# Wideband Penetration Loss through Building Materials and Partitions at 6.75
GHz in FR1(C) and 16.95 GHz in the FR3 Upper Mid-band spectrum

Dipankar Shakya†1, Mingjun Ying†2, Theodore S. Rappaport†3,
Hitesh Poddar*, Peijie Ma†, Yanbo Wang†, and Idris Al-Wazani† This research is
supported by the New York University (NYU) WIRELESS Industrial Affiliates
Program. *Sharp Laboratories of America (SLA), Vancouver, Washington, USA †NYU
WIRELESS, Tandon School of Engineering, New York University, USA
{1dshakya, 2yingmingjun<EMAIL_ADDRESS>
###### Abstract

The 4–8 GHz FR1(C) and 7–24 GHz upper mid-band FR3 spectrum are promising new
6G spectrum allocations being considered by the International
Telecommunications Union (ITU) and major governments around the world. There
is an urgent need to understand the propagation behavior and radio coverage,
outage, and material penetration for the global mobile wireless industry in
both indoor and outdoor environments in these emerging frequency bands. This
work presents measurements and models that describe the penetration loss in
co-polarized and cross-polarized antenna configurations, exhibited by common
materials found inside buildings and on building perimeters, including
concrete, low-emissivity glass, wood, doors, drywall, and whiteboard at 6.75
GHz and 16.95 GHz. Measurement results show consistent lower penetration loss
at 6.75 GHz compared to 16.95 GHz for all ten materials measured for co and
cross-polarized antennas at incidence. For instance, the low-emissivity glass
wall presents 33.7 dB loss at 6.75 GHz, while presenting 42.3 dB loss at 16.95
GHz. Penetration loss at these frequencies is contrasted with measurements at
sub-6 GHz, mmWave and sub-THz frequencies along with 3GPP material penetration
loss models. The results provide critical knowledge for future 5G and 6G
cellular system deployments as well as refinements for the 3GPP material
penetration models.

###### Index Terms:

3GPP, 6G, FR3, FR1(C), penetration loss, XPD, upper mid-band, upper 6 GHz,
partition loss, materials

##  I Introduction

The desire to achieve the wide bandwidths and massive data throughput of the
mmWave and sub-THz frequencies, while maintaining improved coverage with
relatively low gain antennas at sub-6 GHz frequencies has invited strong
interest in the FR1(C) and FR3 upper mid-band spectrum. Often heralded as the
“golden band” due to the promising balance between expansive coverage using
low gain antennas and smaller partition losses, and becoming closer to
offering high capacity that occurs at mmWave and sub-THz bands due to wide
bandwidths. The 4–8 GHz FR1(C) and 7–24 GHz FR3 upper mid-band spectrum bands
are anticipated to play a crucial role in the deployment of next-generation 5G
and 6G cellular systems[1, 2]. Agencies such as ITU and the National
Telecommunications and Information Administration (NTIA) are rigorously
analyzing these bands to ensure effective utilization alongside current
incumbents such as satellite communications, earth exploration, and radio
astronomy [3]. Endeavors by the 3rd Generation Partnership Project (3GPP) and
the Federal Communication Commission (FCC) towards exploration of the FR3
frequencies underscore their critical role in meeting the escalating data
requirements and setting the stage for future cellular standards [4]. However,
there is limited knowledge regarding the radio propagation characteristics at
these frequencies for cellular deployments. Particularly, penetration through
various building materials and partitions, remain under-explored.

