69 research outputs found
Ultra-wideband Channel Modeling for Hurricanes
Maintaining communications during major hurricanes is critically important
for public safety operations by first responders. This requires accurate
knowledge of the propagation channel during hurricane conditions. In this work,
we have carried out ultra-wideband (UWB) channel measurements during hurricane
conditions ranging from Category-1 to Category-4, generated at the Wall of Wind
(WoW) facility of Florida International University (FIU). Time Domain P410
radios are used for channel measurements. From the empirical data analysis in
time domain, we developed a UWB statistical broadband channel model for
hurricanes. In particular, we characterize the effects of rain and wind speed
on large scale and small scale UWB propagation parameters.Comment: Paper accepted in Proc. of VTC Fall 2017, Antenna Systems,
Propagation, and RF Design Paper
UAV Air-to-Ground Channel Characterization for mmWave Systems
Communication at mmWave bands carries critical importance for 5G wireless
networks. In this paper, we study the characterization of mmWave air-to-ground
(AG) channels for unmanned aerial vehicle (UAV) communications. In particular,
we use ray tracing simulations using Remcom Wireless InSite software to study
the behavior of AG mmWave bands at two different frequencies: 28~GHz and
60~GHz. Received signal strength (RSS) and root mean square delay spread
(RMS-DS) of multipath components (MPCs) are analyzed for different UAV heights
considering four different environments: urban, suburban, rural, and over sea.
It is observed that the RSS mostly follows the two ray propagation model along
the UAV flight path for higher altitudes. This two ray propagation model is
affected by the presence of high rise scatterers in urban scenario. Moreover,
we present details of a universal serial radio peripheral (USRP) based channel
sounder that can be used for AG channel measurements for mmWave (60 GHz) UAV
communications.Comment: Comment: Accepted for 5G Millimeter-Wave Channel Measurement, Models,
and Systems workshop, VTC Fall 2017 Comment: Typo corrected in the x-axis of
Fig. 4 and Fig. 5 on page 3 and page
Impact of 3D UWB Antenna Radiation Pattern on Air-to-Ground Drone Connectivity
Three dimensional (3D) radiation pattern of an antenna mounted at a drone can
significantly influence the air-to-ground (A2G) link quality. Even when a drone
transmitter is very close to a ground receiver, if the antenna orientations are
not aligned properly, a significant degradation can be observed in the received
signal power at the receiver. To characterize such effects for a
doughnut-shaped antenna radiation pattern, using an ultra-wideband (UWB)
transmitter at the drone and a UWB receiver at the ground, we carry out A2G
channel measurements to capture the link quality at the ground receiver for
various link distances, drone heights, and antenna orientations. We develop a
simple analytical model to approximate the influence of 3D antenna patterns on
the received signal strength (RSS), which show reasonable agreement with
measurements despite the simplicity of the model and the complicated 3D
radiation from the UWB antennas. We also explore how the signal strength can be
improved when multiple antennas with different orientations are utilized at
transmitter/receiver.Comment: The paper was accepted and presented in VTC Fall 201
UWB Channel Sounding and Modeling for UAV Air-to-Ground Propagation Channels
Unmanned aerial vehicles (UAVs) are expected to be used extensively in the
near future in applications such as aerial surveillance, transportation, and
disaster assistance. The conditions under which UAVs operate are different from
those of conventional piloted aircrafts. This necessitates development of new
air-to-ground (AG) propagation channel models for UAVs. To our best knowledge,
there are limited studies in the literature on sounding and modeling of
ultrawideband (UWB) AG propagation channels. In this work, comprehensive UWB
measurements are conducted for various UAV communication scenarios using Time
Domain P410 UWB kits. Both time and frequency domain analysis of the measured
data are carried out. Based on the measured data, stochastic path loss and
multipath channel models are developed to characterize AG UWB propagation
channels.Comment: IEEE Globecom 2016 Conferenc
Channel Prediction for mmWave Ground-to-Air Propagation under Blockage
Ground-to-air (GA) communication using unmanned aerial vehicles (UAVs) has
gained popularity in recent years and is expected to be part of 5G networks and
beyond. However, the GA links are susceptible to frequent blockages at
millimeter wave (mmWave) frequencies. During a link blockage, the channel
information cannot be obtained reliably. In this work, we provide a novel
method of channel prediction during the GA link blockage at 28 GHz. In our
approach, the multipath components (MPCs) along the UAV flight trajectory are
arranged into independent path bins based on the minimum Euclidean distance
among the channel parameters of the MPCs. After the arrangement, the channel
parameters of the MPCs in individual path bins are forecasted during the
blockage. An autoregressive model is used for forecasting. The results obtained
from ray tracing simulations indicate a close match between the actual and the
predicted mmWave channel.Comment: Under review for IEEE Antenna and Wireless Propagation Letter
Coverage Enhancement for NLOS mmWave Links Using Passive Reflectors
The future 5G networks are expected to use millimeter wave (mmWave) frequency
bands to take advantage of large unused spectrum. However, due to the high path
loss at mmWave frequencies, coverage of mmWave signals can get severely
reduced, especially for non-line-of-sight (NLOS) scenarios as mmWave signals
are severely attenuated when going through obstructions. In this work, we study
the use of passive metallic reflectors of different shapes/sizes to improve 28
GHz mmWave signal coverage for both indoor and outdoor NLOS scenarios. We
quantify the gains that can be achieved in the link quality with metallic
reflectors using measurements, analytical expressions, and ray tracing
simulations. In particular, we provide an analytical model for the end-to-end
