低空无线电扩频引信的测距算法研究

研究分析了扩频技术在低空无线电引信应用中的相关问题,给出了引信回波模型,提出了基于软件无线电扩频引信的接收机结构和相应的测距算法,并对其性能进行了软件仿真,证明了在引信中应用的可行性。     

无线电导航系统扩频码的优选与仿真

针对无线电测距对扩频码的特殊要求,通过对传统的扩频码的比较分析,提出在无线电导航系统中引入移位序列作为扩频地址码。并对其相关特性进行仿真,通过仿真可知,它改进了测距扩频码 m 序列的互相关特性和 Gold 序列的自相关特性,从而提高了系统的性能,成为无线电导航系统扩频码的最优选择。     

高动态中频直扩接收机的设计与实现

简要说明了空战环境中的数据链系统工作原理,介绍了基于软件无线电的中频数字化扩频接收机设计方案。它采用AD6645加FPGA构成核心单元,通过不同的软件配置可实现对不同扩频信号的解扩解调     

多频脉冲测距技术在引信中的应用研究

提出了一种应用在大炸高无线电引信中的多频脉冲测距算法。建立了多频脉冲测距模型；提出了基于相位比对的多频脉冲测距算法，给出了该算法的参数选择方法；从理论上对算法的性能进行了分析；对测距算法进行了软件仿真。仿真结果表明了该算法的可行性和有效性。     

一种16APSK 信号的载波恢复方案设计

针对多幅度高阶 APSK 信号对多普勒频偏的敏感性和载波恢复算法的复杂性,为了探索适用于 APSK 的载波恢复方案,借鉴高阶 QAM调制系统的载波恢复算法,提出了一种对16APSK 信号三次方非线性变换后联合使用极性判决算法和面向判决算法的载波恢复方案;仿真结果表明：该方案频偏捕获范围大,能达到系统符号率的5．4％,稳态抖动方差较小为0．6,具有较强的实用价值。     

序列分割技术在无线电定位中的研究

文中研究了一种无线电定位的新方法，该方法首先将直接序列的扩频信号分成两路低速的窄带信号，然后每路窄带信号再调制互相正交的载波发射，在接收端恢复出原来的高速直扩信号，再使用常规方法得到传输时延，测量出目标的距离。通过分析和仿真，将常规直扩系统的性能和该扩频测距系统的性能做了比较，结果证明在码噪声可忽略的情况下，该方法在带宽仅占常规直扩系统一半的情况下，能够达到与常规直扩测距系统几乎完全相同的测距不确定性，有效地利用了频谱。     

GPS软件接收机相关技术研究

随着卫星导航接收机的发展,软件定义的接收机因其设计的灵活性成为下一代导航接收机的发展趋势。研究了基于GPS软件接收机结构方案;采用基于FFT的并行码相位搜索算法处理卫星信号的捕获问题;分析基本锁相环的原理,并设计可用于软件接收机的码跟踪环和载波跟踪环;根据GPS完好性的要求,设计GPS自主监测算法。实验表明,所设计的软件接收机能较好地对卫星信号进行捕获,可准确跟踪含有多普勒频移的载波,并能正确解调出导航数据,同时可对接收机的完好性进行监测。     

毫米波双频比相定距引信

单频多普勒体制无线电引信在对地面作用时，由于存在不具备测距能力，炸高散布大等缺点，故采用双射频收发回路的多普勒体制无线电引信。通过对双路射频回波的多普勒信号进行相位比较，完成了作用距离的测量。针对引信对地作用的需要，论述了采用双频比相探测体制的测距、测速毫米波引信的测量原理、系统构成方法、系统的关键技术及系统特点等。     

基于软件无线电平台的低轨卫星扩频通信的信号快速捕获和跟踪

本文针对低轨卫星直接序列扩展频谱(DSSS)通信中的信号同步问题,提出了基于软件无线电平台的处理方法.采用了二维联合搜索的快速算法,同时捕获扩频信号的载频和码起点.在持续跟踪中,利用匹配滤波器的相关重构,并采用频率、相位细分和多帧叠加处理的抗噪算法,较好地解决了大动态范围多普勒频移的跟踪难题,同时也对码起点的持续漂移进行了良好的同步处理.最后,给出了试验数据和分析、改进,为低信噪比下的扩频通信提供了重要的技术参考.     

高动态扩频信号捕获的多普勒补偿

分析了多普勒效应对扩频信号捕获的影响,介绍了对载波多普勒和伪码多普勒频率的补偿方法,研究了对于多普勒变化率的补偿方法,并对该方法进行了相应的仿真。仿真结果表明,引入补偿之后,能够有效减少多普勒频移和变化率对于扩频信号捕获的影响,提高捕获门限。     

Stability of the Third Generation Intensifier under Illumination

The stability under illumination of transmission-mode GaAs photocathode sealed in the third generation intensifier is investigated by use of spectral response testing instruments. The variations of spectral response with the illumination times under weak and intense illumination are compared. The variations of photoemission performance parameters are also characterized. The results show that during initial several weak illuminations photocathode behaves no evident decay and a maximum sensitivity is achieved, while under intense illumination the sensitivity of photocathode begin to decrease largely at the first illumination. The calculated performance parameters show that the variation of surface escape probability with illumination times is a direct cause of instability of photocathode. It is also found that under intense illumination peak wavelength is moved towards short-wave and peak response is decreased, which shows that the ability of long-wave response of photocathode is decreased.     

Passive Acoustic Radar for Detecting Supersonic Cruise Missile

A Passive Acoustic Radar is presented as a necessary complement to electromagnetic wave radar, which will be expected to be an effective means for detecting cruise missiles. Acoustic characteristics of supersonic flying projectiles with diverse shapes are expounded via experiment. It is pointed out that simulation experiment could be implemented using bullet or shell instead of cruise missile. Based on theoretical analysis and experiment, the ““acoustic fingerprint““ character of cruise missile is illustrated to identify it in a strong noise environment. After establishing a locating mathematical model, the technique of acoustic embattling is utilized to resolve a problem of confirming the time of early-warning, considering the fact that velocity of sound is much slower than that of light. Thereby, a whole system of passive acoustic radar for detecting supersonic cruise missile is formed.     

Design and Analysis of Test Schemes of Static Postponing Time on Shrapnels Used to Riot Control

The test scheme of static postponing time given in our actual national military test standard on shrapnels used to control riot is a nine-point test scheme on the combined action of three kinds of temperatures and three kinds of pressures,the consumed ammunitions are more excessive. Statistic analysis and tentative checkout about a lot of test data are done,feasibility gists are put forward for optimizing of the test design scheme. The optimizing design and data analysis of test scheme of the item are done by managing uniformity design theory, two scientific and reasonable six-point test schemes are confirmed. The feasibility and reliability of the optimizing design schemes put forward above are proved ulteriorly by test validating. The gained schemes not only have good design uniformity and little ammunition wastage and meet the test demand, but also have better forecast ability for the result data of other points using the mathematic models from the actual test points.     

Super-resolution Restoration of Remote-sensing Images

A novel image restoration scheme, which is super-resolution image restoration algorithm Poisson-maximum-afterword-probability based on Markvo constraint （MPMAP） combined with evaluating image detail parameter D, has been proposed. The advantage of super-resolution algorithm MPMAP incorporated with parameter D lies in the fact that superresolution algorithm MPMAP model is discrete, which is in accordance with remote-sensing imaging model, and the algorithm MPMAP is proved applicable to linear and non-linear imaging models with a unique solution when noise is not severe. According to simulation experiments for practical images, super-resolution algorithm MPMAP can retain image details better than most of traditional restoration methods; at the same time, the proposed parameter D can help to identify real point spread function （PSF） value of degradation process. Processing result of practical remote-sensing images by MPMAP combined with parameter D are given, it illustrates that MPMAP restoration scheme combined PSF estimation has a better restoration result than that of Photoshop processing, based on the same original images. It is proved that the proposed scheme is helpful to offset the lack of resolution of the original remote-sensing images and has its extensive application foreground.     

