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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: 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.Article Citation - WoS: 5Heterogeneity in Classes: Cooperative Problem-Solving Activities Through Cooperative Learning(Fac Teacher Education, 2014) Cigdemoglu, Ceyhan; Kapusuz, Kamil Yavuz; Kara, AliTeachers, from primary schools to college, experience challenges regarding both increased class sizes and a greater diversity of students having a broad spectrum of abilities, interests, needs, and goals. The aim of this paper is to investigate the effect of cooperative learning through Cooperative Problem-Solving (CPS) activities on homogenous and heterogeneous grouping in an engineering course. As a mixed method design, the study utilized both quantitative and qualitative data. The participants, 47 engineering students selected conveniently, were enrolled in a communication systems course. The analysis of the quantitative data indicated that no significant difference (p=.791) exists between the ways in which the students in homogenous and the students in heterogeneous group understand communication systems. In order to reveal the perceptions of students regarding the implementation, they were interviewed at the end of the semester. The qualitative data obtained from these interviews suggests that students prefer heterogeneous to homogenous grouping. The findings also imply that further research should concentrate on heterogeneous grouping strategies and more detailed qualitative data in order to reveal what kind of patterns emerge from students' interactions in different groupings.Article Citation - WoS: 9Citation - Scopus: 12On the Performance of Energy Criterion Method in Wi-Fi Transient Signal Detection(Mdpi, 2022) Mohamed, Ismail; Dalveren, Yaser; Catak, Ferhat Ozgur; Kara, AliIn the development of radiofrequency fingerprinting (RFF), one of the major challenges is to extract subtle and robust features from transmitted signals of wireless devices to be used in accurate identification of possible threats to the wireless network. To overcome this challenge, the use of the transient region of the transmitted signals could be one of the best options. For an efficient transient-based RFF, it is also necessary to accurately and precisely estimate the transient region of the signal. Here, the most important difficulty can be attributed to the detection of the transient starting point. Thus, several methods have been developed to detect transient start in the literature. Among them, the energy criterion method based on the instantaneous amplitude characteristics (EC-a) was shown to be superior in a recent study. The study reported the performance of the EC- a method for a set of Wi-Fi signals captured from a particular Wi-Fi device brand. However, since the transient pattern varies according to the type of wireless device, the device diversity needs to be increased to achieve more reliable results. Therefore, this study is aimed at assessing the efficiency of the EC-a method across a large set ofWi-Fi signals captured from variousWi-Fi devices for the first time. To this end, Wi-Fi signals are first captured from smartphones of five brands, for a wide range of signalto-noise ratio (SNR) values defined as low (3 to 5 dB), medium (5 to 15 dB), and high (15 to 30 dB). Then, the performance of the EC-a method and well-known methods was comparatively assessed, and the efficiency of the EC-a method was verified in terms of detection accuracy.Article Citation - WoS: 9Multipath Exploitation in Emitter Localization for Irregular Terrains(Spolecnost Pro Radioelektronicke inzenyrstvi, 2019) Dalveren, Yaser; Kara, AliElectronic Support Measures (ESM) systems have many operational challenges while locating radar emitter's position around irregular terrains such as islands due to multipath scattering. To overcome these challenges, this paper addresses exploiting multipath scattering in passive localization of radar emitters around irregular terrains. The idea is based on the use of multipath scattered signals as virtual sensor through Geographical Information System (GIS). In this way, it is presented that single receiver (ESM receiver) passive localization can be achieved for radar emitters. The study is initiated with estimating candidate multipath scattering centers over irregular terrain. To do this, ESM receivers' Angle of Arrival (AOA) and Time of Arrival (TOA) information are required for directly received radar pulses along with multipath scattered pulses. The problem then turns out to be multiple-sensor localization problem for which Time Difference of Arrival (TDOA)-based techniques can easily be applied. However, there is high degree of uncertainty in location of candidate multipath scattering centers as the multipath scattering involves diffuse components over irregular terrain. Apparently, this causes large localization errors in TDOA. To reduce this error, a reliability based weighting method is proposed. Simulation results regarding with a simplified 3D model are also presented.Conference Object Citation - WoS: 1Characterization of Satellite Transponder Impairments Based on Simulations with Test Data(Ieee, 2015) Ulubey, Orhan; Gulgonul, Senol; Kara, AliA satellite transponder simulator based on actual test data of TURKSAT 3A satellite has been developed to analyze degradation in multicarrier scenarios. Communication impairment sources through a transponder are explained in conjunction with a methodology defined to characterize total degradation resulting from them. Several transponder utilization scenarios are studied with respect to total degradation and optimum operation conditions are demonstrated.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 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.