received power in an NLOS scenario using reflectors of different shapes and
sizes. For a given size of the flat metallic sheet reflector approaching to the
size of incident plane waves, we show that the reflected received power for the
NLOS link is same as line-of-sight (LOS)free space received power of the same
link distance. Extensive results are provided to study impact of environmental
features and reflector characteristics on NLOS link quality.Comment: The manuscript is submitted to IEEE Transactions on Antennas and
Propagation. arXiv admin note: text overlap with arXiv:1808.0622
Indoor Coverage Enhancement for mmWave Systems with Passive Reflectors: Measurements and Ray Tracing Simulations
The future 5G networks are expected to use millimeter wave (mmWave) frequency
bands, mainly due to the availability of large unused spectrum. However, due to
high path loss at mmWave frequencies, coverage of mmWave signals can get
severely reduced, especially for non-line-of-sight (NLOS) scenarios. In this
work, we study the use of passive metallic reflectors of different shapes/sizes
to improve mmWave signal coverage for indoor NLOS scenarios. Software defined
radio based mmWave transceiver platforms operating at 28 GHz are used for
indoor measurements. Subsequently, ray tracing (RT) simulations are carried out
in a similar environment using Remcom Wireless InSite software. The cumulative
distribution functions of the received signal strength for the RT simulations
in the area of interest are observed to be reasonably close with those obtained
from the measurements. Our measurements and RT simulations both show that there
is significant (on the order of 20 dB) power gain obtained with square metallic
reflectors, when compared to no reflector scenario for an indoor corridor. We
also observe that overall mmWave signal coverage can be improved utilizing
reflectors of different shapes and orientations.Comment: IEEE Wireless Communications Magazine (Currently in review) 201
Correction of Channel Sounding Clock Drift and Antenna Rotation Effects for mmWave Angular Profile Measurements
Millimeter-wave (mmWave) bands will be used for the fifth generation
communication systems to support high data rates. For the proper
characterization of the mmWave propagation channel, it is essential to measure
the power angular-delay profile (PADP) of the channel which includes
angle-of-departure (AoD) and angle-of-arrival (AoA) of the multipath components
(MPCs). In this paper, we first describe in detail our 28 GHz channel sounder
where directional horn antennas are placed on rotating gimbals. Then, for this
specific sounder class, we describe and address the following two problems in
extracting the MPCs from the measurements: 1) For the channel measurements at
large distances between the transmitter (TX) and the receiver (RX), it is not
possible to generate the triggering signal for the TX and the RX using a single
clock (SICL). This necessitates the use of separate clocks (SECLs) which
introduces a random timing drift between the clocks. 2) As the positions of the
antennas change during the scanning process, total distance traveled by the
same MPC differs at each measurement. These two errors together cause missing
some of the MPCs and detecting MPCs that do not exist in reality. We propose an
algorithm to correct the clock drift and the errors in the MPC delays due to
the rotation of the antennas. We compare the MPCs from the SICL measurement and
the corrected SECL measurements using a Hungarian algorithm based MPC matching
method. We show that the percentage of the matched MPCs increases from 28.36%
to 74.13% after the correction process.Comment: 15 pages. Submitted to IEEE Transactions on Antennas and Propagatio
UWB Air-to-Ground Propagation Channel Measurements and Modeling using UAVs
This paper presents an experimental study of the air-to-ground (AG)
propagation channel through ultrawideband(UWB) measurements in an open area
using unmanned-aerial-vehicles (UAVs). Measurements were performed using UWB
radios operating at a frequency range of 3.1 GHz - 4.8 GHz and UWB planar
elliptical dipole antennas having an omni-directional pattern in the azimuth
plane and typical donut shaped pattern in the elevation plane. Three scenarios
were considered for the channel measurements: (i)two receivers (RXs) at
different heights above the ground and placed close to each other in
line-of-sight (LOS) with the transmitter (TX) on the UAV and the UAV is
hovering; (ii) RXs are in obstructed line-of-sight (OLOS) with the UAV TX due
to foliage, and the UAV is hovering; and, (iii) UAV is moving in a circular
path. Different horizontal and vertical distances between the RXs and TX were
used in the measurements. In addition, two different antenna orientations were
used on the UAV antennas (vertical and horizontal) to analyze the effects of
antenna radiation patterns on the UWB AG propagation. From the empirical
results, it was observed that the received power depends mainly on the antenna
radiation pattern in the elevation plane when the antennas are oriented in the
same direction, as expected for these omni-azimuth antennas. Moreover, the
overall antenna gain at the TX and RX can be approximated using trigonometric
functions of the elevation angle.Comment: This paper is accepted for publication in Aerospace 2019 Conferenc
Ultra-Wideband Air-to-Ground Propagation Channel Characterization in an Open Area
This paper studies the air-to-ground (AG) ultra-wideband (UWB) propagation
channel through measurements between 3.1 GHz to 4.8 GHz using
unmanned-aerial-vehicles (UAVs). Different line-of-sight (LOS) and obstructed-
LOS scenarios and two antenna orientations were used in the experiments.
Channel statistics for different propagation scenarios were obtained, and the
Saleh-Valenzuela (SV) model was found to provide a good fit for the statistical
channel model. An analytical path loss model based on antenna gains in the
elevation plane is provided for unobstructed UAV hovering and moving (in a
circular path) propagation scenarios.Comment: Submitted to IEEE Transactions on Aerospace and Electronic Systems
(under review). arXiv admin note: text overlap with arXiv:1812.0660
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