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.     

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.     

Metadata Design for Reconfigurable Protocol Stacks in Systems Beyond 3G

Global consensus on the next generation of wireless mobile communications, broadly termed “beyond 3G”, sketches a heterogeneous infrastructure comprising different wireless systems in a complementary manner and vested with reconfiguration capabilities, which support a flexible and dynamic adaptation of the wireless network and its spectrum resources to meet the ever-changing service requirements. For ubiquitous reconfiguration to become a practical capability of mobile communication systems, it is necessary to establish a global architecture for modeling, expressing, and circulating essential metadata related to reconfiguration, including reconfigurable device capabilities and semantic properties of protocol stacks. We outline the relevant standardization initiatives in the mobile domain, summarize existing work in reconfiguration-supporting architectures, and identify key shortcomings that may hinder the advent of ubiquitously reconfigurable systems. Further on, we point out some major limitations of current metadata standards in the mobile domain for the representation of capability information pertaining to reconfigurable protocol stacks. Next, we identify essential metadata classes in support of reconfigurable communication systems, introducing an associated object-oriented UML model. We elaborate on the design rationale of the UML model, presenting and discussing the alternative metadata representation standards and suitable encoding formats. Finally, we demonstrate the suitability of our UML model by applying our reconfiguration-supporting vocabulary in the cases of a standardized protocol stack of 3G mobile devices and stationary 3G cellular network elements. Vangelis Gazis received his B.Sc. and M.Sc. (Communication Networking) degrees from the Department of Informatics & Telecommunications of the University of Athens, Greece, in 1995, and 1998, respectively. He also received an M.B.A. degree from the Athens University of Economics and Business in 2001. Since 1996 until, he has been with the research staff of the Communication Networks Laboratory (CNL) of the University of Athens. He has participated in national and European research projects (MOBIVAS, ANWIRE) of the IST framework programme. He specializes in reconfigurable mobile systems and networks for beyond 3G, metadata and ontology languages, reflective and component middleware, adaptable services and open API frameworks for telecommunications. He is currently a Ph.D. candidate in the Department of Informatics & Telecommunications of the University of Athens. Nancy Alonistioti holds a B.Sc. degree and a Ph.D. degree in informatics and telecommunications from the University of Athens. Presently, she is a senior researcher in the Department of Informatics and Telecommunications of the University of Athens. In the past, she has held a research position with the Institute of Informatics and Telecommunications of NCSR “Demokritos” in the areas of protocol and service design and testing, mobile systems (UMTS), open architectures, and software defined radio systems and networks. Her current research interests are in reconfigurable mobile systems and networks beyond 3G, and adaptable services, pervasive computing and context awareness. She has participated in several national and European R&D projects, and has been the technical manager of the IST-MOBIVAS and IST-ANWIRE projects, which have had a focus on reconfigurable mobile systems, networks an respective service provision. She is currently a member of the management team and workpackage leader in the FP6 IST-E2R project on reconfigurability; she also serves as technical manager for the University of Athens in the FP6 IST-LIAISON project, which focuses on location based services in working environments. Dr Alonistioti is co-editor and co-author of the book entitled “Software defined radio, Architectures, Systems and Functions”, published by John Wiley in May 2003. She has authored over 55 publications in the area of mobile communications and reconfigurable systems and networks. 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 on the faculty of the Electrical Engineering and Computer Science Department, University of Connecticut, Storrs. From 1986 to 1994, he was on the faculty of the Electrical and Computer Engineering Department, Northeastern University, Boston, MA. During the period 1993D1994, 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.     

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.     

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.     

A Radio Resource Allocation Scheme for Fixed Broadband Wireless Access Systems with Avoidance of Major Interferers

An improved radio resource allocation scheme with avoidance of major interferers is proposed and analyzed for the downlink of Fixed Broadband Wireless Access (FBWA) systems with full frequency reuse. The scheme is based on Enhanced Staggered Resource Allocation (ESRA) and permits the enhancement of the throughput per sector. Simulation results show a maximum downlink throughput per sector in excess of 44% and an increase of 10% with respect to ESRA is achieved, with Base Station (BS) selection procedure, while meeting a 15 dB signal-to-interference ratio (SIR). Nicholas Vaiopoulos was bornin Lamia in 1977. He received his Physics degree and his M.Sc.degree in electronics and radio-communications from the University of Athens, Greecein 2000and 2003, respectively. Currently, he is working towards his Ph.D. degree on the resource allocation techniques with reference to wireless systems at the Department of informatics and Telecommunications at the same University. His research interests include broadband communications systems, scheduling algorithms and power control techniques for wireless systems. Alexander Vavoulaswas born in Athens in 1976. He received his B.Sc. degree in physics and the M.Sc. degree in electronics and radio-communications in 2000 and 2002 respectively,both from the University of Athens, Greece. Currently he is working toward the Ph.D. degree on the radio resource allocation techniques with the same University. His research interest is focused on broadband wireless access and interference management. He is a student nmember of the IEEE. Dimitris Varoutas holds BSc. degree in Physics, M.Sc. in electronics and radio-communi cations and Ph.D. in telecommunications systems and technoeconomics, all from the University of Athens. He is a lecturer in the Department of Informatics and Telecommunications of University of Athens and an adjunct assistant professor in the Department of Telecommunications of the newly founded University of Peloponnese. He has participating in numerous European R&D projects in the RACE I &II, ACTS, Telematics, RISI and IST framework in the areas of telecommunications and Technoeconomics. He is an adviser in several organisations including OTE and EETT (Greek NRA for telecommunications) in the fields of telecommunications, broadband and mobile services, licensing, spectrum management, pricing and legislation. His research interests are optical, microwave communications and technoeconomic evaluation of network architectures and services. He has more than 30 publications in refereed journal and conferences in the area of telecommunications, optoelectronics and technoeconomics. He is a member of IEEE and serves as reviewer in several journals and conferences. Thomas Sphicopoulos received the Physics degree from Athens University in 1976, the D.E.A. degree and Doctorate in Electronics both from the University of Paris VI in 1977 and 1980 respectively, the Doctorat Es Science from the Ecole Polytechnique Federale de Lausanne in 1986. From 1976 to 1977 he worked in Thomson CSF Central Research Laboratories on Microwave Oscillators. From 1977 to 1980 he was an Associate Researcher in Thomson CSF Aeronautics Infrastructure Division. In 1980 he joined the Electromagnetism Laboratory of the Ecole Polytechnique Federal de Lausanne where he carried out research on Applied Electromagnetism. Since 1987 he is with the Athens University engaged in research on Broadband Communications Systems. In 1990 he was elected as an Assistant Professor of Communications in the Department of Informatics & Telecommunications, in 1993 as Associate Professor and since 1998 he is a Professor in the same Department. His main scientific interests are Microwave and Optical Communication Systems and Networks and Techno-economics. He has lead about 40 National and European R&D projects. He has more than 100 publications in scientific journals and conference proceedings. From 1999 he is advisor in several organisations including EETT (Greek NRA for telecommunications) in the fields of market liberalisation, spectrum management techniques and technology convergence.     

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.     

Specification and Dynamic Introduction of 3rd Party,Service-Specific Adaptation Policies for Mobile Applications

The development, delivery and management of mobile services are the subject of many research activities in both the academia and industry. The ultimate goal of these efforts is a dynamic environment that enables the delivery of situation-aware, personalised multimedia services over heterogeneous, ubiquitous infrastructures, commonly termed as systems beyond 3rd generation (3G). Reconfigurability and adaptability are key aspects of the mobile systems beyond 3G. Reconfigurable mobile systems and networks introduce additional requirements and complexity in service adaptation. Moreover, it is widely recognised that services will be increasingly developed by independent third parties, besides mobile operators and equipment vendors. The present contribution complements previous work by the authors, related to mediating service provision platforms and advanced adaptability and profile management frameworks. It introduces mechanisms and middleware that undertake the service adaptation overhead, imposed by the complexity of reconfigurable mobile networks, from application developers and third party service providers. In particular, it enables the introduction of third party policies for adaptation decision. Finally, it facilitates the adaptable application development and service deployment independently from the underlying dynamically reconfigurable communication environment. Nikos Houssos holds a B.Sc. and a Ph.D. degree from the Department of Informatics Telecommunications at the University of Athens, Greece, and an M.Sc. degree (with distinction) in Telematics from the department of Electronic and Electrical Engineering, University of Surrey, UK. Since 1999, he is working at the Communication Networks Laboratory of the University of Athens. He has participated in various research projects of the European Union IST framework (MOBIVAS, ANWIRE, POLOS, E2R). His research interests include middleware platforms and business models for mobile service provision in 3G/4G environments, service adaptability, network reconfigurability and context-aware pervasive systems. Nancy Alonistioti has a B.Sc. degree and a PhD degree in Informatics and Telecommunications (University of Athens). She has been working for several years at the Dept. of Informatics and Telecommunications in University of Athens as a senior researcher and project manager. She has been involved in many European and national projects (CTS, SS#7, ACTS RAINBOW, EURESCOM) in the areas of protocol and service design of mobile systems. She has been the Technical manager of the IST-MOBIVAS and IST-ANWIRE projects. She had been working as expert at the Greek Regulatory Agency. She is member of the core management team of the Greek Universities Network (GUNET). Her current research includes: mobile communications, re-configurable mobile systems and networks, adaptability, service provision, protocol design and mobile computing. Lazaros Merakos received a Diploma in electrical and mechanical engineering form the National Technical University of Athens, Greece, in 1978 and 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 Connectitut, Storrs. From 1986 to 1994 he was on the faculty of the Electrical and Computer Engineering Department at Northeastern University, Boston, Massachusetts. During the period 1993–1994 he served as a 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, New York. In 1994 he joined the faculty of the University of 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 and Services (ACTS) and Information Society Technologies (IST) programs funded by the European Union (projects RAINBOW, Magic WAND, WINE, MOBIVAS, POLOS). He is chairman of board of the Greek Universities Network, the Greek Schools Network, and a 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.This revised version was published online in August 2005 with a corrected cover date.     

