Handover Optimization in Wireless Microcellular ATM Networks

Microcellular solutions in wireless ATM networks increase the network traffic control as a result of frequent handover requests. The blocking probability or the forced termination probability presents a quality of service criterion for evaluation of certain handover techniques. This paper presents a handover protocol that can avoid cell loss and guarantee cell sequence, and a two layer wireless call admission control is studied, using Markov state diagrams, in order to optimize the performance of wireless ATM networks. Spiros Louvros was born in Corfu island, Hellas in 1971. He received his Bachelor in Physics from the University of Crete, Hellas and his Master in telecommunications from the University of Cranfield, U.K. with a scholarship for graduate studies from the Alexandros Onassis Institution. In 2004 he received his PhD from the University of Patras, Hellas, in mobile communications. He has worked for Siemens as a microwave engineer and for Vodafon-Hellas as a switching engineer. His current occupation is section manager in the Maintenance Department in Cosmote S.A. He has participated in several research projects regarding mobile communications. His area of interest is in mobile networks, telecommunication traffic engineering, wireless ATM and optical communications and is documented by over 30 papers in international literature and conference proceedings. He is member of FITCE and Hellenic Physics Union and he holds a position of external researcher in the Wireless telecommunications Lab of the Electrical Engineering department, University of Patras. Dimitrios Karaboulas was born in Patras-Hellas. He received his diploma in Electrical & Computer Engineering from the University of Patras, Hellas in 1994. He has been working, since 1994, as an external consultant-specialist in several telecommunication companies in Hellas and he currently holds a company firm for ISO certification, supervision and technical solutions. He is currently a PhD candidate in the Wireless Laboratory of Electrical & Computer Engineering Department, University of Patras, Hellas and his research interests are in the area of Wireless ATM networking, mobile communications and telecommunication network planning. He has participated in several research projects regarding mobile communications and enterprise telecommunication solutions and is documented by over 50 papers in conference proceedings. He is also an active member of the Technical Chamber of Greece. S. Kotsopoulos was born in Argos-Argolidos (Greece) in the year 1952. He received his B.Sc. in Physics in the year 1975 from the University of Thessaloniki, and in the year 1984 got his Diploma in Electrical and Computer Engineering from the University of Patras. He did his postgraduate studies in the University of Bradford in United Kingdom. And he is an M.Phil and Ph.D. holder since 1978 and 1985 correspondingly. Currently he is member of the academic staff of the Department of Electrical and Computer Engineering of the University of Patras and holds the position of Associate Professor. Since 2004, is the Director of the Wireless Telecommunications Laboratory and develops his professional life teaching and doing research in the scientific area of Telecommunications, with interest in mobile communications, interference, satellite communications, telematics applications, communication services and antennae design. Moreover he is the (co)author of the book titled “mobile telephony”. The research activity is documented by more than 160 publications in scientific journals and proceedings of International Conferences. Associate Professor Kotsopoulos has been the leader of several international and many national research projects. Finally, he is member of the Greek Physicists Society and member of the Technical Chamber of Greece.     

Mean Waiting Time Analysis in Finite Storage Queues for Wireless Cellular Networks

In this paper priority is assigned to the handover calls over new call attempts and blocked handover calls are placed in a finite storage queue. Total handover forced termination probability is evaluated and a suitable function for the mean service time at each position in the queue is theoretically estimated. Quality of service is obtained by introducing a threshold in the maximum waiting time of a handover call in the queue. In case the handover call mean service time at each queue position is found to be greater than this threshold, this call will be blocked. Simulation results show that this scheme provides satisfactory results for both types of calls. Spiros Louvros was born in Corfu Island, Hellas in 1971. He received his Bachelor in Physics from the University of Crete, Hellas and his Master of Science in telecommunications from the University of Cranfield, U.K. with a graduate scholarship from the Alexandros Onassis Institution. In 2004 he received his PhD from the University of Patras, Hellas, in mobile communications. He has worked for Siemens as a microwave engineer, for Vodafon-Hellas as a switching engineer and for Cosmote S.A. as section manager in the Operations, Maintenance & Optimization Department. His current occupation is in the Telecommunication Systems & Networks Department, Technical University of Messologi, Hellas, as an Assistant Professor. He holds several papers in international journals and conferences and he has participated in several research projects regarding mobile communications. His area of interest is in mobile networks, telecommunication traffic engineering, wireless ATM and optical communications and is documented by over 30 papers in international literature and conference proceedings. He is member of FITCE and Hellenic Physics Union. Gerasimos Pylarinos – Stamatelatos was born in Kefalonia, Greece in 1966. He receieved the B.E. in Electrical and Computer Systems Engineering from Monash University, Melbourne, Australia in 1992 and the B.E. in Electrical and Computer Systems Engineering from the University of Patras, Greece in 1994. He received the M.Sc. in Data Communications Systems from Brunel University, United Kingdom. He is currently pursuing the PhD degree at the University of Patras Greece. He has worked at Philips Radio Communication Systems, Melbourne, Australia developing hardware for mobile radio communication systems for 2 years. He subsequently worked as project manager in the Research and Development department at Intracom Radio Communication Systems, Greece for 7 years. He is now manager of the Biomedical Engineering department of Kefalonia Hospital, Greece. His research interests lie in the areas of 3G and 4G wireless communications. S. Kotsopoulos was born in Argos-Argolidos (Greece) in the year 1952. He received his B.Sc. in Physics in the year 1975 from the University of Thessaloniki, and in the year 1984 got his Diploma in Electrical and Computer Engineering from the University of Patras. He did his postgraduate studies in the University of Bradford in United Kingdom. And he is an M.Phil and Ph.D. holder since 1978 and 1985 correspondingly. Currently he is member of the academic staff of the Department of Electrical and Computer Engineering of the University of Patras and holds the position of Associate Professor. Since 2004, is the Director of the Wireless Telecommunications Laboratory and develops his professional life teaching and doing research in the scientific area of Telecommunications, with interest in mobile communications, interference, satellite communications, telematics applications, communication services and antennae design. Moreover he is the (co)author of the book titled “mobile telephony”. The research activity is documented by more than 160 publications in scientific journals and proceedings of International Conferences. Associate Professor Kotsopoulos has been the leader of several international and many national research projects. Finally, he is member of the Greek Physicists Society and member of the Technical Chamber of Greece.     

Vehicle Velocity Estimation Based on RSS Measurements

This paper presents a technique which is based on pattern recognition techniques, in order to estimate Mobile Terminal (MT) velocity. The proposed technique applies on received signal strength (RSS) measurements and more precisely on information extracted from Iub air interface, in wIDeband code-division multiple access (WCDMA) systems for transmission control purposes. Pattern recognition is performed by HIDden Markov Model (HMM), which is trained with downlink signal strength measurements for specific areas, employing Clustering LARge Applications (CLARA) like a clustering method. Accurate results from a single probe vehicle show the potential of the method, when applied to large scale of MTs. Theodore S. Stamoulakatos is a Senior Research Associate with the Department of Electrical and Computer Engineering at National Technical University of Athens (NTUA). He received his B.Sc. in Mathematics from University of the Aegean, Greece, in 1997, and the M.Sc. in Computer Applications from Dublin City University, Ireland, in 1999 with scholarship from the Irish Ministry of Education. On April ’05 he received his Ph.D. degree from the Department of Electrical Engineering and Computer Science of the National Technical University of Athens. He has been lecturing in DCU various courses including Algorithms & Data Structures, Computer Systems, and Advanced Network Management to both undergraduate and postgraduate students. During his research in NTUA, he has been actively involved in many European and National projects that match his research interests. Both his academic as well as his industrial experience (four years in OTEnet S.A.) allow him to publish several papers in journals and international conferences, which are in the fields of Mobile and Personal Communication Networks, Active Networks, Location Based Services as well as Network and Service Management. Dr. Stamoulakatos is a member of the IEEE. Antonis E. Markopoulos obtained his degree in Informatics and Telecommunications Engineering from University of Athens, Greece in 2000. During his studies he participated in various research projects dealing with the management of fixed and wireless networks. He has also industrial experience for 2 years in INTRASOFT International S.A participating in several projects, national and European. He received his PhD in the field of Cellular and Wireless Communication from the National Technical University of Athens in 2005, where he is working as a Senior Research Engineer in the Telecommunication Laboratory. He has published several papers in journals, international conferences and book chapters. His research interests are in the fields of cellular and wireless networks of present and future generation (4G, WLAN/WPAN, WiMAX) and more specific in the areas of radio resource management and security. He has been mainly involved in many European (IST-CELLO, IST-PACWOMAN, IST-MAGNET, a.o) and National (Greek IST, GGRT) projects. Dr Markopoulos is a member of the IEEE and of the Greek Association of Mechanical and Electrical Engineers. Miltiades E. Anagnostou was born in Athens, Greece, in 1958. He received the Electrical Engineer’s Diploma from the National Technical University of Athens (NTUA) in 1981. In 1987 he received his PhD in the area of computer networks. Since 1989 he has been teaching at the Electrical and Computer Engineering School of NTUA, where he is currently a Full Professor. He teaches courses on modern telecommunications, computer networks, formal specification, stochastic processes, and network algorithms. His research spans several fields, including broadband networks, mobile and personal communications, service engineering, mobile agents, pervasive computing, network algorithms and queuing systems. He is a member of the IEEE and the ACM. Michael E. Theologou received the degree in Electrical Engineering from Patras University and his Ph.D. degree from the Department of Electrical Engineering and Computer Science of the National Technical University of Athens. Currently he is a Professor at National Technical University of Athens, Department of Electrical and Computer Engineering conducting teaching and research in the wider area of Telecommunication Networks and Systems. His research interests are in the fields of Mobile and Personal Communication Networks, Computer Networks, Quality of Service. He has many publications in the above areas.     

