Ray-Tracing-Based Numerical Assessment of the Spatiotemporal Duty Cycle of 5G Massive MIMO in an Outdoor Urban Environment

Abstract

In the near future, wireless coverage will be provided by the base stations equipped with dynamically-controlled massive phased antenna arrays that direct the transmission towards the user. This contribution describes a computational method to estimate realistic maximum power levels produced by such base stations, in terms of the time-averaged normalized antenna array gain. The Ray-Tracing method is used to simulate the electromagnetic field (EMF) propagation in an urban outdoor macro-cell environment model. The model geometry entities are generated stochastically, which allowed generalization of the results through statistical analysis. Multiple modes of the base station operation are compared: from LTE multi-user codebook beamforming to the more advanced Maximum Ratio and Zero-Forcing precoding schemes foreseen to be implemented in the massive Multiple-Input Multiple-Output (MIMO) communication protocols. The influence of the antenna array size, from 4 up to 100 elements, in a square planar arrangement is studied. For a 64-element array, the 95th percentile of the maximum time-averaged array gain amounts to around 20% of the theoretical maximum, using the Maximum Ratio precoding with 5 simultaneously connected users, assuming a 10 s connection duration per user. Connection between the average array gain and actual EMF levels in the environment is drawn and its implications on the human exposure in the next generation networks are discussed.

In Situ Assessment of 5G NR Massive MIMO Base Station Exposure in a Commercial Network in Bern, Switzerland

“…Finally, when the objective of the assessment is to measure the maximum actual transmit power, the E max values obtained using the methods described in this paper and in [13] (i.e., the theoretical maximum) shall be scaled with the relevant power reduction factor as described by the working draft of the International Electrotechnical Commission standard IEC 62232 [8,9,15].…”

“…Several studies on the experimental assessment of the exposure due to NR base stations have been published in the past few years [7][8][9][10][11][12][13][14][15]. Furthermore, in [16], drive-test measurements in three NR networks operating in the 3.6 GHz band were performed, collecting samples of the transmit power (Tx) and of the synchronization signal reference signal received power (SS-RSRP) received by a mobile device, while millions of Tx power samples from user equipment were also recorded in two commercial NR networks in [17].…”

Assessment of Human Exposure to Electromagnetic Fields: Review and Future Directions

“…When applied to beamforming antennas, traditional compliance evaluation methods would assume that the theoretical maximum power is transmitted in each possible beam for long periods, leading to unrealistic exposure assessments. Recently, several numerical and experimental studies determined the actual maximum power level contributing to EMF exposure for base stations implementing beamforming (e.g., [79][80][81][82]). Procedures applicable for massive MIMO base stations will be included in the next revision of IEC 62232 [78].…”

Towards Environmental RF-EMF Assessment of mmWave High-Node Density Complex Heterogeneous Environments

“…The novelty of their work is that they propose a localization-enhanced pencil beamforming technique in which the traffic beams are tuned in accordance with the uncertainty localization levels of the User Equipment (UE) in the DL configuration. The authors in Reference [7] presented a computational method based on ray tracing techniques (RT) to estimate human EMF exposure in DL 5G base stations at sub-6 GHz frequencies in outdoor macrocell environments. The same authors presented in References [8][9][10] a combined numerical approach based on RT and Finite Difference Time Domain (FDTD) techniques, which estimates EMF exposure for 5G massive MIMO in different environments, such as an industrial environment [8], an urban microenvironment (UMi) [9] or an urban macro-environment (UMa) [10], all of them at 5G frequencies below 6 GHz.…”

“…As it can be seen from the table, there were few works in the literature that presented an approximation in which simulation estimations were simultaneously combined with measurement results. References [6][7][8][9][10][11] presented different methodologies based only on simulation techniques, all for DL and sub-6 GHz frequency bands. Conversely, the works in References [12][13][14] presented EMF exposure assessment methodologies based on measurements campaigns, again at sub-6 GHz frequency bands and DL assessments.…”