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    20 April 2017 Volume 44 Issue 2
      
    New method for range-ambiguous clutter suppression in non-side-looking airborne radar
    WU Xuzi;LIU Zheng;XIE Rong
    Journal of Xidian University. 2017, 44(2):  1-7.  doi:10.3969/j.issn.1001-2400.2017.02.001
    Abstract ( 397 )   PDF (847KB) ( 470 )   Save
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    To suppress the seriously range-ambiguous clutter, an approach based on the frequency diverse array (FDA) technique is proposed. Based on the space-time signal model in FDA radar, the frequency increment is designed to distinguish the clutter at ambiguous ranges and avoid signal decorrelation. Then, the subspace projection algorithm is used for range-ambiguous clutter suppression. Numerical simulations show the effectiveness of the proposed method. Even when the number of the elevation degrees-of-freedom (DOFs) is limited, the proposed method performs better than the conventional elevation filtering method.

    Method to suppress moving targets in SAR images
    XIAO Li;LI Xueshi;SUN Guangcai;XING Mengdao
    Journal of Xidian University. 2017, 44(2):  8-13.  doi:10.3969/j.issn.1001-2400.2017.02.002
    Abstract ( 360 )   PDF (2105KB) ( 230 )   Save
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    In the high-resolution wide-swath (HRWS) SAR system, the moving targets are usually smeared and imaged at incorrect positions in the resulting SAR image by utilizing the traditional stationary scene imaging processing. Moreover, these defocused moving targets may cover the stationary scene. The number of spatial degrees of freedom required for suppressing moving targets by the traditional space-time adaptive processing framework is equal to the number of the moving targets in the SAR scene multiplied by the PRF undersampling number. This requirement is hard to meet in practice. In order to overcome the above problem, a new space-time adaptive processing framework based on azimuth Deramp processing is proposed in this paper. Firstly, the moving targets are coarsely focused in the space-time plane through the azimuth Deramp processing. In this case, only one spatial degree of freedom is needed for suppressing one moving target. If there are multiple targets, it can effectively reduce the required degrees of freedom by utilizing the dynamic steering vector concept. Last, simulation results are provided to show the validity of the proposed method.

    Novel weak target detection technique based on time-dimension reduced multiple frame detection in the Radon domain
    CHEN Hongmeng;LI Ming;LU Yunlong;WANG Zeyu;LI Gangfei;ZUO Lei;ZHANG Peng
    Journal of Xidian University. 2017, 44(2):  14-19.  doi:10.3969/j.issn.1001-2400.2017.02.003
    Abstract ( 370 )   PDF (1557KB) ( 305 )   Save
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    Low-altitude slow-moving weak target detection in the heavy clutter is a challenging problem for low resolution radar. This paper proposes a time-dimension reduced multiple frame detection algorithm in the Radon domain to solve it. In our framework, adaptive moving target indication (AMTI) and the order statistic constant false alarm rate filter (OS-CFAR) are utilized to suppress the clutter primarily. After resampling and smoothing the combined time-range profiles in the time direction, the Radon transform is applied to this set of new time-range profiles. Then target detection is converted into a problem of feature extraction in the Radon domain, and the moving target can be figured out by two thresholds from the clutter in the parameter domain. Since the differences of skewing angles between the slow-moving targets and clutter in the Radon domain are amplified by time-dimension reduction operator, we can both detect the target and estimate its velocity. Real data demonstrate the effectiveness of the proposed algorithm.

    Novel detection algorithm for high-speed maneuvering multi-target with narrowband radar
    ZHANG Jiancheng;SU Tao
    Journal of Xidian University. 2017, 44(2):  20-26.  doi:10.3969/j.issn.1001-2400.2017.02.004
    Abstract ( 326 )   PDF (3026KB) ( 207 )   Save
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    A novel detection method for the high-speed maneuvering multi-target with a constant acceleration is proposed. Firstly, velocity searching and Second-order Keystone Transform (SKT) are jointly applied to correct the range migration (RM). After the RM correction, the azimuth echoes can be considered as a Linear Frequency Modulation (LFM) signal. Secondly, Lv's Transform (LVT) is performed on the azimuth echoes, target energy will be accumulated into a sole peak in the Centroid Frequency (CF)-Chirp Rate (CR) domain, and an estimated acceleration can be obtained in terms of the peak's location in the CR-axis. Finally, according to the estimated acceleration, a compensation function is constructed to compensate the Doppler Frequency Migration (DFM), after that, the FFT is applied to accomplish coherent integration, and then target detection is carried out, meanwhile, the target's radial velocity can be estimated. Compared with the Radon-Fractional Fourier Transform (RFRFT), the proposed algorithm possesses the advantages of lower computational complexity and better anti-noise performance. The results of simulation and real data demonstrate the validity of the proposed algorithm.

    New ISAR imaging interval selection method for ship targets on the sea
    GAO Yuexin;LI Zhenyu;XING Mengdao;ZHANG Zijing
    Journal of Xidian University. 2017, 44(2):  27-32.  doi:10.3969/j.issn.1001-2400.2017.02.005
    Abstract ( 375 )   PDF (1655KB) ( 231 )   Save
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    Ship targets on the sea swing because of the sea wave, which leads to instability of the rotation speed and variation of the image project plane. As a result, imaging interval selection should be taken into consideration in order to obtain a high quality ISAR image. In this paper, firstly, the relationship between effective rotating speed and image project plane is analyzed in detail, by which the conclusion that the image project plane is stable and the resolution of the ISAR image is best when the valid speed of rotation of a ship target is highest is drawn. Then a new method to select favorable imaging interval based on the rotation speed of ship targets is proposed. In comparison with existing methods, the proposed one can select a better period for ISAR imaging, which leads to an imaging result with higher quality. The effectiveness of the proposed method is verified by simulation and real data processing result.

    Closed-form estimator for widening valid estimation range of Pareto parameter
    HU Chong;LUO Feng;ZHANG Linrang;CHEN Shuailin;FAN Yifei
    Journal of Xidian University. 2017, 44(2):  33-36+113.  doi:10.3969/j.issn.1001-2400.2017.02.006
    Abstract ( 335 )   PDF (699KB) ( 192 )   Save
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    The second order moment of the multi-look Pareto distribution is invalid when the shape parameter is less than 2, so the method of the first two moments cannot estimate the shape parameter less than 2. This paper proposes the method for estimating the shape parameter of multi-look Pareto distribution. The method not only widens the valid range of parameter estimation, but also the expression for estimation is closed. Theoretical analysis and experiment both prove that the method can estimate shape parameter less than 1 compared with the method of moments and that costs are lower in computation than the method of fractional moments.

    CPHD multi-target tracking algorithm with unknown model parameters
    LI Cuiyun;WANG Jingyi;JI Hongbing;WANG Rong
    Journal of Xidian University. 2017, 44(2):  37-41+184.  doi:10.3969/j.issn.1001-2400.2017.02.007
    Abstract ( 304 )   PDF (755KB) ( 234 )   Save
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    Since the multi-object tracking performance of the traditional method will decline with unknown model parameters, a CPHD target tracking algorithm is proposed to jointly estimate the detection probability and measurement noise covariance. Firstly, for model the unknown parameters of multiple targets tracking, the detection probability is considered as a variable in a distribution. The detection probability can be obtained by estimating the mean of the distribution. Then, the Variational Bayesian method is used to estimate the covariance of the measurement noise. Finally, the Gaussian implementation of this algorithm is presented. Simulation results show that the algorithm has good tracking performance under jointly unknown detection probability and the covariance of the measurement noise.

    Antenna radar cross section reduction by a reconfigurable radar absorbing structure
    WANG Fuwei;GUO Lixin;GONG Shuxi
    Journal of Xidian University. 2017, 44(2):  42-46+94.  doi:10.3969/j.issn.1001-2400.2017.02.008
    Abstract ( 281 )   PDF (3235KB) ( 201 )   Save
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    An active reconfigurable Radar absorbing structure using a pin diode for the radar cross section (RCS) reduction of the antenna reflector is proposed, which is able to be switched between metal reflector with OFF-state diodes and absorber with ON-state diodes. The reflection coefficient of the RAS reflector is able to be switched between less than -25.0dB with OFF-state diodes and more than -0.8dB with ON-state diodes around 8.3GHz. The RAS reflector with ON-state diodes is applied to a dipole antenna reflector and gives radiation performance equivalent to that of the dipole with a metal reflector. The RAS reflector with OFF-state diodes is used as a radar absorber for RCS reduction. Meanwhile, a chessboard-like geometry RAS reflector is proposed in response to the wideband RCS reduction. The RCS reduction band covers the working band and is extended to 5~18GHz. The results show that the reconfigurable RAS reflector can contribute to the antenna RCS reduction at the working frequency, with the radiation performance of the dipole antenna preserved.

