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ABSTRACT: In this paper we describe an application of spread spectrum techniques in audio data hiding for watermarking and steganography. The method is self-synchronizing, cover-dependent, and operates in the time domain. We use a special class of frequency-hop signal known as a Welch-Costas array. Welch-Costas arrays have the properties of range and Doppler resolution. This allows us to recover embedded data with a matched filter. We also demonstrate a special case of an adaptive method due to Su and Girod (2002).
Acoustics, Speech, and Signal Processing, 2005. Proceedings. (ICASSP '05). IEEE International Conference on; 04/2005 · 4.63 Impact Factor
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ABSTRACT: Waveforms for active sensors (e.g., radar or active sonar) are often designed to maximize sensitivity to target motion to enhance tracking performance. The paper addresses the complementary problem of waveform design to maximize insensitivity to motion. Insensitivity is desirable in cases where motion is a nuisance to the sensor system. The motion insensitivity problem has been approached in the past using the trajectory diagram, related concepts of trajectory ambiguity, and generalized ambiguity functions. The paper discusses motion insensitivity in terms of both trajectory ambiguity and the generalized ambiguity function. The relationship between trajectory ambiguity and motion insensitivity via a generalized ambiguity function is described mathematically. The hyperbolic FM (HFM) signal is used as an example of a velocity insensitive signal.
Acoustics, Speech, and Signal Processing, 2005. Proceedings. (ICASSP '05). IEEE International Conference on; 04/2005 · 4.63 Impact Factor
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ABSTRACT: Trajectory ambiguity for an active sensor is discussed in the context of a linear time-varying channel. This type of ambiguity representation preserves details of target/channel behavior that are lost in a correlative ambiguity function representation. The trajectory diagram, which is a graphical view of radar and sonar, is used to motivate the discussion. Ambiguity manifests as sets of ambiguous target trajectories: different range versus time profiles for a target that produce identical received signal phase. These trajectories provide a "trajectory domain" picture of ambiguity that is useful for signal analysis and signal design.
IEEE Transactions on Signal Processing 02/2005; · 2.63 Impact Factor
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ABSTRACT: Two low power flexible Rake receiver architectures are presented. The first architecture exploits the statistical distribution of multipath delays in wireless channels to reduce power dissipation. The second Rake architecture is based on a tradeoff between algorithm accuracy and circuit complexity. By introducing a negligible performance degradation, the SRAM memory for the input sample buffer is eliminated, achieving low power consumption and small silicon area. Both Rake architectures are targeted for third generation WCDMA mobile terminals (downlink receivers), but the circuits can also be applied to base station (uplink) receivers. The architectures have been synthesized in a 0.18 μm standard cell CMOS technology using Cadence BuildGates. The proposed architectures achieve significant area and power savings as compared to previous circuits described in the literature.
Circuits and Systems, 2004. ISCAS '04. Proceedings of the 2004 International Symposium on; 06/2004
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ABSTRACT: The signal-dependent error for least squares specular multipath estimators is analyzed for active sensors. The error analysis also applies to other deconvolution techniques for multipath estimation such as projection onto convex sets (POCS) that uses the square error as a constraint. The results explain how the selection of the transmit signal affects the estimator performance. Example mean square error plots are provided for a linear frequency modulation (LFM) signal to demonstrate the results. Given the set of possible locations for multipath components, the optimum signal to minimize the square error can be selected using these results.
Acoustics, Speech, and Signal Processing, 2004. Proceedings. (ICASSP '04). IEEE International Conference on; 06/2004 · 4.63 Impact Factor
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ABSTRACT: In this paper we describe a musical stream note segmentation method that employs time-domain and frequency-domain analysis methods working in conjunction. The method has two demonstrated benefits: first, it leads to reliable results with very low probability of either missing or of falsely detecting notes, and second, it has temporal resolution on the order of 1 msec. We have applied the method to a variety of monophonic musical instrument recordings, including the clarinet, piano and violin, with results that vary from 95% to 100% accuracy.