Design and Simulation of TF and TA Controller for Missile

A nonlinear terrain following(TF) and terrain avoidance(TA) controller is proposed for missile control systems. Based on classical TF algorithm (adaptive angle method), a new method for TF controller is proposed by using angle of attack. A method of obtaining terrain outline data from digital elevation map (DEM) for TF control is discussed in order to save store space. A TA algorithm is proposed by using bank-to-turn technique. The block control model, which is suitable for backstepping design, is given for nonlinear model of missile. Making full use of the characteristics of the system and combining block control principle and backstepping technique, a robust controller design method is proposed. Uncertainties in every sub-block are allowed, and can be canceled by using the idea of nonlinear damping. It is proved that the state tracking errors are converged to a neighborhood of the origin exponentially. Finally, nonlinear six-degree-of-freedom simulation results for the missile model are presented to demonstrate the effectiveness of the proposed control law.     

Design of Non-fragile Satisfactory Estimator for Linear Continuous Perturbed Stochastic Systems

The design problem of non-fragile estimator is addressed for a class of perturbed linear continuous systems. The perturbations occur on the plant and estimator parameters. The estimator designed should force the error system to achieve the desired decay rate and force the steady error variance less than the specified upper bound irrdevancy of the admissible plant perturbations and estimator perturbations. Consistency problem of the decay rate with the variance upper bound is first considered via linear matrix inequality （LMI） approach. The solution of the estimator parameter under specifications to be consistent is then discussed. The consistency condition of specifications and estimator parameter solution are transformed to feasible or minimum problems subject to a set of LMI respectively. The method is illustrated by a numerical example.     

An Improved Scene-based Nonuniformity Correction Algorithm for Infrared Focal Plane Arrays Using Neural Networks

The improved scene-based adaptive nonuniformity correction （NUC） algorithms using a neural network （NNT） approach for infrared image sequences are presented and analyzed. The retlna-like neural networks using steepest descent model was the first proposed infrared focal plane arrays （IRFPA） nonuniformity compensation method, which can perform parameter estimation of the sensors over time on a frame by frame basis. To increase the strength and the robustness of the NNT algorithm and to avoid the presence of ghosting artifacts, some optimization techniques, including momentum term, regularization factor and adaptive learning rate, were executed in the parameter learning process. In this paper, the local median filtering result of Xij （ n ） is proposed as an alternative value of desired network output of neuron Xij （ n ）, denoted as Tij （ n ）, which is the local spatial average of Xij （ n ） in traditional NNT methods. Noticeably, the NUC algorithm is inter-frame adaptive in nature and does not rely on any statistical assumptions on the scene data in the image sequence. Applications of this algorithm to the simulated video sequences and real infrared data taken with PV320 show that the correction results of image sequence are better than that of using original NNT approach, especially for the short-time image sequences （several hundred frames） subjected to the dense impulse noises with a number of dead or saturated pixels.     

Piecewise Filter of Infrared Image Based on Moment Theory

The disadvantages of IR images mostly include high noise, blurry edge and so on. The characteristics make the existent smoothing methods ineffective in preserving edge, To solve this problem, a piecewise moment filter （PMF） is put forward. By using moment and piecewise linear theory, the filter can preserve edge. Based on the statistical model of random noise, a related-coefficient method is presented to estimate the variance of noise. The edge region and model are then detected by the estimated variance. The expectation of first-order derivatives is used in getting the reliable offset of edge. At last, a fast moment filter of double-stair edge model is used to gain the piecewise smoothing results and reduce the calculation. The experimental result shows that the new method has a better capability than other methods in suppressing noise and preserving edge.     

Bistatic Sonar Localization Based on Best Linear Unbiased Estimation

A best linear unbiased estimation （BLUE） algorithm for bistatic sonar localization is proposed. The Cramer-Rao bound for bistatic Sonar and the geometrical dilution of precision （GDOP） in different conditions are given. The simulation results show that the location accuracy of BLUE algorithm is higher than the weighted least square method.     

Research on Gear-broken Fault Diagnosis in a Tank Gearbox

A fault diagnosis method of working position gear in a tank gearbox is put forward based on simulating the fault of working position gear in an actual tank, extracting the envelope of vibration signal by Hilbert transformation amplitude demodulation method, and zooming the low-frequency band to envelope signal.