Table of Content

20 April 2014 Volume 41 Issue 2

  

Original Articles

Traffic allocation algorithm of multi-radio access transmission based on minimizing delay over heterogeneous networks

ZHENG Jie;LI Jiandong;LIU Qin;SHI Hua;YANG Xiaoniu

J4. 2014, 41(2):  1-8.  doi:10.3969/j.issn.1001-2400.2014.02.001

Abstract ( 901 )   PDF (1837KB) ( 874 )   Save

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To minimize the traffic arrival delay, a joint network selection and traffic allocation algorithm is proposed for parallel multi-radio access transmission. The algorithm takes into account the available bit rates and network delays of different networks. Based on the Beckmann transformation method, we obtain the threshold for the optimal traffic allocation. According to such a threshold, a minimal subset of admitted networks can be chosen and traffic allocation among these networks can be done to achieve the minimum delay. Simulation results show that the proposed algorithm could improve the arrival delay effectively and guarantee the maximum throughput under the heavy load condition.

Low complexity transmit antenna selection algorithm for multi-cell interference alignment systems

ZHU Bin;GE Jianhua;SUN Chuiqiang;LI Jing

J4. 2014, 41(2):  9-14.  doi:10.3969/j.issn.1001-2400.2014.02.002

Abstract ( 868 )   PDF (554KB) ( 892 )   Save

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Starting from the investigation of the optimal transmit antenna selection (TAS) algorithm based on the exhaustive search and distributed interference alignment (IA), a low complexity TAS algorithm is proposed for multi-cell IA systems. The proposed algorithm utilizes the greedy search strategy and the distributed IA with partial iterations to reduce the computational complexity. In the proposed algorithm, the TAS scheme for each base station is optimized successively in a way that the system sum capacity is increased under the condition that the TAS schemes for the other base stations remain unchanged. Complexity analysis and simulation results show that the proposed algorithm can sharply reduce the computational complexity while the performance of system sum capacity is close to that of the optimal TAS algorithm. Moreover, by properly choosing the iteration number of partial iterations, the proposed algorithm can achieve an effective tradeoff between system sum capacity and computational complexity.

Attack method against the McEliece cryptosystem based on the correlative quasic-cyclic codes set

LIU Jingmei;WANG Yanli;LIANG Bin;ZHAO Senlin

J4. 2014, 41(2):  15-19+50.  doi:10.3969/j.issn.1001-2400.2014.02.003

Abstract ( 807 )   PDF (476KB) ( 775 )   Save

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Focusing on the security of McEliece public key cryptosystem based on the QC-LDPC code, a new attack algorithm based on the correlative quasi-cyclic(QC) code word is proposed. As the code word in the QC code set is shifted cyclically which is equivalent to information retransmission, the algorithm's effect is better. Performance is analyzed from probability of the correct decipher and computational complexity. Simulation results show that the proposed algorithm possesses a higher probability of the correct decipher (0.999) and a lower work factor (2^40.7).

Proxy re-signature scheme over the lattice

JIANG Mingming;HU Yupu;WANG Baocang;LIU Zhenhua;LAI Qiqi

J4. 2014, 41(2):  20-24.  doi:10.3969/j.issn.1001-2400.2014.02.004

Abstract ( 1092 )   PDF (447KB) ( 876 )   Save

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For the proxy insecurity of the re-signature schemes based on large integer factorization and the discrete logarithm problem in quantum environment, we present a proxy re-signature scheme that can resist the quantum attack. Using Xagawa's proxy re-encryption technology and lattice signatures without trapdoors technology, we construct the first lattice-based proxy re-signature scheme. The security of this scheme is based on the hardness of the Small Integer Solution(SIS) problem. The results of the proof and efficiency analysis show that this scheme has the properties of bidirection, multi-use, optimal key and transparency. Compared with previous schemes relying on other hardness assumptions, it has the advantage of low asymptotic computational complexity. Finally, we extend the scheme to the identity-based proxy re-signature scheme.

