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    20 August 2016 Volume 43 Issue 4
      
    Article
    Sparse Bayesian reconstruction combined with  self-adaptive dictionary learning
    WANG Yong;QIAO Qianqian;YANG Xiaoyu;XU Wenjuan;JIA Zheng;CHEN Chuchu;GAO Quanxue
    Journal of Xidian University. 2016, 43(4):  1-4+122.  doi:10.3969/j.issn.1001-2400.2016.04.001
    Abstract ( 388 )   PDF (1285KB) ( 792 )   Save
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    Bayesian compressive sensing (BCS), a kind of compressive sensing algorithm based on statistical analysis, uses information correspondence to get robust performance in image reconstruction. But it depends on image sparsity strongly. In order to solve further level sparsity of BCS, this paper presents a novel self-adaptive Bayesian compressive sensing algorithm combined with redundancy self-adaptive dictionary learning. The algorithm firstly decomposes an image into local patches and builds the dictionary from the iterating transition image. Then the image is represented by this dictionary space. Finally, the image is reconstructed using the sparse Bayesian learning algorithm. Experimental results show that the proposed algorithm obtains deep sparse representation and improves image reconstruction quality.

    SAR image target recognition in lack of pose images
    DING Jun;LIU Hongwei;CHEN Bo;WANG Yinghua
    Journal of Xidian University. 2016, 43(4):  5-9.  doi:10.3969/j.issn.1001-2400.2016.04.002
    Abstract ( 356 )   PDF (620KB) ( 481 )   Save
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    The performance of synthetic aperture radar (SAR) image target recognition depends on the diversity of pose images in the training set. The problem of lack of pose images is considered, and the method of training data augmented with the synthesized pose images is introduced to train the classifier for target identification. Inspired by the sparse representation model, the model for synthesizing pose images is also developed, which approximately construct the missing pose image by linearly combining several images available. Experimental results on the moving and stationary target acquisition and recognition (MSTAR) dataset show that the proposed method of pose images synthesis can increase the recognition accuracy effectively. In particular, significant improvement can be obtained in the case of serious lack of pose images.

    Resource allocation approach for maneuvering target tracking  in distributed MIMO radar systems
    LI Yanyan;SU Tao
    Journal of Xidian University. 2016, 43(4):  10-16.  doi:10.3969/j.issn.1001-2400.2016.04.003
    Abstract ( 318 )   PDF (681KB) ( 375 )   Save
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    Based on the distributed MIMO radar systems, transmitted power and signal bandwidth are jointly allocated to improve the tracking accuracy for a maneuvering target when the resource is limited. Firstly, the Bayesian Cramer Rao Bound (BCRLB) for the maneuvering target tracking error is deduced. Then, a criterion for minimizing the BCRLB is derived, and the corresponding optimization problem with two independent vectors is solved by the cyclic minimization algorithm together with convex relaxation and convex optimization. Simulations demonstrate that the tracking accuracy is improved by the proposed algorithm.

    Low-delay data transmission algorithm for coding-aware routing
    LU Cunbo;XIAO Song;QUAN Lei;XUE Xiao
    Journal of Xidian University. 2016, 43(4):  17-22+146.  doi:10.3969/j.issn.1001-2400.2016.04.004
    Abstract ( 342 )   PDF (590KB) ( 351 )   Save
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    It is significant to reduce packet delivery delay for real-time applications in a wireless network. Existing coding aware routing algorithms use the opportunistic coding scheme in the packet coding algorithm. They never delay packets to wait for the arrival of a future coding opportunity which results in the degradation of the contribution of network coding to delay performance. To overcome the above problem, for coding-aware routing, this paper presents a low-delay data transmission algorithm based buffer management. In the coding node, this algorithm decides packets according to the queue-length based threshold policy instead of the regular opportunistic coding policy as used in existing coding-aware routing algorithms. This algorithm introduces the network delay training phase before the data transmission phase to make the coding node obtain the optimal threshold for the queue-length based threshold policy. Simulation results show that our algorithm can achieve a lower packet delivery delay, a lower packet loss ratio and a higher throughput than the traditional opportunistic coding policy in network congestion.

