Available via license: CC BY 4.0
Content may be subject to copyright.
International Journal of
Microwave and Wireless
Technologies
cambridge.org/mrf
Research Paper
Cite this article: Inomata M, Yamada W, Kuno
N, Sasaki M, Kitao K, Nakamura M, Tomie T,
Oda Y (2022). Sub-terahertz propagation
characteristics up to 150 GHz for 6G mobile
communication systems. International Journal
of Microwave and Wireless Technologies 1–8.
https://doi.org/10.1017/S1759078722000459
Received: 12 November 2021
Revised: 21 March 2022
Accepted: 23 March 2022
Key words:
6G; frequency dependency; radio propagation
characteristics; sub-terahertz bands
Author for correspondence:
Minoru Inomata,
E-mail: minoru.inomata.va@hco.ntt.co.jp
© The Author(s), 2022. Published by
Cambridge University Press in association with
the European Microwave Association. This is
an Open Access article, distributed under the
terms of the Creative Commons Attribution
licence (https://creativecommons.org/
licenses/by/4.0/), which permits unrestricted
re-use, distribution, and reproduction in any
medium, provided the original work is
properly cited.
Sub-terahertz propagation characteristics up to
150 GHz for 6G mobile communication systems
Minoru Inomata1, Wataru Yamada1, Nobuaki Kuno1, Motoharu Sasaki1,
Koshiro Kitao2, Mitsuki Nakamura2, Takahiro Tomie2and Yasuhiro Oda2
1
NTT Access Network Service Systems Laboratories, NTT Corporation, 1-1 Hikarino-oka, Yokosuka-shi, Kanagawa,
Japan and
2
6G-IOWN Promotion Department, NTT DOCOMO, INC., 3-6 Hikarino-oka, Yokosuka-shi, Kanagawa, Japan
Abstract
Extreme-high-speed communication exceeding 100 Gbps is one requirement for 6G. To satisfy
extreme-high-speed-communication, one solution is to utilize terahertz bands above 100 GHz.
To determine the new radio-interface technologies and service frequency bands for 6G, terahertz
propagation characteristics above 100 GHz need to be understood. In this paper, we introduce
our new radio-network topology for 6G and then show the frequency dependency of key propa-
gation phenomena such as the characteristics of path loss in an urban environment, human
blockage, and scattering from a rough building surface up to 150 GHz. Human blockage loss
increases and the scattering is more diffused as the frequency increases. In the path-loss char-
acteristics, it was found that path-loss frequency dependency is stronger than that given by con-
ventional path-loss model because of scattering effects from a rough building surface.
Introduction
In 2020, fifth generation (5G) mobile communication systems have been rolled out worldwide. 5G
New Radio supports millimeter wave (mmW) bands up to 52.6 GHz, andan extension to 71 GHz is
being examined for future releases [1]. In the 2030s, the new market value created by 5G is expected
to be enlarged through next-generation 6G. Extreme-high-speed communication exceeding 100
Gbps is one requirement for 6G [2]. As one solution, utilization of the terahertz (THz) bands
above 100 GHz has been considered all overtheworld because a remarkably wider frequency band-
width can be utilized than even in 5G [1–3]. We note that the formal definition of the THz bands is
from 300 GHz to 3 THz, but, in this paper, we call the 100–300 GHz bands sub-THz bands. At
WRC-19, the 275–450 GHz bands were newly considered frequency bands for use in land mobile
and fixed services [1]. In addition, the US Federal Communications Commission (FCC) recom-
mends 95 GHz to 3 THz bands for 6G [3]. However, specific new radio-interface technologies
and service frequency bands have yet to be determined because propagation characteristics
above 71 GHz have not been studied sufficiently. In the mmW bands for 5G, the measurement
results show an increased frequency dependency of path loss and an increased number of occur-
rences of some blockage due to humans and small structures [4–7]. Although 5G channel models
have been standardized in ITU-R M.2412, they have been constructed by using measurement fre-
quency bands mainly below 71 GHz [5–7]. For the THz bands for 6G, these phenomena are more
sensitive and introduce increased dependence on frequency. Furthermore, the new propagation
phenomenon, which is not considered by 5G channel models, may be required to exploit the
THz bands. Specifically, in the case of scattering from a rough surface, the higher the frequency,
the larger the scattering power and the lower the reflection power, so it is necessary to clarify the
scattering effects on channel characteristics in the THz bands. Therefore, for the development of
6G mobile communication systems using new frequency bands above 100 GHz, it is important
to clarify the THz propagation phenomena and develop the channel models for the THz bands.
