An overview of shadowed fading wireless channels in terms of a cascaded approach

Wireless channels suffer from short term fading and shadowing simultaneously. While simple models of short term fading are based on the Nakagami-m distribution, short term fading can also be described as a cascading process allowing the modeling of wireless channels having worse fading than what exists in Nakagami-m channels. Shadowing, on the other hand, has been traditionally modeled as a lognormal process, making the analysis of shadowed fading channels cumbersome. Taking note of the fact that the lognormal density arises out of a multiplicative process, it was shown that shadowing can also be modeled as a cascading process. Utilizing such a vision of shadowing, this work provides an overview of a unified cascaded approach to model wireless channels when short term fading and shadowing are simultaneously present. The degradation in such shadowed fading channels is estimated in terms of error rates and outage probabilities. Results are compared to those of the exact model based on lognormal density as well as random number simulation. Analysis demonstrates that error rates and outage probabilities obtained using the exact model (lognormal model for shadowing) agree very well with those obtained through the composite cascaded model as well as random number simulations.     

组合导航传感器容错滤波算法及应用

采用多重渐消Kalan滤波最优自适应算法对基于Kalman滤波器的残差检验方法做出了改进，构造了组合导航传感器容错滤波算法。在保持滤波器最优性和收敛性的同时，具有较好的动静态特性，适用于组合导航传感器故障检测和隔离。该算法简单便于实施。     

Adaptive unsaturated OFDM multimode fiber communication technique based on zero padding

In order to overcome the deterioration of system performance induced by the subcarriers at or near the deep fading nulls in high frequency band-pass regions of multimode fiber, we first propose adaptive unsaturated OFDM technique based on zero padding in this paper. In our proposed method, the subcarriers with low SNR (at or near deep fading nulls) are turned off by zero padding, and data originally transmitted by those subcarriers will be transferred to new subcarriers with high SNR which have been created at high frequency by the adjusting of IFFT points. The results show that the technique proposed can accomplish transmission of 10 Gbps data rate over 1 km multimode with the BER of 4.61e−3 when the OSNR is 20 dB.     

Orthogonal M-ary code shift keying spread spectrum underwater acoustic communication

M-ary and code shift keying（CSK）spread spectrum is generally applied to overcoming the spreading gain versus data rate limitation in underwater acoustic（UWA）communications.In addition,the concept of orthogonal M-ary CSK is introduced to UWA communication to gain higher rates.We propose a scheme employing dual-orthogonal-channel M-ary and CSK spread spectrum UWA communication based on Gold sequences owing large code set and good self and cross correlation.The modulation and demodulation scheme of the orthogonal M-ary CSK is derived algebraically and the factors critical to its performance are discussed.Furthermore,its bit error rate（BER）curve is evaluated via simulations and compared with the dual-channel M-ary CSK.Finally,the validity of the simulations is verified in tank experiments.1096.8 bps data rate of the proposed communication scheme is realized for 10 kbits data volume with no error.Overall through deduction,numerical simulation,and experiment,it is shown that the proposed method offers significantly improved performance.     

三维空间域多普勒功率谱及其多天线系统性能

在三维(3 dimensional,3D)空间域信道建模中,针对波达信号仰角(elevation angle,EA)在不同覆盖区散射体环境中的分布,提出了指数型EA仰角概率密度函数并对其信道特征实现建模.在假设波达信号方位谱为均匀分布时,采用近似算法在对称和非对称两种情况下导出其多普勒功率谱密度(power spectral density,PSD)闭合表达式.从分析结果可发现PSD与仰角函数式及波达信号边界角度参数βmin和βmax关系密切,并与多普勒频移密切相关.对该三维空间域中的多输入多输出(multiple input multiple output,MIMO)多天线信号衰落相关性(spatial fading correlation,SFC)进行了推导和仿真.结果表明MIMO多天线阵元间SFC与βmin和βmax关系密切,而EA仰角概率密度函数参数n对SFC影响较小.本文引入的指数型EA仰角概率密度函数可应用于多种无线通信环境下的信道参数估计,且与传统模型对比表明本模型的信道参数估计结果符合理论和经验值,拓展了对3D空间域统计信道的建模与MIMO多天线分析计算.     

全光纤傅里叶变换光谱仪消偏振衰落技术研究

针对全光纤傅里叶变换光谱仪中光束偏振态在双折射影响下带来的干涉信号“偏振诱导衰落”现象导致测量光谱畸变的问题,根据偏振光学原理,分析了光纤应力、弯曲和扭曲导致的双折射对传输光束偏振态的影响,找到了FFTS在测量宽谱光源发射谱时出现谱线畸变的原因,提出了建立偏振态反馈控制系统来稳定干涉信号可见度的方法.实验结果表明,该方法消除了偏振态变化对测量光谱的影响.     

荷电态对锰酸锂电池储存性能的影响

采用商品化的LiMn2O4和石墨作为正负极材料制作锰酸锂动力电池,研究锰酸锂电池在不同荷电态下的储存性能,并且利用扫描电镜(SEM)、X线衍射(XRD)、循环伏安(CV)和交流阻抗(AC)等分析检测手段表征LiMn2O4电极储存前后的结构、形貌和表面状态变化,测试锰酸锂电池储存前后的电化学性能。研究结果表明:锰酸锂在放电态下储存的容量恢复率最高,达到99.4%;满电储存后容量恢复率最低,为93.6%;储存后锰酸锂电池的循环性能均有所改善,其中满电储存后循环性能最好,170次循环容量保持率为89.7%,储存前170次循环容量保持率为85.4%;锰酸锂电池储存后容量衰减随着荷电态的增加而增加,这主要是由Mn溶解量以及储存后正极表面极化的增加而引起的。     

流动注射-褪色光度法测定铁(Ⅲ)研究

基于铁(Ⅲ)可氧化酸性品红溶液而使之褪色,将该方法与流动注射自动进样技术联用,建立了流动注射-褪色光度法测定微量铁(Ⅲ)的新方法.在最优的实验条件下,该方法线性范围为0.05～1.5 mg/L,检出限(3d)为0.01 mg/L,相对标准偏差(RSD)为2.60%(Fe3+ 0.75 nlg,L,n=11).该方法应用...