Electrical - Electronic Engineering / Elektrik - Elektronik Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/11
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Article Traffic Aware Cell Selection Algorithm for Tetra Trunk Based Professional Mobile Radio(Springer Verlag, 2019) Özbek, Berna; Karataş, Azad; Bardak, Erinç Deniz; Sönmez, İlkerLoad balancing and traffic management are the critical needs in cell selection decision for a better and seamless communication demands in professional mobile radios. For the cases where cell selection algorithms do not consider the traffic load, there may be call drops due to the congestion in networks or longer call setup times for the users. These undesired consequences can cause dramatic quality degradation especially for the emergency cases or public safety services. In this paper, we propose two algorithms for Tetra Trunk based professional mobile radios by considering both traffic load and received signal strength indication (RSSI) in order to reduce the significant delays while establishing transmissions. The proposed full set cell selection algorithm is prioritized to reduce the call setup time for the mobile users and the proposed reduced set cell selection algorithm is focused on minimizing the number of RSSI measurements which causes significant delay in practical professional mobile radio. We illustrate the performance results in terms of delay for Tetra Trunk based professional mobile radio.Article Traffic Load-Based Cell Selection for Apco25 Conventional-Based Professional Mobile Radio(Springer Verlag, 2020) Yılmaz, Saadet Simay; Özbek, Berna; Taş, Murat; Bengür, SıdıkaWireless communication between public safety officers is very important to transmit voice or data during emergency crises. When the public communication networks cannot provide services during crises, disasters, and high traffic cases, Professional or private mobile radio (PMR) such as Association of Public Safety Communications Officials (APCO25) conventional systems are needed to improve the service quality and to provide uninterrupted service to the users. In this paper, we propose traffic-based cell selection algorithms for the APCO25 conventional systems to attach users to base stations in a balanced manner to reduce waiting time while establishing a connection. The simulation results of the proposed traffic load-based cell selection algorithms are illustrated in terms of the RSSI measurements counter, the number of connection requests, the average waiting time, and the number of re-selections for the APCO25 conventional systems.Article Citation - WoS: 3Citation - Scopus: 6Ssim-Based Adaptation for Dash With Svc in Mobile Networks(Springer Verlag, 2020) Çalı, Mehmet; Özbek, NükhetDynamic Adaptive Streaming over HTTP (DASH) depends on adjustment of the quality of a video stream to the available network conditions. In order to increase Quality of Experience, average video quality should be maximized, while keeping the quality switching frequency at low levels. However, achieving high average quality with low switching frequency in highly fluctuating mobile network conditions is a tricky optimization problem. In order to overcome this problem, dynamic structure of Scalable Video Coding (SVC) is utilized in this paper. Another challenge in the quality adaptation algorithms is to proper assessment of the video quality. Most of the adaptation algorithms takes either bitrate or representation level as the input that is used to evaluate the quality of the video. However, bitrate is not strongly correlated with the quality, as it depends on the content of the video. Likewise, representation quality relationship entirely bound to encoding. In this paper, in order to have a more reliable adaptation input, SSIM is used while representing the quality of the video stream. The proposed adaptation is compared with a successful SVC DASH adaptation algorithm using both subjective and objective tests. As a result, considerably higher scores are achieved in terms of both switching frequency and average quality.Article Citation - WoS: 22Citation - Scopus: 27Modelling Impulsive Noise in Indoor Powerline Communication Systems(Springer Verlag, 2020) Karakuş, Oktay; Kuruoğlu, Ercan E.; Altınkaya, Mustafa AzizPowerline communication (PLC) is an emerging technology that has an important role in smart grid systems. Due to making use of existing transmission lines for communication purposes, PLC systems are subject to various noise effects. Among those, the most challenging one is the impulsive noise compared to the background and narrowband noise. In this paper, we present a comparative study on modelling the impulsive noise amplitude in indoor PLC systems by utilising several impulsive distributions. In particular, as candidate distributions, we use the symmetric alpha-Stable (S alpha S), generalised Gaussian, Bernoulli Gaussian and Student's t distribution families as well as the Middleton Class A distribution, which dominates the literature as the impulsive noise model for PLC systems. Real indoor PLC system noise measurements are investigated for the simulation studies, which show that the S alpha S distribution achieves the best modelling success when compared to the other families in terms of the statistical error criteria, especially for the tail characteristics of the measured data sets.Article Citation - WoS: 1Citation - Scopus: 2Secure Multiuser Miso Communication Systems With Limited Feedback Link(Springer Verlag, 2018) Özbek, Berna; Özdoğan Şenol, Özgecan; Karabulut Kurt, GüneşPhysical layer security is one of the promising techniques for the security of next-generation wireless systems. In this paper, we analyze the impact of the limited feedback link on the secrecy capacity for a system which includes a base station with multiple antennas, a single legitimate user