A Dynamic Priority MAC Protocol for Time-Bounded Services in Wireless Networks

Wireless Local Area Networks have gained popularity at an unprecedented rate over the last few years. However, as the spectrum of applications they are called to support broadens, their inefficiency in meeting the diverse requirements of a wider range of applications becomes evident. Most existing access mechanisms cannot provide Quality-of-Service (QoS) assurances. Even those that are QoS aware can only provide relative service differentiation. In this work, we propose a dynamic priority medium access scheme to provide time-bounded services. By approximating an ideal Earliest Deadline First (EDF) scheduler, the proposed scheme can offer delay and delay jitter assurances while achieving high medium utilization. Analytical studies and simulation experiments document and confirm the positive characteristics of the proposed mechanism. Orestis Tsigkas received his Diploma in electrical and computer engineering from the Aristotle University of Thessaloniki, Greece in 2002. He is currently working towards his Ph.D. degree in the same department. His research interests include medium access, as well as quality-of-service provisioning. Fotini-Niovi Pavlidou received the Ph.D. degree in electrical engineering from the Aristotle University of Thessaloniki, Greece, in 1988 and the Diploma in mechanical-electrical engineering in 1979 from the same institution. She is currently a Professor at the Department of Electrical and Computer Engineering at the Aristotle University engaged in teaching for the under- and post-graduate program in the areas of mobile communications and telecommunications networks. Her research interests are in the field of mobile and personal communications, satellite communications, multiple access systems, routing and traffic flow in networks and QoS studies for multimedia applications over the Internet. She is being involved with many national and international projects in these areas (Tempus, COST, Telematics,IST) and she has been chairing the European COST262 Action on “Spread Spectrum Systems and Techniques for Wired and Wireless Communications”. She has served as member of the TPC in many IEEE/IEE conferences and she has organized/chaired some conferences like, the “IST Mobile Summit 2002”, the 6th “International Symposium on Power Lines Communications-ISPLC2002”, the “International Conference on Communications-ICT1998” etc. She is a permanent reviewer for many IEEE/IEE journals. She has published about 80 papers in refereed journals and conferences. She has served as guest-editor on special issues as: “Mobile Ad Hoc Networks (MANETs): Standards, Research, Applications” in the International Journal of Wireless Information Networks and “Power Line Communications and Applications” in the International Journal on Communications Systems. She is a senior member of IEEE, currently chairing the joint IEEE VT&AES Chapter in Greece.     

Turbo Trellis Coded Modulation with Enhanced Transition Metric over Rayleigh Fading Channels

This paper investigates the performance of a new Turbo Trellis Coded Modulation scheme over correlated flat fading channels with channel interleaving. The novelty of the scheme is based on the application of a new modified transition metric incorporated in the symbol-by-symbol MAP algorithm. We consider frequency non-selective, slow Rayleigh fading channels. Extensive simulation results together with EXIT chart analysis show that the proposed scheme achieves better performance compared to the conventional transition metric when channel state information is not available at the decoder. Kostas V. Koutsouvelis was born in Thessaloniki, Greece, on July 16,1970. He received the degree Diploma in Electrical Engineering from Aristotle University of Thessaloniki, Greece in 1996 and the Master degree in Satellite Communications Engineering from University of Surrey in 1997. From 1998 to 2003 he was involved in the development of V5.2 interface as a senior software designer in Intracom plc. In 2004 joined the research and development division of Hellenic Telecommunication Organization (OTE) and his also PhD candidate at Aristotle University of Thessaloniki working with Turbo codes and Turbo Coded Modulation. Christos E. Dimakiswasborn in Serres, Greece, on July 27, 1955.He received the degree Diploma in Electrical Engineering from the Aristotle University of Thessaloniki, Greece, in 1980. Working in the satellite communications and in the error correcting coding area he received his PhD degree in digital telecommunications from the Aristotle University of Thessaloniki, Greece, in 1994. In 1980 he joined the Department of Electrical Engineering, Telecommunications Division of the Aristotle University of Thessaloniki as a research fellow. Since 1997 he is a lecturer of digital communications at the same University. Presently, his research interests include digital modulations, coding theory, satellite and mobile communications and system simulation. Stamatis S. Kouris was born in Corfu, Greece. He received the degree of Doctor Engineer in Electrical Engineering from the University of Rome, Italy and the Diploma of Specialization in Telecommunications of the Instituto Superiore, University of Rome, in 1960 and 1963 respectively. In 1971 he was awarded the PhD Degree of the University of Edinburgh, UK. In the 1974 he was awarded a specialization Diploma in administration from the University of Pomona CA, USA. He is a member of the Technical Chamber of Greece, URSI, IRI and other organizations. Since 1964 he has been involved in research on radio-propagation, antennas and microwaves, working mainly at the Fondazione Bordoni, Italy, University of Edinburgh, UK and University of Thessaloniki, Greece. He has published several papers on radio-propagation, antennas, communication transmission and microwaves and millimeter-waves devices. In 1976 he joined with the Department of Electrical Engineering, School of Engineering Science, Aristotle University of Thessaloniki. He served as professor of telecommunications from 1978 to 2002. Since 2002 he is an emeritus professor.     

