'28GHz 5G SA service domestic commercialization expected in 2021
You must be familiar with the method of assessing the human body's impact due to electromagnetic waves.
Rapid release possible after development of 5G facilities and equipment


It has already been almost a year since 5G networks began commercial services in Korea.

5G technology is considered the foundation technology for the key technologies that will make up the 4th industrial revolution, but it is not able to fully realize its potential due to insufficient infrastructure. It is even called 4.5G rather than 5G. This is because the 5G network commercialized in Korea is a 5G non-standalone mode (NSA) that operates together with LTE and only uses the 3.5GHz band.

Just like LTE, 5G infrastructure is also being built all over the world. It is expected that 5G standalone (SA) service using the 28GHz band will be available in Korea by 2021. As it is clear that 5G networks will become the mainstay of next-generation mobile communications, there are factors that need to be taken into consideration when developing related products. The question is whether 5G radio waves are harmful to the human body.

Kim Byeong-chan, a senior researcher at the Electronics and Telecommunications Research Institute (ETRI), discussed the electromagnetic wave human exposure assessment technology and standards for radio stations and wireless devices, which are core facilities that make up the 5G network, focusing on ITU-T and IEC in his article titled “Trends in Standards for Electromagnetic Wave Human Exposure Assessment Technology for 5G Networks” in the 1939th issue of the Information and Communication Network Evaluation and Planning Institute (ITFIND) Weekly Technology Trends.


Human Impact Assessment for Wireless Networks
The most recent international standard covering the assessment of human exposure to electromagnetic fields in the frequency bands allocated to 5G networks (3.5 GHz and 28 GHz) is 'IEC62232 Ed2.0' published in 2017. Amendments to the measurement procedures and detailed conditions are currently being prepared, targeting 2022.

This standard covers radio-communications base stations that have one or more antennas and radiate intentional electromagnetic waves in the frequency range from 110 MHz to 100 GHz, and also includes radio-communications base stations that use the frequencies from 100 kHz to 300 GHz in the vicinity.

Key topics include in-situ measurement methods for operating radio stations, along with conformity assessment procedures for product certification and radio station installation, and in each case, spatial averaging and uncertainty estimation are included along with the measurement procedures.

ITU-T Study Group 5 (SG5) also published Recommendation K.Suppl.16 on 5G networks and electromagnetic field human impact assessment in 2019, which covered the concept of 5G networks, frequency characteristics, shared technology with LTE networks, health impact issues and exposure standards (5GEMF), and exposure assessment.

In the case of exposure assessment, a method for assessing electromagnetic wave exposure through calculation is presented, and additional measurement methods will be developed to reflect the time when a standalone 5G network is formed. The intention is to ensure that the issue of human health effects caused by electromagnetic waves does not affect the expansion of 5G network infrastructure.

It covers assessment methods that reflect various technological characteristics that are different or advanced from LTE, such as multi-input multi-output (MIMO) antenna technology and more densely installed base stations, in exposure assessment, and also includes contents such as uncertainty estimation.

Currently, the method of measuring radio wave exposure applied to LTE networks, which is not a standalone 5G network but is linked to LTE networks, is being applied, which includes the concept of spatial averaging, which calculates the average value of the electromagnetic wave intensity obtained at three heights from the measurement point.


Human impact assessment of wireless devices
The 5G frequency currently commercialized in Korea is the 3.5GHz band, and the 28GHz band is scheduled to begin service in the second half of this year. In terms of measurement methods for assessing human exposure to electromagnetic waves generated from mobile phones, the 3.5GHz band is expected to be no different from the 2GHz band or the band used in LTE.

For devices used in close proximity to the human body in this frequency band, exposure assessment is conducted based on the Specific Absorption Ratio (SAR). When evaluating SAR, a mock human body simulating the head, upper body, or entire body is created, and the electric field intensity value generated inside it and the dielectric characteristics parameters of the human body are used to calculate using the formula below.


Here, σ and ρ are factors that consider the conductivity and tissue density of the human body, respectively, and E _i is the electric field intensity generated inside the simulated human body.

