干扰条件下的“北斗”信号解扩重构DOA估计

在干扰条件下，卫星导航抗干扰波束形成算法往往需要卫星信号波达方向（Direction-of-Arrival，DOA）的先验信息。但当存在低信噪比信号或主动干扰源时，常规的DOA估计算法性能急剧下降甚至失效。针对此问题，提出了一种被干扰信号压制的低信噪比“北斗”信号的DOA估计算法。该算法首先通过对接收信号进行子空间投影抑制干扰信号，然后对抑制干扰后的信号进行解扩重构处理，最后通过多重信号分类算法完成对“北斗”信号的DOA估计。仿真结果表明，在干扰信号干信比80 dB条件下，“北斗”信号DOA估计误差在5°以内，为下一步进行波束形成计算提供了高精度的入射角信息。     

Design and validation of robotic bionic eye with multiple flexible ropes parallel mechanism inspired by oculomotor law

Producing a stable and agile bionic eye for visual image acquisition in robotics is a challenging task. In this paper, we design a bionic eye with mirror-symmetric distribution and cross-connection of flexible ropes. This mechanism is based on oculomotor law and the physiological structure of the extraocular muscles (EOMs). Specifically, the basic structural parameters are determined by Listing’s law, and the unique connection of the flexible ropes can realize the functions of the recti and oblique muscles. Furthermore, to mimic the trochlea structure, a pulley mechanism is constructed to permit the free movement of the flexible ropes. Through simulation and physical experiments, it is demonstrated that the bionic eye mechanism can move with agility under the structural parameters. The experimental results indicate that the proposed bionic eye mechanism has a superior motion accuracy of 2.798 mm, which is 6.7% of the maximum motion distance, and the repeatable accuracy of the mechanism can up to 0.210 mm.     

An enhanced anti-disturbance attitude control law for flexible spacecrafts subject to multiple disturbances

As well-known disturbance rejection methods, active disturbance rejection control and disturbance observer-based control can effectively improve the control performances of complex systems in the presence of disturbances. However, the accurate rejection of multiple disturbances for control systems of practical engineering, for example, the attitude control system of flexible spacecraft, is still a bottleneck problem. In order to further improve the anti-disturbance capability and reduce the conservativeness, this paper proposes a novel enhanced anti-disturbance control law for the attitude control system of flexible spacecraft by combining active disturbance rejection control and disturbance observer-based control in a unified framework. More specifically, the disturbance from flexible vibration is described by an uncertain exogenous system based on the partially known information including elastic damping ratios and modal frequencies. The disturbance observer-based control is utilized to estimate and thereby reject this disturbance. On the other hand, the other disturbances such as external environmental disturbance and complex model nonlinearity are merged into a equivalent disturbance with bounded derivative, which is compensated by using the active disturbance rejection control law. Stability and robustness analysis are carried out for the disturbance observer and extended state observer. Finally, simulation results of low-earth-orbit flexible satellite are presented to verify the effectiveness of proposed methods.     

Silicon for thin-film transistors

We are standing at the beginning of the industrialization of flexible thin-film transistor (TFT) backplanes. The two important research directions for the TFTs are (i) processability on flexible substrates and (ii) sufficient field-effect mobilities of electrons and holes to support complementary metal insulator semiconductor operation. The most important group of TFT capable semiconductors are the several modifications of silicon films: amorphous, nanocrystalline and microcrystalline. We summarize their TFT properties and their compatibility with foil substrate materials.     

移动卫星通信信道多普勒频移特性研究

在分析移动卫星通信信道特性的基础上，研究增加直射分量的多普勒实时频移和多径信号入射角范围及其变化对移动卫星通信信道多普勒频移特性的影响，推导了其不对称多普勒功率谱形式，对其进行了理论分析并给出了仿真结果。     

一种基于空间到达角的卫星电子侦察信号分选方法

在建立简化的卫星电子侦察空间模型的基础上，提出了一种利用空间到达角分选卫星电子侦察信号的新方法。通过仿真实验验证了这种方法的可行性。该方法可用于密集信号的预处理。     

Evaluation of performance enhancing proxies in internet over satellite

Performance enhancing proxies (PEPs) are widely used to improve the performance of TCP over high delay‐bandwidth product links and links with high error probability. In this paper we analyse the performance of using TCP connection splitting in combination with web caching via traces obtained from a commercial satellite system. We examine the resulting performance gain under different scenarios, including the effect of caching, congestion, random loss and file sizes. We show, via analysing our measurements, that the performance gain from using splitting is highly sensitive to random losses and the number of simultaneous connections, and that such sensitivity is alleviated by caching. On the other hand, the use of a splitting proxy enhances the value of web caching in that cache hits result in much more significant performance improvement over cache misses when TCP splitting is used. We also compare the performance of using different versions of HTTP in such a system. Copyright © 2003 John Wiley & Sons, Ltd.     

小卫星及多星测控的技术发展

本文从小卫星、星座飞速发展以及对测控通信系统新的要求出发，介绍了综合基带、连续波多波束相控阵天线的功能、特点及工作原理，提出了建立新型多功能智能化测控通信站的设想。     

INMARSAT 21世纪工程——全球个人移动卫星通信

本文概述INMARSAT 21世纪工程的规划及为实现这一规划,INMARSAT组织在本世纪末正在进行和即将进行的一系列卫星通信技术工作。着重阐述INMARSAT 21世纪工程的业务性能以及对三种卫星布局方案进行抉择的新动向。     

宽带自适应跳频控制器

本文叙述宽带自适应跳频控制器的原理及方案,频率集的配置、自适应跳频拒收门限及频点更新、跳频码序列及同步等。有效地组织宽带自适应跳频系统能避开大部分固定和半固定性质的单频连续波干扰,使得移动卫星通信系统中实现高可靠性的数据传输。