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Thessaloníki, Greece

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. Source

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. Source

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. Source

Kontogeorgos A.,University of Patras | Tselempis D.,Aristotle University of Thessaloniki | Aggelopoulos S.,Alexander TEI of Thessaloniki
Measuring Business Excellence | Year: 2014

Purpose – The purpose of this paper is mainly to investigate how Greek Farmers perceive service quality provided by the Greek Ministry of Agriculture and secondly, to confirm the five quality dimensions proposed by the SERVQUAL instrument for the Ministry’s service. Design/methodology/approach – A questionnaire based on the SERVQUAL scale, was used to determine farmers’ perceptions of service quality in the area of central Macedonia in Greece. A total of 245 completed questionnaires were collected. Findings – The analysis has shed some light on the quality gaps for the services provided by the Greek Public sector, suggesting that there is scope for improvement strategies. The results revealed a three-dimensional structure instead of the five dimensions of the SERVQUAL instrument. “Social skills” of the human factor were revealed as being the most critical dimension of quality. Practical implications – This paper provides guidelines for policymakers to develop strategies to identify service quality gaps, while the decrease of such gaps could result in the public services’ improvement. Originality/value – The current study is the first attempt to measure farmers’ perceptions of the service provided by the Greece ministry of Rural Development and Food. Secondly, this study provides additional evidence that the modification of the SERVQUAL scale could be used in different service sectors and cultures. © Emerald Group Publishing Limited. Source

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. Source

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