Resource management of IP-enabled DVB-T networks in the context of wireless B3G systems

The wireless beyond 3G systems or the so called Composite Radio Environments (CRE) (or even 4G systems), consist of multiple type radio access technologies, collaborating with each other, providing both diverse access alternatives and QoS improvement, especially as far as concerns protection against traffic congestion and loss of radio coverage situations. The merits deriving from beyond 3G systems interest not only network and service providers but also the mobile users. Additionally, the need of broadband wireless access is directly associated with the intense demand for IP multimedia services (e.g. video streaming or high speed web browsing), mainly inside hot-spot areas. Taking into consideration the above described tendency in the area of wireless network systems, the IP-enabled DVB-T (the terrestrial specification of the Digital Video Broadcasting family) systems appear as an attractive alternative network access in the CRE context. Along this direction, this paper presents the most important aspects of a CRE network management system (NMS), focusing on the component responsible for the DVB-T resource management (RM). Finally, we implement and investigate through simulation a greedy algorithm suitable for DVB-T networks that performs fast resource management and configuration. We also provide some indicative results which prove that the algorithm demonstrates a close to optimal performance at the RM functionality. This work is partially funded by the Commission of the European Communities, under the Fifth Framework Program, within the IST project CREDO (Composite Radio for Enhanced Service Delivery during the Olympics). Dimitris Kouis is currently a research associate at the Electrical Engineers School of the National Technical University of Athens, in Greece. He received his diploma from the Computer Engineering and Informatics department of the Polytechnic School of the University of Patras and a Ph.D. degree in Telecommunications and Computing from the National Technical University of Athens, Greece, in 1999 and 2005 respectively. He has worked in research projects in the context of the IST framework. His research interests include mobile and wireless networking, wireless network resources optimization techniques and large-scale software platforms. He is a member of the Technical Chamber of Greece since 1999. Panagiotis Demestichas received the Diploma and the Ph.D. degrees in Electrical and Computer Engineering from the National Technical University of Athens (NTUA). From September 2002 he is an Assistant Professor at the University of Piraeus, in the department of Technology Education and Digital Systems. From 1993 until August 2002 he has been a senior research engineer with the Telecommunications Laboratory in NTUA. From February 2001 until August 2002 he was a lecturer at NTUA, in the department of Applied Mathematics and Physics, teaching courses on programming languages, data structures, data bases, telecommunications. From September 2000 until August 2002 he taught telecommunication courses, in the department of Electronics of the Technological Education Institute of Piraeus. Most of his current activities focus on the FP6/IST project E2R (End-to-End Reconfigurability). He is also the chairman of Working Group 6 (WG6), titled Reconfigurability, of the Wireless Word Research Forum (WWRF). At the international level he has actively participated in the projects IST MONASIDRE Management of Networks and Services in a Diversified Radio Environment), where he was the project manager, as well as other EU projects under the IST, ACTS, RACE II, EURET, BRITE/EURAM frameworks. His research interests include the design, management and performance evaluation of mobile and broadband networks, service and software engineering, algorithms and complexity theory, and queueing theory. He has authored over 100 publications in these areas in international journals and refereed conferences. He is a member of the IEEE, ACM and the Technical Chamber of Greece. George Koundourakis was born in Alex/polis, Greece, in 1979. He received the degree of Electrical and Computer Engineer from the National Technical University of Athens (NTUA), Greece, in July 2001. He is a Research Associate and PhD candidate at the Telecommunications Laboratory of the Division of Communication, Electronic and Information Engineering at NTUA. He has worked in research projects in the context of the IST framework. He is the author of several scientific papers in the areas of mobile communications. He is a member of the Technical Chamber of Greece. Michael E. Theologou received the degree in Electrical Engineering from Patras University and his Ph.D. degree from the School of Electrical Engineering and Computer Science of the National Technical University of Athens (NTUA). Currently he is a Professor in the School of Electrical Engineering and Computer Science of NTUA. His research interests are in the field of Mobile and Personal communications. He has many publications in the above areas. Dr Theologou is a member of IEEE and the Technical Chamber of Greece.     

MIMO Channel Characterization for Short Range Fixed Wireless Propagation Environments

This paper reports results from wideband MIMO measurements performed in short range fixed wireless environments at 5.2 GHz. The objective is to provide MIMO channel characterization results for the measured environments and contribute to the limited available similar studies. Two kinds of propagation scenarios are investigated, rooftop to rooftop and street to rooftop, at three different sites always under LOS propagation conditions. The analysis of measurement data is performed in the context of non physical modeling, providing insight into the statistics of the measured channels. In particular, the slow time varying nature of the channel is studied and the narrow Doppler spectrum shape is approximated. Furthermore, frequency correlation results are obtained and the typical delay dispersion measures are extracted. Then, the antenna correlation is studied and the error of the Kronecker product approximation is evaluated. Finally, capacity results are provided and the channel measurements are characterized in terms of spatial multiplexing quality and multipath richness through condition number analysis. Nikolaos D. Skentos received his Diploma in Electrical and Computer Engineering from the National Technical University of Athens (NTUA), Greece in October 2000. Since January 2001 he has been a research associate at the Mobile Radio Communications Laboratory at the NTUA, and he is currently working towards the Ph.D. degree. His research interests include channel measurements, MIMO channel characterization, MIMO algorithms and space time processing. He has been active in the IST STINGRAY project, the COST 273 Action and the ACE Network of Excellence. He is also a member of the National Technical Chamber of Greece since 2001. Athanasios G. Kanatas received the Diploma in Electrical Engineering from the National Technical University of Athens, Greece, in 1991, the M.Sc. degree in Satellite Communication Engineering from the University of Surrey, Surrey, UK in 1992, and the Ph.D. degree in Mobile Satellite Communications from the National Technical University of Athens, Greece in February 1997. From 1993 to 1994 he was with National Documentation Center of National Research Institute. In 1995 he joined SPACETEC Ltd. where he was Technical Project Manager for VISA/EMEA VSAT Project in Greece. In 1996 he joined the Mobile Radio Communications Laboratory as a research associate. From 1999 to 2002 he was with the Institute of Communication & Computer Systems. In 2000 he became a member of the Board of Directors of OTESAT S.A. He is an Assistant Professor in the Department of Technology Education and Digital Systems at University of Piraeus. His current research interests include channel characterization and estimation, simulation and modeling for mobile, mobile satellite, and future wireless communication systems. He has been a Senior Member of IEEE since 2002, and is also a member of the Technical Chamber of Greece. In 1999 he was elected Chairman of the Communications Society of the Greek IEEE Section. Panagiotis I. Dallas was born 1967 in Thessaloniki, Greece. He obtained his diploma and Ph.D. degree from the Electrical and Computer Engineering Department of Aristotle University of Thessaloniki, Greece, in 1990 and 1997, respectively. Since 1998 he joined with INTRACOM where he currently is Section Manager of Advanced Communications Technologies branch of Emerging Technologies & Markets department, leading the next generation of broadband wireless access systems for internal and EU projects. He runs the relevant standardization activities (IEEE 802.16 and ETSI/BRAN HIPERMAN) in INTRACOM and he represents the company in WiMAX forum. Finally, he has over 30 publications in international journals and conferences. Philip Constantinou received the Diploma in Physics from the National University of Athens in 1972, the Master of Applied Science in Electrical Engineering from the University of Ottawa, Ontario, Canada in 1976, and the Ph.D. degree in Electrical Engineering in 1983 from Carleton University, Ottawa, Ontario, Canada. From 1976 to 1979 he was with Telesat Canada as a Communications System Engineer. In 1980 he joined the Ministry of Communications in Ottawa, Canada where he was engaged in the area of Mobile Communication. From 1984 to 1989 he was with the National Research Center Demokritos in Athens, Greece where he was involved in several research projects in the area of Mobile Communications. In 1989 he joined the National Technical University of Athens where he is currently a Professor and Director of the Mobile Radio Communications Laboratory. His current research interests include Personal Communications, Mobile Satellite Communications, and Interference Problems on Digital Communications Systems.     

Sequence Number Aided Source Routing for Ad-Hoc Networks

Wireless multihop mobile networks, also known as ad hoc networks, are characterized by stochastic topology variations. Random movements of mobile hosts in and out of each other's range encumber smooth system operation and impose limitations on the network performance. Various routing protocols suitable for such networks have been proposed however implementation and performance issues are still considered top research priorities. This paper proposes a new reactive protocol that introduces the use of sequence numbers for evaluating validity of cached routing information when source routing and route caching are used. The new protocol reduces the possibility of using and spreading across the network stale routing information therefore reduces the overhead involved in finding a route. To demonstrate the performance of the proposed protocol we compare it, through a detailed simulation model, with Dynamic Source Routing (DSR) protocol which also uses source routing and route caching. Results prove that the proposed protocol effectively reduces use of stale routing information, improving performance compared to DSR in terms of both delivery ratio and routing overhead. Evangelos Papapetrou holds a Diploma and a Ph.D. in Electrical & Computer Engineering from the Aristotle University of Thessaloniki, Greece. He is currently a visiting lecturer in the Computer Science Department at the University of Ioannina, Greece, where he is engaged in teaching and research on Mobile and Satellite Communications and Telecommunications Networks. His research interests include traffic analysis and design of Satellite networks, Internet over Satellites, IP networking, routing in networks with periodic or stochastic varying topologies, MANETs and QoS in wireless mobile systems. He has served as a reviewer in several journals and Conferences relevant to mobile communications. In the past he has participated in Greek and European projects regarding satellite communications. He was also involved in COST Actions 253 and 272 and in many European projects undertaken by the Centre for Research and Technology Hellas (CERTH). He is a Member of IEEE and the Joint VTS & AES Greece Chapter and a member of Technical Chamber of Greece. Fotin-Niovi Pavlidou holds a Diploma and a Ph.D. in Telecommunications networks from the Aristotle University of Thessaloniki where she is currently engaged in teaching and research on Mobile Communications and Telecommunications Networks. Her research interests include traffic analysis and design of networks, performance evaluation and QoS studies of mobile satellite communications and multimedia applications over Internet. She is a permanent reviewer in IEEE journals, she has served as Guest-Editor of Special issues on “Ad-Hoc Networks”, “HAPs and applications”, “PLC Systems and Applications” for International Journals like IJWIN, WPC etc. She is the author of a Chapter on Fixed Access Techniques (TDMA/FDMA) in the Wiley Encyclopedia on Telecommunications (Editor:Prof. John Proakis), and of many editions of COST Actions on “Satellite Systems”, “Spread Spectrum Techniques” etc. She is the Delegate of Greece in the European COST Program on Telecommunications (1998–2004) and served as Chairperson for the COST262 Action “Spread Spectrum systems and techniques for wired and wireless Systems”. She is permanently included in the Program Committee of many IEEE conferences (PIMRC, GLOBECOM, VTC'2001, ISSSTA'2000) and she was the Chairperson of the IST Mobile Summit 2002, the annual conference of EU-Unit E4 in the field of Wireless Communications in Thessaloniki, June 16–20, 2002. She is involved in many European Projects (research or Education): Telematics Applications (INTERVUSE, ATTACH, etc.), IST (ISMAEL, B-Bone, SatNEx, OPERA, etc.), Tempus programs on Wireless Systems for Albania, Bulgaria, Poland. She is a Senior Member of IEEE (Communications and Vehicular Technology Society), currently chairing the Joint VTS & AES Greece Chapter.     

Behavioral-Level Performance and Power Exploration of Data-Intensive Applications Mapped on Programmable Processors

The continuous increase of the computational power of programmable processors has established them as an attractive design alternative, for implementation of the most computationally intensive applications, like video compression. To enforce this trend, designers implementing applications on programmable platforms have to be provided with reliable and in-depth data and instruction analysis that will allow for the early selection of the most appropriate application for a given set of specifications. To address this need, we introduce a new methodology for early and accurate estimation of the number of instructions required for the execution of an application, together with the number of data memory transfers on a programmable processor. The high-level estimation is achieved by a series of mathematical formulas; these describe not only the arithmetic operations of an application, but also its control and addressing operations, if it is executed on a programmable core. The comparative study, which is done using three popular processors (ARM, MIPS, and Pentium), shows the high efficiency and accuracy of the methodology proposed, in terms of the number of executed (micro-)instructions (i.e. performance) and the number of data memory transfers (i.e. memory power consumption). Using the proposed methodology we estimated an average deviation of 23% in our estimated figures compared with the measurements taken from the real execution on the CPUs. This work was supported by the project PENED ’99 ED501 funded by GSRT of the Greek Ministry of Development, and the project PRENED ’99 KE 874 funded by the Research Committee of the Democritus University of Thrace. This work was partially sponsored by a scholarship from the Public Benefit Foundation of Alexander S. Onassis (Minas Dasygenis). Nikolaos Kroupis was born in Trikala in 1976. He receiver the engineering degree and Ms.C. degree in Department of Electrical and Computer Engineering from Democritous University of Thrace, Greece, in 2000 and 2002, respectively. Since 2002 he has been a Ph.D. student at the Laboratory of Electrical and Electronic Materials Technology. His research interests are in software/hardware co-design of embedded system for signal processing applications. Nikos D. Zervas received a Diploma in Electrical & Computer Engineering from University of Patras, Greece in 1997. He received the Ph.D. degree in the Department of Electrical and Computer Engineering of the same University in 2004. His research interests are in the area of high-level, power optimization techniques and methodologies for multimedia and telecommunication applications. He has received an award from IEEE Computer Society in the context of Low-Power Design Contest of 2000 IEEE Computer Elements Mesa Workshop. Mr. Zervas is a member of the IEEE, ACM and of the Technical Chamber of Greece. Minas Dasygenis was born in Thessaloniki in 1976. He received his Diploma in Electrical and Computer Engineering in 1999, from the Democritus University of Thrace, Greece, and for his diploma Thesis he was honored by The Technical Chamber of Greece and Ericsson Hellas. In 2005, he received his PhD Degree from the Democritus University of Thrace. His research interests include low-power VLSI design of arithmetic circuits, residue number system, embedded architectures, DSPs, hardware/ software codesign and IT security. He has published more than 20 papers in international journals and conferences and he has been a principal researcher in three European research projects. Konstantinos Tatas received his degree in Electrical and Computer Engineering from the Democritus University of Thrace, Greece in 1999. He received his Ph.D. in the VLSI Design and Testing Center in the same University by June 2005. He has been employed as an RTL designer in INTRACOM SA, Greece between 2000 and 2003. His research interests include low-power VLSI design of DSP and multimedia systems, computer arithmetic, IP core design and design for reuse. Antonios Argyriou received the degree in Electrical and Computer engineering from the Democritous University of Thrace, Greece, in 2001, and the M.S. and Ph.D. degrees in Electrical and Computer engineering from the Georgia Institute of Technology, Atlanta, in 2003 and 2005, respectively. His primary research interests include wireless networks, mobile computing and multimedia communications. He is a member of the IEEE and ACM. Dimitrios Soudris received his Diploma in Electrical Engineering from the University of Patras, Greece, in 1987. He received the Ph.D. Degree in Electrical Engineering, from the University of Patras in 1992. He is currently working as Ass. Professor in Dept. of Electrical and Computer Engineering, Democritus University of Thrace, Greece. His research interests include low power design, parallel architectures, embedded systems design, and VLSI signal processing. He has published more than 140 papers in international journals and conferences. He was leader and principal investigator in numerous research projects funded from the Greek Government and Industry as well as the European Commission (ESPRIT II-III-IV and 5th and 6th IST). He has served as General Chair and Program Chair for the International Workshop on Power and Timing Modelling, Optimisation, and Simulation (PATMOS). He received an award from INTEL and IBM for the project results of LPGD #25256 (ESPRIT IV). He is a member of the IEEE, the VLSI Systems and Applications Technical Committee of IEEE CAS and the ACM. Antonios Thanailakis was born in Greece on August 5, 1940. He received B.Sc. degrees in physics and electrical engineering from the University of Thessaloniki, Greece, 1964 and 1968, respectively, and the Msc. and Ph.D. Degrees in electrical engineering and electronics from UMIST, Manchester, U.K. in 1968 and 1971, respectively. He has been a Professor of Microelectronics in Dept. of Electrical and Computer Eng., Democritus Univ. of Thrace, Xanthi, Greece, since 1977. He has been active in electronic device and VLSI system design research since 1968. His current research activities include microelectronic devices and VLSI systems design. He has published a great number of scientific and technical papers, as well as five textbooks. He was leader for carrying out research and development projects funded by Greece, EU, or other organizations on various topics of Microlectronics and VLSI Systems Design (e.g. NATO, ESPRIT, ACTS, STRIDE).     

