Wideband Directional Measurements in the 32 GHz Frequency Band in a LoS Corridor Situation

Abstract

This work presents a Power Angular Delay Profile (PADP) channel sounder with preliminary measurements at 32 GHz in a corridor. A low cost device has been designed to perform the rotation of the directional antenna with a fully automatic measurement procedure. Initial measurements have been performed at 32 GHz within a bandwidth of 10 GHz, using a vector network analyzer (VNA). Measurements allow the study of the multipath behavior in this indoor environment; a large number of sources of scattering objects were detected. This knowledge is of interest because the signals of 5G and 6G systems will operate in millimeter long wave bands, such as the one used in this work. The different multipath contributions were observed in the angular measurements, especially those produced by the walls at 40 and-40 degrees and those produced by the metal tubes at 25 and-65 degrees. In addition, above 80 degrees and below-80 degrees, the RMS Delay Spread increases up to 60 ns.

Full text

Wideband Directional Measurements in the 32 GHz
Frequency Band in a LoS Corridor Situation
Ricardo Robles Enciso(1), Leandro Juan-Ll´
acer(1), Jos´
e-Mar´
ıa Molina-Garc´
ıa-Pardo(1)
ricardo.robles@edu.upct.es, leandro.juan@upct.es, josemaria.molina@upct.es
(1)Dep. Tecnolog´
ıas de la Informaci´
on y las Comunicaciones, Universidad Polit´
ecnica de Cartagena, Cartagena, Murcia, Espa˜
na
Abstract—This work presents a Power Angular Delay Profile
(PADP) channel sounder with preliminary measurements at 32
GHz in a corridor. A low cost device has been designed to
perform the rotation of the directional antenna with a fully
automatic measurement procedure. Initial measurements have
been performed at 32 GHz within a bandwidth of 10 GHz,
using a vector network analyzer (VNA). Measurements allow
the study of the multipath behavior in this indoor environment;
a large number of sources of scattering objects were detected.
This knowledge is of interest because the signals of 5G and 6G
systems will operate in millimeter long wave bands, such as the
one used in this work. The different multipath contributions
were observed in the angular measurements, especially those
produced by the walls at 40 and -40 degrees and those produced
by the metal tubes at 25 and -65 degrees. In addition, above 80
degrees and below -80 degrees, the RMS Delay Spread increases
up to 60 ns.
I. INTRODUCTION
Recently, there has been great interest in exploring the use
of millimeter-wave frequency (mm Wave) bands due to the
need to increase the capacity of wireless communications for
the fifth generation (5G) [1] [2] and sixth generation (6G) [3]
[4] of cellular systems. Therefore, it has become necessary
to know the behavior of these waves in different propagation
environments, giving rise to numerous works [5] [6] where it
is essential to know the multipath effect in urban environments
[7] and, more importantly, in indoor environments [8]. To this
end, devices based on directive antennas, mechanically rotated
by motorized platforms have been predominantly used [9].
The need to improve channel capacity already at the ra-
dio interface leads to the use of higher frequencies in the
millimeter band, which allows the use of large bandwidths.
Future mobile communication systems using this frequency
band will use adaptive antennas and multiple antenna systems,
which will involve the use of directional antennas with narrow
beamwidths, in contrast to current systems.
Recent studies have shown the need to consider the effect
of the antenna radiation pattern on radio channel character-
ization, in order to propose omnidirectional and directional
propagation models because parameters such as loss expo-
nent, delay spread or angular spread, depend on the antenna
radiation pattern [10].
In this work, the Power Angular Delay Profile (PADP) has
been measured in the 32 GHz band in a situation of line-
of-sight (LoS) between a transmitter (TX) and a receiver
(RX) in a corridor. For this purpose, several reflecting ele-
ments (metal tubes) have been included in the environment
and, by using a directive antenna that is rotated after each
measurement, measurements at different azimuth angles have
been recorded, for which a customized device was designed
to accomplish this task. Section II details the environment
to be measured, the equipment used, the procedure followed
and the configuration and mathematical expressions applied.
Section III describes the device created to achieve the angular
measurements. The results, together with the observations,
are presented in Section IV and, finally, the conclusions are
presented in Section V.
II. MEASUREMENT SETUP
A. Measurement Scenario
The scenario where the measurement campaign was carried
out was the main corridor of the underground level of the
Escuela T´
ecnica Superior de Ingenier´
ıa de Telecomunicaci´
on
(ETSIT) of the Universidad Polit´
ecnica de Cartagena (UPCT).
The corridor has a length of 50 meters and a width of 2.85
meters and is mainly diaphanous (Fig. 2). The antennas were
placed equidistant from the walls, in a direct vision situation
(LoS), at a height of 1 m and at a distance approximately 3.8
m between them (Fig. 1). In addition, several metallic tubes
were placed in order to increase the reflections and to verify
that the measurements were made correctly. The main points
of possible reflectance were labelled A to E.
Fig. 1. Environment of the Testing
Fig. 2. Floor plan of underground level
B. Measurement Equipment
The scheme followed, in order to perform the angular
measurements, is shown in Fig. 3. It consisted of a Rhode

& Schwarz ZVK VNA (10MHz-40GHz) vector network an-
alyzer, which was used to measure S-parameters, specifically
S21. Two electro-optical converters (EMCORE, Optiva OTS-
2, 50MHz-40 GHz) were used to send the electrical signal
from the VNA through an optical fiber to the transmitting
antenna. For the antennas, an omnidirectional (STEATITE
QOM-SL-0.8-40-K-SG-L) was used for transmit (TX) and
a directive (STEATITE QSH-SL-26-40-K-20) was used for
receive (RX). The parameters of the antennas are detailed in
Table I. A device was also used to rotate the directive antenna
in azimuth, specifically created for this purpose, which will
be discussed in Section III.
TABLE I
ANT ENNA PA RAM ETE RS
Type Omnidirectional Directional
Antenna model QOM-SL-0.8-40-K-SG-L QSH-SL-26-40-K-20
Frequency 0.8 to 40 GHz 26.5 to 40 GHz
3db Beamwidth
(azimuth)
NA 14.5º - 22.5º
3db Beamwidth
(elevation)
160º - 18º 22.5º - 14.5º
Fig. 3. Measurement Setup
Fig. 4. Directional-scan-sounding (DSS) system
C. Measurement Procedure and Settings
Measurements were made by centering the antennas in the
corridor and placing them at a distance of 3.8 m from each
other. Both the transmitting and receiving antennas remained
fixed in position. After each measurement, the receiving
antenna was rotated in 5 degree steps in azimuth (Fig. 4)
starting at -180 degrees and ending at 180 degrees.
The channel transfer function, H(f) = S21(f), was mea-
sured at each angular position. Before taking the measure-
ments, the VNA was calibrated to eliminate the delay and
losses introduced by the intermediate elements.
Table II lists the configuration parameters of the vector
network analyzer and the resolutions achieved with them.
D. The Measured PADP
The transformation shown in Eq. (1) was applied to the
frequency transfer function obtained from the VNA, in order
to obtain the Power Delay Profile (PDP) [10]. In this way,
TABLE II
VEC TOR N ETW ORK A NALYZ ER PARA ME TER S AND T HEI R RES OL UTI ON
Center frequency 32 GHz
SPAN 10 GHz
N2001
Frequency resolution 4.9975 MHz
Temporary resolution 1·10−10 s
Spatial resolution 3cm
the different multipath contributions of the medium were ob-
tained. By using a device which rotates the antenna in azimuth
in the horizontal plane after each measurement, it is possible
to measure the PDP for different angles. This results in a
matrix containing the PDP of the different measured angles,
called a Power Angular-Delay Profile (PADP). According
to [10], the RMS Delay Spread which represents the time
dispersion of the radio channel can be obtained by means of
Eq. (2) and (3). This parameter is a good indicator of the
frequency selectivity of the channel.
P DP (τ) = 
I DF T −1(H(f))

2(1)
where I DF T −1is the inverse discrete Fourier transform
and H(f)the channel transfer function obtained from the
VNA.
τ=PN
n=1 τnP DP (τn)
PN
n=1 P DP (τn)(2)
τrms =v
u
u
tPN
n=1 (τn−τ)2P DP (τn)
PN
n=1 P DP (τn)(3)
Where τis the mean delay spread,τrms is the RMS delay
spread and τnis the excess delay spread of path n.
III. AUTOMATIC MEASUREMENT SYSTEM
To achieve the objective of this work, it was necessary to
design a device capable of automatically rotating the directive
antenna to the different angular positions specified by the
control computer, and ensure that these were accurate and
repeatable.
Fig. 5. PADP Assistant Mark I, 3D design
A. Measurement System
The system was designed based on the premise that the
directive antenna detailed in Table I is required to rotate.
To achieve this goal, a Nema 17 stepper motor [11] and
its respective TB6600 controller [12] were used, to which

