Steganographic methods attempt to insert data in multimedia signals in an undetectable fashion. However, these methods often disrupt the underlying signal characteristics, thereby allowing detection under careful steganalysis. Under repeated embedding, disruption of the signal characteristics is the highest for the first embedding and decreases subsequently. That is, the marginal distortions due to repeated embeddings decrease monotonically. We name this general principle as the principle of diminishing marginal distortions (DMD) and illustrate its validity in the audio domain using a morphological distortion metric. The principle of DMD is used to derive a steganalysis tool that detects the presence of hidden messages in uncompressed audio files. Detailed analysis and experimental results are provided for the detection of spread spectrum watermarking and stochastic modulation steganography.

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.

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).

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.

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.

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.

Orthogonal variable spreading factor (OVSF) codes are standard in third generation UMTS cellular systems. The efficient generation of these codes is essential for reducing the area and power of wireless transceivers. In this paper, the basic properties of this family of codes are analyzed from an RTL perspective and two efficient hardware code generators are proposed. Tradeoffs and design solutions as well as low power considerations are discussed. These results represent the first reported implementation of an OVSF code generator.

A complex ±1 multiplier is an integral element in modern CDMA communication systems, specifically as a pseudonoise code scrambler/descrambler. Therefore, an efficient implementation is essential to reduce the critical path delay, power, and area of wireless receivers. A new architecture is proposed to achieve this complex multiplier function. Tradeoffs and design solutions as well as the interface with subsequent arithmetic circuits are discussed. Simulations exhibit a significant speed improvement as compared to alternative architectures. These results are also applicable to other arithmetic circuits.

A method is presented for resolving delay and Doppler specular multipath components using an extension of a previously developed projection onto convex sets (POCS) algorithm. To improve performance and convergence speed, a matched-filter based support constraint is incorporated into the variance of the residual constraint in the style of constrained least squares. The resulting algorithm performs well in a wide variety of delay and Doppler simulated multipath environments. Simulation results for the POCS algorithm are included along with results for matched filtering and least squares for comparative purposes.

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.

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.

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 (/spl omega/(2p-3), /spl omega/, 1, 1), p a prime and /spl omega/*Q/spl les/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.>

In the paper we show that any subset or decomposition of Costas arrays are themselves non-full Costas arrays with ideal auto-, and cross-ambiguity and multiple access properties. The decomposed waveform's "thumbtrack" like auto-ambiguity functions, and their low cross-ambiguity or mutual interference would make them applicable in various multiple access and/or communication systems. The original Costas array and its subsets can be used individually in a matched filter receiver. Also for the single transmitted Costas array we can obtain several channel responses by generating and using several different subsets. The post processing can combine them in a semi-coherent processing scheme or as abutted waveforms for new techniques which require two waveform to provide enhanced range-Doppler resolution and reverberation rejection.>

New families of spread-spectrum codes are constructed, that are applicable to optical synchronous code-division multiple-access (CDMA) communications as well as to arbitrary-medium time-hopping synchronous CDMA communications. Proposed constructions are based on the mappings from integer sequences into binary sequences. The authors use the concept of number theoretic quadratic congruences and a subset of Reed-Solomon codes similar to the one utilized in the Welch-Costas frequency-hop (FH) patterns. The properties of the codes are as good as or better than the properties of existing codes for synchronous CDMA communications: both the number of code-sequences within a single code family and the number of code families with good properties are significantly increased when compared to the known code designs. Possible applications are presented. To evaluate the performance of the proposed codes, a new class of hit arrays called cyclical hit arrays is recalled, which give insight into the previously unknown properties of the few classes of number theoretic FH patterns. Cyclical hit arrays and the proposed mappings are used to determine the exact probability distribution functions of random variables that represent interference between users of a time-hopping or optical CDMA system. Expressions for the bit error probability in multi-user CDMA systems are derived as a function of the number of simultaneous CDMA system users, the length of signature sequences and the threshold of a matched filter detector. The performance results are compared with the results for some previously known codes.>

The problem of the algebraic construction of a particular family of optical codes for use in code-division multiple-access (CDMA) fiber-optic local area networks (LANs) is treated. The conditions that the code families have to satisfy when used in such systems are reviewed. The new codes are called quadratic congruence codes, and the construction of the corresponding sequences is based on the number-theoretic concept of quadratic congruences. It is shown that p-1 codes exist for every odd prime p and can serve as many as p-1 different users in the CDMA fiber-optic system. The codes belong to the family of optical orthogonal codes, their auto- and cross-correlation properties are established, and their performance is compared to that of the previous optical codes. Examples of the codes and examples of their auto- and cross-correlation functions are given.>

