15 results
Search Results
Now showing 1 - 10 of 15
Article Citation - WoS: 1Citation - Scopus: 2A Miniaturized Multi-Layer Microstrip Antenna for Linear Wireless Sensor Network Monitoring Systems(Gazi Univ, 2022) Kara, Ali; Aydın, Elif; Benzaghta, Mohamed; Er, Burak; Bilgin, GulsimaThis article presents a sub-GHz ISM band microstrip patch antenna based on the use of multi-layer compact structure, which overcomes the shortcomings of typical microstrip antennas such as low gain and high resonant frequency. The antenna was simulated using an electromagnetic simulator, ANSYS HFSS, and fabricated on two different substrates: RT Duroid 5880 and FR4 epoxy with a compact size of 100 x 100 x 8 mm3 (0.29λ × 0.29λ × 0.02λ). The simulated results of the antenna were then compared with the measured ones, and the two were observed to have a reasonable agreement. The proposed antenna operates in the sub-GHz license-free ISM band (862-875 MHz), with a gain value of 2.92 dB. Two prototypes of the proposed antenna were fabricated and used in a Linear Wireless Sensor Networks (LWSNs) monitoring system. Results show that the proposed antenna is a good candidate for those types of LWSNs systems.Article ISAR Imaging of Drone Swarms at 77 GHz(Tubitak Scientific & Technological Research Council Turkey, 2025) Coruk, Remziye Busra; Kara, Ali; Aydin, ElifThe proliferation of easily available, internet-purchased drones, coupled with the emergence of coordinated drone swarms, poses a significant security threat for airspace. Detecting these swarms is crucial to prevent potential accidents, criminal misuse, and airspace disruptions. This paper proposes a novel inverse synthetic aperture radar (ISAR) imaging technique for high-resolution reconstruction of drone swarms at 77 GHz millimeter wave (mmWave) frequency, offering a valuable tool for military and defense antidrone systems. The key parameters affecting down-range and cross-range resolution (0.05 m), ultimately enabling the generation of detailed ISAR images are discussed. Here, we create diverse scenarios encompassing various swarm formations, sizes, and payload configurations by employing ANSYS simulations. To enhance image quality, different window functions are evaluated, and the Hamming window is selected due to its highest peak signal-to-noise ratio (PSNR) (16.3645) and structural similarity (SSIM) (0.9067) values, ensuring superior noise reduction and structural preservation. The results demonstrate that the effectiveness of high-resolution ISAR imaging in accurately detecting and characterizing drone swarms pave the way for enhanced airspace security measures.Article Citation - WoS: 27Citation - Scopus: 35A Wavelet-Based Feature Set for Recognizing Pulse Repetition Interval Modulation Patterns(Tubitak Scientific & Technological Research Council Turkey, 2016) Gencol, Kenan; At, Nuray; Kara, AliThis paper presents a new feature set for the problem of recognizing pulse repetition interval (PRI) modulation patterns. The recognition is based upon the features extracted from the multiresolution decomposition of different types of PRI modulated sequences. Special emphasis is placed on the recognition of jittered and stagger type PRI sequences due to the fact that these types of PRI sequences appear predominantly in modern electronic warfare environments for some specific mission requirements and recognition of them is heavily based on histogram features. We test our method with a broad range of PRI modulation parameters. Simulation results show that the proposed feature set is highly robust and separates jittered, stagger, and other modulation patterns very well. Especially for the stagger type of PRI sequences, wavelet-based features outperform conventional histogram-based features. Advantages of the proposed feature set along with its robustness criteria are analyzed in detail.Article Citation - WoS: 4Citation - Scopus: 8Remote Rf Laboratory Requirements: Engineers' and Technicians' Perspective(Anadolu Univ, 2007) Cagiltay, Nergiz Ercil; Aydin, Elif Uray; Kara, Ali; Department of Electrical & Electronics Engineering; Software EngineeringThis study aims to find out requirements and needs to be fulfilled in developing remote Radio Frequency (RF) laboratory. Remote laboratories are newly emerging solutions for better supporting of e-learning platforms and for increasing their efficiency and effectiveness in technical education. By this way, modern universities aim to provide lifelong learning environments to extend their education for a wider area and support learners anytime and anywhere when they need help. However, as far as the authors concern, there is no study investigating the requirements and needs of remote laboratories in that particular field in the literature. This study is based on electrical engineers' and technicians' perspectives on the requirements of a remote laboratory in RF domain. Its scope covers investigation of the participants' perceptions toward computer mediated communication and it attempts to answer the questions: which studying strategies are preferred by the learners and what kind of RF laboratory content should be provided. The analysis of the results showed that, geographic independence, finding quickly the elements of past communication and temporal independence are declared as the most important advantages of computer-mediated communication. However, reading significant amount of information is a problem of these environments. In the context of how to show the content, respondents want to see shorter text on the screen. Therefore the instructions should include little amount of text and must be supported with figures and interactive elements. The instructional materials developed for such learner groups should support both linear and non-linear