In this paper, we briefly introduce our new radio-network topology concept for 6G and key
propagation phenomena that should be clarified in the sub-THz bands to develop channel
models. When using our new radio-network topology for 6G in an urban microcell (UMi),
which is the main scenario of mobile communication systems, designing the new radio-
network topology with high accuracy requires the key propagation phenomena to be clarified,
such as the path-loss characteristics, human blockage, and scattering effects from rough build-
ing surfaces, for the sub-THz bands are needed to be clarified. Therefore, we investigate the
frequency dependency of path-loss characteristics, human blockage, and scattering effects
from rough building surfaces up to 150 GHz bands [8].
Key propagation phenomena affecting sub-THz channel characteristics
Figure 1 shows a new radio-network topology concept [2]. In the sub-THz bands, the path loss
becomes larger than that in the existing mmW bands of 5G. Therefore, when
https://doi.org/10.1017/S1759078722000459 Published online by Cambridge University Press
extreme-high-speed and high-reliability communication are pur-
sued, it is ideal to communicate at as close a distance and in as
unobstructed a path as possible. Cellular networks were con-
structed with a hexagonal cell layout in which base stations’posi-
tions are coordinated. However, to increase the unobstructed and
close paths in the sub-THz bands, a spatially overlapping topology
needs to be constructed. To efficiently actualize a distributed net-
work in the space domain, various solutions need to be investi-
gated such as integrated access and backhaul [9], intelligent
reflecting surface [10], and cooperation with non-terrestrial net-
works. In addition, when using the same frequency band in the
same space, inter-cell interference occurs. Therefore, it is essential
to clarify path-loss and channel characteristics based on the
sub-THz propagation phenomena and evaluate the performance
of those techniques for a new radio-network topology.
To design the new radio-network topology with high accuracy, it
is important to clarify the propagation phenomena and develop
channel models on the basis of use cases for 6G. Figure 2 shows
the key propagation phenomena that affect channel characteristics
for the sub-THz bands in an UMi. ITU-R M.2412 proposed models
that can calculate path loss that building shadowing and human
blockage is considered and the building penetration loss in accord-
ance with the mixing ratio of building materials; however, the mod-
els are constructed by using measurement frequency bands below
71 GHz [4–7]. Also, a representative atmospheric attenuation
model up to 1THz was reported in ITU-R P.676 [11], and rain
attenuation model up to 1 THz was reported in ITU-R P.838
[12]. In addition, vegetation attenuation up to 30 GHz was reported
in ITU-R P.833 [13], and scattering from rough surfaces was mainly
investigated below 71 GHz [5]. As previously mentioned, a number
of studies have been conducted on the channel characteristics of the
THz bands, but the characteristics above the 71GHz band for 6G
have not been sufficiently studied. Therefore, in this paper, we
investigate the frequency dependency of human blockage, scattering
from rough building surfaces and characteristics of path loss in an
UMi from microwave bands to sub-THz bands to evaluate 6G sys-
tem performances.
Frequency dependency of key phenomena
Human blockage
Human blockage loss was measured from 0.8 to 150 GHz bands
to clarify the frequency dependency. We selected 0.8, 2.2, 3.4,
4.7, 27.9, 37.1, and 66.5 GHz to cover the frequency bands
assigned to mobile communication systems up to 5G and 8.5,
97.5, and 150 GHz in 7–10 GHz, and sub-THz bands agreed
with candidate frequency bands for 6G. The measurement para-
meters are shown in Table 1.Figure 3 shows the measurement
setup and results. In Figs 3(a) and 3(b), in the measurement,
the distance between the antenna and the human body was set
to about 2 m, and the antenna height was set to 1.8 m correspond-
ing to human chest height. The human body was moved at inter-
vals of 0.05 m. The Tx and Rx antenna are an omni-directional
antenna with an antenna gain of 2.5 dBi at 0.8 GHz, 2.7 dBi at
2.2 GHz, 2.3 dBi at 3.4 GHz, 2.5 dBi at 4.7 GHz, 2.0 dBi at 8.5
GHz, 3.5 dBi at 27.9 GHz, 2.0 dBi at 37.1 GHz, 3.0 dBi at 66.5
Fig. 1. Evolution of radio-network topology for 6G.
