Loading...
Office

Table of Content

    20 October 2016 Volume 43 Issue 5
      
    Time resource allocation strategy for single beam phased array radar
    QIN Tong;DAI Fengzhou;LIU Hongwei;FANG Ming
    Journal of Xidian University. 2016, 43(5):  1-5.  doi:10.3969/j.issn.1001-2400.2016.05.001
    Abstract ( 450 )   PDF (472KB) ( 502 )   Save
    References | Related Articles | Metrics

    In practical applications, single beam phased array radar can generate multiple directional beams and illuminate multiple targets, respectively. In this paper, we put forward a time-resource and the beam-width-of-joint-management algorithm to save the time resources. This paper describes the tracking precision of the target with the probability density function, and the ranging and velocity precision of the measurement will influence the tracking error. This paper uses the method of optimization to allocate the dwell time and beam width for each target. Simulation results show that, compared with the traditional adaptive methods of resource management, the method in this paper will guarantee the tracking accuracy and save the time resources for traking targets effectively, and will increase the maximum number of the targets the radar can track with the same tracking accuracy.

    Non-unitary joint diagonalization by complex Givens and complex Shear rotation
    LIU Wenjuan;FENG Dazheng
    Journal of Xidian University. 2016, 43(5):  6-11.  doi:10.3969/j.issn.1001-2400.2016.05.002
    Abstract ( 265 )   PDF (629KB) ( 310 )   Save
    References | Related Articles | Metrics

    The proposed algorithm is based on the combination of complex Givens and complex Shear rotations, which decomposes the de-mixing matrix into a product of complex rotation matrices. By ingenious utilization of the structure of the complex Givens and complex Shear rotations, together with the adequate expression of the concerned variables, the minimization of the F-norm criterion function can be transformed into a sequence of problems of calculating the generalized eigenvector of two 3×3 real symmetric matrices. Numerical simulations illustrate the good performance and convergence property of the proposed algorithm.

    Super-resolution imaging method for the SAR target in a strong clutter scene
    JING Guobin;SHENG Jialian;CHEN Jianlai;SUN Guangcai;XING Mengdao;BAO Zheng
    Journal of Xidian University. 2016, 43(5):  12-17+87.  doi:10.3969/j.issn.1001-2400.2016.05.003
    Abstract ( 254 )   PDF (1534KB) ( 242 )   Save
    References | Related Articles | Metrics

    This paper proposes a super-resolution imaging method to solve the problem of extracting targets and enhancing resolution under a strong clutter in the SAR image. Based on singal correlation, an adaptive clutter threshold is proposed to extract strong scatterers of targets. Then weak scatterers of targets are extracted by the gradient descent method. Finally, target resolution is enhanced to realize super-resolution imaging by the simplified regularization method. Real-measured data of reflectors and the stationary vehicle validate the effectiveness of the proposed method.

    Azimuth variation correction method for geosynchronous synthetic aperture radar
    CHEN Jianlai;ZHANG Rui;SUN Guangcai;JING Guobin;XING Mengdao
    Journal of Xidian University. 2016, 43(5):  18-23+62.  doi:10.3969/j.issn.1001-2400.2016.05.004
    Abstract ( 243 )   PDF (1753KB) ( 281 )   Save
    References | Related Articles | Metrics

    Aimed at the severe azimuth variation caused by the ultralong synthetic aperture time and very large scene in geosynchronous synthetic aperture radar (GEOSAR), this paper develops an azimuth variation correction method for GEOSAR. The method firstly obtains the two-dimensional spectrum by the method of series reversion (MSR). The Doppler and azimuth positions of the point target in the two-dimensional spectrum are serious coupled. The singular value decomposition (SVD) can be introduced to separate the Doppler position from the position of the point target. Subsequently, Stolt interpolation is used twice to compensate the high-order phase terms. Thus, a focused scene is obtained. Finally, simulation for scene targets validate the proposed method. All the targets in the scene are focused well.

