Long-time Delay Research Articles

Ergodic Interference Alignment for Spectrum Sharing Radar-Communication Systems

In this paper, we propose an ergodic interference alignment (IA) method for interference elimination in spectrum sharing multiple-input multiple-output (MIMO) radar and multi-user MIMO communication systems. In existing ergodic IA methods, the channel state information (CSI) is generally assumed to be constant, but time-varying channels should be considered in practice. Differently, our proposed ergodic IA allows to time-varying and/or frequency selective channels for spectrum sharing radar-communication systems. The essence is equivalent to design a simple transmit beamforming, which helps to find a pair of desired complementary channels easily without long-time system delay, therefore, the interferences can be effectively cancelled. The proposed method is evaluated by generalized likelihood ratio test (GLRT) and signal to interference plus noise ratio (SINR) for the radar functionality, while the communication functionality is examined by bit error rate (BER) performance. Both theoretical analysis and simulation results validate that the effectiveness of the ergodic IA method for spectrum sharing radar-communication systems.

Statistical study of the time delay of ionospheric TEC storms to geomagnetic storms in Taoyuan, Taiwan

We have studied the time delay of ionospheric storms to geomagnetic storms at a low latitude station Taoyuan (25.02°N, 121.21°E), Taiwan using the Dst and TEC data during 126 geomagnetic storms from the year 2002 to 2014. In addition to the known local time dependence of the time delay, the statistics show that the time delay has significant seasonal characteristics, which can be explained within the framework of the seasonal characteristics of the ionospheric TEC. The data also show that there is no correlation between the time delay and the intensity of magnetic storms. As for the solar activity dependence of the time delay, the results show that there is no relationship between the time delay of positive storms and the solar activity, whereas the time delay of negative storms has weakly negative dependence on the solar activity, with correlation coefficient −0.41. Especially, there are two kinds of extreme events: pre-storm response events and long-time delay events. All of the pre-storm response events occurred during 15–20 LT, manifesting the Equator Ionospheric Anomaly (EIA) feature at Taoyuan. Moreover, the common features of the pre-storm response events suggest the storm sudden commencement (SSC) and weak geomagnetic disturbance before the main phase onset (MPO) of magnetic storms are two main possible causes of the pre-storm response events. By analyzing the geomagnetic indices during the events with long-time delay, we infer that this kind of events may not be caused by magnetic storms, and they might belong to ionospheric Q-disturbances.

Timestamp Representative of Weather Radar Images in the Cockpit

ABSTRACTObjective: The experiment reported here evaluated what a type of timestamp is an easy way for pilots to perceive and quickly assess the length of delay in NEXRAD mosaic radar images.Background: Data-linked mosaic NEXRAD images can be more than 14 min delayed by the time they reach the cockpit for use by pilots. The NTSB issued a safety alert to warn that the NEXRAD “age indicator” can be misleading. Unfortunately, research has indicated that pilots may not be fully aware of the delay and that it can adversely affect their decision-making and performance.Method: The three types of timestamps were “direct age”, “clock”, and “UTC” with three levels of time delay (short, medium, and long). Twenty-one participants read and compared two radar images, via timestamps, to determine the length of delay and which one was more recent.Results: The results indicated that the type of timestamp and the length of time delay significantly affected participants’ response time and accuracy. “UTC” timestamp with a long-time delay was associated with the longest response time and low accuracy. The “direct age” timestamp led to the highest accuracy and shortest response time for all manipulated levels of time delay.Conclusion: Although “UTC” format is commonly used in many weather products, we found the “direct age” format to be the superior method to support perceptions of time delay.

Space‐variant analysis and target echo simulation of geosynchronous SAR

The geosynchronous synthetic aperture radar (GEO SAR) echo simulation has an important significance for GEO SAR system design and image algorithm verification. The study discusses the main steps of the GEO SAR echo simulation process and the calculation of key parameters. At the same time, because GEO SAR has a high orbital altitude and a long-time delay, the error caused by the ‘go-stop-go’ hypothesis must be taken into account. For this reason, the authors have studied the slant range iterative model without the assumption. It is used to calculate the distance between the satellite and target in the echo simulation. Experimental results show that the method is effective and feasible. Based on this, the space variant characteristics of GEO SAR are analysed in detail. It can be seen that the echo signals do not satisfy the range and azimuth invariance.