Improvements on “IP – IAPP”: A fast IP handoff protocol for IEEE 802.11 wireless and mobile clients

One of the most critical issues in introducing Wireless LAN (WLAN) real-time and delay sensitive applications, such as Voice over IP (VoIP), is guaranteeing IP service continuation during inter-subnet Basic Service Set (BSS) transitions. Even though WLANs offer very high channel bandwidth, they exhibit long network-layer handoff latency. This is a restraining factor for mobile clients using interactive multimedia applications such as VoIP or video streaming. In a previous work, we presented a novel fast and efficient IP mobility solution, called “IP-IAPP”, which offers constant IP connectivity to the 802.11 mobile users and successfully preserves their ongoing sessions, even during subnet handoffs (fast recovery of active connections). It is an 802.11-dependent IP mobility solution, which accelerates the network reconfiguration phase after subnet handoffs and significantly reduces the IP handoff latency. It restores L3 connectivity almost simultaneously to the L2 connectivity after a subnet handoff, due to a zero-delay movement detection method. As a result, even the most demanding next generation WLAN applications such as Voice over WLAN (VoWLAN) suffer insignificant disruption. In this paper we present an improved version of the IP-IAPP mobility mechanism (new optimized protocol procedures). Certain extensions have also been incorporated to the initial proposal, for the provision of more advanced services: (a) secure inter-AP IP-IAPP communications, (b) zero patching on the clients s/w, and (c) support of clients which use a dynamic IP address. Performance measurements out of further and more complex testing verify that the proposed method outperforms other existing mobility solutions, and still introduces the lesser imperative amendments to the existing 802.11 wireless LAN framework. Ioanna F. Samprakou received her B. Eng in Computer Engineering and Informatics in 2000 and her MSc. in the same area in 2003 from the University of Patras, Greece. She is currently a Ph.D canditate at the University of Patras. She has joined Atmel SA in 2002, where she is a Senior Wireless System Eng at the System Concept and Design group. She specializes in wireless technologies, and mobile communications, and holds a patent in the field of IP mobility. She has led teams in developing wireless 802.11 products such as Wi-Fi APs, STAs, and VoIP phones. Previously she has worked for the Research & Academic Computer & Technology Institute of Patras (RACTI) as an R&D computer engineer. She is a member of the Technical Chamber of Greece. Christos J. Bouras obtained his Diploma and PhD from the Computer Science and Engineering Department of Patras University (Greece). He is currently an Associate Professor in the above department. Also he is a scientific advisor of Research Unit 6 in Research Academic Computer Technology Institute (CTI), Patras, Greece. His research interests include Analysis of Performance of Networking and Computer Systems, Computer Networks and Protocols, Telematics and New Services, QoS and Pricing for Networks and Services, e – learning, Networked Virtual Environments and WWW Issues. He has extended professional experience in Design and Analysis of Networks, Protocols, Telematics and New Services. He has published 200 papers in various well-known refereed conferences and journals. He is a co-author of 7 books in Greek. He has been a PC member and referee in various international journals and conferences. He has participated in R&D projects such as RACE, ESPRIT, TELEMATICS, EDUCATIONAL MULTIMEDIA, ISPO, EMPLOYMENT, ADAPT, STRIDE, EUROFORM, IST, GROWTH and others. Also he is member of, experts in the Greek Research and Technology Network (GRNET), Advisory Committee Member to the World Wide Web Consortium (W3C), IEEE Learning Technology Task Force, IEEE Technical Community for Services Computing WG 3.3 Research on Education Applications of Information Technologies and W 6.4 Internet Applications Engineering of IFIP, Task Force for Broadband Access in Greece, ACM, IEEE, EDEN, AACE and New York Academy of Sciences. Theodore E. Karoubalis. received his B. Eng in Computer Engineering and Informatics in 1992 and his Ph.D. in the same area in 1996 from the University of Patras, Greece. He has joined ATMEL Hellas SA at 1998. Since 1998 he is the Manager of PSLi software dpt. and since 2002 he is the manager of System and Concepts dpt. His interests include systems on chip, embedded applications, wireless systems etc. He is a member of IEEE and the Technical Chamber of Greece.     

An Algorithm for Adaptive Mean Filtering and Its Hardware Implementation

Noise due to the sensor and the electronics of a camera is an undesirable issue in any machine vision application. Such noise tends to corrupt images and to obstruct any further analysis. An algorithm to detect and cancel such noise, using statistical methods, is presented in this paper. The proposed algorithm is an adaptive mean filter, which filters out image regions that are found to be noise corrupted. The efficiency of the proposed filter was examined both qualitatively and quantitatively, by software simulation in several noisy conditions. The main advantage of the filter in hand is that it is appropriate for hardware implementation and can be easily incorporated to smart cameras. The hardware implementation of the filter is also presented in this paper. This implementation aims at time critical applications such as machine vision, inspection and visual surveillance. Ioannis Gasteratos holds a Diploma in Electrical Engineering from the Department of Electrical and Computer Engineering, Democritus University of Thrace, Greece, 2004. His research interests include digital VLSI design, computer architectures and artificial intelligence. He is a member of the IEEE, and a member of the Technical Chamber of Greece (TEE). Antonios Gasteratos is a Lecturer of Robotics in the Department of Production and Management, Democritus University of Thrace, Greece. He holds a PhD from the Department of Electrical and Computer Engineering, Democritus University of Thrace, Greece, 1999. During 2001–2003 he was a visiting Assistant Professor in the Department of Electrical and Computer Engineering, Democritus Univesrsity of Thrace. He serves as a reviewer to numerous of Scientific Journals and International Conferences. His research interests are mainly in computer and robot vision and sensory data fusion. He is a member of the IEEE, the IAPR, the EURASIP, the Hellenic Society of Artificial Intelligence (SETN) and the Technical Chamber of Greece (TEE). Ioannis Andreadis received the Diploma Degree from the Department of Electrical & Computer Engineering, DUTH, Greece, in 1983 and the MSc and PhD Degrees from the University of Manchester Institute of Science & Technology, UK, in 1985 and 1989, respectively. His research interests are mainly in Intelligent Systems, Machine Vision and VLSI based computing architectures. He joined the Department of Electrical & Computer Engineering, DUTH in 1993. He is a member of the Editorial Board of the Pattern Recognition Journal, TEE and IEEE.     