Fig. 2. Key propagation phenomena for sub-THz bands.
Table 1. Measurement parameters
Frequency 0.8, 2.2, 3.4, 4.7, 8.5, 27.9, 37.1, 66.5, 97.5, 150 GHz
Signal Continuous wave (CW)
Tx/Rx antenna Horn antenna at 150 GHz, omni-directional antenna
at 0.8, 2.2, 3.4, 4.7, 8.5, 27.9, 37.1, 66.5, and 97.5 GHz
Tx/Rx antenna
height
Approximately 1.8 m
2 Minoru Inomata et al.
https://doi.org/10.1017/S1759078722000459 Published online by Cambridge University Press
GHz, and 0 dBi at 97.5 GHz. At 150 GHz, the Tx and Rx antennas
are a horn antenna with a beam width of 20° and an antenna gain
of 23 dBi. Human blockage loss is calculated by subtracting the
free-space path loss from the measurement path loss. The
human blockage area is defined as the measured path loss that
is larger than the free-space path loss due to the Fresnel zone
shielding. In Fig. 3(c), the blockage area depends on frequency
because as the Fresnel radius becomes small, the blockage area
becomes small. Also, as the frequency increases, the human block-
age loss increases. Figure 3(d) shows a comparison of the meas-
urement and calculated results using the M.2412 human
blockage model [4]. In that model, the human blockage loss is cal-
culated by the knife-edge diffraction model using a finite width
screen. In this paper, the diffraction loss is calculated by using a
0.5 × 1.7 m screen, which is the same as the measurement’s
human body size. Also, that model is constructed on the basis
of the results equivalent to those using the omni-directional
antenna. Since the angle required to radiate a human body
from the Tx antenna is about 14°, it is narrower than the beam
width of the Rx antenna at 150 GHz. Therefore, the obtained
measurement of human blockage is equivalent to the results
obtained using the omni-directional antenna. From these results,
we find that the calculation results are similar to the measurement
results, and the human blockage loss increases as the frequency
increases, and the blockage area decreases as the frequency
increases. The root mean square error (RMSE) of the loss is 1.6
dB. Therefore, the M.2412 human blockage model is valid to
evaluate the frequency dependency of human blockage loss up
to the 150 GHz bands.
Scattering from rough surface
There is a trade-off between reflection and scattering from the
rough surface shown in Fig. 4. The power of the incident wave
is divided into the power of reflection and scattering from the
rough surface, and the larger the scattering, the lower the reflec-
tion. Also, since roughness depends on the frequency, the higher
the frequency, the larger the roughness. When the roughness is
larger, the scattering is more significant. Therefore, the higher
the frequency, the larger the roughness, the larger the scattering
power, and the lower the reflection power. Therefore, it is neces-
sary to clarify the relationship between reflected waves and scat-
tered waves in the sub-THz bands. Figure 5 shows the
measurement environment and setup. Scattering measurements
from 2.2 to 97.5 GHz were conducted in front of a building’s
metal wall using the channel sounder summarized in Table 2.
The Tx antenna is an omni-directional antenna with a beam
width of about 60° at 2.2, 26.4, 66.5, and 97.5 GHz, and the Rx
antennas are a Cassegrain antenna with a beam width of 2° at
66.5 and 97.5 GHz and 4° at 26.4 GHz, and a patch array antenna
with a beam width of 8° at 2.2 GHz. The incident angle θ
i
is set to
9° and the power delay profile (PDP) is measured at scattering
angle θ
s
from about −81° to 81° in 6° steps using the same
clock frequency at the Tx and Rx equipments with an accuracy
Fig. 3. Measurement setup and results. (a) Photo of anechoic chamber. (b) Top view of measurement setup. (c) Measurement of human blockage loss. (d)
Comparison between measurement and calculation results using M.2412 human blockage model.
International Journal of Microwave and Wireless Technologies 3
https://doi.org/10.1017/S1759078722000459 Published online by Cambridge University Press
of about ±1.0 × 10
−12
. Calibration was performed so that the
absolute value of the propagation delay distance could be
obtained. The power of the path with the propagation delay dis-
tance of 6 m was defined as the scattering power, and that
power was extracted from the PDP. Figure 6 shows the measured
scattering patterns from the rough building surface. Scattering
power is normalized by the peak value of the measured scattering
power. As shown in Fig. 6, the scattered peak is observed at the
specular reflection direction and the power tends to decrease as
the scattering angle changes from the specular reflection direc-
tion. In addition, the scattering beam width which is defined as
the width in the range 3 dB lower than the scattering peak
becomes wider as the frequency increases (2.2 GHz: 10°, 26.4
GHz: 24°, 66.5 GHz: 60°, 97.5 GHz: 60°). Generally, the peak of
angular profiles becomes wider as the beam width becomes
wider. In addition, the measurement scattering peak for the
higher frequency bands with a narrower beam width of the Rx
antenna becomes wider than that for the lower frequency bands
with a wider beam width. Therefore, the measurement results
included the influence of the difference of Rx antenna beam
width, but it is not the dominant factor. Next, we evaluated the
frequency dependency of scattering by comparing the calculation
results using the effective roughness (ER) model with the meas-
urement results. The ER model is widely used to predict the scat-
tering. Although a number of scattering models and parameters
have been reported [14], models and parameters need to be
appropriately used on the basis of empirical or measurement
results. Therefore, on the basis of measurement results, we calcu-
lated the scattering using a directive scattering (DS) model in
which the scattering lobe is steered toward the direction of the
specular reflection. The electric field E
s
is defined as
|Es|2=K·S
ri·rs
2
·dS ·cos
u
i
F
a
1+cos
C
r
2
a
(1)
F
a
=
p
/2
0
2
p
0
1+cos
C
r
2
a
sin
u
sd
u
sd
w
s,(2)
where F
α
and αare constant values defining the scattering pat-
tern and Ψ
r
is the angle between the reflection direction and the
scattering direction. As αbecomes smaller, the scattering beam
width becomes wider. Kis a constant value depending on the
amplitude of the impinging wave. θ
i
is the incident angle, θ
s
is
the scattering angle, r
i
is the incident vector, r
s
is the scattering
vector, and dS is the size of the surface elements. Sis a scattering
coefficient. In the simulation, the wall size was set to a 10 × 3 m
screen. In the ER model’s parameters, dS is set to 0.1 m. To
investigate the frequency dependency of scattering, the scatter-
ing coefficient Sand the coefficient related to the scattering
beam width αare regressed on the basis of the measured scatter-
ingpatternwithinthemainbeamwidth.InFig. 6,theblueline
indicates the calculation results using the DS model. As shown
in Figs 6(c) and 6(d), the discrepancy outside the main beam
due to the effect of multi-path from the surrounding objects.
However, the calculation results are similar to measurement
results within the main beam. The RMSE within the main
Fig. 4. Relationship between reflection and scattering. (a)
Measurement building wall. (b) Measurement setup.
Fig. 5. Measurement environment and setup. (a) 97.5 GHz, (b) 66.5 GHz, (c) 26.4 GHz, (d) 2.2GHz.
Table 2. Measurement parameters
Tx Frequency 2.2, 26.4, 66.5, 97.5 GHz
Bandwidth 50 MHz at 2.2 GHz, 100MHz at 26.4 GHz,
500 MHz at 66.5 GHz, 97.5 GHz
Modulation OFDM at 97.5 GHz, BPSK at 26.4 GHz
Antenna Omni-directional antenna
Antenna height 1.5 m
Rx Antenna Patch array antenna at 2.2 GHz, Cassegrain
antenna at 26.4, 66.5, 97.5 GHz
Antenna height 1.5 m
4 Minoru Inomata et al.
https://doi.org/10.1017/S1759078722000459 Published online by Cambridge University Press
beam is about 4.7, 2.3, 3.2, and 4.2 dB at 2.2, 26.4, 66.5, and 97.5
GHz, respectively. Therefore, the scattering from the rough sur-
face is the dominant path within the main beam. The regression
results are S=0.7 and α=40 at 2.2GHz, S=0.6 and α=40 at
26.4 GHz, S=0.7 and α=10 at 66.5GHz, and S=0.6 and α=
10 at 97.5 GHz. This indicates that the scattering beam widths
at 66.5 and 97.5 GHz are wider than 2.2 and 26.4 GHz, respect-
ively. In this environment, the wavelengths at 2.2 and 26.4 GHz
were longer than the irregularity of the building wall, which is
about 6 mm. In contrast, the wavelengths at 66.5 and 97.5
GHz were shorter. Therefore, the scattering is considered to
have been more diffused in the 66.5 and 97.5 GHz bands.
Since buildings in an urban environment have various irregular-
ities and rough surfaces, scattering due to them could be more
diffused than in this environment and affect the path-loss
characteristics.
UMi path-loss characteristics
The path-loss measurement environment around Tokyo Station,
Japan is shown in Fig. 7. The measurement parameters are sum-
marized in Table 3. The frequencies for measuring frequency
dependency were from 2.2 to 97.5 GHz. The Tx used these fre-
quencies to transmit CW signals, and the Rx measured the path
loss at those frequencies while moving along the measurement
routes NLOS1, NLOS2, NLOS3, and NLOS4. The M.2412 path-
loss models were compared with the results of regression using
the measurement data [4]. In the LOS environment of M.2412,
the path-loss coefficient nwas obtained by regressing the mea-
sured path loss to the single-frequency close-in (CI) free-space
reference distance model, as expressed by equation (3).
PLCI =10nlog10 (d3D)+FSPL(fc,1m) (3)
Fig. 6. Frequency dependency of scattering from rough building surface.
Fig. 7. Measurement setup. (a) Configuration of Tx antenna. (b) Measurement routes.
International Journal of Microwave and Wireless Technologies 5
https://doi.org/10.1017/S1759078722000459 Published online by Cambridge University Press
FSPL(fc,d3D)=32.4+20 log10 (fc)+20 log10 (d3D), (4)
where d
3D
is Tx-Rx distance and f
c
denotes the frequency. In con-
trast, in the NLOS environment of M.2412, parameters α,β, and γ
were obtained by regressing the measured path loss to the
alpha-beta-gamma (ABG) model, as expressed by equation (5).
PLABG =10
a
log10 (d3D)+
b
+10
g
log10 (fc).(5)
Path-loss characteristics are shown in Figs 8(a) and 8(b), and
the coefficient values of the M.2412 path-loss models and the
results of regression using the measured path loss are compared
in Table 4.FromFig. 8(a) in the LOS environment, the path
loss calculated using the M.2412 path-loss model shows a simi-
lar trend to the measured path loss, and the RMSE is 4.0 dB.
According to Table 4, the path-loss coefficient nis the same
value in the case of the M.2412 path-loss model. This result
confirms that in the LOS environment, the M.2412 path-loss
modelisvalidfrom2.2to97.5GHz.ItisclearfromTable 4
in NLOS environment that the results of regression using equa-
tion (5)ABG
meas
show better prediction accuracy than the path
loss calculated using the M.2412 path-loss model. A possible
Table 3. Parameters used in measurement path loss and power angular profiles
Parameters for path loss Frequency 2.2, 5.2, 26.4, 66.5, 97.5 GHz
Signal CW
Tx/Rx antenna Omni-directional antenna
Tx/Rx antenna height 3.3/2.6 m
Parameters for power angular profiles Frequency 26.4, 97.5 GHz
Modulation BPSK at 26.4 GHz,
OFDM at 97.5 GHz
Bandwidth 100 MHz at 26.4 GHz,
500 MHz at 97.5 GHz
Tx/Rx antenna Omni-directional antenna/Cassegrain antenna
Tx/Rx antenna height 3.3/1.5 m
Fig. 8. Measurement results. (a) Path-loss characteristics in LOS environment. (b) Path-loss characteristics in NLOS environment. (c) Measured power angular
profiles.
6 Minoru Inomata et al.
https://doi.org/10.1017/S1759078722000459 Published online by Cambridge University Press
factor for error is that coefficient γrelated to frequency depend-
ency is larger than that of the M.2412 path-loss model. These
results indicate that the frequency dependency of the measured
path loss is stronger than that of M.2412 path-loss model.
Therefore, we analyzed the measured power angular profiles
(PAPs), and we clarified the factors that affect path-loss fre-
quency dependency. PAPs were measured along NLOS2. The
measurement parameters are summarized in Table 3.
The PDPs at 26.4 and 97.5 GHz were measured while the
Cassegrain antenna was rotated 360 degrees in the azimuth
plane and 0–60 degrees in the elevation plane along NLOS2.
The Rx antenna was a Cassegrain antenna with a beam width
of 2° at 97.5 GHz and 4° at 26.4 GHz. In the post-processing, max-
imum received power in the PDP was extracted first, and maximum
received power elevation angles from 0 to 60 degree was extracted
next, and PAPs in the azimuth plane were obtained. The measured
PAPs at 26.4 and 97.5 GHz along NLOS2 are shown in Fig. 8(c).
Three dominant arrival paths were measured at 26.4 and 97.5
GHz from surrounding buildings and structures. The summation
result of path loss of those three dominant paths at 26.4 GHz is
about 109 dB and that at 97.5 GHz is about 129 dB and the differ-
ence is 20 dB. Since the difference expressed by the Friis FSPL equa-
tion for 26.4 and 97.5 GHz is 20log
10
(97.5/26.4 GHz) ≒11.4 dB, the
frequency dependency is about 8.6 dB larger than that given by the
Friis FSPL equation. In an UMi environment, it is assumed that the
higher the frequency, the scattering is more diffused, and the reflec-
tion power of the arrival paths at 97.5 GHz could be decreased com-
pared with that at 26.4 GHz.
Conclusion
In this paper, we showed the investigation results of frequency
dependency of human blockage, scattering effects from a rough
building surface, and path-loss characteristics in an UMi up to
150 GHz. Human blockage loss increases as the frequency
increases and a representative M.2412 model could evaluate the
frequency dependency of human blockage loss up to 150 GHz
bands. To evaluate scattering from a rough building surface, it
is confirmed that the scattering from a rough surface is considered
to be more diffused in the 66.5 and 97.5 GHz bands than in the
2.2 and 26.4 GHz bands. In the path-loss characteristics in UMi,
a comparison of measured path loss and M.2412 path-loss models
showed that the M.2412 path-loss model is valid in LOS environ-
ment. In contrast, in the NLOS environment, it was found that
path-loss frequency dependency is stronger than that given by
the M.2412 path-loss model. In addition, the measured PAPs
indicate that reflection waves from the surrounding buildings
and structures are the dominant paths in NLOS environment
and the path-loss frequency dependency increases as the power
of reflection waves decreases. By utilizing these characteristics
for the radio propagation simulation, we believed that the accur-
acy of the new 6G radio-network topology design for sub-THz
bands can be improved.
References
1. WRC2019. WRC 2019 agenda item details.
2. NTT DOCOMO, INC (2020). White paper, 5G evolution and 6G.
3. FCC News Release (2019) FCC takes steps to open spectrum horizons for
new services and technologies.
4. Rep. ITU-R M.2412-0 (2017) Guidelines for evaluation of radio interface
technologies for IMT-2020.
5. METIS (2015) Deliverable D1.4, METIS channel models.
6. MiWEBA (2014) Channel modeling and characterization, Deliverable
D5.1.
7. Aalto University, Nokia, AT＆T, NTT DOCOMO, BUPT, New York
University, CMCC, Qualcomm, Ericsson, Samsung, Huawei,
University of Bristol, INTEL, University of Southern California, KT
Corporation (2016) White paper on 5G channel model for bands up to
100 GHz, Global Communications Conference (GLOBECOM), 3rd
Workshop on Mobile Communications in Higher Frequency Bands,
Washington DC, U.S.A.
8. Inomata Minoru, Yamada Wataru, Kuno Nobuaki, Sasaki Motoharu,
Kitao Koshiro, Nakamura Mitsuki, Ishikawa Hironori and Oda
Yasuhiro (2021) Terahertz propagation characteristics for 6G mobile
communication systems, 2021 15th European Conference on Antennas
and Propagation (EuCAP), pp. 1–5.
9. Teyeb Oumer, Muhammad Ajmal, Mildh Gunnar, Dahlman Erik,
Barac Filip and Makki Behrooz (2019) Integrated access backhauled net-
works, IEEE VTC2019-Fall, pp. 1–5.
