A single-chip digitally calibrated 5.15-5.825-GHz 0.18-/spl mu/m CMOS transceiver for 802.11a wireless LAN

The drive for cost reduction has led to the use of CMOS technology in the implementation of highly integrated radios. This paper presents a single-chip 5-GHz fully integrated direct conversion transceiver for IEEE 802.11a WLAN systems, manufactured in 0.18-/spl mu/m CMOS. The IC features an innovative system architecture which takes advantage of the computing resources of the digital companion chip in order to eliminate I/Q mismatch and achieve accurately matched baseband filters. The integrated voltage-controlled oscillator and synthesizer achieve an integrated phase noise of less than 0.8/spl deg/ rms. The receiver has an overall noise figure of 5.2 dB and achieves sensitivity of -75 dBm at 54-Mb/s operation, both referred to the IC input. The transmit error vector magnitude is -33 dB at -5-dBm output power from the integrated power-amplifier driver amplifier. The transceiver occupies an area of 18.5 mm/sup 2/.     

A Scheduling Technique Wireless Personal for Bandwidth Communication Allocation in Networks

Future generation wireless personalcommunication networks (PCN) are expected to providemultimedia capable wireless extensions of fixedATM/B-ISDN. This paper presents a scheduling techniquefor PCN based on TDMA and the leaky bucket regulator, thewell known bandwidth enforcement mechanism for fixedATM. The main objective of the proposed technique is toensure fair and efficient treatment of various types oftraffic on the air interface, includingconstant-bit-rate (CBR) voice and variable-bit-rate(VBR) video. Two alternative priority mechanisms areintroduced and their performance is evaluated. Theperformance comparison of the alternatives reveals aninteresting tradeoff between fairness and quality ofservice (QoS).     

A Multiagent Platform for Ubiquitous Service Provision

The Virtual Home Environment is very important in contemporary mobile telecommunications infrastructure as it caters for the ubiquitous provision of services irrespective of network, location and user device. The universality of systems like Universal Mobile Telecommunications System and wi-fi increases the need for the rapid introduction of efficient VHE schemes. In this paper, we study the adoption of Mobile Agents for handling the VHE functionality. Mobile agents are nicely harmonized with the broader idea of VHE as they allow the autonomous execution of tasks by components that roam from node to node and network to network. We present the detailed modeling of a VHE provisioning architecture and investigate its suitability for different use cases and technical options (e.g., end user devices). The adoption of mobile agents for the ubiquitous provision of telecommunication services is quite promising in terms of efficiency. Through a series of experiments we quantify the performance benefits stemming from the adoption of mobile agents in contrast to conventional service provisioning schemes.     

An Efficient Location Management Protocol for Wireless ATM Customer Premises Networks

In this paper we present a new location management protocol for wireless ATM networks, called LMCP (Location Management and Control Protocol). This protocol is based on the PNNI (Private Network-to-Network Interface) routing functionality to advertise the movement of mobile terminals within predefined areas. Moreover, LMCP uses specialized entities to store and retrieve the current location area of the mobile terminals. These entities are located in mobility enhanced switches that control the execution of mobility procedures (e.g., handovers).The main benefit from the application of LMCP is the establishment of connections that do not contain any misrouted segments. Furthermore, it requires minor modifications to the PNNI and enables its inter-working with other location management mechanisms. The protocol is compared with other similar mechanisms, and its efficiency is demonstrated by the results of an analytical model.     

Supporting the WWW in Wireless Communications Through Mobile Agents

Mobile computing is considered of major importance to the computing industry for the forthcoming years due to the progress in wireless mobile communications. We present a proxy-based architecture that manages to accelerate Web browsing in wireless Customer Premises Networks (CPN). We discuss how such an architecture is implemented using the IBM Aglets framework for mobile agents. The suggested architecture relies heavily on proxy caches – maintained in base stations – which are relocated to follow a roaming user in other control areas (clusters of cells). The cache management scheme involves relocation of full caches to the most-likely-to-be visited control areas, but also fractions of the cache to less-likely-to-be-visited neighbours. A movement prediction algorithm, based on a learning automaton, is used to determine the future location of the terminal. The discussed architecture components have been implemented as Aglets to allow for the efficient introduction of the service in a CPN infrastructure.     

Memory accesses reordering for interconnect power reduction in sum-of-products computations

Techniques for interconnect power consumption reduction in realizations of sum-of-products computations are presented. The proposed techniques reorder the sequence of accesses of the coefficient and data memories to minimize power-costly address and data bus bit switching. The reordering problem is systematically formulated by mapping into the traveling salesman's problem (TSP) for both single and multiple functional unit architectures. The cost function driving the memory accesses reordering procedure explicitly takes into consideration the static information related to algorithms' coefficients and storage addresses and data-related dynamic information. Experimental results from several typical digital signal-processing algorithms prove that the proposed techniques lead to significant bus switching activity savings. The power consumption in the data paths is reduced in most cases as well.     

Multi-parameter performance analysis for decentralized cognitive radio networks

In this paper, we investigate the impact of primary user activity, secondary user activity, interface switching, channel fading and finite-length queuing on the performance of decentralized cognitive radio networks. The individual processes of these service-disruptive effects are modeled as Markov chains based on cross-layer information locally available at the network nodes. A queuing analysis is conducted and various performance measures are derived regarding the packet loss, throughput, spectral efficiency, and packet delay distribution. Numerical results demonstrate the impact of various system parameters on the system performance, providing insights for cross-layer design and autonomous decision making in decentralized cognitive radio networks.     

Advanced adaptability and profile management framework for the support of flexible mobile service provision

The long-term vision of beyond 3G wireless communications describes a mobile service provision environment dramatically different from that of today. Users are expected to raise their demands to a significantly higher level, towards the situation-aware provision of ubiquitous personalized multimedia services. From this perspective, the need is emerging to apply, in a systematic way, adaptability and reconfigurability concepts for service delivery in largely diverse contexts. Generic dynamically extensible adaptation mechanisms that can be employed in a wide variety of situations and are independent of the subject and criteria of adaptation is a significant step in this direction. Moreover, effective profile representation and management becomes an increasingly important issue. In the present article we introduce an advanced adaptability and profile management framework aiming to fulfill these requirements. The proposed system has been designed, implemented, and incorporated in a distributed middleware platform for next-generation mobile service provision.     

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.     

Trade-Off Analysis of a Low-Power Image Coding Algorithm

In this paper, a novel algorithm for low-power image coding and decoding is presented and the various inherent trade-offs are described and investigated in detail. The algorithm reduces the memory requirements of vector quantization, i.e., the size of memory required for the codebook and the number of memory accesses by using small codebooks. This significantly reduces the memory-related power consumption, which is an important part of the total power budget. To compensate for the loss of quality introduced by the small codebook size, simple transformations are applied on the codewords during coding. Thus, small codebooks are extended through computations and the main coding task becomes computation-based rather than memory-based. Each image block is encoded by a codeword index and a set of transformation parameters. The algorithm leads to power savings of a factor of 10 in coding and of a factor of 3 in decoding, at least in comparison to classical full-search vector quantization. In terms of SNR, the image quality is better than or comparable to that corresponding to full-search vector quantization, depending on the size of the codebook that is used. The main disadvantage of the proposed algorithm is the decrease of the compression ratio in comparison to vector quantization. The trade-off between image quality and power consumption is dominant in this algorithm and is mainly determined by the size of the codebook.