Coherence-weighted optimum interferometric phase filtering method

LI Jinwei;LI Zhenfang;LIU Yanyang;BAO Zheng

J4. 2014, 41(2):  25-31.  doi:10.3969/j.issn.1001-2400.2014.02.005

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A coherence-weighted optimum interferometric phase filtering method is presented. It is proved that the optimum weight is the variance reciprocal of the phase noise in the sense of minimum post-filter phase noise variance, and the approach to obtaining the optimum weight through coherence estimation is exhibited. Moreover, in estimating the coherence, the synthetic interferogram of the scene which is proportional to the range difference between targets and radars is computed and compensated with reference DEM firstly, then a group of directional windows is utilized to select the samples adaptively according to the Minimum-Mean-Phase-Difference rule, and simulation experiment has established the reasonable choice of the directional windows' parameters. Finally, the processing results of the real data show that our method can suppress the phase noise and reduce the number of residues dramatically.

Waveform de-correlation method in bistatic MIMO radars

DANG Bo;LIAO Guisheng;LI Jun

J4. 2014, 41(2):  32-36+78.  doi:10.3969/j.issn.1001-2400.2014.02.006

Abstract ( 810 )   PDF (584KB) ( 873 )   Save

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The auto-correlation and cross-correlation properties of transmit waveforms have great effects on the performance of MIMO radar systems. However, it is difficult to design waveforms that have ideal auto-correlation properties as well as cross-correlation ones. In this paper, an MMSE based waveform de-correlation algorithm is proposed to cancel the effects of the auto-correlation and cross-correlation of transmit waveforms in the receiver. The received signal model of bistatic MIMO radars is first derived. Then, the de-correlation filters are derived by using the MMSE method to reduce the influences of colored noise enhancement. Finally, the polynomial expansion method is used to simplify the computational complexity of the proposed de-correlation filters. The performance of the proposed method is verified by applying it to bistatic MIMO radar multi-target localization. Simulation results demonstrate the effectiveness of the proposed algorithm.

High precision stitching algorithm for the DBS image

CHEN Hongmeng;LI Ming;JIA Lu;WU Yan

J4. 2014, 41(2):  37-43.  doi:10.3969/j.issn.1001-2400.2014.02.007

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The stitching quality of the Doppler Beam Sharpening (DBS) image will be greatly affected due to the non-ideal movement of the radar platform (variation in attitude and  position). This paper presents a correction model for the movement error. A novel method based on affine transformation is proposed, which can correct and stitch the DBS image effectively. By compensating the variation in attitude and position simultaneously, the discontinuity could be eliminated. Subsequently, the sub-image is stitched together. Simulation analysis and measured data results show that the algorithm can correct the motion error and stitch the sub-images effectively without increasing the computational complexity.

Analysis of the statistical model with the  two-dimensional cumulant feature applying to modulation classification

LIU Pei;SHUI Penglang;GUO Yongming;LI Ning

J4. 2014, 41(2):  44-50.  doi:10.3969/j.issn.1001-2400.2014.02.008

Abstract ( 779 )   PDF (568KB) ( 732 )   Save

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Higher order cumulants are the key features for implementing digital modulation classification. However, few available literatures focus on the statistical model of cumulant features. A two-dimensional normalized fourth-order cumulant feature is proposed to classify linear digital modulation in the additive white Gaussian noise channel, and then it is derived that the two-dimensional feature asymptotically obeys Gaussian distribution. In order to show the correctness of the proposition, a maximum likelihood classifier is formed in the two-dimensional feature domain according to the Bayesian criterion. The average probability of correct classification of the binary class problem is theoretically determined, which is consistent with the result obtained by simulations, thus justifying the correctness of the proposed theoretical results.