Extensive research efforts have endeavored to characterize the penetration
loss of various materials in mmWave [5, 6] and sub-6 GHz bands [7, 8].
However, investigation into the penetration loss of various materials found in
indoor and outdoor scenarios for the upper mid-bands have been limited.
Muqaibel et al. [9] studied the propagation of ultrawideband (UWB) signals
through common building materials such as drywall, plywood, wooden door,
glass, brick wall, concrete block wall, styrofoam, office cloth partition and
reinforced concrete wall at frequencies between 2-10 GHz. Authors in [10]
measured penetration loss of wood panels 0.6, 1, and 1.4 cm thick using a
narrowband swept network analyzer from 7–15 GHz and reported 1.9, 1.7, and 3.2
dB loss at 7 GHz and 2, 4.1, and 5 dB loss at 15.5 GHz. Authors in [9]
measured the dielectric properties of materials (permittivity and loss
tangent) to characterize attenuation and distortion of UWB signals when
propagating through the stated materials. Landron et al.[11] measured
reflection coefficients of limestone, glass, and brick wall surfaces at 1.9
GHz and 4 GHz for vertical and horizontal antenna polarizations, and found
Freshnel reflection coefficient models with rough surface correction factors
are adequate to model reflection. Rodriguez et al. [12] conducted measurements
to study the outdoor-to-indoor (O2I) attenuation for buildings in Aalborg,
Denmark using a signal generator to sweep a single tone from 800 MHz to 18
GHz, and found modern buildings presented increased penetration loss of 20-25
dB compared to old constructions. Zhang et al. [13] characterized the
penetration loss from 0.9–18 GHz for indoor partitions such as reinforced
concrete and plasterboard walls. Measured results in [13] showed increased
penetration loss with frequency for reinforced concrete wall, however, a
monotonic increase in penetration loss with frequency was not observed for
plasterboard walls.

In this paper, results of penetration loss measurements for several indoor
materials at 6.75 and 16.95 GHz for co and cross-polarized antenna
configurations are presented, using a 1 GHz wideband spread spectrum channel
sounder (Section II) [14, 15]. The wideband channel sounder avoids frequency
selective readings at specific frequencies, which can result in anomalous
penetration measurements due to material frequency selectivity or multipath
with similar propagation delays in the environment [16]. Measurements are
carried out in the 370 Jay Street building, NYU Tandon School of Engineering,
Brooklyn, NY. Calibration procedures and resulting linear operation range of
the channel sounder is detailed in Section III. The antenna cross-polarization
discrimination (XPD) for the horn antennas used at 6.75 and 16.95 GHz are
characterized in Section IV. Section V highlights the measurement procedure
for obtaining the penetration losses. Observations and resulting penetration
loss values for co and cross polarized antenna configurations are discussed in
Section VI. Measurements are compared with 3GPP standard models in Section VII
before the conclusion.

##  II Wideband Sliding Correlation Channel Sounder for FR1(C) and FR3
Measurements

A time-domain channel sounder based on sliding correlation of pseudorandom
noise (PN) sequences was employed for accurate mid-band wideband channel
propagation and penetration measurements [15, 14]. As presented in Fig. 1, the
500 Mcps baseband PN sequence phase modulates a 6.75 GHz carrier to result in
a 1 GHz RF bandwidth (BW) signal that is connected to one of two front-end
modules, custom developed by Mini-circuits. The distinctive co-located
configuration allows a simple transition between the 6.75 GHz and 16.95 GHz
frequency bands through the change of a single cable.

Figure 1: The FR1(C) and FR3 wideband channel sounder system with co-located
RF front-end modules developed by Mini-Circuits. Top module operates at 6.75
GHz and the bottom module at 16.95 GHz.

The TX front-end module operating at 6.75 GHz amplifies, filters, and
transmits the broadband signal through a 15 dBi gain and a 30-degree half-
power beamwidth (HPBW) horn antenna, achieving an effective isotropic radiated
power (EIRP) of 31 dBm to stay within the licensed emission power level of 35
dBm. The 16.95 GHz TX front-end module employs a heterodyne approach to
upconvert the 6.75 GHz intermediate frequency (IF) signal to a RF signal at
16.95 GHz with 1 GHz bandwidth[1]. The wide bandwidth of 1 GHz allows the
channel sounder to overcome frequency selectivity that narrowband and swept
narrowband systems are prone to and resolve close multipath in temporal domain
to ensure accurate penetration measurements. The polarization of the horn
antennas are changeable between vertical (V) and horizontal (H) polarization
using waveguide twists at both bands. A total of four antenna configurations
V-V or H-H co-polarized, and V-H or H-V cross-polarized are used for
measurement of each material under test (MUT).