Acoustics, Speech, and Signal Processing, 2004. Proceedings. (ICASSP '04). IEEE International Conference on; 06/2004 · 4.63 Impact Factor
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ABSTRACT: We describe a representation of musical instrument sounds in which the sound is codified as the time histories of the parameters controlling a nonlinear physical model of the target musical instrument. As opposed to source-filter models often employed in speech, in which an assumed periodic source is filtered by a time varying acoustic transfer function, in our proposed method the nonlinear dynamical behavior of the source generator in interaction with an acoustic filter is directly simulated. The resulting autonomous oscillations of the combined system are controlled by a small number of slowly varying parameters. This representation has two advantages; first, it is extremely compact, requiring only 10's of bytes/sec of data, and second, it naturally captures variations of musical timbre and other nuances of live musical performance. We present preliminary results for recorded clarinet sounds in which the maximum likelihood estimation (MLE) method is used to infer the control parameter histories for an assumed target clarinet model.
Acoustics, Speech, and Signal Processing, 2004. Proceedings. (ICASSP '04). IEEE International Conference on; 06/2004 · 4.63 Impact Factor
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ABSTRACT: Synchronization improvements using traceability information found
in the narrowband auto-ambiguity function (NB AAF) are demonstrated.
This new auto-ambiguity function property, traceability, is the key to
defining a signal design approach for solving the synchronization
problems in spread spectrum system such as communication systems, radar
networks, and sonar systems. This work defines the property and
introduces a new tracing synchronization scheme that significantly
reduces initial synchronization time and the number of false
synchronization events
IEEE Transactions on Aerospace and Electronic Systems 11/2001; · 1.10 Impact Factor
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ABSTRACT: Detection of microvolt T wave alternans (TWA) is a non-invasive
method to identify patients at risk for sudden cardiac death. ECGs show
that visible TWA is often nonstationary. Thus, the authors developed a
new correlation method (CM) for TWA detection, and they tested CM's
ability to detect non-stationary TWA in comparison with an accepted
spectral method (SM). In a simulation study CM and SM were used to
evaluate stationary and non-stationary TWA of different amplitude. Other
simulated conditions included: background noise, poor synchronization
and windowing of the T waves; and amplitude respiration modulation of
the T wave. In the authors' comparison of CM and SM, they found that
only CM was able to detect non-stationary TWA. CM was more robust to a
poor synchronization and windowing of T waves, but affected more by high
amplitude modulation than SM. Both CM and SM detected TWA in the
presence of background noise
Computers in Cardiology 1997; 10/1997
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ABSTRACT: High-resolution multipath parameter estimates can be obtained
through various deconvolution procedures, all of which-in the limit-rely
on some form of inverse filtering. Although deconvolution in a multipath
environment free from Doppler is well understood and well documented,
this is not true for the case when motion of the multipath components
relative to the receiver imposes a Doppler shift on the transmitted
probing signal. This paper describes the effect of Doppler on a broad
class of deconvolution methods by studying the effect of Doppler on the
output of an inverse filter. It is shown that in the presence of
Doppler, the deconvolution outputs are comprised chiefly of two
signal-related functions, one of which may be designed in such a way as
to be free from the range-Doppler coupling effects inherent in
correlation processing. Knowledge of these two functions provides
insight into the signal design issues relevant to deconvolution-based
multipath parameter estimation systems and is useful in designing
appropriate constraints and post-processing algorithms that may lead to
an accurate extraction of the Doppler and delay parameters of the
multipath channel. These results are applied to two known deconvolution
methods: the method of projection onto convex sets (POCS) and the method
of least squares (LS)
IEEE Transactions on Signal Processing 10/1997; · 2.63 Impact Factor
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ABSTRACT: In this paper, analog and digital circuit realizations of a
parallel programmable matched filter are examined. Through wide
variations of the design space parameters, the general trend that is
observed is that short, fast circuits tend to favor an analog
implementation, while longer, slower circuits make a digital
implementation more appropriate. A methodology is provided for choosing
the preferable circuit-implementing technology when power consumption-as