Minimum-Energy Broadcasting in Multi-hop Wireless Networks Using a Single Broadcast Tree

In this paper we address the minimum-energy broadcast problem in multi-hop wireless networks, so that all broadcast requests initiated by different source nodes take place on the same broadcast tree. Our approach differs from the most commonly used one where the determination of the broadcast tree depends on the source node, thus resulting in different tree construction processes for different source nodes. Using a single broadcast tree simplifies considerably the tree maintenance problem and allows scaling to larger networks. We first show that, using the same broadcast tree, the total power consumed for broadcasting from a given source node is at most twice the total power consumed for broadcasting from any other source node. We next develop a polynomial-time approximation algorithm for the construction of a single broadcast tree. The performance analysis of the algorithm indicates that the total power consumed for broadcasting from any source node is within 2H(n−1) from the optimal, where n is the number of nodes in the network and H(n) is the harmonic function. This approximation ratio is close to the best achievable bound in polynomial time. We also provide a useful relation between the minimum-energy broadcast problem and the minimum spanning tree, which shows that a minimum spanning tree may be a good candidate in sparsely connected networks. The performance of our algorithm is also evaluated numerically with simulations. A preliminary version of this work appeared in the Proceedings of WiOpt’04: Modeling and Optimization in Mobile, Ad hoc and Wireless Networks, University of Cambridge, UK, March 2004. Ioannis Papdimitriou was fully supported for this work by the Public Benefit Foundation “ALEXANDER S. ONASSIS”, Athens, Greece. Ioannis Papadimitriou was born in Veria, Greece, in 1976. He received his five year Diploma from the Department of Electronic and Computer Engineering, Technical University of Crete (Chania), Greece, in 1999 (graduating 2nd in class). He is currently a postgraduate student - Ph.D. candidate at the Telecommunications division, Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, Greece. His doctoral thesis deals with the design of wireless ad hoc networks. His research interests include broadcast and multicast communication, energy conservation, routing and topology control protocols, MAC layer and QoS issues. During his studies he has been honored with awards and scholarships by the Technical University of Crete, the Hellenic Telecommunications Organization S.A.(OTE S.A.) and Ericsson Hellas S.A. Mr. Papadimitriou has been a member of the Technical Chamber of Greece (TEE) since March 2000, and he has been supported by the Public Benefit Foundation ALEXANDER S. ONASSIS, Athens, Greece, with a scholarship for his doctoral studies from October 2001 to March 2005. Leonidas Georgiadis received the Diploma degree in electrical engineering from Aristotle University, Thessaloniki, Greece, in 1979, and his M.S. and Ph.D. degrees both in electrical engineering from the University of Connecticut, in 1981 and 1986, respectively. From 1981 to 1983 he was with the Greek army. From 1986 to 1987 he was Research Assistant Professor at the University of Virginia, Charlottesville. In 1987 he joined IBM T.J. Watson Research Center, Yorktown Heights, as a Research Staff Member. Since October 1995, he has been with the Telecommunications Department of Aristotle University, Thessaloniki, Greece. His interests are in the area of wireless networks, high speed networks, distributed systems, routing,scheduling, congestion control, modeling and performance analysis. Prof. Georgiadis is a senior member of IEEE Communications Society. In 1992 he received the IBM Outstanding Innovation Award for his work on goal-oriented workload management for multi-class systems.x     

An Overlay Smart Spaces System for Load Balancing in Wireless LANs

An overlay smart spaces system, called MITOS, is proposed for managing the use of the resources in wireless local area networks (WLAN). MITOS monitors the traffic load distribution in the different WLAN segments, as well as the location of each user, and when necessary, suggests to specific users to change their location in order to improve their quality of service. Enhancements to the basic MITOS architecture are introduced to intelligently manage local congestion, and maintain an almost uniform load level across the network. The approach used for load balancing is based on game theoretic mechanisms, such as the solutions to the Santa Fe Bar Problem. Simulation results are provided showing the efficiency of the proposed system. The research of the author for his PhD studies is supported by the Alexander S. Onassis Foundation Scholarship Programme. George Alyfantis received his B.Sc. degree in Informatics and Telecommunications from the Department of Informatics and Telecommunications, University of Athens, Athens Greece, in 2002. He received his M.Sc. degree in Communication and Network Systems from the same Department, in 2003. Since 2001, he is a member of the Communication Networks Laboratory (CNL) of the University of Athens. Currently, he is working towards his Ph.D. thesis. His research interests include pervasive/mobile computing, middleware for wireless sensor networks, web caching performance and game theory. He is the author of 5 papers in the aforementioned areas. In the course of his studies he received numerous distinctions like the Alexandros Onassis Foundation Scholarship for his Ph.D. studies, the best student award of the Department of Informatics and Telecommunications for graduating first in his B.Sc./M.Sc. class and the best M.Sc. thesis Ericsson Award of Excellence in Telecommunications 2004. Stathes Hadjiefthymiades received his B.Sc. (honors) in Informatics from the Department of Informatics at the University of Athens, Greece, in 1993 and his M.Sc. (honors) in Informatics (Advanced information systems) from the same department in 1996. In 1999 he received his Ph.D. from the University of Athens (Department of Informatics and Telecommunications). In 2002 he received a joint engineering-economics M.Sc. degree from the National Technical University of Athens. In 1992 he joined the Greek consulting firm Advanced Services Group, Ltd., where he was involved in the analysis and specification of information systems and the design-implementation of telematic applications. In 1995 he became a member of the Communication Networks Laboratory (UoA-CNL) of the University of Athens. During the period September 2001–July 2002, he served as a visiting assistant professor at the University of Aegean, Department of Information and Communication Systems Engineering. On the summer of 2002 he joined the faculty of the Hellenic Open University (Department of Informatics), Patras, Greece, as an assistant professor. Since December 2003, he is in the faculty of the Department of Informatics and Telecommunications, University of Athens, where he is presently an assistant professor. He is coordinating the Pervasive Computing Research Group of the Dept. of Informatics and Telecommunications at the University of Athens. He has participated in numerous projects realized in the context of EU programs (ACTS, ORA, TAP, and IST), EURESCOM projects, as well as national initiatives. His research interests are in the areas of web engineering, wireless/mobile computing, and networked multimedia applications. He is the author of over 80 publications in the above areas. Lazaros Merakos received the Diploma in electrical and mechanical engineering from the National Technical University of Athens, Athens, Greece, in 1978, and the M.S. and Ph.D. degrees in electrical engineering from the State University of New York, Buffalo, in 1981 and 1984, respectively. From 1983 to 1986, he was in the faculty of the Electrical Engineering and Computer Science Department University of Connecticut, Storrs. From 1986 to 1994 he was in the faculty of the Electrical and Computer Engineering Department, Northeastern University, Boston, MA. During the period 1993–1994, he served as director of the Communications and Digital Processing Research Center, Northeastern University. During the summers of 1990 and 1991, he was a visiting scientist at the IBM T. J. Watson Research Center, Yorktown Heights, NY. In 1994, he joined the faculty of the University of Athens, Athens, Greece, where he is presently a professor in the Department of Informatics and Telecommunications, and director of the Communication Networks Laboratory (UoA-CNL) and the Networks Operations and Management Center. Since 1995, he is leading the research activities of UoA-CNL in the area of mobile communications, in the framework of the Advanced Communication Technologies and Services (ACTS) and Information Society Technologies (IST) programs funded by the European Union (projects RAINBOW, Magic WAND, WINE, MOBIVAS, POLOS, ANWIRE, E2R, LIAISON). His research interests are in the design and performance analysis of communication networks, and wireless/mobile communication systems and services. He has authored more than 190 papers in the above areas. Dr. Merakos is chairman of the board of the Greek Universities Network, the Greek Schools Network, and member of the board of the Greek Research Network. In 1994, he received the Guanella Award for the best paper presented at the International Zurich Seminar on Mobile Communications.     

