10.6μm激光大气通信的自动瞄准与跟踪

激光大气通信双端的自动瞄准与跟踪，是开发激光大气传输信道、赖以传送大容量信息的一个关键问题。本文在分析扰动大气对光束瞄准跟踪所产生的影响的基础上，提出了适于大气激光通信的跟瞄系统结构和设计准则，建立了跟瞄系统模型，合理地设计了数字式瞄准跟踪系统，并给出了光束跟踪系统的实验结果。１０．６μｍ大气通信瞄准问题，国内外还未见有更深入的研究报告。     

利用极大似然法统计回波信号实现光束闭环瞄准实验研究

瞄准偏差和光束抖动是光束瞄准系统中的两个最重要的误差。对以高斯光束和高斯抖动为基础的光束瞄准目标时产生的光回波信号进行数学建模;结合极大似然估计算法理论,建立并完善了基于回波信号的光束瞄准误差估计模型;并编写程序实现了Monte Carlo模型仿真,搭建了实验室平台。仿真和实验结果表明,极大似然估计算法表现出了优良的性能,能够同时准确地估计出瞄准偏差和光束抖动,信号样本越大其估计精度越高,且实验结果和仿真结果吻合得很好。在此基础上,根据实时偏差估计实现了实验室光束闭环瞄准实验。     

回波信号积分法统计光束偏移误差

激光瞄准系统主要存在的瞄准误差是偏移误差和抖动误差,解决好这两种误差可以使光束能够准确瞄准目标物体,并且在传输过程中减少信号的损失.介绍了一种新的光束瞄准技术,该方法建立在光束远场光强的高斯分布和光束抖动的高斯分布基础上,利用回波信号的统计得到视轴的偏差,精度可以达到5μrad,而且不需要目标自身返回瞄准信息,也无须对目标进行扫描,试验成功验证了这种方法的可行性.     

液晶光学相控技术在卫星通信多接入中的应用

在空间激光通信、组网过程中,为了能够实现一颗卫星终端对多颗卫星终端的物理光束接入,从而使得一颗卫星能与多颗卫星实现数据分发、路由、交换等组网功能,对卫星激光通信捕跟过程中存在的多终端物理接入方法进行了研究。在基于液晶光学相控阵多波束生成能力和多波束赋形的理论基础上,设计了一种新型的多终端接入方法。该方法的核心是利用液晶光学相控阵的多波束生成与控制能力实现对多个终端的接入。对光束在远场光斑的位置信息以及接入过程中的衍射效率和能量损耗情况进行仿真来验证该方案是否满足空间激光通信终端接入要求。仿真结果发现接入过程中的衍射效率大于80%,能量损耗小于1 dB,表明该方案有效可行。     

星地激光通信链路瞄准角度偏差修正及在轨验证

在我国首次星地激光通信链路地面捕获实验初期,由于激光通信终端地面光机装调和整星安装过程中存在的系统误差,在瞄准过程中存在8mrad的瞄准角度偏差,且平均捕获时间大于40s,严重影响星地光通信链路捕获性能。基于此,利用立方棱镜坐标系为桥梁,建立了基于坐标变换的卫星本体坐标系与终端基准坐标系的修正变换矩阵,通过地面坐标系测量,最终对光束瞄准角度偏差进行了有效补偿。海洋二号卫星在轨实测结果表明,星地激光通信链路的瞄准偏差由最初的8mrad减小为0.8mrad,捕获扫描范围显著缩小,链路平均捕获时间由最初的40s减小到小于5s,明显优于国外同类型终端在轨实验性能,对卫星激光通信链路捕获性能的提高具有重大意义。     

卫星激光通信技术

文章详细介绍了卫星激光通信技术在国外的最新发展状况;阐述了实现卫星激光通信的关键技术及其解决方案,特别对捕获、跟踪、瞄准系统进行了详细的分析;最后对卫星激光通信技术的发展作了展望。     

地面对卫星瞄准精度受大气湍流的影响分析

分析了地面对卫星激光瞄准精度受大气湍流效应的影响。首先,提出了大气湍流作用下地面对卫星激光瞄准精度的概念。其次,采用多层相位屏的数值方法求解激光大气传输满足的抛物型方程,仿真研究了不同发射参数下地面对卫星的激光瞄准精度,结果表明:地面对卫星的激光瞄准精度与激光束的发射口径成正比,发射口径越大,瞄准精度越高;而与激光束的发散角成反比,光束发散角越大,瞄准精度越低。最后,比较研究了不同瞄准精度下到达卫星入瞳处的功率以及功率密度。研究成果可为开展地面对抗卫星的试验提供理论依据和数据参考。     