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.     

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.     

Optimizing the QoS of Ultra High and High Speed Moving Terminals in Satellite-Aided Cellular Networks

This paper presents a new channel assignment technique based on a three-layer cellular architecture which optimizes the QoS of Ultra High-Speed (UHSMT) and High-Speed Moving Terminals (HSMT) in a congested urban area. The lower layer of the proposed architecture is based on a microcellular solution, for absorbing the traffic loads of Low Speed Moving Terminals (LSMT). The second layer is based on a macro-cell umbrella solution, for absorbing the traffic load of the HSMT. The higher layer is based on satellite cell and absorbs the traffic load of UHSMT. The results show that assigning the optimum number of channels in every layer, the QoS of UHSMT and HSMT are optimized, having a small bad effect on the QoS of LSMT. Konstantinos Ioannou was born in Patras, Greece, in 1975. He received the Diploma and the PhD in Electrical and Computer Engineering in 1998 and 2004, respectively, from the Polytechnic School of the University of Patras. His dissertation, elaborated at the Wireless Telecommunications Laboratory of the Department of Electrical and Computer Engineers, dealt with Channel Assignment Techniques, Handover Procedures, Traffic Modeling and Call Admission Policies in 2G, 3G Mobile Systems and Security Mobile Systems. During his Postgraduate Studies, he participated in many European and National Research Projects. Since the October of 1999, he is working as an Assistant Professor (under contract) at the Technological Educational Institute of Messolongi – Departments of Applied Informatics in Management & Economy Electronics and Informatics. During the last 2 years, he belongs also to the Technical Consultants Team of the Ministry of Public Order, regarding the C4I Olympic Security System, involved, among others, with TETRA and AVL subsystems. His scientific interests include Mobile and Satellite Communications, Wired and Wireless Networks, Handover and Channel Assignment Techniques and Communication Services. A lot of publications in scientific journals and conference proceedings – 27 and 40, respectively – document his research activity. Konstantinos Ioannou is a member of the Technical Chamber of Greece (TEE). Ioannis Panoutsopoulos was born in Patras, Greece, in 1974. He received the Diploma and the PhD in Electrical and Computer Engineering in 1997 and 2003, respectively, from the Polytechnic School of the University of Patras. His dissertation, elaborated at the Wireless Telecommunications Laboratory of the Department of Electrical and Computer Engineers, dealt with Handover Procedures, Traffic modeling and Call Admission Policies in 2G and 3G Mobile Systems. During his Postgraduate Studies, he participated in many European and National Research Projects. Since the October of 2003, he is working as an Assistant Professor (under contract) at the Technological Educational Institute of Athens - Departments of Electronics and Informatics – teaching Antenna Theory, Electromagnetic Waves Propagation – Transmission Lines and Mobile Telecommunications Systems. During the last 2 years, he belongs also to the Technical Consultants Team of the Ministry of Public Order, regarding the C4I Olympic Security System, involved, among others, with TETRA and AVL subsystems. His scientific interests include Mobile and Satellite Communications, Wired and Wireless Networks, Handover and Channel Assignment Techniques and Communication Services. A lot of publications in scientific journals and conference proceedings – 12 and 18, respectively – document his research activity. Ioannis Panoutsopoulos is a member of the Technical Chamber of Greece (TEE). 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 is an M.Phil and Ph.D. holder since 1978 and 1985 correspondingly. He did his postgraduate studies in the University of Bradford in United Kingdom. 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 Professor. He develops his professional life teaching and doing research at the Laboratory of Wireless Telecommunications (Univ. Of Patras), with interest in mobile communications, interference, satellite communications, telematics, 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 conferences. Ast. 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.     