instructions. While analyzing the content to be provided, we have seen that, most of the participants do not have access to high level equipments and traditional experiments are considered as the necessary ones for both engineers and technicians.Article Quality of Service Assessment: a Case Study on Performance Benchmarking of Cellular Network Operators in Turkey(2015) Kadıoğlu, Rana; Dalveren, Yaser; Kara, AliAbstract: This paper presents findings on performance benchmarking of cellular network operators in Turkey. Bench- marking is based on measurements of standard key performance indicators (KPIs) in one of the metropolitan cities of Turkey, Ankara. Performance benchmarking is formulated by incorporating customer perception by conducting surveys on how important KPIs are from the user s point of view. KPIs are measured, with standard test equipment, by drive test method on specified routes. According to the performance benchmarking results, the GSM and UMTS network operators achieving the best performance were determined in Ankara. Speech qualities of network operators, as the most popular service, were also evaluated by several statistical methods including pdf/cdf analysis and chi-square and Fisher s exact tests. The network operator providing the highest speech quality in Ankara was determined with the methods applied. Overall, the results and approaches on benchmarking of cellular networks in Turkey are reported for the first time in this paper. The approaches proposed in this paper could be adapted to wide-scale benchmarking of services in cellular networks.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 Comparative Assessment and Performance Analysis of Interference Mitigation Techniques for Co-Existent Non-Geostationary and Geostationary Satellites(Wiley, 2024) Ozturk, Faik; Aydin, Elif; Kara, AliIn recent years, technological developments with user demands, reduced production, and launch costs have rapidly increased the number of Low Earth Orbit (LEO) satellites in space. Since LEO satellites use the same frequency band as existing Geostationary Earth Orbit (GEO) satellites, the interference coordination between the two satellite networks is vital. In order to minimize the co-existent interference between these satellite networks, studies perform on different interference mitigation strategies. In this paper, analysis and comparative assessment of these interference mitigation techniques are presented for the co-existent Non-Geostationary Earth (NGEO) and GEO systems. More specifically, power control (PC) and spatial isolation-based link adaptation (SILA) techniques are studied comparatively for the performance evaluation. It is shown that the communication link bandwidth is more efficiently utilized in the SILA technique when compared with the PC technique. Moreover, the multi-objective optimization problem (MOP) approach in the SILA technique is demonstrated to be more effective when compared with the single-objective optimization problem (SOP) approach used in the PC technique as the simultaneous prioritizing objective functions outperforms single prioritization. Finally, it is shown that when the PC technique is applied together with the SILA technique, the exclusive angle (EA) can be reduced up to 8% for 100 Mbps, and 8.5% for 200 Mbps transmission bit rates in different operational scenarios. The presented performance evaluation in this paper may help the satellite operator or decision-maker gain insights on which mitigation technique can be used in the case of a co-existent interference. This paper proposes analysis and comparative assessment of interference mitigation techniques for the co-existent Non-Geostationary Earth (NGEO) and Geostationary Earth Orbit (GEO) systems. Spatial isolation-based link adaptation (SILA) and power control (PC) techniques are studied comparatively for the performance evaluation. The obtained optimization results show that the communication link bandwidth is more efficiently utilized in the SILA technique when compared with the PC technique because of the simultaneous prioritizing of objective functions. imageArticle Citation - WoS: 4Citation - Scopus: 6On 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 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: 5Citation - Scopus: 10Quality of Service Assessment: a Case Study on Performance Benchmarking of Cellular Network Operators in Turkey(Tubitak Scientific & Technological Research Council Turkey, 2015) Kadioglu, Rana; Dalveren, Yaser; Dalveren, Yaser; Kara, Ali; Kara, Ali; Dalveren, Yaser; Kara, Ali; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics EngineeringThis paper presents findings on performance benchmarking of cellular network operators in Turkey. Benchmarking is based on measurements of standard key performance indicators (KPIs) in one of the metropolitan cities of Turkey, Ankara. Performance benchmarking is formulated by incorporating customer perception by conducting surveys on how important KPIs are from the user's point of view. KPIs are measured, with standard test equipment, by drive test method on specified routes. According to the performance benchmarking results, the GSM and UMTS network operators achieving the best performance were determined in Ankara. Speech qualities of network operators, as the most popular service, were also evaluated by several statistical methods including pdf/cdf analysis and chi-square and Fisher's exact tests. The network operator providing the highest speech quality in Ankara was determined with the methods applied. Overall, the results and approaches on benchmarking of cellular networks in Turkey are reported for the first time in this paper. The approaches proposed in this paper could be adapted to wide-scale benchmarking of services in cellular networks.
