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Millimeter-Wave Indoor Directional Propagation Measurements

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Abstract

The millimeter wave (mmWave) band around 60 GHz has been identified as one of the ISM bands for wireless indoor communication systems. In this paper, we present wideband channel measurements conducted at 60 GHz in a seminar room and office environment using state of art Durham University's channel sounder. The statistical channel parameters of power angle profile, root mean square delay spread, and angular spread are presented for different orientations which include line of sight, obstructed line of sight and non-line of sight with the smallest delay spreads and angular spreads values being observed for the line of sight case.
Millimeter-Wave Indoor Directional Propagation
Measurements
Amar Al-jzari, and Sana Salous
1 Department of Engineering, Durham University, Durham, UK,
sana.salous@durham.ac.uk*
Abstract— The millimeter wave (mmWave) band around
60 GHz has been identified as one of the ISM bands for
wireless indoor communication systems. In this paper, we
present wideband channel measurements conducted at 60 GHz
in a seminar room and office environment using state of art
Durham University's channel sounder. The statistical channel
parameters of power angle profile, root mean square delay
spread, and angular spread are presented for different
orientations which include line of sight, obstructed line of sight
and non-line of sight with the smallest delay spreads and
angular spreads values being observed for the line of sight
case.
Index Terms— mmWave, angular spread, rms delay
spread, channel sounder.
I. INTRODUCTION
The demand for higher data traffic in wireless
communication networks and the congestion of the spectrum
below 6 GHz has encouraged the wireless industry, research
community, and regulators to consider alternative bands. The
millimeter wave (mmWave) frequency band has been
identified for next 5G wireless networks due to the
availability of large contiguous bandwidths that can be
exploited to achieve a high data rate with 5-7 GHz being
available around the 60 GHz band. However, these
frequency bands suffer from many challenges due to the very
small wavelengths resulting in different channel propagation
characteristics compared with traditional WLAN systems
operating at lower frequency bands [1-2]. Thus, various
indoor propagation measurements and models are needed in
these frequency bands for future networks system design [3].
In [1]-[10], channel measurements were conducted at
different frequency bands, such as 15, 28, 45, 60, and 73
GHz bands. The measured scenarios include office rooms,
corridors, hallways, museum, shopping mall, and conference
room to estimate path loss, delay spread, small-scale spatial
and temporal statistics, and wall and floor penetration loss. In
this paper, wideband indoor channel measurements in the 60
GHz ISM band are reported in a seminar room and an office
environment set up with desks and computers at Durham
University. Wideband channel parameters such as rms delay
spread are presented for different angular orientation
between the transmitter and the receiver. Angular spread as
well as path loss are also estimated from the measurements.
The rest of the paper is structured as follows. Section II
describes the measurement scenarios and the procedure. The
measurement results and analysis are provided in Section III.
Finally, conclusions are drawn in Section IV.
II. MEASUREMENTS ENVIRONMENT
The present measurements were conducted using the
custom-designed multi-band chirp (FMCW) channel sounder
[8] in a seminar room and an office environment, shown in
Fig. 1. The measurements were performed with a 6 GHz
bandwidth in the frequency range of (59.6 - 65.6 GHz) with
a waveform repetition frequency of 1.22 kHz. An
omnidirectional antenna was used at the transmitter, Tx,
while at the receiver, Rx, a horn antenna with 20 dBi gain
and 18° beamwidth was used to estimate different relative
channel parameters. The measurements were conducted for
both line of sight, LoS, and non-line of sight, NLoS,
scenarios with the Tx location fixed at one end of the room
while the Rx was moved onto predefined locations within the
scenario as shown in Fig. 2. The Tx antenna height was set at
2.3-2.6 𝑚 which is close to a typical height of an access
point while the Rx antenna was set at 1.5 𝑚 for a typical
user. To investigate the wideband channel in the angular
domain and to synthesize an omnidirectional received signal,
a CCTV positioner is used to rotate the directional antennas
in steps of 15 degrees to cover the full 360o in azimuth. At
each angular rotation, the data were recorded for one second
with 40 MHz sampling rate ADC.
(a) (b)
Fig. 1. Indoor measurement environments (a) seminar room, (b) office.
(a) (b)
Fig. 2. Layout of indoor measurement environments (a) Seminar room,
(b) Office.
III. MEASUREMENTS RESULTS AND ANALYSIS
The data were processed with 2 GHz bandwidth to obtain
the power delay profile, PDP, which was then used to
estimate the rms delay spread, the angular spread, the
received power, and the path loss.
A. Power Delay Profile
Fig. 3 displays the measured angular PDPs of one LoS
location and one NLoS location in the seminar room where
the LoS location exhibited a strong component at ~ 10 ns
with few multipath components, while in the NLoS case,
more MPCs can be observed resulting in larger delay spread.
The impact of beam alignment can be further seen in Fig. 4
where a strong component is detected when the receiver
antenna was pointing towards the transmitter and when it
was facing away from it.
(a)
(b)
Fig. 3. Measured PDPs vs. AoA in the seminar room (a) LoS, (b) NLoS.
Fig. 4. Directional PDPs in one location at different azimuth angle.
B. Delay and Angular Spread Characteristics
The rms delay spread is the second central moment of the
measured PDP. For the current measurements, it is estimated
with a 20 dB threshold from the peak power in each PDP.
Fig. 5 displays the cumulative distribution function (CDF) of
the rms delay spread for the office environment where the
estimated delay spread was classified based on the angular
direction between the Tx and Rx antennas, as LoS when the
receive antenna was pointing towards the transmitter, OLoS
when the receive antenna was physically in the LoS of the
transmitter but the antenna beam is misaligned with the
transmitter antenna and NLoS when the receiver and
transmitter were obstructed by a partition as shown in Fig. 2.