    Design of double sample 1.2V 7bit 125MS/s pipelined ADC
    WANG Xiaofei;HAO Yue
    Journal of Xidian University. 2016, 43(4):  23-28.  doi:10.3969/j.issn.1001-2400.2016.04.005
    Abstract ( 289 )   PDF (2133KB) ( 344 )   Save
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    A 7bit 125MS/s double sample pipelined ADC which can achieve a low power and a high performance for the SoC system is presented. The presented ADC with op-amp sharing between two channels and a new timing scheme can not only eliminate sampling timing skew, but also has a low power and a small area. Test results show that the ADC designed in a 0.13μm CMOS process achieves a maximum SNDR of 43.38dB, and that ENOB is 6.8bits. The ADC consumes 10.8mW at 125MS/s under a 1.2V supply voltage.

    Double-threshold GLRT CFAR detection in distributed MIMO radar
    HU Qinzhen;YANG Qian;SU Hongtao;ZHOU Shenghua;LIU Ziwei;YANG Yang
    Journal of Xidian University. 2016, 43(4):  29-33+85.  doi:10.3969/j.issn.1001-2400.2016.04.006
    Abstract ( 388 )   PDF (500KB) ( 372 )   Save
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    To decrease the data transmission rate between fusion center and local radar stations for target detection in distributed multi-input multi-output (MIMO) radar, a double-threshold generalized likelihood ratio test (DT-GLRT) constant false alarm rate algorithm is proposed. Firstly, local GLRT test statistics are censored through the first threshold and the over-threshold local test statistics are transferred to the fusion center. Secondly, the transferred data are fused to decide the target presence according to the second threshold in the fusion center. The closed-form expression for the probability of false alarm of the DT-GLRT is derived. Simulation results demonstrate that the proposed DT-GLRT algorithm can maintain good detection performance with a low data transmission rate.

    Modified MST for the parameter estimation of  polyphase coded signals
    JIANG Li;LI Lin;ZHAO Guoqing
    Journal of Xidian University. 2016, 43(4):  34-38+99.  doi:10.3969/j.issn.1001-2400.2016.04.007
    Abstract ( 224 )   PDF (664KB) ( 301 )   Save
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    The polyphase coded signal is a kind of low probability of intercept radar signal which has the similar time frequency distribution as the linear frequency modulation signal. Now the parameter estimation of the polyphase coded signal has been a new research hotspot. Based on the matched signal transform theory, this paper derives the chirp rate estimation performance when the intercepted signal mismatches the time function. According to the characteristics of the quadratic polynomial function and the problems under actual reconnaissance environment, such as residual frequency error, incomplete signal and noise interferences, a modified matched signal transform based on two-dimension search is proposed. Experiments on the P4 code analyze the parameter estimation performance. Experimental results verify that the algorithm can solve the problem of signal mismatch and has good properties of accuracy, calculation speed and engineering application.

    Improved BP decoding algorithm for Polar codes
    HONG Yinfang;LI Hui;WANG Xinmei
    Journal of Xidian University. 2016, 43(4):  39-44.  doi:10.3969/j.issn.1001-2400.2016.04.008
    Abstract ( 441 )   PDF (576KB) ( 563 )   Save
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    In the decoding algorithm for Polar codes, the belief propagation (BP) decoding algorithm in the log-likelihood ratio domain incurs high computation complexity due to the computation of the hyperbolic functions Motivated by this observation we propose an improved BP decoding algorithm. In the node update rules, our method replaces the hyperbolic functions with the linear approximation functions based on the principle of equal error. Compared with the original BP decoding algorithm, the modified BP decoding algorithm is only implemented by addition and multiplication operations, which greatly reduces computation complexity, and simplifies hardware implementation. Simulation results show that the performance of the modified BP decoding algorithm is almost the same as that of the original BP decoding algorithm in the low Signal to Noise Ratio (SNR) region, and in the high SNR region the performance of our method is slightly worse. Compared with the original BP decoding algorithm, the bit error rate (BER) performance of the modified BP decoding algorithm has about 0.1dB degradation when the length of Polar codes is 256 and the BER is 10<sup>-6</sup>.

    Gaussian shape context descriptors
    FENG Xiangwei;FENG Dazheng;HOU Ruili
    Journal of Xidian University. 2016, 43(4):  45-50.  doi:10.3969/j.issn.1001-2400.2016.04.009
    Abstract ( 359 )   PDF (916KB) ( 337 )   Save
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    The shape context (SC) descriptors based on the Gaussian window (GSC) are proposed. The GSC descriptors can be used to match shapes. Encircling the reference point, the GSC sets up a group of Gaussian window functions. According to the Euclidean distance between the center points and the sampling points, the GSC describes the spatial relations between sampling points based on the shape descriptors calculated by Gaussian window functions by the use of as many sampling points as possible. More accurate correspondences between two shapes are determined by comparing the similarities of the shape descriptors. Experimental results show that the GSC can find more accurate correspondence relations and provide a good initial value. The proposed descriptors can also make the matching algorithm converge fast, while keeping a good anti-noise and robust performance compared with SC.

    Novel algorithm for predicting personalized retweet behavior
    TANG Xing;QUAN Yining;SONG Jianfeng;DENG Kai;ZHU Hai;MIAO Qiguang
    Journal of Xidian University. 2016, 43(4):  51-56+62.  doi:10.3969/j.issn.1001-2400.2016.04.010
    Abstract ( 267 )   PDF (801KB) ( 361 )   Save
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    Recently, models for predicting the user retweet behavior are based mainly on the historical retweet data of all users. However, these models are of homogeneity and could not predict a particular user's behavior. To overcome these problems, we propose an algorithm for predicting personalized retweet behavior. Based on crawled Weibo data, we have conducted an analysis and a selection of retweet features. According to the influential theory, we introduce the multi-task learning framework to divide the tasks into common global tasks and many individual tasks. Our massive experiments show that our algorithm is effective in predicting personalized retweet behavior.

    Effect of properties from a rough target echo signal on the  detection threshold in optical heterodyne detection
    DANG Wenjia;ZENG Xiaodong;LAI Zhi;FENG Zhejun;CAO Changqing;HUO Yaowei
    Journal of Xidian University. 2016, 43(4):  57-62.  doi:10.3969/j.issn.1001-2400.2016.04.011
    Abstract ( 219 )   PDF (996KB) ( 334 )   Save
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    Traditionally, a simple model, such as Gaussian distribution, describes the optical heterodyne detection echo signal of the target, which often leads to judgment errors. In this paper, we present a more accurate method to describe the probability distribution of the echo signal by use of polynomial fitting. The echo signals from a surface coating specimen of an armored car are measured, with the statistical analysis showing that the probability of detection is higher and the probability of false alarm is lower, when using the method of polynomial fitting to determine the decision threshold, rather than using a simple Gaussian distribution to determine it. The results show that by the method of polynomial fitting on the statistical histogram of the measured intermediate frequency signal, the precision of setting the detection threshold will be improved, and that the probability of detection rises by 6.02% and the probability of false alarm falls by 7.7%. The results of this paper provide a quantitative reference for designing the rough surface echo heterodyne detection system and also provide a useful tool for evaluating the performance of the heterodyne detection system.

    Theoretical limit of the indoor visible light-image sensor  positioning system
    ZHAO Xiang;LIN Jiming
    Journal of Xidian University. 2016, 43(4):  63-68.  doi:10.3969/j.issn.1001-2400.2016.04.012
    Abstract ( 308 )   PDF (602KB) ( 296 )   Save
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    To guide the optimization problem of the parameters in the image sensor-based visible light positioning system, theoretical limits on the location estimation of the receiver are calculated by deriving the Cramer-Rao Lower Bound (CRLB). For typical indoor scenes, the observations of the image points at the receiver are affected by the Gaussian white noise, the maximum likelihood estimation(MLE) for the location of the receiver is calculated, and the CRLB for the MLE is derived. By using the real parameters of the location are achievable, with positioning error usually in the order of millimeters. The positioning error depends on the number of transmitters, the focal length of the lens, the vertical distance from roof to receiver, the pixel size and the frame rate of the image sensor.

    Fast IR dim small targets detection and tracking based on  the multi-Bernoulli filter
    LI Cuiyun;LI Ning;JI Hongbing
    Journal of Xidian University. 2016, 43(4):  69-74+190.  doi:10.3969/j.issn.1001-2400.2016.04.013
    Abstract ( 277 )   PDF (1431KB) ( 279 )   Save
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    In view of the problems of tracking instability and non real-time and highly nonlinear measurement model for the detection and tracking of multiple Infrared(IR) dim targets under the complicated background, a fast detection and tracking algorithm based on multi-Bernoulli filter is presented. Firstly, the improved Robinson Guard filter suppresses the background clutter in order to avoid the suppression of the target in the strong background image. Then, the square-root cubature Kalman filter (SCK) performs the multi-Bernoulli track-before-detect (MB-TBD). It can perform real-time tracking in the highly nonlinear model. The numerical instability caused by a negative definite covariance matrix is avoided. The experiments with some real IR background images show that the improved Robinson Guard algorithm can suppress the background clutter effectively and preserve the dim target information. It is also shown that SCK-MB-TBD can estimate the number and states of targets accurately and stably so as to complete target detection and tracking.

    VLSI design of the JPEG-LS near-lossless image encoder
    NIE Yongkang;LEI Jie;LI Yunsong;SONG Changhe;WU Xianyun
    Journal of Xidian University. 2016, 43(4):  75-80.  doi:10.3969/j.issn.1001-2400.2016.04.014
    Abstract ( 309 )   PDF (646KB) ( 333 )   Save
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    The JPEG-LS image compression standard brings excellent performance and low complexity, which makes it the widely used in space communications, medicine and many other fields. However, the prediction of the current pixel requires the reconstruction value of the previous pixel in the near-lossless mode, which leads to complicated computation and a feedback circuit with long latency in hardware implementations. On the basis of an intensive study of the JPEG-LS algorithm, a forward prediction method of reconstruction value is used and the new VLSI implementation of the JPEG-LS encoder is proposed in this paper, which can avoid the feedback latency. Compared with existing implementations, the proposed one has the advantages of higher encoding speed, no nuse of off-chip storages, and lower power consumption, making it suitable for resource-limited spaceborne image compression.

    Resistive FSS applied to the RCS reduction of array antennas
    WANG Fan;GONG Shuxi;WANG Fuwei
    Journal of Xidian University. 2016, 43(4):  81-85.  doi:10.3969/j.issn.1001-2400.2016.04.015
    Abstract ( 312 )   PDF (1095KB) ( 379 )   Save
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    A ring-shaped resistive frequency selective surface (FSS) microwave-absorbing structure is designed and applied to the RCS reduction of the microstrip antenna array. The resistive FSS structure is constructed from resistive treble-square loops arranged in a periodic array. An array with four patch elements is designed, and the resistive FSS is located between two patch elements. Simulated results show that the proposed structure shows a good microwave absorbing characteristic in the frequency range of 6GHz to 22GHz. When loaded in a microstrip antenna array, the RCS of the array antenna can be reduced to the maximum of 27dB with little impact on the antenna's radiation characteristic. And the control of the wideband RCS of the antenna can be realized with this structure.

    Cooperative spectrum sensing method considering anti  camouflage SSDF malicious attacks
    QI Xiaogang;QIN Fengjuan;LIU Lifang
    Journal of Xidian University. 2016, 43(4):  86-91+159.  doi:10.3969/j.issn.1001-2400.2016.04.016
    Abstract ( 192 )   PDF (737KB) ( 276 )   Save
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    We propose a segmented trust value update and defense scheme after considering a more practical cognitive radio network, where malicious users are able to camouflage themselves. First, we choose slow growth and fast recovery of the trust value update mechanism, determine which energy interval the reporting energy value of the node belongs to, and then reduce the malicious node trust value by dynamically updating the trust value and urge the poor performance node to improve its sensing efficiency. Simulation analysis using the Monte Carlo method is made to show the effectiveness of opposing malicious attacks, and guarantee the network performance and throughput.

    Random computational homogenization for  three-dimensional linear elasticity
    WANG Nan;MA Juan;ZHANG Yulin
    Journal of Xidian University. 2016, 43(4):  92-99.  doi:10.3969/j.issn.1001-2400.2016.04.017
    Abstract ( 235 )   PDF (1684KB) ( 264 )   Save
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    The computational homogenization of heterogeneous materials under infinitesimal deformation is addressed in the context of elasticity when the uncertainty in microstructure is fully considered. Based on the multi-scale finite element method and Monte-carlo method, the random homogenization model of heterogeneous materials is established when the randomness of microstructural morphology and of material properties of constituents as well as the correlation of material properties are accounted for simultaneously. The random effective quantities and their numerical characteristics as well as their correlations under different boundary conditions are then found. And the impacts of microstructural parameters on random effective quantities are also investigated and illustrated. Finally, the random stress distributions within a representative volume element under different boundary conditions are revealed as well. Obviously, it is necessary that the randomness and correlation existing in the microstructure should be fully considered during the solution of the effective mechanical properties of heterogeneous materials.

    Imaging algorithm in the frequency domain for helicopter-borne radar
    WEN Jun;YANG Ke;ZHAO Jinchuang;ZOU Xingxing;QIN Tuanfa
    Journal of Xidian University. 2016, 43(4):  100-104.  doi:10.3969/j.issn.1001-2400.2016.04.018
    Abstract ( 686 )   PDF (726KB) ( 276 )   Save
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    Helicopter-borne Radar (HeliRadar) has the advantages of full-perspective imaging and short revisit period, which can ensure the rotor aircrafts flight safety at the low altitude. In order to solve the azimuth mismatch problem of the existing algorithm, the HeliRadar imaging algorithm in the frequency domain is presented in this paper. Through the frequency domain analysis of the characteristics of the HeliRadar echo, this new algorithm can obtain a two-dimensional accurate spectrum, construct the frequency domain correction function and the matching function, and achieve the matching imaging. Simulation results verify the effectiveness of the algorithm.

    Distributed synchronization protocol for wireless sensor networks
    WANG Jing;ZHANG Shuai;GAO Dan;WANG Yingguan
    Journal of Xidian University. 2016, 43(4):  105-110+134.  doi:10.3969/j.issn.1001-2400.2016.04.019
    Abstract ( 458 )   PDF (577KB) ( 329 )   Save
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    Distributed time synchronization and distributed data synchronization are proposed for the synchronization problem in wireless sensor networks. The former requires the cluster head network to execute local information exchange, and it adopts low-pass filtering to remove the noise interference. The latter provides network-wide data mean to nodes, and it requires the cluster head network to execute the proportion consistency algorithm, in which the number of nodes within a cluster is introduced during the iterative process. Experimental results show that the distributed time synchronization maintains anti-noise performance, and that the algorithm converges fast in the earlier stage. Grid-like network and random network experiments show that distributed time synchronization and distributed data synchronization have a low communication overhead, and their convergence rates are faster than that of general data synchronization.

    Upper bound on the ergodic capacity of D-MIMO systems in  double-sidedcorrelated Rayleigh/Lognormal fading channels
    WANG Yongping;CAO Hanqiang;WANG Anwen
    Journal of Xidian University. 2016, 43(4):  111-116+153.  doi:10.3969/j.issn.1001-2400.2016.04.020
    Abstract ( 315 )   PDF (760KB) ( 272 )   Save
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    An analytical upper bound is presented for the ergodic capacity of distributed multiple-input multiple-output (D-MIMO) systems operating in Rayleigh/Lognormal fading with double-sided spatial correlation. A new inequality is constructed by sub-matrix expansion, and then the difficulty in averaging the channel eigen-statistics over the shadowing distribution is resolved. The proposed upper bound is applicable for the arbitrary number of receive and transmit antennas and remains tight over the entire Signal-to-Noise regime. The validity of the conclusion is verified by compu- ter simulation. When the number of receive and transmit nodes is one, the lower bound reduces to the bound on the ergodic capacity of point to point MIMO systems operating in Rayleigh/Lognormal fading with double-sided spatial correlation.

    Design and hardware implementation of the  small-size CMOS camera system
    XU Dongdong;ZHANG Yu;NIE Ting;ZHANG Xingxiang;REN Jianyue
    Journal of Xidian University. 2016, 43(4):  117-122.  doi:10.3969/j.issn.1001-2400.2016.04.021
    Abstract ( 261 )   PDF (1451KB) ( 312 )   Save
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    A camera with a small-size and low-power is designed, using a CMOS MT9V032 as the digital image sensor. Based on the primary aberration theory, the optical system with the small size and compact structure is designed whose focal length is 12.95mm and whose F number is 5, and the modulation transfer functions (MTF) of all fields are better than 0.5 at the spatial frequency of 83lp/mm; we use FPGA as the timing control platform for the electronic system and the digital video signal of the CMOS output which is delivered through the differential chip in the low voltage differential signal (LVDS) output format to the image acquisition card. Finally, we can see the image on the computer. Experimental results show that the designed CMOS camera has a good image quality, low power, portability, and high reliability, and that the frame rate is 60frames/s when the clock is 26.6MHz, and it could achieve a variety of modes by adjusting the values of the internal registers, which is particularly suitable for the high requirements occasion in the camera volume and high imaging quality.

    Optimum sensor array for passive localization from  time differences of arrival
    ZHOU Cheng;HUANG Gaoming;GAO Jun
    Journal of Xidian University. 2016, 43(4):  123-127.  doi:10.3969/j.issn.1001-2400.2016.04.022
    Abstract ( 321 )   PDF (656KB) ( 295 )   Save
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    In the TDOA system, the method for improving the source location accuracy by sensor arrangement is proposed. The trace of the CRLB of a source estimate is the criterion. By analyzing the factors of the CRLB, it is found that the CRLB does not depend on the range between sensor and source, but on the direction from sensor to source. The expression for the trace of the CRLB is derived. Then its minimum value and the condition for achieving the minimum value are obtained. It is shown that the uniform angular array is the optimum sensor array when the source is surrounded by sensors.

    Airtime fairness scheduling algorithm for multi-rate WLANs
    PAN Zhipeng;WU Bin;YE Tianchun
    Journal of Xidian University. 2016, 43(4):  128-134.  doi:10.3969/j.issn.1001-2400.2016.04.023
    Abstract ( 246 )   PDF (948KB) ( 397 )   Save
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    The DCF (Distributed Coordination Function) used in the IEEE 802.11 protocol provides equal transmission opportunities to each station, which will lead to the performance anomaly in the multi-rate wireless local area network (WLAN). In this paper, we propose a round-robin queue scheduler based on linear scaling of airtime fairness after a detailed theoretical analysis of throughput fairness and airtime fairness. It counts the accurate channel occupancy time of each station, then adopts round-robin to ensure the airtime fairness, and finally improves the system throughput. According to the quality of service (QoS) of data flows, the proposed algorithm can achieve a compromise between transmission efficiency and delay performance by dynamically updating the polling cycle. Simulation by NS-3 and verification by the hardware system show that the proposed algorithm can effectively improve the system uplink and downlink throughput performance while ensuring per-station airtime fairness.

    Verifiable outsourcing scheme for batch modular exponentiations
    HUANG Chunshui;REN Yanli;CAI Jianxing
    Journal of Xidian University. 2016, 43(4):  135-140.  doi:10.3969/j.issn.1001-2400.2016.04.024
    Abstract ( 216 )   PDF (458KB) ( 235 )   Save
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    With the development of cloud computing, more and more people focus on how to outsource the expensive computations to the untrusted cloud servers. Currently, the outsourcing schemes for modular exponentiations are mostly based on two untrusted servers, or the checkability is very small. We propose a new outsourcing algorithm for batch modular exponentiations by using the random permutation. The exponent and the base are both private for the server, and the outsourcer can detect the error with probability close to 1. Compared with the previous algorithms, the proposed one is based on a single server, which realizes the privacy of inputs and increases the checkability of the outsourcing result. Finally, we simulate the proposed algorithm, and the experimental result shows that it can greatly reduce the computational cost for the outsourcer.

    Coverage algorithm for finding the minimum working sets in WSNs
    WANG Aimin;LIU Yongqiang;ZHANG Jing;LIU Yanheng
    Journal of Xidian University. 2016, 43(4):  141-146.  doi:10.3969/j.issn.1001-2400.2016.04.025
    Abstract ( 221 )   PDF (541KB) ( 238 )   Save
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    Since the existing coverage algorithm has a lot of redundant nodes, a coverage algorithm for finding the minimum working sets in WSNs(FMWS) is proposed. The algorithm is divided into two phases: the first phase runs an existing coverage algorithm; the second phase runs an algorithm that uses fewer working nodes to replace more working nodes, with the number of working nodes continuously decreasing through iteration. Simulation shows that the proposed algorithm can obtain more sleep nodes than other algorithms. It can make the number of working nodes reduce around 10%, so as to prolong the network life.

    Research on the shared aperture multifunction  wideband array antenna
    LI Longjun;WANG Buhong
    Journal of Xidian University. 2016, 43(4):  147-153.  doi:10.3969/j.issn.1001-2400.2016.04.026
    Abstract ( 344 )   PDF (867KB) ( 314 )   Save
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    The paper presents a new technology for designing the shared aperture wideband array with multiple interleaved sub-arrays based on the energy match of sub-array excitation distribution. In view of the Fourier transform relationship between the array pattern and elements excitation, the mathematical relationship between the array working frequency and elements excitation is achieved. The interleaved thinned sub-arrays with different working frequencies are designed with the positions of the elements achieved by way of the energy match of sub-array excitation distribution and the theory of density weighted array. Theoretical analysis and experimental simulation show that the peak side-lobe levels of the interleaved sub-arrays under different working frequencies which are designed by the proposed method are restrained with the grating lobe suppressed. The multifunction wideband array is achieved as the working bandwidth of array antennas is broadened effectively.

    Three-dimensional simulation of kinetics of carbon nanotubes  under dielectrophoresis
    WANG Xiaochong;AN Libao;GONG Liang;CHEN Yan
    Journal of Xidian University. 2016, 43(4):  154-159.  doi:10.3969/j.issn.1001-2400.2016.04.027
    Abstract ( 301 )   PDF (1105KB) ( 317 )   Save
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    Based on the dielectrophoretic force arising from the polarization of carbon nanotubes (CNTs) in the dielectric fluid under an alternating current electric field and the viscous resistance from the fluid, force and motion models for CNTs under dielectrophoresis (DEP) are established. Simulation is conducted on the translational and rotational motion of CNTs. Three-dimensional trajectories and a distribution region of initial points from where a CNT can be successfully assembled onto the electrode gap are obtained. By calculating the DEP force and translational velocity of a CNT during assembly, we know that the nearer the CNT to the electrode gap, the greater the DEP force and CNT velocity, and that the maximal DEP force and CNT velocity can be respectively of orders 10<sup>-9</sup>N and 10<sup>5<sup>μm/s. The results of simulation provide guidance for DEP assembly of CNTs.

    Temporal subsampling based depth maps coding and  the reconstruction method
    GE Chuan;LIU Ju;YUAN Hui;XIAO Yifan;LI Fengrong
    Journal of Xidian University. 2016, 43(4):  160-165+171.  doi:10.3969/j.issn.1001-2400.2016.04.028
    Abstract ( 224 )   PDF (1220KB) ( 288 )   Save
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    In order to improve the coding efficiency of a three-dimensional video system, a depth temporal subsampling based coding method for the intermediate view is proposed. In this paper, the manner of how to discard depth frames is firstly determined. Then, those discarded depths are reconstructed utilizing temporal consistency and multiview correspondences. Finally, in order to further improve the quality of the reconstructed depth, the wiener filter is implemented on the reconstructed results. Filter coefficients and indicators for selecting the depth predictor should be transmitted to the decoder. Experimental results demonstrate that a maximum 0.229dB and average 0.130dB peak signal-to noise ratio (PSNR) gain could be achieved for the virtual view reconstructed by the decoder while maintaining the same coding bit rate, and that the coding efficiency can be improved.

    ECG front-end subsystem with the driven-right-leg circuit
    YANG Zheng;WANG Jingmin;ZHU Zhangming;YANG Yintang
    Journal of Xidian University. 2016, 43(4):  166-171.  doi:10.3969/j.issn.1001-2400.2016.04.029
    Abstract ( 350 )   PDF (650KB) ( 670 )   Save
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    Under the condition of an un-shielding room, electrocardiogram (ECG) signal detection is a weak signal detection process with a strong common mode interference. In order to improve the performance of common mode rejection of the circuit, a driven-right-leg (DRL) circuit is often utilized. In this paper, a high performance ECG amplifier is proposed. The programmable gain amplifier (PGA) circuit and DRL circuit are applied at this analog front end. The PGA is utilized for ECG signal amplification, with the programmable gain set at 1, 2, 3, 4, 6, 8, 12. The DRL circuit is used to reduce common-mode interference.

