传输参考超宽带信号功率谱的改善设计

通过对传输参考超宽带(TR-UWB)信号功率谱密度特性的理论分析,发现离散谱的消除和限波 带 的产生能有效降低对同频段其它无线通信系统的干扰。将参考部分随机化可以消除频谱中 的离散谱部分,并优选跳时码产生5.2 GHz频段的限波。仿真结果表明,通过这种方法离 散谱得以明显消除,5.2 GHz频段的限波对该频段其它通信系统的干扰降低了30 dB 以上。该方法简单灵活,改善后的频谱特性可以满足传输参考超宽带系统与其它无线通信 系统共存的需要。     

卫星广播信号上重叠发射导航增强信号的方法

提出了一种在卫星广播信号上重叠发射卫星导航增强信号的方法,将差分校正数据经过扩频后发射出去,与卫星广播信号进行频谱重叠,一起经卫星转发。通过参数设计和性能仿真可知,差分增强信号对广播信号的接收解调影响很小,差分接收机可以通过串行干扰抵消的方法从混合信号中提取出差分增强信号,实现解扩与辅助测距,解扩得到的差分校正数据可直接用于差分定位。当混合功率比为26 dB时,捕获概率达99.99%,测距精度为10.67 m,表明了此方法的可行性。     

“北斗”信号重构的导向矢量实时校正

针对导航应用中阵列天线导向矢量误差导致波束合成器性能恶化甚至失效的问题,提出了一种“北斗”信号重构的导向矢量实时校正算法。该算法利用重构的本地“北斗”参考信号与阵列天线接收信号进行相关解扩处理,然后利用信号子空间与信号正交补空间正交的特性,构造代价函数对各卫星方向的阵列导向矢量进行校正。仿真结果表明,经过校正的导向矢量相位误差从-100°~100°降低到-10°~10°范围内,幅度误差从-10~10 dB降低到-4~2 dB范围内;另外,导向矢量校正后,卫星信号波达方向估计误差在0.2°以内,估计精度大大提高。     

“北斗”B2频段导航信号伪码跟踪性能分析

与传统卫星导航信号体制不同,新一代“北斗”B2频段导航信号采用了交替二进制偏移载波调制（AltBOC）体制,因此伪码跟踪性能也与传统信号体制有较大差异。首先介绍了AltBOC调制信号原理及特点,然后根据码跟踪精度理论比较了新型调制信号与传统信号体制的性能差异,分析了不同鉴相器时B2频段信号的码跟踪误差,并对不同相关器间隔、环路带宽、前端带宽、载噪比环境条件下的伪码跟踪误差进行了仿真分析。仿真结果表明,提高信号载噪比、射频前端带宽或减小相关器间隔、环路带宽均能减小码跟踪误差。研究结果对新一代“北斗”导航信号新体制性能的评估以及“北斗”导航接收机的系统设计具有一定指导意义。     

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。     

应用于无线USB的小型超宽带阻带天线

设计了一种用于超宽带无线通信系统的小型化天线。该天线贴片尺寸为20 mm×15 mm ×3 mm,采用U形折叠结构和渐变结构相结合,可使天线具有超宽带特性。为 了减小对无线局域网（WLAN）系统5 GHz频带的干扰,天线采取了叉形谐振结构来实现对相应频带的抑制。采用仿真软件分析了该天线阻抗带宽和不同频点处的辐射方向图。仿真和实测结果显示,该天线在25～4.67 GHz和628～12 GHz内S11<-10 dB,在47～6.2 GHz内S11>-10 dB,因而有效产生带阻特性。     

穿戴式超宽带接收机误码率性能分析

为研究不同接收机的架构、收发天线的角度和判决方式对穿戴式超宽带(UWB)信道RAKE接收机误码率(BER)的影响,利用数字抽样示波器获取时域接收信号,使用CLEAN算法去卷积,得到体表-体表和体表-体外环境下人体信道冲激响应;并采用不同结构不同分支数的RAKE接收机对含有加性高斯噪声的跳时信号进行接收,以分析其对BER的影响。仿真结果表明,包含所有分支的RAKE接收机BER最低但结构复杂;在相同分支数下,包含部分分支的RAKE接收机的BER损失要比选择性RAKE接收机高3 dB,但复杂度较低。对收发天线不同角度的研究表明,收发天线应避免垂直,否则体表反射作用带来的多径分量增多,容易出现码间干扰,从而增加BER。在重复编码情况下,软判决的BER性能要优于硬判决0.2～0.4 dB。该信道模型和误码率分析研究可对穿戴式UWB收发机的架构设计和性能研究提供参考。     

宽带8PSK解调高速数传接收机设计

受卫星信道热噪声、多普勒、畸变影响,传统八进制相位键控（8PSK）接收机性能不 佳,速率不高,较少应用于航天测控通信系统。针对这一问题,设计并实现了一种基于FPGA 的航天测控系统宽带8PSK解调高速数传接收机,采用Gardner算法实现时钟恢复,利用基于 最大似然估计的鉴相算法完成载波同步,并用分数间隔的并行恒模均衡算法提高接收性能。 该技术已应用于某接收系统并实现了600 Mb/s 8PSK信号解调,误码率在1×10-3 ～1×10-8之间时,解调损失与理论值不超过2 dB。宽带8PSK解调高速数传接收 机可为我国二代中继系统提供支持。     

植入式生物医学电子的UWB无线通信可行性建模研究

为考察超宽带（UWB）实现植入式生物医学电子设备无线通信的可行性及信道传播特性,基 于男性活体C T及MRI切片图像,构建了一个频率范围在1～10.8 GHz的高分辨率三维人体电磁模型 ,考虑了85种不同人体组织或器官的电磁特性参数;将模型嵌入基于有限积分法（FIT）的 三维电磁仿真软件进行电磁计算,考察电磁波在人体内的路径损耗及比吸收率特性。实验结 果表明:该模型能较好地描绘真实人体的电磁特性, 信号在人体内的衰减随频率的升高及植 入深度的加深而加重;在植入深度达160 mm时,3.5 GHz信号的路径损耗为75 dB ;参考功率为27 dBm时,人体对3.5 GHz信号的比吸收率在安全值范围内;证实 了采用UWB频段内的3.5 GHz实现植入式生物医学电子无线通信的可行性和安全性。     

多模卫星信号仿真器上位机软件设计与实现

运用面向对象和多线程的技术,在VC++6.0环境下对GPS/GLONASS/BD1三模卫星信号仿真器上位机软件进行了设计与开发,重点分析并完成了多导航系统时空统一、导航电文生成、卫星与用户的伪距仿真和用户轨迹计算等功能模块,实现了统一时基模式下三模卫星信号的高逼真仿真.商业接收机的实验结果表明,该仿真软件操控灵活,与下位机连接合成的信号逼真度高,为各类接收机的性能检测提供了有益支持.     

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.