Telecommunication Engineering Centre

2018

5G EMF Considerations Radio Division, TEC

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1. Introduction

5G is the 5th generation of wireless networks, a significant evolution of the 4G LTE

networks. 5G has been designed to meet the very large growth in data and connectivity of

today’s modern society, the internet of things with billions of connected devices, and

tomorrow’s innovations. The 5G wireless network that enables high-speed data

transmission with ultra-low latency is the key infrastructure for the future technology that

will lead the revolutionary concepts such as artificial intelligence, autonomous vehicle, big

data, and cloud. 5G will initially operate in conjunction with existing 4G networks before

evolving to fully standalone networks in subsequent releases and coverage expansions.

Besides extremely fast wireless data speeds, the next generation mobile technology will

require many more towers than previously needed to provide wireless services due to use

of sub 6 GHz and mmWave frequencies. To provide reliable connections, this dense

network of 5G towers will be located in neighborhoods rather than distant remote

locations, where the large majority of wireless towers are currently located. The concern

with having so many towers based so close to humans is the high-frequency millimeter-

sized radio waves that 5G uses to deliver extremely fast data will increase human exposure

to EMFs. This calls for a timely evolution of EMF exposure assessment methodology for 5G.

Presently, EMF exposure assessment in India to confirm the EMF exposure from base

station installations is done as per the exposure limits prescribed by the Department of

Telecommunications (DoT). A test procedure document developed by Telecommunication

Engineering Centre (TEC) provides the detailed procedure for the certificate of compliance

of EMF exposure norms by the Telecom Service Providers (TSPs) and audit by the Licensed

Service Area (LSA) Units of the Department of Telecommunications.

This paper explores a possible method of EMF compliance assessment using extrapolation

for 5G NR radio station. The method discussed in this paper could be helpful to set up the

EMF compliance assessment method for 5G NR base station since the measurement of

beam-formed radiation power density is very difficult. This paper attempts to identify the

reference signal, i.e. Synchronization Signal or PBCH signal that may be used in the

extrapolation technique using power to estimate the maximum field strength and power

density for 5G NR base station.

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2. Abbreviations and acronyms

3GPP 3rd Generation Partnership Project 5G NR 5G New Radio CP Cyclic Prefix DL Downlink DoT Department of Telecommunications EMF Electromagnetic field FDD Frequency Division Duplex gNB Next generation NodeB IoT Internet of Things LSA Licensed Service Area LTE Long Term Evolution MIMO Multiple-Input Multiple-Output mMIMO massive MIMO mmWave millimeter-Wave OFDM Orthogonal frequency-division multiplexing PBCH Physical Broadcast Channel PDSCH Physical Downlink Shared Channel PRACH Physical Random Access Channel PRB Physical Resource Block PSS Primary Synchronization Signal RAN Radio Access Network SS Synchronization Signal SSB Synchronization Signal Block SSS Secondary Synchronization Signal TDD Time Division Duplex TEC Telecommunication Engineering Centre TSP Telecom Service Provider UE User Equipment UL Uplink

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3. 5G spectrum

5G will use additional spectrum predominately in the 3 – 86 GHz range to add significantly

more capacity compared to the current mobile technologies. The additional spectrum and

greater capacity will enable more users, more data and faster connections. The increased

spectrum also includes the millimetre-wave (mmWave) bands. The mmWave frequencies

provide localized coverage as they mainly operate over short line of sight distances.

Figure 1 shows the existing and new spectrum that will be used for 5G mobile

communications.

Low band (below 1 GHz) — providing widespread coverage across urban, suburban and rural areas and supporting IoT for low data rate applications.

Medium band (1 – 6 GHz) — providing good coverage and high speeds, and including the expected initial 5G range of 3.3 – 3.8 GHz which has been identified as the most likely band for launching 5G globally.

High band (above 6 GHz) — providing ultra-high broadband speeds for advanced mobile broadband applications, and most suitable for applications in dense traffic hotspots. The 26-28 GHz band has been identified by some administrations for future 5G applications.

Figure 1: Existing and new spectrum to be used for 5G mobile communication services

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4. The Radio Access Network

The Radio Access Network (RAN) consists of various types of facilities including small cells,

towers, masts, street furniture and dedicated in-building and home systems which connect

mobile users and wireless devices to the main core network.

Small cells will be a significant feature of 5G networks particularly at the new mmWave

frequencies where the connection range is very short. To provide a continuous connection,

small cells will be distributed in clusters depending on where users require connection, and

this will complement the macro network.

