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141.
随着全球卫星导航系统在经济、军事、国防、民生等领域的广泛发展,提高卫星导航系统的可靠性、安全性和鲁棒性成为当今研究的热点。本文介绍了卫星干扰信号的类型以及相对应的抗干扰和欺骗检测技术,在此基础上分析比较了各个技术的优缺点、实现难度和抗干扰效果,最后对未来研究的重点和方向进行了展望。 相似文献
142.
Generally, the channel capacity of a MIMO system is closely related to its Channel Characteristic Matrix (CCM). In most current studies, the CCMs are formed by an independent identical distribution (i.i.d) model with Rayleigh or Rice distribution and nevertheless incomplete and inaccurate to describe a Broadband Dual-orthogonal Polarized MIMO Land Mobile Satellite (BDM-LMS) channel. In this paper, we build up the BDM-LMS channel model combining a 4-states broadband LMS channel model, time selective fading features, Channel Covariance Information (CCI) model and polarization correlation between antennas. Modeling steps of the channel model are introduced. The main emphasis is placed on the effects of the factors on the channel capacity in BDM-LMS system, such as antenna numbers, temporal correlations, terminal environments, elevation angles and polarization correlations between the DPAs. We provide simulation results to illustrate the effects of these factors through comparisons of the transmit rate, Ergodic Capacity and Outage Capacity. Moreover, the MIMO outage capacity advantages, indicating the benefits of MIMO compared with SISO systems under the same channel condition, are also studied under i.i.d and BDM-LMS channel. 相似文献
143.
Ji-Yen Cheng Chien-Chih Chiang Yah-Ru Cheng Hsuan-Shen Chen Leh-Jame Lin Ta-Chau Chang 《中国化学会会志》1997,44(2):97-100
The spectral features of satellite holes are used to investigate 9-aminoacridine-DNA interactions. The hole depths of the outer ring vibronic modes are reduced more than that of the inner ring vibronic modes, implying that inner ring motion is less perturbed than outer ring motion. As a result, the mode coupling between the inner ring and outer ring is reduced upon binding to DNA. However, similar hole frequency and width of the satellite hole corresponding to the NH2 mode upon binding to DNA imply that the amino group of 9-aminoacridine sits outside the DNA. 相似文献
144.
Magnetic torque attitude control of a satellite using the state-dependent Riccati equation technique
Mohammad Abdelrahman 《International Journal of Non》2011,46(5):758-771
A non-linear attitude control method for a satellite with magnetic torque rods using the state-dependent Riccati equation (SDRE) technique has been developed. The magnetic torque caused by the interaction with the Earth's magnetic field and the magnetic moment of torque rods plays a role of the control torque. The detailed equations of motion for this system are presented using angular velocity and quaternions. The SDRE controller is developed for the non-linear systems which can be formed in pseudo-linear representations using the state-dependent coefficient (SDC) method without linearization procedure. The aim of this control system is to achieve a stable attitude within 5°, and minimize the control effort. The stability regions for the SDRE controlled satellite system are estimated through the investigation of the stability conditions developed for pseudo-linear systems and the application of Lyapunov's theorem. For comparisons, the Linear Quadratic Regulator (LQR) method using the solution of the algebraic Riccati equation (ARE) is also applied to this non-linear system. The performance of the SDRE non-linear control system demonstrates more robustness and stability than the LQR control system when subjected to a wide range of initial conditions. 相似文献
145.
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). 相似文献
146.
Ag-impurity effects on the first- and second-order quadrupole interaction (QI) at 23Na site in an isomorphic mixed system, Na1−xAgxNO2 (x=0, 0.0084, 0.026, 0.079, 0.094, 0.16), have been investigated by employing 23Na (I=3/2) magic angle spinning nuclear magnetic resonance (MAS NMR) technique. The central transition (CT) and satellite transition (ST) are simultaneously observed with this system. From the spectral analysis, the quadrupole parameter and its distribution width are obtained as a function of Ag concentration. From the intensity loss of CT MAS centerband and of the envelope function of ST MAS sidebands due to impurities, the range of their influence on the second- and first-order QI is estimated. The estimated ranges contain the second and first neighbouring Na sites from the resonating 23Na nucleus for the first- and second-order QI, respectively. 相似文献
147.
148.
当移动自组织网用户通过网关经卫星网络发送数据时,存在卫星链路的长传播时延、随机丢包以及移动终端的移动性引起链接的间歇性中断,导致TCP触发拥塞控制机制而降低传输性能降低。针对以上卫星网络的特点,提出了TCP M-Veno方法。在发送端对TCP Veno进行优化改进使得它能够缓解卫星网络中长的传播时延和随机丢包的影响。在网关中结合M-TCP算法来解决卫星融合网络移动终端间歇性中断。仿真表明,所提出的TCP M-Veno比NewReno、Veno以及M-TCP有更好的传输性能。 相似文献
149.
国际标准ISO/IEC9646定义了四种端系统抽象测试方法,其导出的测试框架无法满足第三代对地球同步轨道移动无线接口( Geostationary Earth Orbit Mobile Radio Interface,GMR-1 3G)协议栈测试关于实时性和跨平台性的要求。为了解决这一问题,对中科院提出的“钳形渡口测试法”进行研究,提出了基于GMR-1 3G协议栈的扩展“钳形渡口测试法”,并在实际的协议栈开发中得到应用。在总计与实时性相关的255个测试例执行中,测试通过率为100%。同时,由于利用统一测试框架和统一测试例脚本,既服务于仅有主机的协议逻辑流程测试又服务于仿真真实环境的板级测试,体现了较好的经济性。 相似文献
150.
过程控制技术应用于航天器地面系统开发过程已成为航天领域研究的热点问题。本文基于航天卫星遥测数据管理与应用系统的设计过程,研究了航天卫星遥测数据管理与应用系统设计过程的基本框架,分析了系统结构,以模块化化设计的理念,搭建了遥测数据管理系统的设计过程,给出了各模块系统的定义和功能结构,分析了系统模块的通信协议,最后对系统设计过程的基线确定和基线变更给出了统一的管理过程设计。 相似文献