Measurements of Reflection and Penetration Loss in Indoor Environments in the 39-GHz Band

Full text

Measurements of Reflection and Penetration Loss
in Indoor Environments in the 39-GHz Band
Wenfei Yang∗† , Jie Huang ‡, Jiliang Zhang∗, Yuan Gao†, Sana Salous §, and Jie Zhang∗†
∗Department of Electronic and Electrical Engineering, The University of Sheffield, Sheffield, U.K.,
wyang20@sheffield.ac.uk, jiliang.zhang@sheffield.ac.uk, jie.zhang@sheffield.ac.uk
†Ranplan Wireless Network Design Ltd, Cambridge, U.K., yuan.gao@ranplanwireless.com
‡National Mobile Communications Research Laboratory, School of Information Science and Engineering,
Southeast University, Nanjing, China, j huang@seu.edu.cn
§Department of Engineering, Durham University, Durham, U.K., sana.salous@durham.ac.uk
Abstract—This paper presents measurements for reflection
and penetration loss of building materials in the 39-GHz band.
Measurements were conducted onsite of an interior wall in a
conference room. Assuming the measured interior wall as an
infinite homogeneous single-layer slab, the relative permittivity
was estimated based on the measurements using the least-squares
fitting. The measured material was found similar reflectivity
but less transmissivity than the plasterboard given in the ITU
standards. The measurement results provide insights into elec-
tromagnetic (EM) properties of building materials in the 39-GHz
band, which can be employed in future indoor radio propagation
predictions.
Index Terms—Millimeter-wave (mmWave), onsite measure-
ments, penetration, propagation, reflection, 39 GHz
I. INT RODUCTIO N
As indoor data traffic demands increase rapidly, indoor
wireless networks are expected to operate in the millimeter-
wave (mmWave) bands to boost capacity [1]. Consequently,
understanding of propagation characteristics is important for
mmWave channel modeling in complicated indoor environ-
ments [2].
Based on the measurements in the mmWave bands, statis-
tical channel models have been reported in the literature for
various indoor environments, such as the office environment
at 28, 60 and 73 GHz in [3], [4], [5], the library environment
at 28 GHz in [6], the hospital environment at 60 GHz in [7],
the factory, corridor, classroom, and PC lab environments at
54 and 70 GHz in [8], etc. The statistical channel models
applicable in the mmWave bands were summarized in [9],
[10]. There are two basic types of statistical channel models,
including the close-in (CI) free space reference distance path
loss model and the floating intercept (FI) path loss model.
The CI free space reference distance path loss model captures
the frequency- and distance-dependency of path loss by the
free space path loss (FSPL) of a reference CI distance and
the path loss exponent (PLE), respectively. It is adopted in
the ITU standards with the PLE ranging from 1.3-3.9 in
different indoor environments in the mmWave bands [11].
The FI path loss model is obtained from curve fitting with-
out a physically-based anchor, which addresses the distance-
dependency of path loss in a given frequency band. When
applied to a wide frequency range, it can be extended to
the alpha-beta-gamma (ABG) path loss model including a
frequency-dependent factor [12], [13]. The FI path loss model
is adopted in the WINNER II and 3GPP standards [14],
[15]. These models are assumed to be applicable to the same
type of scenarios, where shadow fading is represented by a
zero-mean Gaussian random variable. Thus, statistical models
show limited accuracy in radio propagation prediction due to
the lack of the site-specific information for each transmitter-
receiver (Tx-Rx) link.
Deterministic methods, such as ray tracing (RT) and
ray launching (RL), approximate propagation in a three-
dimensional (3-D) environment model following the geo-
metrical optic (GO) rules site-specifically. They are widely
employed in radio propagation characterizations in indoor
environments [16], [17]. The accuracy of deterministic channel
modeling lies in the accuracy of the 3-D environment model,
which is composed of the layout of the environment and the
electromagnetic (EM) properties of the building materials [18],
[19], [20], [21].
In the literature, the reflection and transmission coefficients
of common building materials have been measured in multiple
mmWave bands, including the 26.5- to 40-GHz bands in [22],
the 28-GHz band in [23], [24], the 38-GHz band in [24],
the 60-GHz band in [25], and the 73-GHz band in [26],
etc. Previous studies have shown that both the reflection
and transmission coefficients vary with the thickness of the
material, the incident angle, and the EM wave carrier fre-
quency. The relative permittivity of a building material can
be estimated based on these relationships and inserted in the
3-D environment model. The relative permittivity for common
building materials, such as concrete, wood, glass, plasterboard,
and brick, has been obtained in previous works, including [27]
at 41.5 GHz, [28] at 57.5 GHz, [29] at 59.5 GHz, [30], [31]
at 60 GHz, [32] at 62.4 GHz, etc. In [33] and [34], the
measurements of common building materials were reviewed at
2-62.4 GHz and 0.2-67 GHz, respectively. Based on measured
data in the literature, the relative permittivity of multiple
building materials was given in the ITU standards [35, Table
3] for the frequency range from 0.001-100 GHz.
Normally, the measurements of building materials are con-
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(a) Tx (b) Rx
Fig. 1. The mmWave channel sounder.
TABLE I
TX AN D RXANTE NNA S
Parameter Value
Tx antenna Omni
Tx antenna polarization Vertical
Tx antenna gain 6 dB
Tx antenna status Moving
Rx antenna Horn
Rx antenna HPBW ∼55◦
Rx antenna polarization Vertical
Rx antenna gain 13 dB
Rx antenna status Fixed
ducted using laboratory samples. Nevertheless, building ma-
terials vary greatly among different buildings. Moreover, the
EM properties can change with age and temperature [36], [37].
Consequently, the EM properties of practical building mate-
rials may differ from the measured laboratory samples sig-
nificantly. To improve the accuracy of the radio prediction by
deterministic methods, the EM properties of building materials
in the 3-D model can be calibrated by onsite measurements in
the targeted environment [37].
This paper presents onsite measurements of an interior
wall in a conference room at Durham University, U.K. The
reflection loss and penetration loss were measured in the 39-
GHz band. Assuming the interior wall as a single-layer slab,
the relative permittivity and the conductivity were obtained
based on the measured data.
The paper is organized as follows. Section II describes the
channel sounder and the measurement procedures. Section III
obtains the relative permittivity and the conductivity of the
material. Conclusions are presented in Section IV.
II. ME AS UR EM EN T SETUPS
A. Channel Sounder
A custom-designed frequency modulated continuous
wave (FMCW) channel sounder at Durham University
was used for channel measurements [38]. The sounder
has a programmable bandwidth and center frequency.
Using frequency multipliers to convert the intermediate
frequency (IF) to the mmWave band, bandwidths ranging
from 3-9 GHz can be covered in different frequency bands.
For the 39 GHz band a maximum bandwidth of 4.5 GHz
can be covered. The received signal is multiplied by a stored
replica to compress the bandwidth and down-convert the
received signal to baseband, which is then sampled at a rate
of 40 MHz. For the current measurements, the waveform
repetition frequency used was 1.22 kHz.
B. Measurement Procedure
The measurements were conducted at 37-41.5 GHz in a
conference room with dimensions of 10.5×10.6 m2. The
transmitter (Tx) and receiver (Rx) antennas used in the mea-
surements are shown in Fig. 1. Table I gives the configurations
of the Tx and Rx antennas. Fig. 2a shows the interior wall
under measurement with a thickness of 13 cm.
The Rx with the horn antenna was fixed in a corner of
the conference room, which is marked as the red dot in
Fig. 2b. The Tx with the omnidirectional antenna was moved
onto 10 measurement points, which were located inside and
outside of the conference room symmetrically. As shown
in Fig. 2b, the main lobe pointed to the direction A1 for
penetration measurements and the direction A2 for reflection
measurements. The measurement points were 1 m apart to the
wall under measurements and with a 1 m separation.
III. RES ULT S
A. Refection and Penetration Loss
The reflection/penetration loss was determined as the
difference between the measured power of the reflec-
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(a) The interior wall under measurements.
70°
1m
13cm
A1
TX Omni
RX Horn
1m
Reflection
3HQHWUDWLRQ
(b) Measurement plan.
Fig. 2. The interior wall under measurements and the measurement procedure.
tion/transmission component and the received power in the-
oretical free space with the same propagation distance. The
received power in theoretical free space was obtained by
PR(d) = PT+GT+GR−20 log10 4πd
λ[dB] ,(1)
where PTis the transmission power, d[m] is the propagation
distance, λ[m] is the wavelength, GTand GRare the antenna
gains of the Tx and Rx antennas, respectively. We have λ=
7.64 mm for the carrier frequency f= 39.25 GHz. For the
reflection measurements, dis the sum of the length of the
incident and reflected paths. For the penetration measurements,
dis the Tx-Rx separation. The reflection loss and penetration
loss measured on each point are illustrated by the markers in
Fig. 3a and Fig. 3b, respectively.
B. Relative Permittivity and Conductivity
The interior wall was assumed as an infinite homogeneous
single-layer slab [29], [30], [31]. Then the reflection and trans-
mission coefficients for a building material with a thickness
of ζ[m] are
R=1−e−j2q
1−Γ2e−j2qΓ,(2)
and
T=1−Γ2e−jq
1−Γ2e−j2q,(3)
respectively, where
q=2πζ
λqεr−sin2θ, (4)
εris the relative permittivity, θrepresents the incident angle,
and Γis the electric field reflection coefficient depending on
the polarization of the incident wave relative to the slab [35],
[39]. When the electric field vector is perpendicular to the
plane of incidence, i.e., for the transverse electric (TE) polar-
ization, Γis given by
ΓTE =cos θ−pεr−sin2θ
cos θ+pεr−sin2θ
.(5)
TABLE II
EM PROP ERTI ES
Material Relative permittivity εrConductivity σ
Measured wall 2.64 −0.13j0.28
ITU plasterboard 2.94 −0.07j0.16
ITU concrete 5.31 −0.29j0.64
When the electric field vector is parallel to the plane of
incidence, i.e., for the transverse magnetic (TM) polarization,
Γis denoted by
ΓTM =εrcos θ−pεr−sin2θ
εrcos θ+pεr−sin2θ
.(6)
For the measurements presented in this paper, the incident
wave was TE polarized. The complex relative permittivity εr
can be denoted by
εr=ε0
r−jε00
r=ε0
r−jσ
ε0ω,(7)
where ε0
rand ε00
rare the real and imaginary parts, respec-
tively. For the imaginary part, ω= 2πf [Hz] denoting the
angular frequency, σ[S/m] is the conductivity, and ε0=
8.854 ×10−12 F/m denoting the dielectric permittivity of free
space [40].
The least-squares fitting was used to find the values of ε0
r
and σby fitting |R|and |T|to the measured data simultane-
ously [31]. The results are given in II, where the root-mean-
square error (RMSE) of the measured and theoretical values is
0.06. For comparison, the theoretical reflection and penetration
loss of the concrete and the plasterboard were computed with
the EM properties given in the ITU standards [35, Table 3].
The theoretical reflection and penetration loss as a function
of the incident angle are illustrated in Fig. 3, where the
results of the measured material and the materials given in
the ITU standards are represented by the solid line and the
dash lines, respectively. As shown in the figures, the measured
material shows similar reflectivity to the plasterboard, while
its transmissivity is higher than the concrete and lower than
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such as IEEE Xplore under the license granted by the "Agreement Granting EurAAP Rights Related to
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0 20 40 60 80
Incident angle
-14
-12
-10
-8
-6
-4
-2
0
Measured wall
ITU plasterboard
ITU concrete
Measurements
(a) Reflection loss
0 20 40 60 80
Incident angle
-90
-80
-70
-60
-50
-40
-30
-20
-10
Measured wall
ITU plasterboard
ITU concrete
Measurements
(b) Penetration loss
Fig. 3. The reflection loss and penetration loss vary with the incident angle.
the plasterboard. It might be due to a multi-layer material
structure, such as the plasterboard is used on the surfaces and
the heat insulator concrete is embedded inside the wall. Then
the measured material could lead to higher penetration loss
than the single-layer plasterboard with the EM properties given
in the ITU standards.
IV. CON CL USION
In this paper, we have presented measurements of reflection
and penetration loss caused by an interior wall in the 39-GHz
band in a typical conference room. Assuming that the material
under measurements as an infinite homogeneous single-layer
slab, we obtained the relative permittivity of the material
by the least-squares fitting. The measured material shows
similar reflectivity but less transmissivity compared with the
plasterboard given in the ITU standards. The measurement
results provide practical values of the EM properties of the
building material, which can be used in future indoor wireless
network design and evaluation.
ACK NOWLEDGM EN T
The authors would like to acknowledge the support of
EPSRC grant PATRICIAN EP/I00923X/1 under which the
sounder was developed and the subsequent funding under
Impact Acceleration Account (IAA) for the extension of the
frequency range to the Ka-band. The authors would like to
thank Dr Y. Shao, Mr Y. Zhou, Mr S. Yang, Mr C. Chen, and
Mr Y. Yao for their contributions to the measurements.
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