Lab Seminar Series
o
June
30, 2008, 2 to 3 pm, 310 Babbio, “MIMO radar with colocated antennas,” by Dr. Jian
Li (abstract)
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October
31, 2007, 4 to 5 pm, 430 Burchard, “A frequency-domain multi-band
matched-filter approach to passive diver detection,” by Kil Woo Chung (abstract)
o
September
21, 10:30 to 12 pm, 213 Burchard, “The need for integrated solutions in
wireless sensor networks,” by David Floyd (abstract)
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April
6, 2007, 10 to 12 pm, 213 Burchard, “Un-equal gain combining and GLRT detector
for DBPSK over AWGN and Rayleigh fading channels,” by Kil Woo Chung (abstract).
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April
6, 2007, 10 to 12 pm, 213 Burchard, “Space-time adaptive processing for
amplitude/phase-comparison monopulse,” by Mark A. Govoni
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March
30, 2007, 10 to 12 pm, 213 Burchard, “Design of cross-layer ad hoc routing
protocols,” by Dr. Zhi Ren (abstract)
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March
23, 2007, 10 to 12 pm, 213 Burchard, “Recursive parametric tests for
multichannel adaptive signal detection,” by Kwang-June Sohn (abstract)
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March
9, 2007, 10 to 12 pm, 213 Burchard, “Distributed adaptive quantization and
estimation for wireless Sensor networks,” by Dr. Jun Fang (abstract)
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February
23, 2007, 10 to 12 pm, 213 Burchard, “Trellis coded LCD modulation,” by Kiran
Sampath (abstract)
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February
16, 2007, 10 to 12 pm, 213 Burchard, “Spectrum sensing techniques in cognitive
radios,” by Nilay Shah (abstract)
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February
9, 2007, 10 to 12 pm, 213 Burchard, “Time-frequency analysis and parameter
estimation of the polynomial phase signal,” by Pu Wang (abstract)
o
March
6, 2006, 2:30 to 3:30 pm, 213 Burchard, “Blind source separation by kurtosis
maximization with applications in wireless communications,” by Dr. Chung-Yung
Chi (abstract)
o
October
15, 2004, 1 to 2:30 pm, 205 Burchard, “Low-complexity
multiuser timing acquisition for ultra-wideband communications,” by Kwang
June Sohn (abstract).
o
October
1, 2004, 1 to 2:30 pm, 205 Burchard, “Decorrelating Multiuser Code-Timing
Estimation for Long-Code CDMA with Bandlimited Chip Waveforms” by Rensheng Wang
(abstract).
o
September
24, 2004, 1 to 2:30 pm, 205 Burchard, “Performance of
Differential Modulation with Wireless Relays in Rayleigh Fading Channels,” by
Qiang Zhao (abstract).
o
Qiang
Zhao, "New Results on Selection Diversity over Fading Channels," ECE
Department, Stevens Institute of Technology, December 16, 2002.