10. Kitayama Daisuke, Hama Yuto, Goto Kenta, Miyachi Kensuke, Motegi
Takeshi and Kagaya Osamu (2021) Transparent dynamic metasurface for
a visually unaffected reconfigurable intelligent surface: controlling trans-
mission/reflection and making a window into an RF lens. Optics Express
29(18), 29292–29307.
11. Rec. ITU-R P.676-12 (2019) Attenuation by atmospheric gases and
related effects.
12. Rec. ITU-R P.838-3 (2005) Specific attenuation model for rain for use in
prediction methods.
13. Rec. ITU-R P.833-9 (2016) Attenuation in vegetation.
14. Degli-Esposti Vittorio, Fuschini Franco, Vitucci M. Enrico and Falciasecca
Gabriele (2007) Measurement and modelling of scattering from buildings.
Transactions on Antennas and Propagation IEEE 55,143–152.
Minoru Inomata received his B.E. and M.E.
degrees in electrical engineering from Tokyo
University of Science and his Ph.D. degree
from Tokyo Institute of Technology, Japan, in
2009, 2011, and 2019, respectively. Since joining
NTT in 2011, he has been engaged in research
of radio propagation for 6G, 5G, and unlicensed
wireless communication systems.
Wataru Yamada received his B.E., M.E., and
Ph.D. degrees from Hokkaido University,
Japan, in 2000, 2002, and 2010, respectively.
Since joining NTT in 2002, he has been engaged
in research of propagation characteristics for
wideband access systems. He is currently a
Distinguished Researcher in NTT Access
Network Service Systems Laboratories.
Table 4. Comparison results
nConstant loss (dB) RMSE (dB)
LOS CI
meas
2.1 32.4 + 20log
10
f
GHz
4.0
M.2412 2.1 32.4 + 20log
10
f
GHz
4.0
αβ(dB) γRMSE (dB)
NLOS ABG
meas
3.36 19.0 2.65 7.2
M.2412 3.53 22.0 2.13 8.1
International Journal of Microwave and Wireless Technologies 7
https://doi.org/10.1017/S1759078722000459 Published online by Cambridge University Press
Nobuaki Kuno received his B.E. and M.E. degrees
from the University of Electro-Communications,
Tokyo, Japan in 2014 and 2016, respectively. He
joined NTT Access Network Service Systems
Laboratories in 2016. He has been engaged in
research of machine learning for radio propaga-
tion modeling.
Motoharu Sasaki received his B.E. degree in
engineering and his M.E. and Ph.D. degrees
from Kyushu University, Japan in 2007, 2009,
and 2015, respectively. In 2009, he joined NTT
Access Network Service Systems Laboratories,
Japan. He has been engaged in research on
propagation modeling.
Koshiro Kitao received his B.S., M.S., and Ph.D.
degrees from Tottori University, Tottori, Japan
in 1994, 1996, and 2009 respectively. He joined
the Wireless Systems Laboratories, NTT, Japan
in 1996. Since then, he has been engaged in
research of radio propagation for mobile com-
munications. He is now an Assistant Manager
of the 6G-IOWN Promotion Department,
NTT DOCOMO, INC., Japan.
Mitsuki Nakamura received his B.E. and M.E.
degrees from Keio University, Tokyo, Japan in
2012 and 2014, respectively. He joined NTT
Access Network Service Systems Laboratories
in 2014. He has been engaged in research of
radio propagation characteristics and radio
propagation for wireless access systems. He is
now a member of the 6G-IOWN Promotion
Department, NTT DOCOMO, INC.
Takahiro Tomie received his B.S., M.S., and
Ph.D. degrees from Tohoku University, Japan
in 2005, 2007, and 2010, respectively. He joined
the Research Laboratories, NTT DOCOMO,
INC., Japan in 2010. Since then, he has been
engaged in research of radio propagation for
mobile communications.
Yasuhiro Oda received his B.S. degree from
Nagoya University, Nagoya, Japan in 1990. He
joined NTT Laboratories, Japan in 1990. Since
then, he has been engaged in research and
development of cellular systems and radio
propagation. He is now a senior manager in
the 6G-IOWN Promotion Department, NTT
DOCOMO, INC.
8 Minoru Inomata et al.
https://doi.org/10.1017/S1759078722000459 Published online by Cambridge University Press
