高动态条件下测控系统载波跟踪环路优化设计

航天测控系统中载波跟踪误差主要来源于热噪声和航天器动态应力,对载波跟踪环 路的优化一般通过调整环路等效噪声带宽来实现。分析了航天测控系统中航天器的动态应力 特性及环路跟踪误差特性,导出由载噪比和动态应力决定的环路最佳带宽表达式,提出一种 通过环路自身状态估计载噪比和动态应力的方法,通过对载噪比和动态应力的实时估计实现 对环路参数的实时调整。仿真结果表明,该算法在动态应力和载噪比时变的高动态场合可以 实现稳定的载波跟踪,测量精度得到明显改善。     

一种基于再生伪码测距的遥测信号测距方法

为了简化深空探测器无线测量系统设计,解决下行系统受功率、带宽等因素限制遥测信号和测距信号权衡设计问题,在再生伪码测距技术的基础上,提出了一种基于遥测信号测距的新方法,以遥测数据符号代替测距伪码的功能,利用地面跟踪环路对遥测信号的跟踪测量实现下行测距,减少了独立的下行测距信号。分析和仿真结果表明：新方法简化了下行信号形式,降低了系统实现复杂度,在遥测码速率为100 kbit/s左右时,随机测距误差优于传统再生伪码测距模式,且随着遥测码速率的增加测距精度进一步改善。     

脉冲超宽带测控信号时延精密跟踪方法

脉冲超宽带测控新体制可有效提高测控系统的安全性能,且具有潜在的高精度测距能力。为了实现其高精度测距功能,提出了一种基于延迟锁定环路的脉冲超宽带测控信号时延精密跟踪方法。该方法在传统伪码跟踪环的基础上进行改进,利用基于非相干积分的非线性反馈环路对接收信号的脉冲相位进行精密跟踪。理论分析和仿真结果表明,该延迟锁定环路可以完成对脉冲超宽带测控信号的时延精密跟踪。与直扩测控信号相比,在相同条件下,脉冲超宽带测控信号的时延跟踪相对误差更大,但由于脉冲宽度很窄,在一定载噪比条件下,其测量精度仍可达厘米量级甚至更高。     

直扩/跳频测控信号伪码跟踪抗干扰性能分析

研究了直扩/跳频测控信号伪码跟踪的抗干扰性能,通过加权处理使其归结为分析 干扰条件下直扩信号伪码跟踪性能。采用鉴相曲线的过零点偏移表示干扰对跟踪的影响,推 导了伪码跟踪的最大干扰误差表达式。以单音信号作为输入干扰,对最大干扰误差进行了理 论分析,得出了音频干扰对伪码跟踪的影响规律。仿真结果表明,理论分析与仿真结果吻合 较好,验证了理论分析的正确性。     

多径环境下TDDM-BOC信号伪码周期估计

针对低信噪比下存在多径效应的时分数据调制二进制偏移载波(TDDM-BOC)调制信号的伪码周期估计难题,提出了一种基于二次谱的TDDM-BOC信号伪码周期估计算法。该算法首先推导出多径环境下TDDM-BOC信号模型,然后求出多径TDDM-BOC信号的功率谱,再求其二次谱,最后通过检测二次谱的尖峰脉冲间的间距得到多径环境下TDDM-BOC信号的伪码周期。实验过程中采用累加平均的方法可以达到降噪和精确估计的目的。仿真结果表明：该算法能够在多径环境下对TDDM-BOC信号伪码周期进行有效估计,且估计性能与多径环境有密切关系,这为今后我国“北斗”导航接收设备的开发提供了一定的理论参考。     

一种GNSS信号跟踪环路频相直调控制算法

全球卫星导航系统(Global Navigation Satellite System，GNSS)接收机信号跟踪环路正确地锁定导航信号的频率、相位是提取测量值以及导航星历的基础。传统的接收机跟踪环路采用调整频率的方式来调整相位，不能及时消除跟踪误差，并且在弱信号条件下容易受到噪声影响，难以对信号进行精确跟踪。针对这一问题，提出了一种基于非相干预滤波器的频相直调环路控制算法，采用非相干预滤波器提取跟踪误差，并且在本地信号生成阶段直接将载波相位差、载波频率差、码相位差进行消除。实验表明，与传统环路相比，频相直调算法对载波相位、码相位迁入速度分别提高了90%和95%，高动态、弱信号下多普勒估计精度分别提高了69.25%和61.37%，并且频相直调算法能够有效抑制环路参数调整、载体突然机动对载波相位锁定带来的扰动。     

TDRSS并行MSK扩频体制的实验研究

本文讨论跟踪与数据中继卫星系统（TDRSS）一种新通信体制，即并行MSK扩频系统。发射端采用长短码正交扩频的平衡调制，接收端采用一种简单解扩方式简化了并行MSK信号的解调，同时用短码全“1”引导长码同步的方法大大减小了长码的捕获时间。实验结果证明该体制具有良好的伪码同步性能。     

一种适用于遥测测距信号的新型码跟踪环

遥测测距技术采用再生伪码作为上行链路信号。针对飞行器现有码跟踪环结构复杂、低信噪比条件下环路跟踪性能差的问题,提出了一种新的基于锁相环的码跟踪环结构,推导了环路的信号处理流程。该结构降低了环路实现的复杂度,改善了低信噪比条件下的相位测量精度,仿真进一步验证了方法的有效性和稳定性,较现有方法在信噪比为-10 dB时能提高1.5×10－3个码片的精度,适合遥测测距技术。     

基于随机Hough变换的斜率估计多径抑制算法

抑制多径干扰是提高GPS定位精度的关键。针对低载噪比、预相关带宽有限的情况下斜率估计（ELS）的多径抑制技术往往不能正常工作的问题,提出了一种基于能够鲁棒地提取直线斜率的随机Hough变换（RHT）的斜率估计多径抑制算法。该算法主要采用多相关器结构得到多径相关峰的采样值,然后利用RHT得到相关峰两边的斜率,最后结合ELS的基本原理构成具有补偿因子的伪码鉴相器,以达到抑制多径干扰的目的。仿真结果表明,该算法解决了ELS在有限的预相关带宽（4 MHz）和较低载噪比(33 dB-Hz)条件下不能有效提取直线斜率的问题,并且在相同载噪比(44 dB-Hz)条件下,该算法的多径抑制性能也优于ELS算法。     

加性白噪声下基带延迟锁定环跟踪精度的计算

研究了加性白噪声下基带延迟锁定环跟踪精度的计算问题,着重讨论了积分时间和 环路带宽的关系。以码延迟相关鉴别器的等效鉴相模型为基础,研究了相关器输出噪声特性 及其在输入端等效噪声的特性,推导了线性跟踪环输出噪声方差的计算公式,并得到了积分 时间和环路带宽分别起主导作用时的简化计算公式,使两种不同的结论得到了统一。     

Brown＇s Blossom in Britain-China

The overall strategic relationship between U.K. and China is ＂better than ever＂, China- Britain relations have maintained good momentum, with increased high-level exchanges and the reinforcement of strategic mutual trust, with more room for growth in the future.     

Challenge and Opportunity Go Hand in Hand——What Global Economic Agitation Brings to the China's Economy?

Domino effects of the global finance agitation As the origin of the subprime crisis,US financial institutions lost USS45 billion last year,accounted for over half of the total US,EU & Japan loss.Since January 15th,Chtigroup released its financial statement of the 4th quarter,showing a net deficit of USS9.83 billion,which marked the hisoric high of its quarterly deficit.     

Sinosteel：Extraordinary Moves in Industry Chess

Among the Fortune 500 firms,more and more images from China emerge out.On the 2008 list,Sinosteel Corporation,a landmark group of China industries quietly squeezes into the candidate line.As the largest steel service ＆ trade enterprise,its sales reached at RMB 111.24 billion,with a year-on-year increase of 83.03 percent,and the profit grew by 180.03 percent.On the Sinosteel 2008 Work Meeting,the president Huang Tianwen uttered,＂In the coming year,we will work for US$20 billion sales,and look forward to getting a position in Fortune 500 firms for ourselves.＂     

Walk Through Unusual Five Years—— An Exhibitor＇s Canton Fair Course

When the 103rd Canton Fair is approaching, an old friend of Canton Fair, Li Ying from Jiangsu prov-ince recollected his past five years＇ experiences to the grand trade meeting. Each year is special, with some unforgettable memories colored by the year.     

Jean-Pierre Duprieu： Willing to Be A Legate of Sino-French Business

Estaing, former French president, Valery Giscard d＇Estaing attended Sino-French Economic Seminar held in Shanghai in early April and said that the world center has shifted from the west to the east with many European and US companies entering into Asia, and China has the ability to play an important role in the world stage. Estaing, naming himself＂French Confucian＂, then said in Chinese that a cook-group includes 10 people in ancient Chinese soldier system and the cook is in charge of cooking for them. And people who belong to the same cook are actually ＂Partners＂.     

China''''s Stock Market Wave

The annual meeting of the World Economy Forum was held in Davos,a little town in Switzerland,on January 23rd to the 27th this year,with the theme"the Power fo Collaborative Innovation",over 2500 celebrates from ture political and cconomic circles of more than 80 countries and challengred logether to talk about the future of the global economy in 2008,A Forum for the problems and challenges that face whole world,some of the keywords which drew attention during the event were:the U.S.subprime mortgage crisis,soaring energy prices,the economic slowdown in the U.S.ermerging economic bodies,authority funds and the general unpredictable nature of the global economy.     

Trade Promotion from Neighborhood

If you are considering to trade with companies in Japan or expanding your .business to Japan, we are ready to help from the very beginning.＂ You will find this greeting at the first sight on the Chinese website of Japan External Trade Organization （JETRO）. JETRO has committed itself in delivering highly efficient and quality services to meet the demand of internal and external customs including Japanese companies, hence winning a good reputation in the international trade arena. In recent years, with its priority in advancing business cooperation in South and East Asia, JETRO has made great achievement in promoting trade between China and Japan. Therefore, China＇s Foreign Trade interviewed Mr. Yoichi Maine, Deputy Director General of JETRO BEIJING.     

Auto Parts Market Potential Coming into Surface

Looking at the increasingly fierce competition in the world auto market. global automobile manufacturing industry, taking Europe, the U.S. and Japan as representatives, is gradually forming a new type of relationship, mutual cooperation between whole vehicle and parts manufacturers. We can clearly see that auto parts manufacturers have become independent from the whole vehicle manufacturing companies, which means that the former structure of auto industry has greatly changed, and a new relationship,     

Domino Effect on Electricity and Coal Prices

In the middle of last December, the key purchase contracts for coal used in power generation in 2008 were signed, reflecting a demand for more than 1.085 billion tons. It is important to note that the country＇s five biggest power producers, China Huaneng Group, China Guodian Corporation, China Power Investment Corporation, China Huadian Corporation and China Datang Corporation, had settled on the prices on their purchase contracts, and they are expected to consume 290 million tons of coal for generating electricity,     

Slimmed May Day Holiday

Last November the State Council of China decided to renew its holiday system by reducing the seven-day May Day holiday to three days and introducing three new one-day public holidays, namely the Qingming Festival, Dragon Boat Festival and Moon Festival. By doing so, the three golden-week holidays that were introduced in 1999, namely the Spring Festival, May Day and National Day, could be better distributed.