变换域通信系统中的信道估计技术

针对基于OFDM的变换域通信系统在低信噪比时由于噪声的影响很难获得准确的信道估计问题,采用时域和离散傅里叶逆变换(IDFT)域级联降噪的方法降低导频信号的噪声来提高信道估计的准确性。时域利用慢衰落信道环境下信道系数变换缓慢的特点,提出了时间滑动平均、时间遗忘、时间平均与时间遗忘结合等几种降噪方法;IDFT变换域利用多径时延集中在整个时隙的前一段的特点降低噪声。仿真结果表明,该方法在慢衰落信道环境下是有效的。     

Urysohn引理和Tietze扩张定理的拓广

本文对Ｕｒｙｓｏｈｎ引理和Ｔｉｅｔｚｅ扩张定理给予了拓广,并对文［１］的定理１、定理２给出另外证法．     

Super-simple cyclic designs with small values

Super-simple cyclic designs are useful on constructing codes and designs such as superimposed codes, perfect hash families and optical orthogonal codes with index two. In this paper, we show that there exists a super-simple cyclic (v,4,λ)$(v,4,\lambda )$ for 7?v?41$7?v?41$ and all admissible λ$\lambda$ with two definite exceptions of (v,λ)=(9,3),(13,5)$(v,\lambda )=(9,3),(13,5)$ and one possible exception of (v,λ)=(39,18)$(v,\lambda )=(39,18)$. Some useful algorithms are explained for computer search and new designs are displayed.     

Probability matching priors for an extended statistical calibration model

Statistical calibration or inverse prediction involves data collected in two stages. In the first stage, several values of an endogenous variable are observed, each corresponding to a known value of an exogenous variable; in the second stage, one or more values of the endogenous variable are observed which correspond to an unknown value of the exogenous variable. When estimating the value of the latter, it has been suggested that the variability about the regression relationship should not be assumed to be equal for the two stages of data collection. In this paper, the authors present a Bayesian method of analysis based on noninformative priors that takes this heteroscedasticity into account.     

非线性极大极小问题的一个有效算法

针对一类非线性约束极大极小问题,利用极大熵方法将其转化为带等式、不等式约束的非线性规划问题,给出了一种梯度投影算法,解决了一般约束的非线性大系统优化问题,该算法初始点可任意;同时证明了该算法的全局收敛性。初步的数值试验表明,对于该类极大极小问题,算法有良好的数值表现。     

基于投影寻踪方法的陕西省经济发展协调性评价

为了研究陕西省2000—2008年经济发展与环境、资源、人民生活水平三个方面的协调程度,在选择了相应的代表性指标后,利用投影寻踪方法对指标进行降维分析,根据投影函数值对2000—2008年陕西省经济发展的总体协调性进行评价,并采用灰色关联度等方法针对经济—环境、经济—资源、经济—人民生活水平三个方面进行对比分析,阐述了陕西省当前在经济协调发展方面的现状及存在的主要问题。     

古文字中隐含的制图常识

前人识读古文字, 一般重在对具体单字的历时性研究, 较少注意共时性造字符码的破泽。通过古文字的横向比较,揭示出古人造字时已经应用过的投影、多向视图、 质地标志、动态标志等制图学常识, 试图探索出一条研究上古文明、文化和训释、辨认古文字的新的途径。     

Double filter instrumental variable estimation of panel data models with weakly exogenous variables

In this article, we propose instrumental variables (IV) and generalized method of moments (GMM) estimators for panel data models with weakly exogenous variables. The model is allowed to include heterogeneous time trends besides the standard fixed effects (FE). The proposed IV and GMM estimators are obtained by applying a forward filter to the model and a backward filter to the instruments in order to remove FE, thereby called the double filter IV and GMM estimators. We derive the asymptotic properties of the proposed estimators under fixed T and large N, and large T and large N asymptotics where N and T denote the dimensions of cross section and time series, respectively. It is shown that the proposed IV estimator has the same asymptotic distribution as the bias corrected FE estimator when both N and T are large. Monte Carlo simulation results reveal that the proposed estimator performs well in finite samples and outperforms the conventional IV/GMM estimators using instruments in levels in many cases.     

Orthogonal series density estimation for complex surveys

We propose an orthogonal series density estimator for complex surveys, where samples are neither independent nor identically distributed. The proposed estimator is proved to be design-unbiased and asymptotically design-consistent. The asymptotic normality is proved under both design and combined spaces. Two data driven estimators are proposed based on the proposed oracle estimator. We show the efficiency of the proposed estimators in simulation studies. A real survey data example is provided for an illustration.     

Using repeated measures to correct correlated measurement errors through orthogonal decomposition

In a physical activity (PA) study, the 7-day PA log viewed as an alloyed gold standard was used to correct the measurement error in the physical activity questionnaire. Due to correlations between the errors in the two measurements, the usual regression calibration (RC) may result in a biased estimate of the calibration factor. We propose a method for removing the correlation through orthogonal decomposition of the errors, and then the usual RC can be applied. Simulation studies show that our method can effectively correct the bias.