Online force control of large optical grinding machine for brittle materials assisted by force prediction

Trajectory planning of aspherical surfaces with appropriate cutting parameters is always a tedious task, especially on difficult-to-grind materials. Orthogonal experiments are usually designed and conducted first to get a full estimation of forces under different sets of grinding conditions (e.g. depth of cut and feeding velocity). However, all these data will change, as the grinding wheel becomes blunt. To reduce the work on the selection of grinding parameters and keep the grinding process stable, a new force-controlled grinding strategy for large optical grinding machine on brittle material is proposed. The grinding force is controlled by adjusting feeding velocity along the trajectories in real time. The grinding force model is established by analyzing the complex contact area between the arc-shaped wheel and the workpiece. The co-existing of brittle and ductile removal is also considered. For the longtime delay of the system, the controller foresees the grinding force in 0.4 s later based on the model proposed, to prevent the large overshoot of the force (up to 87.5%). The verification of the controller was conducted on silicon carbide ceramics. The force overshoot was reduced to 22.5%, and the motion accuracy was guaranteed by position servo within 5 µm. The subsurface damage along the trajectory was further analyzed and discussed.

A New Predictive Sliding Mode Control Approach for Networked Control Systems With Time Delay and Packet Dropout

This paper investigates the predictive sliding mode control problem of networked control system with long-time delay and consecutive packet dropout in both sensor-controller link and controller-actuator link. A new modeling method that uses only one Markov chain to describe the time delay and packet dropout in a unified model is proposed. As a modification of the original law, a new chattering-free reaching law that is suitable for multiple-input systems is proposed and is later used as the reference trajectory of the designed predictive sliding mode controller. To overcome the influence of time delay and packet dropout, a novel predictive sliding mode controller equipped with a logic zero-order-holder and delay compensator is proposed, and the proposed compensation strategy is theoretically proven to be able to make the system completely free from the influence of long-time delay and consecutive packet dropout. Finally, a simulation example is given to illustrate the validity of the proposed controller.

Efficient networked UAV control using event-triggered predictive control

In this paper, we propose a method to improve the networked UAV control system using event-triggered control and model predictive control (MPC). Although the UAV control over the network has many advantages, it involves a long-time delay and packet loss, which adversely affect real-time control performance. Delay compensation algorithms in the networked control system (NCS) have been proposed to address such issues, however, they do not consider the resource limit of the network so that the network congestion may occur. In that case, the packet loss and network delay issues can even be worsened. In this study, we propose a method to reduce the generation of less important control signals and to use the network more efficiently by using event-triggered control. Since the event-triggered control method is also influenced by the network delay, an event trigger function suitable for NCS is designed. We validated the effectiveness of networked UAV control system and event-triggered control by simulation.

Trap-controlled mechanoluminescence in Pr3+-activated M2Nb2O7 (M = Sr, Ca) isomorphic perovskites

Isomorphic materials tend to exhibit differentiated performance due to the small differences between the constituent atoms and the crystal structures. Inspired by the isomorphic strategy, herein we developed a novel trap-controlled mechanoluminescent (TC-ML) material, Pr3+-activated Sr2Nb2O7, that shows mechanoluminescence (ML) under the mechanical actions of compression and friction. Compared to the isomorphic Ca2Nb2O7:Pr3+ which requires a long-time delay to achieve high-contrast ML due to the strong long-lasting afterglow, Sr2Nb2O7:Pr3+ enables the obtaining of high-contrast ML in a short-time delay because of the weak short-lasting afterglow, which greatly simplifies the imaging process to facilitate the further application of ML. The investigations of structural and optical characteristics between Sr2Nb2O7:Pr3+ and Ca2Nb2O7:Pr3+ reveal that the unique ML of Sr2Nb2O7:Pr3+ should result from its lower trap concentration and shallower trap depth relative to Ca2Nb2O7:Pr3+. Our results are expected to deepen our understanding on the behavioral diversity of isomorphic phosphors and thereby broaden the horizon of designing and regulating TC-ML materials.

