Dimitrios I. Stratakis

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.

IWO-based synthesis of log-periodic dipole array

The Invasive Weed Optimization (IWO) is an effective evolutionary and recently developed method. Due to its better performance in comparison to other well-known optimization methods, IWO has been chosen to solve many complex non-linear problems in telecommunications and electromagnetics. In the present study, the IWO is applied to optimize the geometry of a realistic log-periodic dipole array (LPDA) that operates in the frequency range 800-3300 MHz and therefore is suitable for signal reception from several RF services. The optimization is applied under specific requirements, concerning the standing wave ratio, the forward gain, the gain flatness and the side lobe level, over a wide frequency range. The optimization variables are the lengths and the radii of the dipoles, the distances between them, and the characteristic impedance of the transmission line that connects the dipoles. The optimized LPDA seems to be superior compared to the antenna derived from the practical design procedure.

Exposure levels due to WLAN devices in indoor environments corrected by a time–amplitude factor of distribution of the quasi-stochastic signals

With the development of radiofrequency technology, radiating quasi-stochastic signals like the wireless local area networks (WLAN), a proper procedure of exposure level assessment is needed. No standardised procedure exists at the moment. While channel power measurement proved to overestimate the field strength, weighting techniques were proposed. The paper compares the exposure levels determined by three different procedures, two of them correcting the field level by weighting. Twenty-three experimental cases of WLAN traffic load are analysed in an indoor environment in controlled conditions. The results show the differences obtained when the duty cycle (DC) method is applied comparatively with the application of weighting based on an amplitude-time correction. Significant exposure level reductions of 52.6-79.2 % from the field determined by frequency domain method and of 36.5-72.8 % from the field determined by the DC weighting method were obtained by time-amplitude method. Specificities of weighting factors probability density functions were investigated and regression analysis was applied for a detailed characterisation of this procedure.

Exposure EMF measurements with spectrum analyzers using free and open source software

This paper describes a dedicated Software that was developed using Free and Open Source tools for the automation of Electromagnetic Field (EMF) exposure measurements with Spectrum Analyzers (SAs). This software is used for controlling measurement instrumentation, receiving, storing, processing and analyzing EMF measurement date, while offering a friendly user interface with many options. For the evaluation of the measurement results, all required protocols have been taken into account in order to be consistent with national (Greek Legislation) as well as other international recommendations and standards. The software runs under Ubuntu 14.04 LTS operating system and was developed in Python 3.4 programming language. Remote control and communication with the SAs is achieved with Standard Commands for Programmable Instruments (SCPI) and with the use of National Instruments Virtual Instrument Software Architecture (NI-VISA) in combination with Python Visa (PyVISA).

Energy-Efficient Routing in Cognitive Radio Networks

This chapter proposes a novel routing protocol enriched with a capacity-aware scheme that enables energy conservation and efficient data flow coordination among communication nodes with heterogeneous spectrum availability in distributed cognitive radio networks. Efficient routing protocol operation, as a matter of maximum energy conservation, maximum-possible routing paths establishments and minimum delays is obtained by utilizing both a signaling mechanism and an energy efficient scheme that were implemented based on a simulation scenario. This simulation scenario includes a number of secondary communication nodes, operating over television white spaces (TVWS) under the “spectrum of commons” regulation regime. The validity of the proposed energy efficient routing protocol is verified, by conducting experimental simulations and obtaining performance evaluation results. Simulation results validated routing protocol efficiency for minimizing energy consumption, maximizing resources exchange between secondary communication nodes and minimizing routing delays.

On the performance comparison of the agent-based rate adaptivity scheme for IEEE 802.11n and ZigBee

This work examines the IEEE 802.11, used in WLANs (Wireless Local Area Network), and IEEE 802.15.4, for WPANs (Wireless Personal Area Network), along with the Agent-based Rate Adaptive Scheme. The paper presents the Agent-based Rate Adaptive Scheme, which allows each channel to adaptively set the rate for serving a specific transfer. To this, end Agents are being utilized on each node in order to enable efficient monitoring of the requirements of each transfer and adjust the rate accordingly. Results were extracted by conducting simulation experimentation, and comparing the behavior and performance of a WLAN and a ZigBee network, in a short distance environment such as an office or a house, in order to determine the optimal protocol to be used in applications such as home/building automation. The experiment showed that while the 802.11 protocol performs better when it comes to delay, ZigBee has the upper hand in reliability, as more packets were successfully delivered in the WPAN, rather than the WLAN. Furthermore, this paper takes into consideration parameters such as queuing delay and transmission rate adaptivity, investigates them in a more calculative manner, and presents the findings of our evaluations.

ZAM distribution analysis of radiowave ionospheric propagation interference measurements

This work investigates the occurrence of radiowave propagation disturbances across a wide range of VLF and LF frequencies received prior to a seismic event (Mw=4), that took place on May 12th 2012, the epicenter of which was very close (14Km) to the receiver. The signals analysed were from 4 VLF and 6 LF European transmitters. This seismic event produced precursory ionospheric disturbances, identified as spectral distortion, before its occurrence, providing a distinct pattern. Although the basis of the ionosphere interaction with seismic phenomena has been well documented in previous studies, the close proximity of the receiver to the seismic event provides a new perspective to this study. The received signals have undergone normalisation and then they have been processed by the application of the Zhao-Atlas-Marks Distribution (ZAMD). Diagrams of the signals relevant to the phenomena are presented as well as the the result of the application of the ZAMD.

Evaluation of the electromagnetic fields exposure produced by WiMAX signals

Wireless networking technologies in recent years have witnessed important developments since the advantages benefit both data transmission service providers, and individuals or ordinary users. Ease of installation of a wireless network, led to the development of millions of Wi-Fi networks throughout the world. Nevertheless, Wi-Fi has certain drawbacks that inspired the implementation of a new technology called WiMAX. In 2003, the IEEE 802.16™ standard, also known as WiMAX (Worldwide Interoperability for Microwave Access) was adopted, in order to meet the requirements for broadband wireless access. The purpose of this paper is to study how the electromagnetic fields generated by WiMAX base stations can be evaluated in terms of exposure.