A simple angular alignment technique for apolarization-maintaining-fiber

Simple and accurate techniques for angular alignment of a polarization-maintaining-fiber (PMF) to a linearly polarized input beam are required for many optical-fiber applications. We consider an alignment technique wherein a short length of PMF undergoes a large temperature excursion and the output beam from the fiber is simply monitored by a linear polarizer and a power meter. Upon carefully considering the results for rotation angles near alignment, an accuracy better than 0.2° as well as a measurement of the fiber crosstalk are obtained     

A fast algorithm for signature prediction and image formation usingthe shooting and bouncing ray technique

We present a fast simulation algorithm for generating the range profiles and inverse synthetic aperture radar (ISAR) images of complex targets using the shooting and bouncing ray (SBR) technique. Starting with the time-domain and image-domain ray-tube integration formulas we derived previously, we cast these formulas into a convolution form. The convolution consists of a nonuniformly sampled signal and a closed-form time-domain or image-domain ray spread function. Using a fast scheme proposed by Sullivan (1990), the nonuniformly sampled function is first interpolated onto a uniform grid before the convolution is performed by the fast Fourier transform (FFT) algorithm. Results for several complex targets are presented to demonstrate the tremendous computation time savings and excellent fidelity of the scheme. Using the fast scheme, a speed gain of a factor of 30 is achieved in performing the ray summation as compared to the direct convolution in range profile computation and a factor of 180 in ISAR image formation for a typical aircraft at S-band     

Improved angular ambiguity and accuracy by aperture-modulation technique

A time-domain method for splitting the angular information received by an antenna array is described, where an incident wave is divided into two channels, corresponding to one pattern with low angular ambiguity and another with improved accuracy. Two capital ways of processing both these signals are shown.     

Radar signature prediction using moment method codes via frequencyextrapolation technique

A frequency extrapolation scheme is developed to efficiently predict radar signatures using moment method codes. The approach is to parameterize the induced current on the target based on a multipath excitation model via the ESPRIT superresolution algorithm. The multiple scattering mechanisms at high frequencies are included in the model to ensure the accuracy of the algorithm. The range profiles for several test targets are calculated to demonstrate the performance of the algorithm. A numerical experiment is conducted to find the possible error sources of the algorithm and determine an upper limit on the frequency extrapolation bandwidth. The algorithm is also extended to generate ISAR images by using the frequency extrapolation in conjunction with the bistatic approximation in the angular dimension. The ISAR image of the benchmark VFY-218 airplane is predicted at 400 MHz and compared against the chamber measurement result. The main scattering features in the measured image are successfully predicted using this approach with very modest computational resources     

高层薄卷云消光后向散射比的求解方法

卷云的消光后向散射比是研究卷云光学特性的一个重要参量,我们的工作就是利用米散射激光雷达探测的大气和卷云的后向散射信号来获得间断出现的高层薄卷云的消光后向散射比.在无大的天气系统过境的情况下,通过对定点观测到的雷达上空有卷云和无卷云的大气回波信号的对比求解,得出间歇性卷云的消光后向散射比,并与其他方法进行了对比分析,指明了该方法的可靠性和局限性.     

一种新型数字签名方法

本文利用数学规划中整数不定方程组求解的困难提出了一种全新的数字签名方法。该方法防止破译与伪造的依据是整数不定方程组的求解在计算上是强NP问题.本文提出的签名方法具有类似于DSS的随机特性.有效地防止了伪造签名的可能性。     

A new construction of signature waveforms for synchronous CDMA systems

We consider synchronous code-division multiple access (CDMA) systems over an additive white Gaussian noise (AWGN) channel, where all users are divided into groups of small size. The signature waveforms for users in each group are constructed from the same signature sequence but with different chip waveforms. To minimize the multiple access interference (MAI) at the output of the correlators, Welch-bound-equality (WBE) sequences and chip waveforms having optimal correlation property are employed. The main idea behind the proposed construction is to suppress the inter-group interference from users in different groups as much as possible (even to remove it completely) at the expense of introducing the intra-group interference among the users in the same group. The intra-group interference, however, can be easily handled by a low-complexity, optimal (or suboptimal) multiuser detector(s) if the group size is kept small enough. As special cases, the proposed constructions correspond to the optimal design of the signature waveforms and the conventional system that uses a single chip waveform, respectively. Thus the proposed construction offers a flexibility to trade performance for complexity. In particular, it is demonstrated that, while the conventional system's error performance is very sensitive to even a small amount of overload, the proposed system with two users per group can have up to 100% overload with an excellent error performance.     

