Route Stability in MANETs under the Random Direction Mobility Model

A fundamental issue arising in mobile ad hoc networks (MANETs) is the selection of the optimal path between any two nodes. A method that has been advocated to improve routing efficiency is to select the most stable path so as to reduce the latency and the overhead due to route reconstruction. In this work, we study both the availability and the duration probability of a routing path that is subject to link failures caused by node mobility. In particular, we focus on the case where the network nodes move according to the Random Direction model, and we derive both exact and approximate (but simple) expressions of these probabilities. Through our results, we study the problem of selecting an optimal route in terms of path availability. Finally, we propose an approach to improve the efficiency of reactive routing protocols.     

平稳信号的非均匀采样与仿真

文中引入平稳随机过程点的知识,建立了广义平稳随机信号的非均匀采样序列模型,推导了其数字频谱的一般公式,揭示出了传统的谱分析没有考虑采样时间间隔的非均匀性对信号的统计特性的影响,误把采样所得随机强度序列的功率谱当作平稳随机过程非均匀采样信号的功率谱。丈中分析了几种具有典型分布函数的随机采样情况,证明了均匀采样信号的数字频谱只是非均匀采样数字频谱的一种特例。     

Stationary Random Fields in Space and Time With Rational Spectral Densities

This paper introduces three spatio-temporal stationary random fields with simple correlation functions and rational spectral densities. The correlation functions have similar forms, but are defined on different space-time domains or related to different spatial norms. Positive and negative correlations are allowed, and the domain of certain model parameters may rely on the spatial dimensional parameter so that the model may be available in a limited space or in all dimensions. The distinctions are discussed among the three basic correlation models. Moreover, families of spatio-temporal stationary random fields are derived by randomizing the spatial and temporal coordinates of the base random fields. The resulting correlation functions are semiparametric, and include separable spatio-temporal models as special cases     

How to Achieve Perfect Simulation and a Complete Problem for Non-interactive Perfect Zero-Knowledge

This paper studies perfect zero-knowledge proofs. Such proofs do not allow any simulation errors, and therefore techniques from the study of statistical zero-knowledge (where a small error is allowed) do not apply to them. We introduce a new error shifting technique for building perfect simulators. Using this technique we give the first complete problem for the class of problems admitting non-interactive perfect zero-knowledge (NIPZK) proofs, a hard problem for the class of problems admitting public-coin PZK proofs, and other applications.     

随机海浪下船舶摇荡的计算机仿真

采用P-M随机海浪谱模拟海浪进行的随机扰动,并对随机海浪下船舶的横摇运动、纵摇、垂荡运动进行时域仿真,探讨随机海浪下的各个自由度的船舶运动情况,为研究船舶的稳性高度及船舶配载问题打下基础。     

Multidimensional Random Process Synthesis and Simulation

In thepaper, wide-sense stationary M-D (multidimensional)random processes, defined by their power spectral densities,are synthesised and simulated by using as an approximation M-Dmultisine random processes consisting of a sum of M>-Dsine components with deterministic amplitudes and random phaseshifts. On the basis of the power spectral density function andphase shifts chosen with some well defined random propertiesthe finite discrete Fourier transform of the M-Dmultisine random process is synthesised. The corresponding M-Dmultisine random process approximation is simulated by performingan inverse M-D finite Fourier transform of the synthesisedspectrum. Realisations of the synthesised and simulated randomprocess approximations may be obtained by using an M-Dfast Fourier transform algorithm. The properties of synthesisedM-D multisine random processes are discussed includingM-D white multisine random process.     