湍流大气中激光束抖动频率相关函数和降雨大气中激光束到达角起伏

一、引言 激光束在洁净大气中传播时，由于湍流的影响，光束波阵面到达角将作随机起伏，光束整体将作随机抖动。这些湍流效应严重影响激光大气通信和大气参数的光学法探测，所以人们对此作了大量研究。但是，对激光束在雨和湍流同时存在时传输的到达角起伏和湍流大气中双频光束抖动相关函数研究很少．而这些问题在实际工程应用中常涉及到。     

猎人机器人光通信跟瞄理论和系统研究

首次提出眼孔波通信框架,建立通信跟瞄模型,开辟了短距离光通信的新阶段.进行了信标光捕获方法研究,计算了捕获时间;计算机模拟了二维瞄准误差正态、瑞利分布,模拟了目标瞄准抖动Rician分布,推算模拟了接收透镜光阑探测衰减损失公式;提出三维瞄准误差正态、瑞利分布,提出三维瑞利叠式抖动分布,并计算出仿真结果.仿真结果表明,眼孔波通信的概念已首次建立,跟瞄抖动二维、三维理论模型及衰减模型已建立或提出.     

星地链路中的主动式自适应光学系统室内实验北大核心

针对星地激光通信链路中,由于星上负载有限,无法在卫星上安装调试自适应光学系统来矫正上行接收光束受到的湍流畸变,提出可以使用主动式自适应光学系统解决上行光束的矫正的问题。通过室内矫正实验证明了主动式自适应光学系统实现的可行性,同时为星地激光通信提供了一种改善上行光束质量的方法。     

Laser satellite communication network-vibration effect and possiblesolutions

A number of serious consortiums develop satellite communication networks. The objective of these communication projects is to service personal communication users almost everywhere on Earth. The intersatellite links in those projects use microwave radiation as the carrier. Free-space optical communication between satellites networked together can make possible high-speed communication between different places on Earth. Some advantages of an optical communication system over a microwave communication system in free space are: (1) smaller size and weight, (2) less transmitter power, (3) larger bandwidth, and (4) higher immunity to interference. The pointing from one satellite to another is a complicated problem due to the large distance between the satellite, the narrow beam divergence angle, and vibration of the pointing system. Such vibration of the transmitted beam in the receiver plane decreases the average received signal, which increases the bit error rate. We review: (1) the present status of satellite networks, (2) developing efforts of optical satellite communication around the world, (3) performance results of vibration effects on different kinds of optical communication satellite networks, and (4) seven approaches to overcome the problems caused by transmitter pointing vibration     

Analysis of optical coherence multiplexing networks for satellite communication

Free-space optical communication between satellites networked together can enable a high data rate between the satellites. Coherence multiplexing (CM) is an attractive technique for satellite networking due to its ability to cope with the asynchronous nature of communication traffic and the dynamic changes taking place in the satellite constellation. The use of optical radiation for intersatellite links creates very narrow beam divergence angles. Due to the narrow beam divergence angle, the vibration of the pointing system, the movement of the satellite, and the large distance between them the pointing from one satellite to another is a complicated task. The vibration of the pointing system is caused by two stochastic fundamental mechanisms: 1) tracking noises created by the electrooptic tracker and 2) vibrations created by internal satellite mechanical mechanisms and external environments. We derive mathematical models of signal, noise, the approximate signal-to-noise ratio, and the approximate bit-error rates of optical communication satellite networks as functions of the system's parameters, the number of satellites, and the vibration amplitude for frequency-shift keying coherence multiplexing (FSK-CM). Based on these models, we can calculate the negative impact of both the number of satellites and the optical terminal vibration on the system's performance.     

The SILEX optical interorbit link experiment

The European Space Agency (ESA) has instigated an in-orbit demonstration project known as SILEX (semiconductor laser intersatellite link experiment) using a pre-operational link between the French SPOT-4 low earth orbit satellite and the ESA Advanced Relay and Technology Mission Satellite (ARTEMIS). Such an optical communication system brings some new and challenging requirements. In particular, the communication beam, which has a divergence of around 6 μrad, must achieve and maintain a very demanding pointing accuracy in the presence of both host satellite vibration and relative satellite motion. The authors provide an overview of the SILEX project and describe a novel pointing mechanism     