Localized algorithms for coverage boundary detection in wireless sensor networks

Connected coverage, which reflects how well a target field is monitored under the base station, is the most important performance metric used to measure the quality of surveillance that wireless sensor networks (WSNs) can provide. To facilitate the measurement of this metric, we propose two novel algorithms for individual sensor nodes to identify whether they are on the coverage boundary, i.e., the boundary of a coverage hole or network partition. Our algorithms are based on two novel computational geometric techniques called localized Voronoi and neighbor embracing polygons. Compared to previous work, our algorithms can be applied to WSNs of arbitrary topologies. The algorithms are fully distributed in the sense that only the minimal position information of one-hop neighbors and a limited number of simple local computations are needed, and thus are of high scalability and energy efficiency. We show the correctness and efficiency of our algorithms by theoretical proofs and extensive simulations. Chi Zhang received the B.E. and M.E. degrees in Electrical Engineering from Huazhong University of Science and Technology, Wuhan, China, in July 1999 and January 2002, respectively. Since September 2004, he has been working towards the Ph.D. degree in the Department of Electrical and Computer Engineering at the University of Florida, Gainesville, Florida, USA. His research interests are network and distributed system security, wireless networking, and mobile computing, with emphasis on mobile ad hoc networks, wireless sensor networks, wireless mesh networks, and heterogeneous wired/wireless networks. Yanchao Zhang received the B.E. degree in computer communications from Nanjing University of Posts and Telecommunications, Nanjing, China, in July 1999, the M.E. degree in computer applications from Beijing University of Posts and Telecommunications, Beijing, China, in April 2002, and the Ph.D. degree in electrical and computer engineering from the University of Florida, Gainesville, in August 2006. Since September 2006, he has been an Assistant Professor in the Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark. His research interest include wireless and Internet security, wireless networking, and mobile computing. He is a member of the IEEE and ACM. Yuguang Fang received the BS and MS degrees in Mathematics from Qufu Normal University, Qufu, Shandong, China, in 1984 and 1987, respectively, a Ph.D. degree in Systems and Control Engineering from Department of Systems, Control and Industrial Engineering at Case Western Reserve University, Cleveland, Ohio, in January 1994, and a Ph.D. degree in Electrical Engineering from Department of Electrical and Computer Engineering at Boston University, Massachusetts, in May 1997. From 1987 to 1988, he held research and teaching position in both Department of Mathematics and the Institute of Automation at Qufu Normal University. From September 1989 to December 1993, he was a teaching/research assistant in Department of Systems, Control and Industrial Engineering at Case Western Reserve University, where he held a research associate position from January 1994 to May 1994. He held a post-doctoral position in Department of Electrical and Computer Engineering at Boston University from June 1994 to August 1995. From September 1995 to May 1997, he was a research assistant in Department of Electrical and Computer Engineering at Boston University. From June 1997 to July 1998, he was a Visiting Assistant Professor in Department of Electrical Engineering at the University of Texas at Dallas. From July 1998 to May 2000, he was an Assistant Professor in the Department of Electrical and Computer Engineering at New Jersey Institute of Technology, Newark, New Jersey. In May 2000, he joined the Department of Electrical and Computer Engineering at University of Florida, Gainesville, Florida, where he got early promotion to Associate Professor with tenure in August 2003, and to Full Professor in August 2005. His research interests span many areas including wireless networks, mobile computing, mobile communications, wireless security, automatic control, and neural networks. He has published over one hundred and fifty (150) 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 also received the 2001 CAST Academic Award. He is listed in Marquis Who’s Who in Science and Engineering, Who’s Who in America and Who’s Who in World. Dr. Fang has actively engaged in many professional activities. He is a senior member of the IEEE and a member of the ACM. He is an Editor for IEEE Transactions on Communications, an Editor for IEEE Transactions on Wireless Communications, an Editor for IEEE Transactions on Mobile Computing, an Editor for ACM Wireless Networks, and an Editor for IEEE Wireless Communications. He was an Editor for IEEE Journal on Selected Areas in Communications:Wireless Communications Series, an Area Editor for ACM Mobile Computing and Communications Review, an Editor for Wiley International Journal on Wireless Communications and Mobile Computing, and Feature Editor for Scanning the Literature in IEEE Personal Communications. He has also actively involved with many professional conferences such as ACM MobiCom’02 (Committee Co-Chair for Student Travel Award), MobiCom’01, IEEE INFOCOM’06, INFOCOM’05 (Vice-Chair for Technical Program Committee), INFOCOM’04, INFOCOM’03, INFOCOM’00, INFOCOM’98, IEEE WCNC’04, WCNC’02, WCNC’00 Technical Program Vice-Chair), WCNC’99, IEEE Globecom’04 (Symposium Co-Chair), Globecom’02, and International Conference on Computer Communications and Networking (IC3N) (Technical Program Vice-Chair).     