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.     

On the Performance of the HSLS Routing Protocol for Mobile Ad hoc Networks

The area of mobile ad hoc networks has recently attracted much scientific interest, as a very appealing research area with many open issues and still unsolved problems. One of the main issues that concerns researchers is the development of routing algorithms that present good performance and face a hostile environment. Many routing protocols have been proposed, attempting to minimize routing overhead, or to reduce the energy consumed by nodes in order to maximize their lifetime. A critical issue, though, is the development of routing protocols that have the ability to maintain their good characteristics at an acceptable level as the network population grows, an ability known as scalability. FSR, ZRP, HierLS and FSLS protocol family are only a sample of scalable algorithms that have been proposed so far. The HSLS protocol is a member of the FSLS family that is proved to scale the best among the algorithms of the FSLS protocol family. In this paper we propose a mechanism to enhance the already good characteristics of the HSLS protocol aiming at the reduction of routing overhead of the original protocol. This new scheme, which we called AFHSLS, exploits the so-called border nodes, in order to deliver routing packets to their destinations. The new algorithm is proved through simulations to significantly reduce routing overhead, with minor or practically no effect on other metrics, such as packet delivery ratio and delay of data packets. Georgios Koltsidas received his Diploma in Electrical and Computer Engineering from Aristotle University of Thessaloniki, Greece in 2003.Currently, his is working towards his Ph.D. in the same department. His research interests include routing and medium access for ad hoc and sensor networks, as well as resource management in UMTS networks. Gerasimos Dimitriadis received his Diploma in electrical and computer engineering from the Aristotle University of Thessaloniki, Greece in 2001. He is currently working towards his Ph.D. degree in the same department. His research interests include medium access, as well as routing in multihop wireless networks. Fotini-Niovi Pavlidou holds a Diploma and a PhD 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 in International Journals like IJWIN, WPC etc. She is permanently included in the Program Committee of many IEEE conferences (PIMRC, GLOBECOM, VTC'2001, ISSSTA'2000). 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 (http://newton.ee.auth.gr/ieee)     

Novel Channel and Polarization Assignment Schemes for 2–11 GHz Fixed–Broadband Wireless Access Networks

The scarcity of available spectrum in the 2–11 GHz frequency range and the continuously increasing number of users that require broadband communication services suggest that emerging fixed-broadband wireless access (F-BWA) networks will be deployed with aggressive frequency re-use to cope with capacity demands. In this context, co-channel interference may arise in high levels compromising the system's capacity and robust operation. Interference is further increased when limited directionality terminal antennas are employed to support non line-of-sight operation and in the case where an adaptive-time division duplex is selected for efficient radio resource management in asymmetric and time-varying traffic conditions. In this paper frequency channel assignment (CA) and antenna polarization assignment (PA) are considered as a means of mitigating interference. Two novel CA schemes that consider the distinct characteristics of F-BWA are proposed; the rotated-interleaved channel assignment and the non-uniform channel assignment. According to statistical interference simulation analysis the proposed schemes are more efficient in suppressing interference, achieving higher capacity compared to existing schemes while incurring no further complexity. In addition, instead of exploiting the performance of CA and PA schemes independently a framework for a joint CA-PA consideration is presented, where for a particular CA scheme an optimized PA pattern is developed. Results show that this approach improves the CA-PA interoperability increasing the overall performance. The efficiency of the proposed schemes is investigated for both FDD and adaptive-TDD schemes and is verified for various sectorization, frequency re-use and terminal antenna directivity configurations to ensure compatibility with different deployment scenarios. Bayan Sharif received the bachelor and doctorate degrees from Queens University of Belfast and Ulster University, N. Ireland, in 1984 and 1988. In 1989 he held a research fellowship post at Queens University of Belfast, where he worked on parallel programming algorithms for two-dimensional signal-processing applications. He joined Newcastle University in 1990 as Lecturer, and was promoted to Senior Lecturer and Professor in Digital Communications in 1999 and 2000. During this period he held visiting academic positions with Colorado State University and the UAE Telecommunication Corporation (Etisalat). He is currently Head of the Communications and Signal Processing Research Group at the School of Electrical, Electronic and Computer Engineering and his research interests are in digital communications with a focus on the optimization of wireless networks and DSP algorithms for receiver structures. Prof. Sharif has published over 170 journal and conference papers, and held UK and EU research grants in digital communications and signal processing worth over 2M. He is a Chartered Engineer and Fellow of the IEE. Panos I. Dallas (pdal@intracom.gr) 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. Konstantinos E. Ntagkounak is received the B.Sc. in Electrical Engineering from Technology Institute of Chalkis, Greece, in 1998 and the M.Sc. in Communications & Signal Processing from University of Newcastle, UK, in 2001, where he is currently studying for a Ph.D. in Electrical Engineering. Since 2001, he is with INTRACOM S.A. as a research engineer involved with several European Union IST research projects in the area of Advanced Communication Technologies. His research interests include medium access protocols, radio resource management and network architectures for next generation broadband wireless access systems.     

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

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

MIMO Channel Characterization for Short Range Fixed Wireless Propagation Environments

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

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

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

Satellite Navigation and Communications: An Integrated Vision

The paper addresses advanced layered architectures for the development of integration scenarios between satellite navigation and communications systems and services. This synercic cooperation represents – in author's vision – the core of future global networks. The concept of integration and its translation into an integrated network is displayed, together with examples of possible architectures for navigation-communications applications. In this frame, the paper addresses also the possible exploitation of stratospheric platforms (HAP) as permanent and on-demand blocks concurring to the effective deployment of the integrated vision. Marina Ruggieri graduated in Electronics Engineering in 1984 at the University of Roma. She was: with FACE-ITT and GTC-ITT (Roanoke, VA) in the High Frequency Division (1985–1986); Research and Teaching Assistant at the University of Roma Tor Vergata (RTV) (1986–1991); Associate Professor in Telecommunications at Univ. of L'Aquila (1991–1994) and at the University of RTV (1994–2000). Since November 2000 she is Full Professor in Telecommunications at the RTV (Faculty of Engineering), teaching DSP, Information and Coding. Since 2003 she directs a Master in “Advanced Satellite Communications and Navigation Systems” at RTV.Since 1999 she has been appointed member of the Board of Governors of the IEEE AES Society.Her research mainly concerns space communications and navigation systems (in particular satellites) as well as mobile and multimedia networks.She is the Principal Investigator of satellite scientific communications missions (DAVID, WAVE) of ASI, national research programs (CABIS) on CDMA integrated mobile systems and on satellite-HAP integrated networks for multimedia applications (SHINES), co-financed by MIUR. She co-ordinates RTV Unit in various European Projects: EU FP6 IP MAGNET (My personal Adaptive Global NET); EU ASIA LINK EAGER-NetWIC (Euro-Asian Network for Strengthening Graduate Education and Research in Wireless Communications); EU Network NEXWAY; GALILEO JU 1st Call: VERT (VEhicular Remote Tolling); and in the ASI program on V-band payloads (TRANSPONDERS).She is Editor of the IEEE Transactions on AES for “Space Systems”, Chair of the IEEE AES Space Systems Panel. Since 2002, she is co-chair of Track 2 “Space Missions, Systems, and Architecture” of the AES Conference; she has been re-appointed in the IEEE Judith A. Resnik Award Committee for 2004; she has been member of TPC for PLANS 2004.She was awarded the 1990 Piero Fanti International Prize and she had a nomination for the Harry M.Mimmo Award in 1996 and the Cristoforo Colombo Award in 2002.She is author of about 220 papers, on international journals/transactions and proceedings of international conferences, book chapters and books.She is an IEEE Senior Member (S'84-M'85-SM'94).     