a function of data precision, filter length, operating frequency,
technology scaling, and the maturity of the fabrication process-is used
as the primary metric of comparison. It is shown that neither the analog
nor the digital matched filter implementation is universally more power
efficient than the other. Rather, a surface is mapped in the
multidimensional design space where, on one side of this surface, a
digital solution is preferable, while on the other side of the surface,
an analog circuit is appropriate. Equations are given which delineate
the position of this transitional surface in terms of the design space
parameters, and example calculations and plots depicting the regions of
dominance for the digital and analog matched filters for specific
process and system parameters are presented
IEEE Transactions on Circuits and Systems II Analog and Digital Signal Processing 07/1997;
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ABSTRACT: A new receiving technique for frequency hopping CDMA systems is
proposed. The receiver collects the power of a signal for which it is
matched while the power of the interfering signals remains spread over
the entire bandwidth. The performance of the new receiving technique is
analyzed and evaluated for families of codes designed for a large number
of users in the system. It is possible to increase the number of
messages that each user can send and, therefore, increase the
transmission rate in the system. A hybrid system is also feasible which
has both low and high rate users transmitting at the same time
Vehicular Technology Conference, 1997, IEEE 47th; 06/1997
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ABSTRACT: A novel method for varying the link-rates in a frequency hopping code division multiple access (FH-CDMA) wireless network is introduced. The link-rate increase is proportional to the pattern-overlap coefficient. A new parameter (effective number of interferers) is introduced to calculate the network performance and to relate it to the performance measures of the previously proposed (conventional) FH-CDMA systems
Vehicular Technology Conference, 1997 IEEE 47th; 06/1997
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ABSTRACT: Wireless interference-limited communication systems utilizing
direct-sequence (DS) code-division multiple-access (CDMA) signals are
considered, for packet-based transmission of data of different
statistics and variable bit rates. A scheme for packet transmission is
proposed. The novelty of the scheme is in the fact that a packet is not
transmitted in a continuous arbitrary-length time segment, but rather as
a sequence of smaller data-units called packet-slots which are not
necessarily neighboring each other. The position of a packet slot on the
time axis is determined by hereby demonstrated packet-slot distribution
patterns, and all packet slots are of the same length. Breaking packets
into packet-slots introduces no additional overhead. The patterns are
representable by unipolar binary codes/sequences whose properties based
on number-theoretic proofs are reviewed. The proposed scheme can help
reduce the time variability of the composite interference due to
simultaneous transmissions of numerous DS-CDMA signals over the common
frequency band. Exact probability distribution functions of the
interference among different packet-slot distribution patterns are
computable. By reducing the variance of the overall interference, the
proposed scheme can contribute to increasing the system capacity which
is one of the motivations for utilizing DS-CDMA signals in multipath
fading environments
Global Telecommunications Conference, 1996. GLOBECOM '96. 'Communications: The Key to Global Prosperity; 12/1996
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ABSTRACT: The matched filter or correlator block of a spread-spectrum
communication system occupies a place in the receiver that just follows
the analog RF-to-baseband or RF-to-IF downconversion circuitry and just
precedes the digital data-decoding circuitry. A matched filter may,
therefore, be implemented via either digital or analog circuit
techniques. This paper analyzes and compares a digital and an analog
implementation of a programmable parallel matched filter using power
efficiency-as a function of signal integrity, filter size, operating
frequency, and technology scaling-as the primary metric of comparison. A
methodology is presented and results are given that indicate wherein the
multidimensional design space the digital circuit is more
power-efficient than the analog one, and vice versa
Circuits and Systems, 1996. ISCAS '96., Connecting the World., 1996 IEEE International Symposium on; 06/1996
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ABSTRACT: Phase differences between multipath reflections come from
properties inherent to every multipath channel and they produce problems
in previously introduced multipath parameter (delay, Doppler shift and
amplitude) estimators. Ways of overcoming these problems are suggested,
and the phase is considered as a parameter to be estimated, as well.