Efficient mobile IP registration protocol with AAA using pairing-free certificateless public key cryptography

XU Jie;DANG Lanjun;SHI Guangming

J4. 2014, 41(2):  51-57.  doi:10.3969/j.issn.1001-2400.2014.02.009

Abstract ( 1409 )   PDF (559KB) ( 812 )   Save

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In order to realize the commercial deployment of the mobile IP, AAA (Authentication, Authorization, Accounting) is introduced into mobile IP registration. Aimed at the security and efficiency problems of the registration, a mobile IP registration protocol with AAA is proposed based on pairing-free certificateless public key cryptography. The mutual authentications between AAAF (AAA server in Foreign networks) and AAAH (AAA server in Home networks) are achieved by using a strongly secure and efficient certificateless signature scheme without pairings; the authentication of AAAH to MN (Mobile Node) and that of MN to HA (Home Agent) are realized via the MAC (Message Authentication Code). The user anonymity is achieved via the dynamic TID (Temporary Identity) instread of the user's account information of the NAI (Network Access Identifier). Theoretical analyses show that the protocol reaches the expected security goals. Compared with the protocol proposed by Cao et al., the protocol reduces the registration delay about 20％ while improving the security.

Distributed high-frequency surface wave radar DOA estimation using compressed sensing

WANG Zan;CHEN Baixiao

J4. 2014, 41(2):  58-63+129.  doi:10.3969/j.issn.1001-2400.2014.02.010

Abstract ( 753 )   PDF (671KB) ( 835 )   Save

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In order to solve the problems of “large position, difficulty with location chosen, low angle resolution, and poor flexibility”, and to improve the performance of DOA estimation, a new design of the distributed high frequency surface wave radar is proposed, based on the technology of distributed antennas array and the MIMO radar system. With the new design, we propose a new DOA estimation method using compressed sensing, this method reduces the complexity of data processing and solves the angle ambiguity due to the distributed array. Discrete stochastic and semi-QR factorization is also used for improving the performance of the new DOA estimation. Theoretical analysis and simulation results show the validity of the proposed method.

Orthogonal phase coding signal design for MIMO radar via an algebraic method

DU Xiaolin;WANG Xu;SU Tao;ZHU Wentao

J4. 2014, 41(2):  64-70.  doi:10.3969/j.issn.1001-2400.2014.02.011

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For the problems of complex computation and low efficiency of the traditional numerical optimization method in the designing orthogonal phase coding signal for the MIMO radar, a method based on algebraic theory is proposed. Firstly, the inverse reduction-multiplication method to find the polynomials which are used to design the sequence families is used; then the sequence families can be generated by solving the linear recurrence equations via some linear shift registers, whose character polynomials are exactly the ones obtained in the first step; finally, the signal code sets are obtained by mapping the sequence families. Simulation results demonstrate that the autocorrelation peak side lobe level and the crosscorrelation peak level of the designed code sets are low, and the modulus of the signals is constant. Compared with the numerical optimization method, the number of sequences of the sets in this paper is large enough, and especially, the efficiency of generating the code sets is greatly improved.

Forward and backward secure signature scheme

WANG Mingwei;HU Yupu

J4. 2014, 41(2):  71-78.  doi:10.3969/j.issn.1001-2400.2014.02.012

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A new signature scheme based solely on the MQ-problem is presented, which satisfies the following properties:(1) Forward security, which means that a compromise of a key now does not necessarily expose old traffic. (2) Backward security, which means that a compromise of a key now does not necessarily expose future traffic. We do not have to revoke our public key and re-issue a new key system everytime we detect a key leak. We use two fundamental tools, such as zero knowledge proof and mulitivariate public crypto. Our basic model is Koichi Sakumoto's identifcation scheme which is transformed by parallel processing and Fiat-Shamir transforming. What is novel about our approach is the key updating algortithm, which makes our scheme preserve backward security besides the forward property. Finally, we prove that our scheme satisfies the security under the random oracle model.

Symbolic model checking of Verilog programs with the propositional projection temporal logic

PANG Tao;DUAN Zhenhua;LIU Xiaofang

J4. 2014, 41(2):  79-84.  doi:10.3969/j.issn.1001-2400.2014.02.013

Abstract ( 847 )   PDF (1417KB) ( 920 )   Save

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To insure the correctness of the system on chip(SoC) designed in the Verilog hardware description language,a symbolic model checking methodology for Verilog programs is proposed. With this methodology,the Verilog program to be verified is modeled as a finite-state machine with respect to its formal operational semantics,while the design specifications are expressed in propositional projection temporal logic(PPTL) formulas. Whether the SoC satisfies its specifications or not can be determined with the symbolic model checker proposed in our previous work. A case of a 4-bit synchronous binary counting system described in Verilog programs is studied to illustrate the feasibility of this methodology.

Analysis of the driving mechanism of the large-displacement low-voltage electrostatic micro-actuator based on the principle of vertical-horizontal bending

TIAN Wenchao;CHEN Zhiqiang;JIA Jianyuan

J4. 2014, 41(2):  85-89.  doi:10.3969/j.issn.1001-2400.2014.02.014

Abstract ( 722 )   PDF (581KB) ( 720 )   Save

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In the Micro Electro-Mechanical System (MEMS) field, the traditional electrostatic micro actuator of transverse loading and unidirectional deformation is faces problems of the oversized voltage and undersized displacement. An electrostatic silicon micro actuator featuring large-displacement and low-voltage is presented. Displacement amplification coefficient δ is derived based on the principle of vertically-horizontally bending. Simulation results show that the drive mechanism of the vertically-horizontally bending micro actuator is to amplify the deformation of unidirectional transverse loading by the displacement amplification coefficient δ. The purpose of large-displacement at low-driving voltage is realized. The effects of electrostatic adjustment force, temperature stress and extruding force on micro beam deformation are analyzed, respectively. Simulation shows that when the driving voltage is 5V, the output displacement is as high as 17.5μm. The deformation is much larger than that of the traditional micro actuator of transverse loading and unidirectional deformation.

Optimization of redundant driving force for high-speed cable-driven parallel camera robots

SU Yu;QIU Yuanying;WANG Long;DU Jingli

J4. 2014, 41(2):  90-96.  doi:10.3969/j.issn.1001-2400.2014.02.015

Abstract ( 869 )   PDF (1184KB) ( 737 )   Save

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Determination of redundant tension distribution for completely restrained positioning mechanism is transformed into a polynomial formulation extreme value problem in the convex feasible domain in this paper; and the real-time and continuous indices for measuring cable tension optimization solutions is also presented. A typical cable tension optimal distribution of the CDPCR is determined in order to provide an insight into the problem, so that the real-time and continuity of several tension optimal indices are compared and analyzed. Furthermore, concrete suggestions of index selection are given.

Better method for improvement on fountain flow dynamic simulation

DU Shuxing;LI Xiaozhen;WANG Yunchao

J4. 2014, 41(2):  97-101+164.  doi:10.3969/j.issn.1001-2400.2014.02.016

Abstract ( 848 )   PDF (2378KB) ( 620 )   Save

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For the purpose of improving the dynamic simulation effect of the particle system, this paper focuses on studying the dynamic simulation of the fountain flow based on particle system theory. A fountain particle motion model is constructed by applying the physical dynamic principle. The bead particle is structured by using OpenGL “short line” as the basic particle voxel, which performs better in real-time processing compared with other bead particles, such as sphere, cube and square. To avoid the invisibility of partial particles in 3D scene, the technique of the “△” line combination unit is adopted to implement the dynamic simulation of water beads. In order to agglutinate lots of particles to form water beads with different sizes and show the intermittent cylinder shape of the fountain, the fake particle viscosimetry and the blend operation in OpenGL are also adopted, making the fountain flow more realistic. Experiment indicates that the proposed method can effectively improve the reality and real-time performance of the fountain flow.

Precise measurement of the transient stability of frequency standards

BAI Lina;ZHOU Wei;HUI Xinming;YE Yunxia;SONG Huimin

J4. 2014, 41(2):  102-106.  doi:10.3969/j.issn.1001-2400.2014.02.017

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In order to solve measurement of transient noise and short-term stability of signals by conventional digital counting methods is not only difficult but also low in accuracy. So we introduce a novel phase coincidence detection technology which is an important detection method, and our group has worked on it for decades to measure the frequency source transient stability. According to the results of multiple phase coincidence detection circuits which are combined as a coincidence detection array, the detailed phase variation can be obtained. The measurement resolution depends on the stability of the coincidence detection circuit. In our experiment, the standard signal is a super-high stability crystal oscillator, measured signals are from the high stability crystal oscillator and OCXO whose parameters are significantly worse. Using the phase coincidence detection technique is able to properly reflect the actual stability situation. The measurement of transient stability of the frequency source plays an important part in the real-time short-term stability and the characterization of distal phase noise, so its accurate measurement is of great significance.