双机之间激光通信ATP技术研究

机载激光通信系统中,激光光束的对准是通信能否进行的关键,采用ATP(捕获、跟踪和瞄准)技术来解决两机光端机的对准问题。主要进行了两机之间信标光捕获方法研究以及对跟踪和瞄准光学系统进行设计。给出了具体计算的原理方法和数学模型,同时对ATP系统的跟踪和瞄准精度指标进行确定。     

对准误差对前置光放大卫星激光通信系统性能的影响

发射机及接收机的对准误差都会引起前置光放大卫星激光通信系统信号的衰落,在同时考虑发射机、接收机对准误差的条件下优化系统性能非常重要。将接收机对准误差引起的空间光耦合损耗用一个高斯函数近似,并同时考虑发射机对准误差引起的对准损耗,推导出了接收光功率概率密度的近似解析表达式,应用该概率密度函数,建立了基于平均误码率原则的前置光放大卫星激光通信系统的优化模型。仿真结果表明,在给定平均误码率要求及对准误差一定时,存在一个最佳发射光束宽度、接收天线直径及空间光耦合参数,使所需的发射功率最小,采用更大的接收天线并不能降低对发射功率的要求。     

星间光通信振动对系统性能的影响——直接检测PPM调制方式

星间光通信中振动是影响系统性能的重要因素,即使其中一个卫星的瞄准系统的很小幅度的振动也可以引起整个网络的性能急剧恶化。分析了直接检测脉位调制(PPM)下振动对网络性能的影响。     

星间光通信振动对系统性能的影响--直接检测PPM调制方式

星间光通信中振动是影响系统性能的重要因素，即使其中一个卫星的瞄准系统的很小幅度的振动也可以引起整个网络的性能急剧恶化。分析了直接检测脉位调制（PPM）下振动对网络性能的影响。     

Performance limitation of laser satellite communication due to vibrations and atmospheric turbulence: down‐link scenario

In this paper, we analyse the effects of vibrations and the atmosphere on the performance of a broadband laser inter‐satellite link (BLISL) which was studied within the framework of the BLISL joint Israeli–German applied research project. The use of optical radiation as a carrier between satellites and in satellite‐to‐ground links enables transmission using very narrow beam divergence angles. Due to the narrow beam divergence angle and the large distance between the satellite and the ground station or airplane the pointing is a complicated process. Further complication results from vibration of the pointing system caused by two fundamental mechanisms of a stochastic nature: (1) tracking noise created by the electro‐optic tracker and (2) vibrations caused by internal satellite mechanical mechanisms. Additionally an inhomogeneity in the temperature and pressure of the atmosphere leads to variations of the refractive index along the transmission path. These variations of refractive index as well as pointing vibrations can cause fluctuations in the intensity and the phase of the received signal leading to an increase in link error probability. In this paper, we develop a bit error probability (BEP) model that takes into account both pointing vibrations and turbulence‐induced log amplitude fluctuations (i.e. signal intensity fading) in a regime in which the receiver aperture D₀ is smaller than the turbulence coherence diameter d₀. Our results indicate that BLISL can achieve a BEP of 10^?9 and data rate of 1Gbps with normalized pointing vibration of G_T*σ_θ²=0.05 and turbulence of σ_X=0.3. Copyright © 2003 John Wiley & Sons, Ltd.     

ATP跟瞄精度与最佳信号光发射角的研究

激光星间通信中捕获、跟踪、瞄准(ATP)技术是保障通信正常进行的关键一环，在完成捕获进入跟踪状态下，ATP的跟瞄精度是一个重要指标。然而．在实际系统中，ATP的跟瞄精度受到很多因素的制约．只能达到一定的精度。在这种条件下．信号光束发散角的选取对通信系统的整体性能影响很大。提出了影响光束发散角的三种因素，并进一步分析了在给定跟瞄精度的条件下．信号光束的发散角并不是越小越好而是存在一个最佳发散角．该发散角可以在满足通信系统指标的情况下．对发射端的功率需求最小。     

大气折射对空地卫星光通信链路影响的研究

卫星光通信被认为是解决卫星通信高码率“瓶颈”问题的唯一途径。但是在空地光通信系统中 ,由于大气温度与大气压强的随机变化 ,导致大气折射率不再是常数。当激光在大气中传输时 ,由于折射的影响 ,光束不再沿直线传播 ,而是按折射定律产生折射效应。这就使得光束到达卫星站 (或地球站 )时偏离了原来的位置 ,影响系统的通信性能。同时由于湍流的存在 ,它又会产生一些湍流效应。本文在此基础上给出了大气折射率模型 ,并由大气光路方程得出在空地卫星通信系统中 ,光束在整个大气中的传输特性。它是研究空地卫星光通信中的大气折射的重要课题