Considerations on the EMF Exposure Relating to the Next Generation Non-Terrestrial Networks

Abstract

The emerging fifth generation (5G) and the upcoming sixth generation (6G) communication technologies introduce the use of space- and airborne networks in their architectures under the scope of non-terrestrial networks (NTNs). With this integration of satellite and aerial platform networks, better coverage, network flexibility and easier deployment can be achieved. Correspondingly, satellite broadband internet providers have launched an increasing number of small satellites operating in low earth orbit (LEO). These recent developments imply an increased electromagnetic field (EMF) exposure to humans and the environment. In this work, we provide a short overview of the state of consumer-grade satellite networks including broadband satellites and future NTN services. We also consider the regulatory state governing their operation within the context of EMF exposure. Finally, we highlight the aspects that are relevant to the assessment of EMF exposure in relation to NTNs.

Full text

arXiv:2308.00658v1 [cs.NI] 1 Aug 2023
Considerations on the EMF Exposure Relating to
the Next Generation Non-Terrestrial Networks
Amina Fellan∗, Ainur Daurembekova∗, Hans D. Schotten∗⋄
∗Institute of Wireless Communication and Navigation,
Rheinland-Pf ¨
alzische Technische Universit¨
at Kaiserslautern-Landau (RPTU), Kaiserslautern , Germany.
{fellan, daurembekova, schotten}(at)eit.uni-kl.de
⋄Intelligent Networks, German Research Center for Artificial Intelligence (DFKI), Kaiserslautern, Germany.
Hans Dieter.Schotten(at)dfki.de
Abstract—The emerging fifth generation (5G) and the upcom-
ing sixth generation (6G) communication technologies introduce
the use of space- and airborne networks in their architectures
under the scope of non-terrestrial networks (NTNs). With this
integration of satellite and aerial platform networks, better
coverage, network flexibility and easier deployment can be
achieved. Correspondingly, satellite broadband internet providers
have launched an increasing number of small satellites operating
in low earth orbit (LEO). These recent developments imply an
increased electromagnetic field (EMF) exposure to humans and
the environment. In this work, we provide a short overview
of the state of consumer-grade satellite networks including
broadband satellites and future NTN services. We also consider
the regulatory state governing their operation within the context
of EMF exposure. Finally, we highlight the aspects that are
relevant to the assessment of EMF exposure in relation to NTNs.
Index Terms—non-terrestrial networks, mega-constellations,
6G, human EMF exposure, regulations, satellite networks
I. INTRO DUC TIO N
Discussions about the next sixth generation (6G) of com-
munications systems are well on course in both the academia
and industry communities. Innovative solutions and disruptive
technologies are being proposed to account for the shortcom-
ings and challenges that faced previous generations. One of
the challenges faced by current terrestrial networks (TNs) is
the difficulty and non-feasibility of providing global coverage
to users in remote areas. The infrastructure deployment for
TNs is often costly, rigid, and requires meticulous planning.
Not to mention, in the case of natural disasters, how prone
TNs are to breakdowns and how challenging it could be to
restore their operation.
Non-terrestrial networks (NTNs) are seen as one of the
appealing solutions to complement TNs services and expand
their coverage to remote areas around the globe. Recent
advancements in the satellite and space industries lowered
This work has been funded by the Federal Ministry of Education and Re-
search of Germany (BMBF) (Projects numbers: 16KISK004 and 16KISK067).
This is a preprint version, the full paper has been accepted by The IEEE
International Conference on Mobile Ad-Hoc and Smart Systems (MASS),
Toronto, Canada. September 2023. Please cite as: A. Fellan, A. Daurembekova
and H. D. Schotten, “Considerations on the EMF Exposure Relating to the
Next Generation Non-Terrestrial Networks,” in IEEE International Conference
on Mobile Ad-Hoc and Smart Systems (MASS), 2023
launch costs for satellite systems and advanced the mar-
kets for consumer-service based deployments. Nowadays, the
Third Generation Partnership Project (3GPP) is laying out the
foundations for integrating NTNs in the next generation of
communication networks. With 6G, two connectivity scenarios
would be possible. Namely, direct connectivity between a
satellite or an aerial platform and handset devices as well as
indirect connectivity that exploit the satellites’ connectivity in
the backhaul [1].