6/30/2008
Title: MIMO radar with colocated
antennas
Speaker: Dr. Jian Li
Abstract: A MIMO (multi-input multi-output) radar
system, unlike standard phased-array radar, can transmit via its antennas
multiple probing signals that may be correlated or uncorrelated with each
other. While the companion tutorial by Blum et al. exploits the diversity
offered by widely separated transmit/receive antenna elements, we focus on the
merits of the waveform diversity allowed by transmit and receive antenna arrays
containing elements that are colocated. For the latter type of MIMO radar
systems, we provide here an overview of recent results showing that the said
waveform diversity enables the MIMO radar superiority in several fundamental
aspects, including: 1) significantly improved parameter identifiability, 2)
direct applicability of adaptive arrays for target detection and parameter
estimation, 3) much enhanced flexibility for transmit beampattern design, and
4) waveform optimality for more accurate target parameter estimation and
imaging. Specifically, we show that 1) the maximum number of targets that can
be uniquely identified by the MIMO radar is up to Mt times that of its
phased-array counterpart, where Mt is
the number of transmit antennas, 2) the echoes due to targets at different
locations can be linearly independent of each other, which allows the direct
application of many adaptive techniques to achieve high resolution and
excellent interference rejection capability, 3) the probing signals transmitted
via its antennas can be optimized to obtain several transmit beampattern
designs with superior performance, and 4) the probing signals can also be
optimized by considering several design criteria, including minimizing the
trace, determinant, and the largest eigenvalue of the Cramer-Rao bound (CRB)
matrix, to improve the radar parameter estimation and imaging performance. The
waveform optimization is performed with respect to covariance matrix R of the
waveforms, because optimizing directly with respect to the signal waveform
matrix X is a more complicated problem due to X having more unknowns than R and
the dependence of various performance measures on X is more intricate than the
dependence on R (as R is a quadratic function of X). Hence with R obtained in a
previous (optimization) stage, our problem is to determine a signal waveform
matrix X whose covariance matrix is equal or close to R, and which also
satisfies some practically motivated constraints (such as constant-modulus or
low peak-to-average-power ratio (PAR) constraints). We will explain how a
cyclic optimization algorithm can be used for the synthesis of such an X with
good auto- and cross-correlation properties. Finally, we discuss the use of an
instrumental variables approach to design receive filters that can be used to
minimize the impact of scatters in nearby range bins on the received signals
from the range bin of interest (the so-called range compression problem). Many
numerical examples will be provided to demonstrate the effectiveness of the
proposed methodologies.
10/31/2007
Title: T A Frequency-Domain
Multi-Band Matched-Filter Approach to Passive Diver Detection
Speaker: Kil Woo Chung
Abstract: This talk considers the problem of passive
acoustic detection of a diver in a shallow water environment. A
frequency-domain multi-band matched-filter approach to swimmer detection is
presented. The idea is to break the frequency contents of the hydrophone
signals into multiple narrow frequency bands, followed by time averaged (about
half of a second) energy calculation over each band. Then, spectra composed of
such energy samples over the chosen frequency bands are correlated to form a
decision variable. The frequency bands with highest Signal/Noise ratio are used
for detection. The performance of the proposed
approach was demonstrated for experimental data collected for a diver in the Hudson River, where the suggested technique is able to
detect the diver signal in the presence of strong noise produced by a pile
drive.
9/21/2007
Title: The Need for Integrated
Solutions in Wireless Sensor Networks
Speaker:
David Floyd
Abstract: Wireless Sensor Networks
(WSNs) provide an exciting and promising platform for realizing applications
that can impact many areas of our world. As with most technologies that have
such high potential, there are also many technological hurdles to overcome
before the full potential of WSNs can be realized. One of the major reasons for
this is that WSNs fundamentally change the operating assumptions that have
emerged over decades of engineering innovation. Disciplines that have
traditionally been developed separately (e.g., communications and signal
processing) are increasingly being integrated to meet the unique challenges
posed by WSNs.
In this talk I examine a few of the dominant
obstacles that arise in WSNs. These include distributed detection and the integration of networking
and signal processing to maximize limited resources (e.g., power). I will
discuss some of the problems, current solutions, remaining issues, and
potential future directions for research in these areas.
Title: Un-equal gain combining
and GLRT detector for DBPSK over AWGN and Rayleigh fading channels
Speaker:
Kil Woo
Chung
Abstract:
We consider unequal gain combining (UEGC) for unbalanced diversity channels.
Two diversity channels are used to transmit binary signals differentially
encoded under the AWGN and Rayleigh fading channel model. Two channels are
assumed independent but unbalanced, i.e, different channel has different
average SNR. We consider a receiver that performs UEGC for signals received
over the two branches, based on use of the Generalized Likelihood Ratio Test
(GLRT) principle. For the GLRT detector, the conditional and the average bit
error probabilities are derived. Finally, we provide simulation results that
compare UEGC with the equal gain combining (EGC) as well as the conventional
DBPSK.
