Spatial Characterization of Personal RF-EMF Exposure in Public Transportation Buses

New services and applications within vehicular environments employ multiple wireless communication systems, within a heterogeneous network framework. In this context, evaluation of electromagnetic field impact is compulsory in order to warrant compliance with current exposure limits. In this paper, E-field strength distribution within urban transportation buses is studied, in which different types of buses, as well as network configurations, are considered. E-field estimations are obtained within the complete interior volume of the urban buses, considering all the characteristics in terms of bus structure and materials employed, by means of an in-house-developed deterministic 3D ray-launching (3D-RL) code. In this way, relevant phenomena in terms of electromagnetic propagation and interaction are considered, such as multipath propagation and shadowing, which determine exposure levels as a function of transceiver location within the bus scenarios. The behavior in terms of E-field distribution of wireless public land mobile communication systems within transportation buses have been analyzed by means of measurement campaigns employing personal exposimeter devices. In addition, E-field volumetric distributions by means of 3D-RL simulations have been obtained as a function of user distribution within the buses, with the aim of analyzing the impact of user presence within complex intra-vehicular indoor scenarios, such as urban transportation buses. A comparison with current exposure limits given by currently adopted standards is obtained, showing that E-field levels were below the aforementioned limits. The use of deterministic simulation techniques based on 3D-RL enables E-field exposure analysis in complex indoor scenarios, offering an optimized balance between accuracy and computational cost. These results and the proposed simulation methodology can aid in an adequate assessment of human exposure to non-ionizing radiofrequency fields in public transportation buses, considering the impact of the morphology and the topology of vehicles, for current as well as for future wireless technologies and exposure limits.