Cell-Site Diversity Against Co-Channel Interference in LMDS Networks

LMDS networks are fixed radio systems providing advanced telecommunication services to a variety of users. Millimeter wave frequencies above 20 GHz have been allocated to LMDS systems by ITU-R and CEPT. The design of LMDS systems must take into account how interference affects performance considering the dominant propagation impairments in these frequencies. In the present paper, cell-site diversity, an effective fade mitigation countermeasure for LMDS systems, is considered for the reduction of intersystem interference on downstream LMDS channels. The intersystem cochannel interference may originate from adjacent LMDS networks or from point-to-point links operating at the same frequencies. A physical propagation model for the calculation of carrier-to-interference ratio diversity gain for the downstream channel is presented. Numerical results focus on the impact of frequency of operation, the subscriber's service availability and the climatic conditions on the interference analysis of LMDS networks either using or not cell site diversity. Athanasios D. Panagopoulos was born in Athens, Greece on January 26, 1975. He received the Diploma Degree in Electrical and Computer Engineering (summa cum laude) and the Dr. Engineering Degree from National Technical University of Athens (NTUA) in July 1997 and inAprilxcan l 2002. From May 2002 to July 2003, he had served the Technical Corps of Hellenic Army. In September 2003, he joined School of Pedagogical and Technological Education, as Assistant Professor. He is also Research Assistant in the Wireless & Satellite Communications Group of NTUA. He has published more than eighty papers in international journals and conference proceedings. He is the recipient of URSI General AssemblyYoung ScientistAward in 2002 and 2005 respectively. His research interests include radio communication systems design, wireless and satellite communications networks and the propagation effects on multiple access systems and on communication protocols. He is member of IEEE and member of Technical Chamber of Greece. Konstantinos P. Liolis was born in Athens, Greece in 1981. He received the Diploma degree in electrical and computer engineering from the National Technical University of Athens (NTUA) and the M.Sc. degree in electrical engineering from the University of California, San Diego (UCSD) in July 2004 and December 2005, respectively. He is currently working towards his Ph.D. degree in electrical engineering at NTUA. From September 2004 to December 2005, he was research assistant in the California Institute for Telecommunications and Information Technology (Cal-IT2) within UCSD. Since June 2006, he has been with the European Space Agency Research and Technology Centre (ESA/ESTEC), Noordwijk, The Netherlands. His research interests are in the areas of multiple antenna (MIMO) and multicarrier (OFDM) transmission techniques and their application to broadband fixed wireless access and satellite communication networks. He is student member of the IEEE and member of the Technical Chamber of Greece (TEE). He received the 3rd Best Student Paper Award in the 2006 IEEE Radio and Wireless Symposium. Panayotis G. Cottis was born in Thessaloniki, Greece, in 1956. He received the Dipl. (mechanical and electrical engineering) and Dr.Eng. degrees from the National Technical University of Athens (NTUA), Greece, in 1979 and 1984, respectively, and the M.Sc. degree from the University of Manchester, (UMIST), Manchester, U.K., in 1980. In 1986, he joined the Department of Electrical and Computer Engineering, National Technical University of Athens (NTUA), Greece, where he is currently a Professor. He has published more than seventy papers in international journals and transactions. His research interests include microwave theory and applications, wave propagation in anisotropic media, electromagnetic scattering, wireless and satellite communications. Since September 2003, he is the Vice Rector of NTUA.     

Medium Access Control for Integrated Multimedia Wireless Access with the Use of a Video Packet Discard Scheme

A well designed Medium Access Control (MAC) protocol for wireless networks should provide an efficient mechanism to share the limited bandwidth resources, and satisfy the diverse and usually contradictory Quality of Service (QoS) requirements of each traffic class. In this paper a new MAC protocol for next generation wireless communications is presented and investigated. The protocol uses a combined Packet Discard/Forward Error Correction scheme in order to efficiently integrate MPEG-4 videoconference packet traffic with voice, SMS data and web packet traffic over a noisy wireless channel of high capacity. Our scheme achieves high aggregate channel throughput in all cases of traffic load, while preserving the Quality of Service (QoS) requirements of each traffic type, and is shown to clearly outperform DPRMA, another efficient MAC protocol proposed in the literature for multimedia traffic integration over wireless networks. Dr. Polychronis Koutsakis was born in Hania, Greece, in 1974. He received his 5-year Diploma in Electrical Engineering in 1997 from the University of Patras, Greece and his MSc and Ph.D. degrees in Electronic and Computer Engineering in 1999 and 2002, respectively, from the Technical University of Crete, Greece. He was a Visiting Lecturer at the Electronic and Computer Engineering Department of the same University for three years (2003–2006). He is currently an Assistant Professor at the Electrical and Computer Engineering Department of McMaster University, Canada. His research interests focus on the design, modeling and performance evaluation of computer communication networks, and especially on the design and evaluation of multiple access schemes for multimedia integration over wireless networks, on call admission control and traffic policing schemes for both wireless and wired networks, on multiple access control protocols for mobile satellite networks, wireless sensor networks and powerline networks, and on traffic modeling. Dr. Koutsakis has authored more than 45 peer-reviewed papers in the above mentioned areas, has served as a Guest Editor for an issue of the ACM Mobile Computing and Communications Review, as a TPC member for conferences such as IEEE GLOBECOM, IEEE LCN and IEEE PerCom, will serve as Session Chair for the IEEE GLOBECOM 2006 Symposium on Satellite & Space Communications and serves as a reviewer for most of the major journal publications focused on his research field. Moisis Vafiadis was born in Elefsina, Greece, in 1980. He has recently completed his studies towards the Diploma in Electronic Engineering at the Technological Educational Institute of Crete, Greece. His research interests focus on wireless personal communication networks, and especially on the MAC layer and on the development and testing of wireless multimedia applications.     

Improved Performance of Maximum Likelihood Decoding Algorithm with Efficient Use of Algebraic Decoder

A new soft decision maximum-likelihood decoding algorithm, which generates the minimum set of candidate codewords by efficiently applying the algebraic decoder is proposed. As a result, the decoding complexity is reduced without degradation of performance. The new algorithm is tested and verified by simulation results.Panagiotis G. Babalis was born in Athens, Greece, on January 3, 1974. He received his Diploma of electrical and computer engineering and the Ph.D. degree, both from National Technical University of Athens (NTUA), Athens, Greece, in 1996 and 2001, respectively. His main research interests include mobile satellite communications, modulation, and wireless communications systems coding. Dr. Babalis is a member of the technical Chamber of Greece.Panagiotis T. Trakadas was born in Athens, Greece, on January 14, 1972. He received his Diploma of Electrical and Computer Engineering and the Ph.D. degree from National Technical University of Athens (NTUA), Athens, Greece, in 1996, and 2001, respectively. From 1998 to 2001, he participated in many European projects as a researcher. His main research interests include mobile communications systems and electromagnetic compatibility topics. Dr. Trakadas is a member of the Technical Chamber of Greece and IEEE Society.Theodore B. Zahariadis received his Ph.D. degree in electrical and computer engineering from the National Technical University of Athens, Greece, and his Dipl.-Ing. Degree in computer engineering and information science from the University of Patras, Greece. Currently, he is the technical director of Ellemedia Technologies, where he leads R&D of end-to-end interactive multimedia services, embedded systems, and 3G/4G core network services. Since 1994 he has participated in many European co-funded projects. His research interests are in the fields of broadband wireline/wireless/mobile communications, interactive service deployment, management of IP/WDM networks, and embedded systems. He has published more than 30 papers. He has been a reviewer and principal guest editor in many journals and magazines. He is a member of the ACM and the Technical Chamber of Greece.Christos N. Capsalis was born in Greece, in 1956. He received the diploma in electrical and mechanical engineering from the National Technical University of Athens (NTUA), Athens, Greece, in 1979, the B.Sc. degree in economics from the University of Athens, Athens, Greece, in 1983, and the Ph.D. degree in electrical engineering from NTUA in 1985. He is currently a Professor at NTUA and Director of the wireless communications laboratory. His current research activities include wireless and satellite communications systems and EMC topics.     