3/30/2007
Title: Design of cross-layer ad
hoc routing protocols
Speaker: Dr. Zhi Ren
Abstract:
The design of cross-layer routing protocols in mobile ad hoc networks (MANETs)
is considered. Recently the research on MANETs is active. The design of routing
protocols is an important aspect and the Internet engineering task force (IETF)
MANET Working Group is mainly dedicated to this area. At the same time,
cross-layer design is an effective way to optimize the performance of routing
protocols. First, the presentation introduces MANETs and ad hoc routing
protocols. Then, a cross-layer ad hoc routing protocol which derives from ad
hoc on-demand distance vector routing protocol (AODV) is presented. In this
protocol, we improve the network performance by utilizing the cross-layer
method. Finally, we present a cross-layer directional on-demand routing
protocol which uses cross-layer and directional methods to address the “hidden
terminal & exposed terminal” problem. Numerical results show that the two
proposed protocols improve the network performance, such as throughput and
end-to-end delay.
3/23/2007
Title: Recursive parametric
tests for multichannel adaptive signal detection
Speaker: Kwang-June Sohn
Abstract:
The problem of detecting a multichannel signal in spatially and temporally
colored disturbances is considered. The parametric Rao and parametric
generalized likelihood ratio test (GLRT) detectors, recently developed by
modeling the disturbance as a multichannel autoregressive (AR) process, have
been shown to perform well with limited or even no training data. These
parametric detectors, however, assume that the model order of the multichannel
AR process is known to the detector a priori. In practice, the model order has
to be estimated by some model order selection technique. Meanwhile, a standard
nonrecursive implementation of the parametric detectors is computationally
intensive since the unknown parameters have to be estimated for all possible
model order, before the best one is identified. To address these issues, we
consider herein joint model order selection, parameter estimation, and target
detection. We present recursive versions of the aforementioned parametric
detectors, utilizing the multichannel Levinson algorithm to solve the
multichannel Yule-Walker equations recursively and find the estimates of the
unknown parameters, along with a generalized Akaike Information Criterion
(GAIC) for the model order selection. Numerical results show that the proposed
recursive parametric detectors that assume no knowledge about the model order
perform nearly identically to the corresponding non-recursive parametric
detectors with perfect knowledge of the model order, while the formers have
reduced computational complexity.
3/9/2007
Title: Distributed adaptive
quantization and estimation for wireless sensor networks
Speaker: Dr. Jun Fang
Abstract: We discuss the
distributed parameter estimation in a wireless sensor network, where due to
bandwidth constraint, all sensor nodes have to quantize their observations and
send quantized data to a fusion center. We consider the most stringent case
where each sensor can send only one bit of information. We present a new
distributed adaptive quantization scheme by which each individual sensor node
dynamically adjusts the threshold of its quantizer based on earlier
transmissions from other sensor nodes. The maximum likelihood estimator (MLE)
and the Cramer-Rao bound (CRB) associated with our distributed adaptive
quantization scheme are derived. Numerical results depicting the performance
and advantages of our approach over a fixed quantization scheme are presented.
Title: Trellis coded LCD
modulation
Speaker: Kiran Sampath
Abstract: This talk will present concatenated Trellis Coded
modulation for a novel group of codes called Linear Constellation Decimation
(LCD) Codes, which are especially suitable for frequency-selective channels.
LCD codes are a class of non-binary block codes obtained by decimating a
Phase-Shift-Keying (PSK) constellation with a group of decimation factors that
are co-prime with the constellation size. The motivation behind the
concatenation of Trellis coding to the LCD codes (which offer full spectral
diversity) is to increase the coding gain and also the rate. It will also
present a systematic method of set-partitioning the non-binary LCD codebook
vectors (set of constituent LCD codewords). Further it will discuss the
expansion of LCD codebook so as to facilitate the increase of spectral
efficiency.
