Nikolaos Papadakis

Microcellular propagation measurements and simulation at 1.8 GHz in urban radio environment

This paper presents the results of measurements performed at 1.8 GHz in a microcellular environment in a city center (Athens, Greece). Studies have shown that the microcellular environment is dissimilar to the conventional macrocell area, therefore, accurate knowledge of propagation characteristics is essential. The aim of the measurement campaign is to provide a clear understanding of the propagation parameters affecting the design of a personal communication system (PCS) in a city center. Theoretical predictions developed using ray tracing techniques and measurement-based models are plotted versus distance for alternative configurations. The measurement procedure, data analysis, and comparison between theoretical and experimental results are given.

Indoor mobile radio channel measurements and characterization for DECT picocells

Indoor radio communication systems gain increasing interest of cellular network operators. A prerequisite to the design of these systems is the knowledge of indoor radio propagation characteristics. This knowledge should include information, concerning the in-building structure that strongly affects the signal transmission. The results presented in this paper provide characterization, of signal behavior in indoor wireless environment. Narrowband propagation measurements were conducted within a thirteen-story building (OTE-Hellenic Telecommunication Organization premises) in Athens, Greece. The purpose of the measurement campaign is to the indoor signal behavior and characterization considering she specific information. A description of the measurement environment and experimental setup is given. Path loss exponents and absolute path loss values are estimated for each measured case. Statistical analysis of the measured data is also presented.

MEMPHIS: a mobile agent-based system for enabling acquisition of multilingual content and providing flexible format internet premium services

Mobile Agent technology is an interesting concept for large network-based system structures. In this paper we describe a Java-based agent environment which integrates agent execution platforms into World Wide Web servers promoting a world wide infrastructure for Mobile Agents. This system has been developed within the framework of MEMPHIS IST project, which involves the definition, development and validation of a new system for commercially significant multilingual premium services, focused on thin clients such as mobile phones, Personal Digital Assistants, etc. The concept relies on the extraction of multilingual information from various web-based content sources in different formats. The system is composed by three different Modules, namely the Acquisition, the Transformation and the Distribution Module. The content acquisition is based on dynamic user profiles. The acquired content is transformed into a meta-representation, which enables content storage independent both of source and destination format and language. The output format is based on the requirements of employed thin client terminals and the output document is distributed via the appropriate networks. The end-user receives the required information as premium services via the chosen output medium. The system supports both pull and push services. An evaluation of the system is also presented.

Wideband Propagation Indoor Environment Measurements and Modeling in

This paper presents the results of widebandmeasurements of an indoor wireless radio channel at 1.8GHz. Propagation measurements were carried out in anindoor environment at the Technical University of Athens with a network analyzer. From themeasured impulse response (IR) profiles collected, meanexcess delay tau and root mean square of delay spreadtau Statistical analysis of delay spread and amplitude fading has been performed. Comparison withsimulation results extracted from SIRCIM Simulatorpackage has also been made. have beenestimated.

Radio propagation measurements and modelling using ray tracing techniques

This paper presents the results of the propagation measurements performed in the centre of Athens for the complete characterisation of channel behaviour. The objective of the measurement campaign is to derive a prediction model for the path loss estimation for a microcell environment. For all types of measurements the variation of signal strength with distance was recorded for comparison with models extracted using ray tracing techniques. Some preliminary results were obtained and integrated using additional rays option for accurate path loss estimation. The paper also describes the conclusions of the comparison between theoretical and experimental results.<<ETX>>

SHIELD: A novel NFV-based cybersecurity framework

SHIELD is an EU-funded project, targeting at the design and development of a novel cybersecurity framework, which offers security-as-a-Service in an evolved telco environment. The SHIELD framework leverages NFV (Network Functions Virtualization) and SDN (Software-Defined Networking) for virtualization and dynamic placement of virtualised security appliances in the network (virtual Network Security Functions - vNSFs), Big Data analytics for real-time incident detection and mitigation, as well as attestation techniques for securing both the infrastructure and the services. This papers discusses key use cases and requirements for the SHIELD framework and presents a high-level architectural approach.