Handover Optimization in Wireless Microcellular ATM Networks

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

Update Propagation Algorithms for Supporting Disconnected Write in Mobile Wireless Systems with Data Broadcasting Capability

We develop and analyze algorithms for propagating updates by mobile hosts in wireless client–server environments that support disconnected write operations, with the goal of minimizing the tuning time for update propagation to the server. These algorithms allow a mobile host to update cached data objects while disconnected and propagate the updates to the server upon reconnection for conflict resolutions. We investigate two algorithms applicable to mobile systems in which invalidation reports/data can be broadcast to mobile hosts periodically. We show that there exists an optimal broadcasting period under which the tuning time is minimized for update propagations. We perform a comparative analysis between these two update propagation algorithms that rely on broadcasting data and an algorithm that does not, and identify conditions under which an algorithm should be applied to reduce the total tuning time for update propagation by the mobile user to save the valuable battery power and avoid high communication cost. For real-time applications, we address the tradeoff between tuning time and access time with the goal to select the best update propagation algorithm that can minimize the tuning time while satisfying the imposed real-time deadline constraint. The analysis result is applicable to file/data objects that mobile users may need to modify while on the move. Ing-Ray Chen received the BS degree from the National Taiwan University, Taipei, Taiwan, and the MS and PhD degrees in computer science from the University of Houston. He is currently an associate professor in the Department of Computer Science at Virginia Tech. His research interests include mobile computing, pervasive computing, multimedia, distributed systems, real-time intelligent systems, and reliability and performance analysis. Dr. Chen has served on the program committee of numerous conferences, including as program chair for 29th IEEE Annual International Computer Software and Application Conference in 2005, 14th IEEE International Conference on Tools with Artificial Intelligence in 2002, and 3rd IEEE Symposium on Application-Specific Systems and Software Engineering Technology in 2000. Dr. Chen currently serves as an Associate Editor for IEEE Transactions on Knowledge and Data Engineering, The Computer Journal, and International Journal on Artificial Intelligence Tools. He is a member of the IEEE/CS and ACM. Ngoc Anh Phan received her Bachelor of Science degree from Moscow Technical University of Communication and Computer Science in 1997, and a Master of Science degree in Computer Science from Virginia Polytechnic Institute and State University (Virginia Tech) in 1999. She is currently a Ph.D student at Virginia Tech and a Senior Software Engineer at America Online Inc. Her research interests include wireless communications, data management, sensor networks, fault tolerance, and mobile computing. I-Ling Yen received her BS degree from Tsing-Hua University, Taiwan, and her MS and PhD degrees in Computer Science from the University of Houston. She is currently an Associate Professor of Computer Science at the University of Texas at Dallas. Dr. Yen's research interests are in distributed systems, fault-tolerant computing, self-stabilization algorithms, and security. She has served as program co-chair for the 1997 IEEE High Assurance Systems Engineering Workshop, the 1999 IEEE Symposium on Application-Specific Systems and Software Engineering Technology, and the 1999 Annual IEEE International Conference on Computer Software and Applications Conference. Dr. Yen is a member of the IEEE/CS.     

