5G networks are the next generation of mobile systems that will provide faster speeds, lower latencies, and extended connectivity than existing 4G networks. The new 5G system will provide a vast range of new services, while extended connectivity is necessary for IoT, smart home applications, and areas where smart devices are widely used.
5G NR will also include higher frequency electromagnetic waves of at least up to 30 GHz in the millimeter-wave region. These new frequencies are more affected by natural hurdles such as obstructions and extreme weather conditions and can, therefore, cover shorter distances. The use of such high frequencies is expected to increase the number of mobile antenna stations needed to cover the same geographical areas.
But how are the transmitter power limits of the antenna set, and are these emissions and the use of more antennas potentially harmful to humans?
Electromagnetic waves
Electromagnetic waves consist of electric and magnetic fields that propagate into space in the form of waves. Electromagnetic waves generally propagate at the speed of light. The levels of electromagnetic radiation differ from each other and are dependent on the frequency or length of each successive wave.
The electromagnetic wavelength is the distance covered by a wave cycle. The frequency is defined as the number of wave cycles passing a particular point during a one second period.
Radio waves are generated by the electric charge movement on the antennas and are referred to as radio frequency (RF) electromagnetic radiation as they radiate away from their source, that is, the transmitting antenna.
Microwaves are electromagnetic waves with frequencies between 300 MHz and 300 GHz. Their wavelengths range from one meter to as short as one millimeter respectively. These types of electromagnetic signals are widely used for various telecommunications applications such as cell-phone (mobile) phones, radars, airport scanners, radio and satellite communications.
Electromagnetic radiation
Non-ionizing radiation is electromagnetic radiation that carries relatively low energy that is insufficient to cause ionization. Non-ionizing radiation is not capable of generating electrical, chemical, and other effects on the human body. Microwaves are radio waves that belong to this category of non-ionizing radiation.
Unlike ionization, which is dangerous because it can lead to alterations to the genetic material and cause harmful health effects such as cancer (e.g., X-rays, gamma rays, etc.), the main biological result of radio waves under certain conditions is the increase in temperature of tissues exposed to it. Research to date has not substantiated a deterministic relationship between this type of radiation and harmful effects on human health.
It is, therefore, essential to distinguish between ionizing and non-ionizing radiation and be able to differentiate the perceived real risks potentially caused by electromagnetic radiation.
Non-ionizing radiation characteristics
Potential harmful effects on health for non-ionizing radiation are those that occur during or immediately after the expiration of exposure and only when exceeding exposure on specific limit values.
Taking into account the specificities of each person and the fact that there are particular groups of people such as young children, patients, and elderly people, there are “basic restrictions” that ensure their observance and the absence of harmful health effects. The primary constraints arise from the limits of the proven adverse effects on health since significant safety factors are adopted.
However, the significant limitations do not directly concern measurable sizes in the emission imaging environment, but the inherent magnitudes within the body of people that are difficult to measure. For this reason, and taking into account the less favorable conditions of coupling of radiation to humans, “reference levels” are easily measurable characteristics of the electromagnetic radiation. Their observance also ensures compliance with the specified limits and hence, the absence of harmful effects for human health.
Regulation
Concerning electromagnetic fields in the 0-300GHz frequency range, the World Health Organization, the International Commission on Ionizing Radiation Protection and the European Union, adopted basic values and reference levels and issued limits for the safe exposure of the public to a low and high-frequency environment throughout the range of modern applications and services.
The International Commission on Non-Ionizing Radiation Protection (ICNIRP) describes the calculation methodology, applied in different countries. The maximum allowed electrical field strength and power flux density depend on the frequency of the radiated signal.
The calculations are usually based on a worst case scenario, on the assumption that the maximum antenna gain is permanently applied to the complete service area, even though in reality the maximum antenna gain is continuously moving in position in a specific range, for example, +/-60° horizontally and +/-30° vertically.
5G NR Transmit Power
The RF output power is strongly depending on the available bandwidth and on the target data rate. Output power is typically limited by the EMF constraints of the site.
In general, the nominal output power has to be defined by the cell size and the required data rate at the cell edge. Nevertheless, assuming that a 3.5GHz 5G antenna has between 22 dBi and 24 dBi antenna gain, ensures that most of the additional free air loss is compensated (3.5GHz has ca. 6-9 dB additional propagation loss compared to 1.8 GHz plus 5 dB extra building penetration loss). To keep the power density per MHz similar to LTE systems, the 100MHz 3.5GHz spectrum will require 5x 80 W, which is not easy to be achieved. 5G trials need to define a realistic output power trade-off between coverage, power consumption, EMF limits, and performance.
For 100MHz bandwidth, typically 120W RF output power distributed over the available TRX paths shall be used. This, in relation to the available bandwidth, is significantly lower than for LTE (80W/20MHz). However, the uplink with the fixed user equipment output power of 23dBm (20mW) will be anyway the limiting factor.
User equipment output power will be limited to 23dBm. This is also related to how many transmitting paths are to be assumed. In a typical 5G configuration, the UE has to support 4Rx diversity as a minimum.
EMF on 5G RAN Antenna Systems
EMF stands for “electromagnetic field,” and indicates the impacts and the countermeasures of electromagnetic fields to the human body. For obtaining a RAN Site deployment permission, the network operator has to prove that the exposure of people to EMF is below the given thresholds.
Compared to the conventional antenna systems (e.g., passive Antennas with 2×2 MIMO), massive MIMO will bring higher power flux density into the field. This is because the mMIMO Antenna Systems will have around 26dBi Antenna Gain, and the power feed into the antenna will rise from 2x40Watt to 120Watt and more. Conventional Antenna systems typically only have 18dBi Gain.
EMF calculation for 5G systems
The typically applied method for obtaining the RAN Site deployment permission is to calculate the maximum possible radiated power around the antenna system. In some cases the calculation is complemented or even replaced by RF measurements, that can bring additional costs. Calculation of the needed safety distances to the antenna system should also be taken into account. Typically two safety distances are calculated, softer limits for skilled workers, who know how to behave close to antennas, and harder limits for all other people, for “public access,” that may even not be aware of the antenna system presence.
The details of the applied methods differ from country to country. The most common countermeasure is to deploy the antenna system in a position where public access is not possible, for example, on a mast or a rooftop. If the antenna system is implemented on street level with public access, lower power levels should be used.
Several approaches are currently under discussion, regarding 5G massive MIMO antennas implementation. The total EMF limits have to be taken into account during site deployments to ensure high performance but also provide the required safety, in order to reassure the public opinion on 5G radiation and continue towards the evolution of 5G systems.
