Noise-like Signals Research Articles

Energy characteristics of beam-plasma interaction in a closed volume

Energy exchange between an electron beam and plasma during a beam-plasma discharge in a closed cavity excited by the electron beam is analyzed using computer simulations by the KARAT code. A method allowing one to analyze the beam-plasma interaction in the quasi-steady stage of the discharge is proposed. Qualitative characteristics of energy exchange (such as beam energy losses and the energy distributions of beam electrons and plasma particles leaving the discharge) both during spontaneous discharge excitation and in the presence of initial beam modulation by regular or noiselike signals are determined. The results obtained enable one to estimate the energy characteristics of a plasma processing reactor based on a beam-plasma discharge.

Enhanced Robustness for Digital Images Using Geometric Attack simulation

The effectiveness of a digital watermarking algorithm is indicated by the robustness of embedded watermarks against various attacks. Attacks which attempt to destroy watermarks have two types, noise-like signal processing and geometric distortions. To select a non-overlapping region, some reference parameters have been used, the regions with higher feature corner response are selected when the Harris–Laplacian or Harris–affine detector is used. The number of neighboring feature points inside a region is a major reference for obtaining a non-overlapping set in the watermarking method based on Mexican Hat wavelet scale interaction. A watermarked feature region may have different degrees of robustness against different techniques if there is prior knowledge of each region's attack resistance capability. We proposed a feature region selection method based on the idea of simulated attacking and finding the Optimal feature region set.

Joint robustness and security enhancement for feature-based image watermarking using invariant feature regions

Local image features have been widely applied in feature-based watermarking schemes. The feature invariance is exploited to achieve robustness against attacks, but the leakage of information about hidden watermarks from publicly known locations and sizes of features are often unconsidered in security. This paper, therefore, proposes a novel image watermarking approach, which adopts invariant feature regions to jointly enhance its robustness and security. Initially, circular feature regions are determined by the scale-adapted auto-correlation matrix and the Laplacian-of-Gaussian operation. Leakage of secret information is also controlled carefully during feature detection procedure. An optimal selection process formulated as a multidimensional knapsack problem is then proposed to select robust non-overlapping regions from those circular feature regions to resist various attacks. This process is implemented by a genetic algorithm-based approach, and incorporates randomization to mitigate the security risk. Finally, each selected region is normalized to obtain a geometrically invariant feature region, and embedded with a region-dependent watermark to overcome the weakness of multiple-redundant watermarks. The evaluation results based on the StirMark benchmark present the proposed scheme can tolerate various attacks, including noise-like signal processing and geometric distortions. A security analysis in terms of differential entropy also confirms the security improvement of the proposed method.

Experimental study of the effect of external noise-like signal on the dynamics of vircator with magnetron injection gun

The effect of an external noise-like signal on the operation of a low-voltage vircator with magnetron injection gun has been experimentally studied. The results show that the noise-like input signal allows the output characteristics of the low-voltage vircator to be controlled so as to drive it to operate at either maximum output power or maximum generation bandwidth.

40 Gb/s, secure optical communication based upon fast reconfigurable time domain spectral phase en/decoding with 40 Gchip/s optical code and symbol overlapping

We propose and experimentally demonstrate a 40 Gb/s secure optical communication system with on-off-keying (OOK) modulation format by using a time domain spectral phase en/decoding scheme, which employs a highly dispersive element and high-speed phase modulator for introducing significant symbol overlapping for both the encoded and incorrectly decoded noiselike signals to enhance the information security against eavesdropping using a power detector. The influence of dispersion and chip modulation rate on the symbol overlapping of the incorrectly decoded signal has been analytically investigated and experimentally verified. Security enhancement for 40 Gb/s OOK data using fast reconfigurable 40 Gchip/s optical codes with code lengths of up to 1024 has been demonstrated and compared with a 10 Gb/s system.

A novel view of biologically active electromagnetic fields

Over the past decades, strong evidence has accumulated that low-frequency electromagnetic fields (EMFs) can be useful in treating human pathologies, such as bone fractures, soft tissue illnesses, and pain. Common strategies for the design of commercial therapeutic devices are to generate EMFs that simulate body endogenous EMFs, or EMFs that resonate with a particular biological process, such as the natural motions of ions. We recently came across a biologically active commercial EMF signal that seems to be different. The signal is generated by summing the fundamental frequencies and harmonics of several periodic base signals which remain proprietary to the company. When first examined in the time domain, the signal resembled electronic noise; however, when critically analyzed, the signal is not identical with noise. Rather, it is a highly complex waveform exhibiting a very wide range of values for the time derivative of the magnetic field density (dB/dt) and a beat frequency in the Extremely Low-Frequency range. In this paper, we speculate on the mechanism of action of this and similar signals. We consider it less likely that cells, or cell components, act like filters to extract and couple with individual signals that make up the complex EMF signal. Consequently, we favor the possibility that with the signal discussed here cells respond to the very complex signal and that the biological response can be modified by the presence of a beat in the signal, in this case a low-frequency beat. More generally, this would suggest the hypothesis that biological processes can be regulated by noise-like signals and that the effects of a noisy signal can be modified by the presence of signal repetition patterns, such as beats. Given the very small energy that signals like these can transduce into a biological system, biological effects can be expected only when the molecular processes involved are poised so that the available energy leads to molecular reactions that achieve the activation state for the reaction.