    Research on phaseless near-field antenna measurement
    SHANG Junping;ZUO Yanchun;HU Yonghao;WANG Yuan;SONG Kang
    Journal of Xidian University. 2017, 44(2):  47-51.  doi:10.3969/j.issn.1001-2400.2017.02.009
    Abstract ( 449 )   PDF (1152KB) ( 271 )   Save
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    A method of phaseless near-field measurement is studied which can reconstruct the far-field characteristics of the antenna by analyzing the near-field amplitude-only data. The method includes a dual-plane scanning strategy which lets the linear polarization probe collect the amplitude-only data on the two scanning planes respectively. The phase of each sampling points at one of the scanning planes can be retrieved using the iterative fourier transform algorithm. Then the far-field properties of the antenna are obtained by applying the near-field/far-field transformation technique. Theoretical research and simulations show that the phaseless near-field measurement strategy can reconstruct the far-field pattern effectively and that a better choice of the initial iterate phase can help to improve the convergence rate and the convergence precision of the method.

    Design of dual-band shared-aperture circularly polarized antenna with a wide beam for aircraft platforms
    JIANG Li;JIANG Dong;ZHANG Fushun
    Journal of Xidian University. 2017, 44(2):  52-56.  doi:10.3969/j.issn.1001-2400.2017.02.010
    Abstract ( 268 )   PDF (2998KB) ( 190 )   Save
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    Most of published shared-antennas focus mainly on the characteristics of multi-band and multi-polarization, that is, a high profile and a complex structure. A dual-band circularly polarized shared-antenna is presented with a simple structure and wide beam coverage. Firstly, to reduce the size and weight, the shared-aperture antenna is applied for the quad-operating frequencies (UHF1/UHF2/S1/S2) with a stacked microstrip patch antenna and high dielectric constant substrates. All the quad-operating bands can be freely tuned by changing the lengths of patches. Secondly, the substrate with a high dielectric constant is added on the patch to improve the gain of the antenna in the low elevation direction, broadening the antenna beam. Next, to obtain the quad-band circularly polarization (CP) radiation pattern, the feeding structure with the broadband phase shifter is also designed. Finally, the proposed antenna prototype is fabricated and measured. Its measured impedance bandwidth, axial ratio and radiation pattern are in good agreement with simulation results. The proposed antenna has already been applied to a special airborne communication system. Additionally, the antenna synthesis method may be further extended to realize the shared-aperture circularly polarized antenna with more than two bands.

    Attribute-based encryption with location verification and policy adjusting supporting the cloud mobile office
    YING Zuobin;MA Jianfeng;CUI Jiangtao
    Journal of Xidian University. 2017, 44(2):  57-62+190.  doi:10.3969/j.issn.1001-2400.2017.02.011
    Abstract ( 249 )   PDF (817KB) ( 150 )   Save
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    Facing the problems of the users' location privacy leakage and the indirect adjusting policies of the ciphertext stored in the cloud, in a mobile officie environment with cloud, a Ciphertext-Policy Attribute-Based Encryption with the Location Verification and Policy Adjusting (LVPA-CP-ABE) scheme is proposed. In the scheme, we apply BGV (Brakerski-Gentry-Vaikuntanathan) homomorphic encryption to protect the users' location privacy and updating key generated by the data owner directly to adjust the policy of the ciphertext stored in the cloud in the meantime. Moreover, in consideration of the endurance of mobile devices, the idea of outsourcing the BGV computation and BGV decryption as well as the ciphertext adjusting part is also introduced. The simulation indicates that our scheme is highly efficient in terms of users' computational cost.

