扩频通信技术及其应用

扩频通信是现代通信系统中新的通信方式,它具有较强的抗干扰、抗衰落和抗多径性能,频谱利用率高的特点。扩展频谱通信是一种将信息的带宽扩展很多倍进行通信的技术,近年来在现代科技的许多领域中,应用非常广泛。着重叙述了扩频通信的工作原理、特点、及其发展应用。     

Saturation in multivariate simultaneous approximation

In this paper we present a new result on the saturation of sequences of linear operators in a multivariate and simultaneous setting. Specifically, a small o saturation result is obtained for the partial derivatives of the classical Bernstein bivariate operators on the unit simplex. Solutions of boundary value problems for certain partial differential equations of elliptic type play an important role.     

Bernstein-type operators which preserve polynomials

In this paper we present the sequence of linear Bernstein-type operators defined for f∈C[0,1] by B_n(f°τ⁻¹)°τ, B_n being the classical Bernstein operators and τ being any function that is continuously differentiable ∞ times on [0,1], such that τ(0)=0, τ(1)=1 and τ^′(x)>0 for x∈[0,1]. We investigate its shape preserving and convergence properties, as well as its asymptotic behavior and saturation. Moreover, these operators and others of King type are compared with each other and with B_n. We present as an interesting byproduct sequences of positive linear operators of polynomial type with nice geometric shape preserving properties, which converge to the identity, which in a certain sense improve B_n in approximating a number of increasing functions, and which, apart from the constant functions, fix suitable polynomials of a prescribed degree. The notion of convexity with respect to τ plays an important role.     

Mean square asymptotic behavior of stochastic neural networks with infinitely distributed delays

In this paper, according to classic -matrix method, integral–differential inequality technique and Ito formula, we study asymptotic behavior in mean square sense of stochastic neural networks with infinitely distributed delays by establishing a generalized Halanay inequality. This is a new means for investigating asymptotic behavior of stochastic differential equation. Some useful results are derived. Especially, our methods can be extended to research p-moment asymptotic behavior easily. At last, example and simulations demonstrate the power of our methods.     

A Galerkin finite element scheme for time–space fractional diffusion equation

In this paper, a Galerkin finite element scheme to approximate the time–space fractional diffusion equation is studied. Firstly, the fractional diffusion equation is transformed into a fractional Volterra integro-differential equation. And a second-order fractional trapezoidal formula is used to approach the time fractional integral. Then a Galerkin finite element method is introduced in space direction, where the semi-discretization scheme and fully discrete scheme are given separately. The stability analysis of semi-discretization scheme is discussed in detail. Furthermore, convergence analysis of semi-discretization scheme and fully discrete scheme are given in details. Finally, two numerical examples are displayed to demonstrate the effectiveness of the proposed method.     

具有测量数据丢失的离散不确定时滞系统鲁棒Kalman滤波

研究了具有测量数据丢失的离散不确定时滞系统鲁棒Kalman滤波问题, 其中时延存在于系统状态和观测值中. 模型的不确定性通过在系统矩阵中引入随机参数扰动来表示, 测量数据丢失现象则通过一个满足Bernoulli分布且统计特性已知的随机变量来描述. 基于最小方差估计准则, 利用射影性质和递归射影公式得到一个新的滤波器设计方法, 并且保证了滤波器的维数与原系统相等. 与传统的状态增广方法相比, 当时延比较大时, 该方法可以有效降低计算量. 最后, 给出一个仿真例子说明所提方法的有效性.     

基于对数的NTC热敏电阻测温系统的设计

针对NTC热敏电阻阻值与温度(R-T)的非线性特性,为了提高测温精度,提出一种三阶对数公式法对R-T特性进行分段曲线拟合.该测温系统以三阶对数公式为基础进行了软硬件设计,实现了对船用柴油机的机油温度、冷却水温度的高精度测量.通过实验测试表明,在0～120℃温度范围内,采用该测温系统的测温误差小于±0.3℃.该测温系统已...     

计算机视觉系统框架的新构思

计算机视觉是人类视觉的模拟。计算机视觉四十多年的发展既取得了成绩也存在不足。在计算机视觉发展过程中,相继提出了三个主要的理论框架：计算视觉理论,基于知识的视觉理论和主动视觉理论。该文对这三个理论框架及其存在的问题进行了讨论,并提出了一个完善和通用的计算机视觉的系统框架。     

A characterization of span program size and improved lower bounds for monotone span programs

We give a characterization of span program size by a combinatorial-algebraic measure. The measure we consider is a generalization of a measure on covers which has been used to prove lower bounds on formula size and has also been studied with respect to communication complexity.?In the monotone case our new methods yield lower bounds for the monotone span program complexity of explicit Boolean functions in n variables over arbitrary fields, improving the previous lower bounds on monotone span program size. Our characterization of span program size implies that any matrix with superpolynomial separation between its rank and cover number can be used to obtain superpolynomial lower bounds on monotone span program size. We also identify a property of bipartite graphs that is suficient for constructing Boolean functions with large monotone span program complexity. Received: September 30, 2000.     

误差最小的计算机插补原理

从包括的思想出发,解决了对单调光滑函数曲线构造一个带域,在此带域中所确定的绘图路径是误差最小的。另外,文中应用带域提出了一种误差最小插补法,得到递推公式,每次要计算的是进给步数,跟过去一贯采用的每走一步都要计算判别函数的传统方法比较,具有较强的优越性,最后给出计算实例。