##  III Calibration of the Channel Sounder System for Penetration Loss
Measurements

Calibration ensures the accuracy of the channel impulse response measurements
and path loss results, and are conducted at the beginning and end of each
measurement day to ensure power levels obtained during the penetration tests
are consistent throughout the day. The calibration determines the system gain
and linear range of received powers through identification of the correct
attenuator settings at the TX and RX, and power levels of the LO signals.
Particularly, the attenuator settings determined from the calibration are
adjusted during penetration measurements to ensure the received power falls in
the linear range of operation, especially when measuring the cross-polarized
antenna configurations.

The correct settings are ascertained through a free-space path loss (FSPL)
measurement at a fixed transmitter-receiver (T-R) separation distance,
exceeding 5 $\times$ far-field distance ($D_{f}$) of the horn antenna (here, 4
m T-R separation is used), and antenna height (here, 1.5 m height is used),
avoiding ground or ceiling reflected multipath, adhering to the criteria
described in [17]. The transmit power before the TX horn antenna is captured
with a power-meter prior to initiating the calibration process. During
calibration, power under the first PDP peak yields the total received power in
the LOS multipath for different configurations of the TX and RX attenuator and
LO input powers [17, 18]. Varying the TX and RX attenuators allows for a total
50 dB linear operation range during the penetration measurements over a 150 dB
power range. Calibration at the end of day typically shows differences of
under 0.2 dB for FSPL.

TABLE I: System Parameters for the Upper-Mid Band Channel Sounder at NYU WIRELESS Carrier Frequency |  6.75 GHz |  16.95 GHz
---|---|---
Free Space PL at 1m reference distance |  49 dB |  57 dB
Baseband signal | 11th order PN sequence (2047 chips)
TX PN Code Chip Rate | 500 Mcps
TX PN Code Chip Width | 2.0 ns
RX PN Code Chip Rate | 499.9375 Mcps
Slide factor | 8000
Digitizer Sampling rate at RX Oscilloscope | 2.5 Msps
RF BW (Null-to-null) | 1 GHz
Max Transmit Power (fed into the horn antenna) |  29 dBm |  26.5 dBm
TX/RX Antenna Type | Pyramidal Horn Antenna
TX/RX Antenna Dim. |  3.75”$\times$2.65” |  3.08”$\times$2.33”
TX/RX Antenna Far-field |  41 cm |  69 cm
TX/RX Antenna Gain |  15 dBi |  20 dBi
TX/RX Ant. HPBW (Az/El) |  30∘ / 30∘ |  15∘ / 15∘
XPD |  35 dB |  38 dB
Max EIRP |  44 dBm |  46.5 dBm
Max EIRP used | 31 dBm
Max Measurable Path Loss (at 5 dB SNR) |  155.6 dB |  159.2 dB
TX Polarization | Vertical/Horizontal
RX Polarization | Vertical/Horizontal
TX/RX Waveguide Size |  WR137 |  WR62

##  IV Antenna Cross-Polarization Discrimination

During propagation, interaction with the environment can cause the transmitted
signal energy to be captured in cross-polarized antenna orientation.
Particularly, different materials can exhibit varying penetration loss for co
and cross-polarized antenna configurations[17]. Thus, observing the cross-
polarization discrimination (XPD) facilitates the characterization of energy
captured in the orthogonal orientation. In this study, we used all four
possible polarizations during the penetration loss measurements of each
material. To accurately determine material pentration loss, the free space
(XPD) must be measured. Fig. 2 shows the antenna XPD measured for the channel
sounder system at (a) 6.75 GHz and (b) 16.95 GHz in V-V and V-H polarizations,
using the calibration method in [17]. Waveguide twists at WR-137 and WR-62
facilitate the change in polarization.