5G macro cells will use antennas that have multiple elements to send and receive more

data simultaneously and cater for multiple connections. The benefit to users is that more

people can simultaneously connect to the network and maintain high throughput. Antenna

arrays for 5G are often referred to as ‘massive MIMO’ (mMIMO) due to the large number

of multiple elements.

5. 5G Massive MIMO antenna configurations

5G Massive MIMO (mMIMO) antennas are similar to existing 3G and 4G base station

antennas, however with a much higher frequency, the individual element size is smaller

allowing more elements (for example 64 or 512). Figure 2 shows the difference between

conventional sector antennas and the mMIMO antennas used in 5G networks.

Figure 2: 4G base station with sector antennas and 5G base station with multi-element

Massive MIMO antenna array

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Beam steering and beamforming is a technology that allows the mMIMO base station

antennas to direct the radio signal to the users and devices rather than in all directions. The

beam steering technology uses advanced signal processing algorithms to determine the

best path for the radio signal to reach the user. This increases efficiency as it reduces

interference (unwanted radio signals). Figure 3 illustrates how beam steering and

beamforming works in a 5G network.

Figure 3: Massive MIMO beamforming and beam steering in a 5G network

6. 5G wireless network RF-EMF exposure compliance assessment

RF-EMF compliance assessments for 5G networks will require careful analysis of the design

and configuration of the site to be evaluated, and whether a mMIMO or small cell

configuration has been deployed. Calculations or measurements may be conducted close to

a base station site, in areas which are accessible for the general public, to verify that the

RF-EMF exposure levels are below the applicable limits.

For EMF exposure assessments of 5G sites using mMIMO, it is important to accurately

determine the actual maximum transmitted power. Massive MIMO base stations transmit a

number of simultaneous beams to the connected devices. These beams vary rapidly in both

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time and space, and there will not be transmission in a certain direction at the rated

maximum power for longer times.

The configuration of a massive MIMO 5G site will vary depending on the operator network

design and implementation of the applicable 3GPP standards. The calculation of actual

maximum transmitted power and actual maximum EMF exposure from a mMIMO 5G

antenna array requires a number of factors to be considered, including:

Total maximum transmitted power

Fraction of power used for traffic beams and broadcast/synchronization beams

Beam steering ranges and half-power beamwidths

Antenna radiation pattern (envelope of all traffic beams)

Maximum gain for traffic beams and broadcast/synchronization beams

Number of possible simultaneous traffic beams

Installation environment

Distribution of connected devices

Time Division Duplex (TDD) or Frequency Division Duplex (FDD)

7. Frame Structure

When EMF assessment of 5G NR use LTE TDD based air interface between base station and

user equipment, it needs to consider data traffic according to the number of UE connection

and data throughput. TDD is unlike FDD based system, data frame shares the downlink and

uplink in slot level. Unlikely traditional radio services, there are some complexities for the

LTE TDD based beamforming with 5G NR protocol. To overcome these difficulties of EMF

measurement, the understanding of frame structures in time domain and physical resource

block in frequency domain is required.

NR Frame Structure that is specified in 3GPP specification (38.211) is explained below:

I. Numerology - Subcarrier Spacing NR supports multiple different types of subcarrier spacing (in LTE there is only one

type of subcarrier spacing, 15 KHz). The types NR numerology is summarized in 3GPP

TS 38.211 and produced below in Figure 4.

As can be seen here, each numerology is labeled as a parameter (u, mu in Greek).

The numerology (u = 0) represents 15 kHz which is same as LTE. And it can be seen in

the second column the subcarrier spacing of other u is derived from (u=0) by scaling

up in the power of 2.

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Figure 4: 5G NR Frame Structure

II. Radio Frame Structure As described above, in 5G/NR multiple numerologies (waveform configuration like

subframe spacing) are supported and the radio frame structure gets a little bit

different depending on the type of the numerology. However, regardless of

numerology the length of one radio frame and the length of one subfame is same.

The length of a Radio Frame is always 10 ms and the length of a subframe is always 1

ms.

Now let's look into the details of radio frame structure for some numerologies and

slot configuration.

< Normal CP, Numerology = 0 >

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In this configuration, a subframe has only one slot in it, it means a radio frame

contains 10 slots in it. The number of OFDM symbols within a slot is 14.

