Analyses of noncommensurate sampling used in high-precision regenerative pseudo-noise ranging systems

A high-precision pseudo-noise ranging system is often required in satellite-formation missions. But in an actual PN ranging system, digital signal processing limits the ranging accuracy, only level up with meter-scale. Using non-integer chip to sample time ratio, noncommensurate sampling was seen as an effective solution to cope with the drawback of digital effects. However, researchers only paid attention to selecting specific ratios or giving a simulation model to verify the effectiveness of the noncommensurate ratios. A qualitative analysis model is proposed to characterize the relationship between the range accuracy and the noncommensurate sampling parameters. Moreover, a method is also presented which can be used to choose the noncommensurate ratio and the correlation length to get higher phase delay distinguishability and lower range jitter. The simulation results indicate the correctness of our analyses and the optimal ranging accuracy can be up to centimeter-level with the proposed approach.

Influence of high overload on the collimating lenses of laser ranging systems

Collimating lenses are an important component of laser ranging systems,and high overload environments severely affect the beam shaping effect of such lenses.This study proposes a buffer isolation method on the basis of impact stress wave attenuation theory for collimating lens spacers,ANSYS finite element software was applied to simulate the high load dynamics of collimating lenses,and the buffer isolation performance of different materials and composite structures was compared and analysed.Optical simulation analysis of the collimating lenses under different buffer conditions was performed using ZEMAX software to study the mechanism by which a high overload affects the collimating lenses.High overload and optical shaping experiments based on theoretical analysis were further conducted.Results showed the superiority of butadiene rubber to polytetrafluoroethylene after application of 70000 g impact acceleration.The combination-gasket method was superior to the single-gasket method,and the sandwich combination-gasket method was superior to the double-layer combination-gasket method.

Performance analysis of an indoor UWB ranging system

To evaluate the ranging performance of impulse radio ultra wideband （IR-UWB） signals, an experiment is performed in a typical indoor environment. In order to mitigate the ranging error caused by theoretical algorithm and practical circuits, one way-time difference of the arrival （OW-TDOA） ranging method and corresponding approaches are proposed and carried out according to the structure of UWB transceivers. Generalized maximum likelihood （GML） estimator based on energy detection is applied for the time of arrival estimation. The obtained results show that this UWB ranging system can achieve a relative high ranging accuracy in a multipath environment （e.g. about 5 cm at ranges up to 6 m）, which is practical and meaningful for many sensor applications.

A correction method of encoder bias in satellite laser ranging system

In a satellite laser ranging telescope system, well-aligned encoders of the elevation and azimuth axes are essential for tracking objects. However, it is very difficult and time-consuming to correct the bias between the absolute-position indices of the encoders and the astronomical coordinates, especially in the absence of a finder scope for our system. To solve this problem, a method is presented based on the phenomenon that all stars move anti-clockwise around Polaris in the northern hemisphere. Tests of the proposed adjustment procedure in a satellite laser ranging （SLR）system demonstrated the effectiveness and the time saved by using the approach, which greatly facilitates the optimization of a trackin~ svstem.

Design, analysis and optimization of random access inter-satellite ranging system

In this paper, a random access inter-satellite ranging(RAISR) system is designed. The ranging accuracy is optimized by an algorithm to greatly improve the ranging accuracy. This paper verifies the feasibility of the RAISR system through a series of theoretical analysis, numerical simulation, hardware system design and testing. The research work brings the solution to the design and accuracy optimization problem of the RAISR system,which eliminates the main error caused by the satellite dynamic characteristics and frequency source drift of the RAISR system.The accuracy of the measurement system has been significantly improved.

Progress of the satellite laser ranging system TROS1000

The mobile satellite laser ranging system TROS1000, successfully developed in 2010, achieves a high repetition rate and enables daytime laser ranging. Its measurement range has reached up to 36000 km with an accuracy as precise as 1 cm. Using recent observations in Wuhan, Jiufeng, Xianning, and Rongcheng, Shandong, we introduce the progress made using this mobile observation system.

