一种抗多径效应的非相干无人机测距方案

多径效应是造成无人机测控系统可用性降低的重要原因之一。为了降低多径效应对无人机（UAV）测控系统的影响,提出了一种非相干测距技术方案。该方案利用了单载波频域均衡（SC-FDE）技术以及优化遥控帧与伪码速率关系及发送位置的方法,降低了机上测距数据下传误码率,同时提高了机上采样精度。经仿真验证,在反射路径信号比直达路径小6 dB且信噪比大于7 dB时,系统的测距精度满足无人机测控系统的指标要求。     

无人机空中加油过程中编队飞行控制

针对空中加油中无人机位置保持问题,进行了时变质量UAV的动力学建模与非线性控制设计。综合考虑了燃油传输对UAV的质量、惯性矩阵和质心位置的影响,基于相对于惯性系的状态变量,推导了UAV时变质量动力学方程。分析燃油传输带来的动力学影响,并设计神经网络动态逆控制律来实现UAV的位置保持,通过非线性仿真验证了控制律的有效性。     

Direct sequence spread spectrum Walsh-QPSK modulation

We present Walsh-quadrature phase-shift keying (Walsh-QPSK) pseudonoise (PN) modulation schemes for both coherent and noncoherent direct-sequence code-division multiple-access (DS-CDMA) systems, wherein the PN spreading sequences for in-phase and quadrature data in a conventional QPSK PN modulation scheme are coded by Walsh sequences indexed by a special rule to reduce the envelope variation of the transmitted signal. The signal characteristics of the two schemes are analyzed when a rectangular-shaped PN chip pulse is used, and it is shown that the proposed coherent DS-CDMA system has a constant envelope even in the presence of a transmitted phase reference. We simulate the signals to obtain the envelope variations when a spectrally efficient shaped PN chip pulse is used, and compare the results with those of conventional QPSK and orthogonal QPSK (OQPSK) PN modulation schemes. The results show that both the noncoherent and coherent Walsh-QPSK schemes have smaller envelope variations than the conventional noncoherent QPSK and OQPSK PN modulation schemes, even though in the coherent Walsh-QPSK scheme the pilot channel is added to the signal channel     

面向无人飞行器的模糊闭环控制系统研究

通过对无人飞行器的建模,针对无人飞行器自动定向和自动定高,以及速度在内的一些参数提出了改进控制结构和底层控制方法。针对自动定高、定位等水平面控制提出了串级双闭环控制结构,改进了控制的响应速度和调节精度。针对传统PID控制方法采用粒子群算法(PSO)对PID参数进行优化,与设计的模糊控制器进行对比无人飞行器在底层控制上的优劣。通过仿真对比发现,粒子群优化的PID(PSO-PID)控制效果明显强于普通PID算法,但由于无人飞行器数学模型的不确定性,弱于模糊控制器。仿真实验证明提出的方法具有快速的动态响应,并具有一定的鲁棒性。     

基于ISCP-DPSK调制的直接序列扩频技术

使用符号内连续相位差分相移键控(ISCP-DPSK)调制的直接序列扩频方法可以在实现扩频抗干扰的同时保留ISCP-DPSK调制信号的准恒包络特性和优良的频谱特性,有利于非线性和功率受限的应用场合。由于采用非相干的信号解扩解调方法,避免了低信噪比下的载波和相位估计与跟踪,简化了系统设计。计算机仿真表明,基于ISCP-DPSK调制的直接序列扩频能有效对抗本振偏离、多普勒频移等引起的符号间相位变化影响,8倍扩频和16倍扩频的增益仅与理论值分别相差0.1 dB和0.2 dB。     

基于北斗导航的植保无人机定位设计

农用植保无人机是农业植保领域的重要设备,具有效率高、运行费用低的特点,已经逐渐取代了人工植物保护,成为农业植保领域的中流砥柱.研发和制作出高精度的基于北斗导航植保无人机定位系统是将来农业植保无人机推向市场的重要冲破点.长期以来则一直是各大高校研究的热点,且在实际使用过程中获得了长足的发展.GPS是应用在多旋翼无人机上完成独立飞行的普遍使用方式.而国内的BDS定位体系是在GPS、"格雷纳斯"、"伽利略"卫星导航系统之后,由本国自主研发、拥有全部知识产权,稳定覆盖亚太地区的一种全新定位方式.     

兼顾民用无人机通信的5G网络部署方案探讨

对民用无人机通信方式的现状和存在的问题进行分析,提出5G时代无人机通信的需求,并阐述当前5G网络的部署策略,指出该策略在无人机通信方面存在的不足之处。提出5G网络部署对民用无人机通信的几种解决方案,并重点提出在现有网络部署策略的基础上,兼顾民用无人机的解决方案。同时以福州城区为例估算利用5G基站解决民用无人机通信问题的数量,进一步论证其可行性。最后提出无人机通信的5G网络部署需要考虑的问题。     

直接序列扩频系统的SystemView仿真

利用Systemview软件作为平台,对扩频通信中最典型的扩频工作方式--直接序列扩频系统(DSSS)进行了仿真分析;结果表明直扩系统的抗干扰能力远远大于普通的二进制系统,并且随着扩频增益的增大,系统的误码率越小;同时扩频系统性能的好坏很大程度上还取决于扩频码的特性.     

直接序列扩频分组映射码索引调制

针对直接序列扩频码索引调制发射端使用大量伪随机(PN)码的问题,提出了一种使用较少PN码的分组映射码索引调制方案.该方案在发射端并行设置多个调制子块独立进行幅相调制,同时集中选取各调制子块间同相、正交支路扩频所需的PN码,经索引值大小排序后依次扩频各调制子块中调制符号的同相、正交分量.分析和仿真结果表明,相同频谱效率条件下所提方案比直接序列扩频码索引调制方案使用的PN码个数更少,并在加性噪声信道下,信噪比高于10 dB时,保持着约1 dB的误比特率性能优势,并远优于空间调制在最优检测算法下的误比特率性能.     

激光供能无人机光伏接收器设计原则

小型电动无人机在情报获取、战场监视等方面发挥着重要作用,但续航时间短的问题严重限制其效能的发挥。为解决该问题,采用激光无线能量传输技术为飞行中的无人机进行充电,大幅提高其续航时间,增强作战效能。光伏接收器作为能量转换器件,是系统设计需要考虑的核心器件之一。以电动无人机激光供能系统结构原理为基础,针对小型电动无人机的特点,提出在设计光伏接收器时所应满足的具体性能要求,并对影响光伏接收器设计的五个主要因素:系统工作模式,光伏电池,接收器结构布局,散热系统和角度衰减系数进行分析,为光伏接收器的设计提供基础研究。     

直接序列扩频智能超声雷达建模与信号处理

为了解决多套相邻智能雷达设备同时使用时的相互干扰问题,提出了直接序列扩频体制雷达的方案,利用相关处理分离同频发射机的回波,提出了由相关函数生成距离-多普勒图像的信号处理方法。建立了直接序列扩频超声雷达手势识别系统的收发信号和收发机的模拟模型,其中提出的滤波器收发器模型仿真了有限带宽效应,发射波回溯的手势回波生成算法支持各种复杂调制方式的仿真。模拟实验表明采用所提信号处理方法的直接序列扩频雷达能够实现不同发射器信号的分离,并分别得到正确的手势距离-多普勒图像,达到15%以内的测量误差和约4.03cm的分辨率。     

无人机光电探测距离分析

针对低空消费级无人机这种低慢小目标,采用理论建模和对实验中飞行温度参数实测的方法,建立了目标红外辐射模型以及背景辐射参数模型,得到了与实测结果比较相符的红外探测距离。指出了对这类低红外辐射目标,对阳光反射和背景噪声必须精细估算才能得到比较准确的红外作用距离。另外,通过对分析结果的讨论,对未来无人机红外探测系统的设计提出了一些建议。     

A Model-based dehazing scheme for unmanned aerial vehicle system using radiance boundary constraint and graph model

Unmanned aerial vehicle system (UAVs) imaging has become a challenging area of research due to the dynamic atmospheric environment. The images captured by UAVs are often deteriorated by factors such as clouds occlusion, poor atmospheric illumination, and limited capability of the imaging system. To tackle problems, this paper presents a novel visibility restoration scheme for UAVs images by considering the following two assumptions: (1) The actual scene radiance of a UAVs image is bounded. (2) Pixels sharing the same appearance must have the same transmission value in a local neighborhood. Inspired by above assumptions, an image boundary constraint utilizing the median filter has been imposed on the RGB channel for the rough estimation of transmission-map in aerial images. Furthermore, a graph-model based optimization technique has been used for the transmission-map refinement. The experimental results demonstrate the efficiency of the proposed method in terms of metrics correspond to the human-visual-system (HVS).     