The figure shows the increase in the rms delay spread of the
OLoS and NLoS scenarios due to the misalignment of the
beam and to the presence of the partition. To characterize the
delay spread, the CDFs were fitted with a Gaussian Normal
distribution 𝑁 (𝜇, 𝜎) and the estimated 𝜎 parameter of the
distribution as well as the 50% and 90% values of the CDF
are given in Table I. The angular spread is used to
characterize the dispersion properties of the power angle
profile (PAP) where the PAP is the received power at each
azimuth angle. Fig. 6 shows an example of the computed
PAP in one location for the LoS and NLoS scenarios in the
seminar room environment. The angular spread was
estimated as outlined in [8-9], the 50% and 90% CDF values
of the angular spread as well as the standard deviation are
given in Table II. The table indicates that in both measured
environments, the LoS locations exhibit a smaller angular
spread value compared with NLoS locations due to less
reflectors and scatterers.
Fig. 5. CDF of the rms delay spread for the office environment.
Fig. 6. Power Angle profile for the seminar room environment.
TABEL I. Delay spread values in (ns) and the distribution parameters for
both measured environments.
Delay Spread Statistic
CDF = 50 %; CDF = 90%; 
F
itting Parameter
s
Scenario
L
S
NLoS
L
o
S
(BS)
OL
S (NBS)
Seminar
Room
2.60; 2.94; 0.86 18.5; 27.48; 8.51 16.48, 28.67; 8.66
Office 1.88; 2.66; 0.59 11.76; 21.74; 7.43 18.79; 26.69; 8.81
TABEL II. Angular spread values in degrees for both measured
environments.
Angular Spread Statistic
CDF = 50 %; CDF = 90%; 
Scenario
L
S
NL
S
Seminar
Room
137.09; 149.54; 12.35 161.03; 174.74; 10.54
Office. 38.08; 74.08; 27.79 122.24; 138.83; 43.22
C. Directional and Synthesized Omnidirectional Path Loss
Path loss (PL) is an essential channel parameter in
wireless communication. The path loss model parameters
were investigated using the floating Intercept (FI) model.
The FI model parameters including the distance coefficient
(α) and the PL intercept coefficient (PLo) were estimated
from the measurements. A detailed calculation of the FI
model can be found in [8-9]. In the present work, the path
loss was estimated for different possible antenna
alignments.
TABEL III. Estimated PL model parameters.
Type of
Env. Scenario PL estimation
method
FI model
(PLo, , σ)
Seminar
Room
LoS
Strongest beam 61.7, 3.4, 3.1
Synthesized back beam 79.2, 1.9, 2.2
Synthesized omni 61.9, 2.6, 2.6
NLoS Strongest beam 99.1, 0.4, 4.3
Synthesized omni 87.8, 0.7, 2.9
Office
LoS
Strongest beam 64.4, 3.3, 1.9
Synthesized back beam 75.1, 2.6, 1.3
Synthesi
z
ed omni
61.1, 2.8, 1.1
NLoS
Strongest
beam
97.3, 0.4, 3
.
3
Synthesi
z
ed omni
86.2, 1.3, 2.1
Fig. 7 (a)-(c) presents measured path loss data for the LoS
peak (strongest component), the OLoS (synthesized back
beam) and the NLoS (strongest component) cases, as well as
the corresponding fits.
(a) LoS Peak (Strongest Component) Scenario.
(b) OLoS Angles (Synthesized back beam) Scenario.
(c) NLoS (Strongest Component) Scenario.
Fig. 7. Path loss for different receive angles in seminar room environment.
To compare the directional with a synthesized
omnidirectional receive antenna, the path loss for the LoS
and NLoS scenario was synthesized from the directional
measurements as shown in Fig. 8. Table III provides a
summary of the path loss modeling results for the
directional and synthesized omnidirectional path loss in both
measured environments. It can be seen that the synthesized
omnidirectional beam results are close to the strongest
component results. This is due to the fact that the received
power was dominated by the LoS path. The table indicates
that the path loss intercept is higher for the synthesized back
beam compared with the strongest component in the LoS
case scenario. The results also show that the synthesized
omnidirectional beam in the LoS scenario has lower path
loss intercept than in the NLoS scenario.
Fig. 8. Synthesized Omnidirectional PL in seminar room environment.
IV. CONCLUSION
In this paper, mmWave directional channel
measurements performed in the 60 GHz band in a seminar
room and an office environment using the multiband chirp-
based channel sounder at Durham University were analyzed
to study the impact of beam misalignment on path loss, rms
delay spread and angular spread. The angular spread values
emphasize the fact that indoor environments are multipath
rich and therefore have high angular spread values. The
estimated rms delay spread in the LoS scenario has smaller
values than in the OLoS and NLoS scenarios as the LoS
component has a significantly higher amplitude than the
reflected components. Significant path loss variations were
estimated for different antenna alignments which varied
between 10 to more than 30 dB. The strongest beam PL, the
synthesized back beam PL and the synthesized
omnidirectional PL parameters were estimated. The results
indicate that the path loss of the back beam is higher
compared with the synthesized omnidirectional and the
strongest component path loss. Moreover, higher synthesized
omnidirectional path loss intercept was observed in NLoS
case compared with LoS case due to the obstruction between
the Tx and the Rx antennas. Further measurements using
omni-directional antennas at both ends of the link are
planned to generate a significant number of data points for
accurate estimation of the path loss coefficients.
ACKNOWLEDGMENT
The authors would like to acknowledge the support of
WaveComBE project, under Horizon 2020 research and
innovation program, grant agreement No. 766231. The 60
GHz sounder was developed under the EPSRC grant
PATRICIAN EP/I00923X/1.
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