Condition-based maintenance can arrange preventive maintenance according to the operating condition of the equipment,which is an effective way to solve the degradation failure and ensure the availability of equipments.In this paper,we focuse on the core components of the UAVs and develop the condition-based maintenance model as well as replacement policy with the method of continuous-time Markov chain by dividing the deterioration into different states happened in the operational process.In the model,the maximal steady state availability of the system is used as the indicator to arrange maintenance,while the impact of the such factors as average time of the deterioration between two adjacent stages,the average detection time,the average time of preventive maintenance and the time for part replacing and etc,is also taken into account.Ultimately,the optimal frequency of testing system and the threshold of condition-based maintenance as well as the replacement policy are determined by using a recursive algorithm to solve the model according to the principle of statistical equilibrium in the steady state of Markov process.The result shows that the presented the model can describe the degradation process effectively,and can be used to optimize the maintenance policies.

Several problems on the flight control system design of Near Space Vehicle (NSV) are discussed.Firstly,the recent developments and the importance of NSV research are introduced.Then,several important problems for the NSV flight control are discussed,including:1) modeling of NSV flight motion control;2) robustness of NSV flight attitude control；3) integrated coordination control between flight attitude and centre-of-gravity motion;4) integrated coordination control between flight and engine control;and 5) anti-disturbance of flight control.The corresponding view is given and methods are proposed for solution of the problems.At last,the authors viewpoints on design principles of NSV flight control system are presented,and the significance of applying integrated coordination control idea in NSV flight control system design is pointed out.Key words：讨论了近空间飞行器飞行控制系统研究设计的几个问题。首先指出了研究近空间飞行器的国内外形势和近空间飞行器研究的重要性;接着就近空间飞行器飞行控制的几个重要问题：飞行运动控制的建模问题，飞行姿态控制的鲁棒性问题，飞行姿态与重心运动的一体化协调控制问题，飞行与发动机的一体化协调控制问题，飞行控制的抗干扰问题提出了相应的方法和看法;最后就近空间飞行器飞行控制系统的设计原则提出了自己的体会和看法，指出了用一体化协调控制的思想进行近空间飞行器飞行控制系统分析设计的重要性。

In order to solve the clutter suppression problem of MIMO radar,a rapid dimension-reduced STAP algorithm,Fast JDL (F-JDL) algorithm,is proposed.Firstly,the space-time data is reflected accurately to the angle-Doppler bins of localized processing region by employing an over-complete basis set,which is consisted of all the interested testing angles.Then the matrix block-inversion is used to dispose the clutter covariance matrix.This method combines the advantages of both the JDL dimension-reduced algorithm and matrix block-inversion.The simulation results show that:F-JDL algorithm makes full use of the advantage of MIMO radar of large DOF (Degree of Freedom),and significantly decreases the computational cost and training samples required,which presents better clutter suppression performance.

Considering the problem of trajectory prediction of low-altitude free flight targets,a new method was proposed from both strategic and tactical considerations.Based on TC report from surveillance data by ADS-B,multi-parameter offset value of target were taken into consideration,and the fading memory and moving window smoothing model were introduced into comprehensive historical information.The flight intent inference was achieved,which was suitable for low-altitude flight,then the trajectory by strategic prediction was obtained.A trajectory prediction idea based on both tactical prediction and strategic prediction was also proposed according to a new algorithm for tracking and monitoring,which can be used for predict the medium and long term future trajectory of a target.

The effective use of road information is probably the most important for improving ground target tracking.A modeling and filtering method for ground moving target tracking under road constraints is proposed in this paper.A mathematic model of road net and a process noise modification method with road constraints are given.Then the method of state and covariance correcting for a target moving from one road to another is presented based on maximum posterior probability.A variable structure of multiple models (VSMM) approach generated by adaptive filtering model of current road is proposed for reducing dynamic error between filtering model and the true path of target.Monte Carlo simulation result shows the good performance of proposed method.

In view of the problem that the back-end optimaziation for conventional incremental Graph SLAM alrgorithm cannot efficiently remove the influence of false close-loop,R-iSAM,a robust close-loop incremental Graph SLAM algorithm is put forward based on iSAM algorithm and SC algorithm.In the incremental process,R-iSAM makes a preliminary approximate calculation of the close-loop constrained conversion variables introduced at the current time,obtaining reasonable node positions of robot.In the off-line process,it makes a refined calculation of all close-loop constrained conversion variables in the current period,to judge the correctness of current-period close-loop,and lay a foundation for node optimization later on.The algorithm experiment of public data set (DS) show that under the condition of adding different types and numbers of fault close-loops,the proposed algorithm is well adaptive to different DS,and the convergence rate satisfies the real-time requirement of incremental SLAM,proving the validity of this algorithm.

Nowadays,there exist different data sources in combat effectiveness evaluation,such as simulation data,expert evaluation data,and measured data.The various data may contain different evaluation criteria,and even sometimes contain contradictory information.How to effectively fuse the different data sources to build up a robust effectiveness evaluation method has become one of the key problems in effectiveness evaluation.In this paper,different evaluation methods are used for different information sources and decision fusion is made based on DS reasoning.Considering that contradictory decisions may exist among different data sources,a revised DS evidence theoretical formula is established by revision of both the combination rule and evidence source.Thus a modified DS evidence reasoning is established.

Traditional Receiver Autonomous Integrity Monitoring (RAIM) algorithm uses integrity risk minimum criterion to determine the threshold,the threshold solving method is too conservative and may increase the risk of the continuity to aviation users.In view of the differences between the aviation users integrity requirements,a RAIM threshold optimization algorithm based on minimum total risk cost function is proposed.Taking the sum of false alarm probability and missed detection probability in hypothesis test as the total risk cost function,on the premise of ensuring RNP and RAIM availability,the total risk cost function is minimized to determine the RAIM optimize threshold and achieve the trade-off between integrity and continuity.The simulation results show that after the minimum total risk cost function trade-off,the continuity risks of users can be reasonably reduced,and the RAIM availability can be judged in the pseudorange domain.

The basic Particle Swarm Optimization (PSO) algorithm has the problem of easy to get into local optimum when used in geomagnetic navigation path planning.Based on PSO and Quantum Evolution (QE) algorithm,the Quantum Particle Swarm Optimization (QPSO) algorithm was applied to solve the problem.Combined with constraints of aircrafts and characteristics of geomagnetic matching navigation,an adaptive evaluation function was designed as fitness function.The simulation results show that QPSO has faster convergence speed and can avoid falling into local optimum effectively,which prove the availability and feasibility of QPSO for applying to path planning based on geomagnetic matching navigation.

In view of the existing problems and shortcomings of system communication in the shadow channel of vehicle-mounted Sat-com on the move(SOTM),based on the characteristics of SOTM channel,the reason for low transmission efficiency in the channel is analyzed,and an algorithm of self-adaptive control based on burst communication is put forward.According to the analysis of shadow channel,it is concluded that the original transmission method is of poor adaptability.By introducing a frame-number self-adaptive algorithm,the high pocket loss rate of shadow channel is decreased,and the communication efficiency is increased.The experimental results show that self-adaptive burst control for shadow channel is able to effectively decrease the pocket loss rate and improve the efficiency of channel communication.

By volume element dividing of the laser fuse field,a mathematical model for approximate calculation of the fuse cloud-and-fog scattering echo was established based on Mie scattering theory.The scattering echo of uniform cloud-and-fog particles as well as cloud-and-fog particles complying with certain spectral distribution was calculated out with this model.The influence of incident laser wavelength,particle concentration and spectral distribution parameters on the intensity of scattering echo was analyzed.The research results show that:1) For uniform cloud-and-fog particles,the oscillation of fuse scattering echo enhances with the increase of particle size; 2) For the same particle concentration,scattering echo of the cloud-and-fog particle swarm with large radius is significantly higher than that of the cloud-and-fog particle swarm with small radius;and 3) For laser of different wavelength and with a significant difference in the imaginary part of refractive index,the intensity of their scattering echo differs significantly,i.e.,the cloud-and-fog scattering light intensity of laser with a smaller imaginary part is significantly higher than that of laser with a larger imaginary part.The study may provide a theoretical basis for laser fuse anti-cloud-and-fog interference.