    Successive cancellation multibit-flipping decoding algorithm for polar codes
    LI Guiping;MU Jianjun;JIAO Xiaopeng
    Journal of Xidian University. 2017, 44(2):  63-68.  doi:10.3969/j.issn.1001-2400.2017.02.012
    Abstract ( 329 )   PDF (604KB) ( 162 )   Save
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    The investigation of the probability of error bits in a codeword shows that single-bit errors and 2-bit errors are main reasons that influence the decoding performance of polar codes with a short or moderate blocklength. Based on the statistical analysis of the error bits, a successive cancellation(SC) multibit-flipping decoding algorithm is proposed. Compared with the SC single-bit-flipping decoding, the proposed scheme can obtain better performance gains for polar codes with a short blocklength. Compared with the SC list decoding by exploring multiple paths simultaneously, the proposed scheme has a lower space complexity. Moreover, the decoding complexity of the proposed decoding algorithm decreases as the signal to noise ratio(SNR) increases. Simulation shows that for polar codes with a short or moderate blocklength, the performance of the proposed decoder can approach that of the SC list decoding with lower decoding complexity in high SNR regions.

    Algorithm for estimating confusion states of flexible manufacturing systems
    WANG Qi;CHEN Xiaoliang
    Journal of Xidian University. 2017, 44(2):  69-74.  doi:10.3969/j.issn.1001-2400.2017.02.013
    Abstract ( 312 )   PDF (647KB) ( 217 )   Save
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    As confusions have an impact on the multi-thread running and decision-making of flexible manufacturing systems (FMS), this paper aims to present a novel algorithm for finding all confusions of such an FMS, which can be considered as the foundation of further system modeling and control. An algebraic method is presented by analyzing the characters of confusion states, based on the available detection schemes of the subnet structure of Petri nets. The method implements state estimation of confusions by inputting a system static structure and an initial state instead of supervising system states. This result can be applied to conflict rationality analysis in the system modeling phase. Finally, an example of FMS is employed to simulate the proposed algorithm. The result shows that all confusion states of the target system can be estimated effectively by using the method.

    Circuit of time-domain quality factor measurement in 0.35μm CMOS process
    REN Xiaojiao;ZHANG Ming;LLASER Nicolas;YUE Baihe;ZHUANG Yiqi
    Journal of Xidian University. 2017, 44(2):  75-80.  doi:10.3969/j.issn.1001-2400.2017.02.014
    Abstract ( 260 )   PDF (1372KB) ( 122 )   Save
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    Based on the time-domain quality factor (Q-factor) measurement principle, an architecture which not only achieves an accurate Q-factor at the specific frequency but also covers a range of frequencies without any loss in Q-factor measurement accuracy is proposed. Based on a reconfigurable structure, an improved peak detector compensation method is presented. To guide the design of such an architecture, a theoretical analysis for reaching the required accuracy and expanding the input frequency range has been first developed in this paper. Besides, the system power dissipation can be reduced by 7.5% thanks to the improved digital control logic. In this paper, circuit is realized in a 0.35μm CMOS process for the first time. With the 5V supply voltage and 1MHz input frequency, the post-layout simulation result have demonstrated that an accuracy of the Q-factor measurement is within 0.2%. Furthermore, the input frequency range that can be measured by this circuit is extended from 100kHz to 1.5MHz with the same accuracy.

    Adaptive fuzzy classifier with a fixed number of fuzzy rules
    SHI Shaoying;WANG Xiaomo;CAO Chen;ZHANG Jing
    Journal of Xidian University. 2017, 44(2):  81-87.  doi:10.3969/j.issn.1001-2400.2017.02.015
    Abstract ( 324 )   PDF (563KB) ( 110 )   Save
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    The adaptive fuzzy system has many advantages over the neural network. It can be used to design a fuzzy classifier. However, there is the “Dimension Calamity” with the number of inputs increasing in the adaptive fuzzy system. In this paper, an adaptive fuzzy classifier with a fixed number of fuzzy rules is proposed. This classifier is combined by several fuzzy reasoning machines so that one fuzzy reasoning machine recognizes only one class. Every fuzzy reasoning machine includes two “If-Then” fuzzy rules. The total fuzzy rules number of the classifier is confirmed by the number of classes of the patterns being classified. The classifier uses the “Error Back-Propagation Training” arithmetic as the learning arithmetic. Compared with the BP neural network classifier, the new classifier and BP neural network classifier are both tested by the famous iris dataset and Ripley's synthetic dataset. It is proved that the new classifier has a good classification ability and learning ability even if the data have been polluted.

    Overlapped layered belief-propagation LDPC decoding algorithm
    FAN Ya'nan;WANG Lichong;YAO Xiujuan;MENG Xin
    Journal of Xidian University. 2017, 44(2):  88-94.  doi:10.3969/j.issn.1001-2400.2017.02.016
    Abstract ( 293 )   PDF (707KB) ( 156 )   Save
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    An Overlapped Layered-BP(OLBP) decoding algorithm is proposed aiming at further increasing the convergence speed and enhancing the error performance of the Layered Belief-Propagation(LBP) algorithm. In this algorithm, more than one sub-decoders are used to decode simultaneously, and sub-decoders have different check node updating orders from each other. The most reliable messages are kept and used for the next iteration for every check node, and thus a faster convergence can be provided. Simulation result shows that, compared with the LBP algorithm, the OLBP algorithm possesses a better error performance as well as a higher convergence speed and introducing no extra storage requirement. Moreover, the proposed algorithm is effective for both regular and irregular LDPC codes.

    Design of the low power wake-up receiver for internet of things communication
    MENG Fanzhen;LIU Hong;WANG Mingliang;LIN Shuiyang;TIAN Tong
    Journal of Xidian University. 2017, 44(2):  95-100.  doi:10.3969/j.issn.1001-2400.2017.02.017
    Abstract ( 420 )   PDF (1624KB) ( 201 )   Save
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    A wake-up receiver with high energy efficiency and low power consumption is proposed for solving the power consuming problems of wireless nodes communication in the Internet of Things. The proposed wake-up receiver based on the wake-up mechanism can effectively schedule the network nodes communication, and use the simple envelope detection structure to achieve frequency down-conversion, which can flexibly manage energy and reduce power consumption. Based on UMC 65nm CMOS process technology, the wake-up receiver is designed and simulated. The results show that it can achieve S<sub>11</sub> of -21dBm and a sensitivity of -75dBm at a data rate of 1Mb/s, when operating at the central frequency of 780MHz and input signal adopting an on-off keying (OOK) modulation, and the power consumption is 82μW at 1.2V voltage supply.

    Optimal radar waveform design method in colored and non-Gaussian noise
    ZHU Hong;ZHANG Hai;TANG Gaodi;LI Zhongyun;LIU Yinong
    Journal of Xidian University. 2017, 44(2):  101-106.  doi:10.3969/j.issn.1001-2400.2017.02.018
    Abstract ( 263 )   PDF (683KB) ( 141 )   Save
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    This paper considers the design of optimal waveforms for detection of point targets in colored non-Gaussian noise. We present the likelihood ratio processor and derive an expression for its output signal-to-noise ratio (SNR), and then use this as the basis for a cost function in a waveform design optimization which is solved by using a one dimensional alternating maximization algorithm. Finally simulations are performed to verify the effectiveness of the new waveforms.

    Statistical spectrum analysis and allocation in cognitive radio networks
    HUANG Jie;ZENG Xiaoping;JIAN Xin;TAN Xiaoheng;ZHANG Yaole
    Journal of Xidian University. 2017, 44(2):  107-113.  doi:10.3969/j.issn.1001-2400.2017.02.019
    Abstract ( 332 )   PDF (780KB) ( 196 )   Save
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    The bandwidth of spectrum holes is time-varied in cognitive radio networks with dynamic spectrum environment, which leads to the traditional static spectrum allocation poor performance. To solve this issue, this paper derives the probability density function of bandwidth of spectrum holes and presents a novel spectrum allocation algorithm based on the stochastic multiple knapsack problem. Simulation results illustrate that the proposed algorithm can achieve a better performance than the existing algorithms when the bandwidth of spectrum holes is time-varied.