On the other hand, over the past decade, several companies
announced revolutionary plans to provide high-speed internet
access using constellations of a large number of satellites
to serve user terminals around the globe. This increasing
interest in bringing NTNs closer to end-users raises questions
about how would such deployments affect the overall level of
electromagnetic field (EMF) exposure experienced by humans
and the environments.
For TNs, organizations such as the World Health Orga-
nization (WHO), International Commission on Non-Ionizing
Radiation Protection (ICNIRP), Institute of Electrical and
Electronics Engineers (IEEE), and International Telecommu-
nication Union (ITU) are concerned with evaluating research
and studies on human EMF exposure [2]–[5]. The outcomes
of their evaluation is used to derive safe limits and guidelines
to restrict the levels of EMF exposure. In this work, we
consider previous efforts done to study EMF exposure related
to satellite communications.
This work is organized as follows. In Section II, we provide
a summary on existing broadband internet satellite networks as
well as the next generation NTN networks as proposed by the
3GPP. Section III explores considerations with respect to EMF
exposure from satellite and airborne networks and possible
challenges related to EMF measurements for such scenarios.
The state of regulations concerning EMF exposure within the
scope of satellite communications is explored in Section IV.
Finally, our conclusions are given in V.
II. NON -T E RR E ST RIA L NETW OR K S
Interest in leveraging satellite and airborne networks for
civilian applications has been gaining momentum over the
recent years. Compared to TNs, satellite networks have the
advantage of a larger coverage area which translates to better

TABLE I: Frequencies allocated to NTNs by the 3GPP [6]
NR Satellite Frequency Duplex Coexisting terrestrial
band band Uplink Downlink mode NR bands
n255 L 1626.5 MHz – 1660.5 MHz 1525 MHz – 1559 MHz FDD n24*, n99*
n256 S 1980 MHz – 2010 MHz 2170 MHz – 2200 MHz FDD n2, n25, n65, n66, n70
∗US-specific.
accessibility to remote and rural areas where the deployment
of TNs can be challenging, not feasible, or not possible. NTNs
could also ensure a fallback solution in natural disasters situa-
tions on the occasion that TNs’ services are disrupted. Within
the scope of 6G networks, the introduction and integration
of NTNs in the overall network architecture play an essential
role in providing global network coverage and improving the
network’s resiliency. This will not be the first attempt to extend
the coverage of TNs via satellite connectivity [7], nor to
provide mobile satellite services to users around the globe [8].
However, the advent of the new low-cost space- and air-borne
vehicles as well as the substantial development of communi-
cations technologies and markets makes the reintroduction of
NTNs to support TNs quite attractive.
In this section we provide an overview of the state of the
current and upcoming satellite networks, focusing particularly
on those providing direct links of two-way satellite commu-
nications to user terminals and handheld devices. We first
consider the 3GPP’s ongoing work on NTNs, followed by
existing examples of mega-constellations of non-geostationary
satellite orbit (NGSO) satellite systems.
A. New Radio - Non-Terrestrial Networks
UE
gNB
Gateway
UAS
VSAT
5GCN
Feeder link
Service link
Radio link
Text is not SVG - cannot display
Fig. 1: NTN architecture according to the different scenarios
considered by the 3GPP’s study in [9]
As per the 3GPP’s vision, the scope of NTNs includes
spaceborne systems operating in the geostationary earth orbit
(GEO), NGSO (including low earth orbit (LEO) and medium
earth orbit (MEO)), as well as airborne platforms such as
high altitude platform station (HAPS) and unmanned aerial
systems (UASs) [10]. The ongoing work on the NTN standards
can be broadly split into two classes, namely, new radio
(NR)-NTN and Internet of Things (IoT)-NTN. The former
addresses enhanced mobile broadband (eMBB) use cases,
thus complementing and expanding the capacity of services
provided by TNs over a larger coverage area. Whereas the
latter is concerned with massive machine type communication
(mMTC) applications, providing satellite connectivity to IoT
devices.
The first studies considering the introduction of NTNs to the
fifth generation (5G) NR were initiated in 2017 by the 3GPP
and appear in Rel-15 under TR 38.811 [9]. The 3GPP study
considered use cases, propagation channel models, network
architectures, deployment scenarios, and potential challenges
associated with the integration of NTNs with the NR interface.