Title: Spectrum sensing
techniques in cognitive radios
Speaker: Nilay Shah
Abstract: In this presentation, a
brief overview of the cognitive radio technology would be provided. Then we
would discuss spectrum sensing problem (primary user detection) and challenges
associated with that in cognitive network. Next part of the presentation would
concentrate on the solution for spectrum sensing from detection theory point of
view. We would look at different detection techniques and performance with
single cognitive sensor in network. Talk would also include requirement of
cooperation between cognitive radios and how cooperation can improve detection
performance. At the end we would have opportunity to discuss further
development possibility in spectrum sensing.
Title:
Time-frequency
analysis and parameter estimation of the polynomial phase signal
Speaker: Pu Wang
Abstract: In this presentation,
two problems are addressed. The first one is the time-frequency analysis of
multicomponent chirp signals (polynomial phase signal with order 2). This part
reviews the adaptive kernel design techniques based on the product ambiguity
function and its application to
multicomponent with unbalanced amplitudes.
Meanwhile, the time-frequency rate distribution will be mentioned
in this part since its concept on
time-instantaneous frequency rate (IFR)
is similar with the time-frequency distribution on time-instantaneous frequency (IF). A robust form of the
time-frequency rate distribution will be presented.
The other one
is the parameter estimation of the polynomial phase signal. In this part, we
will first address the identifiability problem using the cubic phase function
to analyze multicomponent signals. Then two improved algorithms are proposed
for this problem: product form and radon
form. Moreover, we will present our new developments on the cubic phase
function which is named as general phase function for high-order polynomial
phase function. Some further developments on these algorithms will be discussed
in the end.
Title:
Blind source
separation by kurtosis maximization with applications in wireless
communications
Speaker: Dr. Chong-Yung Chi
Abstract: The kurtosis
maximization criterion has been effectively used for blind spatial extraction
of one source from an instantaneous mixture of multiple non-Gaussian sources,
such as the kurtosis maximization algorithm by Ding and Nguyen, and the fast
kurtosis maximization algorithm (FKMA) by Chi and Chen. By empirical studies we
found that the smaller the normalized kurtosis magnitude of the extracted
source signal, the worse the performance of these algorithms. In this talk,
with the assumption that each source is a non-Gaussian linear process, a novel
blind source extraction algorithm, called turbo source extraction algorithm
(TSEA), is introduced. The ideas of the TSEA are to exploit signal temporal
properties for increasing the normalized kurtosis magnitude, and to apply
spatial and temporal processing in a cyclic fashion to improve the signal
extraction performance. The proposed TSEA not only outperforms the FKMA, but
also shares the convergence and computation advantages enjoyed by the latter.
We also consider
the extraction of multiple sources, also known as source separation, by
incorporating the proposed TSEA into the widely used multistage successive
cancellation (MSC) procedure. A problem with the MSC procedure is its
susceptibility to error propagation accumulated at each stage. We introduce two
non-cancellation multistage (NCMS) algorithms, referred to as NCMS-FKMA and
NCMS-TSEA, that are free from the error propagation effects. Simulation results
are presented to show that the NCMS-TSEA yields substantial performance gain
compared with some existing blind separation algorithms, together with a
computational complexity comparison. Then applications and simulation results
of the TSEA in wireless communications will be addressed. Finally, we draw some
conclusions.
Speaker’s
Biography: Chong-Yung
Chi received the Ph.D. degree in Electrical Engineering from the University of Southern California in 1983. From 1983
to 1988, he was with the Jet Propulsion Laboratory, Pasadena, California.