A Laser Ranging System Using Chaotic Light

A novel laser ranging system using chaotic laser as probe light source is designed and presented.The system is made up of five components:chaotic light source,transmitter,receiver,data acquisition unit and data processing unit.Chaotic light is generated by an 808 nm,500 mW,single-mode laser diode with optical feedback cavity.Single target detection and multi-target detection are experimentally realized by correlating the chaotic reference light and the reflected or backscattered probe light.The performances,including the resolution of 18 cm within at least 130 m range and the sensitivity of-20 dB,are achieved and analyzed.

Laser back scatter: Limitation to higher repetition rate [kHz] Satellite Laser Ranging system

Satellite laser ranging(SLR)with higher repetition rate is the recent trend for its various advantages.Laser backscatter(coincidence between recently transmitted pulses and received pulses near the detector)is found to be a constraint for the repetition rates higher than 20 kHz,due to,overlapping with photons returning from a satellite with the present constellation of most of the SLR systems.Such an overlap occurs at every 75 km satellite distance change at 2 kHz repetition rate,and remains for about 7.5 km;for a 20 kHz system however,it will occur after every 7.5 km and remains for 7.5 km,resulting in constant backscatter overlap e leaving no chance to avoid it.The resulting noise is 5 times more than before causing a serious problem in detection and lowers the signal to noise ratio of the overall SLR system.However,decreasing energy per shot at higher repetition rates e assuming a constant power laser e the resulting backscatter may decrease fractionally.

Volumetric assessment of hepatic grafts using a light detection and ranging system for 3D scanning:Preliminary data

BACKGROUND Liver transplantation has evolved into a safe life-saving operation and remains the golden standard in the treatment of end stage liver disease.The main limiting factor in the application of liver transplantation is graft shortage.Many strategies have been developed in order to alleviate graft shortage,such as living donor partial liver transplantation and split liver transplantation for adult and pediatric patients.In these strategies,liver volume assessment is of paramount importance,as size mismatch can have severe consequences in the success of liver transplantation.AIM To evaluate the safety,feasibility,and accuracy of light detection and ranging(LIDAR)3D photography in the prediction of whole liver graft volume and mass.METHODS Seven liver grafts procured for orthotopic liver transplantation from brain deceased donors were prospectively measured with an LIDAR handheld camera and their mass was calculated and compared to their actual weight.RESULTS The mean error of all measurements was 17.03 g(range 3.56-59.33 g).Statistical analysis of the data yielded a Pearson correlation coefficient index of 0.9968,indicating a strong correlation between the values and a Student’s t-test P value of 0.26.Mean accuracy of the measurements was calculated at 97.88%.CONCLUSION Our preliminary data indicate that LIDAR scanning of liver grafts is a safe,cost-effective,and feasible method of ex vivo determination of whole liver volume and mass.More data are needed to determine the precision and accuracy of this method.

Hybrid pedestrian positioning system using wearable inertial sensors and ultrasonic ranging

Pedestrian positioning system(PPS)using wearable inertial sensors has wide applications towards various emerging fields such as smart healthcare,emergency rescue,soldier positioning,etc.The performance of traditional PPS is limited by the cumulative error of inertial sensors,complex motion modes of pedestrians,and the low robustness of the multi-sensor collaboration structure.This paper presents a hybrid pedestrian positioning system using the combination of wearable inertial sensors and ultrasonic ranging(H-PPS).A robust two nodes integration structure is developed to adaptively combine the motion data acquired from the single waist-mounted and foot-mounted node,and enhanced by a novel ellipsoid constraint model.In addition,a deep-learning-based walking speed estimator is proposed by considering all the motion features provided by different nodes,which effectively reduces the cumulative error originating from inertial sensors.Finally,a comprehensive data and model dual-driven model is presented to effectively combine the motion data provided by different sensor nodes and walking speed estimator,and multi-level constraints are extracted to further improve the performance of the overall system.Experimental results indicate that the proposed H-PPS significantly improves the performance of the single PPS and outperforms existing algorithms in accuracy index under complex indoor scenarios.

