - Scopus: 16Reliability of Linear Wsns: a Complementary Overview and Analysis of Impact of Cascaded Failures on Network Lifetime(Elsevier, 2022) Carsancakli, Muhammed Fatih; Imran, Md Abdullah Al; Yildiz, Huseyin Ugur; Kara, Ali; Tavli, BulentLinear Wireless Sensor Networks (LWSNs) are used in applications where deployment scenarios necessitate sensor nodes to be placed over a line topology. However, such a deployment raises reliability concerns because almost all the nodes in the network are critical with respect to the survivability of the LWSN. It is possible that an LWSN can stay connected even if a subset of the nodes are eliminated, yet, the potential reduction in Network Lifetime (NL) due to such an occurrence can be significant. In this study, after presenting a concise survey of the literature on LWSN reliability, we present an elaborate optimization framework to model the operation of an LWSN, which is built upon a comprehensive system model. Our framework encompasses three transmission power and packet size assignment strategies, which are instrumental in characterizing LWSN behavior. Furthermore, we utilized two-node failure models (i.e., random and coordinated) to assess the vulnerability of LWSNs from multiple perspectives. The results of this study reveal that the impact of coordinated node failures on NL is more severe than the impact of random node failures to such extent that in strongly connected LWSNs, the percentage decrease in NL due to coordinated node failures can be more than a magnitude higher than the NL decrease due to random node failures.Article Citation - WoS: 8Citation - Scopus: 15Distributed denial-of-service attack mitigation in network functions virtualization-based 5G networks using management and orchestration(Wiley, 2021) Koksal, Sarp; Dalveren, Yaser; Maiga, Bamoye; Kara, AliThe fifth generation (5G) technology is expected to allow connectivity to billions of devices, known as Internet of Things (IoT). However, IoT devices will inevitably be the main target of various cyberattack types. The most common one is known as distributed denial-of-service (DDoS) attack. In order to mitigate such attacks, network functions virtualization (NFV) has a great potential to provide the benefit of elasticity and low-cost solutions for protecting 5G networks. In this context, this study proposes a new mechanism developed to mitigate DDoS attacks in 5G NFV networks. The proposed mechanism utilizes intrusion prevention system's (IPS) virtual machines (VMs) to intercept the queries. Based on the volume of DDoS traffic, IPS's VMs are dynamically deployed by means of management and orchestration (MANO) in order to balance the load. To evaluate the effectiveness of the mechanism, experiments are conducted in a real 5G NFV environment built by using 5G NFV environment tools. To our best knowledge, this is the first time that NFV-based mechanism is experimentally tested in a real 5G NFV environment for mitigating DDoS attacks in 5G networks. The experimental results verify that the proposed mechanism can mitigate DDoS attacks effectively.Article W-Band RCS Prediction of Small Objects: Comparing Two Widely Used Methods with Experimental Validation(Gazi University, 2025) Kara, Ali; Aydın, Elif; Yardım, Funda Ergün; Sezgin, DenizThis paper compares the accuracy of Shooting and Bouncing Rays and Electric Field Integral Equation methods for Radar Cross Section prediction of small objects at 77-81 GHz band. Existing studies on RCS prediction methods often lack comprehensive comparisons between computational and experimental results, particularly for small objects measured with a 77 GHz radar. This study addresses this gap by presenting an in-depth analysis of both simulation and measurement data. In this work, three targets with varying geometries and materials were measured with a frequency modulated continuous wave radar and simulated using Ansys HFSS and CST Studio Suite. The measurements were performed with a commercial off-the-shelf (COTS) frequency modulated continuous wave radar operating at 77–81 GHz. This study aims to emphasize the importance of considering both efficiency and accuracy when opting for an RCS prediction method. Overall, the outcomes of both methods have largely demonstrated good alignment. It has been noted that, while Shooting and Bouncing Rays method offers promising time-saving advantages, Electric Field Integral Equation method remains a valuable tool for complex geometries where precise results are crucial.Article Citation - WoS: 3Citation - Scopus: 3Modeling and Measurement of Human Body Blockage Loss at 28 Ghz(Taylor & Francis Ltd, 2023) Benzaghta, Mohamed; Gokdogan, Bengisu Yalcinkaya; Coruk, Remziye Busra; Kara, AliMillimeter-wave (mm-Wave) spectrum is an essential enabler to the fifth generation (5G) wireless technology. Humans are one of the most noticeable blockers that cause temporal variation in indoor radio channels. This paper presents human blockage measurements at 28 GHz, with several humans of different sizes. The effect of the crossing orientations of the human bodies is investigated for three different transmitter heights. A human blockage model based on the Fresnel diffraction scheme is shown to be applicable in estimating the human blockage loss in indoor radio links considering various body sizes, different crossing orientations, and different transmitter heights. The findings reported in this paper could help improve indoor radio channel models at 28 GHz bands for 5G technologies considering the presence of human body blockages.