Figure 1 illustrates some of the possible scenarios considered
for NTNs based on [9].
In Rel-16 under TR 32.321, the 3GPP resumed its inves-
tigation relating to the support of NR protocols in NTNs,
focusing mainly on satellite nodes but also considering other
non-terrestrial platforms such as UASs and HAPSs [11]. The
technical report provided a refined proposal for NTN-based
next generation radio access network (NG-RAN) architectures,
system- and link-level simulations for the physical layer,
and considerations of issues relating to delay, Doppler shifts,
tracking area and user mobility that are particular to NTNs.
Rel-17 builds upon the first studies carried out in [9] and
[11] to define an initial set of specifications to support NTNs
in NR. Co-existence issues between NTNs and TNs channels
as well as the radio frequency (RF) requirements for satellite
access nodes (SANs) and NTN-supporting user equipments
(UEs) were the central point that the 3GPP considered in
TR 38.863 [6]. Based on the ITU radio regulations [12], the
frequency bands n255 and n256 in the L- and the S-bands
were designated by the 3GPP for NTN operation in the United
States and internationally, respectively. Details of the 3GPP
approved allocated frequencies to NTNs are listed in Table
I. At present, frequency division duplex (FDD) channels are
supported with plans to consider time division duplex (TDD)
subsequently. For the operation at frequencies above 10 GHz,
the satellite Ka-band is being considered [11].
In the current Rel-18, the 3GPP is discussing in TR 38.882
the regulatory aspects and challenges arising from the verifi-
cation of UEs location information within the coverage area
of NTNs [13]. The definition and allocation of frequencies
to the uplink and downlink in frequency range (FR)2 is also
currently under consideration.
Despite the fact that the specifications and standardization
of NTNs are at the moment still being defined by the 3GPP,
the first initiatives to realize the 3GPP’s NTN vision of a
global hybrid mobile network are currently underway. For

instance, the Omnispace Spark program has launched its first
nanosatellite in 2022, part of a global NGSO network and is
foreseen to operate in the S-band, supporting the specifications
of the 3GPP’s n256 band and targeting mainly IoT applications
[14]. Another milestone is the first UE chipset supporting NR-
NTN. It was announced in February 2023 by MediaTek [15].
The chipset is compliant with the 3GPP’s specifications for
NR-NTN defined in Rel-17. It is capable of supporting two-
way satellite communications and is seen as an enabler for
NTNs services in future 5G smartphones and satellite-enabled
UEs.
B. Satellite Networks
Over the last decade, we witnessed a surge in the num-
ber of satellites being launched into space. With companies
such as SpaceX, OneWeb, Telesat, and Blue Origin racing
to kick-off their mega-constellations by sending hundreds of
LEO satellites to space [16]. The main goal of LEO mega-
constellations is to provide global broadband internet access to
end-users over a fixed satellite service (FSS). The architecture
of mega-constellation satellite systems consists of three main
components: the constellation of satellites in LEO, a network
of ground gateway stations, and user terminals; in the form
of very small aperture terminals (VSATs). We consider here
aspects of two of the currently largest constellations, namely,
SpaceX and OneWeb.
In 2015, SpaceX announced its Starlink program with
initial plans to deploy more than 4000 LEO satellites in
orbit. Starlink satellites are operated on circular orbits at an
altitude of 550 km. As of the time of this writing, more than
3500 of Starlink’s mini-satellites are in-orbit. The Ku and
Ka satellite frequency bands are used for the satellite-to-user
and satellite-to-ground links, respectively [17]. The satellite
and earth terminals support beamforming transmissions using
phase-array antennas. Each satellite could support at least 8
beams. The peak effective isotropic radiated power (EIRP)
values for the user’s downlink could reach 36.71 dBW [17].
OneWeb’s constellation is planned to operate polar orbit
planes at an altitude of 1200 km. A total number of 648
satellites are to be delivered in orbit to establish a global
coverage of OneWeb’s satellite network. Between the satellite
and user terminals, the Ku band is used for communications
while the Ka band is allocated for the satellite to gateway links.
OneWeb satellites can support up to 16 beams. The maximum
EIRP for the user’s downlink is around 34.6 dBW. Table II
lists a comparison between characteristics of the two major
NGSO constellations currently in operation.