MI-MERCURY: A mobile agent architecture for ubiquitous retrieval and delivery of multimedia information

Mining multimedia information in the Web is in general an arduous task, due to the fact that, (a) humans perceive media content using high level concepts, (b) the subjective and vagueness of content interpretation, and (c) the fact that relevant data are often hidden in a huge amount of irrelevant information. In addition, delivering and distributing the retrieved information to a wide range of terminal devices of different properties over a wide range of networks to users of different preferences requires new tools and mechanisms for content transformation and adaptation. Other problems concern the language that the data are stored, which may not be the user’s preferred language. To address these issues we propose an integrated, reconfigurable, adaptable and open architecture for mining, indexing and retrieving multimedia information based on a mobile agent technology scheme. The proposed architecture consists of three integral subsystems: the acquisition module, responsible for searching and retrieving media data (both textual and visual), the transformation module, able to adapt and transform the mined information to other forms of representation, and the distribution module for delivering and adapting the retrieved data in terms of terminal devices, network channels and user’s preferences. The system is based on a reconfigurable architecture which is able to dynamically and automatically update the system response to user’s actual needs and preferences, by extending descriptor classes that are considered more relevant by the users. New innovative algorithms are presented in this paper both at each system module as well as in the system integration. The system supports efficient content adaptation mechanisms, textual and visual summarization (both sequential and hierarchical), automatic language translation, ontological representation, visual processing and web-based data mining. Experimental analysis on real-life web sites has been performed to test the efficiency of the proposed scheme and compare it with other approaches presented in the literature.

An empirical model for high elevation angle land-mobile satellite channels at urban environment

A land mobile satellite system (LMSS) propagation measurement campaign at 1.8 GHz was launched in Athens city center during June 1996 for high elevation angle (60/spl deg/, 70/spl deg/ and 80/spl deg/) channels. Four narrow streets with large building blocks and heavy traffic were tested. A new empirical model is extracted to calculate the link margin required to compensate for multipath fading in urban environments. A comparison with an existing model is presented. The results show a considerable increase in the fade depth compared to suburban and rural environments. In general, the fade depth decreases with increasing elevation angle, and the overall analysis indicates a strong dependence of the signal attenuation on the width of the streets, the average building height and the vegetation at the edges of the streets.

Visual pathways for detection of landmark points

We describe a neuron multi-layered architecture that extracts landmark points of high curvature from 2d shapes and resembles the visual pathway of primates. We demonstrate how the rotated orientation specific receptive fields of the simple neurons that were discovered by Hubel and Wiesel can perform landmark point detection on the 2d contour of the shape that is projected on the retina of the eye. Detection of landmark points of high curvature is a trivial task with sophisticated machine equipment but we demonstrate how such a task can be accomplished by only using the hardware of the visual cortex of primates abiding to the discoveries of Hubel and Wiesel regarding the rotated arrangements of orientation specific simple neurons. The proposed layered architecture first extracts the 2dimensional shape from the projection on the retina then it rotates the extracted shape in multiple layers in order to detect the landmark points. Since rotating the image about the focal origin is equivalent to the rotation of the simple cells orientation field, our model offers an explanation regarding the mystery of the arrangement of the cortical cells in the areas of layer 2 and 3 on the basis of shape cognition from its landmark points.

Space and Polarization Diversity Measurements in an Indoor Radio Environment at 1800 MHz Using a Dual-Channel Receiver

Diversity techniques have been extensivelyconsidered for application in propagation media,examining various combining schemes, to mitigate theeffects of short-term fading probability andconsequently to reduce the required fading margin.Narrowband propagation measurements were conductedwithin a four-story building at Technical University ofAthens under a number of different radio pathconditions, using a dual-channel-receiving unit, consistingof two spectrum analyzers, controlled by a personalcomputer. This paper presents the results of indoorradio propagation using space and cross-polarization diversity measurements in an indoor wirelessradio channel at 1.8 GHz. Moreover, the diversity gainat 99% signal reliability level and correspondingcross-correlation coefficients have been estimated by considering selection and maximalratio-combining diversity schemes. The results are veryimportant for system designers of indoor communicationsystems, involving data transmission on wireless mobilenetworks. A detailed description of the measurementenvironment and experimental setup is given. From themeasurements collected, the parameters of power decayfactor and temporal fading signal statistics were also estimated and analyzed.