时延约束多载波系统中多用户分集性能

多用户分集是最近多用户信息理论确定的无线通信网络中固有的分集方式，它在不考虑单独用户数据速率和时延约束情况下可以达到系统容量最大化。为此，提出一种用于多载波系统的基于并行无线调度策略和注水算法，并满足明确服务质量参数约束的多用户分集算法，分析了时延约束条件下多载波系统中多用户分集性能。仿真结果表明，算法相对固定分配资源和单用户最优资源分配的多载波系统可以获得显著的系统容量增益。     

一种Eureka-147数字声音广播系统频率捕获算法

提出了一种新的Eureka-147数字声音广播(DAB)系统的频率捕获算法.该算法采用了基于相邻子载波之间差分检测的频率估计,消除了符号定时误差引起的相移影响,根据频率估计测度的最高值与其左右邻近值关系将粗频率估计分辨率提高到0.5,频率捕获残留的载波频率偏移减少到-0.25～0.25,避免了通常的精频率偏差估计算法在±0.5左右时性能严重恶化的问题.     

取样光纤光栅及其应用研究

概述了取样光纤光栅在色散、色散斜率补偿中的应用,在不同取样情况下对取样光栅的光学特性进行了数值模拟和分析,并对基于取样光栅的色散和色散斜率补偿器件进行了比较和讨论.分析显示,取样光纤光栅特别是纯相位取样光纤光栅在飞速发展的WDM系统中有着非常好的应用前景.     

基于GPS的FAST望远镜馈源平台自动测量控制系统

500m直径大射电望远镜(简称FAST望远镜)的跟踪观测是由馈源的空间运动来实现,因此馈源在搜索运动过程中要保持很高的稳定性。就馈源平台自动控制系统对位置和姿态测量精度要求进行分析,提出了采用实时动态技术和全球定位系统(GPS)姿态测量技术进行馈源平台的实时监控,以实现整个FAST望远镜对宇宙射电源的自动化跟踪。介绍了GPS时实动态姿态测量原理和FAST监测系统的构成,以及姿态测量的数学模型和解算方法。该方法在50mFAST馈源模型上试验得到馈源平台中心点位精度为5.65mm、姿态精度0.345°可以满足FAST望远镜一次支撑的精度要求。     

光的偏振与光矢量的相位及其方向的关系研究

研究光在介质中传播时,相位和偏振方向的关系及相位对光矢量指向的影响,表明相位与偏振方向无关,相位的变化对光矢量指向的影响能用相关公式进行处理.     

Approaches to prediction of impact of Qinghai-Tibet Railway construction on alpine ecosystems alongside and its recovery

With the aid of the Remote Sensing (RS) and Geographic Information System (GIS) technology, the ecosystem pattern and fragility distribution maps of the 50-km-wide zone along the Qinghai-Tibet Railway were compiled and by using the superimposition method, range, area and indexes of the impact of various engineering activities on the ecosystems alongside the railway were studied. By making reference to the ecosystem recovery process of the Qinghai-Tibet Highway, mechanisms of recovery of the alpine ecosystems alongside the Qinghai-Tibet Railway were studied and extents and rates of the recovery were predicted.The results indicate that the impact of the railway engineering on the Alpine ecosystem depends mainly on how much the original surface soil in the zone has been disturbed and how fragile of the ecosystem per se. Restoration of vegetation coverage and species abundance shows a significantly reverse relationship with disturbance of the original surface soil but an extremely positive one with the length of the restoration period and mean annual precipitation and annual mean relative humidity in the period and no obvious bearings with altitude and temperature. In sections with an annual precipitation over 200mm, as long as a certain percentage of original soil is left in situ, it takes only 30 years or so for biodiversity to get basically restored to the original level after the construction is completed but at least 45-60 years or more for vegetation coverage.     

Changes in permafrost ecosystem under the influences of human engineering activities and its enlightenment to railway construction

~~disturbedhigh-coldmeadowarea,theoriginalvegetationisverydifficulttorestorealthoughitssurfacelandscapecanberestoredtoacertaindegree.Borrowpitsandpilinggroundshavegreatdestructiontothehigh-coldmeadow,thehigh-coldmeadowecosystemalmostcannotbere-storedbynaturalprocesses,therefore,greateffortsshouldbemadetoavoidsettingupborrowgroundinthehigh-coldmeadowregion.AcknowledgementsThisworkwassupportedbytheNationalNaturalScienceFoundationofChina(GrantNos.90102001and30270255)andtheKeyProjectionofKnowl…     

R(o)ssler超混沌系统的参数辨析与同步研究

首先给出两种方法实现对四维罗斯勒超混沌系统未知参数的准确快速辨析，第一种方法通过将系统反馈控制到任意不动点，求解平衡点的方程得到未知参数辨析的数学表达式；第二种方法基于稳定性理论，通过构造参数观测器，设定恰当的初始值，解析地给出基于参数观测器的表达式，数值计算表明两种方法都很有效。基于线性化误差理论，求解误差演化的雅克比矩阵的特征值，解析地获得相位同步和全局同步控制器的表达式，详细分析了雅克比矩阵为零对应相同步问题，数值计算与理论分析一致。     

多载波CDMA中的多用户判决反馈检测器

提出了基于多载波的最小均方误差(minimummean squarederror,MMSE)多用户判决反馈检测器(deci sion feedbackdetector,DFD)。MMSEDFD具有结构比较简单且性能优于线性多用户检测器(LMMSE)的特点。多载波系统相对于传统的单载波系统能够有效地消除频率选择性衰落。在多载波的合并上,采用了等增益合并(equalgaincombination,EGC)和最大比合并(maximalratecombination,MRC)方式。仿真表明,MC DS/CDMA系统中的MMSEDFDEGC接收机和MMSEDFDMRC接收机相对于LMMSE接收机可以提高系统性能,特别是MMSEDFDMRC接收机能够明显提高系统性能。     

基于OFDM系统的空时频分组编码方案

提出了一种空时频分组编码方案,其设计思路是:接收端通过子信道的相关特性确定不相关子载波组,并反馈给发射端;发射端基于反馈信息,利用星座旋转预编码矩阵和空时分组编码技术构建空时频分组编码。该方案只反馈子信道的相关性而无需反馈整个信道信息,可应用于任意数量的发射/接收天线,能获得极高的分集增益和带宽效率,且只有较低的解码复杂度。在瑞利衰落环境下的仿真结果证实了此方案的鲁棒性。