Abstract:In order to describe the effects of interference cancellation performance on the simultaneous jamming and intercepting system quantitatively, the concept of jamming-intercepting outage probability with imperfect interference cancellation was proposed, the closed-form expression for jamming-intercepting outage probability was derived and the asymptotical expression was further obtained for ideal interference cancellation. Based on the derived performance closed-form expression, the optimal jamming power that minimizes the jamming-intercepting outage probability was identified. Accuracy of the analytical results and the correctness of optimal jamming power were justified through Monte-Carlo simulations. The results demonstrate that the jamming-intercepting outage probability decreases as the interference cancellation rate increases, decreases first and then increases as the jamming power and the transmit power increases, and the optimal jamming power increases as the transmit power increases, while the optimal jamming-intercepting outage probability converges to constant as the transmit power increases.

Abstract:The sum-difference four-channel mainlobe interference cancellation technique for monopulse radar at subarray level was studied. To this end, the signal model of four-channel interference cancellation at two-dimensional subarray level for monopulse radar was established, and a quantitative method using the signal-to-noise ratio loss of the useful signal as an indicator to characterize the angular resolution of mainlobe interference cancellation was proposed. Based on this, an analytical expression for the angular resolution of interference cancellation was further derived, and the theoretical boundary of the cancellation angle blind zone was clarified. The correctness of the analytical formula is verified by simulation and anechoic chamber experiment results. This research can provide a reference for the theoretical boundary analysis and engineering implementation of four-channel mainlobe interference cancellation technology.

Abstract:To solve the problem of multi-source interference suppression in wideband interference cancellation, the theoretical model of multi-source wideband interference cancellation was established, and the influence law of the number of sampling antennas and time-domain filters on the interference suppression performance was obtained. The effect of correlation between interference sources on interference suppression performance was analyzed, and the difference of ICR(interference cancellation ratio) between multiple interference sources and single interference source was studied, and the compression coefficient was proposed as an index to measure the interference cancellation ratio of multiple interference sources. And the interference suppression requirement of multi-source wideband interference cancellation was obtained. Experiment results show that increasing the number of sampling antennas and time domain filters can significantly improve the interference cancellation ratio of the double interference sources. Besides, in the same scene, the ICR of double interference sources is more than 10 dB lower than that of single interference source. As the power difference between two interference sources becomes larger, the compression coefficient decreases, and the interference cancellation ratio gradually decreases. When the power difference between the two sources exceeds 25 dB, the compression coefficient is close to 1, and the double interference sources are equivalent to single interference source.

Abstract:Aiming at the problem of 3D target detection in complex environment with random false target interference and strong clutter, a multi-level track before detect algorithm based on the parallel-line-coordinate transformation was proposed. Radar measurement points were placed in the normalized radial range-time plane, azimuth-time plane and pitch angle-time plane successively, the non-coherent accumulation and points filtering were carried out in each level, and each level was processed only on the results of the previous level. Based on the prior information, track constraint and track fusion were carried out to obtain the final detection result. The performance of the algorithm was verified and analyzed through simulation. The results show that the proposed algorithm can effectively filter out false measurement points and achieve the detection of real tracks under different signal-to-interference clutter ratios, measurement errors, and clutter density.

Abstract:A new subband division and reconstruction framework around the requirements of broadband communication interference cancellation was proposed, and the subband division filter banks and the reconstruction filter were designed, which simplified the conditions for complete reconstruction and made the reconstruction filter have the characteristics of complementary transition in band amplitude. The simulation and experiment results show that the reconstruction filter can effectively reduce the bit error rate of reconstructed communication signals and solve the spectrum fluctuation phenomenon in the process of subband signal splicing. Therefore, the subband division and reconstruction framework and the design of the reconstruction filter proposed can effectively reconstruct the frequency-hopping communication signal, which provide new technical route and theoretical method for subband division and reconstruction engineering practice of broadband interference cancellation.

