移动通信中的多谱勒频偏估计方法

针对几种多普勒频偏估计方法,分别为对数包络法、自相关函数法、各阶电平通过率法和均方相位差分法,在理论上分析了瑞利信道中它们的估计原理和估计偏差,说明了这些估计方法各自的适用场合.同时推导了多普勒频偏估计器的CRB (Cramer Rao bound),并且提出了一种新的利用二阶多项式拟合的修正方法以提高多普勒频偏估计精度.算法验证采用门特卡罗计算机仿真,结果表明,相对于原始估计方法,拟合修正后的方法估计性能得到了较大的提高.     

解根、猜根、设根——研究导函数零点的三步曲

<正>导数引入高中数学教材以后,对多项式函数、指数函数、对数函数等混合型函数性质的研究多了一个重要工具.在利用导数研究函数的单调性或极值时,求解导函数的零点是一个基本问题,而我们遇到的导函数可能是初等函数、含参函数或者超越函数,导函数的零点或易或难,也成为制约大家能否顺利解题的一个关键点.本文拟通过几例谈谈处理这些问题的常见策略,以飨读者.1 利用因式分解求根,直接代入函数求解问题1 已知函数f(x)=2tlnx,g(x)=x²-k(     

第二类Beta算子对一类导数有界函数的逼近

研究了第二类Beta算子的逼近性质,通过直接计算得到第二类Beta算子Ln（t-x｜,z）的一阶绝对矩的最优估计,由此估计结果结合Bojanic-Cheng-Khan的方法以及分析技巧,导出第二类Beta算子对一类导数有界函数的渐近估计,得出该算子的一个渐近展开公式．     

半变系数模型的估计及性质

半变系数模型在统计中具有重要的应用,本文时该模型的常数系数,采用局部多项式估计方法和平均方法,给出了它的估计,对于函数系数的估计通过应用常数系数的估计,采用局部多项式估计方法给出其估计,并给出估计的渐近正态性和证明．     

多项式函数极值点的本质——导函数的奇重零点

苏敦版普通高中课程标准实验教科书选修2～2《导数及其应用》--章以基本初等函数为载体,介绍了导数的概念、儿何意义以及运用导数研究函数的肇调性与极值等内容．由于许多初等函数如．f（x）=（x^3＋ax^2＋b）e^2的单调性与极值问题最终町以化归为多项式函数的单调性与极值问题,因此揭示多项式函数极值点的本质特征,对导数的教学有重要意义．     

导数考点分析

一、考纲内容 1.导数在函数中的应用（1）了解函数单调性和导数的关系;能利用倒数研究函数的单调性,会求函数的单调区间（其中多项式函数一般不超过三次）.（2）了解函数在某点处取得极值的必要条件和充分条件;会用导数求函数的极大值、极小值（其中多项式函数一般不超过三次）;会求闭区间上函数的最大值、最小值（其中多项式函数一般不超过三次）.（3）利用导数求函数在某点处的切线斜率及切线的方程问题.     

一个求三次曲线的切线问题引发的思考

用导数求一些高次多项式函数所对应的曲线在某一点处的切线方程是导数几何意义的一个重要应用．课本上介绍的例题多是已知切点的情况下来求切线的方程，因此直接应用导数的几何意义即可解决问题．学生在学习这节内容时，不可避免地会遇到一些已知点不是切点的情况，对此类问题只要假设出切点即可解决．     

无线通信MIMO中的频率同步

分别针对无线通信集中式多入多出（MIMO）和分布式MIMO系统,对频偏估计和频偏补偿这两个方面的基本原理和研究现状进行了详细分析,总结出已有研究的不足之处在于对分布式MIMO中的频偏估计以及分布式MIMO-OFDM（正交频分复用）中的频偏补偿的研究尚不完善,指出未来可能的研究方向应主要集中在分布式MIMO中基于一般系统模型的频偏估计方法和分布式MIMO-OFDM中具有实用价值的低复杂度频偏补偿方法两个方面.     

用单调性定义求解三次函数单调性问题

应用函数的单调性定义论证函数的单调性是高中数学教学训练中的一项基础工作．现行教材由于导数的引入,使得近年高考试卷中以三次函数为载体、以考察函数单调性为核心的函数综合题成为命题一大亮点．这些试题综合性强、难度大,命题者本意是考察导数知识的灵活应用．本文给出用单调性定义解决所有三次函数单调性的一种方法,能够成功地避开导数知识,使得这种难度较大的试题可以推向高一年级实施训练,让学生较早地接触、了解、熟悉三次函数及其基本性质,更有利于提高学生应用数学基础知识求解含参数问题的能力．     

浅谈高考中三次函数解题能力的培养

正新课标高考考试大纲说明在导数中阐明了能利用导数研究函数的单调性,会求函数的单调区间(对多项式函数一般不超过三次)。会用导数求函数的极大值、极小值(对多项式函数一般不超过三次);会求闭区间上函数的最大值、最小值(对多项式函数一般不超过三次)。提示我们三次函数是多项式考查的重点。又由于三次函数的导函数是二次函数,而二次函数是高中数学中的重要内容,所以三次函数的问题,已经成为高考命题的一个新的热点和亮点。因此近年来高考以及各地模拟试题中,对函数的考查并不仅仅局限在一些基本初等函数上,出现了不少以三次函数为背景的好试题,需要教师和考生多进行研究,以便掌握规律培养三次函数的解题能力。     