Mobile Phone Antenna Performance and Power Absorption in Terms of Handset Size and Distance from User’s Head

In this work numerical simulation and measurements of three-dimensional radiation patterns of a mobile handset model in the presence of a human head phantom were performed at 1800 MHz. Based on theoretical and experimental results, the influence of the human head on the radiation efficiency of the handset has been investigated as a function of the handset size and the distance between the head and the handset during its operation. Furthermore, the relative amount of the electromagnetic power absorbed in the head has been obtained. It was found that significant reduction of the absorbed power (about 50%) with proportional increment of the handset radiation efficiency could be achieved by moving the phone for 1 cm only away from the head. Agreement between theoretical and experimental results was found to be very good.Theodore Zervos was born in Athens, Greece, on October 5, 1978. He received the diploma in Electrical & Computer Engineering from the University of Patras, Patras, Greece, in 2001. He is currently a Postgraduate Student at the Laboratory of Electromagnetics, Department of Electrical & Computer Engineering, University of Patras. He is also a doctoral scholar at the Mobile Communications Laboratory of the Institute of Informatics and Telecommunications of NCSR Demokritos, Athens. His research interests include electromagnetic modelling, EM radiation measurements and interaction between the human body and mobile handsets antenna. Dipl. T. Zervos is a Member of the Technical Chamber of Greece. In June 2002, his thesis received the 2nd Award of Excellence in Telecommunications from Ericsson.Antonis Alexandridis (1962) is senior researcher in the Institute of informatics and Telecommunications (IIT) of Greek National Research Centre (NCSR) Demokritos. He received the diploma in Electrical Engineering from Technical University ofPatras, Greece (1985), and the Ph.D. degree from the same University (1992). From 1993 he is working in the Mobile Communications Lab of NCSR. Since 1999 he is responsible for the operation of the RF Anechoic Chamber of the IIT. His current interests include mobile communications, propagation models, spread spectrum systems and CDMA techniques, EMC measurements, human exposure to EM fields, interaction between human body and mobile terminals antennas and smart antennas.Vladimir V. Petrovic was born in 1965 in Belgrade, Serbia. He received the B.Sc., M.Sc., and D.Sc., degrees from the University of Belgrade, Serbia and Montenegro in 1989, 1993, and 1996, respectively. He joined the Faculty of Electrical Engineering, University of Belgrade in 1990, where at present he is an Assistant Professor in Electromagnetics and Fundamentals of Electrical Engineering. He is a co-author of a chapter in a monograph, a software package AWAS 2.0 (Artech House – Boston, London, 2002) and several journal and conference articles. His research interests are in numerical electromagnetics, especially in radiation and propagation problems in layered media.Kostas Dangakis was born in Kavala, Greece, in 1950. He received his Diploma in Electrical Engineering from NTUA (Athens, 1973) and his Ph.D. on Digital Modulation/Data Transmission from Techn. Univ. of Patras, Dept. of Electrical Engineering (1984). Since 1977, he has worked at the Inst. of Inform. & Telecom. (IIT) of NCSR Demokritos, in projects related to voice/data/video signal encryption, synchronisation techniques in TDM systems, digital modulation techniques/data transmission, Spread Spectrum/CDMA techniques, mobile communications, conformance testing (DECT, ERMES), radio propagation, channel characterization and antennas. He is research director at IIT and has been project leader of several R & D projects.Branko M. Kolundzija Antonije R. Djordjevic was born in Belgrade, Yugoslavia, on April 28, 1952. He received the B.Sc., M.Sc., and D.Sc. degrees from the Faculty of Electrical Engineering, University of Belgrade, in 1975, 1977, and 1979, respectively. In 1975, he joined the School of Electrical Engineering, University of Belgrade, as a Teaching Assistant. He was promoted to an Assistant Professor, Associate Professor, and Professor, in 1982, 1988, and 1992, respectively. In 1983, he was a Visiting Associate Professor at Rochester Institute of Technology, Rochester, NY. Since 1992, he has also been an Adjunct Scholar with Syracuse University, Syracuse, NY. In 1997, he was elected a Corresponding Member of the Serbian Academy of Sciences and Arts. His main area of interest is numerical electromagnetics, in particular applied to fast digital signal interconnects, wire and surface antennas, microwave passive circuits, and electromagnetic-compatibility problems.C. Soras received both his diploma and Ph.D. in electrical engineering from the University of Patras, Patras, Greece, in 1981 and 1989 respectively. He was a Lecturer in the Laboratory of Electromagnetics of the Electrical and Computer Engineering department of the University of Patras in Greece from 1991 to 2001, where currently serves as an Assistant Professor. He is teaching the basic electromagnetic courses and at the senior undergraduate / graduate level computational electromagnetics. His current research interests focus on computational electromagnetics, multiple element antennas for diversity and MIMO terminal devices and indoor radio wave propagation. Prof. Soras is a member of IEEE, Applied Computational Electromagnetics Society and the Technical Chamber of Greece.     

Delay Performance Analysis and Evaluation of IEEE 802.11e EDCA in Finite Load Conditions

The paper presents an analytical model for the performance evaluation of IEEE 802.11e EDCA scheme under finite load conditions on the basis of various instances of delay metric (i.e., media access delay, queuing delay and total delay). The simulation results show that the analytical estimated instances of the delay metric are almost accurate. The paper exhibits that concerning the delay of serving classes, EDCA compared to the conventional DCF, favors high priority classes against low priority ones, while almost does not affect the behavior of medium ones. Dimitris Vassis was born in Ioannina, Greece, in 1978. He received the Diploma in Electrical and Computing Engineering and the MBA in Techno-economic Systems both from the National Technical University of Athens (NTUA), Greece, in 2001 and 2004 respectively. Currently, he is a Ph.D. student in the University of the Aegean, Department of Information and Communication Systems Engineering. His research interests are in the fields of performance evaluation and performance analysis of wireless access networks. George Kormentzas is currently lecturer in the University of the Aegean, Department of Information and Communication Systems Engineering. He was born in Athens, Greece on 1973. He received the Diploma in Electrical and Computer Engineering and the Ph.D. in Computer Science both from the National Technical University of Athens (NTUA), Greece, in 1995 and 2000, respectively. From 2000 to 2002, he was a research associate with the Institute of Informatics & Telecommunications of the Greek National Center for Scientific Research “Demokritos”. His research interests are in the fields of traffic analysis, network control, resource management and quality of service in broadband networks. He has published extensively in the fields above, in international scientific journals, edited books and conference proceedings. He is a member of pronounced professional societies, an active reviewer and guest editor for several journals and conferences and EU-evaluator for Marie Curie Actions. George Kormentzas has participated in a number of national and international research projects, serving in some instances as the project's technical representative for University of Aegean and/or as WP leader and/or as the project's Technical Manager.     