Study of the dynamic scenes model for laser imaging radar simulation

CHAI Guobei;ZHANG Jianqi;HUANG Xi;GUO Bingtao;TIAN Limin

J4. 2014, 41(2):  107-113.  doi:10.3969/j.issn.1001-2400.2014.02.018

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A laser scattering scene model capable of the real-time rendering of the laser radar imaging is proposed. It is based on the basic theory of laser radar imaging, combining true performance of the surface characteristics. Using the framework and taking advantage of powerful parallel computing ability of the GPU(Graphic Processing Unit), the radiance distribution under different laser incident angles, viewing angles and locations is implemented. A simulated calculation of a laser scattering scene image under a typical 3D scene is conducted. A comparison of the calculated results with the real lidar image is made, which shows that the laser scattering scene image obtained by the laser scattering scene model is similar to the one received by the lidar system. Quantitative analysis shows that there also exists difference, with the reasons analyzed.

Attacking direction of laser in laser warning systems

ZHANG Yingyuan;LIU Fei;HAN Pingli

J4. 2014, 41(2):  114-119.  doi:10.3969/j.issn.1001-2400.2014.02.019

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In order to detect the attacking direction of laser from the enemy, scattering warning detectors with the capability to locate the maximum irradiance in the propagating direction of the laser beam are employed with the help of the Mie scattering theory. In the orienting, two detectors are needed to lay foundation for the different location relations with the object. Then discussion is conducted. Theoretical calculations and experiments demonstrate that the laser from arbitrary direction can be oriented. There are several evident advantages: firstly, the detecting system is simplified; secondly, the locations of the detectors are unrestricted by the off-axis distance or other factors; thirdly, the data to be processed are somewhat fewer.

Calculation and analysis of the conduction band-structure of strained Germanium

DAI Xianying;LI Jinlong;HAO Yue

J4. 2014, 41(2):  120-124+171.  doi:10.3969/j.issn.1001-2400.2014.02.020

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This paper estabilishes the strained-tensor model by Hooke's law and calculates the energy-level shifts of L, Δ and Γ valleys by the deformation potential theory. By enforcing the uniaxial stress in germanium along <001> direction, the edge band of the Δ valley is split with the bottom energy-level being the lowest one among all valleys when the compressive stress is 1.8GPa. When the strained direction is <110>, the edge bands of L and Δ valleys are split. The L valley is split as the strained direction is <111>. When the biaxial tensile-strain is applied, we obtain the conclusion that the strained Ge can become the direct band gap from the indirect band gap as a tensile in-plane strain is 1.8％.

Design of the S band 6bits high precision phase shifter

YANG Xiaofeng;SHI Jiangyi;MA Peijun;HAO Yue

J4. 2014, 41(2):  125-129.  doi:10.3969/j.issn.1001-2400.2014.02.021

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A digital 6-bit phase shifter for S-band based 0.25μm GaAs HEMT technology is presented. The high-pass/low-pass network and all-pass network are utilized synthetically for the topology of the phase shifter, with both the phase precision improvement technique and the series scatter restrain technique adopted. The relative phase shift varies from 0 to 360 at the step of 5.625°. Over the design band of 2.1～2.7GHz, the minimum rms phase error is 1.13°, and a low insertion loss is less than 6.3dB, of which the amplitude fluctuation is less than 0.4dB and the input and output scatter parameter is less than -10dB under all conditions.

Iteratively reweighted second-order regularization based multiplicative noise removal model

WANG Xudong;FENG Xiangchu;ZHANG Xuande

J4. 2014, 41(2):  130-136.  doi:10.3969/j.issn.1001-2400.2014.02.022

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In order to remove the multiplicative noise in an image, an iteratively reweighted second order derivatives(Frobenius norm of Hessian matrix) regularization model is proposed under the assumption that the multiplicative noise follows a Gamma distribution, which is an extension of the iteratively reweighted total variation model. A primal-dual algorithm for iteratively reweighted Frobenius norm of the Hessian matrix regularization model is designed. Numerical experiments show that the proposed model and algorithm can remove noise effectively while preserving details, restraining the staircase effect and avoiding edge blurring.