selected from multiple active ones and multiple eavesdroppers. We propose to design a limited feedback link by reducing the feedback load and quantizing the channel state information (CSI) of legitimate users to establish a secure communication system. The feedback load is decreased with a self discrimination criterion at the legitimate users’ side while keeping the secrecy capacity constant. The best legitimate user is selected based on the quantized CSI through a limited feedback link. We also analyze the impact of CSI of eavesdroppers, which information may or may not be available at transmitter. In practical cases where eavesdroppers are passive and their location is not known by the transmitter, an artificial noise is used to disrupt their reception. When the CSI of eavesdroppers is known, the generalized singular value decomposition is applied. We illustrate the performance results of the proposed limited feedback link through the availability of CSI of eavesdroppers at the transmitter.Article Citation - WoS: 3Citation - Scopus: 3Channel and Queue Aware Joint Relay Selection and Resource Allocation for Miso-Ofdma Based User-Relay Assisted Cellular Networks(Springer Verlag, 2018) Baştürk, İlhan; Özbek, BernaUser-relay assisted orthogonal frequency division multiple access (OFDMA) networks are cost-effective solutions to meet the growing capacity and coverage demands of the next generation cellular networks. These networks can be used with multiple antennas technology in order to obtain a diversity gain to combat signal fading and to obtain more capacity gain without increasing the bandwidth or transmit power. Efficient relay selection and resource allocation are crucial in such a multi-user, multi-relay and multi-antenna environment to fully exploit the benefits of the combination of user-relaying and multiple antennas technology. Thus, we propose a channel and queue aware joint relay selection and resource allocation algorithm for multiple-input single-output (MISO)-OFDMA based user-relay assisted downlink cellular networks. Since, the proposed algorithm is not only channel but also queue-aware, the system resources are allocated efficiently among the users. The proposed algorithm for the MISO-OFDMA based user-relay assisted scheme is compared to existing MISO-OFDMA based non-relaying and fixed relay assisted schemes and it is also compared with the existing single-input single-output (SISO)-OFDMA based user-relay assisted scheme. Simulation results revealed that the proposed scheme outperforms the existing schemes in terms of cell-edge users’ total data rate, average backlog and average delay.Article Citation - WoS: 2Citation - Scopus: 3Joint Beamforming and Power Control Technique for Femtocell Networks(Springer Verlag, 2017) Özbek, Berna; Bayrak, UğurThe need for high data rate increases with the growing demand for wireless communication. In order to meet this demand, one of the most effective ways is deployment of small cells which are considered as a promising technique for future wireless networks. However, the deployment of these low-power base stations brings many challenges. Interference management will be one of the major drawbacks for the deployment of small cells in coverage of the macro base stations. In order to cope with interference problem, we propose a joint beamforming and power allocation technique for a two-tier network system involving femtocell and macrocell layers to design power efficient networks. The beamforming technique is applied by using partial zero-forcing method to remove the highest cross-tier interference while satisfying the macro and femtocell users’ data rate requirements. Then, we perform power allocation to further reduce interference and design power efficient femtocell networks. The performance results of the proposed technique are illustrated in terms of power consumption in femtocell networks.Article Citation - WoS: 10Citation - Scopus: 10Observer-Based Adaptive Output Feedback Tracking Control of Dynamically Positioned Surface Vessels(Springer Verlag, 2017) Bıdıklı, Barış; Tatlıcıoğlu, Enver; Zergeroğlu, ErkanIn this work, we propose an observer-based adaptive output feedback tracking controller for dynamically positioned surface vessels. Specifically, to remove the velocity measurement dependency of the control formulation a nonlinear, model-free observer formulation have been proposed. The proposed observer does not make use of the system dynamics and together with the proposed controller structure ensure that the tracking error signal and the velocity estimation error asymptotically converges to zero. Stability of the closed-loop system is ensured by Lyapunov-based arguments. Simulation studies are also presented to illustrate the effectiveness of the proposed method.Article Citation - WoS: 6Citation - Scopus: 7On Adaptive Output Feedback Controf Robotic Manipulators With Online Disturbance Estimation(Springer Verlag, 2017) Aksoy, Orhan; Zergeroğlu, Erkan; Tatlıcıoğlu, EnverThe problem of disturbance estimation and compensation for adaptive output feedback type controllers are investigated. Specifically two adaptive output feedback controllers designed for robotic manipulators are extended to compensate external disturbances which are common in robotic applications with repetitive task. The uncertain disturbance term in the robot dynamics is modeled as a fixed term plus a combination of sinusoidal signals. The overall stability and convergence of the tracking error for both controllers is ensured via Lyapunov based analysis. Extensive simulation studies are presented to illustrate the feasibility of the proposed method.Other Erratum To: on Stream Selection for Interference Alignment in Heterogeneous Networks(Springer Verlag, 2016) Aycan, Esra; Özbek, Berna; Le Ruyet, Didier
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