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.     

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.     

Mobile multi-layered IPsec

To achieve high throughput in wireless networks, smart forwarding and processing of packets in access routers is critical for overcoming the effects of the wireless links. However, these services cannot be provided if data sessions are protected using end-to-end encryption as with IPsec, because the information needed by these algorithms resides inside the portion of the packet that is encrypted, and can therefore not be used by the access routers. A previously proposed protocol, called Multi-layered IPsec (ML-IPsec) modifies IPsec in a way so that certain portions of the datagram may be exposed to intermediate network elements, enabling these elements to provide performance enhancements. In this paper we extend ML-IPsec to deal with mobility and make it suitable for wireless networks. We define and implement an efficient key distribution protocol to enable fast ML-IPsec session initialization, and two mobility protocols that are compatible with Mobile IP and maintain ML-IPsec sessions. Our measurements show that, depending on the mobility protocol chosen, integrated Mobile IP/ML-IPsec handoffs result in a pause of 53–100 milliseconds, of which only 28–75 milliseconds may be attributed to ML-IPsec. Further, we provide detailed discussion and performance measurements of our MML-IPsec implementation. We find the resulting protocol, when coupled with SNOOP, greatly increases throughput over scenarios using standard TCP over IPsec (165% on average). By profiling the MML-IPsec implementation, we determine the bottleneck to be sending packets over the wireless link. In addition, we propose and implement an extension to MML-IPsec, called dynamic MML-IPsec, in which a flow may switch between plaintext, IPsec and MML-IPsec. Using dynamic MML-IPsec, we can balance the tradeoff between performance and security. Heesook Choi is a Ph.D. candidate in the Department of Computer Science and Engineering at the Pennsylvania State University. She received her B.S. degree in Computer Science and Statistics and M.S. degree in Computer Science from the Chungnam National University, Korea, in 1990 and 1992 respectively. She was a senior research staff in Electronics and Telecommunications Research Institute (ETRI) in Korea before she enrolled in the Ph.D. program at the Pennsylvania State University in August 2002. Her research interests lie in security and privacy in distributed systems and wireless mobile networks, focusing on designing algorithms and conducting system research. Hui Song is a Ph.D. candidate in the Department of Computer Science and Engineering at the Pennsylvania State University, University Park. He received the M.E. degree in Computer Science from Tsinghua University, China in 2000. His research interests are in the areas of network and system security, wireless ad-hoc and sensor networks, and mobile computing. He was a recipient of the research assistant award of the Department of Computer Science and Engineering at the Pennsylvania State University in 2005. Guohong Cao received his BS degree from Xian Jiaotong University, Xian, China. He received the MS degree and Ph.D. degree in computer science from the Ohio State University in 1997 and 1999 respectively. Since then, he has been with the Department of Computer Science and Engineering at the Pennsylvania State University, where he is currently an Associate Professor. His research interests are wireless networks and mobile computing. He has published over one hundred papers in the areas of sensor networks, wireless network security, data dissemination, resource management, and distributed fault-tolerant computing. He is an editor of the IEEE Transactions on Mobile Computing and IEEE Transactions on Wireless Communications, a guest editor of special issue on heterogeneous wireless networks in ACM/Kluwer Mobile Networking and Applications, and has served on the program committee of many conferences. He was a recipient of the NSF CAREER award in 2001. Thomas F. La Porta received his B.S.E.E. and M.S.E.E. degrees from The Cooper Union, New York, NY, and his Ph.D. degree in Electrical Engineering from Columbia University, New York, NY. He joined the Computer Science and Engineering Department at Penn State in 2002 as a Full Professor. He is the Director of the Networking and Security Research Center at Penn State. Prior to joining Penn State, Dr. La Porta was with Bell Laboratories since 1986. He was the Director of the Mobile Networking Research Department in Bell Laboratories, Lucent Technologies where he led various projects in wireless and mobile networking. He is a Bell Labs Fellow. Dr. La Porta was the founding Editor-in-Chief of the IEEE Transactions on Mobile Computing and served as Editor-in-Chief of IEEE Personal Communications Magazine. He is currently the Director of Magazines for the IEEE Communications Society and is a member of the Communications Society Board of Governors. He has published over 50 technical papers and holds 28 patents. His research interests include mobility management, signaling and control for wireless networks, mobile data systems, and protocol design.     

