Keywords

1 5G NR Mobile Communication System

1.1 Introduction of 3GPP Release 15, 16, 17 for the History of 5G

The 3GPP (Third Generation Mobile Partnership Project) announces a version freeze every once in a while, which means that no new technical features will be added to that version, and newly generated technological innovations will be reflected in the next version. 5G is a technology that continues to evolve over a decade, and currently 5G has gone through three versions, R15, R16 and R17.

The 5G R15 version was frozen in June 2018, with R15 focusing on eMBB (enhanced mobile broadband), laying the foundation for 5G.

The 5G R16 version freezes in July 2020, adding NR-U, eURLLC, NR V2X, 5G broadcast, etc., expanding industry applications, especially in vertical areas.

The 5G R17 release freeze in June 2022 further extends the 5G technology base in terms of network coverage, mobility, power consumption and reliability, and broadens 5G to new use cases, deployment methods and network topologies [1, 1].

1.2 Channel and Beam Profile for 5G NR

In 3GPP TS38.104, the bandwidth requirements for the use of the 5G FR1 band range from a minimum of 5 MHz to a maximum of 100 MHz.5G NR defines two downlink synchronization signals: Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS). PSS, SSS and the physical broadcast channel PBCH together form a structure called SS/PBCH Block, or SSB for short, which occupies a limited and fixed physical bandwidth [3].

The SSB is sent in the 5G NR downlink frame with a default period of 20 ms for terminal synchronization [4]. The number of SSBs per 20 ms is the number of beams. The number of beams varies from 1 to 8 and is transmitted in different directions. This is shown in Fig. 1.

Fig. 1
A schematic diagram defines how the mobile receives a signal from a tower through eight beams, which are transmitted in different directions.

5G NR downlink beam transmitting schematic

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In the downlink transmission between base station and terminal, SSB is only responsible for synchronization and broadcasting information, while the service information of each terminal is carried in the physical downlink shared channel with the maximum bandwidth up to 100 MHz.

2 Electromagnetic Radiation from 5G Base Stations in Different 5G Terminal Application Scenarios

2.1 Application Scenarios Specified in HJ1151-2020

According to the “5G mobile communication base station electromagnetic radiation environmental monitoring methods (for trial implementation)” (HJ1151-2020), Sect. 2.4 application scenario requirements, 5G mobile communication application scenarios include: enhanced mobile broadband (eMBB), ultra-high reliability and low latency communication (uRLLC), large-scale machine-like communication (mMTC), such as data transmission, video interaction, gaming and entertainment, virtual shopping, smart medical, industrial applications [5].

In order to get several application scenarios, Sect. 2.3 in HJ1151-2020 requires that: when monitoring, the monitored mobile communication base station should be in normal working condition, and the 5G terminal equipment should be connected to the monitored 5G mobile communication base station and be in at least one typical application scenario.

When monitoring, the monitoring instrument probe is placed on the monitoring instrument stand, and the distance between the tip of the probe and the operator’s torso is not less than 0.5 m, and the 5G terminal equipment is kept within 1–3 m; avoid or minimize the interference of other electromagnetic radiation sources incidental to the surrounding area and the impact of leakage current from the monitoring instrument stand [6].

2.2 Problem Formulation

We can’t help but ask the following questions: In the HJ1151-2020 standard, why does the application scenario for 5G terminal equipment and the relative distance between the 5G terminal setup and the probe make a description of the requirements, namely:

  1. 1.

    What impact will the different application scenarios of 5G terminals have on the measured electromagnetic radiation values of 5G base stations?

  2. 2.

    What effect will the different relative positions of the 5G terminal and the probe of the monitoring instrument have on the electromagnetic radiation measurement value of the 5G base station?

In order to solve the above two questions, we use the base station electromagnetic radiation function of the EMF meter to measure a 5G base station, and use the 5G NR spectrum analyzer as an auxiliary instrument to verify the cause of the corresponding phenomenon.

2.3 Practical Testing

To verify question 1, we use the 5G terminal working in non-data download state (other mode) as well as data transmission in two application scenarios, respectively, at the same measurement location and when the 5G terminal is close to the probe (1–3 m range).

