Vassilios Zacharopoulos

Overall Uncertainty Estimation in Multiple Narrow-Band In Situ Electromagnetic Field Measurements

The possible adverse effects on human health of exposure to nonionizing electromagnetic fields have led international organizations and several countries to adopt exposure limits regarding public or occupational safety. To ensure compliance with these limits, specifically designed measurements with suitable instruments have to be performed. Since uncertainty is always present even when expensive instrumentation is employed, the final results from computations of the measured data deviate from the respective true values. The divergence depends on the instrumentation employed, the used methodology, or even the random effects, e.g., human factors or environmental conditions. In this paper, a method for evaluating total uncertainty when multiple narrow-band electromagnetic field measurements are performed is proposed. This is very common when exposure in residential areas is assessed.

On the Spatial Averaging of Multiple Narrowband Electromagnetic Field Measurements: Methods and Uncertainty Estimation

Methods of computational prediction can be used or specific measurements have to be performed for the estimation of human exposure to nonionizing electromagnetic fields at a certain place. According to the exposure standards, the predicted or the measured values have to be spatially averaged in an area representing the dimensions of the human body and compared with the adopted maximum permissible levels of exposure. In this paper, methods for spatial averaging nonionizing electromagnetic fields are discussed. Moreover, methods for estimating spatial average uncertainty of the total field strength values and of the summation of exposure quotients when narrowband measurements are performed in a multiple-frequency environment are proposed. Furthermore, since maximum field values have to be averaged according to the most widely accepted exposure standards, the traffic-dependent power level variation issue is also addressed. In particular, for GSM systems, an extrapolation method to the maximum possible field levels using data from real-time measurements when the frequency allocation per operator base station and the spatial distribution of the exposure sources are unknown is also proposed. Finally, an uncertainty estimation procedure associated to the extrapolated levels is presented.

On the uncertainty estimation of electromagnetic field measurements using field sensors: a general approach

One of the most common and popular practices on measuring the non-ionising electric and/or magnetic field strength employs field meters and the appropriate electric and/or magnetic field strength sensors. These measurements have to meet several requirements proposed by specific guidelines or standards. On the other hand, performing non-ionising exposure assessment using real measurement data can be a very difficult task due to instrumentation limits and uncertainties. In addition, each measuring technique, practice and recommendation has its own drawbacks. In this paper, a methodology for estimating the overall uncertainty for such measurements, including uncertainty estimation of spatial average values of electric or magnetic field strengths, is proposed. Estimating and reporting measurement uncertainty are of great importance, especially when the measured values are very close to the established limits of human exposure to non-ionising electromagnetic fields.

Experimental Infrastructures for IP/DVB Convergence: an Actual Substantiation for Triple Play Services Provision at Remote Areas

This paper introduces and validates an experimental infrastructure of a fusion IP/DVB networking environment for the provision of triple play services at remote areas exploiting the synergy of Broadcasting, Internet and Telecommunication sectors technologies. This synergy constitutes a challenge for creating a networking platform which exploits the particularities and complementarities of these sectors for the support of ubiquitous services and always-on connectivity enabling passive rural citizens to become active Information Society participants. This paper describes important directions for exploiting the proposed unified platform alleviating the digital divide that currently exists not only among countries but also within most regions of the same country.

Optimised network resource exploitation in interactive broadcasting environments via P2P constellations

This paper proposes the utilisation of peer-to-peer (P2P) concept in interactive broadcasting environments, as an enabling technology for optimised network resource exploitation. Building upon a regenerative DVB-T platform, it presents a decentralised architecture that exploits the broadcasting stream as part of the core/backbone network, providing interactive IP services to rural/urban citizens. Towards enhancing the scalability as well as the performance of the entire network, the paper studies the realisation of IP overlays by exploiting P2P technology, and proposes a prototype configuration for optimum resource exploitation and increased Service/Bandwidth gain both at the core and access segments. Performance evaluation experiments carried-out under real transmission/reception conditions with a number of real users verified the validity of the proposed architecture, besides outlining fields for future research.