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.     

On the Economics of 3G Mobile Virtual Network Operators (MVNOs)

The paper assesses the market conditions and dynamics, the architectures and the different approaches for deployment of 3G Mobile Virtual Network Operators (MVNOs), in an attempt to address specific advantages and pitfalls. Following the definition of appropriate service sets and tariff structures, and taking into account demand scenarios, a techno-economic model has been developed, in order to compute key economic indicators. The paper presents techno-economic results of specific business cases and deployment alternatives for an average “large” European country and a smaller, Nordic-type country. Fixed and variable costs have been identified and the business case shows how different service sets lead to different costs. Different MVNO business profiles have been investigated. Profitability for all scenarios and business profiles has been calculated, presented and discussed. Major opportunities and threats, as well as critical parameters and uncertainties have been identified through sensitivity analysis. Dimitris Varoutas holds Physics degree and M.Sc. and Ph.D degrees in electronics and radio-communications from the University of Athens. He is a research fellow and adjunct lecturer in the Department of Informatics and Telecommunications of University of Athens. He is also an adjunct lecturer in the Department of Telecommunications of the newly founded University of Peloponnese. He has participating in numerous European R&D projects in the RACE I &II, ACTS, Telematics, RISI and IST framework in the areas of telecommunications and Technoeconomics. He is an adviser in several organisations including OTE and EETT (Greek NRA for telecommunications) in the fields of telecommunications, broadband and mobile services, licensing, spectrum management, pricing and legislation. His research interests are optical, microwave communications and technoeconomic evaluation of network architectures and services. He has more than 30 publications in refereed journal and conferences in the area of telecommunications, optoelectronics and technoeconomics. He is a member of IEEE and serves as reviewer in several journals and conferences. Dimitris Katsianis received the Informatics degree and the M.Sc in Signal Processing and Computational Systems from the University of Athens. He is a research fellow in the Informatics Department of University of Athens. He was technical consultant scientific co-operator for Hellenic Telecommunication Organisation (OTE) in networking aspects concerning simulation of ATM networks and Management in an all Optical network, participating in several Eurescom (European Institute for Research and Strategic Studies in Telecommunication) projects. He was consultant in investment analysis projects for OTE Consulting S.A. He was also technical consultant in Telecommunication and signal processing for Space Hellas and technical consultant in Networking Applications for ICL-Hellas. He was participating in several ACTS and IST projects (AC364 OPTIMUM, AC364TERA, IST 25172-TONIC, etc.) as the case study leader for 3G and 4G business cases. He has more than 25 publications in journal and conferences in the field of techno-economics and 3G-network design. Thomas Sphicopoulos received the Physics degree from Athens University in 1976, the D.E.A. degree and Doctorate in Electronics both from the University of Paris VI in 1977 and 1980 respectively, the Doctorat Es Science from the Ecole Polytechnique Federale de Lausanne in 1986. From 1976 to 1977 he worked in Thomson CSF Central Research Laboratories on Microwave Oscillators. From 1977 to 1980 he was an Associate Researcher in Thomson CSF Aeronautics Infrastructure Division. In 1980 he joined the Electromagnetism Laboratory of the Ecole Polytechnique Federal de Lausanne where he carried out research on Applied Electromagnetism. Since 1987 he is with the Athens University engaged in research on Broadband Communications Systems. In 1990 he was elected as an Assistant Professor of Communications in the Department of Informatics, in 1993 as Associate Professor and since 1998 he is a Professor in the same Department. His main scientific interests are Microwave and Optical Communication Systems and Networks and Techno-economics. He is leading about 30 National and European R&D projects (RACE I and II, ACTS, RISI, HCM, COST, Eurescom, etc.) including Synthesis and TITAN. He has more than 80 publications in scientific journals and conference proceedings. He is also a reviewer in journals of IEEE and IEE and auditor and evaluator of RACE and ACTS projects. He is the Chairman of the IEEE LEOS Chapter (Bulgaria, Greece, Romania and Yugoslavia). From 1999 he is advisor in several organisations including EETT (Greek NRA for telecommunications) in the fields of market liberalisation, spectrum management techniques and technology convergence. Kjell Stordahl received his M.Sc. from Oslo University in 1972. He has been at the Research Department Telenor for 15 years; 7 years as a manager of the Teletraffic field. He joined Telenor Networks in 1989 as Chief Planning Manager until 1996. He has been manager of Market analysis in Telenor Networks 1997–2002. Kjell Stordahl was appointed associated reporter and special reporter 1981–1988 in CCITT SGII for “Forecasting International Traffic”. From 1985 to 1988 he participated in CCITT GAS 10 and developed a forecasting handbook. He has also worked for ITU's headquarter as a specialist on forecasting. From 1994 to 1997 he was on the Board of Telenor Consult AS. He was referee for Project Imagine 21 in the ESPRIT Programme 1999–2001. Kjell Stordahl was on the Technical Advisory Board of Virtual Photonics 2000–2002. Since 1992 he has participated in various projects funded by the European Commission: RACE/TITAN, ACTS/OPTIMUM and TERA, IST/TONIC and CELTIC/ECOSYS. Kjell Stordahl has published over 150 papers in International Journals and Conferences.     

