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Multi-user MIMO downlink eigen-mode transmission over jointly correlated MIMO channels

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Science china(Information Sciences) 2011年第10期54卷 2124-2137页

作者： LI Xiao ,JIN Shi & GAO XiQi National Mobile communications Research Laboratory,Southeast university,Nanjing 210096,china National Mobile communications Research Laboratory Southeast University Nanjing China

The study of multi-user multiple-input multiple-output (MU-MIMO) systems has emerged recently as an important research topic because such systems have the potential to combine the high capacity that can be achieved through MIMO processing with the benefits of spatial-division ***,receiver and transmitter channel state information (CSI) is generally required,especially for the downlink *** this paper,MU-MIMO downlink transmission systems with statistical CSI at the transmitter are studied for jointly correlated MIMO ***-mode space division multiple access transmission is derived based on the maximization of the ergodic sum rate,and two eigen-mode power allocation algorithms are proposed using matrix permanent and convex optimization *** new algorithms can overcome the limitations of the existing multi-user downlink transmission algorithm in practical applications.

关键词： MIMO eigen-mode multi-user downlink

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communications in Nonlinear Science and Numerical Simulation 1999年第3期4卷 186-190页

作者： Guoqian CHEN and J. H. W. LEE(Centre for Environmental Sciences, Peking university, beijing 100871, china) (Department of Civil Engineering, university of Hong Kong, Hong Kong, china) Centre for Environmental Sciences Peking University Beijing 100871 China Department of Civil Engineering University of Hong Kong Hong Kong China

IntroductionThethermal,abodyofbuoyalfluidinafluidwithwhichitcanmixandgivennamebygliderpilotstothosemassesofwarmairrisingfromhotgroundwarmedbysunshineinwhichtheycansoar,***],duetoi... 详细信息

IntroductionThethermal,abodyofbuoyalfluidinafluidwithwhichitcanmixandgivennamebygliderpilotstothosemassesofwarmairrisingfromhotgroundwarmedbysunshineinwhichtheycansoar,***],duetoi...

关键词： environmental fluid mechanics thermal turbulence modeling

Conjugate adjoining problem in braid groups and new design of braid-based signatures

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Science china(Information Sciences) 2010年第3期53卷 524-536页

作者： WANG LiCheng1,2, WANG LiHua2, CAO ZhenFu3, YANG YiXian1 & NIU XinXin1 Information Security Center, State Key Laboratory of Networking and Switching Technology, beijing university of Posts and Telecommunications, beijing 100876, china 2National Institute of Information and communications Technology, Tokyo 184-8795, Japan 3Trusted Digital Technology Laboratory, Shanghai Jiao Tong university, Shanghai 200240, china Information Security Center State Key Laboratory of Networking and Switching Technology Beijing University of Posts and Telecommunications Beijing China National Institute of Information and communications Technology Tokyo Japan Trusted Digital Technology Laboratory Shanghai Jiao Tong University Shanghai China

The development of quantum computation casts serious threats to the securities of most existing public-key cryptosystems. Braid-based cryptography is one of the alternatives that have potential advantages in resisting quantum attacks. In this paper, the state of the art of braid cryptography is surveyed, and then a new cryptographic problem-conjugate adjoining problem related to braid groups is proposed. Based on this problem, we design a new braid-based signature scheme. This scheme is efficient and provably secure in the random oracle model. Further, we present the comparison between braid-based signatures and RSA-based ones. The signing process of the braid-based schemes is more efficient than that of RSA-based ones, while the verifying process of the braid-based ones is observably slow. Hence, braid-based signatures are suitable for scenarios where the signing process has to be as quick as possible but delays are permitted in the verifying process, for example, in off-line e-cash systems. The key sizes in braid-based schemes are considerably large-about 2K bits in the case of secret keys and 12K bits in the case of public keys. However, braid operations are much simpler and more efficient than modular exponential operations. Therefore, braid-based schemes can be embedded into devices with low computational ability and large memory space. The capability of braid cryptosystems to resist currently known quantum attacks is also discussed from the perspective of hidden subgroup problems.

关键词： braid group conjugate adjoining problem digital signature provable security resistance to quantum attack

Measurement of Mean Burst Period in WallTurbulence by Wavelet Analysis

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communications in Nonlinear Science and Numerical Simulation 1999年第3期4卷 3-5页

作者： Li LI Chunxiao XU Zhaoshun ZHANG and Guialang CUI(Department of Engineering Mechanics, Tsinghua university, beijing 100084, china) Department of Engineering Mechanics Tsinghua University Beijing 100084 China

IntroductionInwallturbulence,theejectionoflow-speedfluidfromthewallandthesweepofth***urst,andwhentheflowisbursting,therealwaysea... 详细信息

IntroductionInwallturbulence,theejectionoflow-speedfluidfromthewallandthesweepofth***urst,andwhentheflowisbursting,therealwaysea...

