Statistical model of the human RF exposure in small cell environment

Abstract

Small cells are one of the solutions to face the imperative demand on increasing mobile data traffic. They are low-powered base stations installed close to the users to offer better network services and to deal with increased data traffic. In this paper, the global exposure induced in such networks as a whole from user equipment and base stations has been investigated. As the small cell is close to the user, the propagation channel becomes highly variable and strongly susceptible by environmental factors such as the road traffic. An innovative statistical path loss model is constructed based on measurements on two French commercial LTE small cells, operating at LTE 1800 MHz and 2600 MHz . This statistical path loss model is then used to assess global exposure of the adult proportion of a population in a scenario composed of a street lined with buildings, indoor and outdoor data users.Keywords RF exposure · Small cell · exposure index · drive test measurements · path loss · statistical modeling 1 Introduction Nowadays radio frequency (RF) wireless communication systems are intensively used in different aspects of daily life. Phenomenal progresses in technologies, new applications, wireless devices and networks have led to a strong growth in data traffic over the last decade [1] . To respond to such demand, research efforts have been carried out to improve the efficiency of communication protocols. Current mobile networks are essentially made up of long-range radio equipment (macro cells) deployed to ensure coverage in the different territories. To face 5G ambitious aims (even more data traffic, higher frequency bands with poorer propagation capacities), this long-range layer will be supplemented by medium-range antennas (small cells) to improve coverage and connectivity for all, as the population increasingly uses mobile networks.Small cells (SC) are low-powered base stations (BS). Deploying SCs results in offloading traffic from macro cells, hence, network performance, coverage, and capacity are increased. The coverage of a SC is less than a macro cell: it is ranged typically from a few meters to a few hundreds of meters [2]. Furthermore, SC antenna is often deployed at a low height, e.g., on top of a bus station. As a consequence, SC can be more numerous than macro cells and antennas closer to the users than macro antennas typically installed on a roof top or on top of a mast. By bringing the antennas closer to the users, it is also expecting to reduce the emitted power by user equipements (UE) and to increase the available throughput for users. UEs are therefore able to benefit from SCs, their greater quality and larger throughput than those of classical macro cells. SCs are expected to be deployed massively in order to cover the maximum number of users but such deployment can result to an important raise in public concerns. Despite the intensive use of wireless communication devices and existing international safety limits, there is still public concerns and risk perceptions about human exposure to RF electrom...

Discrepancies of Measured SAR between Traditional and Fast Measuring Systems

“…For simulation techniques, when the distance is large (relative to the wavelength of the electric field), the front of incident wave upon the body can be treated as planar [10; 11], while near fields need to be analyzed with a high-resolution human module with a numerical code (FDTD [12] or FEM [13]) when the human body is close to sources [14; 15; 16]. In measurements, the exposure to base stations is usually estimated by measuring the intensity of the electric field at various locations and through the construction of a path loss model it is possible to have a statistical view [17]. The exposure to user equipment is traditionally measured by moving a probe inside a liquid-filled phantom, which simulates the composition of human body or head, to estimate the whole-body and/or local SAR [9].…”