    Feature extraction of point clouds using the DBSCAN clustering
    ZHANG Yuhe;GENG Guohua;WEI Xiaoran;SHI Chenchen;ZHANG Shunli
    Journal of Xidian University. 2017, 44(2):  114-120.  doi:10.3969/j.issn.1001-2400.2017.02.020
    Abstract ( 448 )   PDF (1705KB) ( 191 )   Save
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    The existing feature extraction methods often depend on the global fixed thresholds and the local information of features, resulting in sensitivity to significance of features and failure in models with different surfaces. To overcome those problems, a novel method based on DBSCAN Clustering is proposed. First, a new reverse k nearest neighbors(kNN) of points are defined as a new feature detection operator. Second, the scales of the reverse k nearest neighbors of points are utilized as the density information of points and then the introduction of the global constraints information is proposed. Finally, based on the redefinition of the concepts of the DBSCAN clustering method and the creation of a new feature recognition criterion, an improved version of the DBSCAN clustering method is used to extract features. Experimental results show that the method is simple, effective and robust, which takes into account the local information and global constraint information and outperforms existing feature detection methods on point clouds with surfaces that have diverse geometries.

    Analysis of scattering of the parallel multi-cylinder using the iterative induced field ratio algorithm
    ZHOU Hui;XING Feng;LIU Qikun
    Journal of Xidian University. 2017, 44(2):  121-126.  doi:10.3969/j.issn.1001-2400.2017.02.021
    Abstract ( 250 )   PDF (1333KB) ( 103 )   Save
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    To analyze the electromagnetic scattering characteristics on multi-cylinders faster and as accuractely as possible, the iterative induced field ratio(IIFR) algorithm is proposed. The rapidity of the induced field ratio(IFR) theory and precision of the iterative algorithm are mixed together. The iterative induced field ratio of the two-dimensional infinite parallel cylinder array is derived with which the scattering far field of the cylinders array are easily obtained. Furthermore, the relationship between scattering coefficient and iterative times are discussed. The results shows that not only the precision of the proposed algorithm has been improved compared with the traditional induced field ratio method, but also a lot of computer memory and calculating time are saved compared with the method of moments(MoM).

    Fuzzy clustering based load balancing algorithm with feature weighted
    HUANG Weihua;MA Zhong;DAI Xinfa;XU Mingdi;GAO Yi;LIU Limin
    Journal of Xidian University. 2017, 44(2):  127-132.  doi:10.3969/j.issn.1001-2400.2017.02.022
    Abstract ( 313 )   PDF (572KB) ( 121 )   Save
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    Focusing on the data fusion problem of various loads, a fuzzy clustering based load balancing algorithm with feature weighted is proposed. First of all, various system resources are considered as dimensions for load metrics, and features for different dimensions are weighted so as to quantify comprehensive loads; then, this algorithm introduces fuzzy clustering, optimizes weight constraints, and adds penalty terms. Hence, the most suitable objective node cluster for load transferring is resolved through fuzzy clustering. Experimental results show that this algorithm can effectively fuse multidimensional load data and reduce standard deviation for node loads within the cluster by 21% compared with existing algorithms.

    Reversible adder circuits with the quantum-dot cellular automata
    QIN Tao;CAI Li;YANG Xiaokuo
    Journal of Xidian University. 2017, 44(2):  133-139.  doi:10.3969/j.issn.1001-2400.2017.02.023
    Abstract ( 266 )   PDF (2914KB) ( 205 )   Save
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    The reversible logic is found to be very useful in fields of low power digital circuits and quantum computers due to its feature of ultra low power consumption. A new reversible logic gate (NRG) is proposed in this paper, which can perform majority computation, Exclusive-OR and Inclusive-OR operations. The proposed NRG is realized by quantum-dot cellular automata (QCA) technology, and reversible QCA adder circuits are designed with the proposed NRG. Simulation results with the QCA Designer tool indicate that the proposed NRG and reversible adder circuits perform well. Moreover, the reversible adder with the NRG requires fewer gates, while generating fewer garbage outputs.

    MTL model of the capacitive pulse interference coupling equipment
    CUI Zhitong;SUN Dongyang;MAO Congguang
    Journal of Xidian University. 2017, 44(2):  140-144+150.  doi:10.3969/j.issn.1001-2400.2017.02.024
    Abstract ( 314 )   PDF (1048KB) ( 128 )   Save
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    An MTL (multi-conductor transmission line) model of the capacitive coupling clamp is developed to analyze the capacitive pulse interference injection method in the electromagnetic immunity test. According to different physical characters, the per-unit-length parameters of each part in the model are obtained by the analytical or numerical method as well as by deriving from experimental data. Then the 2n matrix and its equations are constructed. The solution of the MTL equations show a good agreement with the experimental results. The model can be used to predict the interference pulse entering the equipment.