The Inhibition of Stuttering Via the Perceptions and Production of Syllable Repetitions

ABSTRACTIn contrast to most therapeutic protocols for stuttering that induce fluency while producing speech targets, we investigated the possibility of inducing “carry-over” fluency prior to normal speech production. Ten adults who stutter read 7–12 syllable phrases after actively producing (via shadowing) or passively listening to: (a) repeating syllables, matched to the initial syllable of the target utterance; (b) repeating syllables, not matched to the initial syllable of the target; (c) nonrepeating syllables; and (d) fricative /noise-like acoustic signals. Relative to baseline, all active syllabic conditions produced ∼70% inhibition (reduction) of stuttering in the ensuing target utterances, which is attributed to carry-over from fluent shadowing. The most robust passive inhibition (56%) resulted from listening to matched repeating syllables. These findings further sustain that a perception-production link in speech, possibly resulting from mirror neuron activity, can facilitate the inhibition of stuttering. However, in this study we further demonstrate gestural and temporal flexibility of this mechanism, showing that this inhibitory strategy may be enacted prior to producing speech targets. We discuss possible clinical implications and draw comparisons between core stuttering behaviors (i.e., repetitions and prolongations) and behavioral therapeutic strategies (e.g., slowed speech, preparatory sets) used to inhibit or eliminate stuttering.

Optimal recognition of gravitational signals

An optimal algorithm for recognition of a useful noise-like signal at the output of resonant gravitational antennas with overlapping directional diagrams is discussed.

Electron transport and microwave dynamics of hybrid Nb/Au/CaSrCuO/YBaCuO planar Josephson junctions

We report on measurements of dc electron transport and microwave dynamics of thin film hybrid Josephson junctions with an oxide antiferromagnetic interlayer. The base superconducting electrode YBaCuO and the antiferromagnetic (AF) interlayer CaSrCuO (with thickness d = 20 – 70 nm) were grown by laser ablation on NdGaO3 substrates. I-V curves were well fitted to RSJ model and had no excess current, ICRN products were of order 0.2 mV at T=4.2 K. We did not observe any noticeable reduction of ICRN with increasing d. Such "tunnellike" behaviour also resulted in appearance of singularities on I-V curve when magnetic field was applied. Oscillating with microwave power integer and half-integer Shapiro steps were registered along with sub-harmonic detector response. Moreover, for some of junctions a "devil" staircase structure was observed on I-V curves and giant noise-like signals were measured in 1-2 GHz band at the certain levels of microwave power. Observed features, noise performance and the impact of the second harmonic in current-phase relation on junction dynamics are discussed taking into account data for structures without AF interlayer.

Adaptive Signal Modeling Based on Sparse Approximations for Scalable Parametric Audio Coding

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper deals with the application of adaptive signal models for parametric audio coding. A fully parametric audio coder, which decomposes the audio signal into sinusoids, transients and noise, is here proposed. Adaptive signal models for sinusoidal, transient, and noise modeling are therefore included in the parametric scheme in order to achieve high-quality and low bit-rate audio coding. In this paper, a new sinusoidal modeling method based on a perceptual distortion measure is proposed. For transient modeling, a fast and effective method based on matching pursuit with a mixed dictionary is chosen. The residue of the previous models is analyzed as a noise-like signal. The proposed parametric audio coder allows high quality audio coding for one-channel audio signals at 16 kbits/s (average bit rate). A bit-rate scalable version of the parametric audio coder is also proposed in this work. Bit-rate scalability is intended for audio streaming applications, which are highly demanded nowadays. The performance of the proposed parametric audio coders (nonscalable and scalable coders) is assessed in comparison to widely used audio coders operating at similar bit rates. </para>

10.1007/s11487-008-2014-2

An optimal algorithm for seeking a noiselike signal with the minimum frequency-shift keying is synthesized. The algorithm involves estimation of the signal delay time. The noise immunity of quasi-optimal algorithms is analyzed. The proposed algorithms are recommended for application in correlation receivers of noiselike signals with the minimum frequency-shift keying.

Passive bistatic noise radar using DVB-T signals

This study presents a new approach to passively detect targets using noise-like emitters of opportunity. This method combines the Wiener filtering to achieve clutter rejection and a proposed adaptation to noise-like signals of the amplitude and phase estimation (APES) method. This theoretical approach is confirmed by the detection of a helicopter by a bistatic radar using a digital video broadcasting terrestrial (DVB-T) transmitter.