TV White Spaces exploitation utilizing a Cognitive Radio system based on DVB-H

The transition from analogue to digital terrestrial television (i.e. Digital Switchover — DSO) releases a significant amount of valuable spectrum (i.e. Digital Dividend), in UHF band. Digital Dividend will be available in the form of a “cleared spectrum” of contiguous channels, as well as in the form of “interleaved spectrum”, namely TV White Spaces (i.e. TVWS), unused within given geographical locations, in order to avoid causing interference to co-channel or adjacent channel DVB-T transmitters. “Cleared spectrum” and TVWS provide an opportunity to deploy Cognitive Radio (CR) networks, able to operate in UHF band, by sharing the available spectrum with other licensed systems. In this context, this paper elaborates on the efficient sharing of TVWS by proposing a mobile TV network with CR capabilities, based on DVB-H. The proposed network operates as an unlicensed secondary system, accessing TVWS via a spectrum broker, which is in charge of assigning the available spectrum.

Distributed NQoS provision in interactive DVB-T systems

This paper discusses a Distributed Network Quality of Service (NQoS) provision approach in decentralized interactive DVB-T systems (IDVB-T), enabling for scalable and fault tolerant operation. The paper describes the design and overall architecture of a regenerative IDVB-T infrastructure, where network resource allocation and service classification processes are performed at local level within each intermediate distribution node (Cell Main Node CMN), setting the basis for a CMN-to-CMN NQoS provision. Validity of the proposed approach is experimentally verified, and the test-results are compared against the aggregated and federated NQoS provision approaches, indicating similar performance but better scalability and fault-tolerant design.

Enhancing legacy infrastructures with content-aware enablers towards a networked-media platform

This paper presents a novel user-centric networked-media architecture, where content-aware capabilities at the network layer are intimately tied-up with network-aware functions at the services layer, towards maximum possible QoS/QoE provision. Focusing on the network segment, the paper initially presents the design of a novel virtual layer on top of the traditional network plane capable to enable content awareness, describes its operational components and functions, while elaborating on its communication with legacy infrastructures.

Electromagnetic exposure compliance estimation using narrowband directional measurements

The increased number of everyday applications that rely on wireless communication has drawn an attention to several concerns on the adverse health effects that prolonged or even short time exposure might have on humans. International organisations and countries have adopted guides and legislation for the public safety. They include reference levels (RLs) regarding field strength electromagnetic quantities. To check for RLs compliance in an environment with multiple transmitters of various types, analytical simulation models may be implemented provided that all the necessary information are available. Since this is not generally the case in the most practical situations, on-site measurements have to be performed. The necessary equipment for measurements of this type usually includes broadband field metres suitable to measure the field strength over the whole bandwidth of the field sensor used. These types of measurements have several drawbacks; to begin with, given that RLs are frequency depended, compliance evaluation can be misleading since no information is available regarding the measured spectrum distribution. Furthermore, in a multi-transmitter environment there is no way of distinguishing the contribution of a specific source to the overall field measured. Of course, this problem can be resolved using narrowband directional receiver antennas, yet there is always the need for a priori knowledge of the polarisation of the incident electromagnetic wave. In this work, the use of measurement schemes of this type is addressed. A method independent to the polarisation of the incident wave is proposed and a way to evaluate a single source contribution to the total field in a multi-transmitter environment and the polarisation of the measured incident wave is presented.

Self-powering wireless sensors in typical building environment

Electromagnetic Radiation found in a typical building today is an integral part of technology evolution. Electric power distribution networks are present in every building producing time variable magnetic and electric fields in a low frequency range (50 Hz - 100 KHz) commonly named as Extremely Low Frequencies (ELF). On the other hand wireless networks and other high frequency activity, in the range of Radio Frequencies (RF) 100 KHz up to 6 GHz produce ElectroMagnetic Fields (EMF) that radiate in the indoor environment. In this work the potential to take advantage of such electromagnetic pollution to provide power supply to micro-devices (such as wireless sensors) is examined. This is based in real EMF measurements in a typical office environment.