    Spread spectrum directional modulation method based on the  irrelevantly switched antenna for physical layer security transmission
    GUO Bin;YANG Yuhong;XIN Gang;TANG Yanqun
    Journal of Xidian University. 2017, 44(2):  145-150.  doi:10.3969/j.issn.1001-2400.2017.02.025
    Abstract ( 250 )   PDF (572KB) ( 118 )   Save
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    In order to improve the security of wireless communication, a spread spectrum directional modulation method based on the irrelevantly switched antenna is presented. First, the security vulnerabilities of the existing spread spectrum directional modulation method are analyzed, indicating that the existing method has the risk of security leakage in some particular directions. Then by locating the security vulnerabilities of the existing method, a security-enhanced method is proposed by separating the antenna switching from the spectrum spreading to eliminate the security vulnerabilities. Finally, the physical layer security performance of two directional modulation methods is simulated, with the results showing that the proposed method has a better low detection performance and anti-jamming capability.

    Multi-target tracking method based on the adaptive fragment and multi-feature fusion
    BIE Xiude;LIU Hongbin;CHANG Faliang;PENG Zhiyong
    Journal of Xidian University. 2017, 44(2):  151-157.  doi:10.3969/j.issn.1001-2400.2017.02.026
    Abstract ( 736 )   PDF (3966KB) ( 156 )   Save
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    In order to solve the problems of occlusion, appearance change and similar targets in multi-target tracking, this paper proposes a multi-target tracking method with the particle filter based on the adaptive fragment and multi-feature fusion. First, we divide each target into a few fragments adaptively according to its gray projection and describe each fragment with the color histogram and histogram of oriented gradient(HOG) feature, of which similarity can be obtained by adopting the weighted Bhattacharyya Coefficient. Then, we obtain particle sets of each target by FCM clustering. The optimal state estimation of each target is calculated through particles state in the subgroup. Finally, the weighting factor of each fragment is updated according to the reliability which is calculated by considering particles space information. Experimental results show that the proposed method can track the targets in many complex circumstances accurately and robustly.

    Fast nonlinear Shrinkage LMS Newton equalization algorithm over the satellite nonlinear channel
    LI Liangshan;YANG Yuhong;WANG Lan
    Journal of Xidian University. 2017, 44(2):  158-164.  doi:10.3969/j.issn.1001-2400.2017.02.027
    Abstract ( 357 )   PDF (1025KB) ( 150 )   Save
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    The adaptive Volterra equalizer is an effective technique for compensating the nonlinearity over satellite channels. However, its adaptive algorithm has a slow convergence speed. To counteract this problem, a new shrinkage least mean square Newton algorithm is devised for the adaptive Volterra equalizer over the satellite nonlinear channel. A noise-free posteriori and priori error signal is obtained by using a known Shrinkage method and L1-L2 minimization formulation. Furthermore, by minimizing the energy of the noise-free posteriori error signal, the SHLMS Newton method is able to provide a variable step size to update the weight vector for the adaptive Volterra equalizer, significantly enhancing the convergence speed. Simulation results indicate that the SHLMS Newton adaptive Volterra equalizer can effectively correct signal amplitude and phase distortions and satellite nonlinear channel distortion.Additionally, the SHLMS Newton algorithm can obtain a faster convergence speed than the traditional algorithms.

    Joint estimation algorithms based on LMS and RLS in the presence of impulsive noise
    YANG Wei;LIU Hongqing;LI Yong;ZHOU Yi
    Journal of Xidian University. 2017, 44(2):  165-170.  doi:10.3969/j.issn.1001-2400.2017.02.028
    Abstract ( 295 )   PDF (753KB) ( 190 )   Save
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    In order to solve the problem that the traditional adaptive algorithms are not able to perform well under the impulsive noise case,this paper develops new adaptive filtering algorithms in the presence of impulsive noise. A close inspection of the impulsive noise reveals that the noise has the sparse property in the time domain because it contains few large values and lots of small values in amplitude.By reformulating the cost functions utilizing this feature of noise into traditional adaptive algorithms,joint sparse online estimation algorithms are developed.The proposed algorithms exploit the noise structure to better suppress the noise.The results demonstrate the superior performance of the proposed methods compared to the existing p-norm algorithms in terms of convergence speed and steady-state error.