Abstract:Under the background of noncooperative interference cancellation, through the establishment of the received signal models of different array manifolds, the representation parameters of spatial resolution were proposed to measure the resolution and cancellation ability of different array manifolds to the close reach angles of interference signals and communication signals, and the influencing factors of spatial resolution were analyzed. The new evaluation criterion for array design of noncooperative interference cancellation was provided. The array transfer factor and output signal to interference plus noise ratio were derived as the evaluation criterions of array spatial resolution. From three aspects of array configuration, number of array element and array radius, the spatial resolution of different array manifolds were analyzed by simulation. And the results were verified by experiments. The experimental results are in good agreement with theoretical analysis and simulation, and the importance of spatial resolution on interference cancellation is proved. It provides the basis for subsequent array manifold optimization and auxiliary antenna design.

Abstract:Aiming at the zero dynamic instability caused by nonminimum phase property of hypersonic vehicles, a model transformation method based on the B-I (Byrnes-Isidori) standard form was proposed to achieve decoupling of internal and external dynamics of the system. A dynamic integral sliding mode stabilization control method was proposed, an augmented closed-loop system with internal dynamics, external dynamics and dynamic parameters was formed. A sliding mode parameter tuning method was proposed to make the augmented system remain dynamic stable under different operating conditions and perturbation conditions, and the trimmed point of external output was always zero. The proposed method could accurately track the output trajectory command with zero dynamic stability, and realize the longitudinal trajectory stability tracking control of nonminimum phase hypersonic vehicle. Lyapunov stability analysis was used to prove the stability of the proposed control method, and constant dynamic pressure trajectory tracking and Monte Carlo simulations were carried out. Simulation results show that the dynamic integral sliding mode control method maintains good tracking accuracy and robustness under perturbation conditions, and stabilizes the zero dynamics of the system effectively.

Abstract:Aiming at the influence of the nonlinear part of the electric cylinder lifting servo mechanism on the servo performance of the weapon station, the optimization method of servo performance was studied based on the application background. The mechanism of gain fluctuation, gap width, unbalanced moment, and friction moment in the designable nonlinear part was analyzed. The mathematical models, design constraints, and objective optimization functions of kinematics, dynamics, and control strategies were established based on the mechanism layout and controller parameters. A sub-global parallel optimization method was proposed. The multi-objective optimization based on the interior point method was carried out for the designable nonlinear part, and the local optimization problem of local serial optimization was solved. The composite control strategy based on PI controller + DOB observer was designed separately, and the mismatch between the mechanical inertia parameters, controller parameters, and observer nominal model was solved. It is verified that the optimization results of the sub-global parallel optimization method are better on the whole and more in line with the engineering practice.

Abstract:In the multi-level interdependent network where the target node was under load, in order to prevent the occurrence of large-scale cascading failures, enhance the robustness of the network and improve the efficiency of load completion, a cascading failure model with adjustable parameters was proposed. New initial loads and node capacities were set in this model, a load delay distribution mechanism was constructed and load redistribution rules were formulated on the basis of the heterogeneity and uniformity of load distribution. The cascading failure conditions of this model were analyzed and parsed, and simulation experiments were carried out through the WS-BA interdependent network. The results show that under a certain network capacity, the robustness and efficiency of the network can be improved by reasonably adjusting the heterogeneity and uniformity parameters.

Abstract:Traditional energy detection method is susceptible to the interference of low SNR(signal-to-noise ratio) environment in the field of spectrum sensing, and neglecting the localization of available spectrum could also affect the discriminative results of spectrum states. In order to improve the noise sensitivity and discrimination accuracy of energy detection, an adaptive energy detection method by combining wavelet-frequency domain transform was proposed. Signal was decomposed by discrete wavelet packet transform to calculate the sub-band energy; the computational complexity of the adaptive threshold was reduced by combining the norm of energy so as to facilitate comparison with the sub-band energy; the available spectrum was located by fast Fourier transform. And the method was simulated to explore the variable relationship between the adaptive threshold and different performance parameters. Simulation results show that the method has good environmental adaptability and system stability, while the detection error is smaller in different SNR environments. In addition, the frequency domain analysis of the sub-band signal to achieve the reordering of the normalized frequency range, which further improves the accuracy of spectrum sensing.

