Computer Science
Permanent URI for this collectionhttps://hdl.handle.net/10679/43
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Browsing by Institution Author "ERCAN, Ali Özer"
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Conference ObjectPublication Metadata only Analysis of energy harvesting for green cognitive radio networks(IEEE, 2014) Ercan, Ali Özer; Sunay, Mehmet Oğuz; Pollin, S.; Electrical & Electronics Engineering; Computer Science; ERCAN, Ali Özer; SUNAY, Mehmet OğuzThis paper develops a Markov Chain analysis framework for an RF energy harvesting cognitive radio network where the secondary system users are furnished with finite-sized batteries. We consider a network where the only source of energy for the secondary system is the RF signals of the primary system resulting in an inter-play between energy harvesting and transmission for the secondary network. We show that an RF energy harvesting cognitive radio using todays technology is suitable for a delay-tolerant sensor network where the nodes need to transmit sensor output values very sporadically. We observe that the interplay between primary user traffic arrival and departure rates as well as probabilities of missed detection and false alarm for the secondary user detector and available battery size is of importance and that a percentile channel occupation of the primary network on its own is not a sufficient metric.ArticlePublication Metadata only Fault masking as a service(Wiley, 2014-07) Gülcü, Koray; Sözer, Hasan; Aktemur, Tankut Barış; Ercan, Ali Özer; Electrical & Electronics Engineering; Computer Science; SÖZER, Hasan; AKTEMUR, Tankut Bariş; ERCAN, Ali Özer; Gülcü, KorayIn SOA, composite services depend on a set of partner services to perform their tasks. These partner services may become unavailable because of system and/or network faults, leading to an increased error rate for the composite service. In this paper, we propose an approach to prevent the occurrence of errors that result from the unavailability of partner services. We introduce an external Web service, dubbed Fault Avoidance Service (FAS), to which composite services can register at will. After registration, FAS periodically checks the partner links, detects unavailable partner services, and updates the composite service with available alternatives. Thus, in case of a partner service error, the composite service will have been updated before attempting an ill-destined request. We provide mathematical analysis regarding the error rate and the false positive rate with respect to the monitoring frequency of FAS for two models. We obtained empirical results by conducting several tests on the Amazon Elastic Compute Cloud to evaluate our mathematical analyses. We also introduce an industrial case study for improving the quality of a service-oriented system from the broadcasting and content delivery domain.Conference ObjectPublication Metadata only Girişim bulunan IEEE 802.11ac aǧlarda TCP sıkışıklık denetim algoritmalarinin başarımları(IEEE, 2016) Çakmak, Kıvanç; Sunay, Mehmet Oğuz; Ercan, Ali Özer; Karaca, M.; Electrical & Electronics Engineering; Computer Science; SUNAY, Mehmet Oğuz; ERCAN, Ali Özer; Çakmak, KıvançIn order to meet the incremental requirements from clients, fifth generation Wireless Local Area Network(WLAN) protocol IEEE 802.11ac provides a lot more throughput than his predecessors. However, in all distributed channel access 802.11 protocols, probability of packet loss increases with respect to number of available stations; consecutive packet losses in link layer activates congestion control mechanism of TCP which decreases throughput. In this work, we investigated the performance of congestion control algorithms of TCP protocol when interference available wireless medium is used in between the IEEE 802.11ac capable devices. As a benchmark, we repeated the experiments with UDP protocol which does not have reliable connection and congestion control mechanism. According to our experiments, we observed that UDP provides more throughput than all other TCP congestion control algorithms. When we compare TCP congestion control algorithms by themselves, we observed that the algorithms which does not decrease congestion window size too much during interference and have more aggressive increment of congestion window -such as Cubic and Illinois, Scalable have better performance in terms of throughput and standard deviation.Conference ObjectPublication Metadata only IEEE 802.11ac aǧların çok kullanıcılı ÇGÇÇ özelliǧi üzerine incelemeler(IEEE, 2016) Çakmak, Kıvanç; Sunay, Mehmet Oğuz; Ercan, Ali Özer; Electrical & Electronics Engineering; Computer Science; SUNAY, Mehmet Oğuz; ERCAN, Ali Özer; Çakmak, KıvançThis paper studies the multi-user MIMO feature of IEEE 802.11ac networks that serve, along with IEEE 802.11ac nodes, also legacy IEEE 802.11n nodes. For this purpose, we develop a simulator that models the IEEE 802.11ac and IEEE 802.11n networks. Then, using a setup, we first study the tradeoff between the amount of