The 28GHz band has a wavelength of about 1/8th that of 3.5GHz. The shorter the wavelength, the more transmission power is required to transmit the same distance. The greater the transmission power, the greater the strength of the electric field, which is not good in terms of SAR. The lower the SAR value, the less the impact on the human body.

Therefore, radio stations, which are one of the key infrastructures that make up the 5G network, should be installed relatively more densely than previous wireless network technologies to reduce the transmission and reception power required for communication with mobile phones as much as possible.

The electromagnetic waves of the 28GHz band have a much shorter wavelength than LTE and the straightness of the radio waves is stronger, so it is difficult to penetrate human tissues with relatively high permittivity. This is called the skin effect. Since almost no electric field is formed inside the human body, no magnetic field is created to transmit energy, so the electromagnetic waves cannot propagate. When looking at the propagation characteristics of electromagnetic waves based on the skin effect, electromagnetic waves of this frequency band cannot penetrate the inside of the human body and only exist on the surface of the human skin.

Human impact assessment cannot be based on SAR, which requires internal electric field strength, and must be based on power density. In other words, the basis for exposure restrictions in the 28 GHz band is also thermal effects, and the physical parameter for estimating human exposure based on this is power density.

When the human body is very close to an electromagnetic wave source such as a mobile phone, that is, in the near field, both electric and magnetic field intensities are needed to evaluate the power density because the ratio of electric and magnetic field intensities does not have a specific value (377Ω) as in the far field.

The criterion for distinguishing between near-field and far-field is the distance from the electromagnetic wave source, that is, the distance between the antenna of the mobile phone and the human body. Generally, anything less than 3 wavelengths is considered a near-field. Equipment that can measure electric field strength and magnetic field strength has already been developed, and some equipment and methods that can measure power density have been developed, but the reliability problem of the measured values has not been resolved.

In May 2019, ITU-T SG5 agreed to develop a recommendation (K.devices: Assessment of the wireless radio-communication devices operating close to the human body) to address the assessment of electromagnetic field exposure from wireless devices that will emerge after 5G, with the goal of completion in 2020.

Although there has not been much research conducted worldwide to assess human exposure to 5G wireless devices used in close proximity to the human body, the easiest way to assess power density is to measure the electric and magnetic field strengths separately and then take the product. However, it is important to consider the difference in the distribution of electromagnetic fields when a human body, which has a high dielectric constant, is present nearby compared to free space.


Uncertainty assessment
Uncertainty is a physical quantity that must be accompanied by a confidence interval for the results of a measurement or calculation, as it is a value that shows how close the results of a measurement or calculation are to the true value. It can also be seen as an error in the sense of how much it differs from the true value. However, it is reasonable to accept it as a range that multiple measurement results performed under the same conditions can have, as a difference in measured values due to repeated measurements, not a measurement error.

For 5G networks, exposure assessments must be performed more precisely and exposure levels must be expressed more accurately, as the human body is exposed to EMF in a more complex environment than before. Although IEC62232 Ed2.0 covers a wide range of technical topics regarding uncertainty estimation and recommends considering various sources of uncertainty, the factors required for uncertainty estimation in real environments are presented in Recommendation K.100 published by ITU-T.

The factors used for uncertainty estimation are usually classified into A and B type factors. Type A factors are obtained from the probability distribution function of data acquired through measurement, and type B factors are derived from the measuring equipment and are usually provided by the manufacturer. When assessing the human body's impact on electromagnetic waves generated from radio stations, they are generally divided into factors corresponding to measuring equipment, physical factors, and mechanical constraints.


Electromagnetic wave measurements also required for next-generation wireless network technology
The ITU and IEC are developing standards for electromagnetic wave human impact assessment technology for wireless equipment, which is the foundation of next-generation wireless networks. At the same time, ongoing research is being conducted to incorporate newly emerging technologies. Researcher Kim Byeong-chan expects that most of it will be completed by 2022.

In the future, next-generation wireless network technologies that are superior to those of today will be introduced. In terms of assessing human exposure to electromagnetic waves, the increasingly complex electromagnetic environment requires more precise measurement values, and thus more sophisticated measurement methods are also needed. Accordingly, the importance of measurement uncertainty assessment is expected to increase.