He has been a Professor with the Department of Electrical Engineering since
August 1989 and the Institute of Communications Engineering (ICE) since August
1999 (also the Chairman of ICE for August 2002-July 2005), National Tsing
Hua University,
Hsinchu, Taiwan. He has published a
technical book, Blind Equalization and System Identification, Springer-Verlag,
2006, and more than 120 technical papers in radar remote sensing, system
identification and estimation theory, deconvolution and channel equalization,
digital filter design, spectral estimation, higher-order statistics (HOS) based
signal processing, and wireless communications. His current research interests
include signal processing for wireless communications, statistical signal
processing and digital signal processing and their applications.
Dr. Chi is a
member of European Association for Signal Processing, and an active member of
the Chinese Institute of Electrical Engineering. He has been a Technical
Program Committee member for many IEEE sponsored workshops, symposiums and
conferences on signal processing and wireless communications, including
co-organizer and a general co-chairman of 2001 IEEE Signal Processing SPAWC
Workshop. He was also the Chair of Information Theory Chapter of IEEE Taipei
Section (7/2001-6/2003). Currently, he is an Associate Editor for the IEEE
Trans. Signal Processing, an Associate Editor for the IEEE Trans. Circuits and
Systems II, and a Guest Editor of the JASP, a member of Editorial Board of
EURASIP Signal Processing Journal, and a member of Technical Committee on
Signal Processing Theory and Methods of IEEE Signal Processing Society.
Title:
Low-complexity
multiuser timing acquisition for ultra-wideband communications
Speaker: Kwang June Sohn
Abstract: This talk will address
the problem of multi-user timing acquisition for ultra-wideband (UWB)
communications. After a brief review of UWB communications, a low computational
complexity multi-user timing acquisition method is presented. By taking the
discrete Fourier transform (DFT) of the output samples of pulse-matched filter,
followed by least squares (LS) estimation, the timing acquisition problem is
converted to a sinusoidal parameter estimation problem which can be solved by a
wealth of good sinusoidal parameter estimations. Moreover, due to a unique
block diagonal structure of the correlation matrix of frequency-domain user
signatures, our LS estimator has a complexity that is linear with respect to
the number of samples per frame (i.e., linear complexity with respect to the
sampling rate).
Title: Decorrelating multiuser
code-timing estimation for long-code CDMA with bandlimited chip waveforms
Speaker: Rensheng Wang
Abstract: This talk will address
the problem of multiuser code-timing estimation for asynchronous uplink code-division
multiple-access (CDMA) systems with aperiodic spreading codes and bandlimited
chip waveforms. Two decorrelating code-timing estimation schemes, namely the
frequency-domain least-squares (FLS) and frequency-domain weighted
least-squares (FWLS) estimators, are developed. The two proposed estimators
offer different tradeoffs between complexity and estimation accuracy. Due to a
unique signal structure in the frequency domain, both the FLS and FWLS
estimators admit efficient implementations that result in significant
complexity reductions. Numerical results show that both of the proposed
estimators can support overloaded systems (with more users than the processing
gain) in multipath fading environments, and significantly outperform a
conventional technique based on matched-filter processing.
9/24/2004
Title: Performance of
Differential Modulation with Wireless Relays in Rayleigh Fading Channels
Speaker: Qiang Zhao
Abstract: Cooperative diversity
techniques have gained significant interest recently. The basic idea is to use
one or more nodes acting as relays that forward the received signal to the
destination node. This unique cooperative diversity technique may see
applications in ad-hoc wireless networks, sensor networks, etc. Most of related studies at the physical lay,
however, focus on coherent modulation, assuming that the channels can be
reliably estimated at the relay and destination nodes. Meanwhile, channel estimation
for the multiple wireless links is costly and challenging in a fading
environment. To obviate the channel estimation and reduce the complexity of the
receiver design, we examine differential modulation for wireless relay systems.
We propose a new amplify-and-forward relay scheme that does not need the
instantaneous channel states and, thus, is more suitable for differential
modulation. For performance assessment, a closed-form bit error rate expression
is derived and it is shown that the proposed scheme outperforms the standard
non-cooperative differential counterpart without relays.