Thessaloníki, Greece
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Baltoglou G.,KTH Royal Institute of Technology | Karapistoli E.,Alexander TEI of Thessaloniki | Chatzimisios P.,Alexander TEI of Thessaloniki
Proceedings - IEEE Symposium on Computers and Communications | Year: 2011

Internet Protocol Television or IPTV is defined as an alternate method of distributing television content over IP by a telecom carrier or an Internet service provider (ISP) and it is increasingly gaining market share in modern communication networks. IPTV poses specific requirements on the network infrastructure and at the same time it requires that several network performance characteristics are maintained under defined levels in order for the end user to have an assured viewing experience. In this paper, our main motivation is to investigate how a real life network performs in terms of distributing this inelastic and high-bandwidth type of service utilizing traffic measurements. Furthermore, our goal is to verify and analyze whether the studied network is suited for multicast IPTV traffic. © 2011 IEEE.


Laya A.,KTH Royal Institute of Technology | Laya A.,Polytechnic University of Catalonia | Alonso L.,Polytechnic University of Catalonia | Chatzimisios P.,Alexander TEI of Thessaloniki | Alonso-Zarate J.,Catalonia Technology Center of Telecomunications
Mobile Networks and Applications | Year: 2015

The 3GPP is working towards the definition of service requirements and technical solutions to provide support for energy-efficient Machine Type Communications (MTC) in the forthcoming generations of cellular networks. One of the envisioned solutions consists in applying group management policies to clusters of devices in order to reduce control signaling and improve upon energy efficiency, e.g., multicast Over-The-Air (OTA) firmware updates. In this paper, a Multi-Radio Cooperative Retransmission Scheme is proposed to efficiently carry out multicast transmissions in MTC networks, reducing both control signaling and improving energy-efficiency. The proposal can be executed in networks composed by devices equipped with multiple radio interfaces which enable them to connect to both a cellular access network, e.g., LTE, and a short-range MTC area network, e.g., Low-Power Wi-Fi or ZigBee, as foreseen by the MTC architecture defined by ETSI. The main idea is to carry out retransmissions over the M2M area network upon error in the main cellular link. This yields a reduction in both the traffic load over the cellular link and the energy consumption of the devices. Computer-based simulations with ns-3 have been conducted to analyze the performance of the proposed scheme in terms of energy consumption and assess its superior performance compared to non-cooperative retransmission schemes, thus validating its suitability for energy-constrained MTC applications. © 2015, Springer Science+Business Media New York.


Maraslis K.,University of Peloponnese | Chatzimisios P.,Alexander TEI of Thessaloniki | Boucouvalas A.,University of Peloponnese
IEEE International Conference on Communications | Year: 2012

Transmitting multimedia streams over IEEE 802.11 Wireless Local Area Networks (WLANs) with high performance and reliability is a challenging task. In the current paper, we study the basic problems that video transmission encounters in wireless LANs and we present some of the proposed solutions. In particular, we will outline the solutions that were selected for the 802.11aa amendment to the IEEE 802.11 standard in order to provide reliable and robust transport of video streams in IEEE 802.11 wireless LANs. © 2012 IEEE.


Boucouvalas A.C.,University of Peloponnese | Chatzimisios P.,Alexander TEI of Thessaloniki | Ghassemlooy Z.,Northumbria University | Uysal M.,Ozyegin University | Yiannopoulos K.,University of Peloponnese
IEEE Communications Magazine | Year: 2015

The application of Optical Wireless Communications (OWC) has grown in recent years that the whole industry would benefit from common standards to which competitive products comply. Standards are essential, particularly when the market expands into high-volume products like home appliances and other consumer goods. This article offers a timely review of standards-writing activity, as OWCs find their way into diverse products varying from TV remote controls to satellite links. This article discusses the most popular standards for optical wireless communications. We outline the IEEE 802.11 standard for optical wireless local area networks, and the ongoing standardization effort by IrDA on personal optical wireless systems. The article concludes with a discussion of the recently announced IEEE 802.15.7 standard on visible light communications. © 2015 IEEE.


Karapetsas E.,University of Tokyo | Stamatis D.,Alexander TEI of Thessaloniki
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2010

In this paper we present a neural network approach to solving the problem of a robot agent (Mazebot) navigating in and creating a topological map of a reconfigurable maze. The robotics system used is based on an SRV-1 Robot extended both in hardware and software to accomplish the task. The main algorithm of the system is vision based, requiring only a single camera and a dead reckoning sensor. For the purposes of our algorithm a database of images from various maze configurations has been created. Neural Networks are utilized to train the agent at first and later to analyze features extracted from the images and enable agent navigation inside the maze. The advantage of our approach lies in the minimal number of sensors required by the robot agent to achieve success in its task. © 2010 Springer-Verlag Berlin Heidelberg.


Vasileiadis A.,Lund University | Iossifides A.C.,Alexander TEI of Thessaloniki
2016 23rd International Conference on Telecommunications, ICT 2016 | Year: 2016

This paper investigates the performance of high rate IEEE 802.15.4 UWB PHY schemes. Evaluation takes place over office, residential and outdoor IEEE channel models via Monte-Carlo simulation. Special attention is given to the highest rate (27.24 Mbps) scheme that suffers from intersymbol interference (ISI) over NLOS outdoor and residential channels. Optimum bit-to-symbol mapping (OBM), ISI cancellation and MLSE techniques are proposed and evaluated in conjunction with RAKE reception. Significant gains are attained with the proposed enhancements while keeping complexity low. On the other hand, the coverage range of high rate schemes is estimated for a given BEP. It is deduced that 27.24 Mbps and 6.81 Mbps schemes are well applicable to all LOS channels. However, the maximum allowable transmission power deteriorates range in NLOS cases. Overall, high rate schemes are shown to deserve more attention in the context of high rate sensor applications. © 2016 IEEE.


Ilioudis V.C.,Alexander TEI of Thessaloniki
2015 56th International Scientific Conference on Power and Electrical Engineering of Riga Technical University, RTUCON 2015 | Year: 2015

This paper presents a new antiwindup (AW) speed controller for sensorless control of salient-pole Synchronous Machine (SM) by means of serially connected AW loops. The control method is based on saturation feedback using multiple loops for controller output adaptation. Unwanted windup phenomena due to the physical limitations are restricted passing the initial controller output through multiple AW loops and choosing suitably the controller transfer functions. This AW approach leads the operation of actuator towards to the linear area using a relatively simple adaptation technique of saturation limits in each AW level. Simulation results demonstrate that the application of multiple AW loops is an effective control scheme capable to achieve improved performance. © 2015 IEEE.


Ougiaroglou S.,University of Macedonia | Evangelidis G.,University of Macedonia | Dervos D.A.,Alexander TEI of Thessaloniki
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

A well known classification method is the k-Nearest Neighbors (k-NN) classifier. However, sequentially searching for the nearest neighbors in large datasets downgrades its performance because of the high computational cost involved. This paper proposes a cluster-based classification model for speeding up the k-NN classifier. The model aims to reduce the cost as much as possible and to maintain the classification accuracy at a high level. It consists of a simple data structure and a hybrid, adaptive algorithm that accesses this structure. Initially, a preprocessing clustering procedure builds the data structure. Then, the proposed algorithm, based on user-defined acceptance criteria, attempts to classify an incoming item using the nearest cluster centroids. Upon failure, the incoming item is classified by searching for the k nearest neighbors within specific clusters. The proposed approach was tested on five real life datasets. The results show that it can be used either to achieve a high accuracy with gains in cost or to reduce the cost at a minimum level with slightly lower accuracy. © 2012 Springer-Verlag.


Papaioannou E.,University of Macedonia | Assimakopoulos C.,Alexander TEI of Thessaloniki | Sarmaniotis C.,Alexander TEI of Thessaloniki | Georgiadis C.K.,University of Macedonia
Information Systems and e-Business Management | Year: 2013

Over the recent years, C2C (consumer-to-consumer) electronic market has increased rapidly, and has become the most active segment of e-markets today. Despite the growth and popularity of online auctions and especially of e-Bay, which has been considered to be one of the most profitable e-commerce companies, the online auction environment is risky and transactions are complex due to the fact that buyer and seller do not know each other and they are not familiar. Although many studies have examined the impact of e-service quality on customer satisfaction in B2C (business-to-consumer) or B2B (business-to-business) commerce, the literature is insufficient in the case of C2C commerce. However, a number of authors have conducted research in C2C and particularly in e-Bay but in all of the cases, data source from e-Bay's feedback system was employed in order to investigate service quality issues. Nevertheless, in this study a field research was conducted in order to collect the necessary data and thus reducing possible bias. The purpose of this paper is to examine some determinants of satisfaction with service quality dimensions in the online auction environment. More specifically, this paper is examining the case of e-Bay, in order to have a better understanding of buyers' satisfaction in this risky environment. The paper's aim is accomplished through an empirical investigation of a sample of 2,099 buyers of e-Bay, examining buyers' expectation and perception levels towards service quality of e-Bay. Gap analysis was first employed in order to identify users' disconfirmation dimensions in the online auction market place. Some research hypotheses are formulated to find out whether these dimensions have a positive disconfirmation. In most of the cases a positive disconfirmation is tracked down. Secondly, factor analysis was utilized to identify broad determinants of e-Bay service quality. The pool of the initial items deduced to four factors. These factors are, to a degree, differentiated in the Greek environment from factors found in other studies. A second round of research hypotheses are formulated again to find out whether those factors are related to the users' disconfirmation dimensions. Finally, a new theoretical model is proposed based on the above mentioned hypotheses. © 2012 Springer-Verlag Berlin Heidelberg.


Katsikiotis C.,French Institute for Research in Computer Science and Automation | Zorbas D.,French Institute for Research in Computer Science and Automation | Chatzimisios P.,Alexander TEI of Thessaloniki
Lecture Notes of the Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering, LNICST | Year: 2014

Connectivity restoration after a node failure is one of the major issues in wireless ad-hoc networks. In particular, failures can lead to a network partitioning and a huge loss of information. Therefore, a fast mechanism is needed to heal the network between the partitions. In this paper, we consider the scenario where an intermediate node failures and a mobile system is moving autonomously to restore connectivity and provide the best service. We propose a fast connectivity restoration algorithm that is based only on local information. We implement our solution on a real robotic platform and we present some experimental results using a simple case scenario. © Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2014.

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