    ISAR imaging algorithm for targets with the complex motion based on the high-order ambiguity function-Lv's distribution
    LV Qian;SU Tao;WU Kai;ZHANG Jiancheng
    Journal of Xidian University. 2016, 43(5):  24-30.  doi:10.3969/j.issn.1001-2400.2016.05.005
    Abstract ( 635 )   PDF (1500KB) ( 283 )   Save
    References | Related Articles | Metrics

    In ISAR imaging for targets with the complex motion, since the azimuth high order phase terms caused by the time-varying rotation vector will deteriorate the azimuth focusing quality, the traditional RD algorithm and LFM model are not appropriate. Thereby, in the case when the received signal can be modeled as cubic phase signals (CPSs), this paper proposes an ISAR imaging algorithm based on HAF-LVD (high-order ambiguity function-Lv's distribution). First, this algorithm defines a novel double lag parametric instantaneous autocorrelation function, and then applies the scaling operator to remove the coupling and utilizes FFT to achieve the energy accumulation. Finally, the non-searching estimation of the moving parameter and the ISAR images for targets are accomplished by the obtained HAF-LVD. Because of the introduction of the scaling factor, this algorithm can flexibly deal with more changeful and hostile ISAR environment without loss of the anti-noise performance and computational efficiency. Simulation results validate the effectiveness of the ISAR imaging approach.

    Approach to joint translational and rotational phase auto-focusing
    ZHANG Yuhong;XING Mengdao
    Journal of Xidian University. 2016, 43(5):  31-35.  doi:10.3969/j.issn.1001-2400.2016.05.006
    Abstract ( 348 )   PDF (806KB) ( 233 )   Save
    References | Related Articles | Metrics

    In high-resolution inverse synthetic aperture radar imaging, the rotational motion of the targets tends to introduce the time-variant Doppler modulation in the echo, which acts as the range-variant phase errors in phase history. Moreover, the performance of translational phase error compensation may be dramatically degraded without properly considering the range-variant phase errors. In this paper, an approach to joint translational and rotational phase auto-focusing is proposed. In the procedure, the joint phase error correction is modeled as range-invariant and range-variant phase errors using a metric of minimum entropy. Then the minimum-entropy optimization is solved by employing a coordinate descend method based on the quasi-Newton solver. Finally, experiment based on simulated data is performed to confirm the effectiveness of the proposed algorithm.

    Modified algorithm for complex-time distribution
    JIANG Li;ZHAO Guoqing;LI Lin
    Journal of Xidian University. 2016, 43(5):  36-40.  doi:10.3969/j.issn.1001-2400.2016.05.007
    Abstract ( 266 )   PDF (2100KB) ( 183 )   Save
    References | Related Articles | Metrics

    Aiming at the problems of computer precision and even overflow, a new modified algorithm is proposed. The complex-time distribution algorithm can be accomplished effectively by frequency spectrum iteration estimation and signal scale conversion. Simulation results show that the proposed method has a good ability to suppress the influence of noise interferences, improve the energy convergence, and provide theoretical and technical support for the enginnering application.

    Static beamforming method of frequency diverse array
    XU Yanhong;SHI Xiaowei;WEN Jun
    Journal of Xidian University. 2016, 43(5):  41-45+166.  doi:10.3969/j.issn.1001-2400.2016.05.008
    Abstract ( 269 )   PDF (1771KB) ( 260 )   Save
    References | Related Articles | Metrics

    Focused on the time-varying property of the transmit beampattern of the frequency diverse array, a static transmit beamforming method is proposed to control the beampattern of the pulsed frequency diverse array, and the characteristics of its radiating pattern are studied. With a tiny progressive incremental frequency shift applied between the adjacent antenna elements, a range-angle dependent radiating pattern is achieved. Compared with the conventional phased array, the frequency diverse array is low in price and small in complexity without the use of phase shifters, which enables it to be suitable for the miniaturization design of an array antenna. Moreover, its range-angle dependent characteristic significantly enhances the flexibility of antenna beam scanning. Simulation experiments demonstrate the effectiveness of the proposed method.

    Optimization of matrix filling in the large scale parallel RWG basis based method of moments
    CHEN Yan;ZHANG Yu;WANG Yong;ZHAO Xunwang;LIN Zhongchao
    Journal of Xidian University. 2016, 43(5):  46-51.  doi:10.3969/j.issn.1001-2400.2016.05.009
    Abstract ( 252 )   PDF (1230KB) ( 239 )   Save
    References | Related Articles | Metrics

    To solve the issue of inter-process redundant integrals in the parallel Method of Moments (MoM) using RWG basis functions, an efficient parallel matrix filling scheme is proposed through mesh index optimization. Based on a block-cyclic matrix distribution strategy, the common edges of triangles are renumbered to make the matrix elements that need the same triangular integrals be assigned to one process, thus drastically reducing the inter-process redundant integrals. Numerical results show that the proposed scheme eliminates most of the inter-process redundant integrals and greatly improves the efficiency of parallel matrix filling.

