Density Of Output Signal Research Articles

Stochastic resonance in parabolic-bistable potential system with an additive colour noise

We propose a new model (parabolic bistable system) with a colour noise source. In the presence of periodic input signal, we investigate the output signal to-noise ratio and the power spectral density of output signal, in which the self-correlation time may be an arbitrary value with no restriction. We find that the curves of signal-to-noise ratio versus the noise intensity D exhibits a bell-shape behaviour. The peak height increases with the increasing value of amplitude A0 of the input signal. However, the position of peak does not shift. Moreover, the signal-to-noise ratio is insensitive to the modulation frequency Ω, which completely differs from result of Ref.[6]. The power spectral density also has similar behaviour.

Influence of fluctuations of the weight coefficients on the characteristics of adaptive antenna arrays

We analyze theoretically the influence of the weight-coefficient fluctuations on the characteristics of adaptive antenna arrays (AAAs) with gradient adjustment algorithms under the assumption that the useful and noise signals have different correlation times. We obtain expressions for the correlation function and the spectral power density of the AAA output signal, find the average radiation pattern (RP), and derive an expression for the correlation matrix of the weight-coefficient fluctuations. It is shown that the weight-coefficient fluctuations bring about distortions of the useful signal and decrease its output power compared with the case of no fluctuations. In the frequency spectrum, this “overcompensation” phenomenon results in the depression of the output signal spectrum of the antenna array in the frequency band where high-power noise exists. As an example, we calculate the spectral power density of the output signal for an AAA with single linear constraints and plot the fluctuation RP and the variance of the weight-coefficient fluctuations versus the noise arrival angle.

Laser Doppler velocimeter with a differential photodiode array

A laser Doppler velocimeter is analyzed based on a Fourier optical model. A relation between power spectral density of output signal and structure of optical elements is derived. Based on the relation, a low-frequency disturbance, which appears in an ordinary LDV output, is shown to be canceled by using a differential detector. The output signal becomes a pure narrowband signal whose center frequency is proportional to the object velocity. A velocity measurement experiment result shows the usefulness of the differential detector method.