Signal Processing - September 2017 - 11

PRESIDENT'S MESSAGE

NATIONAL UNIVERSITY OF SINGAPORE

UAVs. Yet due to the radical structural
differences between VTOL and fixed-
wing UAVs, the researchers faced a huge
challenge in combining the two function-
alities into a single aircraft.
Wang believes that he and Ke have
surmounted the fundamental obstacles
blocking the development of a reliable
hybrid UAV. Advanced modeling and
control algorithms are used to over-
come the uncertainties in transition
between configurations, allowing the
aircraft to achieve autonomous full-
envelope flight. "Compared to conven-
tional rotorcraft, our platform is much
more efficient with much longer flying
endurance," he explains. "It can transit
to a VTOL mode anytime for effective
surveillance and monitoring." Addition-
ally, in comparison to other currently
available hybrid UAV platforms, almost
all of which are a simple combination of
a fixed-wing aircraft and a rotorcraft,
Wang and Ke designed U-Lion to use
only a single propulsion system. "It is
thus more compact, optimal, and effi-
cient," Wang says.
An autonomous hybrid UAV can be
used for long-range and long-endurance
flying missions. Yet the aircraft's VTOL
capability allows it to be used almost
anywhere. "U-Lion has the potential to
be employed for forestation and preci-
sion agriculture, geographical mapping,
sea surveillance, powerline inspection,
disaster reactions, and many other appli-
cations," Wang says.
Signal processing makes the U-Lion
possible. "We need to process signals

FIGURE 3. The U-Lion is a hybrid UAV that can take off and land vertically and fly horizontally at
high speed.

from onboard sensors, including the
accelerometer, gyroscope, magnetom-
eter, barometer, airspeed sensor, and
global positioning system (GPS) sensor
to obtain and estimate the orientation,
velocity and position of the aircraft for its
whole flight envelope," Wang continues.
"Advanced signal processing techniques,
such as extended Kalman filter (EKF)
and sensor fusion, are of vital importance
to the autonomous control of the UAV."
Sampling data is retrieved from the
accelerometer and gyro sensors at a fre-
quency of 1 kHz. Magnetometer and
barometer data are collected at a sam-
pling rate of 200 Hz. "Some very care-
fully selected low-pass filters are applied
to process the obtained raw data to get rid
of high-frequency noises," Wang says. An
EKF is applied to estimate the orientation
of the U-Lion. A sensor fusion technique
is used to fuse orientation with GPS and
barometer data for the estimation of the
aircraft position and velocity.

The researchers opted to use an EKF
for its relatively lower computational
intensity. "As our platform is highly non-
linear in nature, the best suitable choice
for signal processing and sensor fusion
would perhaps be using a UKF instead,"
Wang says, adding, "It would certainly be
the direction of our future development
once we have integrated a more powerful
processing hardware unit onboard."
Wang says that he and his partner are
now researching and developing plat-
forms featuring an optimized mechani-
cal structures and energy supply systems,
as well as advanced signal processing
and flight control techniques. After that,
the next step will be creating platforms
capable of carrying larger payloads on
longer flights.

Author
John Edwards (jedwards@johnedwards
media.com) is a technolgy writer based
SP
in the Phoenix, Arizona, area.

(continued from page 5)

Consulting), Jill Nelson (George Ma-
son University), Meng Wang (Rensse-
laer Polytechnic Institute), and Ervin
Sejdic (University of Pittsburgh and
2016 recipient of the U.S. Presidential
Early Career Award).
These distinguished professionals are
committed to advancing society and mak-

ing a positive change through their work
and expertise in signal processing. The
IEEE SPS offers endless opportunities-
providing educational avenues, ca-
reer development, networking, and
volunteerism-to help the bright minds of
tomorrow begin their careers and make an
impact. Through our collaborative efforts,
IEEE SIGNAL PROCESSING MAGAZINE

September 2017

we can bring signal processing to the fore-
front as a viable and exciting career path
for young professionals. Let's get started
and find our future colleagues!

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Table of Contents for the Digital Edition of Signal Processing - September 2017