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

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

Real-time traffic support in heterogeneous mobile networks

Multi-hop mobile wireless networks have been proposed for a variety of applications where support for real-time multimedia services will be necessary. Support for these applications requires that the network is able to offer quality of service (QoS) appropriate for the latency and jitter bounds of the real-time application constraints. In this paper, we analyze the primary challenges of realizing QoS in mobile wireless networks with heterogeneous devices and propose a QoS framework for real-time traffic support. We address the problem in three ways: estimate the path quality for real-time flows, mitigate the impact of node heterogeneity on service performance, and reduce the impact of interfering non-real-time traffic. Specifically, our proposed QoS framework first utilizes a call setup protocol at the IP layer to discover paths for real-time flows, as well as to perform admission control by accurate service quality prediction. The underlying routing protocol also enables transparent path selection among heterogeneous nodes to provide stable paths for real-time traffic delivery. We then use a prioritized MAC protocol to provide priority access for flows with real-time constraints to reduce interference from unregulated non-real-time traffic. We foresee the utility of our proposed solution in heterogeneous mobile networks, such as campus or community-wide wireless networks. In these environments, resource-rich or fixed wireless routers may be leveraged to achieve better service quality when heterogeneity of node capability and movement is significant. Through experimental results, we demonstrate the utility and efficiency of our approach. Yuan Sun received her Ph.D. from the Department of Computer Science at the University of California, Santa Barbara in 2005. She worked with Prof. Elizabeth Belding-Royer in the MOMENT Lab. Her thesis work focused on providing QoS for mobile networks. Dr. Sun is currently employed at Google. Elizabeth M. Belding-Royer is an Associate Professor in the Department of Computer Science at the University of California, Santa Barbara. Elizabeth’s research focuses on mobile networking, specifically ad hoc and mesh networks, multimedia, monitoring, and advanced service support. She is the founder of the Mobility Management and Networking (MOMENT) Laboratory (moment.cs.ucsb.edu) at UCSB. Elizabeth is the author of over 50 papers related to mobile networking and has served on over 40 program committees for networking conferences. Elizabeth served as the TPC Co-Chair of ACM MobiCom 2005 and IEEE SECON 2005, and is currently on the editorial board for the IEEE Transactions on Mobile Computing. Elizabeth is the recipient of an NSF CAREER award, and a 2002 Technology Review 100 award, awarded to the world’s top young investigators. See ebelding for further details. Xia Gao is currently a Staff Engineer at Ubicom. He received his Ph.D of ECE from the University of Illinois at Urbana-Champaign in 2001. Before joining Ubicom, he had worked in DoCoMo Communications Laboratory for 4 years where he conducted research on 3G-4G wireless communication system and handset technologies and WiFi systems. He has published more than 30 conference and journal papers. He has chaired several International conferences and served as TPC members for many others. He is a member of IEEE and a honored member of Sigma Xi. James Kempf is a Research Fellow at DoCoMo USA Laboratories. He holds a Ph.D. from the University of Arizona, Tucson, AZ. Previously, James worked at Sun Microsystems for 13 years, and contributed to numerous research projects involving wireless networking, mobile computing, and service discovery. James is a former member of the Internet Architecture Board, and co-chaired the SEND and Seamoby IETF Working Groups. James continues to be an active contributor to Internet standards in the areas of security and mobility for next generation, Internet protocol-based mobile systems.     

Enhanced efficiency and frequency assignment by optimizing the base stations location in a mobile radio network

Most mobile radio networks have been planned based on the classical cellular concept. However, alternative planning strategies that lead to more efficient network configurations are necessary due to the fact that the traffic density is generally far from constant throughout the service area, making necessary the relocation of base stations inside the traffic hotspots. If the traffic is characterized in a discrete way, the optimization of base stations location resembles vector quantization, a well-known problem in signal processing. In this paper, we use this analogy to propose a mobile radio network planning algorithm. Simulation results show that higher trunking efficiency as well as improved frequency assignment can be obtained if an existing mobile radio network is redesigned using the presented strategy. Raúl Chávez-Santiago was born in Oaxaca City, Mexico. He obtained the B.Sc. degree in communications and electronics engineering in 1997 from the School of Mechanical and Electrical Engineering (ESIME-IPN), and the M.Sc. degree in electrical engineering in 2001 from the Center of Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV-IPN) in Mexico City. He has professional experience as Computer Networking Engineer, and Research and Teaching Assistant. Currently, he is completing his studies toward the Ph.D. degree at Ben-Gurion University (BGU) of the Negev, Israel. In 2002, he received the URSI Young Scientist Award. His main research interests are the optimal planning of radio communication networks, the electromagnetic compatibility of terrestrial and satellite radio systems, and the efficient use of the radio spectrum. He is an IEEE and IEICE student member, and a URSI radio scientist. Avi Raymond was born in Yavne, Israel. He received the B.Sc. and M.Sc. degrees in electrical engineering from Ben-Gurion University (BGU) of the Negev in 2000 and 2005, respectively. He worked for two years in a communication company in the field of Telephony and Broadband Services. He also worked as a Research Assistant in the communications laboratory at BGU. He currently works at Elta Electronic Industries Ltd. as System Engineer and pursues studies toward a second M.Sc. degree in systems engineering at the Technion Institute of Technology, Haifa, Israel. His research interests are the optimization algorithms for frequency assignment in cellular networks. Vladimir Lyandres was born in 1944, in Vologda, Russia. He received the M.Sc. degree in communications engineering in 1966 and the Ph.D. degree in communications theory in 1972 from the State University of Telecommunications (SUT), Saint Petersburg, Russia. He was with SUT until 1990 holding a position of Senior Scientific Associate and working on research and development of digital transmission systems, modeling of radio communication channels and algorithms of frequency planning for broadcasting and cellular systems. Since 1991 he holds a position of Researcher at the communications laboratory and Professor at the Department of Electrical and Computer Engineering, Ben-Gurion University (BGU) of the Negev, Israel. His research interests include synthesis of Markov models, combinatorial optimization, and adaptive power loading. He is a senior member of IEEE and member of IEICE.     