Phase estimates are important if multipath components are to be
eliminated, or recombined with the direct signal. Cramer-Rao bounds for
the estimates of one-path channel parameters (with and without phase)
are derived, and final expressions are discussed in light of the
influence of phase
Acoustics, Speech, and Signal Processing, 1996. ICASSP-96. Conference Proceedings., 1996 IEEE International Conference on; 06/1996 · 4.63 Impact Factor
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ABSTRACT: A number of personal communication systems (PCS) call for the use of spread-spectrum techniques for transmitting digital data through multiple-access channels. In these systems, a correlator or matched filter is used within the receiver to despread the encoded waveform before the underlying digital data is recovered. The matched filter may be implemented either before or after the received waveform has undergone analog-to-digital conversion. Since power consumption is a principal concern for portable PCS terminals, it is proper to consider which matched filter implementation-analog or digital-leads to a more power efficient spread-spectrum receiver. These two different implementations are examined, and a methodology is provided for choosing the appropriate circuit-implementing technology using power consumption as the primary metric of comparison, It is shown that neither the analog nor the digital matched filter implementation is universally appropriate. Rather, a surface is mapped out in the multi-dimensional design space where, on one side of this surface, a digital solution is preferable, while on the other side of the surface, an analog circuit is appropriate. Equations are given which delineate the position of this transitional surface in terms of the design space parameters, and example calculations and plots depicting the regions of dominance for the digital and analog matched filters for specific process and system parameters are provided.
Wireless Communication System Symposium, 1995., IEEE; 12/1995
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ABSTRACT: It has been shown previously that, using a deconvolution method
such as projection onto convex sets (POCS), which relies on some form of
inverse filtering, one can increase the resolution of multipath
parameter estimation in a Doppler environment beyond that which is
achievable using correlation processing alone. This paper shows that the
output of an inverse filter in the presence of Doppler can be
characterized by two signal-related functions: one of which is free from
the range-Doppler coupling effects inherent in correlation processing
Acoustics, Speech, and Signal Processing, 1995. ICASSP-95., 1995 International Conference on; 06/1995 · 4.63 Impact Factor
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ABSTRACT: A construction of a new family of optical orthogonal codes (OOCs)
for use in code division multiple access (CDMA) fiber-optic networks is
given. Previous families of OOCs are reviewed and basic requirements for
successful implementation of the fiber-optic CDMA system given. The new
code construction is based on Costas (1970) arrays and the codes are
proved to be (ω(2p-3), ω, 1, 1), p a prime and
ω*Q⩽p-1, where Q is the maximum number of users, OOCs. The
probability of error (using the Gaussian approximation) in the multiuser
system as a performance measure is calculated and compared with that of
existing OOCs. The size of the code family is compared against the
Johnson bound
IEEE Transactions on Communications 03/1995; · 1.68 Impact Factor
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ABSTRACT: We discuss cross-ambiguity properties of a specific family of
Costas arrays called Welch-Costas (W-C) arrays. These properties are of
interest in multiuser radar and sonar system, especially since Costas
arrays are known to possess ideal auto-ambiguity functions. The theory
of W-C arrays is reviewed. It is then proved that only pairs of W-C
arrays can have at most two hits in their cross-ambiguity function (best
possible case). The maximum number of hits in the cross-ambiguity
functions of a family of W-C arrays is shown to be a function of the
number of W-C arrays in the family. The upper bound on the number of
hits in the cross ambiguity functions for a family of W-C arrays is also
derived. Specific examples of how reducing the number of W-C arrays
improves the cross-ambiguity properties are given for various types of
prime numbers
IEEE Transactions on Aerospace and Electronic Systems 11/1994; · 1.10 Impact Factor