A high performance frequency offset estimator for OFDM

INTRODUCTION Orthogonal frequency division multiplexing (OFDM) has become a promising technology for future wireless communication systems (Kim et al., 2003; 3GPP TSG-RAN-1.TR, 2004) due to its ability to transform a wideband frequency selective channel to a set of parallel flat-fading narrow-band channels, which substantially simplifies the channel equaliza- tion problem. However, a critical weakness of OFDM is its sensitivity to carrier frequency offset (CFO) since it can only t…     

Particle filter for joint frequency offset and channel estimation in MIMO-OFDM systems

A particle filter is proposed to perform joint estimation of the carrier frequency offset (CFO) and the channel in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) wireless communication systems. It marginalizes out the channel parameters from the sampling space in sequential importance sampling (SIS), and propagates them with the Kalman filter. Then the importance weights of the CFO particles are evaluated according to the imaginary part of the error between measurement and estimation. The varieties of particles are maintained by sequential importance resampling (SIR). Simulation results demonstrate this algorithm can estimate the CFO and the channel parameters with high accuracy. At the same time, some robustness is kept when the channel model has small variations.     

Performance of a novel carrier frequency offset estimation algorithm for OFDM-based WLANs

INTRODUCTION Orthogonal frequency division multiplexing (OFDM) has been treated as the key transmission method in Wireless Local Area Networks (WLANs) based on IEEE802.11a protocol (IEEE Standard 802.11a- 1999). However, the sensitivity of the scheme to the frequency offset limits its development. Moose (1994) proposed maximum likelihood esti-mation for the carrier frequency offset by using two different received symbols, but the limitation of this method is that the acquisition r…     

求解多项式最大公因式的一个算法

研究了用辗转相除法求解多项式最大公因式的一个迭代算法。算法将两个多项式相乘,相除等过程用矩阵方法来处理,从而获得了用Matlab软件求解多项式最大公因式的迭代算法。     

Efficient timing and frequency offset estimation scheme for OFDM systems

A new training symbol weighted by pseudo-noise(PN) sequence is designed and an efficient timing and fre quency offset estimation scheme for orthogonal frequency division multiplcxing(OFDM)systems is proposed.The timing synchronization is accomplished by using the piecewise symmetric conjugate of the primitive training symbol and the good autocorrelation of PN weighted factor.The frequency synchronization is finished by utilizing the training symbol whose PN weighted factor is removed after the timing synchronization.Compared with conventional schemes,the proposed scheme can achieve a smaller mean square error and provide a wider frequency acquisition range.     

Phase factor sequences algorithm in partial transmit sequence

Partial transmit sequence(PTS)is a promising technique for peak-to-average power ratio(PAPR)reduction in orthogonal frequency division multiplexing(OFDM).While in optimal PTS,an exhaustive search for all combinations of phase factor sequences is required,this results in huge computation.In this paper,by introducing the orthogonal design,a phase factor sequences algorithm is proposed.The algorithm uses orthogonal table to gencrate phase factor sequences,and the regular PAPR computation result is then followed by the parameter estimation.The simulation result shows that the proposed algorithm reduces the computation notably and obtains a good PAPR performance approaching the optimal PTS.     

Educating for Character in the Sexual Domain

Econometric cost functions have begun to appear in education adequacy cases with greater frequency. Cost functions are superficially attractive because they give the impression of objectivity, holding out the promise of scientifically estimating the cost of achieving specified levels of performance from actual data on spending. By contrast, the opinions of educators form the basis of the most common approach to estimating the cost of adequacy, the professional judgment method. The problem is that education cost functions do not in fact tell us the cost of achieving any specified level of performance. Instead, they provide estimates of average spending for districts of given characteristics and current performance. It is a huge and unwarranted stretch to go from this interpretation of regression results to the claim that they provide estimates of the minimum cost of achieving current performance levels, and it is even more problematic to extrapolate the cost of achieving at higher levels. In this article we review the cost-function technique and provide evidence that draws into question the usefulness of the cost-function approach for estimating the cost of an adequate education.     

PTS方法中基于相关性的子块划分设计(英文)

为了提高部分传输序列(PTS)方法在正交频分复用(OFDM)系统中降低峰均功率比(PAPR)的能力,研究了PTS方法中的子块划分问题.通过PTS的自相关函数(ACFs)和备选信号的互相关函数(CCFs),将子块划分和降低PAPR的能力相关联.这里用Q表示ACFs的均方幅度的方差.研究发现Q值越小PTS方法所能达到的PAPR性能越好,并以此作为子块划分的设计准则.依据这一准则,对4种常见的分块方法做了比较并提出一种有效的子块划分策略.比较结果表明具有良好结构性的子块划分方法在具有低运算复杂度的同时ACFs的均方幅度方差较大,因此PAPR性能不佳.新策略可以看作是在PAPR性能和运算复杂度间所做的一种折中.仿真结果表明该策略可以在相对低的复杂度的条件下达到最优性能,同时也不会增加附加信息.     

Time-domain training sequences design for MIMO OFDM channel estimation

This paper describes a Least Squares （LS） channel estimation scheme for MIMO OFDM systems based on time-domain training sequence. We first compute the minimum mean square error （MSE） of the LS channel estimation, and then derive the optimal criteria of the training sequence with respect to the minimum MSE. It is shown that optimal time-domain training sequence should satisfy two criteria. First, the autocorrelation of the sequence transmitted from the same antenna is an impulse function in a region longer than the channel maximum delay. Second, the cross-correlation between sequences transmitted from different antennas is zero in this region. Simulation results show that the estimator using optimal time-domain training sequences has better performance than that using optimal frequency training sequence at low signal-to-noise ratio （SNR）. To reduce the training overhead, a suboptimal training sequence is also proposed. Comparing with optimal training sequence, it has low computation complexity and high transmission efficiency at the expense of little performance degradation.