Foam rolling and stretching do not provide superior acute flexibility and stiffness improvements compared to any other warm-up intervention: A systematic review with meta-analysis

Background:Acute improvement in range of motion(ROM)is a widely reported effect of stretching and foam rolling,which is commonly explained by changes in pain threshold and/or musculotendinous stiffness.Interestingly,these effects were also reported in response to various other active and passive interventions that induce responses such as enhanced muscle temperature.Therefore,we hypothesized that acute ROM enhancements could be induced by a wide variety of interventions other than stretching or foam rolling that promote an increase in muscle temperature.Methods:After a systematic search in PubMed,Web of Science,and SPORTDiscus databases,38 studies comparing the effects of stretching and foam rolling with several other interventions on ROM and passive properties were included.These studies had 1134 participants in total,and the data analysis resulted in 140 effect sizes(ESs).ES calculations were performed using robust variance estimation model with R-package.Results:Study quality of the included studies was classified as fair(PEDro score=4.58)with low to moderate certainty of evidence.Results showed no significant differences in ROM(ES=0.01,p=0.88),stiffness(ES=0.09,p=0.67),or passive peak torque(ES=-0.30,p=0.14)between stretching or foam rolling and the other identified activities.Funnel plots revealed no publication bias.Conclusion:Based on current literature,our results challenge the established view on stretching and foam rolling as a recommended component of warm-up programs.The lack of significant difference between interventions suggests there is no need to emphasize stretching or foam rolling to induce acute ROM,passive peak torque increases,or stiffness reductions.

Characteristic analysis of 5D symmetric Hamiltonian conservative hyperchaotic system with hidden multiple stability

Conservative chaotic systems have unique advantages over dissipative chaotic systems in the fields of secure communication and pseudo-random number generator because they do not have attractors but possess good traversal and pseudorandomness. In this work, a novel five-dimensional(5D) Hamiltonian conservative hyperchaotic system is proposed based on the 5D Euler equation. The proposed system can have different types of coordinate transformations and time reversal symmetries. In this work, Hamilton energy and Casimir energy are analyzed firstly, and it is proved that the new system satisfies Hamilton energy conservation and can generate chaos. Then, the complex dynamic characteristics of the system are demonstrated and the conservatism and chaos characteristics of the system are verified through the correlation analysis methods such as phase diagram, equilibrium point, Lyapunov exponent, bifurcation diagram, and SE complexity. In addition, a detailed analysis of the multistable characteristics of the system reveals that many energy-related coexisting orbits exist. Based on the infinite number of center-type and saddle-type equilibrium points, the dynamic characteristics of the hidden multistability of the system are revealed. Then, the National Institute of Standards and Technology(NIST)test of the new system shows that the chaotic sequence generated by the system has strong pseudo-random. Finally, the circuit simulation and hardware circuit experiment of the system are carried out with Multisim simulation software and digital signal processor(DSP) respectively. The experimental results confirm that the new system has good ergodicity and realizability.

Co-Sharing Waveform Design for Millimeter-Wave Radar Communication Systems

Millimeter-wave(mmWave)radar communication has emerged as an important technique for future wireless systems.However,the interference between the radar signal and communication data is the main issue that should be considered for the joint radar communication system.In this paper,a co-sharing waveform(CSW)is proposed to achieve communication and radar sensing simultaneously.To eliminate the co-interference between the communication and sensing signal,signal splitting and processing methods for communication data demodulation and radar signal processing are given respectively.Simulation results show that the bit error rate(BER)of CSW is close to that of the pure communication waveform.Moreover,the proposed CSW can achieve better performance than the existing waveforms in terms of range and velocity estimation.

NLOS error mitigation with information fusion algorithm for UWB ranging systems

This article puts forward a scalar weighting information fusion （IF） smoother with modified biased Kalman filter （BKF） and maximum likelihood estimation （MLE） to mitigate the ranging errors in ultra wide band （UWB） systems. The information fusion algorithm uses both the time of arrival （TOA） and received signal strength （RSS） measurement data to improve the ranging accuracy. At first, the ranging protocol of IEEE 802.15.4a acts as a multi-sensor system with multi-scale sampling. Then the scalar-based IF smoother accurately estimates the range measurement in the line of sight （LOS） and non-line of sight （NLOS） condition of UWB sensor network, during which the effectiveness of the IF in mitigating errors is especially focused during the LOS/NLOS transitions. Simulation results show that the proposed hybrid TOA-RSS fusion approach indicates a performance improvement compared with the usual TOA-only and other IF method, and the estimated ranging metrics can be used for achieving higher accuracy in location estimation and target tracking.

