Impacts of space-time-frequency synchronization errors onwide-band target echo characteristics of bistatic/multistatic radar

Bistatic/multistatic radar has great potential advantages over its monostatic counterpart. However, the separation of a transmitter and a receiver leads to difficulties in locating the target position accurately and guaranteeing space-timefrequency synchronization of the transmitter and the receiver.The error model of space-time-frequency synchronization in a motion platform of bistatic/multistatic radar is studied. The relationship between the space synchronization error and the transmitter platform position, receiver platform position, moving state, and beam pointing error, is analyzed. The effect of space synchronization error on target echo power is studied. The target scattering characteristics are restructured by many separate scattering centers of the target in high frequency regions. Based on the scattering centers model of the radar target, this radar target echo model and the simulation method are discussed. The algorithm of bistatic/multistatic radar target echo accurately reflects the scattering characteristics of the radar target, pulse modulation speciality of radar transmitting signals, and spacetime-frequency synchronization error characteristics between the transmitter station and the receiver station. The simulation of bistatic radar is completed in computer, and the results of the simulation validate the feasibility of the method.

Human Perception of Group Synchronization Error in Remote Learning: Dependencies of Voice and Video Contents in One-Way Communication

This paper examines dependencies of voice and video contents on human perception of group (or inter-destination) synchronization error in remote learning by Quality of Experience (QoE) assessment. In our assessment, we use two videos and three voices (two voices for one video and one voice for the other video). We also investigate influences of silence periods in the voices and temporal relations between the voices and videos (called the tightly-coupled and loosely-coupled contents here). The voices are spoken by a teacher according to the videos. Each subject as a student assesses the group synchronization quality by watching each lecture video and the corresponding explanation voice, and then the subject answers whether he/she perceives the group synchronization error or not. As a result, assessment results illustrate that silence periods mitigate the perception rate of the error, and we can also find that we can more easily perceive the error for tightly-coupled contents than loosely-coupled ones.

Dynamic synchronous motion accuracy measurement and estimation for a five-axis mirror milling system

A mirror milling system(MMS)comprises two face-to-face five-axis machine tools,one for the cutting spindle and the other for the support tool.Since it is essential to maintain the cutter and support coaxial during the cutting process,synchronous motion accuracy is the key index of the MMS.This paper proposed a novel method for measuring and estimating the synchronous motion accuracy of the dual five-axis machine tools.The method simultaneously detects errors in the tool center point(TCP)and tool axis direction(TAD)during synchronous motion.To implement the suggested method,a measurement device,with five high-precision displacement sensors was developed.A kinematic model was then developed to estimate the synchronous motion accuracy from the displacement sensor output.The screw theory was used to obtain the analytical expression of the inverse kinematic model,and the synchronous motion error was compensated and adjusted based on the inverse kinematic model of the dual five-axis machine tools.TCP and TAD quasi-static errors,such as geometric and backlash errors,were first compensated.By adjusting the servo parameters,the dynamic TCP and TAD errors,such as gain mismatch and reversal spike,were also reduced.The proposed method and device were tested in a large MMS,and the measured quasi-static and dynamic errors were all reduced when the compensation and adjustment method was used.Monte Carlo simulations were also used to estimate the uncertainty of the proposed scheme.

High-precision time domain reactive power measurement in the presence of interharmonics

When interharmonics exist in power system signals,large errors emerge in traditional time domain reactive power measurement.In this paper,we present a novel time domain integral method with good effect of restraining interharmonics,synchronization error,and white noise,as well as the principle of the selection of the sampling periods when employing this approach.The current signal and phase-shifted voltage signal are reconstructed after the harmonic components of signals are extracted,so that the interharmonics are filtered.The influence of the synchronization error on the measurement is reduced through removing the weight coefficients of the reactive components.In the simulation,we apply several cosine windows to the proposed method and analyze signals containing both harmonics and interharmonics.The results show that,in the presence of interharmonics,synchronization error,and white noise (with a fundamental signal-to-noise ratio of 40 dB) all together,the relative errors are within the magnitude of 10 4,which perfectly satisfies the practical requirement.