Mega-constellation operators have been also extending their
operations to include mobile satellite service (MSS) applica-
tions. SpaceX and T-Mobile announced in 2022 their plans to
provide ”Coverage Above and Beyond” services that support
direct satellite connectivity to cellphone users over a long
term evolution (LTE) interface [18]. The new service will be
hosted on SpaceX’s second generation NGSO satellites and
will support text messaging at the initial stage, with voice
and data services to follow. The satellite-to-cellular links are
TABLE II: Summary of Starlink and OneWeb constellations
operational characteristics
Parameter Starlink OneWeb
Altitude 550 km 1200 km
Satellite 4408 648
constellation (initial phase)
Number of user beams ≥8 16
User-to-space
Uplink frequency 14.0 – 14.5 GHz 14.0-14.5 GHz
Downlink frequency 10.7 – 12.7 GHz 10.7-12.7 GHz
Gateway-to-space
Uplink frequency 27.5 – 29.1 GHz 27.5-30.0 GHz
Downlink frequency 17.8 – 18.6 GHz 17.8-19.3 GHz
planned to operate on LTE band 25 frequencies, namely, 1910-
1915 MHz and 1990-1995 MHz for the earth-to-space and
space-to-earth links, respectively [19].
Mega-constellation satellites are not the only nor the pioneer
providers for MSS. Commercial two-way communication for
voice and data services was available by companies like
Iridium, Inmarsat, Globalstar, and Thuraya ever since the late
1990s and early 2000s. For instance, the Iridium satellite
constellation provides global voice and data services to mobile
users via its 66 LEO satellites [8]. Its services are available
to its subscribers on the L-band (from 1616-1626.5 MHz). In
2017, Iridium launched the second generation of its satellites,
known as Iridium-NEXT [20].
Figure 2 depicts the number of satellites launches of the
major mobile satellite communication providers over the last
decade with a clear upward trend. In 2019, Iridium-NEXT
has launched the required number of satellites to complete its
planned constellation and provide a stable operation. Addi-
tional satellites could be launched in the future as spares to
maintain the constellation. OneWeb and Starlink are still in
the process of building their constellations.
2017 2018 2019 2020 2021 2022
Year
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Number of satellite launches
Starlink
OneWeb
Iridium-NEXT
Total launches
Fig. 2: Number of satellite launches within the period of
2017-2022 for the three major satellite mobile communication
providers. Based on data from [21]

III. MEA SU REM E NT S CON SID ERATI ONS A ND CH ALL E NG E S
The recent growing interest in ubiquitous satellite com-
munications with direct connectivity to UEs calls for more
measurement and simulation studies on the exposure lev-
els to users and the environment. Measurement studies on
EMF exposure near satellite earth stations are scarce and the
emerging technologies to be implemented in both TNs and
NTNs require more attention to their implications on the EMF
exposure levels. Table III summarizes some of the aspects that
might prove relevant when comparing between EMF exposure
assessment methods for TNs and NTNs.
Hankin in [22], supported by the US Environmental Protec-
tion Agency, provides one of the earliest and few measurement
studies assessing the EMF exposure levels from satellite
communication systems. He first evaluated mathematically the
EMF exposure in terms of power density as a function of
distance from the source, then he performed measurements in
the vicinity of the sources to determine the actual exposure
levels. However, the study considers satellite communication
earth terminals transmitting at an EIRP in the orders of
megawatts, unlike the case for NTNs which will transmit
at considerably lower powers. Moreover, such terminals are
normally located away from the general population and are
within sites that are restricted to public access. Besides,
EMF measurement equipment and satellite communication
technologies have evolved significantly since the 1970s, when
this study took place.
More recent measurement studies were conducted in [23]
and [24], where the authors evaluated the EMF exposure using
broadband EMF meters in the vicinity of maritime satellite
transmitters and satellite earth terminals, respectively. They
later on compared it to the ICNIRP guidelines levels for
occupational and general public scenarios. In [25], the authors
consider the exposure from large-phased array antennas used
to communicate with LEO satellite systems and provide a
device-based time-averaging method to estimate the EMF
exposure based on the time-averaged power density.
In this section we present a few considerations on EMF
exposure measurements for NTNs communications scenarios.