a planetary gear with a 5:1 ratio was coupled, to increase
the motor torque and angular resolution. A stepper motor
was used for its virtues of torque, angular accuracy, and
ability to rotate continuously. The Nema 17 motor used had a
resolution of 200 steps per revolution, or 1.8 degrees per step.
The gearbox achieved an angular resolution of 0.36 degrees
per step. The structural parts were designed to hold these
components, printed using 3D printing technology.
Figure 5 shows the 3D design of the device, which was
created taking into account certain design features: there must
be sufficient clearance between the antenna and the motor to
prevent the antenna coaxial cable from getting caught when
rotating. Another feature was that the phase center of the
antenna must be centered with the axis of rotation of the
motor. It was also been taken into account that the design
should be mounted on a tripod.
The device had an ATmega2560 [13] microcontroller, which
translates the angular position sent from the control computer
to the digital signals needed by the stepper motor controller
to make it work. The device is controlled from the control
computer through a TTL serial communication; the orders
are sent by the MATLAB software. In this way, the data from
the VNA were obtained from MATLAB and, once processed,
the order to rotate the antenna was sent. This control scheme
is shown in Fig. 6. Figure 7 shows a photo of the real device.
Fig. 6. Diagram of elements involved
Fig. 7. PADP Assistant Mark I, photo
IV. MEASUREMENT RES ULTS AND DISCUSSION
Figure 8 shows the PDP for the 0 degree position, the
angular reference in the RX is the straight line that joins the
TX with the RX. To facilitate its observation, a noise floor
filter was applied between the maximum measured and the
noise floor(with a margin of 40 dB). In this way, a function
like that shown in Figure 9, is obtained, and an additional
zoom is applied, to focus on the peaks of interest. The highest
power peak represents the direct path, while the rest of the
peaks represent the path of the contributions reflected in the
surrounding elements.
Fig. 8. PDP in the 32 GHz band at 0 Degrees
Fig. 9. PDP filtered in the 32 GHz band at 0 Degrees, zoom
Figure 10 shows the PADP in the form of a heat map for
easy visualization where the Y-axis represents the angular po-
sition at which the PDP was measured. The X-axis represents
the distance of the delay (in meters), and is calculated as
the time delay multiplied by the propagation velocity. The
colored Z-axis represents the received power, in dBm. In
addition, the maximum value of each PDP has been marked
with white dots. The hotter points represent the path of the
direct contribution and the path of the reflected contributions
on the walls. These, and the rest of the points, are analyzed
in Table III; the colors and points cited in the observations
correspond to those seen in image 1.
Fig. 10. PADP in the 32 GHz band, zoom and values
Fig. 11. RMS Delay Spread per angle
Figure 11 shows the RMS Delay Spread as a function of the
angle of the receiving antenna with a threshold level of 40 dB.
It can be seen to increase as the antenna moves away from the
LoS pointing, angle 0, and encounters reflective elements such

TABLE III
CONTRIBUTIONS OBTAINED THROUGH PADP
Angle (º) Distance (m) Observed Reflection
0 3.78 Direct beam, red dashed line -
25 4.2 Indirect contribution, dotted
blue line, due to reflection with
the metal tubes to the right of
the transmitter.
A
-40 4.71 Indirect contribution, dotted
purple line, due to reflection
with the left wall.
C
40 4.77 Indirect contribution, dotted
purple line, due to reflection
with the right wall.
D
-65 6.09 Indirect contribution, dotted
green line, due to reflection
with the metal tubes to the left
of the transmitter.
B
-170 6.12 Indirect contribution, dashed
yellow line, due to reflection
with the metal tubes behind the
receiver.
E
-70 6.81 Inconclusive, presumably it
may be the reflection with the
wall behind the RX as it is re-
peated identically for positive
and negative angles.
-
as metal pipes and walls.It also has a symmetrical shape with
respect to 0 degrees. It can be observed that, for the 0 degree
position there is an RMS Delay Spread of 7.9 ns, while, for
positions above 80 degrees, or below -80 degrees, maximums
of over 60 ns are reached. The result is very similar to the
one discussed in [14] for the 28 GHz and 38 GHz band
in a LoS situation, giving delay values of less than 10 ns.
Similar results were reported in [15], where the RMS delay
spreads can change significantly due to different objects in the
environment. The peaks at positions -25 and 20 degrees are
due to the fact that the signal that follows the direct path and
the one that follows the path originated by the reflection on
the wall (points Cand D) arrive at that position with almost
the same power level.
V. CONCLUSION AND FUTURE WORK
In this work, we have created a high performance, low
cost device designed to rotate a directive antenna in the
azimuth axis, and angular measurements have been performed
in order to know the multipath behavior of a corridor for
the millimeter wave band. Based on the results, it can be
concluded that it is of great interest to perform angular
measurements with directional antennas to know the multipath
behavior of the different propagation environments that can
occur in millimeter wave communications; it can be achieved
with a DIY device.
Finally, since the device is expected to be used in field
measurements, and with antennas other than those used in this
work, it can be redesigned to increase mechanical resistance
and allow any antenna to be screwed into it, either directly or
by means of a fastening piece that centers the phase center
of the antenna with the axis of rotation. This design is shown
in Fig. 12. There is also a plan to include a coaxial rotary
joint to prevent the antenna cable from tangling, in addition to
allowing the feature of being able to make continuous sweeps.
ACKNOWLEDGMENTS
This work was carried out within in the frame-
work of the project PID2019-107885GB-C33, funded by
MCIN/AEI/10.13039/501100011033.
Fig. 12. PADP Assistant Mark II
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