(a)

(b)

Figure 2: Measurement of the antenna XPD at (a) 6.75 GHz with 15 dBi, 30∘ HPBW
WR137 horn antennas, and (b) 16.95 GHz with 20 dBi, 15∘ HPBW WR62 horn
antennas, using method in [17].

To obtain empirical XPD for the horn antennas used in this penetration loss
campaign, measurements of FSPL are made for the different antenna polarization
configurations starting in the far field from T-R separation distances of 3 m
with increments of 0.5 m up to 6 m. An open lab area ensured the ground and
ceiling multipath were avoided and only LOS path was captured[16]. The
difference in path loss (PL) between the co-polarized (V-V or H-H) and cross-
polarized (V-H or H-V) configurations at a T-R separation distance, $d$,
yields the XPD, as shown in (1). A mean XPD of 35.75 dB is observed at 6.75
GHz with $\sigma_{XPD}=1.12$ dB. Likewise, mean XPD at 16.95 GHz is obtained
as 38.41 dB with $\sigma_{XPD}=1.01$ dB.

$\begin{split}XPD(d)[dB]=PL_{V-V}(d)[dB]-PL_{V-H}(d)[dB],\\\ \end{split}$ (1)
$PL[dB]=P_{t}[dBm]-P_{r}[dBm]+G_{TX}[dBi]+G_{RX}[dBi]$

$P_{t}$ in (1) denotes the true transmit power recorded with the power meter
during calibration. $P_{r}$ represents the power in the first arriving
multipath in the PDP. $G_{TX}$ and $G_{RX}$ are the antenna gains.

##  V Measurement procedure for Penetration Loss

The penetration loss, $L$, for a co-polarized or cross-polarized antenna
configuration, is determined by observing the difference between the received
powers, $P_{r}$, at identical T-R separation distances, first in free-space
and then with the material under test (MUT) in the line-of-sight path of the
TX and RX, with a path that is perpendicular to the span of the MUT (e.g. on
boresight, or on normal incidence), (2). $P_{r}$ in (2) is obtained as the
power received in the first arriving multipath in the captured PDP ignoring
the other multipath [18, 7]. The 1 GHz bandwidth channel sounder allows
temporal resolution of multipath up to 1 ns apart (e.g 1 foot or 0.3 m) to
ensure that reflected multipath are not within the first arriving LOS
multipath component in a PDP and thus avoiding frequency selectivity of
narrowband systems [16].

$\begin{split}L[dB]=P_{r}^{FS}[dB]-P_{r}^{MUT}[dB],\\\ \end{split}$ (2)

Measurements are made for three T-R separation distances of 2.0, 2.5, and 3.0
m (all measured distances are in the far field). Following the measurement of
$P_{r}^{FS}$, the MUT (the MUT dimensions exceed $15\times\lambda$ in all
directions for each MUT) is placed halfway between the TX and RX to ensure the
entire wavefront illuminates the MUT. When measuring in-situ partitions, such
as a drywall partition in an indoor corridor or wooden doors in rooms that
prevented the TX and RX from being spaced equally, the TX is placed at a fixed
separation of 1 m, while the RX is moved further at distances ranging from 1
to 2 m from the MUT to achieve the overall T-R separation distance of 2 to 3
m. Though a separation much greater than 5$\times D_{f}$ is recommended [17]
for the TX/RX and MUT, the larger antenna dimension and the HPBW at 6.75 and
16.95 GHz makes achieving such separation impractical considering the MUT
dimensions, ceiling and antenna height, and available space.

