Table of Content

20 April 2018 Volume 45 Issue 2

  

Symmetry decoupling technique in joint frequency-phase estimation

SUN Jinhua;WANG Hao;YU Zhongyang

Journal of Xidian University. 2018, 45(2):  1-6.  doi:10.3969/j.issn.1001-2400.2018.02.001

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In burst-mode communication systems, considering the great influence of the residual frequency offset on the phase estimation in joint frequency-phase estimation, the symmetry decoupling technique is proposed. First, the characteristic is analyzed that the symmetrical set of sampling instants can decouple the joint frequency-phase estimation. Then the concept of symmetry decoupling technique is proposed. Second, the symmetry decoupling technique is applied to the joint frequency-phase estimation under both the data-aided mode and non-data-aided mode. Also, the relative theoretical analysis is given. On this basis, the concepts of serial/parallel joint frequency-phase estimators are proposed. Theoretical analysis and simulation results show that the structure processed by the symmetry decoupling technique can achieve a lower mean square error and improve the ability to tolerate the residual frequency offset by three times at least. Besides, the proposed technique has universality which can be applied to other joint frequency-phase estimation algorithms.

Improved strobe correlation discrimination method for time-multiplex binary offset carrier modulated signal

LI Wengang;WANG Yiwei;HUANG Chen

Journal of Xidian University. 2018, 45(2):  7-12.  doi:10.3969/j.issn.1001-2400.2018.02.002

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In order to solve the problem of ambiguous tracking and multipath mitigation of new signal time-multiplexed binary offset carrier modulated signal in the global navigation satellite system, this paper proposes an improved strobe correlation method which calculates the correlation of the received TMBOC signal with the W2 strobe waveform in 0.5 code offset and the pseudo-random code code in 0.5 code offset, respectively, and then the two correlations are multiplied. In this way an unambiguous and good symmetrical code discrimination curve is obtained. The characteristics of the obtained code discrimination curve by the proposed method is analyzed and simulated, and the result shows: the proposed method is easy to realize, and the obtained code discrimination curve has good central symmetry, strong multipath mitigation capability and can be used for an unambiguous tracking, so it is more suitable for the TMBOC signal discrimination compared with the existing strobe correlation methods and improved methods.

Compressed sensing-based Bayesian channel estimation algorithm

LV Zhiguo;LI Ying

Journal of Xidian University. 2018, 45(2):  13-18+25.  doi:10.3969/j.issn.1001-2400.2018.02.003

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The high-order multiple-input multiple-output system can improve the energy efficiency and transmission reliability. However, it is difficult to perform channel estimation because of the large number of antennas. Although the SABMP (Support Agnostic Bayesian Matching Pursuit) algorithm can estimate the channel accurately, the complexity is too high. To address this issue, an EPMP (Expectation Prune Matching Pursuit) algorithm is proposed in the paper. At each sparsity level of the channel, an expanded support set is given by adding some positions corresponding to the atoms that have a larger inner product value with the current residual signal. Then the best support set is obtained by removing the wrong positions in the expanded support set. The estimated channel and the relative probability of the best support set at each sparse level are calculated. Finally, the expectation of the channel is calculated and regarded as the estimation of the channel. Compared with the SABMP algorithm, the EPMP algorithm can reduce the computational complexity while maintaining the estimation accuracy. The effectiveness of the EPMP algorithm is validated by simulation results.