Abstract:After establishing the infrared radiation ellipsoid modal of plume, the way for calculating IR (infrared radiation) of the fight plane was improved and the space distribution curve of IR in the 3～5 μm band of a certain type of fight plane was obtained. The curve showed that there were four directions which had the same maximum IR at the plane nose and the plane rear. Considering the IR absorption of O₃ in the 3～5 μm band, the IR transmitting obstruction by the ground and the detecting object in outer atmosphere. The IR atmosphere transmitted model in the 3～5 μm band was further improved with the concept of the IR transmission distance in the atmosphere.Taking the infrared system constructed by two kinds of infrared detectors with different normalized detection degrees as an example, the curve of the operating distance to fight plane varying with the detection direction was simulated. The calculation results show that the extreme value of the operating distance for the infrared system to the fight plane is not in the direction of the extreme value for the IR of the fight plane, and when the operating distance of the system is long, the influence of atmospheric attenuation on the operating distance will exceed the influence of the IR of the fight plane.

Abstract:In precise testing and control occasions, a stable air pressure supply is often required. However, the use of pressure regulating valves has low accuracy and slow response, which cannot meet the requirements of high-precision air supply and is difficult to deal with leakage situations. A high-precision constant pressure control system based on Fuzzy PI was designed for small volume chambers by using a proportional valve with high frequency response. In order to verify the effectiveness of the system under leakage conditions, an additional proportional valve was connected to the chamber to carry out a series of experimental studies under three conditions of confinement, constant leakage, and variable leakage.The results showed that the designed constant pressure control system can adapt to a variety of harsh operating conditions. The maximum steady-state errors of the pressure control for the 10 L, 20 L and 30 L chambers were around 610 Pa, 550 Pa and 490 Pa under the condition of greatly varying leakage, respectively. The pressure control precision achieved was close to the precision of the pressure sensor itself, much higher than the precision regulated by the traditional precision pressure reducing valve, and much faster in response. In addition, the test results also showed that the designed controller has good adaptability to the chambers with a volume range of 10 L to 30 L.

Abstract:Aiming at the problem that the dual-channel configuration of the traditional GNSS-R(global navigation satellite system-reflected) passive radar system has a large amount of computation in signal processing and a high hardware cost in engineering implementation, a blind detection method of the weak target echo of single-channel GNSS-R passive radar based on higher-order cyclic cumulant was presented. Strong direct wave signal was extracted from the single-channel mixed signal using the principal component analysis method. Higher-order cyclic frequency of weak target echo was estimated by higher-order cyclic frequency of direct wave signal. Weak echo signal was extracted from the single-channel mixed signal based on its different characteristics of higher-order cyclic frequency from other signals, so that the object detection was realized by matched filtering. Simulation results show that the proposed method can effectively extract the weak target echo without prior information, and has better target detection performance compared with the traditional two-dimensional matched filter target detection method.

Abstract:To study the influence of dynamic characteristics of the arresting hook of carrier-based aircraft on arresting results, the rigid body dynamics model of the plane motion carrier-based aircraft was established. The rigid body dynamics model of the spatial motion arresting hook was established considering the effect of longitudinal cushioning of the arresting hook. Lagrange′s equation of first kind was employed to establish the revolute joint model of the carrier-based aircraft and the arresting hook, and then the dynamics models of the system consists of the carrier-based aircraft and its arresting hook were established. The models were united with dynamics model of arresting gear to form the complete blocking dynamic simulation model. The experiment of the arresting process of aircraft was carried out. The experiment results and simulation results of the arresting process were compared and analyzed. The results demonstrate the effectiveness and accuracy of the dynamics model of the carrier-based aircraft and arresting hook, and reveal the significant influence of characteristics of the arresting hook on arresting overload.

Abstract:In order to ensure the successful on-orbit scientific test mission of TianTou-5 satellite, the possible risks of each component of the satellite propulsion system were systematically and comprehensively evaluated from the perspectives of incidence and severity by using failure mode and impact analysis methods. According to the working characteristics of the satellite propulsion system, a set of fault detection and location methods were proposed according to its on-orbit working state and standby state respectively. The effectiveness of the method is verified in the on-orbit practice, and the healthy operation of TianTuo-5 is successfully guaranteed, and valuable experience is accumulated for the fault diagnosis of the satellite propulsion system in the future.