Improved ray tracing prediction model in urban microcellular environments

LIU Zhongyu;GUO Lixin;ZHONG Zhimeng;LU Xiaofeng

J4. 2014, 41(2):  137-143.  doi:10.3969/j.issn.1001-2400.2014.02.023

Abstract ( 928 )   PDF (709KB) ( 787 )   Save

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The traditional ray tracing model usually has a disadvantage of low efficiency in creating a virtual source tree. In this paper, an improved quasi three-dimensional ray tracing model based on creating a new virtual source tree in which the relationship between neighbor nodes is a left-son-and-right-brother one is presented. In the model, a preprocessing technique for the reflection is used in order to accelerate the calculation of visible faces of the reflection source. Furthermore, the avoidance of unnecessary overlapping and intersection tests is achieved by using an improved polar sweep algorithm. Simulation results demonstrate that the proposed model is efficient and can provide the reliable theoretical basis for radio-wave propagation prediction and network planning in urban microcellular environments.

Non-iterative GLRAM algorithm for face recognition

ZHAO Yangyang;ZHOU Shuisheng;WU Yajing

J4. 2014, 41(2):  144-150.  doi:10.3969/j.issn.1001-2400.2014.02.024

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In this paper, we get the right projection transform matrix by the covariance matrix of the 2DPCA algorithm, and gain the left projection transform matrix by dimensional reduction of the feature matrix of the 2DPCA. Then we propose a new non-iterative algorithm for generalized low rank approximation of matrices (NGLRAM).Experiments on ORL and AR face database show that the new NGLRAM saves a lot of training time to get the similar performance with GLRAM in image reconstruction and image recognition. Compared with the 2DPCA, the NGLRAM can lead to better results in image reconstruction and image recognition at a larger compression rate.

Privacy-preserving query over the encrypted image in cloud computing

ZHU Xudong;LI Hui;GUO Zhen

J4. 2014, 41(2):  151-158.  doi:10.3969/j.issn.1001-2400.2014.02.025

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In the emerging cloud computing paradigm, data owners become increasingly motivated to outsource their complex data management systems from local sites to the commercial public cloud for great flexibility and economic savings. For the consideration of users' privacy, sensitive images have to be encrypted before outsourcing, which makes effective data utilization a very challenging task. In this paper, firstly, we define the problem of privacy-preserving query over encrypted images in cloud computing. And to solve the problem, we design a computable encryption scheme based on vector and matrix calculations. The scheme pre-builds a feature-based index to provide feature-related information about each encrypted image, and then chooses the efficient image similarity measure as the pruning tool to carry out the retrieval procedure. Security analysis and performance evaluation show that the scheme is IND-CCA.

Distributed relay assignment method in green energy efficiency

LI Yun;CHEN Quan;LIU Qilie;CAO Bin

J4. 2014, 41(2):  159-164.  doi:10.3969/j.issn.1001-2400.2014.02.026

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Recently, cooperative communication has been regarded as one of the most promising techniques, which can achieve the spatial diversity with one antenna. In cooperative communication, the energy efficiency could be improved with the fixed transmission power. The relay node has a significant effect on the performance of cooperation. Therefore, how to allocate relay nodes becomes an important issue which should be addressed. However, existing work just focuses on the advantage cooperation gain, with the adverse effect ignored. Moreover, the advantage cooperation gain might not cover the adverse effect. To this end, we propose a Distributed Relay Node Assignment Method (DRNAM), considering both advantage and adverse effects caused by cooperation. Based on simulation results, the DRNAM can improve the energy efficiency significantly.

