Graduate Exam Abstract

Wenbing Dang

Ph.D. Final
November 22, 2013, 9am-11am
ENGRG 102 Suite, CBE Conference Room
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 reflectors. 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 resolution. 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, "Doppler resilient transmit-receive filters for radar pulse compression", submitted to IEEE Trans. on Signal Processing. W. Dang, A. Pezeshki, R. A. Bartels, "Sensitivity to line-scanned compressed sensing optical imaging to misfocus", submitted to J. Opt. Soc. Am. A. W. Dang, A. Pezeshki, S. D. Howard, W. Moran, and R. Calderbank, "MIMO radar signal integrity in the presence of Doppler", 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, W. Moran, and R. Calderbank, "Signal integrity of MIMO phase-array radar in the presence of Doppler", IEEE Radar Conference 2014, submitted. 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: