多窗口传输协议及其在航空电子系统大数据传输中的应用

随着航空电子系统模块化技术的发展,系统内大数据传输的需求越来越明显,现有的几种大数据传输方式或需要更改现存系统架构,或需要系统具有特定功能支持,难以在不同的航空电子系统中进行广泛应用。为解决这一问题,本文提出一种可在系统应用层中实现的多窗口传输协议及其实现方法。该协议使用额外的资源同时进行多窗口信息传输,保证了在机载网络不稳定环境下传输的速率和稳定性,满足系统大数据传输的需求。而且方法在应用层实现,避免了对系统现有硬件和软件架构的更改,适用范围较广。     

利用GPS实现高轨卫星定位的抗远近效应算法

针对GPS应用于高轨卫星定位面临的远近效应问题, 提出利用正交相关的联合极大似然估计算法来对GPS信号进行二维搜索, 可以得到正确的码延时及多普勒估计. 极大似然估计算法首先利用滑行相关法对仿真信号中的强信号进行搜索, 得到强信号模型, 然后利用正交相关去掉强信号, 最终实现对弱信号的正确捕获. 本文对高轨卫星接收到的GPS信号进行了功率分析, 并建立了信号模型, 进行了算法仿真. 结果表明, 这种估计算法能够提高二维搜索性能, 有效解决远近效应问题.      

基于高轨航天器的GNSS接收机技术

全球导航卫星系统（GlobalNavigationSatelliteSystem,GNSS）应用于高轨航天器时,因轨道高于导航卫星,可见星数量急剧减少,空间信号功率微弱,信号的快速捕获和跟踪十分困难。文章对高轨地球同步轨道（GeosynchronousEarthOrbit,GEO）接收技术进行了研究。以中国实践十七号卫星为研究对象,采用官方正式发布的发射天线方向图对GEO下GNSS信号特征及可用性开展研究分析,并针对高轨道航天器GNSS信号微弱的特点,采用长时间积分处理的梳状滤波方法、差分相干累加比特同步算法和基于动力学模型补偿的扩展卡尔曼滤波自主定轨算法设计GNSS接收机,并在半物理仿真平台进行了测试验证。试验结果表明：GNSS接收机捕获灵敏度优于-173dBW,跟踪灵敏度优于-175dBW,定轨位置精度优于50m,速度精度优于0.01m/s。     

Precision analysis of troposphere sensing using GPS single-frequency signals

Various studies have been performed to investigate the accuracy of troposphere zenith wet delays (ZWDs) determined from GPS. Most of these studies use dual-frequency GPS data of large-scale networks with long baselines to determine the absolute ZWDs. For small-scale networks the estimability of the absolute ZWDs deteriorates due to high correlation between the solutions of the ZWDs and satellite-specific parameters as satellite clocks. However, as relative ZWDs (rZWDs) can always be estimated, irrespective of the size of the network, it is of interest to understand how the large-scale network rZWD-performance of dual-frequency GPS using an ionosphere-float model compares to the small-scale network rZWD-performance of single-frequency GPS using an ionosphere-weighted model. In this contribution such an analysis is performed using undifferenced and uncombined network parametrization modelling. In this context we demonstrate the ionosphere weighted constraints, which allows the determination of the rZWDs independent from signals on the second frequency. Based on an analysis of both simulated and real data, it is found that under quiet ionosphere conditions, the accuracy of the single-frequency determined rZWDs in the ionosphere-weighted network is comparable to that of the large-scale dual-frequency network without ionospheric constraints. Making use of the real data from two baselines of 15?days, it was found that the absolute differences of the rZWDs applying the two strategies are within 1?cm in over 90% and 95% of the time for ambiguity-float and -fixed cases, respectively.     

Characterization of GPS-TEC over African equatorial ionization anomaly (EIA) region during 2009–2016