Sacrificing trap density to achieve short-delay and high-contrast mechanoluminescence for stress imaging

Trap-controlled mechanoluminescence (ML) enables the direct observation of stress concentration of load-bearing objects through imaging the ML distribution, showing numerous prospects in stress detection, bio-imaging and optical displays. However, the applications of trap-controlled ML materials universally require long-time delay to fade the noise of symbiotic persistent luminescence (PersL) in order to achieve high-contrast ML images. In view of the difficulty to solve the PersL problem through individually eliminating the PersL traps, herein we propose a novel strategy of sacrificing trap density which decreases PersL and ML traps as a whole. By employing Sr2+ substitution to decrease the trap density of Ca2Nb2O7:Pr3+, we identify a novel composition of (Ca0.5Sr0.5)2Nb2O7:Pr3+ displaying short-delay and high-contrast ML images, and evaluate its practicability through a 2-dimensional in-situ imaging experiment of dynamic stress distribution. The underlying mechanism is ascribed to the greater decrease ratio of PersL intensity than ML intensity as a result of the larger detrapping rate of traps due to stress (leading to ML) than that due to thermal energy (PersL). Furthermore, multi-spectral investigations of (Ca,Sr)2Nb2O7:Pr3+ system reveal a distinctive electron transition process co-regulated by trap levels, charge transfer state and crystal field. The proposed strategy and the associated phosphors are expected to initiate the reconstruction of PersL-type ML materials and bring important implications for real-world stress imaging.

Analysis and algebraic­symbolic determination of conditions forsafe motion of a vessel in a non­stationary environment

We have proposed a method for the algebraic formalization of predicativedetermining of zones for safe and dangerous areas of navigation for the criterion Computational stability – continuity. It is not possible tobuild effective mathematical models for all cases of direct application of integrated and differential equations that describe statistical correlation functions of the space-time continuum. At the same time, there are always significant difficulties in operative processing of large volumes of information. Numerical results determine known long-time delays in the work of computers in the systems of navigation and operational control over the motion of a vessel. We have analyzed and obtainedconditions for the effective technology of structuring a safemaneuvering trajectorybased on typical sequences of formalized symbolic elementary zones. Briefpredicative fragments describe effective steps to maneuver in a safe area of navigation. Analytical description of the structural processes that transformthe input informational situational parameters into controlled effective parts and integrated modelsmakes it possible to increase technological speed of operational decision-making. Situational symbolic control over the qualities of adequate safe motion of a vessel is executedunder specific non-stationary changes in theinfluence from a dynamic external environment. Actual effects of the influencefrom external factors in a non-stationary environment that surrounds the hull of a moving vessel were symbolically formulated. In this case, typical estimates of degrees in thenon-stationary environment are algebraically collapsed into integrated safety criteria. We have established the target effect of modeling in terms of computational dynamics of processes for operational rapid control over motion of the vessel. In this case,vector regularized parameters ofevents are continuously entered in real time as corrections for initial data. We have solved the problem on predictive modeling of maneuvering variants for the criteria that guarantee current safety of motion along a planned strategic route. To effectively solve the taskon stable safety of motion, numerical methods to solve integral-differential nonlinear dynamic systems are typically employed. However, they are effective only for the substantiation of strategic routes. Delays in time at these stages are significant and accepted. It is proposed to manage and control algorithmic processes in real time by using alternative methods of symbolic algebra. The modelsproposed would make it possibleto find variants that are guaranteed to be adaptive to a specific current situation based on the transversal trajectory of a vessel motion. It is proven that in the areas where there may occur situations of conflict and risk, local rules that guarantee a safe motion trajectory areimplemented by connecting the boundary conditions for safe navigation area taking into account the presence of adjacent zones with threats, perturbations, obstacles.

Erratum and addendum to the paper ‘A new ZTD model based on permanent ground-based GNSS-ZTD data’, Survey Review, 2016, 48(351), 385–391

We correct some errors and give some more research for our paper published in Survey Review, 2016, 48(351), 385–391. This note is a correction owing to the use of the questionable surface meteorological measurements of the International GNSS Service (IGS) and also gives more sufficient studies to validate our method due to our inadequate study. Numerical weather model values of surface meteorological data were used to check the IGS surface meteorological measurements and long-time zenith tropospheric delay values at 76 radiosonde stations in Russia and near Russia were added as test data. Revised, updated and additional results were shown and analysed, which provide more evidence to show that the new proposed ISAAS model has a better accuracy than the Saastamoinen in Russia.

