Browsing by Author "Kara, Ali"

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Comparative Assessment and Performance Analysis of Interference Mitigation Techniques for Co-Existent Non-Geostationary and Geostationary Satellites
(Wiley, 2024) Ozturk, Faik; Aydin, Elif; Kara, Ali; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
In 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. image
ISAR Imaging of Drone Swarms at 77 GHz
(TÜBİTAK Scientific & Technological Research Council of Turkey, 2025) Coruk, Remziye Busra; Kara, Ali; Aydin, Elif; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
The 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.
Citation - WoS: 1
Citation - Scopus: 1
Millimeter-Wave Sar Imaging for Sub-Millimeter Defect Detection With Non-Destructive Testing
(Mdpi, 2025) Yalcinkaya, Bengisu; Aydin, Elif; Kara, Ali; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
This paper introduces a high-resolution 77-81 GHz mmWave Synthetic Aperture Radar (SAR) imaging methodology integrating low-cost hardware with modified radar signal characteristics specifically for NDT applications. The system is optimized to detect minimal defects in materials, including low-reflectivity ones. In contrast to the existing studies, by optimizing key system parameters, including frequency slope, sampling interval, and scanning aperture, high-resolution SAR images are achieved with reduced computational complexity and storage requirements. The experiments demonstrate the effectiveness of the system in detecting optically undetectable minimal surface defects down to 0.4 mm, such as bonded adhesive lines on low-reflectivity materials with 2500 measurement points and sub-millimeter features on metallic targets at a distance of 30 cm. The results show that the proposed system achieves comparable or superior image quality to existing high-cost setups while requiring fewer data points and simpler signal processing. Low-cost, low-complexity, and easy-to-build mmWave SAR imaging is constructed for high-resolution SAR imagery of targets with a focus on detecting defects in low-reflectivity materials. This approach has significant potential for practical NDT applications with a unique emphasis on scalability, cost-effectiveness, and enhanced performance on low-reflectivity materials for industries such as manufacturing, civil engineering, and 3D printing.
Remote laboratory development as an action research: A case study
(2012) Çağıltay, Nergiz Erçil; Tokdemir, Gül; Aydın, Elif; Kara, Ali; 17411; 06.01. Bilgisayar Mühendisliği; 06.03. Elektrik-Elektronik Mühendisliği; 06. Mühendislik Fakültesi; 01. Çankaya Üniversitesi
This work presents a case study about how action research (AR) has been conducted in developing a real-life educational system. An explanation is given of the modified implementation of the classical AR methodology, based on the requirements of a remote laboratory system developed for the vocational training of students in higher education. This study reports a successful implementation of AR stages which established for the development process of a remote laboratory system along with the design of several research questions explored in each step of the system development process. It is believed that the outcomes of the study will help AR implementers to organize their research objectives, more appropriately, by addressing the organizational problems. The results of this study are also expected to guide the AR implementers to better integrate their research in solving domain specific practical problems