新型激光多波束系统供能无人机集群方案研究

由于单无人机执行任务量有限、整体效率低,故而无人机集群运动以其稳定性好,执行任务多样性,易操作,易控制等特点受到越来越多的关注。在激光供能无人机集群中,针对无人机的机载能量限制了任务的范围和时长、传统供能方式仅能完成一对一供能导致供能效率较低等问题,本文提出了一种基于光学相控阵技术的新型激光多波束供能系统,包括整体的激光无线能量传输方案、系统工作的整体流程、基于领航跟随法的无人机集群编队控制等,此方案可完成一对多的自调节供能,满足整个无人机集群的能量需求,提高传能距离及传输效率,并通过对无人机集群进行算法控制精准到达预设供能区域。对未来激光无线能量传输应用的领域和方式具有参考价值。     

无人飞行器自主降落区识别方法研究

为实现无人飞行器的自主降落,针对降落平坦区域包含特征较少、且分布没规律、形状各异等特点,本文设计了一种基于点云几何特征的快速点云分块和平坦区识别方法。该方法通过无人飞行器上的相机获取二维图像,并使用多视角立体三维重建技术获得场景三维点云,提出了以空间距离作为平滑项、以点在Z方向上的高度作为相似项的三维点云滤波算法对三维点云滤波,设计了基于点云法线和曲率的聚类分块对点云进行区域划分,然后改进RANSAC算法拟合点云平面,筛选出无人飞行器飞经场景的平坦区,并最终确定出无人飞行器的最佳降落区。最后,用本文所设计方法对戈壁人工沟壑、戈壁自然沟壑和小区花园等实拍场景图像进行降落区识别,实测结果显示识别出的区域地形起伏均小于0.125m@m~2,满足无人飞行器降落要求。     

Adaptive offloading with MPTCP for unmanned aerial vehicle surveillance system

Unmanned aerial vehicles (UAVs) are utilized in the surveillance and reconnaissance system of hazardous locations by utilizing the feature that they can freely move away from space constraints. Furthermore, the application scope of the UAVs expanded not only for simple image data collection but also for analysis of complex image data without human intervention. However, mobile UAV systems, such as drone, have limited computing resources and battery power which makes it a challenge to use these systems for long periods of time. In this paper, we propose an AOM, Adaptive Offloading with MPTCP (Multipath TCP), architecture for increasing drone operating time. We design not only the task offloading management module via the MPTCP to utilize heterogeneous network but also the response time prediction module for mission critical task offloading decision. Through the prototype drone implementation, we show the AOM reduces the task response time and increases drone operation time.     

X波段无人机载SAR发射机的设计

介绍了一种无人机载SAR发射机的设计，主要叙述了系统的构成，以及高压电源、辅助电源、调制器和监控电路的设计。解决了无人机载SAR发射机面临的体积小、重量轻、高可靠性，以及高空低气压下的绝缘和散热等设计难题。     

基于单目视觉的无人机障碍探测算法研究

针对低空飞行无人机的避障问题,研究了一种基于单目视觉的障碍物深度提取算法。在无人机前视摄像机获取的图像中,通过Harris角点检测算法提取角点作为特征点,使用归一化互相关算法进行角点的匹配,根据图像序列中特征点间距离的变化和无人机的运动计算障碍物的深度。对用于单个障碍物深度计算方法进行了改进,使用RANSAC算法区分不同深度的障碍物。仿真表明,该算法可以有效发现并区分不同深度的障碍物。     

A small unmanned polar research aerial vehicle based on the composite control method

Focusing on the polar extreme environment, a composite control method is proposed to finish the polar scientific research task in this paper. Based on the vector field and the linear quadratic regulator (LQR) control method, the small unmanned aerial vehicle can realize precise trajectory following control under wind disturbance. Through vector filed method, system constructs the corresponding vector fields for the planed research trajectory, generates the desired course inputs for the small aerial vehicle. Furthermore, the LQR control method is proposed and utilized as the inner control loop to realize the precise attitude control. Lyapunov stability arguments are used to demonstrate the asymptotic decay of trajectory following errors in the presence of wind disturbances. Experimental flight results are given to show that the small unmanned aerial vehicle can get the high trajectory following performance in the polar environment.     

Real-time vision-based tracking control of an unmanned vehicle

Recent advances in manufacturing automation have motivated vision-based control of autonomous vehicles operated in unattended factories, material handling processes, warehouse operations, and hazardous environment explorations. Existing vision-based tracking control systems of autonomous vehicles, however, have been limited in real-time applications due to slow and/or expensive visual feedback and complicated dynamics and control with nonholonomic constraints. This paper presents a practical real-time sion-based cking control system of an unmanned vehicle, ViTra. Unlike the conventional RS170 video-based machine vision systems, ViTra uses a DSP-based flexible integrated vision system (FNS) which is characterized by low cost, computational efficiency, control flexibility, and a friendly user interface.

In particular, this paper focuses on developing a framework for vision tracking systems, designing generic fiducial patterns, and applying real-time vision systems to tracking control of autonomous vehicles. A laboratory prototype vision-based tracking system developed at Georgia Institute of Technology permits the uniquely designed fiducial landmarks to be evaluated experimentally, the control strategy and the path planning algorithm derived in the paper to be validated in real-time, and the issues of simplifying nonlinear dynamics and dealing with nonholonomic constraints to be addressed in practice. Experimental results reveal interesting insights into the design, manufacture, modeling, and control of vision-based tracking control systems of autonomous vehicles.