High Performance Wireless Switch Protocol for IEEE 802.11 Wireless Networks

All mobile stations (STAs) in IEEE 802.11 infrastructure wireless local area networks (IWLAN) are coordinated by an access point (AP). Within the 2.4 GHz unlicensed industry, science, and medicine (ISM) band defined in the IEEE 802.11 2.4 GHz physical layer (PHY) specifications, three channels are available for concurrently transferring data packets at the coverage area of an AP. In most of small/medium enterprises or home environments, an AP with one selected channel is sufficient for covering whole service area, but this implies that the radio resources for the remaining two channels are wasted. In order to overcome the drawback, we propose a new and simple media access control (MAC) protocol, named wireless switch protocol (WSP), for increasing the throughput of IEEE 802.11 IWLAN network to support high quality multimedia traffic. This is achieved by allowing any pair of STAs in IWLAN to exchange data packets in one of other idle channels after their handshake with each other in the common channel controlled by AP. Simulation results show that the total network throughput of WSP depends on the time taken by channel switching, and on the ‘Intranet’ and ‘Internet’ traffic distribution, where the Intranet and Internet mean data transmission between STAs in IWLAN and between the STA and wired host, respectively. When all data packets are Intranet traffic and the traffic load is heavy, the ratio of Goodput for the proposed WSP to that of IEEE 802.11 standard approximates 400%. In the worse case of all Internet traffic, the proposed WSP still obtains the similar throughput as that of IEEE 802.11 standard.Jenhui Chen was born on October 12, 1971 in Taipei, Taiwan, Republic of China. He received the Bachelor’s and Ph.D. degree in Computer Science and Information Engineering (CSIE) from Tamkang University in 1998 and 2003, respectively. In the Spring of 2003, he joined the faculty of Computer Science and Information Engineering Department at Chang Gung University and served as the Assistant Professor. He occupies the supervisor of Network Department in the Information Center, Chang Gung University. Dr. Chen once served the reviewer of IEEE Transactions on Wireless Communications, ACM/Kluwer Mobile Networks and Applications (MONET), and Journal of Information Science and Engineering. His main research interests include design, analysis, and implementation of communication and network protocols, wireless networks, milibots, and artificial intelligence. He is a member of ACM and IEEE.Ai-Chun Pang was born in Hsinchu, Taiwan, R.O.C., in 1973. She received the B.S., M.S. and Ph.D. degrees in Computer Science and Information Engineering from National Chiao Tung University (NCTU) in 1996, 1998 and 2002, respectively. She joined the Department of Computer Science and Information Engineering, National Taiwan University (NTU), Taipei, Taiwan, as an Assistant Professor in 2002. Her research interests include design and analysis of personal communications services network, mobile computing, voice over IP, and performance modeling.Shiann-Tsong Sheu received his B.S. degree in Applied Mathematics from National Chung Hsing University in 1990, and obtained his Ph.D. degree in Computer Science from National Tsing Hua University in May of 1995. From 1995 to 2002, he was an Associate Professor at the Department of Electrical Engineering, Tamkang University. Since Feb. 2002, he has become a Professor at the Department of Electrical Engineering, Tamkang University. Dr. Sheu received the outstanding young researcher award by the IEEE Communication Society Asia Pacific Board in 2002. His research interests include next-generation wireless communication, WDM networks and intelligent control algorithms.Hsueh-Wen Tseng received his B.S. degree in electrical engineering from Tamkang University, Taipei country, Taiwan, in 2001 and M.S. degree in electrical engineering from National Taiwan University of Science and Technology, Taipei, Taiwan, in 2003. He is currently pursuing the Ph. D. degree at the Department of Computer Science and Information Engineering, National Taiwan University, Taipei, Taiwan. His research interests include design, analysis and implementation of network protocols and wireless communications.     