Self-Interference Channel Estimation Algorithm Based on Maximum-Likelihood Estimator in In-Band Full-Duplex Underwater Acoustic Communication System

To efficiently cancel the self-interference (SI) caused by the simultaneous transmission and reception in in-band full-duplex (IBFD) underwater acoustic (UWA) communication system, we propose a novel channel estimation approach to estimate the sparse SI channel, the proposed channel estimation algorithm has a better estimation performance than the traditional channel estimator. In the IBFD radio communication system, the SI and intended channels are estimated through using training symbols in different time slots, and therefore, the effect of intended signal can be avoided in SI channel estimation. Because of the time variable and longtime delay in the UWA channel, we cannot estimate the SI and intended channel in different time slots. The intended signal is treated as additive noise when estimating SI channel in the IBFD-UWA communication system, and thus, the SI channel estimation is affected by non-Gaussian noise and the traditional algorithms designed for Gaussian noise typically perform poor. In view of this situation, we propose a maximum likelihood (ML) with sparse constraint to estimate the sparse SI channel. The ML with sparse constraint is derived via combining a sparse constraint into conventional ML cost function and using stochastic gradient algorithm to get the iterative formula, thereby resulting in a better performance. Extensive simulations and experimental results show that the proposed algorithm has faster convergence and better cancelation performance compared with traditional ML and least square. We also present the convergence and steady-state mean-squared error analysis of the proposed algorithm.

Inspection of Prebaked Carbon Anodes Using Multi-Spectral Acousto-Ultrasonic Excitation

Reduction cell operation in primary aluminum production is strongly influenced by the properties of baked anodes. Producing consistent anode quality is more challenging nowadays due to the increasing variability of raw materials. Taking timely corrective actions to attenuate the impact of raw material fluctuations on anode quality is also difficult based on the core sampling and characterization scheme currently used by most anode manufacturers, because it is applied on a very small proportion of the anode production (about 1%), and long-time delays are required for lab characterization. The objective of this work is to develop rapid and non-destructive methods for the inspection of baked anodes. Previous work has established that sequential excitation of smaller parts collected from an industrial sized anode using acousto-ultrasonic signals at different frequencies allowed detecting and discriminating anode defects (pores and cracks). This was validated qualitatively using X-ray computed tomography. This work improves the method by using frequency-modulated excitation and building quantitative relationships between the acousto-ultrasonic signals and defects extracted from tomography images using Wavelet Transforms and Partial Least Squares (PLS) regression. The new excitation approach was found to provide similar or better inspection performance compared with sequential excitation, while requiring a shorter cycle time.

중산층의 장시간 보육 이탈로 인한 성평등 지연 : 학습중심 모성과 아동기의 형성

중산층의 장시간 보육 이탈로 인한 성평등 지연 : 학습중심 모성과 아동기의 형성

Autonomous homing control of a powered parafoil with insufficient altitude

In order to realize safe and accurate homing of a powered parafoil under the condition of insufficient initial altitude, a multiphase homing path is designed according to the flight characteristics of the vehicle. With consideration that the traditional control methods cannot ensure the quality of path following because of the nonlinear, large inertial and longtime delay existed in the system and strong disturbances in a complex environment, a homing controller, composed of the vertical and horizontal trajectory tracking controllers, is designed based on active disturbance rejection control (ADRC). Then autonomous homing simulation experiment of the powered parafoil with insufficient altitude is carried on in a windy environment. The simulation results show that the planned multiphase homing trajectory can fulfill the requirements of fixed-point homing and flare landing; the designed homing controller can overcome the influences of uncertain items of the internal and external disturbances, track the desired homing path more rapidly and steadily, and possesses better control performances than traditional PID controllers.