    Novel power plane with an electromagnetic bandgap structure for suppression of simultaneous switching noise
    ZHANG Guangshuo;LU Hongmin;TAN Kangbo;GUANG Qiao;XIAO Junfei
    Journal of Xidian University. 2016, 43(5):  52-56+189.  doi:10.3969/j.issn.1001-2400.2016.05.010
    Abstract ( 292 )   PDF (2127KB) ( 145 )   Save
    References | Related Articles | Metrics

    For ultra-wideband suppression of simultaneous switching noise between the power plane and the ground plane within the printed circuit board, a novel power plane with planar electromagnetic bandgap structures is proposed. When the suppression depth of the bandgap is -30dB, the width of the stop-band is 11.14GHz and the lower cut-off frequency is 0.28GHz. The simulated and measured results of the novel power plane with planar electromagnetic bandgap structures are in good ageement. The new EBG's stop-band is dramatically increased about 48.7%, with the lower cut-off frequency decreased to 0.46GHz compared with the L-bridged EBG structure with the same parameters. The signal integrity of the new EBG power plane can be improved by using differential transmission lines. This work is helpful for the EMC improvement of high speed digital circuits.

    Optimizing the parallel adaptive indexing algorithm on multi-core CPUs
    YUAN Tong;LIU Zhijing;LIU Hui
    Journal of Xidian University. 2016, 43(5):  57-62.  doi:10.3969/j.issn.1001-2400.2016.05.011
    Abstract ( 227 )   PDF (772KB) ( 157 )   Save
    References | Related Articles | Metrics

    An improved parallel adaptive indexing algorithm on multi-core CPUs is proposed to solve the problems that the parallel adaptive indexing algorithms cannot take full advantage of the CMP's parallel execution resource, and properly process the sequential query pattern. Based on the optimization of the Refined Partition Merge algorithm, our improved parallel adaptive indexing algorithm combines the Parallel Database Cracking method with the Refined Partition Merge algorithm. In our algorithm, when fewer data chunks are in the index, we use the optimized Refined Partition Merge algorithm so as to reduce the probability of conflict between threads, decrease the waiting time, and increase the utilization of the threads, and when more data chunks are in the index, we use the Parallel Database Cracking method so as to take full advantage of the CMP's parallel execution resources. Besides, we propose an optimization for the robustness, which makes our algorithm suitable for two common query patterns. Experiments show that our method can reduce the query time by 25.7%~33.2%, and suit with common query patterns.

    Motion stable control for cable-driven parallel camera robots with high speeds
    WEI Huiling;QIU Yuanying;SHENG Ying
    Journal of Xidian University. 2016, 43(5):  63-69+104.  doi:10.3969/j.issn.1001-2400.2016.05.012
    Abstract ( 306 )   PDF (1071KB) ( 192 )   Save
    References | Related Articles | Metrics

    A method for motion stability control is proposed on the problem that it is difficult for the camera robot to achieve the high speed and steady movement. First, the dynamic model is established. Then, the trajectory of the camera robot to the stable tracking of high maneuverability target is planned. And, high order polynomial interpolation is performed to improve the stability of the start and stop motion for the camera platform. Furthermore, a hybrid controller based on the PD feed forward controller and disturbance observer is designed in order to achieve stable motion. Finally, the rapid turning motion is discussed by numerical simulation, and the validity of the proposed method is verified.

    Real time feature extraction method for complex industrial big data
    KONG Xianguang;ZHANG Xiong;MA Hongbo;CHANG Jiantao;NIU Meng
    Journal of Xidian University. 2016, 43(5):  70-74+152.  doi:10.3969/j.issn.1001-2400.2016.05.013
    Abstract ( 361 )   PDF (503KB) ( 377 )   Save
    References | Related Articles | Metrics

    Industrial big data have the traits of big volume, multi-sources, continuous sampling and low value density, which results in high complexity, real-time and high abnormality. Traditional feature extraction methods cannot meet the real-time requirements of complex industrial big data. In addition, the processing method for industrial big data is different from the internet data stream processing method, which has a higher accuracy requirement. Therefore, this paper proposes a robust incremental on-line feature extraction method as the Robust Incremental Principal Component Analysis. It uses the sliding window to update new coming data dynamically and filter the abnormal data in windows, then the incremental principal component analysis is implemented on data in windows in order to meet the accuracy and real-time requirements of industrial big data processing. Experimental results show that the proposed method can effectively extract the data stream in real time with high accuracy.

    Stochastic homogenized thermal properties of composites with an uncertain microstructure
    YOU Fang;CHEN Jianjun;MA Juan;CAO Hongjun
    Journal of Xidian University. 2016, 43(5):  75-80.  doi:10.3969/j.issn.1001-2400.2016.05.014
    Abstract ( 239 )   PDF (469KB) ( 129 )   Save
    References | Related Articles | Metrics

    Random homogenization analysis of the effective thermal properties of a three-dimensional composite material with unidirectional fibers is presented by combining the equivalent inclusion method with the Random Factor Method (RFM). The randomness of the micro-structural morphology and constituent material properties as well as the correlation among these random parameters are completely accounted for, and stochastic effective thermal properties as thermal expansion coefficients as well as their correlation are then found. Results from the RFM and the Monte-Carlo Method (MCM) are compared. The impact of randomness and correlation of the micro-structural parameters on the random homogenized results is revealed by two methods simultaneously, with some important conclusions obtained.

    Power control in wireless sensor networks based on robust optimization
    QIAO Junfeng;LIU Sanyang;QI Xiaogang
    Journal of Xidian University. 2016, 43(5):  81-87.  doi:10.3969/j.issn.1001-2400.2016.05.015
    Abstract ( 287 )   PDF (615KB) ( 191 )   Save
    References | Related Articles | Metrics

    Topology control is a critical issue for energy efficient wireless sensor networks. Distance between sensors plays an important role in the problem of topology control in that it directly determines the accuracy of the node position. However, distance is generally affected by uncertain external factors, such as measurement error and actual interference. The actual performance of a topology control strategy can be severely influenced by distance uncertainty. Based on the robust discrete optimization theory and methodology, a power control algorithm is proposed to deal with distance uncertainty. First, related works on robust optimization is introduced. Then the problem of power control is formulated as a robust minimum spanning tree model under distance uncertainty, which is solved by Prim's algorithm. In computational experiments, the influence of the adjusting parameter on network performance is studied. Simulation results show that a robust solution can provide an improvement when the distance is uncertain at the expense of the less optimal value compared with a deterministic solution.

    Biogeography based optimization-proximal point algorithm for nonlinear minimax problems
    YANG Guoping;LIU Sanyang;ZHANG Jianke
    Journal of Xidian University. 2016, 43(5):  88-92+182.  doi:10.3969/j.issn.1001-2400.2016.05.016
    Abstract ( 234 )   PDF (448KB) ( 248 )   Save
    References | Related Articles | Metrics

    Concerning the discrete nonlinear minimax problems with the convex function as each of its components, a new method, called the biogeography based optimization-proximal point algorithm, is presented. By using maximum-entropy methods, the minimax problem is transformed into the unconstrained optimization problem of the smooth function. The algorithm employs the proximal point algorithm as the outer algorithm, and the biogeography based optimization as the internal algorithm. The proposed algorithm which resolves several minimax problems is global convergent. Preliminary numerical experiments show that the proposed algorithm is an effective algorithm for nonlinear minimax problems.

    Rapidly transient response with the flexible mode and high-efficiency buck-boost converter
    CHENG Liye;LAI Xinquan
    Journal of Xidian University. 2016, 43(5):  93-97+196.  doi:10.3969/j.issn.1001-2400.2016.05.017
    Abstract ( 226 )   PDF (1377KB) ( 243 )   Save
    References | Related Articles | Metrics

    A novel current sensing technique with a rapidly transient and flexible mode buck-boost converter is presented. The converter can work in an appropriate mode according to the input voltage (V<sub>IN</sub>) and inductor current (I<sub>L</sub>), with smooth transition and flexible working modes achieved. The average current sensing (AVCS) circuit has an accurate measurement of I<sub>L</sub>. The transient response time is also decreased. The current sensing converter is implemented in the Silterra 0.18μm COMS process. Experimental results show 95% peak efficiency at an output current 1A with 4.2V V<sub>IN</sub>, so that the converter can extend the battery life. The output transient with the load current altering from 0 to 2A is 6mV and the recovery time is 60μs.

    Object tracking via online low rank representation
    WANG Haijun;GE Hongjuan;ZHANG Shengyan
    Journal of Xidian University. 2016, 43(5):  98-104.  doi:10.3969/j.issn.1001-2400.2016.05.018
    Abstract ( 277 )   PDF (3261KB) ( 235 )   Save
    References | Related Articles | Metrics

    Object tracking is an active research topic in computer vision. The traditional tracking methods based on the generative model are sensitive to noise and occlusion, which leads to the failure of tracking results. In order to solve this problem, the tracking results of the first few frames are used as the observation matrix, and the low rank features of the observation model are solved by the the RPCA model. When the new video streams come, a new incremental RPCA is proposed to compute the new observation matrix by the augmented Lagrangian algorithm. The tracking model is established in the Bayesian framework, and the dictionary matrix is updated with the low rank feature. We have tested the proposed algorithm and six state-of-the-art approaches on eight publicly available sequences. Experimental results show that the proposed method has a lower pixel center position error and a higher overlap ratio.

    Novel RAIM algorithm GNSS receiver based on virtual triple-frequency techniques
    LU Hu;HAN Leijin;XIE Yan
    Journal of Xidian University. 2016, 43(5):  105-110.  doi:10.3969/j.issn.1001-2400.2016.05.019
    Abstract ( 230 )   PDF (757KB) ( 162 )   Save
    References | Related Articles | Metrics

    In the GNSS era, how to effectively enhance the navigation signal integrity monitoring capacity by using multi-frequency information is becoming a hot topic and the mainstream of RAIM technique. Based on the “virtual” multi-frequency ionospheric delay model of the single-frequency receiver, the paper proposes a novel virtual multi-frequency integrity monitoring technique for the single-frequency receiver, then presents the virtual multi-frequency criterion for fault detection and identification. Simulating results show that the “virtual multi-frequency” RAIM technique not only breaks through the limit to the number of visible satellites of traditional RAIM algorithms, but also greatly enhances the RAIM performance of the receiver without changing the hardware structure of the receiver, which would be of a tempting theoretical and practical value.

    Linear track estimation by double pulse sources for moving target
    WANG Qian;HOU Hong;LI Jianchen;CHEN Zhifei
    Journal of Xidian University. 2016, 43(5):  111-115.  doi:10.3969/j.issn.1001-2400.2016.05.020
    Abstract ( 269 )   PDF (602KB) ( 137 )   Save
    References | Related Articles | Metrics

    The double pulse sources method (DPS) is used to estimate the track of the high speed underwater vehicle. The linear track parameters and the speed at each time will be achieved based on the direction estimated by two CW pulse reference sources, the emitted and recorded time of each pulse front, and the dual-source distance which is known in advance. Simulation results show that the DPS method improves the performance of the traditional source estimation reference method. In the reservoir simulation experiments, the deviation of direction estimation is less than 1% and the deviation of distance estimation is controlled to within 9% by the DPS algorithm. The DPS is suitable for underwater vehicle track estimation.

    Tensor decomposition of generalized generating function-based blind identification of underdetermined mixtures
    ZHOU Zhiwen;HUANG Gaoming;GAO Jun
    Journal of Xidian University. 2016, 43(5):  116-120.  doi:10.3969/j.issn.1001-2400.2016.05.021
    Abstract ( 217 )   PDF (472KB) ( 189 )   Save
    References | Related Articles | Metrics

    Aimed at the problem of underdetermined blind identification, an algorithm based on generalized generating function decomposition is proposed, which no longer imposes sparsity restrictions on source signals. First, the second derivative matrices of the generalized generating function are stacked to the third-order tensor form, from which the number of source signals can be blindly estimated. Then the tensor is decomposed with singular value decomposition, and the mixture matrix is estimated by the joint diagonalization method. Simulation results validate the effectiveness of the proposed algorithm, and show that the proposed algorithm can acquire a better estimation precision than other classical algorithms with the same SNRs in the conditions of well-posed and underdetermined mixtures, meanwhile it extends the field of blind source separation application via the generalized generating function restricted only to the well-posed case.

    Secure link status routing protocol based on node trustworthiness
    LIANG Hongquan;WU Wei
    Journal of Xidian University. 2016, 43(5):  121-127.  doi:10.3969/j.issn.1001-2400.2016.05.022
    Abstract ( 282 )   PDF (928KB) ( 185 )   Save
    References | Related Articles | Metrics

    To develop secure routing technology for the current Internet, a trusted measurement model based on dynamic Bayesian networks(TMMDBN) is introduced by taking both node identity and its interaction into account. Combining the security authentication technology based on the combined public key(CPK), a new secure link state routing protocol(SLSRP) is proposed by applying the model to the OSPF protocol, which can determine a high security and trusted path for data transmission. Simulation results show that SLSRP achieves a much better security performance than OSPF with little increase in signaling overhead and computational complexity. Moreover, SLSRP has an adaptive capability and can quickly react to the denial of the service attack, which can effectively suppress the threat of an abnormal entity.

    SMVQ-index classified coding for lossless data hiding
    LIU Juanni;ZHOU Quan
    Journal of Xidian University. 2016, 43(5):  128-132+146.  doi:10.3969/j.issn.1001-2400.2016.05.023
    Abstract ( 267 )   PDF (2253KB) ( 162 )   Save
    References | Related Articles | Metrics

    In order to increase the embedding capacity of the VQ-based data hiding scheme, a lossless data hiding method based on the state-codebook sorted SMVQ-index classified coding is proposed. First, when doing SMVQ compression, the proposed SCS method is used to reduce the indices values and increase the embeddable indices percentage. Then according to the indices' distribution characteristic, the indices less than eight are classified into four cases. Finally, the secret data are embedded into the code stream of these indices. Experimental results indicate that, with the same image quality as that of VQ, the embedding capacity of the proposed scheme is superior to some that of previous schemes. Compared with the lossless data hiding scheme based on SMVQ-index residual value coding and the ASCM method, the embedding efficiency is increased by 4.5% and 48.8% respectively.

    Study of speech enhancement in the background of ship-radiated noise
    LI Dawei;YANG Rijie;HAN Jianhui
    Journal of Xidian University. 2016, 43(5):  133-138.  doi:10.3969/j.issn.1001-2400.2016.05.024
    Abstract ( 245 )   PDF (1156KB) ( 176 )   Save
    References | Related Articles | Metrics

    Spectral subtraction is wildly used in speech enhancement. But it is not always available in the ship working environment because of the fact that it is hard to discriminate the speech duration with the ship noise. So, in this paper, we propose a new approach, which first computes the frequency spectrum similarity and then discriminates the signal segments into speech or noise roughly. And then by the frame shifting method, we achieve a high discrimination precision. Finally, the improved algorithm is benchmarked on a large measured data and experimental results show that the proposed method can be used in various ship-radiated noise environments. The discrimination accuracy is 98% for ship-radiated noise and 96% for speech.

    Fair resource allocation algorithm for the smart TV system
    CHEN Junjie;ZHOU Hui;ZHANG Xiaomei
    Journal of Xidian University. 2016, 43(5):  139-146.  doi:10.3969/j.issn.1001-2400.2016.05.025
    Abstract ( 318 )   PDF (557KB) ( 251 )   Save
    References | Related Articles | Metrics

    In order to address the resource allocation problem of the smart TV system, a resource allocation algorithm based on the nonlinear elastic task model is proposed. First, we define fairness of QoS levels and describe the fair resource allocation problem of the smart TV system. Then, based on the nonlinear elastic task model, a fixed-point iteration method is used to solve the resource allocation problem and a sufficient condition for the convergence of the method is derived. Finally, nonlinear elastic task model is applied to the adaptive fair sharing controller. Simulation results show that the proposed algorithm can obtain fair resource allocation with a faster convergence speed than existing algorithms.

    Method of time delay measurement based on fast maximum likelihood for pulsar pulse profile
    JIANG Ruomei;SHE Yan
    Journal of Xidian University. 2016, 43(5):  147-152.  doi:10.3969/j.issn.1001-2400.2016.05.026
    Abstract ( 287 )   PDF (535KB) ( 142 )   Save
    References | Related Articles | Metrics

    The time delay of the pulsar integrated pulse profile relative to the standard pulse profile is one of the important observations in an X-ray pulsar-based navigation system, with the measuring accuracy directly affecting the the pulsar-based navigation system. In order to improve the measuring accuracy of the time delay of the pulsar integrated pulse profile and reduce the computation complexity, a method called fast maximum likelihood (FML) estimation is proposed in this paper, which first distills the pulse profile of the X-ray pulsar by the epoch folding. Then, the likelihood function is estimated to obtain the time delay of the pulsar integrated pulse profile. This paper also improves the fast maximum likelihood time delay estimation by narrowing the phase interval of the standard pulse profile and combines rough estimation with accurate estimation to effectively compute the time delay. Real pulsar data observed by the Rossi X-ray Timing Explorer (RXTE) are used to validate the effectiveness of the proposed method from the aspects of the observed time and computational complexity. Compared with the Taylor FFT algorithm, the measurement accuracy of the proposed method can be significantly improved while keeping the total computational complexity.

    Two-level searching tracking algorithm based on fast Fourier transform
    ZHANG Lang;HOU Zhiqiang;YU Wangsheng;XU Wanjun
    Journal of Xidian University. 2016, 43(5):  153-159.  doi:10.3969/j.issn.1001-2400.2016.05.027
    Abstract ( 259 )   PDF (4121KB) ( 202 )   Save
    References | Related Articles | Metrics

    In order to solve the problems of appearance change, scale and rotation change in the visual tracking, a two-level searching tracking algorithm based on Fast Fourier Transform(FFT)is proposed. It achieves two-level searching by establishing the object's kernel ridge regression model in the Cartesian coordinates and log-polar coordinates, respectively, and the efficiency can be improved by transforming the operation into the frequency domain based on FFT. First, the kernel ridge regression model is constructed in the Cartesian coordinate and the object's center position is obtained by the exhaustive search method based on the circular structure matrix. Then, it transforms the object area to the log-polar coordinates and searches the shift using the kernel ridge regression model in the log-polar coordinates. Finally, the object's state is calculated according to the searching results and the object's model is updated. Experimental results indicate that the proposed algorithm not only can obtain a distinct improvement in coping with the appearance change, scale and rotation change, but also have a high tracking efficiency.

    Algorithm for error-tolerant delimitation for the protocol data unit based on best path searching
    FAN Liang;WANG Xiaomei;YANG Dongyu
    Journal of Xidian University. 2016, 43(5):  160-166.  doi:10.3969/j.issn.1001-2400.2016.05.028
    Abstract ( 245 )   PDF (655KB) ( 123 )   Save
    References | Related Articles | Metrics

    Aiming at the error delimitation caused by the high bit error rate in a wireless network, an algorithm for error-tolerant delimitation for the Protocol Data Unit (PDU) based on best path searching is proposed. With the analysis of the protocol redundancy in delimitation, the PDU delimitating is treated as a path searching problem exploiting the rough delimitation result, then an algorithm based on best path searching is provided. Simulation and analysis of the ATM Adaption Layer 5 (AAL5) and Internet Protocol (IP) protocols in the Asynchronous Transfer Mode (ATM) network show that this method can decrease the rate of error delimitation, overcoming the conventional one's sensitivity to error and achieving a better error-tolerant performance.

    Research on nonlinear dynamics features of emotional speech
    YAO Hui;SUN Ying;ZHANG Xueying
    Journal of Xidian University. 2016, 43(5):  167-172.  doi:10.3969/j.issn.1001-2400.2016.05.029
    Abstract ( 257 )   PDF (691KB) ( 238 )   Save
    References | Related Articles | Metrics

    The application of nonlinear measures based on the chaotic characteristics of emotional speech is proposed. Nonlinear features such as minimum delay time, dimension correlation, Kolmogorov entropy, Lyapunov exponent and Hurst exponent are extracted from the emotional speech signal. The performance of nonlinear features is verified by the comparisons of recognition rates of different features (nonlinear characteristics, prosodic features and MFCC features). First, the Berlin emotional speech database and TYUT2.0 emotional speech database are chosen as the corpus independently, both covering three emotional classifications (anger, happiness and fear). The effectiveness of the nonlinear characteristics is tested on the Support Vector Machine Network. The result shows that the performance of nonlinear features outperforms that of prosodic features on the Berlin emotional speech database and that of prosodic features and MFCC on TYUT2.0 emotional speech database. In addition, nonlinear features have obvious advantage in detecting more natural emotional speech and better robustness.

    Interaction between the chaotic neural network and the CPG
    MA Zhenpeng;WU Zongfa
    Journal of Xidian University. 2016, 43(5):  173-177.  doi:10.3969/j.issn.1001-2400.2016.05.030
    Abstract ( 308 )   PDF (658KB) ( 147 )   Save
    References | Related Articles | Metrics

    The cerebral cortex is a chaotic nonlinear system. The Central Pattern Generator(CPG) can generate a rhythmic movement. According to biological knowledge, the CPG is controlled by the central nervous. But the study of the mechanism for biological motion control is still an open question. In this paper, we establish the model for depicting the interaction between the chaotic neural network and CPG. Bifurcation analysis and phase are used to describe changes in system behavior and show the interaction mechanism. In addition, the influences of CPG parameters on the model are discussed. Many modes described at state equilibrium points in the cerebral cortex correspond to gait patterns, and the change of state equilibrium points in the cerebral cortex leads to the change of gait patterns. At the same time, the results show that the brain cortex patterns can be changed by adjusting the value of the brain cortex' external input and CPG's feedback to the cerebral cortex.

    Effect of growth parameters on GaN in a vertical MOCVD reactor
    FENG Lansheng;GUO Runqiu;ZHANG Jincheng
    Journal of Xidian University. 2016, 43(5):  178-182.  doi:10.3969/j.issn.1001-2400.2016.05.031
    Abstract ( 368 )   PDF (1689KB) ( 201 )   Save
    References | Related Articles | Metrics

    A simulation of reactants in the transfer and reaction process during the GaN growth in a vertical MOCVD reactor is presented. The results show that the GaN growth rate and thickness uniformity are all affected by the chamber pressure and the velocity of reactants into the chamber. With the increasing velocity of reactants into the chamber, pre-reaction will be enhanced, GaN growth rate will be increased and thickness uniformity decreased. With the inlet velocity remaining the same and chamber pressure decreasing, the growth rate is improved within a certain scope, but the thickness uniformity may be increased at the same time with the thickness of the central region of the substrate increased.

    Simulation of X-ray pulsar signals with multiphysical properties
    SHEN Lirong;LI Xiaoping;LIU Yanming;FANG Haiyan;SUN Haifeng;PEI Chenxing
    Journal of Xidian University. 2016, 43(5):  183-189.  doi:10.3969/j.issn.1001-2400.2016.05.032
    Abstract ( 260 )   PDF (1177KB) ( 238 )   Save
    References | Related Articles | Metrics

    In view of the few and discontinuous X-ray pulsar data, based on the physical properties of the X-ray pulsar real data from the Rossi X-ray Timing Explorer (RXTE) spacecraft, this paper adopts the fast iterative method and the 10 μs time transformation model, simulates the X-ray pulsar signals which have the periodic property, spectral property, and the background noise property as well as a variety of delay effects. We design and implement simulation software which can simulate the X-ray pulsar signals with multi-physical properties. The results of comparing the real data and simulation data in the same situation show that the simulation noises and the actual noises have the same distribution, that the period stability of the simulated X-ray pulsar data agrees with the real data, with the error of only 0.43%, in different energy levels, that the simulated data's integrated profile and the real data's standard profile are highly correlated with the Pearson correlation coefficient of 0.99, and that under the 10μs time transformation model, the time conversion accuracy of the simulation data can reach 10<sup>-7</sup>s, the error between the simulation and the real data being just only 10<sup>-7</sup>s, which meets the time transformation accuracy. Therefore, the proposed method can realize the high-fidelity simulations and generate the continuous pulsar signal with many physical properties.

    Multi-band empirical model for backscattering coefficients prediction from typical land surfaces
    ZHANG Yuanyuan;WU Zhensen;ZHANG Yushi
    Journal of Xidian University. 2016, 43(5):  190-196.  doi:10.3969/j.issn.1001-2400.2016.05.033
    Abstract ( 271 )   PDF (1141KB) ( 188 )   Save
    References | Related Articles | Metrics

    Based on the electromagnetic scattering theory of the rough surface and discrete random medium, a multi-band empirical model for land backscattering prediction in 1~16GHz is proposed to tap the potential of remote sensing in application for agricultural production and targets detection efficiently. It should be noticed that this empirical model only have seven unknowns, and that it overcomes the problems in numerous inputs and inaccuracies echoes prediction. It is verified by the measured data of soil, sand and concrete in the L/S/X/Ku band for HH and VV polarizations. The results show that the backscattering coefficients from soil, sand and concrete predicted by the empirical model are in good agreement with the measured data. Meanwhile, this multi-band empirical model can be used to forecast the backscattering echoes at any frequency in 1~16GHz accurately. So this empirical model has a great application value for it can greatly improve the computational efficiency for the backscattering coefficients prediction, and also it can effectively reduce the workload in the field experiments.