Performance of a burst-frame-based CSMA/CA protocol: Analysis and enhancement

In this paper, we develop an analytical model to evaluate the delay performance of the burst-frame-based CSMA/CA protocol under unsaturated conditions, which has not been fully addressed in the literature. Our delay analysis is unique in that we consider the end-to-end packet delay, which is the duration from the epoch that a packet enters the queue at the MAC layer of the transmitter side to the epoch that the packet is successfully received at the receiver side. The analytical results give excellent agreement with the simulation results, which represents the accuracy of our analytical model. The results also provide important guideline on how to set the parameters of the burst assembly policy. Based on these results, we further develop an efficient adaptive burst assembly policy so as to optimize the throughput and delay performance of the burst-frame-based CSMA/CA protocol. Kejie Lu received the B.E. and M.E. degrees in Telecommunications Engineering from Beijing University of Posts and Telecommunications, Beijing, China, in 1994 and 1997, respectively. He received the Ph.D. degree in Electrical Engineering from the University of Texas at Dallas in 2003. In 2004 and 2005, he was a postdoctoral research associate in the Department of Electrical and Computer Engineering, University of Florida. Currently, he is an assistant professor in the Department of Electrical and Computer Engineering, University of Puerto Rico at Mayagüez. His research interests include architecture and protocols design for computer and communication networks, performance analysis, network security, and wireless communications. Jianfeng Wang received the B.E. and M.E. degrees in electrical engineering from Huazhong University of Science and Technology, China, in 1999 and 2002, respectively, and the Ph.D. degree in electrical engineering from University of Florida in 2006. From January 2006 to July 2006, he was a research intern in wireless standards and technology group, Intel Corporation. In October 2006, he joined Philips Research North America as a senior member research staff in wireless communications and networking department. He is engaged in research and standardization on wireless networks with emphasis on medium access control (MAC). Dapeng Wu received B.E. in Electrical Engineering from Huazhong University of Science and Technology, Wuhan, China, in 1990, M.E. in Electrical Engineering from Beijing University of Posts and Telecommunications, Beijing, China, in 1997, and Ph.D. in Electrical and Computer Engineering from Carnegie Mellon University, Pittsburgh, PA, in 2003. Since August 2003, he has been with Electrical and Computer Engineering Department at University of Florida, Gainesville, FL, as an Assistant Professor. His research interests are in the areas of networking, communications, multimedia, signal processing, and information and network security. He received the IEEE Circuits and Systems for Video Technology (CSVT) Transactions Best Paper Award for Year 2001, and the Best Paper Award in International Conference on Quality of Service in Heterogeneous Wired/Wireless Networks (QShine) 2006. Currently, he serves as the Editor-in-Chief of Journal of Advances in Multimedia, and an Associate Editor for IEEE Transactions on Wireless Communications, IEEE Transactions on Circuits and Systems for Video Technology, IEEE Transactions on Vehicular Technology, and International Journal of Ad Hoc and Ubiquitous Computing. He is also a guest-editor for IEEE Journal on Selected Areas in Communications (JSAC), Special Issue on Cross-layer Optimized Wireless Multimedia Communications. He served as Program Chair for IEEE/ACM First International Workshop on Broadband Wireless Services and Applications (BroadWISE 2004); and as a technical program committee member of over 30 conferences. He is Vice Chair of Mobile and wireless multimedia Interest Group (MobIG), Technical Committee on Multimedia Communications, IEEE Communications Society. He is a member of the Best Paper Award Committee, Technical Committee on Multimedia Communications, IEEE Communications Society. Yuguang Fang received a Ph.D. degree in Systems Engineering from Case Western Reserve University in January 1994 and a Ph.D. degree in Electrical Engineering from Boston University in May 1997. He was an assistant professor in the Department of Electrical and Computer Engineering at New Jersey Institute of Technology from July 1998 to May 2000. He then joined the Department of Electrical and Computer Engineering at University of Florida in May 2000 as an assistant professor and got an early promotion to an associate professor with tenure in August 2003 and to a full professor in August 2005. He has published over 200 papers in refereed professional journals and conferences. He received the National Science Foundation Faculty Early Career Award in 2001 and the Office of Naval Research Young Investigator Award in 2002. He has served on several editorial boards of technical journals including IEEE Transactions on Communications, IEEE Transactions on Wireless Communications, IEEE Transactions on Mobile Computing and ACM Wireless Networks. He have also been actively participating in professional conference organizations such as serving as The Steering Committee Co-Chair for QShine, the Technical Program Vice-Chair for IEEE INFOCOM’2005, Technical Program Symposium Co-Chair for IEEE Globecom’2004, and a member of Technical Program Committee for IEEE INFOCOM (1998, 2000, 2003–2007). He is a senior member of the IEEE.     

A Unified Mechanism for Multimedia Downlink Scheduling and Call Admission Control for Future Error-Prone Wireless Networks

In this paper we design and evaluate the performance of a unified mechanism for downlink scheduling and call admission control of multimedia traffic in a high-capacity TDMA wireless channel. In our scheme, the Base Station interacts with the Call Admission Controller and incorporates predictions on the channel condition in its decision making. Our results show that, with the use of the “intelligent” scheduler-admission controller mechanism, system performance is significantly enhanced compared to two other schemes without prediction on the channel condition. Polychronis Koutsakis was born in Hania, Greece, in 1974. He received his 5-year Diploma in Electrical Engineering in 1997 from the University of Patras, Greece and his MSc and Ph.D. degrees in Electronic and Computer Engineering in 1999 and 2002, respectively, from the Technical University of Crete, Greece. He is currently a Visiting Lecturer at the Electronic and Computer Engineering Department of the same University. His research interests focus on the design, modeling and performance evaluation of wireless personal communication networks, and especially on the design and evaluation of multiple access schemes for multimedia integration over wireless and mobile satellite networks, on call admission control and traffic policing schemes for both wireless and wired networks and on traffic modeling. Dr. Koutsakis has authored more than 25 peer-reviewed papers in the above mentioned areas, and serves as a reviewer for many of the major journal publications focused on his research field. He is a member of the Greek Chamber of Professional Engineers and of the Greek Association of Electrical and Mechanical Engineers.     

Alternative Schemes for Dynamic Secure VPN Deployment in UMTS

Three alternative schemes for secure Virtual Private Network (VPN) deployment over the Universal Mobile Telecommunication System (UMTS) are proposed and analyzed. The proposed schemes enable a mobile node to voluntarily establish an IPsec-based secure channel to a private network. The alternative schemes differ in the location where the IPsec functionality is placed within the UMTS network architecture (mobile node, access network, and UMTS network border), depending on the employed security model, and whether data in transit are ever in clear-text, or available to be tapped by outsiders. The provided levels of privacy in the deployed VPN schemes, as well as the employed authentication models are examined. An analysis in terms of cost, complexity, and performance overhead that each method imposes to the underlying network architecture, as well as to the mobile devices is presented. The level of system reliability and scalability in granting security services is presented. The VPN management, usability, and trusted relations, as well as their behavior when a mobile user moves are analyzed. The use of special applications that require access to encapsulated data traffic is explored. Finally, an overall comparison of the proposed schemes from the security and operation point of view summarizes their relative performance. Christos Xenakis received his B.Sc. degree in computer science in 1993 and his M.Sc. degree in telecommunication and computer networks in 1996, both from the Department of Informatics and Telecommunications, University of Athens, Greece. In 2004 he received his Ph.D. from the University of Athens (Department of Informatics and Telecommunications). From 1998–2000 was with the Greek telecoms system development firm Teletel S.A., where was involved in the design and development of advanced telecommunications subsystems for ISDN, ATM, GSM, and GPRS. Since 1996 he has been a member of the Communication Networks Laboratory of the University of Athens. He has participated in numerous projects realized in the context of EU Programs (ACTS, ESPRIT, IST). His research interests are in the field of mobile/wireless networks, security and distributed network management. He is the author of over 15 papers in the above areas. Lazaros Merakos received the Diploma in electrical and mechanical engineering from the National Technical University of Athens, Greece, in 1978, and the M.S. and Ph.D. degrees in electrical engineering from the State University of New York, Buffalo, in 1981 and 1984, respectively. From 1983 to 1986, he was on the faculty of Electrical Engineering and Computer Science at the University of Connecticut, Storrs. From 1986 to 1994 he was on the faculty of the Electrical and Computer Engineering Department at Northeastern University, Boston, MA. During the period 1993–1994 he served as Director of the Communications and Digital Processing Research Center at Northeastern University. During the summers of 1990 and 1991, he was a Visiting Scientist at the IBM T. J. Watson Research Center, Yorktown Heights, NY. In 1994, he joined the faculty of the University of Athens, Athens, Greece, where he is presently a Professor in the Department of Informatics and Telecommunications, and Director of the Communication Networks Laboratory (UoA-CNL) and the Networks Operations and Management Center. His research interests are in the design and performance analysis of broadband networks, and wireless/mobile communication systems and services. He has authored more than 150 papers in the above areas. Since 1995, he is leading the research activities of UoA-CNL in the area of mobile communications, in the framework of the Advanced Communication Technologies & Services (ACTS) and Information Society Technologies (IST) programmes funded by the European Union (projects RAINBOW, Magic WAND, WINE, MOBIVAS, POLOS, ANWIRE). He is chairman of the board of the Greek Universities Network, the Greek Schools Network, and member of the board of the Greek Research Network. In 1994, he received the Guanella Award for the Best Paper presented at the International Zurich Seminar on Mobile Communications.