Graduate Exam Abstract
November 14, 2012, 9:30am-11:30am
ECE Conference Room C101B Engineering
Signal Design for Active Sensing
Abstract: Active sensing is an emerging sensing technology
with numerous applications in science and
engineering. Advances in active sensors bring in
increasingly agile transmitter and receivers. This
enable arbitrary waveform illumination of the
scene using increased degrees of freedoms, and
processing of the scene return to form an image,
estimate parameters, or detect targets. In this
thesis we focus on two featured applications of
active sensing: radar and optical imaging.
The signal design for radar imaging typically lies
in two categories: ambiguity function theory and
interference cancellation. The ambiguity function
theory applies for the scenario of point targets
in white noise. The principle for ambiguity
function theory is to design good radar ambiguity
functions with sharp mainlobe and small sidelobe
in range and Doppler. The interference
cancellation addresses radar imaging when targets
are interfered by structured perturbations which
come from clutters for instance.
Modern radars are increasingly being equipped with
arbitrary waveform generators that enable the
transmission of different waveforms across
multiple degrees of freedoms: time, frequency,
polarization, and aperture. This gives us the
opportunity to revisit and extend the classical
signal design for radar imaging.
For ambiguity function theory, we develop a
general framework for designing Doppler resilient
illuminations through waveform coordination across
time, frequency, and aperture. The issue of
sensitivity to Doppler exists for all traditional
phase coded radar waveforms with impulse-like
auto-correlation functions. Off the zero Doppler
axis, the magnitude of range sidelobe of the
ambiguity function of a phase code waveform can be
significant, meaning that a weak target that is
located in range near a strong reflector with a
different velocity/Doppler frequency may be masked
by the range sidelobe of centered at the delay-
Doppler position of the stronger reflector. In
contrast, we show that by properly coordinating
the waveforms phase coded by complementary
sequences, we can annihilate the range sidelobe of
ambiguity function inside a modest Doppler
interval, and hence bring out the weak targets
from the range sidelobe of nearby strong
For interference cancellation we study a joint
design of transmitter and receiver for multiple-
in-multiple-out (MIMO) phased-array radar, using a
joint optimization of transmit waveform, receive
filter bank, and receive beamformer based on the
minimum variance distortionless response (MVDR)
principle. This MIMO radar system is capable to
perform radar imaging when targets and clutters in
scene are extended in range, Doppler, and azimuth
angle. The subspace for the target response vector
is derived in a closed form. The design objective
is to select the transmit waveform, receive filter
bank, and receive beamformer to minimize the
beamformer output power with a fixed signal power.
The advances in optical imaging also promise
sophisticated illumination design and receiver
design. The spatial light modulators (SLMs) and
optical masks enable structured illumination or
excitation on the object, and the optical
detectors, such as charge-coupled device (CCD)
detectors, enable a two dimensional sampling of
light intensity. Vast combinations of structure
illumination and receive processing provide us
opportunities to investigate the optical imaging
methods with faster imaging speed and higher
For optical imaging, we consider an optical
imaging with a single-pixel detector. Compared to
the 2-D detectors, a single detector can work in a
broader band. The imaging approach utilizes a
spatial structured illumination generated by an
SLM or optical mask. The measurements are inner
products between the line-scans of object
transmittance and the mask representations.
Therefore the imaging speed can be much faster
than that of the conventional point-by-point
scanning methods. We exploit compressed sensing
(CS) as a principle for line-scanned imaging with
single-pixel detector. We study the robustness of
CS to the misfocus effect. It turns out the CS
design is reliable at moderate demagnification
factors. However, at high demagnification factors,
CS design becomes less credible or even useless.
Adviser: Ali Pezeshki
Co-Adviser: Mahmood R. Azimi-Sadjadi
Non-ECE Member: Chris Peterson, Math
Member 3: Edwin Chong, ECE/Math
Addional Members: N/A
W. Dang, A. Pezeshki, S. D. Howard, W. Moran, and R. Calderbank, "Coordinating complementary waveforms for sidelobe suppression", IEEE Trans. on Signal Processing, to be submitted.
W. Dang, A. Pezeshki, R. A. Bartels, "Sensitivity to line-scanned compressed sensing optical imaging to misfocus", J. Opt. Soc. Am. A, to be submitted.
W. Dang, A. Pezeshki, S. D. Howard, W. Moran, and R. Calderbank, "Coordinating complementary waveforms across time and frequency", IEEE Trans. on Signal Processing, in preparation.
W. Dang and L. L. Scharf, "Extensions to the theory of widely linear complex Kalman filtering", IEEE Trans. on Signal Processing, Dec. 2012 or Jan. 2013, to appear.
W. Dang, M. Tao, H. Mu and J. Huang, "Subcarrier-pair based resource allocation for cooperative multi-relay OFDM systems", IEEE Trans. on Wireless Communications, vol. 9, no. 5, pp. 1640-1649, May 2010.
W. Dang, A. Pezeshki, S. D. Howard and W. Moran, "Coordinating complementary waveforms across time and frequency", IEEE Statistical Signal Proc. Workshop, Ann Arbor, MI, Aug. 5-8, 2012.
W. Dang, D. G. Winters, D. Higley, A. Pezeshki and R. A. Bartels, "High-speed single-pixel line-scan imaging with a time sequence of intensity masks reconstructed through compressed sensing", SPIE Photonics West, San Francisco, CA, Jan. 21-26, 2012.
W. Dang, A. Pezeshki, S. D. Howard, W. Moran and A. R. Calderbank, "Coordinating complementary waveforms for sidelobe suppression", Forty-fifth Asilomar Conf. Signals, Syst., Comput., Pacific Grove, CA, Nov. 6-9, 2011.
R. Bartels, D. Winters, D. Kupka, W. Dang, A. Pezeshki, "Extracting information from optical fields through spatial and temporal modulation", Frontiers in Optics, San Jose, CA, Oct. 16, 2011.
A. Pezeshki, W. Dang and R. A. Bartels, "Mask Design for High-resolution Optical Imaging", SPIE Wavelets and Sparsity XIV, San Diego, CA, Aug. 21-25, 2011.
W. Dang, M. Tao, H. Mu and J. Huang, "Subcarrier-pair based resource allocation for cooperative AF multi-relay OFDM systems", IEEE GLOBECOM'09, Honolulu, HI, USA, Nov. 30-Dec. 3, 2009.
H. Mu, M. Tao, W. Dang and Y. Xiao, "Joint subcarrier-relay assignment and power allocation for decoded-and-forward multi-relay OFDM systems", ChinaCom'09, Xi'an, China, Aug. 26-28, 2009.
Program of Study: