Long term integration algorithm for high-dynamic targets

A new long term integration algorithm is proposed forhigh-dynamic targets, which can resolve the problems of spectrumspread, frequency walk and pseudorandom noise （PRN）code phase curvature caused by the motion of targets. This algorithmfirst applies a keystone transform based improved discretepolynomial-phase transform （KT-IDPT） to estimate the Dopplerchirp rate. Then, based on the estimated Doppler chirp rate,dechirping and envelope translation are performed on the partialcorrelation results to correct the spectrum spread and the codephase curvature. The simulation results demonstrate that the proposedmethod has low integration loss and computational burden.

Two-step compressed acquisition method for Doppler frequency and Doppler rate estimation in high-dynamic and weak signal environments

To acquire global navigation satellite system(GNSS)signals means four-dimension acquisition of bit transition,Doppler frequency,Doppler rate,and code phase in high-dynamic and weak signal environments,which needs a high computational cost.To reduce the computations,this paper proposes a twostep compressed acquisition method(TCAM)for the post-correlation signal parameters estimation.Compared with the fast Fourier transform(FFT)based methods,TCAM uses fewer frequency search points.In this way,the proposed method reduces complex multiplications,and uses real multiplications instead of improving the accuracy of the Doppler frequency and the Doppler rate.Furthermore,the differential process between two adjacent milliseconds is used for avoiding the impact of bit transition and the Doppler frequency on the integration peak.The results demonstrate that due to the reduction of complex multiplications,the computational cost of TCAM is lower than that of the FFT based method under the same signal to noise ratio(SNR).

Perception-Driven Learning of High-Dynamic Jumping Motions for Single-Legged Robots

Legged robots show great potential for high-dynamic motions in continuous interaction with the physical environment,yet achieving animal-like agility remains significant challenges.Legged animals usually predict and plan their next locomotion by combining high-dimensional information from proprioception and exteroception,and adjust the stiffness of the body’s skeletal muscle system to adapt to the current environment.Traditional control methods have limitations in handling high-dimensional state information or complex robot motion that are difficult to plan manually,and Deep Reinforcement Learning(DRL)algorithms provide new solutions to robot motioncontrol problems.Inspired by biomimetics theory,we propose a perception-driven high-dynamic jump adaptive learning algorithm by combining DRL algorithms with Virtual Model Control(VMC)method.The robot will be fully trained in simulation to explore its motion potential by learning the factors related to continuous jumping while knowing its real-time jumping height.The policy trained in simulation is successfully deployed on the bio-inspired single-legged robot testing platform without further adjustments.Experimental results show that the robot can achieve continuous and ideal vertical jumping motion through simple training.

VEHICULAR NODE POSITIONING BASED ON DOPPLER-SHIFTED FREQUENCY MEASUREMENT ON HIGHWAY

Vehicular node positioning needs to be quick and precise on highway for safety considera-tion.In this paper,we present a novel and practical vehicular node positioning method which can achieve a higher accuracy and more reliability than the existing global-positioning-system-based po-sitioning solutions by making use of Doppler-shifted frequency measurements taken by vehicular node itself.This positioning method uses infrastructure nodes which are placed on the roadside every several kilometers as radiation sources to estimate the relative distances of vehicle to the infrastructure node.Through coordinate conversion,we get the absolute coordinates of vehicular node based on known absolute coordinates of infrastructure node.We also analyze the optimal distance of neighbor infra-structure nodes in order to ensure a high accuracy.In addition,simulation results demonstrate that the accuracy of our method with Extended Kalman Filtering(EKF) is superior to the method without EKF.

A fine acquisition algorithm based on fast three-time FRFT for dynamic and weak GNSS signals

As high-dynamics and weak-signal are of two primary concerns of navigation using Global Navigation Satellite System(GNSS)signals,an acquisition algorithm based on threetime fractional Fourier transform(FRFT)is presented to simplify the calculation effectively.Firstly,the correlation results similar to linear frequency modulated(LFM)signals are derived on the basis of the high dynamic GNSS signal model.Then,the principle of obtaining the optimum rotation angle is analyzed,which is measured by FRFT projection lengths with two selected rotation angles.Finally,Doppler shift,Doppler rate,and code phase are accurately estimated in a real-time and low signal to noise ratio(SNR)wireless communication system.The theoretical analysis and simulation results show that the fast FRFT algorithm can accurately estimate the high dynamic parameters by converting the traditional two-dimensional search process to only three times FRFT.While the acquisition performance is basically the same,the computational complexity and running time are greatly reduced,which is more conductive to practical application.