A. Downlink: space-to-earth
Path loss. By the time the signal arrives at the earth
terminal, it would have experienced high losses due to several
factors such as, free space path loss, atmospheric loss, and
ionospheric and tropospheric scintillation losses. Free space
path loss is dependant on the distance between the transmitter
and receiver, which in the case of NTNs can be anywhere
between 300 km for LEO satellites and could reach up to
35,786 km for GEO satellites. The free space path loss LF S
is given by:
LF S (dB) = 20 log(4π d f
c)(1)
where dis the distance between the transmitter and receiver,
fis the frequency, and cis the speed of light in vacuum.
Atmospheric loss is the gaseous attenuation caused by oxygen
and water vapor density [26]. Whereas scintillation losses are
caused by irregularities in the atmosphere [27]. The overall
path loss is dependant on the elevation angles of a satellite.
Figure 3 depicts the path loss experienced at frequencies
where satellite communications are operated, mainly from the
L- to the Ka-bands. The highlighted and zoomed-in section
corresponds to NR bands n255 and n256 that are planned
for NTNs’ operation to support mobile satellite services. Five
different elevations for NTN space terminals are considered.
Namely, 20 km for HAPS, 300 km for the lower LEO satellites
altitude range, 1500 km for the upper LEO satellites altitude
range, 20,000 km for an average MEO satellite altitude, and
35,786 km for GEO satellites.
Fig. 3: Path loss due to free space (FS) and atmospheric gas
(AG) conditions at a temperature of 20°C and corresponding
to the frequency range of satellite communications
B. Uplink: earth-to-space
Path loss The uplink undergoes similar free space path
loss to that experienced by the downlink. As a result, higher
antenna gains are required at the user terminals transmitting
from earth to space.
Terminal type. Depending on the earth terminal type,
the maximum transmitted power is defined accordingly. For
instance, in [6] the 3GPP has assigned the UE power class 3 to
UEs for NTN use-cases, which include handheld devices and
allows a maximum transmit power of 26 dBm with a power
tolerance level of +/- 2 dB for any transmission bandwidth
within the channel bandwidth. UE power class 3 is the default
power class for TNs as well. Other terminal types such as
VSATs and earth stations in motions (ESIMs) are configured
to transmit at higher powers. VSATs and ESIMs would provide
users indirect access to NTN services. They are planned to be
used for FR2 operation in NTN.
Antenna type. In contrast to UEs, VSATs and ESIMs would
use directional antennae such as parabolic antennae, i.e., the
resulting EMF exposure is concentrated in their antennae’s
main transmission lobe. Thus additional safety measures need

to be taken into account when mounting such terminals to
ensure the safety of users.
Service usage profiles. For handheld UE devices, a major
component of the EMF exposure occurs in the antenna’s near-
field. Adequate specific absorption rate (SAR) assessments
methods are thus necessary in this case to determine the level
of RF power absorbed by the human body [3]. The usage
profile (voice calls, texting, browsing, etc.) influences factors
such as the proximity of the device to the body, the duration of
usage, and consequently the intensity of EMF exposure [28].
TABLE III: Comparison of some of the consideration on TNs
vs NTNs
Network TN NTN
Antenna type omni-directional directional
Cell stationary stationary (GEO),
coverage mobile (NGSO)
Coverage up to 30km up to 1000 km (NGSO),
radius up to 3500 km (GEO)
Frequency FR1, FR1,
range (FR) FR2 FR2*
Operation up to 7.125 GHz, 1-2 GHz
frequencies 24.25-71.0 GHz above 10 GHz*
Duplex mode TDD / FDD FDD*
Terminal UE UE,
type VSAT,
ESIM
UE power class 2, class 3
class class 3
∗NTN specifics are still underdevelopment by 3GPP.
IV. REG ULATIO NS A N D STA NDAR DI Z ATION
The recent advancements of wireless communications net-
works and their pervasiveness in our daily lives raised few
calls from the public concerning the increased levels of EMF
exposure in the environment. Several organizations, such as
the WHO, ICNIRP, IEEE, ITU and International Electrotech-
nical Commission (IEC), evaluate continuously the research
studying the influence of EMF exposure on humans. They use
the outcome of their evaluations to define and maintain the
guidelines and recommendations with the goal to protect hu-
mans and the environment against any possible harmful effects
caused by the exposure to radio-frequency electromagnetic
fields [3], [4], [29], [30].