After positioning the TX and RX on either side of the MUT with a fixed
separation, the TX and RX antenna orientations in both co and cross
polarization are adjusted to establish a boresight configuration with the
strongest first-arriving (LOS) multipath component. To mitigate potential RX
antenna misalignment effects due to large HPBWs, the RX antenna is
subsequently moved in azimuth and elevation by 1° increments around its
boresight, resulting in a total of five PDPs recorded at each RX pointing
direction. The penetration loss, $L$, at each distance is obtained by
subtracting the linear average of these five recorded powers expressed in dB,
$P_{r}^{MUT}$ from $P_{r}^{FS}$, as shown in (2). Once $L$ at each distance is
calculated, the average penetration loss for the MUT is recorded as the mean
of $L$ in linear scale at the different distances. Thereafter, $P_{r}^{MUT}$
and $P_{r}^{FS}$ are obtained for V-H, H-V, and H-H antenna polarization.
Finally, $L_{VV}$ and $L_{HH}$ are linearly averaged to obtain $L$ for co-
polarized antennas, and $L_{VH}$ and $L_{HV}$ for cross-polarized antennas.

Ten commonly found indoor materials are measured. Panel sheets of the all the
tested materials are employed to ensure a uniform material upon which the
incident wavefront impinges. Images of the materials and partitions being
measured are shown in Fig. 3 and specifications are listed below:

  * •

Drywall panel: Penetration through a USG Sheetrock brand gypsum drywall panel
is measured. Dimensions of the drywall sheet are 4 ft$\times$8 ft with 3 cm
thickness.

  * •

Birch Wood panel: A thick Birch plywood panel with 13 plies pressed together
is measured. The plywood panel has dimensions of 4 ft$\times$8 ft with 2 cm
thickness.

  * •

Whiteboard: A rollable glass whiteboard with front and back writing faces is
used. The whiteboard has a tempered glass finish over the laminated backing.
Dimensions of the whiteboard are 72”$\times$40” with 3 cm thickness.

  * •

Low-emissivity (low-e) or IRR glass window: The window used for the
measurement is a 59”$\times$59” sliding panel with low-e double pane glass.
Argon gas is filled in the cavity between the two panes and the window has a
U-value rating of 0.29 (insulating capability of the glass, lower values
indicate greater insulation[19]). Total thickness of the two panes is 2 cm.
The outer frame of the window is white vinyl plastic.

Figure 3: Various MUT measured; Large panels of different materials, such as
drywall were measured in a lab setup. Partitions, such as IRR glass walls
required TX and RX to be set up on both sides.

Other common building partitions and walls such as plasterboard wall,
cinderblock wall, and doors found in-situ within the building were also
measured. An O2I penetration was measured with the massive glass curtain wall
on the perimeter of the 370 Jay Street building. The details of these indoor
and O2I partitions are as follows:

  * •

Wooden Door: Large capacity lecture halls at the NYU Tandon School of
Engineering have a large wooden double door. The door is made of a fire safety
rated solid wood core with 4.5 cm thickness. The door has door handles on one
side and a push bar on the other side. The TX and RX heights were raised for
the incident wave to impinge on a uniform door surface.

  * •

Steel Door: Hallway entrances and some labs in the 370 Jay Street building at
NYU Tandon use large doors with a skin of steel material. The steel door also
has a metal push bar at the middle of the door. The TX and RX heights were
raised to ensure penetration loss of a uniform steel door (without the metal
push bar) was captured.

  * •

Clear glass wall: The measured partition is a single panel transparent glass
wall without any coating having 0.5 cm thickness used on the periphery of the
Wireless RF Propagation Lab at 370 Jay Street.

  * •

Low-e or IRR glass wall: The 370 Jay Street building has a glass curtain wall
on the ground floor. Double-pane tinted glass with $1/2$” thick panels and
Argon gas filling between the glass panes is used for the curtain wall with
individual panels supported by a metal frame. The glass achieves a U-value of
0.26. The total thickness of the glass panels is 3 cm.

  * •

Cinderblock wall: Few classroom partitions on the NYU campus are cinderblock
walls with a coat of paint. Some foam soundboards are placed with irregular
spacing on the concrete walls for sound absorption in the classroom. The
cinderblock wall measures 22 cm thick.