    Low-rank and dual approximation method for  image inpainting problems
    FENG Xiangchu;WANG Siqi;LI Xiaoping
    Journal of Xidian University. 2016, 43(4):  172-177.  doi:10.3969/j.issn.1001-2400.2016.04.030
    Abstract ( 237 )   PDF (7710KB) ( 320 )   Save
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    A novel image inpainting algorithm is proposed to improve the traditional exemplar-based inpainting methods. The new approach uses a salient-based ranking method to ensure the priority of the target patch with structure edges, whose similar exemplars would be measured by the image Euclidean distance. And a low-rank and dual approximation of the selected exemplar matrix is used to extract the available information for inpainting. Experimental results show that the new algorithm preferentially repairs significant structures accurately, and performs well in different kinds of missing or damaged cases.

    Spectrum analysis compression algorithm of measure report data
    CHENG Fei;LIU Kai;DING Wenwen;SHI Huan;ZHANG Baijian
    Journal of Xidian University. 2016, 43(4):  178-183.  doi:10.3969/j.issn.1001-2400.2016.04.031
    Abstract ( 219 )   PDF (839KB) ( 305 )   Save
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    To solve to the problem that with the increment of the number of mobile users, the network bandwidth cannot meet the mass transfer of the measure report. This paper defines the conception of the spectrum of the measure report and proposes a spectrum analysis compression algorithm for the measure report. The algorithm utilizes two step sorting in order to reduce the distance between similar contents according to the analysis of the spectrum of measure report data. Furthermore, this algorithm employs several context models, which are regarded as the input nodes of the neural network. The prediction probability is calculated by the linear combination of the probability of each context model, and the weight in each link is tuned by the next bit in order to increase the possibility of matching. Experimental results reveal that the algorithm not only decreases the compression consuming time, but also ascends the compression ratio with the increment of the size of compression data. Compared with other competitors, this algorithm can effectively increase the compression ratio of the measure report to gain a better transfer time.

    Neurofilament protein automatic tracking of the  particle filter algorithm based on multiple methods fusion
    JU Gang;YUAN Liang;LIU Xiaoyue
    Journal of Xidian University. 2016, 43(4):  184-190.  doi:10.3969/j.issn.1001-2400.2016.04.032
    Abstract ( 296 )   PDF (3208KB) ( 323 )   Save
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    The neurofilament protein serves as the marker of the state for ALS (Amyotrophic Lateral Sclerosis) in the medical filed. In order to accurately capture the motion characteristics of the neurofilament protein in the axon, a new-type algorithm based on the particle filtering of multiple methods-fusion is introduced in this paper. This fusion algorithm integrates the advantages of the color histogram, kernel function method, and graph model strength into the particle filtering algorithm. In addition, in order to solve the problem of sample impoverishment, which will lead to the majority of particles overlapping on one single point in the computation of the particle filter, the re-sampling method is utilitied. However, the re-sampling method easily causes the loss of the particle anisotropy, which will reduce the tracking precision or even fail to the track. We present a new re-sampling constrained method to improve the particle anisotropy in the particle filtering. Experimental results indicate that the algorithm based on the improved method of re-sampling and the particle filter of multiple methods-fusion can effectively reduce the number of overlapping particles and precisely track the deformed neurofilament protein. Such a tracking method will be helpful in the research on the neurofilament protein in the medical filed.

    Method for relay tracked target handover using  the spectrum bag of words
    ZHANG Xiaojun;LIU Zhijing;XUE Hongmin
    Journal of Xidian University. 2016, 43(4):  191-196.  doi:10.3969/j.issn.1001-2400.2016.04.033
    Abstract ( 288 )   PDF (2250KB) ( 275 )   Save
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    Aiming at the difficulty of the relay-tracked target handover across cameras, a method using the spectrum Bag Of Words(BOW) is proposed. Firstly, 2 or more target images from the first camera are divided into blocks. The Fourier features of the blocks are extracted and then clustered by Kmeans. The averaged vectors of the compact clusters are used as the normal words of the BOW, while an abnormal vector is used as the abnormal word. The targets from the first and second cameras are described in BOW words.The Euclidean distance between the BOW descriptions is used as the target similarity metrics. Experiments show that the proposed method has some definite improvement in target recognition and robustness compared with several common methods based on the texture.