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     

A secure authentication and billing architecture for wireless mesh networks

Wireless mesh networks (WMNs) are gaining growing interest as a promising technology for ubiquitous high-speed network access. While much effort has been made to address issues at physical, data link, and network layers, little attention has been paid to the security aspect central to the realistic deployment of WMNs. We propose UPASS, the first known secure authentication and billing architecture for large-scale WMNs. UPASS features a novel user-broker-operator trust model built upon the conventional certificate-based cryptography and the emerging ID-based cryptography. Based on the trust model, each user is furnished with a universal pass whereby to realize seamless roaming across WMN domains and get ubiquitous network access. In UPASS, the incontestable billing of mobile users is fulfilled through a lightweight realtime micropayment protocol built on the combination of digital signature and one-way hash-chain techniques. Compared to conventional solutions relying on a home-foreign-domain concept, UPASS eliminates the need for establishing bilateral roaming agreements and having realtime interactions between potentially numerous WMN operators. Our UPASS is shown to be secure and lightweight, and thus can be a practical and effective solution for future large-scale WMNs. Yanchao Zhang received the B.E. degree in Computer Communications from Nanjing University of Posts and Telecommunications, Nanjing, China, in July 1999, and the M.E. degree in Computer Applications from Beijing University of Posts and Telecommunications, Beijing, China, in April 2002. Since September 2002, he has been working towards the Ph.D. degree in the Department of Electrical and Computer Engineering at the University of Florida, Gainesville, Florida, USA. His research interests are network and distributed system security, wireless networking, and mobile computing, with emphasis on mobile ad hoc networks, wireless sensor networks, wireless mesh networks, and heterogeneous wired/wireless networks. Yuguang Fang received the BS and MS degrees in Mathematics from Qufu Normal University, Qufu, Shandong, China, in 1984 and 1987, respectively, a Ph.D degree in Systems and Control Engineering from Department of Systems, Control and Industrial Engineering at Case Western Reserve University, Cleveland, Ohio, in January 1994, and a Ph.D degree in Electrical Engineering from Department of Electrical and Computer Engineering at Boston University, Massachusetts, in May 1997. From 1987 to 1988, he held research and teaching position in both Department of Mathematics and the Institute of Automation at Qufu Normal University. From September 1989 to December 1993, he was a teaching/research assistant in Department of Systems, Control and Industrial Engineering at Case Western Reserve University, where he held a research associate position from January 1994 to May 1994. He held a post-doctoral position in Department of Electrical and Computer Engineering at Boston University from June 1994 to August 1995. From September 1995 to May 1997, he was a research assistant in Department of Electrical and Computer Engineering at Boston University. From June 1997 to July 1998, he was a Visiting Assistant Professor in Department of Electrical Engineering at the University of Texas at Dallas. From July 1998 to May 2000, he was an Assistant Professor in the Department of Electrical and Computer Engineering at New Jersey Institute of Technology, Newark, New Jersey. In May 2000, he joined the Department of Electrical and Computer Engineering at University of Florida, Gainesville, Florida, where he got early promotion to Associate Professor with tenure in August 2003, and to Full Professor in August 2005. His research interests span many areas including wireless networks, mobile computing, mobile communications, wireless security, automatic control, and neural networks. He has published over one hundred and fifty (150) 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 also received the 2001 CAST Academic Award. He is listed in Marquis Who’s Who in Science and Engineering, Who’s Who in America and Who’s Who in World. Dr. Fang has actively engaged in many professional activities. He is a senior member of the IEEE and a member of the ACM. He is an Editor for IEEE Transactions on Communications, an Editor for IEEE Transactions on Wireless Communications, an Editor for IEEE Transactions on Mobile Computing, an Editor for ACM Wireless Networks, and an Editor for IEEE Wireless Communications. He was an Editor for IEEE Journal on Selected Areas in Communications: Wireless Communications Series, an Area Editor for ACM Mobile Computing and Communications Review, an Editor for Wiley International Journal on Wireless Communications and Mobile Computing, and Feature Editor for Scanning the Literature in IEEE Personal Communications. He has also actively involved with many professional conferences such as ACM MobiCom’02 (Committee Co-Chair for Student Travel Award), MobiCom’01, IEEE INFOCOM’06, INFOCOM’05 (Vice-Chair for Technical Program Committee), INFOCOM’04, INFOCOM’03, INFOCOM’00, INFOCOM’98, IEEE WCNC’04, WCNC’02, WCNC’00 (Technical Program Vice-Chair), WCNC’99, IEEE Globecom’04 (Symposium Co-Chair), Globecom’02, and International Conference on Computer Communications and Networking (IC3N) (Technical Program Vice-Chair).     