  * •

Plasterboard wall: The room partitions in the NYU WIRELESS Research Center are
composed of sheets of drywall placed on a metal frame. Some plasterboard
partitions are also known to have metal studs between the sheets. A stud
detector helped ensure no studs were present in the region of the measurement.

##  VI Penetration Measurement Results

The penetration loss measurement results are presented in Table II. For both
co-polarized and cross-polarized antennas, the measured penetration loss
exhibits minimal variation across the employed T-R separation distances. Co-
pol penetration loss is computed by linearly averaging $L$ evaluated for V-V
and H-H, while cross-pol penetration loss is obtained as the linear average of
$L$ for V-H and H-V, as detailed in Section V. The penetration loss at 6.75
GHz is consistently lower compared to 16.75 GHz for both co and cross-
polarized configurations. The largest loss measured is for the steel door
exhibiting over 40 dB and 50 dB penetration loss at the 6.75 GHz and 16.95 GHz
frequencies, respectively. The low-e glass curtain wall, used on the building
outer surface, also exhibits strong attenuation of over 30 dB at both
measurement frequencies for co and cross polarizations. The low-e window also
shows significant attenuation, interestingly, loss for the cross-polarized
configuration is much lower compared to the co-polarized measurements (29.7 dB
Co Pol; 15.3 dB Cross Pol @ 6.75 GHz, and 32.68 dB Co Pol; 19.52 dB Cross Pol
@ 16.95 GHz). This indicates a strong dependence on polarization for low-e
window glass attenuation.

TABLE II: Measured Penetration Loss of materials for Co-pol and Cross-pol for FR1(C) and FR3 MUT |  Width (cm) | Pol |  Frequency |
---|---|---|---|---
6.75 GHz |  16.95 GHz |  $\Delta_{\mu}$ (dB)
$\mu$ (dB) |  $\sigma$ (dB) |  $\mu$ (dB) |  $\sigma$ (dB) |  16.95-6.75 GHz
Cinderblock Wall |  22 | Co |  13.4 |  1.6 |  15.0 |  1.1 |  1.6
Cross |  10.7 |  1.6 |  11.5 |  0.7 |  0.9
Low-e tinted glass wall |  3 | Co |  33.7 |  0.9 |  42.3 |  0.2 |  8.6
Cross |  38.4 |  1.2 |  46.5 |  1.0 |  8.2
Low-e glass window |  2 | Co |  29.7 |  1.4 |  32.7 |  2.6 |  3.0
Cross |  15.4 |  0.7 |  18.5 |  2.3 |  3.1
Clear Glass |  1 | Co |  3.6 |  0.3 |  3.7 |  0.4 |  0.1
Cross |  4.2 |  0.4 |  4.4 |  0.6 |  0.2
Birch Wood panel |  2 | Co |  2.4 |  0.7 |  6.1 |  0.4 |  3.7
Cross |  2.0 |  0.9 |  5.5 |  0.9 |  3.5
Wooden door |  4.5 | Co |  5.8 |  1.1 |  6.1 |  1.3 |  0.3
Cross |  7.1 |  2.2 |  7.7 |  0.8 |  0.6
Steel door |  4.7 | Co |  43.2 |  0.5 |  58.5 |  1.4 |  15.3
Cross |  41.8 |  0.8 |  56.4 |  1.7 |  14.6
Plasterboard wall |  13.7 | Co |  2.1 |  1.0 |  4.5 |  0.4 |  2.4
Cross |  3.0 |  0.6 |  6.1 |  1.2 |  3.2
Drywall panel |  3 | Co |  0.6 |  0.1 |  1.2 |  0.5 |  0.6
Cross |  1.5 |  0.2 |  2.3 |  1.2 |  0.8
White Board |  3 | Co |  3.1 |  0.3 |  6.9 |  0.5 |  3.8
Cross |  4.1 |  0.7 |  7.5 |  1.3 |  3.4

