Human exposure to EMF from 5G base stations: analysis, evaluation and comparison of different

Abstract

Human exposure to EMF from 5G base stations: analysis, evaluation and comparison of different assessment methods Expósito I, Hakizimali C, Sánchez MG, Cuiñas I, Verhaevert J. Human exposure to EMF from 5G base stations: analysis, evaluation and comparison of different assessment methods. Measurement, Volume 229, 2024. doi: 10.1016/j.measurement.2024.114434. Highlights This paper analyzes the feasibility of assessing the 5G base stations compliance using broadband field probes and compares their performance with alternative methodologies and equipment. Performance of three different methodologies and equipment (broadband probes, spectrum analyzers, and drive test scanners), in the context of human exposure to electromagnetic fields (EMF) from 5G base stations, is compared. Quantification of the uncertainty that the fluctuation in 5G signal levels induces in the assessment of electromagnetic fields exposure is provided. The use of broadband field probes for 5G exposure assessment is still possible under certain considerations and correcting the results considering the base station load and beamforming effects. Abstract 5G networks deployment poses new challenges when evaluating human exposure to electromagnetic fields. Fast variation of the user load and beamforming techniques may cause large fluctuations of 5G base stations field level. They may be underestimated, resulting in compliance of base stations not fitting the requirements. Apparently, broadband field meters would not be adequate for measuring such environments. However, we analyze the feasibility of confidently using broadband field meters and compare their performance with alternative equipment. Measurements based on the synchronization signals power level, using spectrum analyzers or drive test scanners, may be valid, if gain differences between the signaling and data radiation patterns are characterized. These methods lead to good results but require more time and knowledge. Nevertheless, using broadband field meters is still possible if the measurement results are corrected considering the base station load. Under specific conditions, explained here, fast assessment of 5G compliance could be provided. Conclusions Assessing human exposure to an electromagnetic field in presence of a 5G base station is not an easy task. The implementation of M−MIMO techniques in 5G base stations results in adaptive beamforming. This makes difficult to guarantee that the field levels are at their maximum at the measurement location during the complete measurement period, which would limit the applicability of broadband instruments as having been done for previous generations. In this research, we have compared different methods for 5G exposure assessment, using a broadband field meter with an isotropic probe, a spectrum analyzer and a drive test scanner. Along the paper, we first give an overview of the 5G signal structure, describing the frequency domain and time domain specifications. Afterwards, possible assessment methods are described. The SSB level is measured using the Keysight FieldFox N9913A SA and the Rohde & Schwarz TSM6 DTS. The values are extrapolated to the worst-case exposure and compared to the measurements done with the Wavecontrol WPF8 broadband field probe. Measurements are repeated increasing the base station load by performing a heavy download from a 5G user terminal located near the testers. The proposed methods were field tested at the University of Vigo, Spain, with a commercial 5G base station located on its campus. The measurements were performed at 7 locations in LOS conditions around the base station, gathering data with the three different equipment at the same locations and at the same time. This data collection allows the comparison of the three methodologies under the same radiating conditions. All results have been analyzed considering the specific measurement uncertainties, which allows a deeper and more precise comparison among them. From the measurement results, we can extract that the exposure levels are low at this stage of the 5G deployment. When loading the base station, the results showed that using the broadband field meter can overestimate the field level. Thus, it is still a useful method to check if the field levels comply with the regulation in human exposure; very simple and cost-effective compared with others. In-situ measurements of human exposure to EMF have to be practical and easy to carry, involving only the resources and equipment strictly necessary, but without compromising the validity of the results. When the reference levels are surpassed, more accurate methods based in the assessment and extrapolation of the SSB level could be a solution. The drawback is the required post processing, specially correcting the gain difference between SSB and data signals. If not provided by the network operator, this difference can be determined through measurements, as explained along this document. Measuring with an SA in max-hold mode in the bandwidth of the SSB does not work in 5G as it does in LTE, as we cannot be sure if the measured level corresponds to the SSB or to the user data, no matter if we are forcing the load of the station or not. The analysis of the results demonstrate that broadband instruments can be used for assessing human exposure to EMF in the vicinity of 5G base stations, which radiating elements provide fields with extreme fluctuations in their intensity as a function of the system load and beamforming configuration. This is accurate when measurements are done by forcing an extra load of the station and the pointing of an antenna beam towards the probe. The validation of this fast method as a first attempt to assess the compliance of 5G stations permits the testing of these base stations in an efficient way. Only when broadband instrument results (including their uncertainties) would overpass the reference levels, a more detailed analysis would be necessary, which procedure and tips are also depicted along this paper. sciencedirect.com

AI evidence extraction

Main findings

Field tests at 7 line-of-sight locations around a commercial 5G base station found exposure levels were low at this stage of deployment. Methods based on measuring synchronization signal block (SSB) levels with a spectrum analyzer or drive test scanner can provide good results but require characterization/correction of gain differences between signaling and data radiation patterns and more time/knowledge. Broadband field meters can still be used for fast compliance assessment if results are corrected for base-station load and beamforming effects; when the base station was loaded, the broadband meter could overestimate field level.

Outcomes measured

• Feasibility of using broadband field meters/probes for 5G base-station compliance assessment
• Comparison of 5G exposure assessment methodologies/equipment (broadband probe vs spectrum analyzer vs drive test scanner)
• Uncertainty due to 5G signal fluctuations (load and beamforming) in exposure assessment
• Estimated/observed field levels near a commercial 5G base station under different load conditions

Limitations

• Frequency band(s) / carrier frequency not stated in provided text
• Small number of measurement locations (7) and single site (University of Vigo campus)
• Results described as specific to this stage of 5G deployment and to specific conditions (e.g., forced load and beam pointing)
• Broadband method validity depends on corrections (e.g., load/beamforming) and uncertainty handling; details not fully specified in provided text

Suggested hubs

• 5g-policy (0.62)
  Focuses on assessing 5G base-station compliance/exposure assessment methods relevant to 5G deployment.

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    "main_findings": "Field tests at 7 line-of-sight locations around a commercial 5G base station found exposure levels were low at this stage of deployment. Methods based on measuring synchronization signal block (SSB) levels with a spectrum analyzer or drive test scanner can provide good results but require characterization/correction of gain differences between signaling and data radiation patterns and more time/knowledge. Broadband field meters can still be used for fast compliance assessment if results are corrected for base-station load and beamforming effects; when the base station was loaded, the broadband meter could overestimate field level.",
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        "Broadband method validity depends on corrections (e.g., load/beamforming) and uncertainty handling; details not fully specified in provided text"
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    "keywords": [
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