Influence analysis of time delay to active mass damper control system using pole assignment method

To reduce the influence of time delay on the Active Mass Damper (AMD) control systems, influence analysis of time delay on system poles and stability is applied in the paper. A formula of the maximum time delay for ensuring system stability is established, by which the influence analysis of control gains on system stability is further arisen. In addition, the compensation controller is designed based on the given analysis results and pole assignment. A numerical example and an experiment are illustrated to verify that the performance of time-delay system. The result is consistent to that of the long-time delay control system, as well as to proof the better effectiveness of the new method proposed in this article.

A Comparative Study of Si-BaSO4 and Si-CaSO4 Pyrotechnic Time-Delay Compositions

Slow-burning Si-BaSO4 pyrotechnic delay compositions are employed commercially for intermediate to long-time delays. However, there is very little information on this composition available in open literature. The reactivity of this composition was therefore characterized and compared to that of Si-CaSO4. The Si-BaSO4 composition supported combustion in the range of 20–60 wt% Si in the bomb calorimeter. However, burning was only sustained between 20 and 40 wt% Si in rigid aluminum tubes, with burning rates of between 8.4 and 16 mm s−1. These values are comparable to those for the Si-CaSO4 system (6.9–12.5 mm s−1). However, the CaSO4-based formulations tended to have higher energy output and produced more transient pressure compared to the barium sulfate compositions. Both formulations were insensitive to impact, friction, and electrostatic discharge stimuli. The reaction products were a complex mixture that contained crystalline phases in addition to an amorphous phase. Although barium sulfate is insoluble in water and decidedly nontoxic, the reaction products produced by the Si-BaSO4 compositions were found to release soluble barium ions when contacted with water. This ranged from 50 to 140 mg per gram of barium sulfate reacted.

Active Control Experiment Study of a Flexible Beam with Multiple Time Delays

In this paper, active control for vibration of a flexible beam with multiple time delays is studied numerically and experimentally. Piezoelectric (PZT) patches are used as actuators, and foil gauges were used as sensors. Firstly the motion equation of a flexible beam with multiple time delays and Piezoelectric patches is presented and written into a state space form. Then the state equation is discretized and transformed into a standard form without any explicit time delay by a particular augmentation for state variables. So time-delay controller could be designed based on the standard state equation using the discrete active control method. Finally, numerical and experimental studies are presented to verify the validity of the time-delay processing method using the discrete optimal control method and the discrete variable structure control method, respectively. An experimental setup is constructed using DSP TMS320F2812. The numerical and experimental results show that the proposed time-delay controller is effective in suppressing the beam vibration. It is also applicable to both shortand longtime delays.

Performance Analysis of IEEE 802.11 DCF Based on OFDM

In order to evaluate the throughput performance of DCF about both ultra-rate and longtime delay wireless local area network (WLAN) based on Orthogonal Frequency Division Multiplexing (OFDM) modulation channel, this paper analyzes the operating principle of DCF and the throughput of system on the basis of two-dimensional Markov Model. Through theoretical analysis of the relationship among 802.11a/g throughput, the number of node and the length of data packet are acquired. Analysis, calculation and simulation are done on the influences of bit number of information carried by OFDM, free aslottime and time span of OFDM symbol on system throughput. Results of theoretical calculation and simulation testing explain that under the environment of high speed and high delay, throughput of DCF would decrease in which throughput of basic schema is generally higher than that of RTS/CTS. Furthermore, our results indicate that the longer aslotime and OFDM symbol have and the higher wireless physical channel rate is, the lower throughput of DCF is. Index Terms—OFDM, throughput, stability, CSMA/CA, DCF, Ultra Rate WLAN

Fault Diagnosis Method for a Network Control System with Long-Time Delay and Data Packet Loss Based on <i>H∞</i> Filtering

Improving network control system---NCS reliability and safety has important practical significance because NCS is a hot research subject in these years. Fault diagnosis methods are researched in this paper according to NCS with long-time delay and data packet loss. Firstly, given a NCS with long-time delay, a state observer is structured. Secondly, make the state estimation error equation equivalent to an asynchronous dynamical system having event incidence constraint according to whether the system having data packets loss. The problem of fault diagnosis is converted to filtering problem through structuring filtering residual system based on the observer, then giving a corresponding filter designing algorithm. The designed fault diagnosis filter system not only make sure the stability of the closed loop system but also make the residual systems norm less than given reduction level. Finally, the simulation results prove that the algorithm can diagnose faults effectively.