Fig. 4 (a) depicts the penetration loss of ten materials investigated in this
paper at specific FR1C and FR3 frequencies, along with their penetration loss
values in sub-6 GHz, mmWave, and sub-THz bands, as reported in [20, 21, 22,
23, 24, 25, 26, 27, 28, 13, 29]. To facilitate direct comparison of the
material penetration loss across the entire frequency range of 0.5-150 GHz,
the dB/cm penetration loss values for each material is multiplied by their
respective thicknesses. The comparisons reveal an increasing penetration loss
with increasing frequency for all ten of the materials measured. For example,
the yellow rings for drywall in Fig. 4(a) shows a clear increase with
frequency when measurements from this paper are augmented with values reported
in [22, 20, 24]. On the other hand, Fig. 4 (b) only shows the penetration loss
from the measurements conducted in this paper at 6.75 and 16.95 GHz.

(a)

(b)

Figure 4: Penetration loss of various materials at different frequencies
compared with the 3GPP TR-38.901 material penetration models. (a) Range 0-150
GHz. (b) Range 0-30 GHz.

##  VII Comparison with 3GPP Material Penetration Loss Model

Penetration loss data in the 7–24 GHz range is sparse in the literature.
Recent 3GPP discussions emphasize a critical gap in channel measurement and
O2I loss data for the 7–24 GHz band. Over 80% of the channel measurement data
submitted in 3GPP falls outside the 7–24 GHz band, concentrated below 6 GHz or
exceeding 28 GHz [30]. Thus, validation of the 3GPP TR 38.901 model for
material penetration loss within the 7–24 GHz range is needed.

The current 3GPP model for material penetration loss (Table 7.4.3-1, 3GPP TR
38.901 Release 18 [31]) provides model paramters for concrete walls, IRR
glass, standard multipane glass (clear glass), and wood that vary linearly
with frequency. The Root Mean Square Error (RMSE) calculated between the
measured and the 3GPP predicted penetration losses for the materials at 6.75
GHz and 16.95 GHz, demonstrates a close adherence to the 3GPP model for
conventional materials like clear glass (RMSE = 1.2 dB) and wood (RMSE = 2.4
dB). This indicates the 3GPP model validity for wood and standard multi-pane
glass. Conversely, concrete walls and IRR glass walls exhibit significantly
higher RMSE values (42.9 dB and 11.8 dB, respectively) at both frequencies.
The 3GPP model consistently under-predicts the loss for IRR glass. However,
for concrete walls, the observed discrepancy may be attributed to measurements
in this paper characterizing penetration through an indoor cinderblock wall,
which differs substantially from the thicker building exterior walls
considered by the 3GPP model. Results suggest revisions may be required for
3GPP material penetration models for IRR glass and concrete [32].

## Conclusion

The empirical propagation penetration loss exhibited by common materials found
indoors and on building perimeters was reported in the paper. The measurements
were made with a wideband sliding correlation-based channel sounder operating
at 6.75 GHz and 16.95 GHz. Penetration loss was consistently observed to be
lower at 6.75 GHz compared to 16.75 GHz for co and cross-polarized antennas
encompassing V-V, V-H, H-V, and H-H configurations. Low-e glass windows
exhibited polarization-dependent attenuation of the signal. Upon comparing
with penetration loss measurements at mmWave and sub-THz frequencies, the
materials exhibited increasing loss at higher frequencies. Comparisons with
the 3GPP models for material penetration show close adherence for wood and
clear glass, while IRR glass and concrete showed RMSE errors above 10 dB,
suggesting revisions may be required to current models. Reported material
characteristics provide valuable information for future 5G and 6G wireless
systems in the FR1(C) and FR3 upper mid-band spectrum.

## Acknowledgment

Authors thank Profs. Sundeep Rangan and Marco Mezzavilla for support with
experimental licensing in the FR3 bands.

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