自由空间激光通信及其关键技术

阐述了自由空间激光通信的概念以及激光通信的优点和特点,介绍了激光通信的发展及其研究现状,并详细地论述了激光通信的关键技术,说明了在我国开展激光通信研究工作的必要性和可行性．     

机载激光通信特点与应用简介

机载激光通信由于平台特性,受到外部环境约束较多,需要攻克的技术难题也较复杂,但作为未来自由空间光网络的重要节点,机载平台地位越来越重要,得到普遍关注。总结机载激光通信的特点,重点介绍三项关键技术,最后简要展望机载激光通信的应用前景。     

空间光通信ATP系统中的跟瞄技术

在空间光通信中,为实现准确捕获和高精度跟踪,ATP系统采用复合轴控制技术。复合轴控制系统的主轴控制,即粗跟踪控制, 其系统由速度环路和位置环路组成, 控制过程由TMS320VC5416 高性能DSP芯片来完成。仿真和实验结果表明,主轴控制系统的跟踪精度在1 以内,满足ATP系统对精度的要求。     

无线光通信系统捕获、瞄准和跟踪研究进展

无线光通信是指以光波作为载体在自由空间中传递信息的技术,具有带宽高、成本低和安全性高等优点。捕获、瞄准和跟踪(acquisition, pointing and tracking, APT)系统是建立无线光通信系统的前提,简单、可靠、动态性能好的APT系统可以克服由机械平台震动及外界环境变化对无线光通信系统的影响。因此,需要对APT系统进行较为深入的理论和实验研究,从而设计出一种适合无线光通信的捕获、瞄准和跟踪方法。本文分析了国内外在捕获、瞄准、跟踪方面的研究成果,同时介绍了西安理工大学在自动瞄准方面所做的工作,主要包括初始捕获系统、非共视轴控制系统、光束检测系统等方面的进展,以及1.3 km、5.2 km、10.2 km、100 km距离链路的外场实验,验证了APT系统的有效性。最后展望了无线光通信中APT的发展。     

基于MSComm控件下的激光跟踪系统串口通信研究

为了实现控制台对激光跟踪系统的测量控制,设计了一种基于MSComm控件下的串口通信.控制台与激光跟踪仪之间采用了两个串口进行连接,通信协议为RS422,串口一发出触发信号,串口二进行信号采集,整个编程环境在Delphi下进行,程序中通过MSComm控件采集信号和对信号进行处理,给出了程序部分关键代码.通过实验测量,程序运行良好,最终达到了对激光跟踪仪角度信号的提取和对被测物体角度测量的目的,系统有良好的测量精度和灵敏度.     

激光通信精跟踪中PZT驱动器非线性的研究

为了保证空间激光通信的顺利进行,精跟踪单元中PZT驱动器的设计至关重要。PZT驱动器具有位移分辨率高、体积小,响应快、不发热等优点,但其固有的迟滞、蠕变和非线性,严重影响了它的定位精度,本文通过采用DSP为主控单元建立闭环系统对PZT内在的非线性进行控制补偿,对实验的结果进行仿真验证。     

激光通信中雨滴、烟雾信道相干带宽特性研究

本文选用合理的模型模拟了大气信道中雨滴、烟雾带来的相干带宽,并进行了数值计算。结果表明:对于雨滴、轻雾信道,相干带宽很宽;而对于烟雾浓度较大的信道,信道的相干带宽应引起激光大气通信的重视。     

激光跟踪测量系统

介绍了激光跟踪测量系统的组成、工作原理、测量方法,并就其使用中应注意的问题作了阐述.     

四象限探测器的信号光捕获与跟踪技术研究

针对空间激光通信系统小型化设计的需求,提出了使用四象限探测器实现捕获与跟踪的方案。通过分析四象限探测器上光斑的位置分布,推导了三种光斑分布的4QD捕获牵引模型,通过对4QD光斑位置的解算以及与跟踪机构的精准标定,实现了4QD的高精度跟踪。在实验室基于一台激光终端与系统测试平台,对四象限探测器的捕获与跟踪方案及性能进行了实验验证,测试结果表明,在实验室动态条件下,用4QD作为捕获及跟踪探测器,捕获概率高达100%,跟踪精度优于3μrad,验证了该方案的可行性,为激光终端小型化设计奠定了基础。     

大气激光通信机的设计

光束发散角和接收口径是大气激光通信机设计的主要参数。根据高斯光束的光强分布特性,分析激光大气通信中主要的几何扩展损耗,并提出了基于该损耗的光端机设计新方法。通过对几何扩展损耗与发散角、接收口径的相互关系数值分析,确定出适合于数公里级大气激光通信机的主要参数:光束发散角可取0.8mrad～1.2mrad,接收口径为120mm。研制了155Mbps,4km大气激光通信机,初步实验结果表明在能见度大于4km的情况下,系统性能满足误码率低于10-9要求。     

深空光通信中恒星信标的捕获跟踪技术研究

提出一种深空光通信系统的信标捕获、跟踪方案,该方案是以恒星作为信标,根据恒星在惯性坐标系中的绝对位置信息,基于航天器和地球星历表、航天器的姿态信息来进行下行光束瞄准方向的精确控制。理论分析和计算机仿真都表明,星敏感器的测量精度和焦距,下行信号光的束散角将影响激光链路成功建立概率。下行信号光束散角为30μrad,星敏感器视场为8°×8°,焦距为143mm,恒星的中心位置测量精度达到0.10个像素时,链路成功建立的概率达到96.4%,表明该方案是可行的。     

一种全新的激光自动跟踪方法在激光移动通信中的应用

介绍了传统激光移动通信的特点及其不足，提出一种基于MOEMS(微光机电系统)技术的全新的激光自动跟踪方法。给出一个基于这种方法的激光移动通信系统实例，这种系统结构简单、体积小、重量轻、功耗低、控制简便，在一定的角度范围内能够自动跟踪目标实现移动通信。实验研究结果表明，这种系统能够很好地满足激光移动通信所要求的功能。     

A hierarchical classification scheme to define and order the design space for integral snap-fit assembly

The diversity of integral attachment snap-fit feature types (e.g. cantilever hooks, bayonet-fingers, compressive hooks, annular snaps, and others), and their possible combinations, sizes and locations and orientations on parts to enable assembly has made it appear that design possibilities may be unbounded. Attempts at understanding, no less optimization, seemed intractable. This paper presents a hierarchical classification scheme that brings order to the design space, and uses that classification scheme to define boundaries and size of the design space for achieving attachment at a level above feature detailing. Classification is based on the essential geometry of parts being assembled. The result is surprising order and simplicity, and the ability to reduce viable options for any assembly situation to a number (e.g. 8–10) that will permit true optimization.     

Using clustered assembly elements in the estimation of potential design for assembly benefits

This paper addresses the variation problem in design for assembly (DFA) benefits in different products. It investigated 12 product cases that employed DFA methodology in their redesign and found that DFA benefits correlate with certain product assembly properties. It explored the correlation relationships using assembly factors consisting of clustered manual handling and insertion assembly elements. Two sets of correlation models for estimating potential DFA benefits were developed. An example is provided to illustrate the estimation procedure and its result.     

Reciprocal path-scattering effects for a ground-based, monostatic laser radar tracking a space target through turbulence

A phenomenological model is developed for the strength and spatial width of the coherent intensity peak of backscatter produced by reciprocal path scattering through atmospheric turbulence. The model is applied to a ground-based, monostatic laser radar tracking a space target under the condition of optical atmospheric turbulence saturation.     

Optimum divergence angle of a Gaussian beam wave in the presence of random jitter in free-space laser communication systems

The average bit error rate (BER) of optical communication systems is considered in the presence of random angular jitter. First, the received power and the BER in the absence of jitter are reviewed. Then the average BER is obtained in the presence of circularly symmetric, normally distributed jitter by using the probability density function of the optical signal. By minimizing the power penalty for average BER, the optimum ratio of the divergence angle of the laser beam to the random angular jitter at the desired BER is obtained. An analytic approximation of the optimum ratio is derived as a function of the desired average BER. The results can be used for designing the link budget of optical communication and tracking channels in the presence of jitter.     

Channel correlation of free space optical communication systems with receiver diversity in non-Kolmogorov atmospheric turbulence

Spatial diversity as an effective technique to mitigate the turbulence fading has been widely utilized in free space optical (FSO) communication systems. The received signals, however, will suffer from channel correlation due to insufficient spacing between component antennas. In this paper, the new expressions of the channel correlation coefficient and specifically its components (the large- and small-scale channel correlation coefficients) for a plane wave with aperture effects are derived for horizontal link in moderate-to-strong turbulence, using a non-Kolmogorov spectrum that has a generalized power law in the range of 3–4 instead of the fixed classical Kolmogorov power law of 11/3. And then the influence of power law variations on the channel correlation coefficient and its components are analysed. The numerical results indicated that various value of the power law lead to varying effects on the channel correlation coefficient and its components. This work will help with the further investigation on the fading correlation in spatial diversity systems.     

Quality assessment of coarse models and surrogates for space mapping optimization

One of the central issues in space mapping optimization is the quality of the underlying coarse models and surrogates. Whether a coarse model is sufficiently similar to the fine model may be critical to the performance of the space mapping optimization algorithm and a poor coarse model may result in lack of convergence. Although similarity requirements can be expressed with proper analytical conditions, it is difficult to verify such conditions beforehand for real-world engineering optimization problems. In this paper, we provide methods of assessing the quality of coarse/surrogate models. These methods can be used to predict whether a given model might be successfully used in space mapping optimization, to compare the quality of different coarse models, or to choose the proper type of space mapping which would be suitable to a given engineering design problem. Our quality estimation methods are derived from convergence results for space mapping algorithms. We provide illustrations and several practical application examples. This work was supported in part by the Natural Sciences and Engineering Research Council of Canada under Grants RGPIN7239-06 and STPGP336760-06.