To verify question 2, we move the 5G terminal away from the field intensity meter probe, while the 5G terminal and the electromagnetic probe are in the same beam area and different beam areas of the 5G base station, respectively, and the 5G terminal performs data transmission application scenarios.

During the experiment, a EMF meter and a 5G NR spectrum analyzer are placed close to a 5G base station at a distance of about 100 m, and the probe of the EMF meter is at the same height as the antenna of the spectrum analyzer, with a position difference of 20 cm. The tester places the 5G terminal at different ranges from the EMF probe and works in different application scenarios to observe the measured radiation values of the base station and the spectrum tested by the spectrum analyzer.

Use the frequency selective measurement function of the EMF meter; use the waterfall spectrum function of the spectrum analyzer to observe the 5G base station signal emission and electromagnetic radiation in different application scenarios of the 5G terminal, respectively.

For this test, we selected China Mobile’s 5G NR n41 band. The China Mobile n41 band uses TDD time division multiplexing mode with a bandwidth of 100 MHz.

  • Group 1 and Group 2 tests

Relative distance from the 5G terminal to the electromagnetic probe

The distance between the 5G NR terminal and the probe of the EMF meter is 1 m, and the 5G NR terminal and the probe are located in the same beam radiation direction of the base station. As shown in Fig. 2.

Fig. 2
A schematic diagram defines how the mobile receives the signal from a tower. A probe is located at a distance of 1 meter from the mobile. The tower transmits signals through eight beams in different directions.

The first group and the second group test layout diagram

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Table 1 Group 1 and group 2 test application scenarios
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The first group of test results

From the electromagnetic field intensity meter’s frequency selection measurement mode we measured that the average value of electromagnetic radiation within 6 min for the China Mobile n41 5G band was 0.003 uW/cm2. Use the waterfall spectrum function of the spectrum analyzer. As shown in Fig. 3.

Fig. 3
Two screenshots of the Devser window. Each plots the R M S and the color gradient for the first group. Window 1 traces two fluctuating signals with multiple spikes and dips. Window 2 traces a spectrum and a fluctuating signal. The parameters are in a foreign language.

The first group of test measurement results

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The second group of test results

From the selected frequency measurement mode of the EMF strength meter we measured that the average value of electromagnetic radiation in 6 min for the China Mobile n41 5G band is 8.249 uW/cm2. Use the waterfall spectrum function of the spectrum analyzer, as shown in Fig. 4. This value is much higher than the value of the first group of tests.

Fig. 4
Two screenshots of the Devser window. Each plots the R M S and the color gradient for the second group. Window 1 traces two fluctuating signals with multiple spikes and dips. Window 2 traces a spectrum and a fluctuating signal. The parameters are in a foreign language.

The second group of test measurement results

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We observe that the power values are strong for the vast majority of frequencies in the 100 MHz spectrum. Also on the waterfall plot, we observe that the vast majority is red, indicating a strong signal. It also contrasts with the first set of tests. In this scenario we see that the 5G base station service channel has to use the majority of the service channel transmit power within the 100 MHz frequency to transmit data as it has to carry large data volumes of data transmission information.

As seen from the test findings in Table 2, the radiation field strength values of the 5G base station are low when the 5G terminal is not performing data interaction services. The radiation field intensity value of the 5G base station is high when the 5G terminal is carrying out data transmission application scenarios.

Table 2 Conclusions of group 1 and group 2 tests
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The low radiated field strength of the 5G base station in the first test group can also be verified from the spectrum analyzer measurements because most of the RBs in the 100 MHz bandwidth are not loaded and do not send strong power signals. The reason for the high radiated field strength of the 5G base stations in the second group of tests is that most of the RBs in the 100 MHz bandwidth are loaded and send strong power signals in order to achieve high throughput data compliance.

  • Group 3 test

Compared with the first and second group of tests, in the third group of tests, the position of the electromagnetic probe relative to the base station remains the same, while the relative distance from the 5G terminal to the electromagnetic probe is changed. The distance between the 5G terminal and the EMF meter probe is 20 m and the 5G NR terminal and the electromagnetic probe are located in the same beam radiation direction of the 5G base station. As shown in Fig. 5.

Fig. 5
A schematic diagram defines how the mobile receives the signal from a tower. A probe is located at a distance of 20 meters from the mobile. The tower transmits signals through eight beams in different directions.