Effect of chip rate on the ranging accuracy in a regenerative pseudo-noise ranging system

The ranging accuracy of a pseudo-noise ranging system is mainly decided by range jitter and time delay discrimination. Many factors can affect the ranging accuracy, one of which is the chip rate. In digital signal processing, the time delay discrimination and autocorrelation function of sampled ranging sequences of different chip rates are very different. An approximation simulation model is established according to an in-phase quadrature (I/Q) correlator which is used to evaluate the time delay. Simulation results of the range jitter and time delay discrimination show that the chip rate which provides a non-integer sample-to-chip rate ratio can achieve a higher ranging accuracy, and some test results validate the simulation model. In some design missions, the simulation results may help to select an optimum sample-to-chip rate ratio to satisfy the design requirement on the ranging accuracy.

Design and observations of satellite laser ranging system for daylight tracking at Shanghai Observatory

The first satellite laser ranging system for daylight tracking in China was set up at Shanghai Observatory, Chinese Academy of Sciences. Both false alarm probability due to strong background noises and detection probability of the laser returns with single photon level from satellite in daylight for our system are analysed. The system design and performance characteristics of subsystems, adopted techniques and satellite ranging observations are given.

Design and derivation of the dual transponder carrier ranging system

The accuracy of microwave ranging is mainly limited by the frequency instability of the oscillator that generates the carrier phase signal. A dual transponder carrier ranging method is used to minimize the oscillator noise by combining the reference and the to-and-fro measurements. This ranging approach together with pseudo-noise ranging or other means can be used to measure the inter-satellite distance with a high precision. The pseudo-noise ranging system or other ranging systems help to solve the integer circles while the dual transponder ranging system guarantees the accurate fractional circle. The two satellites work in the master-slave mode. The range measurements are derived on the master satellite while the slave satellite just coherently transfers the received signal, so that the dual transponder ranging system does not need to rely on the time tagging system to synchronize the two satellites. This study first describes the dual transponder carrier ranging system and shows how the system removes most of the oscillator noise components effectively. Then, a detailed design scheme on the frequency planning of the ranging system is presented and the supporting analysis illustrates the feasibility of this system. Based on the design innovation, a laboratory demonstration system is assembled to verify the realizability of the dual transponder ranging system. The experimental results demonstrate that a high level of accuracy (about 30 μm under laboratory circumstance) can be achieved by the use of the proposed dual transponder carrier ranging system.

High speed pseudorandom modulation f iber laser ranging system

A laser ranging system using all fiber high speed pseudorandom （PN） coded laser at 1550 nm and photon counting is proposed to realize high spatial resolution. Different lengths of PN code are employed in the optical fiber delay ranging test, the results show the improvement in both ranging accuracy and signal-tonoise ratio （SNR） as PN code trains increase. A ranging accuracy of 3 cm is acquired when transmitting pulses propagate to a target of 1.77 km away and received by an InGaAs/InP avalanche photodiode （APD）. Simulation is also carried out under space borne condition based on current system. The system is demonstrated to have a potential for remote ranging and imaging.

Design and Research of Active Heave Compensation System Based on Laser Ranging Sensor

Marine resource exploitation and marine cargo transportation were increasingly frequent. Due to the impact of the marine environment, ships or platforms were affected. In this paper, a servo electric cylinder was used as a wave compensation actuator to design a wave compensation system. The laser sensor was used to measure the displacement in the direction of the heave platform, and the obtained displacement was applied to the wave compensation in the heave direction to verify the feasibility of the compensation system.

Measurement of Refractive Index Ranging from 1.42847 to 2.48272 at 1064 nm Using a Quasi-Common-Path Laser Feedback System

Wavelength 1064 nm is one of the most widely used laser wavelengths in industries and science. The high-precision measurement of the refractive index of optical materials at 1064 nm is significant for improving the optical design. We study the direct measurement of refractive index at 1064nm of lasers, including cMcium fluoride （CaF2）, fused silica and zinc selenide （ZnSe）, whose refractive indices cover a large range from 1.42847 to 2.48272. The measurement system is built based on the quasi-common-path Nd：YAG laser feedback interferometry. The thickness can be measured simultaneously with the refractive index. The results demonstrate that the system has absolute uncertainties of ~10-5 and ~10-4 mm in refractive index and thickness measurement, respectively.