Influence of phase noise on OFDM data transmission systems

We discuss the influence of the phase noise on OFDM data transmission systems. It is shown that intercarrier interference appearing due to the influence of the phase fluctuations on the OFDM communication system can be represented as two components, one of which has a uniform distribution across all the subcarriers, while the other has a nonuniform frequency-selective distribution determined by the transmission function of the communication channel. Therefore, the total distribution of intercarrier interference is frequency-selective with a higher power concentrated at stronger subcarriers. It is shown that the phase-noise influence on the OFDM communication system in frequency-selective communication channels is relatively weaker than that in frequency-flat channels without time dispersion.     

Quasi-monochromatic noise in bistable systems: The nature of large occasional fluctuations

Il Nuovo Cimento D - The response of an overdamped system to quasi-monochromatic (high-frequency narrow band) noise (QMN) has been investigated by means of analogue electronic experiments....     

Effect of traffic noise on the cyclical nature of sleep

Sleep changes from shallow to deep and back again in a cyclical manner with a period of around 90 min. The sleep of 12 subjects, each sleeping for 24 nights, was monitored by EEG. The results indicate that the cyclical nature may be somewhat disturbed by continuous free-flowing traffic noise, at a level of 60 dB, if, for instance, waking is always considered as the end of one cycle. However, if a cycle is judged from a bird's-eye view of the sleep record, then it appears that the average subject persists in his normal cycle and the effect of noise is negligible. But individual differences are great and may even be in opposite directions [G. J. Thiessen and A.C. Lapointe, J. Acoust. Soc. Am. 64, 1078-1080 (1978)], which may result in obscuring real effects when data are averaged over a number of individuals. Defining a "sleep cycle" is of importance in view of reports [M. Herbert and R.T. Wilkinson, Proc. of Congress on Biological Effects on Noise, Dubrovnik, Yugoslavia (1973)] that the disturbance of the sleep rhythm has an effect on performance during the following day.     

Higher instabilities in synergetic systems with continuou sysmmetries

We derive the order parameter equations for higher instabilities in synergetic systems with continuous symmetry. For the case of a multidimensional Lie-group we show that the state vector can be decomposed into a drift along the group orbit defined by the unstable state vector and a motion transvers to the group orbit.     

Influence of turbulence on train noise

The subject of this paper is the long distance propagation of train noise. The sound exposure level of train noise L_AE was measured. To describe the results of measurements, a semi-analytical model was used. It takes into account the wave-front divergence, air absorption, ground effect, and the turbulence destroying the coherent nature of the ground effect. The model contains three adjustable parameters that must be estimated at the site. To verify the model, we performed measurements of L_AE at the distance D = 450 m from the train track center. The difference between the calculated and measured mean values of L_AE equals 1.3 dB.     

On the nature of idling noise of circular saw blades

An experimental investigation of the effects of important saw blade geometric and kinematic parameters on idling circular saw noise was conducted. Blade tip speed was determined t0 be the dominant factor in the noise production. The sound power generated was found to vary approximately as the 5·3 power of the tip velocity. Variations in blade geometry, which included the number of teeth, the blade thickness, and the tooth-gullet shape, produce effects in the radiated sound of the order of 6 dB for the blades tested. It is shown that slotted disks may be used to provide a closely controlled simulation of the saw blade noise produced aerodynamically. Results suggest that the sources are likely to be compact and are dominated by the unsteady forces acting on the tooth surfaces resulting from the interaction 0f the tooth and the incident unsteady flow in the wake of the preceding tooth.     

热噪声对约瑟夫森结I-V特性及微波感应台阶的影响研究

采用数值仿真的方法研究了热噪声对约瑟夫森结I-V特性及微波感应台阶的影响。研究表明,热噪声导致约瑟夫森结的I-V特性曲线呈现"圆拱化",也使得微波感应台阶高度减小。得出了取不同约瑟夫森结临界电流和结电阻时,热噪声对台阶的影响规律     

Effect of noise on coupled chaotic systems

The effect of noise in inducing order on various chaotically evolving systems is reviewed, with special emphasis on systems consisting of coupled chaotic elements. In many situations it is observed that the uncoupled elements when driven by identical noise, show synchronization phenomena where chaotic trajectories exponentially converge towards a single noisy trajectory, independent of the initial conditions. In a random neural network, with infinite range coupling, chaos is suppressed due to noise and the system evolves towards a fixed point. Spatiotemporal stochastic resonance phenomenon has been observed in a square array of coupled threshold devices where a temporal characteristic of the system resonates at a given noise strength. In a chaotically evolving coupled map lattice with the logistic map as local dynamics and driven by identical noise at each site, we report that the number ofstructures (a structure is a group of neighbouring lattice sites for values of the variable follow which the certain predefined pattern) follows a power-law decay with the length of the structure. An interesting phenomenon, which we callstochastic coherence, is also reported in which the abundance and lifetimes of these structures show characteristic peaks at some intermediate noise strength.     