Motion features of the modern aircraft are becoming much more complex.The change of antenna coverage properties caused by the change of aircraft attitude may result the change of signal gain in the antenna frontend.The traditional method of GPS signal simulation did not take the above effects into consideration.In order to reflect the influence of carrier attitude on GPS signal,the antenna lobe pattern, coordinate system transformation and aircraft attitude were integrated together to deduce the model of GPS signal gain.This study can provide a reference for the engineering application of satellite signal simulation.

With the development of the Global Navigation Satellite System (GNSS),the number of visible satellites increases greatly.In order to lower the computational complexity of the receiver,a satellite selection algorithm is essential for choosing a subset of the visible satellites.This paper analyses the Global Dilution of Position (GDOP) of a joint distribution,which contains the N optimal distributions of four satellites and the k (k≤3) satellites in an optimal distribution of four satellites.According to the comparison of the GDOP between the joint distribution and the optimal distribution of 4N+k satellites,a four-based satellite selection algorithm is proposed,which has low computational cost and is close to the optimal.The proposed algorithm can select any number of satellites more than four through the iteration and portion of the classic satellite selection algorithm of four satellites,such as maximum-volume algorithm and four-step satellite selection method.Simulations indicate that the proposed method requires less computational cost and achieves lower GDOP than the quasi-optimal algorithm.

Considering the fact that conventional K-means algorithm is susceptible to the outliers and noise points,and lacking in robustness,a new K-means algorithm based on co-entropy is proposed. The proposed algorithm employs co-entropy as a means of local similarity measurement,and follows the co-entropy maximization principle to solve the optimal cluster centers. An iteratively reweighted optimization technique is employed to quickly find the optimal cluster centers. For outliers and noisy data points with larger residuals,they will be assigned smaller weights in updating the cluster centers. Experimental results demonstrate that the proposed co-entropy based K-means algorithm is robust,winning a better clustering effect.

Based on the analysis to ARINC763 Standard and ARINC834 Standard,and considering the flexibility and expansibility requirements to safe connectivity of current civil airborne network,we designed an Avionics Interface Application(AIA)software for the airborne network service system.The key points of the design include:1) the definition of Avionics Interface Data Communication Protocol,which integrates and expands the protocol models defined in ARINC834 by adding application registration and monitoring capability;and 2) the combination of application access control and data authentication,which refines the architecture defined in ARINC763 and reduces the system complexity.The software has already been applied in a civil aircraft development project,which can realize secure data communication between core avionic network and network service system.

In view of the problem that GNSS intermediate frequency (IF) signal has a large amount of data and the traditional data acquisition card is expensive,a new GNSS IF data acquisition system based on USB2.0 serial bus and FPGA was designed under Linux operating system,and corresponding software and hardware design were accomplished.State machine was used for controlling the read-write status of each endpoint cache in CY7C68013A chip,to accomplish the high-speed data transmission.IF data was cached through FPGA to effectively improve the system data transmission bandwidth.A complete GNSS software receiver was realized under Linux,realizing the receiver user interface software based on QT and the data graphic display window based on Qwt plug-in.The test results show that the transmission rate of this data acquisition system can be up to more than 200 Mbit/s,which effectively solves the problem of mass data transmission while reducing the cost.The software receiver satisfies the requirement for positioning accuracy,with good flexibility and adaptability,and its easy to expand and upgrade the algorithm.

Area-oriented geosynchronous orbit (GEO) IR early-warning satellite can provide reliable early-warning information in time for anti-missile operation in specified area.With the scenario of longitude and latitude ranges of early-warning area,it was proposed to deploy GEO early-warning satellite by using airspace coverage performance and positioning accuracy as the performance criterion.Firstly,a satellite airspace coverage performance model was established based on GEO satellite-to-ground coverage model,space geometry relation of GEO satellite with the specified early-warning area was then analyzed.By using geometric dilution of precision (GDOP) as the positioning accuracy measurement index,a positioning accuracy model of GEO satellite to the early-warning area was established.Finally,a comprehensive analysis is made by simulation of how different ways of satellite deployment affect the airspace coverage performance and positioning accuracy,drawing a guidance conclusion for area-oriented GEO IR early-warning satellite deployment.