This study characterizes total electron content (TEC) measured by Global Positioning System (GPS) over African equatorial ionization anomaly (EIA) region for 2009–2016 period during both quiet geomagnetic conditions (Kp?≤?1) and normal conditions (1?>?Kp?≤?4). GPS-TEC data from four equatorial/low-latitude stations, namely, Addis Ababa (ADIS: 9.04°N, 38.77°E, mag. lat: 0.2°N) [Ethiopia]; Yamoussoukro (YKRO: 6.87°N, 5.24°W, mag. lat: 2.6°S) [Ivory Coast]; Malindi (MAL2; 3.00°S, 40.19°E, mag. lat: 12.4°S) [Kenya] and Libreville (NKLG; 0.35°N, 9.67°W, mag. lat: 13.5°S) [Gabon] were used for this study. Interesting features like noontime TEC bite-out, winter anomaly during the ascending and maximum phases of solar cycle 24, diurnal and seasonal variations with solar activity have been observed and investigated in this study. The day-to-day variations exhibited ionospheric TEC asymmetry on an annual scale. TEC observed at equatorial stations (EIA-trough) and EIA-crest reach maximum values between ～1300–1600 LT and ～1300–1600 LT, respectively. About 76% of the high TEC values were recorded in equinoctial months while the June solstice predominantly exhibited low TEC values. Yearly, the estimated TEC values increases or decreases with solar activity, with 2014 having the highest TEC value. Solar activity dependence of TEC within the EIA zone reveals that both F10.7?cm index and EUV flux (24–36?nm) gives a stronger correlation with TEC than Sunspot Number (SSN). A slightly higher degree of dependence is on EUV flux with the mean highest correlation coefficient (R) value of 0.70, 0.83, 0.82 and 0.88 for quiet geomagnetic conditions (Kp?≤?1) at stations ADIS, MAL2, NKLG, and YKRO, respectively. The correlation results for the entire period consequently reveals that SSN and solar flux F10.7?cm index might not be an ideal index as a proxy for EUV flux as well as to measure the variability of TEC strength within the EIA zone. The estimated TEC along the EIA crest (MAL2 and NKLG) exhibited double-hump maximum, as well as post-sunset peaks (night time enhancement of TEC) between ～2100 and 2300 LT. EIA formation was prominent during evening/post-noon hours.     

Entropy based inverse design of aircraft mission success space in system-of-systems confrontation

This paper presents a practical and efficient design method for aircraft Mission Success Space (MSS) based on the entropy measurement (EM). First, fundamentals regarding MSS, Inverse Design (ID) and entropy are discussed. Then, two EM schemes of entropy-based ID and the whole MSS ID procedure are given to demonstrate alternative ways of entropy quantification and MSS design. After that, Genetic Algorithm (GA) is utilized as a search algorithm to find the optimal MSS design with the minimum objective, entropy, in each EM scheme. A simulation case of aircraft penetration mission is given for the method validation where the best aircraft MSS design is obtained by GA according to the minimum entropy. Results from two schemes are compared at the end.     

全球卫星导航系统兼容性分析方法研究

根据全球卫星导航系统信号捕获、载波跟踪和数据解调的原理,优化了等效载波功率与噪声密度比模型。针对有多普勒频率时的情况,提出了C/A码自干扰时的捕获-频谱隔离系数。结果显示,随着多普勒频率的变化,频谱隔离系数有着明显的变化。通过对仿真结果的分析,验证了模型的有效性,也为后续卫星导航信号的优化设计提供了支持。     

分离模块航天器研究综述

对分离模块航天器产生的背景及概念进行了阐述和分析,介绍了包括F6系统、天基群组系统、SkyLAN（空间局域网）等在内的几种主要分离模块航天器系统,并在此基础上归纳总结出了分离模块航天器在同轨多模块系统设计、功能系统设计、信息交互技术、队形保持重组及功能适变技术、无线信息传输技术、分布式天线技术等方面的技术特点及难点,最后讨论了分离模块航天器进一步的研究方向和发展前景。     

航电系统开发过程中的权衡研究

航电系统的开发既要满足系统需求、保证系统完整性、达到系统安全性目标,同时还要满足相关条例、公务要求和商业要求。而这些要求往往相互制约、相互冲突,这就使得权衡研究在航电系统的开发过程中成为一项必不可少的工作。阐明了权衡研究在航电系统开发过程中的必要性和重要性;然后说明了权衡研究在航电系统开发过程各阶段中的作用;接着分析了权衡研究应遵循的过程;最后,将权衡研究分析方法中的效用曲线法应用到了航电系统的网络权衡中,并提出航电系统开发过程中如何进行权衡研究的一些建议。     

Web开放平台安全体系的研究与设计

Web开放平台是Web2.0时代的发展产物,它能提供更多的可能性,具有更强的渗透能力,随之也面临着更多的安全问题。本文分析了开放平台原理,设计了开放平台安全通信流程;通过研究开放带来的一系列安全问题,明确了开放平台安全的设计方案;并且从平台整体安全的角度完成了安全体系的设计,保证了系统网络间相互连接关系的清晰合理。Web开放平台安全体系的研究和设计能够为互联网安全、以及开发人员提供有力的帮助。