Abstract:Based on the synchronous orbit precession characteristics, the constellation evolution of Starlink phase Ⅰ and phase Ⅱ was analyzed, the problems of multiple Walker-δ sub-constellation configuration were revealed, the mechanism of the recursive orbit and common track constellation configuration of Starlink phase Ⅲ was studied, and the coverage characteristics was simulated and analyzed. Results show that:the recursive orbit and common track satellite chains with different inclination can achieve synchronous precession with small differences in orbital altitude, and have continuous and compact ground coverage bands, which has the obvious advantages of more stable configuration and better coverage performance compared to the multiple Walker-δ sub-constellation configuration, especially suitable for giant LEO internet satellite systems. This study can provide a reference for accelerating the construction of similar satellite systems in China.

Abstract:A thermal simulation model of 5 A emission current hollow cathode was established by using finite element method, and the model verification and temperature analysis under typical working condition were investigated. The results show that the model can better reflect the energy transmission process inside the hollow cathode. The comparison error between the simulation results and the test results is less than 5%. The temperature difference of hollow cathode is mainly caused by heating current. The ambient temperature mainly affect the external components of hollow cathode, and the high ambient temperature under the influence of solar irradiation is more conducive to the start-up of the thruster. When the hollow cathode is heated and in self-sustaining discharge state, the temperature of the emitter reaches 2 122 ℃ and 2 126 ℃ at the ambient temperatures of 0 ℃ and 94 ℃, respectively, which is close to the temperature resistance limit of the emitter. Therefore, the hollow cathode must avoid the extreme condition.

Abstract:Aiming at the fatigue fracture problem of light Al-Li alloy in service environment, the third generation aluminum-lithium alloy 2195-T8 was taken as the research object. Experimental and simulation of the fatigue crack propagation behavior of the third-generation 2195-T8 Al-Li alloy with defects was investigated by constant amplitude tensile fatigue test and equivalent crack model. The results show that the fatigue crack starts at the bottom of the defect, and the crack growth rate is the fastest in the surface length direction, but the slowest in the depth direction. The fatigue fracture of 2195-T8 aluminum-lithium alloy has a typical delamination phenomenon, and the delamination of alloy greatly hinds the crack tip depth direction expansion, resulting in crack bifurcation. After the crack bifurcation, the propagation rate increases sharply, and the plastic region volume at the tip increases rapidly, which makes the alloy enter the rapid fracture zone. The above results show that the fatigue life of 2195-T8 Al-Li alloy with defects is reduced by crack propagation inclination and delamination.

Abstract:To study the transverse combustion instability characteristics of the rocket combustor, numerical simulations of transverse combustion instability in a model rocket combustor were conducted based on the detailed chemical reaction mechanism (GRI Mech 3.0) and the flamelet-generated manifolds method. Accuracy of the numerical model was verified by comparing it with the experimental data. Pressure field was analyzed by the dynamic mode decomposition method, and the dynamic characteristics of the flow fields were investigated. Driving characteristics of combustion instability were quantitatively estimated by Rayleigh index. Result shows that the transverse combustion instability that occurred in the experiment can be effectively captured by the numerical model. Dominant frequency identified by the numerical study differ from the experimental value by less than 1%. Transverse pressure oscillations in the combustion chamber are coupled with that the longitudinal mode in the oxidizer post, leading to the pulsated propellant mass flow rate. Driving regions of combustion instability are mainly located on both sides of the combustion chamber, and the most marginal injectors played a critical role in keeping combustion instability. Heat release pulsations which periodically provide the energy source for the pressure oscillations are highly enhanced by the interactions between the propellant and the sidewall of the combustion chamber. And the combustion instability limit-cycle is formed.

Abstract:When estimating the maximum transmission delay Δt between adjacent nodes according to TSN (time-sensitive networking) standards, it was inevitable to introduce additional ineffective waiting time, which was referred to as “bubble delay”. The negative effect of bubble delay on increasing the end-to-end delay and decreasing the planning success rate was analyzed, and the precise measurement method of Δt was proposed for the first time based on analyzing the delay composition of Δt in fine granularity. Based on the exact Δt, the bubble delay caused by TSN planning was eliminated. A real test environment was built based on two customized TSN switching devices. The test results show that the bubble delay accounted for 26.4% of the end-to-end delay at least, and the planning success rate increased by 8.9% to 39.1% after eliminating the bubble delay.