密码学中的随机预言模型与标准模型

随机预言模型与标准模型是密码学可证明安全理论中非常重要的两类模型。在此对这两种模型进行了描述,并研究了运用它们证明密码方案或协议安全性时所采取的不同技术,包括随机预言模型在加密和数字签名方案中的应用研究,以及标准模型下可证明安全性理论在加密方案中的应用研究。此外对进一步研究方向进行了展望。     

On the Stability of Peak Current-Controlled Converters: Analysis, Simulation, and Experiments

Mathematical models are developed for the stability analysis of switching regulators operating in the current programmed, or Peak Current Control (PCC), mode. In this paper derivations are detailed for the necessary and sufficient conditions that the parameters of the PCC converter must satisfy in both the single-ended and the push-pull versions of the circuit. Furthermore, the effect of the stabilizing ramp on the steady-state performance is investigated; it is found that there is an optimum value for which the dc output error is truly zero independently of the input disturbance, and another value which results in a ``deadbeat' response for disturbances of short duration. Finally, an interactive simulation program was developed for the single-ended version of the PCC converter, and implemented on a PDP-15 minicomputer. The results of these simulations agree closely with the predicted behavior, as well as with experimental observations.     

Scaling Laws for One- and Two-Dimensional Random Wireless Networks in the Low-Attenuation Regime

The capacity scaling of extended two-dimensional wireless networks is known in the high-attenuation regime, i.e., when the power path loss exponent alpha is greater than 4. This has been accomplished by deriving information-theoretic upper bounds for this regime that match the corresponding lower bounds. On the contrary, not much is known in the so-called low-attenuation regime when 2lesalphales4. (For one-dimensional networks, the uncharacterized regime is 1lesalphales2.5.) The dichotomy is due to the fact that while communication is highly power-limited in the first case and power-based arguments suffice to get tight upper bounds, the study of the low-attenuation regime requires a more precise analysis of the degrees of freedom involved. In this paper, we study the capacity scaling of extended wireless networks with an emphasis on the low-attenuation regime and show that in the absence of small scale fading, the low attenuation regime does not behave significantly different from the high attenuation regime.     

Perfect binary codes: constructions, properties, and enumeration

Properties of nonlinear perfect binary codes are investigated and several new constructions of perfect codes are derived from these properties. An upper bound on the cardinality of the intersection of two perfect codes of length n is presented, and perfect codes whose intersection attains the upper bound are constructed for all n. As an immediate consequence of the proof of the upper bound the authors obtain a simple closed-form expression for the weight distribution of a perfect code. Furthermore, they prove that the characters of a perfect code satisfy certain constraints, and provide a sufficient condition for a binary code to be perfect. The latter result is employed to derive a generalization of the construction of Phelps (1983), which is shown to give rise to some perfect codes that are nonequivalent to the perfect codes obtained from the known constructions. Moreover, for any m⩾4 the authors construct full-rank perfect binary codes of length 2^m -1. These codes are obviously nonequivalent to any of the previously known perfect codes. Furthermore the latter construction exhibits the existence of full-rank perfect tilings. Finally, they construct a set of 2(2^cn) nonequivalent perfect codes of length n, for sufficiently large n and a constant c=0.5-ϵ. Precise enumeration of the number of codes in this set provides a slight improvement over the results reported by Phelps     

Player Simulation and General Adversary Structures in Perfect Multiparty Computation

The goal of secure multiparty computation is to transform a given protocol involving a trusted party into a protocol without need for the trusted party, by simulating the party among the players. Indeed, by the same means, one can simulate an arbitrary player in any given protocol. We formally define what it means to simulate a player by a multiparty protocol among a set of (new) players, and we derive the resilience of the new protocol as a function of the resiliences of the original protocol and the protocol used for the simulation. In contrast to all previous protocols that specify the tolerable adversaries by the number of corruptible players (a threshold), we consider general adversaries characterized by an adversary structure, a set of subsets of the player set, where the adversary may corrupt the players of one set in the structure. Recursively applying the simulation technique to standard threshold multiparty protocols results in protocols secure against general adversaries. The classical results in unconditional multiparty computation among a set of n players state that, in the passive model, any adversary that corrupts less than n/2 players can be tolerated, and in the active model, any adversary that corrupts less than n/3 players can be tolerated. Strictly generalizing these results we prove that, in the passive model, every function (more generally, every cooperation specified by involving a trusted party) can be computed securely with respect to a given adversary structure if and only if no two sets in the adversary structure cover the full set of players, and, in the active model, if and only if no three sets cover the full set of players. The complexities of the protocols are polynomial in the number of maximal adverse player sets in the adversary structure. Received 31 December 1997 and revised 26 February 1999     