The serial PCIe interface is the third-generation I/O interconnection standard.Characterized by high speed and high bandwidth,it overcomes the inherent shortcomings of traditional PCI bus in system bandwidth and transmission speed,and has a good application prospect.Use of FPGA to design PCIe bus-based data transmission can reduce the design cost of hardware and improve its integration level,as well as improving the design flexibility and adaptability by making use of the programmable feature of FPGA.Based on a brief overview of PCIe bus,PCIe hard core structure inserted into FPGA and PCIe transmission message,a solution to realize DMA transmission based on PCIe hard core inserted into FPGA is proposed,with a detailed description of the design proposal.An evaluation and analysis of the design is made,and the test results of transmission bandwidth are given.

In view of the problems in ship-borne helicopter support capability evaluation,such as the data is incomplete,and the decision-makers preference needs to be considered in evaluation,a model for evaluating the ship-borne helicopter support capability based on deviation preference method was studied.On the basis of investigation and the reality of ship-borne helicopter support,a support capability evaluation index system was constructed,and a reciprocal judgment matrix for evaluation subjects was established according to decision-makers preference.A deviation preference method was adopted in support capability evaluation,the weight of each index was redefined from the perspective of sequencing the evaluation subjects,and a deviation function of the value with preference matrix was established.Its shown by case analysis that this model is more practical and simple in process,which is suitable for current study on the support capability evaluation problem of ship-borne helicopter and is of some application value.

In order to decrease temperature related errors in MEMS gyroscope,a novel method based on array technique is proposed for temperature compensation of the gyroscope.The advantage of this method is that it is not need to measure the temperature,in stead,data fusion of the output of several gyroscopes is used to reduce the influence of temperature,and the system structure is simplified.The BP neural network optimized by genetic algorithms is used in data fusion of the gyroscope data,which compensates the error of the output of gyroscopes directly,while the zero bias and scale factors are compensated separately in general.The results of the experiments show that the method proposed can significantly reduce the error of gyroscope caused by temperature,and thus can improve the accuracy.

The binary-phase-coded echo signal is modulated by both Doppler and the echo phase displacement.Aiming at this problem,we analyzed the echo model and the power distribution characteristic of the echo signal of radar altimeter,and proposed a demodulation algorithm for the binary-phase-coded echo signal based on nadir point.In the algorithm,the Doppler and the phase displacement information of the nadir point echo was detected,and corresponding compensation was made to realize demodulation.Simulation and experiment results show that the maximum error of the Doppler frequency is less than 20 Hz and the maximum error of the phase is less than 2°.It proves that the algorithm is effective to demodulate the echo signal.

With the increase of complexity of modern embedded system software,it becomes more difficult to discover and handle all potential software faults.Practical application has shown that there are still some software runtime errors that cannot be discovered by conventional test method.A method was proposed by introducing software health management into the design of embedded system software,to improve the reliability of embedded system software.This method was realized by constructing runtime error monitoring,diagnosis and recovery models in the embedded system software.To verify its effectiveness,taking software errors occurred in 2005 in airborne ADIRU of Malaysian Air Flight 124 as an example,a software model was established for ADIRU by using AADL language,and the effectiveness of software health management was proved through this model.

At present,modeling for lifetime prediction seldom takes the effect of the drift coefficient change into consideration,which is neither reasonable nor truthful.To solve the problem,a degradation model is proposed based on Kalman filter and Wiener process.Based on which,Kalman filter and EM algorithm are utilized for parameter estimation and updating.Finally,an example of remaining useful life prediction of a gyroscope verifies the effectiveness of the proposed method.

Level of Repair Analysis (LORA) plays a significant role in Integrated Logistics Support Analysis of shipboard aircrafts,and is important for whole-system and whole-life management of the aircrafts.The current analysis model of LORA problem is insufficient for equipment mission and logistics support system.The analysis model is incomplete for LORA decision-making,and may affect the operational use and logistics support decision.To solve the problem,an analysis model of LORA is presented based on expected backorders (EBO) of spare parts.Firstly,the maintenance support mode of shipboard aircraft is analyzed.Then a multi-stage EBO model is established based on the actual situation of shipboard aircraft logistics support,and an optimization analysis model is presented based on EBO.Finally,analysis is made to the application of EBO based LORA according to an actual example.