高动态范围电视系统技术漫谈

超高清电视是当下电视发展的重要方向,高动态范围(HDR)是超高清电视的一项关键技术,涉及端到端的技术和产业实现。本文简要概括了高动态范围HDR内容采集、传输、显示的关键技术点,并梳理了国际上主要标准化体系下技术的进展情况。

CRAMER-RAO BOUNDS OF THE FREQUENCY ESTIMATION IN THE TIME SELECTIVE RADIO CHANNELS WITH DOPPLER SPREAD

The mobile channel is slow fading and time selective, thus the multiplicative and additive noise of the channel will smear the spectral line, or arouse Doppler spread. This spread will make the parameters estimation accuracy degrade. The goal of this paper is to analytically assess this degradation when Carrier Frequency Offset (CFO) and Doppler shift exist jointly. Then the finite-sample Cramer-Rao Lower Bound (CRLB) is derived and close-form asymptotical expression is given for large-sample CRLB. These expressions give insights into the performance room for frequency estimation. Also the variance of Doppler shift estimator is simulated to illustrate the theoretical results.

Doppler radial velocity detection based on Doppler asymmetric spatial heterodyne spectroscopy technique for absorption lines

Doppler asymmetric spatial heterodyne spectroscopy(DASH)technique has developed rapidly in passive Doppler-shift measurements of atmospheric emission lines over the last decade.With the advantages of high phase shift sensitivity,compact,and rugged structure,DASH is proposed to be used for celestial autonomous navigation based on Doppler radial velocity measurement in this work.Unlike atmospheric emission lines,almost all targeted lines in the research field of deep-space exploration are the absorption lines of stars,so a mathematical model for the Doppler-shift measurements of absorption lines with a DASH interferometer is established.According to the analysis of the components of the interferogram received by the detector array,we find that the interferogram generated only by absorption lines in a passband can be extracted and processed by a method similar to the approach to studying the emission lines.In the end,numerical simulation experiments of Doppler-shift measurements of absorption lines are carried out.The simulation results show that the relative errors of the retrieved speeds are less than 0.7%under ideal conditions,proving the feasibility of measuring Doppler shifts of absorption lines by DASH instruments.

Measurement of high-dynamic temperature field using high-speed quadriwave lateral shearing interferometer

An approach to measure a high-dynamic two-dimensional(2 D) temperature field using a high-speed quadriwave lateral shearing interferometer(QWLSI) is proposed. The detailed theoretical derivation to express the wavefront reconstruct principle of the proposed method is presented. The comparison experiment with thermocouples shows that the temperature field measurement using QWLSI has a precision of ±0.5 °C. An experiment for measuring the highdynamic temperature field generated by an electrical heater is carried out. A 200 frame rate temperature field video with 512 × 512 resolution is obtained finally. Experimental results show that the temperature field measurement system using a QWLSI has the advantage of high sensitivity and high resolution.

Multiscale structural analysis inspired by exceptional load cases concerning the immersed tunnel of the Hong Kong-Zhuhai-Macao Bridge

This paper contains an assessment of the added value of multiscale material models for concrete in the context of macroscopic struc-tural analysis of(steel-reinforced)concrete structures.Two examples are discussed.They are inspired by the possibility of car accidents inside the immersed tunnel of the Hong Kong-Zhuhai-Macao Bridge(HZMB).The first example deals with vehicles crashing into the tunnel wall.The high-dynamic strengthening effect of concrete is studied based on an engineering mechanics model.The structural nature of the dynamic strength increase factor(DIF)is demonstrated by means of high-dynamic strength values measured on mortar cylinders of different size.Furthermore,the evolution of the DIF as a function of hardening of concrete at material ages beyond 28 days is studied.A validated multiscale model for concrete renders a customized analysis for the specific concrete used for the aforementioned tunnel possible.It is found that the DIF decreases with progressive hardening of concrete at material ages beyond 28 days.The second example is inspired by tunnel fires as may happen after car accidents.The study refers to thermal stresses in steel-reinforced concrete beams sub-jected to sudden heating.The thermal expansion coefficient of the concrete of the tunnel is quantified by means of a multiscale model.It is used as input for linear thermo-mechanical Finite-Element simulations of steel-reinforced concrete beams.The essential macroscopic simulation results are temperature distributions and associated stress fields.They are employed for top-down quantification of micro-scopic stress states inside the cement paste and the aggregates.This allows for quantifying two sources of microstructural stress fluctu-ations:(i)the macro-to-micro stress concentration and(ii)the mismatch of microscopic thermal expansion coefficients.In both examples,the multiscale models for concrete have increased the informative content of the structural simulations.