离散随机介质系统模型的研究

本文以雨介质为例，把离散随机介持视为一随机系统，应用系统辨识方法，得到了雨介质的传递函数矩阵模型和模型参数。利用两雨介质的系统模型，结合电波传播理论，求出雨介 一个重要传输参数；路么平均雨滴尺寸分布。计算结果与实测值对比表明本文提出的方法是简便有效的。     

新型振荡采样随机源电路与快速仿真

基于对振荡电路的研究,设计实现了一种振荡采样随机源电路。该电路结构中采用了由组合逻辑电路与复杂反馈回路相结合实现的新型快速振荡器,相较于传统的环形振荡器在保留容易实现、受环境影响小等特点的同时,还有提高随机位产生速率、增强随机性等优势。为实现电路的快速仿真,利用MATLAB/Simulink建立了该随机源的模型,并且为提高仿真准确性,建模过程中考虑了CMOS中的主要噪声,引入噪声模型。最后对系统进行仿真测试,结果表明该模型的输出序列具有较好的随机性。     

The Effect of Random Voids in the Modified Gurson Model

The porous plasticity model (usually referred to as the Gurson–Tvergaard–Needleman model or modified Gurson model) has been widely used in the study of microvoid-induced ductile fracture. In this paper, we studied the effects of random voids on the porous plasticity model. Finite-element simulations were conducted to study a copper/tin/copper joint bar under uniaxial tension using the commercial finite-element package ABAQUS. A randomly distributed initial void volume fraction with different types of distribution was introduced, and the effects of this randomness on the crack path and macroscopic stress–strain behavior were studied. It was found that consideration of the random voids is able to capture more detailed and localized deformation features, such as different crack paths and different ultimate tensile strengths, and meanwhile does not change the macroscopic stress–strain behavior. It seems that the random voids are able to qualitatively explain the scattered observations in experiments while keeping the macroscopic measurements consistent.     

一种基于随机文件的C#与非托管C代码交互模式

在大型科学计算过程中往往会出现海量中间数据,需要在不同开发平台或语言之间传递,此时中间数据会消耗大量系统资源,引起系统性能急剧下降;此外,中间数据长度的不确定性和跨平台的移植性都对科学计算算法提出了较高的接口要求;为保证系统的稳定性和可移植性,文中提出一种基于随机文件读写进行数据传递的简单实用方法,来实现在C#．NET平台下的托管代码中调用C语言开发的非托管代码的交互模式。     

Stability Analysis, Design, and Simulation of a Closed-Loop Converter-Controlled DC Drive

A method for the design of controllers for closed-loop converter-controlled dc drives is given. Popov's stability criterion has been applied for analyzing stability in the large of the drive system. The paper includes experimental and digital simulation results of a dc drive.     

基于Henon混沌模型的随机交织器设计

本文对Turbo码中的关键组成部分-交织器作了分析，阐明了交织器在Turbo码中的重要作用；提出了一种基于Henon混沌模型的随机交织器设计方法，通过仿真实验，本文设计的交织器整体性能优于CDMA2000标准中Turbo码交织器性能，在高斯信道下，纠错性能平均改善0.15dB。     

集群系统与公用网互连的仿真模型和模拟算法

在讨论ＭＰＴ１３２７信令的集群移动通信系统与国内Ｎｏ．７信令的ＰＳＴＮ网间互连，帝现两种信令配合中，研究了集群系统的仿真模型和模拟算法，同时模拟出整个集群系统的工作情况，运行结果证实了所提方案的可行性与准确性。     

地空信道二径模型及仿真

在对地空通信信道充分研究的基础上,提出“二径模型”可以较好地模拟地空通信链路“通视”条件下的信道。对二径模型的仿真结果表明,主反射波与直射波干涉现象产生的深衰落点附近电平可能会低于系统灵敏度电平,可能会造成系统数据丢失或失去跟踪。三维仿真表明,信道不仅随着距离的变化会出现深衰落,还对某些频率的信号衰落较严重,而另一些频率则衰落较小。这对系统频率的选取有一定的指导作用。