Formal modeling of cyber-physical systems using object-oriented Petri nets

LI Ye;WANG Yinghui;YU Zhenhua

J4. 2014, 41(2):  165-171.  doi:10.3969/j.issn.1001-2400.2014.02.027

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A cyber-physical systems architecture model (CPSAM) is set up based on Object-Oriented Petri nets from the point of view of multi-agent systems, which is composed of sensor node agents, actuator agents, and controller agents. The CPSAM can accurately and unambiguously model the overall and individual characteristics, as well as static and dynamic semantics of CPS. Moreover, the CPSAM can be simulated, analyzed and verified by the well-established analysis methods and supporting tools of Petri nets. Consequently, the defects in the early design stage can be detected, and the correctness and reliability can be improved. The modeling, analysis and design of the target tracking systems demonstrate that the CPSAM can effectively design and develop CPS.

Novel phase-locked loop with direct phase detection for two frequency different signals

QU Bayi;SONG Huansheng;ZHOU Wei;LI Shanshan;MENG Qiang

J4. 2014, 41(2):  172-177.  doi:10.3969/j.issn.1001-2400.2014.02.028

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It is difficult to do a frequency conversion using the current phase-locked technology when the input and output frequencies are approximatly equal or have an approximate integer multiple relationship. Based on the change law of the phase difference between the two different frequency signals, by using the phase coincidence detection circuits, the equivalent phase demodulation circuits and a filter with an adjustable bias, a new type of PLL is realized. Experimental studies are done with the results showing that the phase-locked loop has characteristics such as low noise, high stability, the easy-to-adjust output frequency.

Extrapolation to the transient field for FDTD in two-dimensional half-space

JIANG Yannan;GE Debiao;YANG Lixia;YU Xinhua

J4. 2014, 41(2):  178-184.  doi:10.3969/j.issn.1001-2400.2014.02.029

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An algorithm for extrapolating the transient field in two-dimensional half-space for the finite-difference time-domain(FDTD) method is firstly presented. In this algorithm, the far-zone scattered field consists of three parts. The first two parts of the field are generated by the equivalent electromagnetic currents at the extrapolation bound in upper space, propagating along the paths of directed and reflected waves, respectively. And the third part is resulted by that currents at that bound in lower space, its propagation following the path of the transmitted wave. To caculate the latter two parts, the reflection and transmission points should be determined with the knowledge of Snell's law and then projected on to the observation time bins, moreover the proper time of the wave propagating from the equivalent source to those points should also be worked out and used to delay those bins, with the reflection or transmission coefficients used as the contribution factor to the far field. Then the proposed algorithm is validated by the applying far-zone scattered fields to two examples.

Information hiding scheme for 3D models based on skeleton and inscribed sphere analysis

ZHANG Tao;MU Dejun;REN Shuai;JU Yongfeng;LING Yao

J4. 2014, 41(2):  185-190.  doi:10.3969/j.issn.1001-2400.2014.02.030

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An information hiding scheme based on skeleton theory and inscribed sphere analysis for 3D models is proposed to improve the robustness and capacity of the existing algorithms. According to the definition of the skeleton, the model is analyzed by the Euclidean inscribed sphere analysis theory with each skeleton point as the center of the sphere. The number of times of minimum inscribed sphere analysis of skeleton points is considered as the modification for secret information. Preprocessing of carriers is unrelated with the number of vertexes, the change of coordinates and topology modification, so visual changes of carriers due to secret information embedding can be minimized. Experimental results show that this scheme is of strong robustness and good imperceptivity. Especially robustness against rotation is up to 100%, robustness against other common attacks is strong, and the capacity is larger.

Prefetching method for Hadoop MapReduce environments

ZHANG Xiaohong;LUO Fen;JIA Zongpu;SHEN Jiquan

J4. 2014, 41(2):  191-196.  doi:10.3969/j.issn.1001-2400.2014.02.031

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Due to the data dependency and the special task execution mode in MapReduce environments, reduce tasks always cause massive remote data access delay and unnecessary resource competition, which degrades the system performance. To solve the performance problem, we propose a pre-fetching method based on pre-scheduling. The method hides the remote data access delay by pre-fetching, and controls the resource competition by adjusting resource allocation of reduce tasks. The method is implemented in Hadoop-0.20.2. The experimental results show that the method improves the system performance by more than 10％, compared with default Hadoop MapReduce and Hadoop Online Prototype.