汉字签名自动辨识的一种结构描述方法

在充分分析了签名图像的基础上提出了一种针对汉字签名利用结构描述来进行签名自动辨识的方法。其基本思想是在汉字骨架基础上提取构成汉字的各个基本笔段并同时提取表征各笔段的特征值，从而形成带有属性的模式串，以便进行串的比较并根据一定的判断准则给出判断结果。     

A subspace method for signature waveform estimation in synchronousCDMA systems

Synchronous code-division multiple-access (CDMA) techniques possess intrinsic protection against co-channel interference due to orthogonal codes employed and thus, offers higher capacity than existing frequency-division multiple-access (FDMA) or time-division multiple-access (TDMA) systems. In the presence of multipath, however, each signal is subject to frequency-selective fading and the orthogonality condition does not necessarily hold leading to increased cross correlation. In these scenarios, multiuser detection need to be performed to suppress interference and recover the message symbols. To implement such a technique, explicit knowledge of the (nonorthogonal) signature waveforms of all users is required. We propose a blind estimation scheme that provides closed-form estimates of the signature waveforms by exploiting the structure information of the data output. In particular, we show that the subspace of the data matrix contains sufficient information for unique determination of the signature waveforms. Based on this observation, a multiple signal classification (MUSIC)-like algorithm is derived. Performance analysis of the new approach is also presented     

一种新的并行多消息签名方案

在现有的数字签名方案中,一个人可以对一个文件签名,也可以同时对多个文件签名。如果需要多个人对多个文件签名,往往采用顺序签名或者需要一个第三者代理多个人签名。有时需要多个签名人在没有代理人的情况下对多个消息并行(同时)签名,现有的签名方案都满足不了这样的需要。本文给出一种能够满足这种需要的并行多消息签名方案,并给出了安全性证明,签名的验证也是并行的。     

A new digital instrument for measuring angular velocity and acceleration

A new approach to the digital measurement of angular velocity and acceleration is discussed. The proposed instruments provide a very high precision and resolution in measurement. The measurements can be made in a very short time, which may be regarded as almost instantaneous for many practical applications.     

一个新的自认证聚合签名方案

为了克服基于身份的数字签名所固有的问题,同时解决签名在一些特殊环境中产生的效率问题,利用双线性对的技术,结合自认证签名和聚合签名的概念,提出了一个自认证聚合签名方案,该方案合并了自认证签名和聚合签名的优势。最后在随机预言模型下给出了方案的安全性证明。     

Aging signature properties and an efficient signature determination tool for online monitoring

Increased reliability problems in deep sub-micron CMOS technologies have led to a dramatic decrease of lifetime of analog integrated circuits. To palliate this problem, several reliability-aware design approaches have been developed. Reconfigurable circuit design is one of those approaches, which is based on reconfiguring the circuit considering degradation in circuit performances. Sense & React (S & R) approach is the well-known reconfigurable design approach, where degradation in circuit performances are sensed and a pre-established recovery operation is applied to heal the circuit. In practice, indirect measurements are preferred during sense operation, in which electrical quantities are measured in order to determine time to recovery. Determination of the time to recover is the most critical part of a S & R system. One or more circuit variables are selected out of all measurable circuit quantities. The selected signature should have some attributes to be used as the aging signature to reduce the measurement cost. However, efficient aging signature properties have not been defined in the literature yet. Moreover, the designer determines the aging signature manually by performing an iterative search and evaluation on aging simulation results, and there is no tool to ease this time consuming process. This paper clearly describes the aging signature properties and proposes an automatic signature selection tool that determines the most efficient signature for sense operation.     