In radar and sonar applications in which channel multipaths are present or targets are doubly spread, the scattering function is used to characterize the effects of the complex target on the problem of target detection. Thus, it is important to minimize the reverberation effects when measuring the channel scattering function. In the authors' recent work (see ibid., p.1337, 1991) the twin processor method for measuring the scattering function was proposed. It had improved capabilities over the traditional matched filter receivers for measuring target and/or channel structures by reducing sidelobe interactions. In the method two signals were transmitted and processed, thus having an implicit 3-dB SNR improvement. For the twin processor to be useful, more than 3-dB SNR improvement is desired, and in this work the authors address this issue by considering different outputs, real and imaginary parts, of the receiver proposed in their previous work.>

Using the fact that any Wigner distribution function (WDF) of two signals can be related to an ambiguity function of two (possibly different) signals, the concept of hit arrays is applied to predict the hit structure (inner or outer interference terms), together with location and shape of the hits, of the WDF. A graphical technique and algebraic expressions are derived and used to obtain the time reversed frequency hop codes. Since the time reversed codes are still a (possibly different) frequency hop code of the same type, all properties, signal design criteria and results available for hit arrays and ambiguity functions can not be directly applied to the WDF. This has opened a new approach to designing for signals for desired WDFs.>

A method for the estimation of the parameters of multipath communication channels is developed. The method makes use of matched filtering, set-theoretic deconvolution and autoregressive modeling. Pulse compression waveforms are used as channel probing signals. The results of a feasibility study in which the proposed method is applied to specular multipath channels to estimate the multipath parameters at a number of different signal-to-noise ratios (SNR) are presented.>

The problem of constructing frequency hop codes for use in multiuser communication systems such as multiple-access spread-spectrum communications and multiuser radar and sonar systems is addressed. Previous frequency hopping techniques are reviewed. The construction of a new family of frequency hopping codes called hyperbolic frequency hop codes is given. The concepts of multiple-access spread-spectrum communication systems and multiuser radar and sonar systems are reviewed, and it is shown that the hyperbolic frequency hop codes possess nearly ideal characteristics for use in both types of system. Specifically, in multiple-access communications the codes achieve minimum error probability, while in radar and sonar systems the codes have at most two hits in their auto- and cross-ambiguity function. Examples of address assignment for multiple-access communications systems and radar and sonar auto- and cross-ambiguity functions are also given.>

A method for the estimation of the parameters of specular multipath communication channels is presented. The method takes advantage of the matched filtering, set-theoretic deconvolution and autoregressive modeling. Pulse compression waveforms such as chip and frequency-hop coding waveforms are used as channel problem signals. The proposed method, applied to a number of multipath channel models with closely spaced path components, produces high-resolution estimates of multipath parameters at signal-to-noise ratios higher than 5 dB.>

A method is proposed for measuring the scattering function. This method has improved capabilities for measuring target and/or channel structuring by reducing sidelobe interactions, and thereby reducing reverberation or clutter distortion effects. This improved capability is maintained in the presence of all levels of white Gaussian noise.>

The cross-ambiguity properties of Costas-array frequency-hop coded signals for use in wideband multiuser sonar systems are established. In order to prevent system crosstalk, cross-ambiguity function for the signals should be minimized. The conditions under which Costas arrays achieve the minimum value of their cross-ambiguity functions are provided. The upper bound on the maximum number of hits in the cross-ambiguity function for Welch-Costas arrays is given, and it is shown that the maximum number of hits depends on the form of the prime over which the arrays are constructed.>

The radar ambiguity function is useful as a criterion of goodness for modulation signals used to discriminate the range and range-rate of point targets. It is often desirable to change existing ambiguity functions to meet new specifications of resolvability. One way of accomplishing this task is by using linear transformations of the ambiguity function. A review of the properties of ambiguity functions pertinent to the paper is included. Sufficient conditions for linear transformations to result in new ambiguity functions are presented in several forms. Then, necessary and sufficient conditions for kernels of the linear transformations to correspond to linear signal transformations are derived.