The EMF exposure limits set by the regulatory organizations
target the overall maximum possible radiation at a given
frequency and location. This maximum level should take into
consideration the EMF exposure due to all different sources
and radio access technologys (RATs) surrounding the point
of evaluation. Also, it has to take into account characteristics
of the transmissions present, for instance, whether they are
continuous or pulsed [3]. In practice, such assessments are
not necessarily straight-forward with regular measurement
equipment as they only provide the instantaneous and average
values of EMF radiation at a given location.
The ICNIRP guidelines are the most widely adopted recom-
mendations internationally. They define the reference levels for
limiting the EMF exposure from sources operating at frequen-
cies up to 300 GHz [3]. The reference levels are frequency
dependant and can be evaluated in terms of the electric field,
magnetic field, or the power flux density. Depending on the
type of exposure in question, e.g., due to a handheld device
versus due to a base station, they are defined for local and
whole-body exposure. Table IV lists the exposure limits as
specified by the reference levels defined by the ICNIRP in
[3]. For instance, the incident power density caused by a
VSAT terminal transmitting in the Ku-band, and taking into
consideration any other sources transmitting in the same band,
when measured in the far-field of its antenna (i.e., at a distance
greater than 2D2/ λ (m); where Dis the largest dimension
of the VSAT antenna and λis the wavelength) should not
exceed the limit of 10 W/m2when averaged over a duration
of 30 minutes and over the whole-body. On the other hand, for
handheld devices, due to the fact that they are used in close
proximity to the body and particularly to certain critical parts
such as the head, reference levels concerned with local EMF
exposure apply in this case. Handheld devices must undergo
rigorous EMF exposure testing to determine the SAR levels.
As per the ICNIRP, for the general public, the local SAR limit
for the head and trunk lies at 2W/kg averaged over 10 gof
cubic mass and for exposure intervals greater than or equal to
6 minutes [3].
The ITU is the foremost authority regulating and organizing
international access to the space spectrum [12]. The ITU also
provides recommendations on measuring the EMF radiation by
broadcast stations and considerations regarding the placement
of satellite earth stations in [31]. The choice of the location
for such stations needs to be carefully determined such that
the near-field and transition zones are far from residential
and industrial areas. Since satellite earth stations transmit to
satellites at higher powers, it is very likely that the resulting
EMF field exceeds the reference levels. Thus, access to such
facilities must be restricted against unauthorized personnel.
With the introduction of NTNs, the existing guidelines and
recommendations need to be re-assessed to take into account
the increased number of satellites in space, and user terminals
on earth and any resulting consequences on the EMF levels.
V. CO NCL USI ON S
In this work, we presented a short overview of the state
of the next generation NTNs and their position in future 6G
networks. Given this growing interest in NTNs, questions
on how to assess their possible contribution to the EMF
exposure on humans and the environment need to be taken
into account. NTNs will bring direct connectivity of UEs,
such as smartphones and tablets, to satellite and air-bone
communication systems, which raises questions on the levels
of EMF exposures the users are subject to experience in
such scenarios. We provided considerations regarding the
implications of the spread of these technologies on EMF
exposure levels in the environment from the downlink and
uplink perspectives. We observed there is a shortage of EMF
assessment studies concerned with NTN scenarios. More

TABLE IV: ICNIRP reference levels for exposure to electromagnetic fields at frequencies relevant to satellite communication
applications, as defined in [3].
Exposure type Frequency (MHz) Averaging time (min) E-field strength (V/m) H-field strength (A/m) Power density (W/m2)
Whole-
body
400 - 2000 30 1.375f1/2 0.0037f1/2 f/200
2000 - 300000 N/A N/A 10
Local
400 - 2000
6
4.72f0.43 0.0123f0.43 0.058f0.86
2000 - 6000 N/A N/A 40
6000 - 300000 N/A N/A 55/f0.177
measurement and simulation studies are required to better
understand the possible EMF exposure levels on the uplink and
to ensure the compliance of such communications links with
the recommended reference levels defined by the respective
organizations.
ACK NOWL E DG MEN T
This work has been funded by the Federal Ministry of
Education and Research of Germany (BMBF) partially under
the projects “Open6GHub” (grant number 16KISK004) and
6G-TakeOff (grant number 16KISK067). The authors alone
are responsible for the content of this paper.
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