The third group of test layout diagram

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The application scenarios for the third group of tests: 5G NR terminal working in data transmission state.

Results of Group 3 tests

From the electromagnetic field intensity meter’s frequency selection measurement mode we measured that the average value of electromagnetic radiation within 6 min for the China Mobile n41 5G band was 4.932 uW/cm2, and waterfall spectrum as shown in Fig. 6.

Fig. 6
Two screenshots of the Devser window. Each plots the R M S and the color gradient for the third group. Window 1 traces two fluctuating signals with multiple spikes and dips. Window 2 traces a spectrum and a fluctuating signal. The parameters are in a foreign language.

The third group of test measurement results

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During the test, it can be observed that the real-time measurement value of the electromagnetic radiation field strength meter immediately becomes larger while the spectrum amplitude of the spectrum analyzer waterfall graph becomes larger, but the color of the spectrum analyzer waterfall graph display is not darker than that of the second group test, indicating that the received power at the spectrum analyzer of the third group test is not as large as the received power of the second group test, which also verifies the test value of the electromagnetic field strength meter.

As seen in Table 3, when the 5G terminal is 20 m away from the probe of the EMF meter, and the 5G terminal and the probe are located in the same beam radiation direction of the base station, the tested downlink electromagnetic radiation value of the 5G base station is smaller than the value when the 5G terminal is closer to the electromagnetic probe, but it can still capture the downlink signal during data transmission.

Table 3 Third group of test findings
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  • Group 4 test

Compared with the first and second group of tests, the position of the electromagnetic probe relative to the base station remains unchanged in the fourth group of tests, while the relative distance from the 5G terminal to the electromagnetic probe is changed. The distance between the 5G NR terminal and the probe of the EMF meter is 20 m, but the 5G NR terminal and the probe are located in different beams radiation direction of the base station. As shown in Fig. 7.

Fig. 7
A schematic diagram defines how the mobile receives the signal from a tower. A probe is located at a vertical distance of 20 meters from the mobile. The tower transmits signals through eight beams in different directions.

The fourth group of test layout diagram

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The application scenarios of the fourth group of tests: 5G NR terminal working in data transmission state.

Results of Group 4 test

From the electromagnetic field intensity meter's frequency selection measurement mode we measured that the average value of electromagnetic radiation within 6 min for the China Mobile n41 5G band was 0.389 uW/cm2, and waterfall spectrum as shown in Fig. 8.

Fig. 8
Two screenshots of the Devser window. Each plots the R M S and the color gradient for the fourth group. Window 1 traces two fluctuating signals with multiple spikes and dips. Window 2 traces a spectrum and a fluctuating signal. The parameters are in a foreign language.

The fourth group of test frequency selection electromagnetic measurement results

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During the test, it was observed that the real-time measurements of the electromagnetic radiation field strength meter did not become significantly stronger when the 5G terminal went from the resting state to the moment of starting data transmission, and the spectrum amplitude of the spectrum analyzer waterfall plot could not be observed to become significantly larger.

As seen in Table 4 in the 5G NR terminal and EMF meter probe distance of 20 m, and 5G terminal and the probe is located in different beam radiation direction of the base station, the tested 5G base station downlink electromagnetic radiation value than the 5G terminal distance electromagnetic 20 m but in the same base station beam direction is much smaller, indicating that the 5G base station according to the beam to 5G terminal to transmit downlink signals, in different beam coverage of the electromagnetic field intensity meter can test the radiation value is very low.

Table 4 Group 4 test findings
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Four groups of test conclusions:

  • When the 5G terminal is in two different application scenarios of non-data transmission and data transmission, the electromagnetic radiation values of 5G base stations are different. It shows that the test report of HJ1151-2020 standard indicates that the application scenario is critical.

  • When the 5G terminal is far away from the electromagnetic probe, but still in the same beam coverage of the 5G base station as the electromagnetic probe, the tested electromagnetic radiation value is lower than that when the 5G terminal is close to the electromagnetic probe.

  • When the 5G terminal is far away from the EM probe, and the EM probe is in a different beam coverage of the 5G base station, the tested EM radiation value will be much lower. This means that the 5G base station's beam is aligned with the 5G terminal, and the EMF radiation value is low because the EM probe is not in the same downlink beam signal emission direction.