overhead used in channel sounding and the corresponding rate of information, concluding that in this setting, channel sounding with all clients lead to better throughput. Secondly, we observe the negative impact of IEEE 802.11n nodes on the IEEE 802.11ac traffic due to the deafness problem, and analyze the performance of the usage of RTS/CTS handshake and cts2self mechanisms to mitigate this effect. We show that the regular RTS/CTS handshake mitigates the deafness problem to a certain degree. However, the cts2self mechanism achieves a better performance since no airtime is wasted to collisions with the RTS frames.Conference ObjectPublication Metadata only A multi-sensor integrated head-mounted display setup for augmented reality applications(IEEE, 2015) Kermen, Ahmet; Aydın, T.; Ercan, Ali Özer; Erdem, Tanju; Electrical & Electronics Engineering; Computer Science; ERCAN, Ali Özer; ERDEM, Arif Tanju; Kermen, AhmetWe present an HMD based AR system comprising visual and inertial sensors. The visual sensor is a camera pair and the inertial sensors consist of an accelerometer and a gyroscope. We discuss the temporal and spatial calibration issues that relate to such a system. We introduce simple yet effective methods for estimating the time lag between the camera and the inertial sensors and for estimating the relative pose between the camera and the inertial sensors. These methods do not require a complicated setup for data collection and involve simple equations to solve. Sample results are presented to demonstrate the visual performance of the system.ArticlePublication Open Access Multivariate sensor data analysis for oil refineries and multi-mode identification of system behavior in real-time(IEEE, 2018) Khodabakhsh, Athar; Arı, İsmail; Bakır, M.; Ercan, Ali Özer; Electrical & Electronics Engineering; Computer Science; ARI, Ismail; ERCAN, Ali Özer; Khodabakhsh, AtharLarge-scale oil refineries are equipped with mission-critical heavy machinery (boilers, engines, turbines, and so on) and are continuously monitored by thousands of sensors for process efficiency, environmental safety, and predictive maintenance purposes. However, sensors themselves are also prone to errors and failure. The quality of data received from these sensors should be verified before being used in system modeling. There is a need for reliable methods and systems that can provide data validation and reconciliation in real-time with high accuracy. In this paper, we develop a novel method for real-time data validation, gross error detection and classification over multivariate sensor data streams. The validated and high-quality data obtained from these processes is used for pattern analysis and modeling of industrial plants. We obtain sensor data from the power and petrochemical plants of an oil refinery and analyze them using various time-series modeling and data mining techniques that we integrate into a complex event processing engine. Next, we study the computational performance implications of the proposed methods and uncover regimes where they are sustainable over fast streams of sensor data. Finally, we detect shifts among steady-states of data, which represent systems' multiple operating modes and identify the time when a model reconstruction is required using DBSCAN clustering algorithm.Conference ObjectPublication Metadata only Rafinerilerdeki büyük veri problemlerine gerçek-zamanlı veri uzlaştırma çözümleri(IEEE, 2014) Bakır, M.; Aydoğan, B.; Aydın, M.; Khodabakhsh, Athar; Arı, İsmail; Ercan, Ali Özer; Electrical & Electronics Engineering; Computer Science; ARI, Ismail; ERCAN, Ali Özer; Khodabakhsh, AtharRafineriler tonlarca ham petrolün, her gün faklı kimyasal işlemden geçirilerek benzine ve diğer yan ürünlere dönüştürüldüğü dev endüstriyel tesislerdir. Bu makalede sensör-tabanlı petrol rafinelerine özel endüstriyel büyük veri problemleri tanımlanmakta (hacim hız çeşitlilik tutarsızlık) ve bu ortamlara uygun gerçek-zamanlı veri doğrulama ve uzlaştırma çözümleri sunulmaktadır."Conference ObjectPublication Metadata only Successive refinement of models for model-based testing to increase system test effectiveness(IEEE, 2016) Sahin Gebizli, C.; Sözer, Hasan; Ercan, Ali Özer; Electrical & Electronics Engineering; Computer Science; SÖZER, Hasan; ERCAN, Ali ÖzerModel-based testing is used for automatically generating test cases based on models of the system under test. The effectiveness of tests depends on the contents of these models. Therefore, we introduce a novel three-step model refinement approach. We represent test models in the form of Markov chains. First, we update state transition probabilities in these models based on usage profile. Second, we perform an update based on fault likelihood that is estimated with static code analysis. Our third update is based on error likelihood that is estimated with dynamic analysis. We generate and execute test cases after each refinement. We applied our approach for model-based testing of a Smart TV system and new faults were revealed after each refinement.