Learning in synergetic systems for pattern recognition and associative action

Synergetic systems are in particular physical systems which can produce spatial or temporal patterns by means of the interaction of their individual parts. We show how such a system can be devised or even learn by itself to reproduce given patterns described by their probability distribution function. If an initial state close to one of the learned patterns is presented to such a system, it will pull the initial state into an attractor belonging to the learned state (pattern recognition via associative memory). Furthermore we show how such a system can be devised or can learn to perform any prescribed stationary continous Markov process. If a set of incomplete or partly incorrect initial data is offered to such a system, it may correct it and perform associative action.     

Harmonic noise: Effect on bistable systems

The coordinate of a white noise driven harmonic oscillator is used as a stochastic source term in bistable dynamics. This new kind of Gaussian colored noise gives rise to resonance phenomena due to a peak in the spectrum. We investigate its effect on linear and bistable systems. We derive a Markovian approximation for driven bistable oscillators and overdamped systems. In the resonance region computer simulations were carried out using an extension of Fox' algorithm procedure for colored noise. We find an increase of the transition rates in bistable systems as compared with the case of bistable systems driven by white and exponentially correlated noise.     

The nature of respiration noise and its multifractal properties

Using a conventional and original technique of recording normal human vesicular and tracheal respiration noise and their fractal analysis, it has been established that noise has a multifractal character and the nature of the occurrence of vesicular and tracheal noise is different. It is been demonstrated that vesicular noise occurs as a result of expansion-contraction deformation of the lung parenchyma during act of respiration, and tracheal noise, as is known, occurs due to pressure pulsations on the internal surface of the trachea caused by nonstationary airflow in the glottal zone.     

On the description of noise in quantum systems

A formalism of probability operators which generalizes the notion of density operator is introduced into the theory of noisy quantum systems. The Markov property and the connexion between Heisenberg and Schrödinger picture for systems undergoing an irreversible change are discussed in detail. The probability-operator treatment of noise is related to the Langevin method discussed byLax through a generalized Einstein-relation. The master equation for the quantum mechanical oscillator with linear damping is written down in a Fokker-Planck-type approximation. By means of the Einstein-relation the coefficients in the Fokker-Planck-equation are related to the parameters in the phenomenological equations.     

Multi-rate sensor fusion-based adaptive discrete finite-time synergetic control for flexible-joint mechanical systems

This paper proposes an adaptive discrete finite-time synergetic control （ADFTSC） scheme based on a multi-rate sensor fusion estimator for flexible-joint mechanical systems in the presence of unmeasured states and dynamic uncertainties. Multi-rate sensors are employed to observe the system states which cannot be directly obtained by encoders due to the existence of joint flexibilities. By using an extended Kalman filter （EKF）, the finite-time synergetic controller is designed based on a sensor fusion estimator which estimates states and parameters of the mechanical system with multi-rate measurements. The proposed controller can guarantee the finite-time convergence of tracking errors by the theoretical derivation. Simulation and experimental studies are included to validate the effectiveness of the proposed approach.     

Effects of strong noise on attractors of dynamical systems

Stationary solutions of the Fokker-Planck equation are found by expansions of the probability distribution with respect to the reciprocal noise strength. It is shown that this expansion is convergent. Explicit representations for the probability distribution are obtained by numerical simulations for the Lorenz model and for a model of generators with inertial nonlinearity (GIN). The obtained distributions show an increasing amount of fine structure with decreasing noise which more and more reflects the fractal attractor structure. Results of measurements of the power spectrum of the GIN and of the distribution in the phase space are presented in dependence on the noise strengths.     

Effect of noise on characteristics of optical waveguide systems

Transient regimes of an optical waveguide system in the presence of additive and multiplicative noises are studied. The presence of noise is shown to result in a transformation of the spectrum of radiation modes. The effect of noise on the efficiency of input of electromagnetic energy into a waveguide system is studied.     

Influence of the nature of the filling gas and the radial temperature profile on the density profiles of the plasma components in closed systems

Calculations are carried out for the compositions of the plasmas which are produced in closed cylindrical volumes filled with Xe, N₂, O₂, and CO₂, with the radial temperature profile T(r) approximated by a step function. The redistribution of the plasma density is shown to be strongly influenced by the magnitude of the temperature drop and the ratio of the volumes of the regions at the two different temperatures.     

On the effect of the noise in dynamical systems

Summary We discuss the complexity in dynamical systems with a random perturbation by considering the rateK of divergence of nearby orbits evolving under two different noise realization. This quantity has a clear meaning in the context of the information theory and it has physical relevance for the analysis of experimental data. Our definition of complexity becomes crucial for strongly intermittent systems whereK is very different from the Lyapunov exponent. Paper presented at the International Workshop ?Fluctuations in Physics and Biology: Stochastic Resonance, Signal Processing and Related Phenomena?, Elba, 5–10 June 1994.