Efficient radar signature prediction using a frequency-aspectinterpolation technique based on adaptive feature extraction

A radar cross section (RCS) interpolation technique in both frequency and aspect is proposed for the efficient prediction of radar signatures from computational electromagnetics data. Our approach is based on a multiple-arrival model for the induced current on the target. The model parameters are determined by an adaptive feature extraction (AFE) algorithm, which uses an iterative search-and-extract procedure to find the individual model features. Random frequency and aspect sampling is used to circumvent the ambiguity in selecting the features. Numerical examples are presented to test the interpolation algorithm. It is found that sufficient accuracy in the predicted radar features can be achieved even when the original computed data is sampled at 5:1 below the Nyquist criterion in either frequency or aspect. The algorithm is also applied to efficiently predict the radar images of the benchmark VFY218 airplane at UHF band with good results     

辨析数字签名与电子签名

从概念上讲，数字签名(digital signature)与电子签名(electronic signature)是不同的。电子签名是一般化的概念，凡是具有签名功能的电子手段均可称之为电子签名。而数字签名，由于历史的原因，已经被特指为利用公钥密码和散列算法而生成的签名。数字签名是电子签名的一种特定形式。之所以会产生这两个概念，有其历史的原因和现实的意义。 数字签名的概念最早产生于学术界，并广泛应用于科学技术领域。早在1976年Diffie提出公钥密码思想的时候(New Directions inCryptography)，就认为“签名”是公钥密码的一个重要应用，只是当时并未…     

Spaceborne lidar calibration from cirrus and molecular backscatter returns

In order to make optimal quantitative use of multiwavelength spaceborne lidar data, it is essential that the lidar be well calibrated. Due to system gain/efficiency changes that can be expected to occur during the course of a shuttle or satellite mission, it is essential to employ a calibration approach that can be implemented on-orbit, preferably repeatable at least a few times per orbit. For wavelengths less than about 550 nm, in situ calibration can be accomplished via normalization to high-altitude nearly molecular scattering regions. However, for longer wavelengths beyond about 800 nm, particularly the popular Nd: YAG fundamental wavelength at 1064 nm, the Rayleigh normalization approach becomes questionable due to both an inherently weaker signal and a stronger, variable, and somewhat unknown aerosol scattering contribution. For lidars operating at both longer and shorter wavelengths, a viable approach is to retrieve the longer wavelength calibrations ratioed to the shorter wavelength calibrations via comparisons of spectral backscatter from known/quantifiable scatterers. Cirrus clouds are good for this purpose because they occur at high altitudes with significant frequency and provide strong nearly spectrally flat backscatter. This paper presents both the molecular normalization and cirrus spectral backscatter ratio calibration approaches, including results obtained from case studies of lidar data collected during the LITE shuttle mission. Attention is focused on developing a simple autonomous approach applicable to satellite lidar missions such as Cloud-Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) and the Geoscience Laser Altimeter System (GLAS).     

授权子集的群签名方案

基于有限域上的方程根提出一个新的授权子集的签名方案,参与者的签名通过方程根的性质验证,而与现有方案比较,该方案具有秘密计算复杂度低,所需公共信息量小的优点。方案的安全性是基于双线性对的DH问题的困难性。分析表明文中的方案是一个安全、有效的方案。     

新的代理数字签名方案

谷利泽等人提出一个新型代理数字签名方案,鲁荣波等人对其进行了分析与改进,杨丽等人证明了改进方案不满足公钥替换攻击,给出了攻击方法,并在此基础上提出一种改进的代理签名方案。分析杨丽等人提出的新方案,指出该方案增加了计算复杂度,并提出两种改进的代理数字签名方案。实验结果表明改进的方案具有较强的安全性也能够防止公钥替换工具,并减少了计算复杂度,提高了效率。     

A ring signature scheme over braid groups

Quantum algorithms bring great challenges to classical public key cryptosystems, which makes cryptosystems based on non-commutative algebraic systems hop topic. The braid groups, which are non-commutative, have attracted much attention as a new platform for constructing quantum attack-resistant cryptosystems. A ring signature scheme is proposed based on the difficulty of the root extraction problem over braid groups, which can resist existential forgery against the adaptively chosen-message attack under the random oracle model.     

不含双线性对的无证书签名方案

与传统的公钥密码体制和基于身份的密码体制不同,无证书公钥密码体制不需要证书来证明公钥的真实性,同时也避免了基于身份的公钥密码体制中存在的密钥托管问题。现有的无证书签名方案大多是使用双线性对来构造的,因而计算代价比较大。为了解决上述问题,提出了一个不含双线性对的无证书签名方案。基于离散对数困难问题假定,在随机预言模型下证明所提出的方案是安全的。