    Energy efficient distributed sensor management algorithm
    FANG Deliang;RAN Xiaomin;LI Ou
    Journal of Xidian University. 2017, 44(2):  171-177.  doi:10.3969/j.issn.1001-2400.2017.02.029
    Abstract ( 324 )   PDF (634KB) ( 171 )   Save
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    Considering the limitation of energy in wireless sensor networks(WSN),a distributed sensor management algorithm is proposed for multi-target tracking with high accuracy and efficient energy conservation. The predicted coordinate of the target and information gain are used to establish the optimization model. The method introduces the auction theory and adjusts the price of the sensor resources, and once the balance of the market is reached,the target-sensor assignment problem is solved. In order to shorten the decision-making time and save the energy consumption,the carrier sense multiple access(CSMA) mechanism is introduced and the decision-making can be completed with local information and a few iterations. The convergence and effectiveness of the algorithm are proved,and simulation results show that the algorithm can effectively deal with multi-target tracking problem,guarantee the tracking performance and save the energy to prolong the network lifetime. So the proposed algorithm has a strong adaptability for the energy constrained WSN.

    2-D Doppler shift-frequency intermittent sampling jamming against SAR
    DONG Chunxi;CHANG Xin
    Journal of Xidian University. 2017, 44(2):  178-184.  doi:10.3969/j.issn.1001-2400.2017.02.030
    Abstract ( 343 )   PDF (911KB) ( 108 )   Save
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    To generate the false targets in the desired area accurately, a novel two dimensional(2-D) intermittent sampling jamming algorithm against synthetic aperture radar(SAR) is presented. The intercepted radar signals are processed via 2-D intermittent sampling and Doppler shift-frequency and retransmitted to radar. Hence, the false target-lattice emerges in the specified area. The generation mechanism, position and distribution characteristics of false target-lattice are discussed. Meanwhile, the reason for the asymmetric amplitude of the target false-lattice and the modulation factor of energy compensation are presented. The correctness of theoretical analysis and validity of the proposed algorithm are verified through simulation experiments. Compared with conventional methods, the critical requirement of the jammer position can be reduced by the proposed method.

    Relation between torque and passive intermodulation in microwave devices
    LI Jun;XU Zhuo;MA Xiaofei;LI Tuanjie
    Journal of Xidian University. 2017, 44(2):  185-190.  doi:10.3969/j.issn.1001-2400.2017.02.031
    Abstract ( 257 )   PDF (1051KB) ( 105 )   Save
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    Passive intermodulation (PIM) is a complex problem in high-power microwave devices and satellite communications. In this paper, an effective calculation method is proposed for revealing the mathematical model between torque and PIM power levels of microwave devices. First, the analytical formula for the intermodulation voltage is derived based on the nonlinear I-V characteristics of microwave devices. Second, the mathematical model of point sources is constructed by the transmission line theory. And the nonlinear coefficients are calculated by the I-V curves from measured experiments. By substituting the nonlinear coefficients into the point source model, PIM power levels under different torques are obtained. Eventually, the accuracy with which the point source model predicts the three-order power level is verified by experiments, which solves the problem of PIM prediction under different torques in microwave devices.

    Combined software randomization security defense method
    HAN Kun;ZHANG Hailin;WU Bo;XIN Dan;REN Zhiyuan
    Journal of Xidian University. 2017, 44(2):  191-196.  doi:10.3969/j.issn.1001-2400.2017.02.032
    Abstract ( 294 )   PDF (838KB) ( 126 )   Save
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    The traditional software security defense approach has always been faced with the problem of being easy to conquer and hard to defend, so in order to build a software security defense system that is easy to defend and hard to conquer, based on the idea of moving target defense, a combined defense in depth method for software security is designed and implemented to resist the attacks due to software vulnerabilities. The method introduces the mechanism of randomization on the source code and binary code level, and makes those mechanisms work together comprehensively through the design of metadata database, and finally forms a defense in depth for software security protection. The experimental results of the prototype system show that the proposed method can automatically and effectively build a diversity of software, and the generated software shows the uncertainty from both static analysis and dynamic aspects, which makes it difficult to analyze and attack, thus being able to effectively resist the network attacks based on software vulnerabilities.