Correlation functions of single symbols of meander signals in new-generation satellite radio navigation systems

Mathematical models of meander noise-like signals (binary offset carrier modulated signals (BOC signals)) of new-generation satellite radio navigation systems (SRNSs), in particular, the modernized GPS, the Galileo system, and the QZSS are presented. An analytic expression for the correlation function (CF) of single symbols of meander pulses is obtained for the arbitrary value of the multiplicity coefficient. The properties of CFs of various meander symbols are analyzed. The features of CFs are revealed for the even and odd values of the multiplicity coefficient. Examples of CFs are considered, and CFs of single symbols of BOC signals applied in new-generation SRNSs are plotted.

Investigation of the performance characteristics of a system for the incoherent search for noise-like signals

A system for the search for the noise-like signals with verification of the results is considered for the case of incoherent reception. Basic statistical characteristics of the system are determined. The problem of decreasing the mean acquisition time is studied. It is shown that the proposed algorithm provides selection of the points of possible detection and thus reduction of the mean acquisition time. The probability of error in the selection of the points of possible detection is estimated.

Propagation Effects on Noise-Modulated Randomly Polarized Ultrawideband Communication System

A noise-modulated ultrawideband covert communication system has been developed in order to conceal data sent over wireless channels. The modulated signal containing the coherent carrier is mixed with a sample of an ultrawideband (UWB) random noise signal. The frequency range of the UWB noise signal is chosen such that the lower sideband of the mixing process falls over its own frequency range. The frequency-converted noise-like signal and the noise key are simultaneously transmitted over orthogonal horizontal (H) and vertical (V) polarizations. At the receiver, both orthogonally polarized signals are amplified, mixed together in an upper sideband up-converter and demodulated. The H and the V polarized signals are affected differently due to the differential attenuation and phase shift in the propagation channel. Results of simulations to assess the impact of various propagation factors, such as frequency-selective fading and absorption, multipath, and differential attenuation on polarization channels on bit error rate (BER) performance, are presented. The primary cause of degradation in error performance is high multipath reflection.

Remote, aerial, translayer, nonlinear downlink underwater acoustic communication.

The nonlinear mechanism for optical to acoustic energy conversion is explored for optoacoustic communication from an in-air platform to a submerged platform. This downlink communication can provide a bell ringer function and transmission of text and data. The nonlinear conversion mechanism, also known as the nonlinear optoacoustic regime where focused laser energy is converted to sound at the air-water interface, involves a phase change of the water medium through evaporation and vaporization leading to plasma production. The nonlinear conversion mechanism provides a more efficient, i.e., higher source level, controllable method for producing underwater acoustic signals. A means of deterministically controlling the spectrum of the underwater acoustic signal has been investigated and demonstrated by varying the laser-pulse repetition rate to provide M-ary frequency shift keyed signaling. This physics-based conversion process provides a methodology for providing low probability of intercept signals whose information is embedded in noiselike signals. These laser generated signals can then be used in a frequency hopped spread spectrum technique with the use of the proper receiver structures to take advantage of the frequency diversity and periodicity inherent in this type of signal structure that could also be used to combat frequency selective fading in underwater acoustic channels.

A phase-lock system for a receiver of periodic noise-like signals

Quasi-optimal algorithms of phase and frequency discrimination are proposed for a system that tracks the phase of a periodic noise-like signal with minimal frequency-shift keying. The considered algorithms are statistically simulated, and their noise immunity is analyzed.

Experimental study of the propagation of noise-like acoustic signals in aqueous and air media

The propagation of acoustic signals of special form, having a phase modulated by noise-like phasecoded sequences with a single-level cyclic autocorrelation function, in aqueous and air media has been experimentally investigated. The data transfer by noise-like signals at subkilometer distances is reported.

Design, Analysis, and Performance of a Noise Modulated Covert Communications System

Ultrawideband (UWB) random noise signals provide secure communications because they cannot, in general, be detected using conventional receivers and are jam-resistant. We describe the theoretical underpinnings of a novel spread spectrum technique that can be used for covert communications using transmissions over orthogonal polarization channels. The noise key and the noise-like modulated signal are transmitted over orthogonal polarizations to mimic unpolarized noise. Since the transmitted signal is featureless and appears unpolarized and noise-like, linearly polarized receivers are unable to identify, detect, or otherwise extract useful information from the signal. The wide bandwidth of the transmitting signal provides significant immunity from interference. Dispersive effects caused by the atmosphere and other factors are significantly reduced since both polarization channels operate over the same frequency band. The received signals are mixed together to accomplish demodulation. Excellent bit error rate performance is achieved even under adverse propagation conditions.

Chaotic Watermarking for Video Authentication in Surveillance Applications

Installing video cameras in public facilities for surveillance becomes more and more popular. This paper proposes a novel authentication scheme based on chaotic semi-fragile watermarking. The timing information of video frames is modulated into the parameters of a chaotic system. The system output, which is a noise-like signal, is used as a watermark and embedded into the block-based discrete cosine transform domain. The embedded information is demodulated by a maximum likelihood estimator. Temporal tampering can be detected by the mismatch between the extracted and the observed timing information. In addition, the deviation of the extracted watermark from the original one allows us to locate spatial tampering. It is shown that the proposed scheme can satisfy the peculiar requirements of authenticating a digital video surveillance system.