< Normal CP, Numerology = 1 >

In this configuration, a subframe has 2 slots in it, it means a radio frame contains 20

slots in it. The number of OFDM symbols within a slot is 14.

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< Normal CP, Numerology = 2 >

In this configuration, a subframe has 4 slots in it, it means a radio frame contains 40

slots in it. The number of OFDM symbols within a slot is 14.

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III. Slot Format There are a lot of different slot format defined in 3GPP TS 38.213. The concept would

be similar to legacy LTE TDD subframe configuration, but main differences from LTE

TDD subframe configuration are in NR slot format. The DL and UL assignment

changes at a symbol level in NR slot format whereas in LTE TDD the UL/DL

assignment is done in a subframe level. Also, in NR slot format, there are much

diverse patterns comparing to LTE TDD subframe configuration. Some examples of

slot formats are shown below:

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So many different types of slot formats will make NR scheduling flexible especially for

TDD operation. By applying a slot format or combining different slot formats in

sequence, we can implement various different types of scheduling.

IV. Resource Grid

The resource grid for NR looks identical to LTE resource grid, but the physical

dimension (i.e., subcarrier spacing, number of OFDM symbols within a radio frame)

varies in NR depending on numerology.

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The maximum and minimum number of Resource blocks for downlink and uplink is

defined as below (this is different from LTE).

Following is the table converted for the downlink portions of above table into

frequency bandwidth just to give the idea on what is the maximum RF bandwidth

that a UE / gNB need to support for single carrier.

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8. Technical considerations for 5G NR base station EMF assessment

To get the maximum EMF exposure field strength or power density of 5G NR beamforming

or radiation, there is a need to measure a reference signal power radiation and

extrapolating it for the entire service bandwidth. The initial access between UE and gNB

(5G base station or next generation Node B) is composed of the following physical channels

and signals:

Downlink - Primary Synchronization Signal (PSS)

- Secondary Synchronization Signal (SSS)

- Physical Broadcast Channel (PBCH)

Uplink - Physical Random Access Channel (PRACH)

PSS, SSS and PBCH are the only always-on signals in 5G NR.

Both SS (PSS and SSS) and PBCH detection helps UE synchronize with the gNB during initial

network entry phase. By detecting and decoding SS, UE can obtain physical cell identity,

achieve downlink synchronization in time/frequency domain and acquire time instants of

PBCH channel. Center frequency of PSS/SSS is aligned with center frequency of PBCH.

PBCH carries very basic 5G NR system information for UEs. Any 5G NR compatible UE must

have to decode information on PBCH in order to access the 5G cell.

Information carried by PBCH include following:

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Downlink System BW

Timing information in radio frame

SS burst set periodicity

System frame number

Other upper layer information

SS (PSS and SSS) and PBCH in NR are transmitted in the same 4 symbol block. SS/PBCH

block consists of 240 contiguous subcarriers (20 RBs). The subcarriers are numbered in

increasing order from 0 to 239 within the SS/PBCH block. Following is the SSB (SS Block)

composition.

I. SS Block SS Block (SSB) stands for Synchronization Signal Block and in reality it refers to

Synchronization/PBCH block because synchronization signal and PBCH channel are

packed as a single block that always moves together. In NR, there are many different

cases of time domain pattern of SSB Transmission as illustrated below:

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II. Beam Sweeping by SSB This is about how beam sweeping is implemented by changing beam direction for

each SSB transmission. Below is an example of how beam sweeping is implemented

by changing beam direction for sub 6 GHz band:

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This is the mechanism by which UE measure and identifies the best beam for a UE.

i) Multiple SSBs are being transmitted with a certain interval.

ii) Each SSB can be identified by a unique number called SSB index.

iii) Each SSB is transmitted via a specific beam radiated in a certain direction

iv) Multiple UEs are located at various places around a gNB.

v) UE measures the signal strength of each SSB it detected for a certain period (a

period of one SSB Set).

vi) From the measurement result, UE can identify the SSB index with the strongest

signal strength. This SSB with the strongest signal strength is the best beam for the

UE.

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NOTE : How many different beams are being transmitted is determined by how many

SSBs are being transmitted within a SSB Burst Set(a set of SSBs being transmitted in 5

ms window of SSB transmission). The parameter defining the maximum number of

SSBs within a SSB set is called Lmax. In sub 6 Ghz, Lmax is 4 or 8 and in mmWave Lmax

is 64. In other words, in sub 6 GHz, max 4 or 8 different beams can be used and they

sweep in one dimension (horizontal only or vertical only). In mmWave max 64

different beams can be used and they can sweep in two dimensions (horizontal and

vertical directions).

III. SS Burst Set Definition It is expressed as a SS burst signal in 5G NR. It consists of some SSB decided by beam

numbers.

The transmission of SSBs within SS Burst Set is confined to a 5 ms window. SS Burst

Set transmission is periodic. An IDLE UE assumes a default periodicity of 20 ms.

9. Extrapolation Technique for 5G NR EMF assessment

As an example, the structure of SSB for sub 6 GHz band and sub carrier spacing of 30 KHz is

given below:

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Figure: Structure of SSB

Due to the characteristics of 5G NR air interface, only SS Burst signals radiate continuously

with 5ms, 10ms, 20ms, 40ms, 80ms, 160ms time interval.

Figure: 5G NR frame stream in time domain ( =8)

To assess EMF exposure for 5G NR radio station, it is required to monitor 10ms frame

length and extrapolation with using SSB signal measurement containing PBCH power or PSS

power for the calculation of the maximum EMF. If we can measure one resource element

power in SSB, we can extrapolate to whole service frequency bandwidth.

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The instant maximum electromagnetic field strength can be calculated with measuring

reference signal field strength and multiplying extrapolation factor.

Extrapolated maximum electromagnetic field strength of cell (V/m)

Measured electromagnetic field strength of reference signal per RE (V/m)

Extrapolation factor of cell

However, there is a need to consider following two types of compensation factors:

During radiation, there is a need to consider deducting radiated field strength for empty symbols based on SS burst period.

There is also a need to add uplink symbols deduction according to slot format type.

Taking into account these two compensating factors, the resultant field can be calculated

as:

Compensation factor for empty symbols in one SS Burst period and uplink symbols

deduction according to slot format type.

This work is based on 5G EMF measurement studies going on in ITU-T Study Group-5. The

studies are not final and conclusive but still under development and deliberation phases

and will be adopted once ratified and approved by members.

10. Conclusion

As in the case of EMF exposure assessment in case of LTE, where the measurement of

reference signal transmitted by the base station at a constant power level is done and

extrapolated to the maximum power density, this paper attempts to identify a reference

signal, i.e. Synchronization Signal Block (SSB) consisting of PSS, SSS and PBCH whose

measurement maybe extrapolated to find maximum electric field/ power density.

However, care has to be taken to account for compensatory factors to avoid

overestimation of measurement. The method needs to be further developed for calculating

extrapolated values keeping in mind different frequency bands, subcarrier spacings,

multitude of slot formats to name a few.

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Similar studies are being carried out by Republic of Korea in ITU-T which are based on EMF

compliance assessment using extrapolation for 5G NR radio station. Other works in this

area are based on supplement to ITU Recommendation K.Supp 5G which provides guidance

on the RF-EMF compliance assessment considerations for 5G wireless networks; and other

being conduction of 5G EMF surveys at 5G innovation centres in the form of in-situ RF

exposure measurements on the 5G trial networks.

In future, the findings of EMF exposure assessment studies of shared mobile

telecommunications sites where 2G, 3G, 4G, and 5G base stations might be co-located, may

be presented and discussed in ITU to further guide the studies on EMF exposure

assessment. Also, international standards bodies, the IEC and IEEE are following

collaborative working approach to harmonize EMF safety compliance assessment standards

for 5G devices and are conducting a number of case studies on base stations. In such

scenario, the membership and active participation in working groups of IEC and IEEE which

are involved in standardization and case studies on 5G may be a prudent approach to be

future ready in terms of EMF compliance assessment.

REFERENCES

1. EMF extrapolation method of 5G radio stations for compliance assessment: Sung-Won Moon, Sam- Young Chung & Byung Chan Kim

2. ITU- K. Supl 16: Electromagnetic field (EMF) compliance assessments for 5G wireless networks

3. http://www.sharetechnote.com/html/5G/5G_SS_Block.html 4. http://www.rfwireless-world.com/5G/5G-NR-SSB-SS-PBCH.html 5. Understanding the 5G NR Physical Layer: Javier Campos 6. https://turbofuture.com/cell-phones/Are-5G-Wireless-Networks-Safe-The-Dangers-of-

5G-EMFs 7. http://www.sharetechnote.com/5Gframestructure.html 8. http://www.sharetechnote.com/waveform_candidate.html