关键词： turbulence burst phenomena wavelet analysis

Effective capacity region of two-user opportunistic spectrum access

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Science china(Information Sciences) 2011年第9期54卷 1928-1937页

作者： XU YuHua,WANG JinLong & WU QiHui Institute of communications Engineering,PLA university of Science and Technology,Nanjing 210007,china Institute of communications Engineering PLA University of Science and Technology Nanjing China

The effective capacity region of the two-user opportunistic spectrum access (OSA) system in Rayleigh fading environment is derived in this *** OSA is a contemporary research topic,little attention has been given to the capacity analysis under quality-of-service (QoS) ***,we use the effective capacity,which is a powerful tool to analyze the QoS requirements in wireless communication systems,to study the sustainable packet arrival rate of the secondary users while meeting statistical QoS *** derive the effective capacity region of the two-user OSA system and propose a method to obtain the capacity region *** addition,by combining the finite state channel model and the activity of the primary user,an extended finite state channel model for the two-user OSA system is also proposed.

关键词： cognitive radio opportunistic spectrum access effective capacity

Study on near-wall turbulence structures with local Reynolds stress

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communications in Nonlinear Science and Numerical Simulation 2000年第3期5卷 105-117页

作者： Li LI Chunxiao XU Guixiang CUI and Zhaoshun ZHANG(Department of Engineering Mechanics, Tsinghua university, beijing 100084, china) Department of Engineering Mechanics Tsinghua University Beijing 100084 China

The direct- numerical- simulated ch annel turbulence is analyzed with two-dimensional wavelet transform. Considering the relation between turbulence coherent structure and Reynolds stress in near wall region, the local Reynolds stress (LRS) is defined.A new method for extracting coherent signals from turbulence based on the LRS is developed. Velocity fiuctuations are decomposed to coherent signals and background signals. It is found that the scaling exponents of coherent signals have a considerable deviation from the Kolmogorov scaling law q/3 (K41 theory), while that of background signals is very close to q/3. It is confirmed that coherent signals are mainly responsible for the anomalous *** characterized by the positive peaks of LRS, the typical structures in near wall region are obtained by conditional statistical averaging. It is shown that the local character of near-wall turbulence structures can be effectively described with LRS.

关键词： wavelet channel turbulence the local Reynolds stress

Exact Periodic-Wave Solutions for(2+1)-Dimensional Boussinesq Equation and (3+1)-Dimensional KP Equation

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communications in Theoretical Physics 2004年第8期42卷 239-241页

作者： ZHAO Qiang LIU Shi-Kuo FU Zun-Tao School of Physics, Peking university, beijing 100871, china School of Physics Peking University Beijing 100871 China

The(2+1)-dimensional Boussinesq equation and(3+1)-dimensional KP equation are studied by using theextended Jacobi elliptic-function *** exact periodic-wave solutions for the two equations are obtained.

关键词： Jacobi elliptic-function method (2+l)-dimensional Boussinesq equation (3+l)-dimensional KP equation periodic-wave solutions

M-ary CDMA multiuser underwater acoustic communication and its experimental results

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Science china(Information Sciences) 2011年第8期54卷 1747-1755页

作者： HE ChengBing 1,HUANG JianGuo 1,YAN ZhengHua 2 & ZHANG QunFei 1 1 College of Marine Engineering,Northwestern Polytechnical university,Xi’an 710072,china 2 china Ship Research and Development Academy,beijing 100085,china College of Marine Engineering Northwestern Polytechnical University Xi’an China china Ship Research and Development Academy Beijing China

A novel M-ary code division multiple access (M-ary CDMA) underwater acoustic communication (UAC) that utilizes quasi-orthogonal sequences has been proposed for the multiple mobile unmanned underwater vehicle (UUV).Its performance has been verified in both four-user synchronous and three-user asynchronous scenarios through a lake experiment over a very shallow-water *** a chip rate of 2 kilochips per second,good bandwidth efficiency and robust links have been achieved both at 5 and 15 km *** performance of M-ary CDMA in mobile condition (3 m/s) is demonstrated by using the recorded lake experimental data. Experimental results show that the proposed scheme is suitable for multi-user communication platform in long-range shallow-water channel with simple receiver algorithms.

关键词： underwater acoustic communications M-ary code division multiple access (M-ary CDMA) Doppler shift compensation shallow-water acoustic network unmanned underwater vehicle

A method for exploring some new solutions of complex lamellar flow

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communications in Nonlinear Science and Numerical Simulation 2000年第1期5卷 17-20页

作者： Xin HU Yongnian HUANG and Yi ZENG Department of Mechanics and Engineering Science, State Key Laboratory for Turbulence Research, Peking university, beijing 100871, china Basic Department, Jiaotong university of Eastern china, Nanchang 330013, china Dept. of Mechanics and Eng. Science State Key Lab. for Turbulence Res. Peking University Beijing 100871 China Basic Department Jiaotong University of Eastern China Nanchang 330013 China

Complex lamellar flow is a typical flow in fluid mechanics. Its research has high theoretical value. Generally speaking, there are only two typical flows in nature: one is Beltrami flow, the other is complex lamellar flow. We have known much about the former. But the solutions of the latter are hard to obtain because it is difficult to solve the N-S equation or Euler equation. From the incompressible condition, if we let the form of the velocity satisfy some special conditions, we would obtain some new solutions of this flow.

关键词： Beltrami flow complex lamellar flow exact solution incompressible condition