Abstract:RMT (reconfigurable match table) is a programmable pipeline architecture for packet processing. In order to enable the programmable data plane to support more different network protocols, the deparser based on RMT was extended. A protocol-independent network slicing programmable data plane model was formed by using the extended deparser and two RMT pipelines. Since reduced instruction set was used in RMT architecture and complex instruction set was used in the extended deparser, the extended architecture was called HiRMT(hybrid-instruction RMT). HiRMT can support segment routing IPv6, multiple semantics for SID(segment ID), micro SID, multi-protocol label switching and virtual extensible local area network. This architecture has broad application prospects. The performance of the deparser module was tested on the Corundum prototype platform, and the results show that the extended deparser can process the packet size up to 512 B with a throughput of 100 Gbit/s with fewer resources.

Abstract:An efficient multi-level parallel training method suitable for training MiniGo agents on large-scale heterogeneous computing platforms was proposed, including task level parallelism between nodes, CPU-DSP(central processing unit-digital signal process) heterogeneous parallelism and DSP core parallelism. Efficient input/output deployment and eliminated the bottleneck of network communication were realized. A heterogeneous computing memory management oriented to CPU-DSP shared memory structure was proposed to reduce the data handling between heterogeneous devices. Shared memory programming optimization was realized, and the dense convolution calculation operator acceleration optimization was realized by DSP. Results show that compared with 16 core CPU calculation, the maximum acceleration ratio of single core DSP operator acceleration is 16.44. In this method, the scale of computing nodes is expanded from 1 067 to 4 139, the time required to reach the given termination condition is reduced from 43.02 h to 16.05 h, and the expansion efficiency is 69.1%. Evaluation shows that this method can realize the efficient parallel training of MiniGo on large-scale heterogeneous computing platforms.

Abstract:A parallel rendering algorithm based on wrapping surface reconstruction was proposed for large-scale particles in distributed environments so as to visualize the particles in high quality. In the algorithm, particle clusters were represented and then rendered in the form of a series of continuous surfaces, where the distribution of the physical variable was also shown. The algorithm was parallelized in distributed environments, thus more than a hundred million particles can be visualized using a lot of processing cores. In terms of algorithm implementation, the issue of inter-block cracks during parallel computation was be solved, and the method for rapidly finding adjacent particles was presented. Meanwhile, based on visibility culling, the particle data was filtered and thus the rendering efficiency was improved. As a result, smooth surfaces with lighting can be used to expressively exhibit inner structures and physical variable distributions of particle clusters for large-scale particles. Experiment results demonstrate that using the proposed algorithm, the rendering of more than 100 million particles is realized in 5 seconds on 512 processing cores with about 60% parallel efficiency. The proposed algorithm has been successfully applied to practical simulation applications such as massively parallel non-equilibrium molecular dynamics simulations.

Abstract:For the problem of workflow job scheduling, the critical path method was proposed to predict the execution time of the workflow and allocate resources. The parallel application directed acyclic graph was used to describe the relationships among the sub-jobs of a workflow in the workflow execution time prediction algorithm. Based on this order, the system resources were logically allocated to the sub-jobs. According to the characteristics and resource allocation information of sub-jobs, the gradient boosting decision tree-based algorithm was used to predict the execution time of sub-jobs, and the critical path of workflow was calculated. The sum of the completion time of all sub-jobs on the critical path is the execution time of the workflow. If the predicted workflow execution time satisfies the user′s requirements, job scheduling was executed according to the sub-job execution sequence and resource allocation scheme, and the workflow was executed. Comparative experiments show that the prediction errors of the execution time of two workflows are 5.72% and 1.57%, respectively. Compared with the default scheduling algorithm of Spark, the workflow scheduling algorithm reduces the completion time of the two workflows by 15.71% and 15.44%, respectively.