一种基于EM算法的MIMO-OFDM系统信道估计技术

从提高多输入多输出正交频分复用（MIMO—OFDM）系统频谱利用率的目的出发，提出了一种改进型的基于EM（Expectation Maximization）算法的信道估计技术。仿真结果表明，改进后的算法可以显著提高频谱利用率，同时保持原算法的精度。     

短波通信多组空时编码中等效MIMO模型ZF解码

面向短波通信提出了多组空时编码(MGSTC)的一种等效多输入多输出（MIMO）模型迫零（ZF）解码算法。该算法以降低运算复杂度为目的,将原多时隙MIMO系统拆分为多个多时隙单输入多输出（SIMO）系统并分别等效为多个新的单时隙MIMO系统模型,通过各自左乘等效信道矩阵的共轭转置后进行最大比合并（MRC）以及ZF解码获得发送信号估计值,避免了球形解码（SD）中对高阶矩阵的QR分解。仿真结果表明,与虚拟MIMO模型SD解码算法相比,等效MIMO模型ZF解码算法在误码率（BER）性能1 dB损耗的情况下,运算量降低一个数量级以上。     

采用数据辅助的大规模MIMO信道半盲迭代估计

由于大规模多输入多输出(Multiple-Input Multiple-Output,MIMO)信道衰落参数的维度较高,导致最优估计算法计算量大且需要的导频数较多而影响到频谱效率。为降低计算复杂度并减少导频开销,提出了两种基于期望最大化(Expectation Maximization,EM)估计的半盲迭代改进算法。利用少量正交导频序列估计出信道初值,通过用户与基站间信道的大尺度衰落系数把用户分簇,根据这些系数按比例地分配接收噪声,再利用数据的统计特性推导出信道衰落参数的均值和方差。仿真结果表明,当导频数远少于待估计参数的个数时,半盲估计算法的均方误差(Mean Square Error,MSE)优于导频估计的极大似然(Maximum likelihood,ML)算法。     

一种基于CMA和DDLMS算法的双模式盲均衡算法

为进一步改进盲均衡算法收敛速度慢、稳态误差大、计算复杂度高等问题,提出一种切换模式和加权模式联合CMA(Constant Modulus Algorithm)+DDLMS(Direct Decision Least Mean Square)双模式盲均衡算法。综合切换双模式盲均衡算法和加权双模式盲均衡算法的优缺点,对切换、加权模式联合的CMA+DDLMS双模式盲均衡算法进行仿真。在不同信噪比条件下,对CMA算法、MCMA(Modified CMA)算法、DDLMS算法和CMA+DDLMS双模式盲均衡算法进行仿真,结果表明,所提算法收敛速度快,约为600个符号;稳态误差小,约为0.1;误码率小,在信噪比为25 dB时,误码率约为10-6。该算法可广泛应用于无线通信、光通信、声呐和雷达等众多领域。     

多径衰落信道MPSK信号超指数迭代盲解调算法

为了提高多径衰落信道下的盲解调性能,提出了一种结构简单的MPSK信号盲解调算法。首先利用超指数迭代分数间隔盲均衡器实现联合定时同步与均衡,然后对均衡器输出信号进行非线性变换实现载波频偏的估计,最后利用二阶数字判决锁相环跟踪相位变化纠正剩余频偏和相偏。仿真结果表明,在多径衰落信道条件下,与现有算法相比,基于超指数迭代分数间隔盲均衡器的盲解调算法实现简单,误码率低,而且具有收敛速度快、性能稳定等优点。     

MIMO系统中改进的二进制粒子群天线选择算法

在多输入多输出系统中,发射端和接收端的多天线配置提高了信道容量和传输可靠性,而天线选择技术能在保持系统优点的同时有效地降低运算复杂度以及硬件成本。为了能在时变的信道条件下快速地选择出一组最优的天线子集,提出了一种基于二进制粒子群算法的改进的天线选择算法。推导出了二进制粒子群联合收发端天线选择的信道容量公式,并将其作为粒子群算法的适应度函数,使天线选择问题转换成二进制编码串的组合优化问题。通过改进模糊函数提高粒子群算法的收敛性,让二进制粒子群尽可能地收敛于全局最优位置。仿真结果表明,改进的算法能在降低运算复杂度的同时提高收敛性,且系统信道容量趋近于最优算法。     

平坦信道下的MIMO信道估计误差分析

基于导频序列推导了频率平坦多输入多输出(MIMO)信道下的最小二乘信道估计(LS)误差;将信道估计误差等效为高斯噪声,推导了信道估计条件下系统的等效信噪比,提出了用系统的等效信噪比来分析和评估在信道估计误差条件下系统的误码性能;最后用等效信噪比的方法评估了ZF-V-BLAST算法在信道估计下的性能,结果表明和计算机仿真结果基本相吻合。     

一种新的最小均方误差线性合并算法

针对未编码的多输入多输出系统,将基于训练序列的最小均方误差(MMSE)信道估计算法与最优线性无偏估计结构(BLUE)相结合对已估计的信道参数进行估计.仿真结果表明,使用线性合并的MMSE算法比传统的MMSE算法具有较小的参数估计误差,比使用线性合并的LS算法性能更好.     

一种MB-OFDM系统中改进的盲自适应信道缩短算法

针对MB-OFDM(多频带正交频分复用)系统中Merry算法收敛速度慢的问题,提出一种改进的盲自适应信道缩短算法.利用RLS算法实现均衡器抽头的迭代计算,改善了算法的收敛性和鲁棒性.同时提出一种最优初始化算法,提高了算法的收敛速率.仿真结果表明对于具有很强时变性的超宽带信道,该算法在收敛性和稳健性方面都具有良好的性能.     

基于CP分解的MIMO-OFDM系统接收信号盲检测

多输入多输出-正交频分复用（MIMO-OFDM）无线通信系统中接收信号从空间、时间、频率的维度形成多因素的阵列信号,传统的矢量或者矩阵代数的建模方法在处理多因素信号问题上显得不足,无法利用多因素间的关系,而张量分析在解决多维阵列信号处理的问题上具有优势。针对MIMO无线通信系统,结合OFDM技术,研究了张量信号的建模及分解方法,并充分利用张量信号的分解唯一性提高无线接收信号的检测能力。提出了基于CP（CANDECOMP/PARAFAC）张量分解方法对未知信道状态（CSI）的MIMO-OFDM系统进行接收端的张量信号建模和盲检测,并通过仿真分析验证了模型的可行性。仿真结果表明,在接收天线数目大于发送天线数目且各径信道独立情况下,基于CP分解的接收信号盲检测算法在误码率为10-4时,随着接收天线数目增加,信噪比可获得约5 dB的增益。     

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,     

Public Financial Expenditure——A Reflection of the Livelihood Improvement

In recent years.China's public finance put social construction high on the agenda and attaches more importance on livelihood insurance and improvement.The 2003-2007 public financial expenditure reflects a fact that the government isputting more emphasis on livelihood andissues concerning the people.     

Voices from the MPC and CPPCC

"Crucial for economic growth.energy utilization has its role in all economic sectors and every aspect of people's daily life.Now we are in dire need of a new profession,namely energy manager.We not only need to have passion and responsibility,but also a scientific approach to conserve energy and cut emissions.APpropriate legislation should be in place.and a special profession should be introduced to ensure the implementation of these laws and regulations."