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

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

Effect of Antenna Beam Pattern and Layout on Cellular Performance in High Altitude Platform Communications

High Altitude Platforms may offer high spectrum efficiency by deploying multi-beam, multi-cell communications networks. The properties of the antennas carried by the HAP payload are key to the effective exploitation of these benefits. This paper compares different models for the antenna sidelobe region and quantifies, in each case, the carrier to interference ratio for a 3 channel re-use plan. Networks of 121 and 313 cells are compared. We show how the ITU recommended pattern for the 47/48 GHz band leads to pessimistic results compared to an adapted pattern which fits that of measured data for an elliptic beam lens antenna. The method is then extended to consider other radiation patterns. Spectrum sharing issues are explored with reference to further ITU recommendations and comparison with measurement data. Finally, an ITU type cellular layout which uses the same antenna for each cell is compared to an alternative hexagonal layout where each cell has equal size. John Thornton is a physics graduate of the University of York, UK, obtained an MSc. in microwave physics from the University of Portsmouth, UK, in 1995 and a PhD from the UK's Open University in 2002. He has held research posts at the Rutherford Appleton Laboratory, UK, developing sub-millimetre wave solid state sources and receivers, and at the University of Oxford, on projects including passive radar transponders, array antennas and superconducting filters. In 2000 he returned to York to join the Department of Electronics as a Research Fellow, where his research interests include microwave techniques, wireless broadband and scanning antennas. David Pearce BA(Cantab), DPhil(York) MIEEE, AMIEE, is a lecturer in the Department of Electronics in the University of York and has worked in the field of Fixed Wireless Access schemes for the last five years. Prior to this he worked developing new copper-based local area network schemes in both academia and industry; including heavy involvement in the standardisation work for ISO-8802.5 token ring. Current research interests are focused on media access schemes for multimedia traffic and adaptive techniques for optimising the bandwidth efficiency of wireless networks. David Grace received his MEng in Electronic Systems Engineering and D.Phil from the University of York, UK in 1993 and 1999 respectively. Since 1994 he has been a member of the Communications Research Group where he is now a Senior Research Fellow whose current interests include radio resource management for broadband communications, particularly from high-altitude platform, and terrestrial ad hoc networks. He is Principal Scientific Officer for CAPANINA, a major European Framework 6 project developing broadband communications from high-altitude platforms. He has been an invited speaker at several conferences and industrial locations in the fields of HAP systems. He is a nominated Researcher in the European NEWCOM Network of Excellence, and a Director of SkyLARC Technologies Ltd, a York based company, specialising in broadband communications from aerial platforms. He is a member of IEE and IEEE. Masayuki Oodo received B.E., M.E., and D.E. degrees in Electrical and Electronic Engineering from Tokyo Institute of Technology, Japan, respectively in 1992,1994, and 1997. In 1997, he joined the Communications Research Laboratory (CRL), now part of the National Institute of Information and Communication Technology (NICT). Since July 2004 he has been a visiting research fellow at the University of York. His research interests are array antennas for wireless communications and frequency-sharing between HAPS and other systems. Dr. Oodo received the Paper Presentation Award from IEEJ (The Institute of Electrical Engineers of Japan) in 1995, the Young Scientist Award from URSI in 1996, the Young Engineer Award from IEICE (The Institute of Electronics, Information and Communication Engineers) of Japan in 1997, and the Young Engineer Award from IEEE AP-S Tokyo Chapter in 1998. Konstantinos Katzis received his BEng degree in Computer Systems Engineering in 2000 and his MSc in Radio Systems Engineering in 2001, both from the University of Hull, UK. Since 2001 he has been a member of the Communications Research Group at York where he has been working on Resource Allocation Techniques for HAPs for his PhD degree. Currently he is a Research Associate working on Radio Resource Management for the European project CAPANINA. His current research interests include Resource allocation and spectrum management, multiple access schemes and medium access control protocol modelling. Tim Tozer MA(Cantab), CEng, FIEE, MIEEE, is Senior Lecturer in Electronics at York, since 1987, and leader of the Communications Research Group. Research interests include: wireless access techniques; multi-user, satellite and High Altitude Platform communications. He has held numerous grants and research contracts from industry, government and international organisations, and is a named author on over 180 technical publications. He is active in the IEE Professional Network on Satellite Systems and Applications. Tim is a regular invited presenter at international conferences, workshops and tutorials, in the fields of VSAT and HAPs communications. He has previous experience in industry, including work on military satellite systems at DERA (now QinetiQ). Tim is also Managing Director of SkyLARC Technologies Ltd.     