A secure incentive protocol for mobile ad hoc networks

The proper functioning of mobile ad hoc networks depends on the hypothesis that each individual node is ready to forward packets for others. This common assumption, however, might be undermined by the existence of selfish users who are reluctant to act as packet relays in order to save their own resources. Such non-cooperative behavior would cause the sharp degradation of network throughput. To address this problem, we propose a credit-based Secure Incentive Protocol (SIP) to stimulate cooperation among mobile nodes with individual interests. SIP can be implemented in a fully distributed way and does not require any pre-deployed infrastructure. In addition, SIP is immune to a wide range of attacks and is of low communication overhead by using a Bloom filter. Detailed simulation studies have confirmed the efficacy and efficiency of SIP. This work was supported in part by the U.S. Office of Naval Research under Young Investigator Award N000140210464 and under grant N000140210554. Yanchao Zhang received the B.E. degree in Computer Communications from Nanjing University of Posts and Telecommunications, Nanjing, China, in July 1999, and the M.E. degree in Computer Applications from Beijing University of Posts and Telecommunications, Beijing, China, in April 2002. Since September 2002, he has been working towards the Ph.D. degree in the Department of Electrical and Computer Engineering at the University of Florida, Gainesville, Florida, USA. His research interests are network and distributed system security, wireless networking, and mobile computing, with emphasis on mobile ad hoc networks, wireless sensor networks, wireless mesh networks, and heterogeneous wired/wireless networks. Wenjing Lou is an assistant professor in the Electrical and Computer Engineering department at Worcester Polytechnic Institute. She obtained her Ph.D degree in Electrical and Computer Engineering from University of Florida in 2003. She received the M.A.Sc degree from Nanyang Technological University, Singapore, in 1998, the M.E degree and the B.E degree in Computer Science and Engineering from Xi'an Jiaotong University, China, in 1996 and 1993 respectively. From Dec 1997 to Jul 1999, she worked as a Research Engineer in Network Technology Research Center, Nanyang Technological University. Her current research interests are in the areas of ad hoc and sensor networks, with emphases on network security and routing issues. Wei Liu received his B.E. and M.E. in Electrical and Information Engineering from Huazhong University of Science and Technology, Wuhan, China, in 1998 and 2001. In August 2005, he received his PhD in Electrical and Computer Engineering from University of Florida. Currently, he is a senior technical member with Scalable Network Technologies. His research interest includes cross-layer design, and communication protocols for mobile ad hoc networks, wireless sensor networks and cellular networks. 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, got an early promotion to an associate professor with tenure in August 2003 and a professor in August 2005. He has published over 150 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 many 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 is a senior member of the IEEE.