共查询到20条相似文献,搜索用时 9 毫秒
1.
Dae-Young Seol Tae-Won Yune Gi-Hong Im 《Communications Letters, IEEE》2009,13(5):321-323
The identification of primary networks improves efficiency in dynamic spectrum access. We propose a spatial diversity signature for the primary signal detection, which exploits the structure of space-time or space-frequency codeword based on Alamouti scheme. The signature pattern informs the secondary user which network transmits the primary signal and enables to maintain an experiential database for each primary network. The proposed scheme provides reliable detection and network identification performance over frequency-selective fading channels in low signal-to-noise ratio regimes, without sacrificing the data rate of primary system. 相似文献
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Two-dimensional synchronization patterns for minimum ambiguity 总被引:1,自引:0,他引:1
《IEEE transactions on information theory / Professional Technical Group on Information Theory》1982,28(4):600-604
A number of closely related combinatorial problems corresponding to specific assumptions about the type of time-frequency sequence which may be appropriate in a particular application, are formulated in terms of square or rectangular arrays of dots with appropriate constraints on the two-dimensional correlation function. The current state of knowledge concerning each of these problems is summarized. It is hoped that more general constructions may be found, leading to larger families of solutions, as well as better computational algorithms for finding individual solutions which may lie outside of the general families. 相似文献
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Neff J.A. Athale R.A. Lee S.H. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1990,78(5):826-855
Two-dimensional spatial light modulators (SLMs) modulate one of the properties of an optical wavefront (amplitude, phase, polarization) as a function of two spatial dimensions and time in response to information-bearing control signals that may be either optical or electrical. These devices form a critical part of optical information processing systems, serving as input transducers as well as performing several basic processing operations on optical wavefronts. A tutorial overview of the 2-D SLMs is given. their applications are outlined, a classification scheme for them is given, and major types of SLMs that are under active development are described 相似文献
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《Solid-state electronics》1987,30(4):445-455
We present a two-dimensional model of ion implantation which allows for position dependent lateral moments. The lateral standard deviation and the lateral kurtosis as a function of depth have been calculated by 2-D Monte-Carlo simulations for boron, phosphorus, arsenic, and antimony in silicon for energies in the range of 10–300 keV. The lateral moments as a function of depth and energy as well as the vertical moments as a function of energy have been fitted by simple formulae. We specify two types of distribution functions the parameters of which can be adjusted to given values of standard deviation and kurtosis. In this way the depth dependent lateral moments can be included into analytical distribution functions. 相似文献
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This paper considers the problem of estimating the parameters of known signals received asynchronously by an array of antennas. The parameters of primary interest are the time delays of the signals and their spatial signatures at the array. Estimates of the signal directions of arrival are also considered but are of secondary importance in this work. Maximum likelihood algorithms and more computationally efficient approximations are developed for both the case where all received signals are identical (the channel estimation/overlapping echo problem) and where they are all distinct. Conditions are also derived under which the standard matched filter approach yields consistent and statistically efficient parameter estimates. The issue of solution uniqueness is addressed, and in particular, an upper bound on the number of signals whose parameters may be uniquely identified is derived for a number of different cases. Typically, the bound is far greater than the number of sensors and is limited only by the number of data samples collected. Some representative simulation examples are also included to illustrate the algorithms' performance relative to the Cramer-Rao bound 相似文献
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L1-norm-based common spatial patterns 总被引:1,自引:0,他引:1
Common spatial patterns (CSP) is a commonly used method of spatial filtering for multichannel electroencephalogram (EEG) signals. The formulation of the CSP criterion is based on variance using L2-norm, which implies that CSP is sensitive to outliers. In this paper, we propose a robust version of CSP, called CSP-L1, by maximizing the ratio of filtered dispersion of one class to the other class, both of which are formulated by using L1-norm rather than L2-norm. The spatial filters of CSP-L1 are obtained by introducing an iterative algorithm, which is easy to implement and is theoretically justified. CSP-L1 is robust to outliers. Experiment results on a toy example and datasets of BCI competitions demonstrate the efficacy of the proposed method. 相似文献
8.
Shiann-Shiun Jeng Xu G. Hsin-Piao Lin Vogel W.J. 《Antennas and Propagation, IEEE Transactions on》1998,46(7):953-962
A spatial signature is the response vector of a base-station antenna array to a mobile unit at a certain location. Mobile subscribers at different locations exhibit different spatial signatures. The exploitation of spatial diversity (or the difference of spatial signatures) is the basic idea behind the so-called space-division multiple-access (SDMA) scheme, which can be used to significantly increase the channel capacity and quality of a wireless communication system. Although SDMA schemes have been studied by a number of researchers, most of these studies are based on theoretical analyses and computer simulations with ideal assumptions. Not much experimental study, has been reported on spatial signature variation due to nonideal perturbations in a real wireless communication environment. The purpose of this paper is to present, for the first time, extensive experimental results of spatial signature variation using a smart antenna testbed. The results presented include the spatial signature variation with time, frequency, small displacement, multipath angle spread and beamforming performance. The experimental results show the rich spatial diversity and potential benefits of using an antenna array for wireless communication applications 相似文献
9.
Blind spatial signature estimation via time-varying user power loading and parallel factor analysis 总被引:5,自引:0,他引:5
Yue Rong Vorobyov S.A. Gershman A.B. Sidiropoulos N.D. 《Signal Processing, IEEE Transactions on》2005,53(5):1697-1710
In this paper, the problem of blind spatial signature estimation using the parallel factor (PARAFAC) analysis model is addressed in application to wireless communications. A time-varying user power loading in the uplink mode is proposed to make the model identifiable and to enable application of PARAFAC analysis. Then, identifiability issues are studied in detail and closed-form expressions for the corresponding modified Crame/spl acute/r-Rao bound (CRB) are obtained. Furthermore, two blind spatial signature estimation algorithms are developed. The first technique is based on the PARAFAC fitting trilinear alternating least squares (TALS) regression procedure, whereas the second one makes use of the joint approximate diagonalization algorithm. These techniques do not require any knowledge of the propagation channel and/or sensor array manifold and are applicable to a more general class of scenarios than earlier approaches to blind spatial signature estimation. 相似文献
10.
We address two shortcomings of the common spatial patterns (CSP) algorithm for spatial filtering in the context of brain--computer interfaces (BCIs) based on electroencephalography/magnetoencephalography (EEG/MEG): First, the question of optimality of CSP in terms of the minimal achievable classification error remains unsolved. Second, CSP has been initially proposed for two-class paradigms. Extensions to multiclass paradigms have been suggested, but are based on heuristics. We address these shortcomings in the framework of information theoretic feature extraction (ITFE). We show that for two-class paradigms, CSP maximizes an approximation of mutual information of extracted EEG/MEG components and class labels. This establishes a link between CSP and the minimal classification error. For multiclass paradigms, we point out that CSP by joint approximate diagonalization (JAD) is equivalent to independent component analysis (ICA), and provide a method to choose those independent components (ICs) that approximately maximize mutual information of ICs and class labels. This eliminates the need for heuristics in multiclass CSP, and allows incorporating prior class probabilities. The proposed method is applied to the dataset IIIa of the third BCI competition, and is shown to increase the mean classification accuracy by 23.4% in comparison to multiclass CSP. 相似文献
11.
以均匀直线阵和四阶累积量为基础,提出了一种新的空间特征盲估计算法.该算法首先利用阵列输出四阶累积量构造了一种空间特征矩阵,对其作特征分解可以得到各用户的空间特征估计.然后,在空间特征估计基础上,结合前向/共轭后向空间平滑技术进行了多径波达方向(Direction of Arrival,DOA)估计.该方法突破了传统MUSIC、ESPRIT等算法的局限,可以利用M阵元估计2M2/3个DOA,且各DOA与信源自动配对.该算法不依赖于信号具体特征,适用于任意加性高斯噪声(如有色噪声)环境.理论分析和仿真结果说明了算法的有效性和鲁棒性. 相似文献
12.