Convergence Towards 4G: A Novel View of Integration

Integration and convergence of different access technology is a key concept of 4G systems. This integration also includes the interface among terrestrial and aero-space components, whose importance has been so far under-estimated and not deeply understood. In this paper, a layered model of the 4G integrated network vision is introduced, highlighting details about the aero-space component. The concept of integration is discussed under different viewpoints, particularly highlighing integration among aero-space segments and related services (i.e. navigation). Examples of integration scenarios identified and investigated in the frame of research programs co-funded by Italian institutions are also displayed in the paper.Ernestina Cianca graduated cum laude in Electronics Engineering in 1997 at the University of L’Aquila. She was Italtel/Siemens (L’Aquila) from 1997 to 1998. She got her Ph.D. degree from the University of Rome Tor Vergata (URTV). The thesis work was on power management in CDMA-based satellite systems. She has been employed by the University of Aalborg, Denmark, in the Wireless Networking Groups (WING), as Research engineer (2000–2001) and as Assistant Professor (2001–2003). In particular, from Sept. 2002 she has been Technical Manager of Aalborg University for the IST-STRIKE project. She is currently Assistant Professor in Telecommunications at the URTV (Dpt. of Electronics Engineering), teaching DSP, Information and Coding. Her research mainly concerns wireless access technologies (CDMA and MIMO-OFDM-based systems), in particular, Radio Resource Management at PHY/MAC layer, ARQ/HARQ, TCP-IP issues over wireless links, integration of terrestrial and satellite systems. She has been the vice-coordinator of the following national research programs: CABIS, on CDMA integrated mobile systems (2000–2002) and SHINES, on satellite-HAP integrated networks for multimedia applications co-financed by MIUR (2002–2004). She currently working on various European Projects. She is author of about 40 papers, on international journals/transactions and proceedings of international conferences.Mauro De Sanctis received the “Laurea” degree in Telecommunications Engineering from the University of Roma “Tor Vergata” in 2002. He is currently a Ph.D. Student and Assistant Professor in the Department of Electronics Engineering of the same University. He is involved in the DAVID (DAta and Video Interactive Distribution) satellite mission of the ASI (Italian Space Agency); his research is funded by the ASI. He is also involved in the MAGNET (My personal Adaptive Global NET) European FP6 integrated project and in the SatNEx European network of excellence. He worked on Italian national research projects on satellite-terrestrial systems integration such as SHINES (Satellite and HAP Integrated Networks and Services) and CABIS (CDMA for Broadband mobile terrestrial-satellite Integrated Systems). On autumn 2004 he joined the CTIF (Center for TeleInFrastructure), a research center focusing on modern telecommunications technologies located at the University of Aalborg (Denmark). His main areas of interest are: integration of different satellite networks, stratospheric platforms and terrestrial networks in a multi-layered fashion, internetworking and resource management in satellite systems and energy efficiency of WPAN systems.Marina Ruggieri graduated in Electronics Engineering in 1984 at the University of Roma. She was: with FACE-ITT and GTC-ITT (Roanoke, VA) in the High Frequency Division (1985–1986); Research and Teaching Assistant at the University of Roma Tor Vergata (URTV) (1986–1991); Associate Professor in Telecommunications at the University of L’Aquila (1991–1994). Since November 2000 she is Full Professor in Telecommunications at the URTV (Dpt. of Electronics Engineering), teaching DSP, Information and Coding. Since 1999 she is member of the Board of Governors of the IEEE AES Society. Since 2004 she is member of the Technical-Scientific Committee of the Italian Space Agency (ASI). Her research mainly concerns space communications and navigation systems (in particular satellites) as well as mobile and multimedia networks. She is the Principal Investigator of: satellite scientific communications missions (DAVID, WAVE) of ASI; national research programs (CABIS) on CDMA integrated mobile systems (2000–2002) and on satellite-HAP integrated networks for multimedia applications (SHINES), co-financed by MIUR (2002–2004). She co-ordinates the URTV Unit in various European Projects: EU FP6 IP MAGNET (My personal Adaptive Global NET); EU ASIA LINK EAGER-NetWIC (Euro-Asian Network for Strengthening Graduate Education and Research in Wireless Communications); EU Network of excellence NEXWAY; GALILEO JU 1st Call – July 2003: VERT (VEhicular Remote Tolling); and in the ASI program on V-band payloads (TRANSPONDERS). She is Editor for Space Systems of the IEEE Transactions on AES. She was awarded the 1990 Piero Fanti International Prize and she had a nomination for the Harry M. Mimmo Award in 1996 and the Cristoforo Colombo Award in 2002. She is author of about 180 papers, on international journals/transactions and proceedings of international conferences, book chapters and books.     

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.