Abstract-The knowledge of electromagnetic properties of biological tissues is required to assess the radio frequency energy deposition in children exposed to electromagnetic fields. The issue whether children should be considered a dosimetric sensitive group in comparison to adults, to which the confirmation of age-dependence of human tissue electromagnetic properties potentially may contribute remains debatable at scientific forums. This paper derives the formula for calculation of electromagnetic properties (permittivity and conductivity) of children tissues, as a function of height, weight, and age, respectively. By using the proposed formula, we have calculated and presented electromagnetic properties of the muscle, brain (gray matter) and skin for 1-year-old to 10-year-old children for 900 MHz, 1800 MHz and 2.4 GHz, at which frequencies most of radio frequency devices used by children operate. The trend over the age of child electromagnetic properties has been presented, and electromagnetic properties at different frequencies for the same child age have also been compared. For certain tissues, comparison between the children at various age and adult electromagnetic parameters has been given. A database with electromagnetic properties for children, of all ages, tissues and frequencies may be built up with the proposed approach. It will further advance research on the assessment of children exposure to electromagnetic fields. Formula can also be used for the determination of electromagnetic parameters for children with specific height and weight.

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With the advent of analog to digital transition in TV broadcasting, a substantial amount of spectrum has become available in TV bands. To take advantage of this, the idea for cognitive radios was introduced for two major reasons: better utilization of spectrum in urban areas and facilitation of wireless connectivity in rural areas. To achieve these two goals, however, many challenges have to be addressed first. Considering that these frequencies are commonly licensed, besides primary user detection, a serious challenge remains the detection and identification of other secondary devices and networks. The problems arising from this issue concern the coexistence problems happening from having several primary and secondary networks of different technologies cohabiting the same licensed spectrum simultaneously and from many secondary systems/users coexisting at the same place while using identical or different technologies. In this survey we provide a review of existing works and outline new challenges regarding coexistence and self-coexistence in heterogeneous wireless networks in TV White Spaces including a comparative analysis between selected coexistence mechanisms.

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In this study we conduct an assessment of usage and availability of frequency bands, traditionally assigned to TV broadcasters, in urban environments in Kosovo. The assessment was performed for VHF and UHF bands at 8 different urban locations. Localized measurements indicate that a major part of these frequencies is severely under-utilized even in highly urbanized areas where a higher utilization level would be expected. Preliminary results further show that spectrum utilization level varies significantly with altitude and is much lower in indoor environments. Our initial calculations show that current percentage of availability of TV bands in tested locations varies between 87.5% and 100%. These results indicate that spectrum utilization in these bands could be greatly improved by allowing the opportunistic use of spectrum by cognitive radios and other wireless communication technologies, such as future cellular networks.

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Theoretical, software-computed and experimental evaluations of the exposure levels to electromagnetic fields generated by GSM 900, GSM 1800 and 3G base stations in urban areas, including determination of the minimum safe distances for population and occupational exposure, are presented. Using the software package SPECTRAemc with the P.1546 propagation wave model and a topographic digital map, the electromagnetic field levels were assessed considering the height of the receiving antenna to be at the height of human. At a few locations in the direction of maximum radiation intensity, in situ measurements of the electric field strength were performed. The base station power densities measured at a few exposure sites were in the range of 0.11 (µW/cm 2) to 6.73 (µW/cm 2). The results of Kosovo experimental survey are compared with surveys done in 21 countries in five continents. The power density values obtained in Kosovo are higher, but many times below the safety standard limits.