Certificateless signature and blind signature 总被引:3,自引:0,他引:3
Certificateless public key cryptography is a new paradigm introduced by Al-Riyami and Paterson. It eliminates the need of the certificates in traditional public key cryptosystems and the key escrow problem in IDentity-based Public Key Cryptography (ID-PKC). Due to the advantages of the certificateless public key cryptography, a new efficient certificateless pairing-based signature scheme is presented, which has some advantages over previous constructions in computational cost. Based on this new signature scheme, a certificateless blind signature scheme is proposed. The security of our schemes is proven based on the hardness of computational Diffie-Hellman problem. 相似文献
13.
刘海龙 《信息安全与通信保密》2003,(4)
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… 相似文献
14.
YU Yong YANG Bo State Key Laboratory of ISN Xidian University Xi’an China SUN Ying College of information South China Agricultural University Guangzhou China 《中国邮电高校学报(英文版)》2007,14(2):69-74
Proxy signature schemes allow an original signer to delegate his signing rights to a proxy signer. However, many proxy signature schemes have the defect which is the inability to solve the proxy revocation problem. In this article, we firstly propose an identity-based threshold signature scheme and show that it has the properties of unforgeability and robustness. In our threshold signature scheme, we adopt such a method that the private key associated with an identity rather than the master key is shared. Then, based on the threshold signature scheme, an identity-based mediated proxy signature scheme is proposed where a security mediator (SEM) is introduced to help a proxy signer to generate valid proxy signatures, examine whether a proxy signer signs according to the warrant, and check the revocation of a proxy signer. It is shown that the proposed scheme satisfies all the security requirements of a secure proxy signature. Moreover, a proxy signer must cooperate with the SEM to generate a valid proxy signature, which makes the new scheme have an effective and fast proxy revocation . 相似文献
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《Electron Devices, IEEE Transactions on》1983,30(7):744-749
This paper introduces the first general two-dimensional oxidation model based on steady-state oxygen diffusion and the slow incompressible viscous flow of oxide. The moving-boundary problem is solved through a novel numerical technique based on pressure/velocity iteration and a boundary-value approach. The simulation results obtained for oxide shape and bird's beak size versus pad-oxide thickness are in excellent agreement with experiments. This model is also able to calculate stress on the silicon interface during oxidation; this calculated value (6 × 109dyne/cm2) also agrees with the measurement and reveals the tendency of stress to decrease with increasing pad-oxide thickness. 相似文献
18.
ID-based group signature 总被引:9,自引:0,他引:9
Sangjoon Park Seungjoo Kim Dongho Won 《Electronics letters》1997,33(19):1616-1617
The authors present an ID-based group signature which is based on ordinary ID-based signature schemes such as Ohta-Okamoto's scheme and Guillou-Quisquater's scheme. Thus, the group signature is verified from the identities of group members. A signer proves that, by verifiable encryption of his ordinary signature, a group authority can identify him and, by Schoenmaker's method, he proves that he knows a signature of a group member 相似文献
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Goggins W. Jr. Blacksmith P. Sletten C. 《Antennas and Propagation, IEEE Transactions on》1974,22(6):774-780
The identification and classification of radar targets is facilitated by a newly developed technique based on measurements of the differential phase shift of the target scattering obtained at harmonic phase-locked frequencies. These phase differences are independent of target range and relative motion. It is mathematically proved that for a smooth conducting body in the Rayleigh region the copolarized terms of the scattering matrix have zero phase shift. Based on this, the absolute target phase can be measured. The differential phase shift between two harmonic frequencies has been measured for various types of targets. The experimental results indicate that the differential phase shift is a useful parameter for classifying or identifying targets, and one that can be readily measured in practical radars. 相似文献