SAR images change detection based on saliency map denoising in the NSCT domain

MU Caihong;WU Shengcai;LIU Yi;PENG Peng;LIU Ruochen

Journal of Xidian University. 2018, 45(2):  19-25.  doi:合成孔径雷达图像|变化检测|非下采样轮廓变换|显著图|k均值方法

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Aiming at solving the problem of low detection accuracy of traditional synthetic aperture radar (SAR) image change detection methods this paper proposes a change detection method which combines salient information to construct the fused difference image in the nonsubsampled contourlet transform (NSCT) domain. First, three difference images including the mean ratio image, log ratio image and neighborhood log ratio image are constructed with two input images and then the saliency image is extracted from the log ratio image Second, the mean ratio image and neighborhood log ratio image are decomposed by the NSCT method. The low-pass sub-bands of the neighborhood log ratio image are restricted by the saliency image to highlight the change region of the fused difference image. The directional sub-bands are selectively denoised by the saliency image in different scales and then fused according to the principle of minimum local energy. Finally, the NSCT inverse transform is used to obtain a fused difference image and the change detection map is generated by using the k-means clustering method. The experimental results show that this method can get a better edge and detailed information as well as a higher detection accuracy.

Auto-corrected convex relaxation algorithm for power allocation in multi-radar system used as target localization

FENG Hanzhe;YAN Junkun;LIU Hongwei

Journal of Xidian University. 2018, 45(2):  26-30+140.  doi:10.3969/j.issn.1001-2400.2018.02.005

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To improve the radar performance under limited transmit energy, this paper improves a power allocation algorithm for the distributed multi-radar system. First, the Cramer-Rao Lower Bound (CRLB) of the target localization mean square error(MSE) of the distributed multi-radar system is given in this paper, and can be used as a suitable cost function to perform the power resource allocation. Then, in order to be close to the optimal solution, this paper improves the classical convex relaxation methods. We make full use of the limited resources multi-radar system to approximate the optimal result by the auto-correct convex-relaxation parameter to reduce the extra error caused by the convex relaxation process. Finally, simulation results prove that the proposed algorithm is effective.

Terrain elevation adaptive method for spaceborne InSAR coregistration

ZHANG Jinqiang;SUO Zhiyong;LI Zhenfang;BAO Zheng

Journal of Xidian University. 2018, 45(2):  31-36.  doi:10.3969/j.issn.1001-2400.2018.02.006

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The shifts between master and slave images are influenced by the terrain elevation in the case of long baselines and/or rough topography for spaceborne interferometric synthetic aperture radar (InSAR). It is inaccurate to approximate the shifts using a two-dimensional (2-D) two-variable polynomial of a low degree. Furthermore, the performance of the method to estimate the polynomial coefficients using the shifts of control points is affected by the number and distribution of the control points greatly. To tackle the problems above, a terrain elevation adaptive reduced-dimension image coregistration method is proposed. The shifts are approximated by a 2-D three-variable polynomial of the first degree including the variable associated with the terrain elevation. The polynomial can pursuit the variations of the shifts with the terrain elevation and increase the precision of shift approximation. The first-order coefficients of the polynomial are calculated by the imaging parameters and orbital data of master and slave images, and two constants are estimated from the shifts of control points. The robustness of the coefficient estimation is improved. The precision and robustness of the proposed method are validated by data acquired by the TerraSAR-X.

Design of the electromagnetic coupling sensor based on double leaky coaxial cables

GUANG Qiao;LU Hongmin;TAN Kangbo;LAN Yanrui;SUN Dong

Journal of Xidian University. 2018, 45(2):  37-42.  doi:10.3969/j.issn.1001-2400.2018.02.007

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In order to solve the security issues of the important facilities, districts and national boundaries caused by a threat to terrorists and other insecurity factors, it is an urgent need that the intruder detection system is designed by new technologies and methods. Based on the double leaky coaxial cable, a novel electromagnetic coupling sensor is structured, its working principle is analyzed with the array antenna theory, the transmission characteristic of the port is simulated by the electromagnetic simulation software HFSS, and a new approach to designing the electromagnetic sensor is put forward. According to the national standard, the HLRHTCYZ-50-42L leaky coaxial cable with the operating frequency of 40MHz is selected as the simulation model, the electrical performance of the model is simulated and optimized, the changes of the transmission attenuation and coupling loss with the length and inclination of LCX's aperture are obtained. The electrical characteristics of the single LCX are measured, the coupling losses (95％) of the horizontal and vertical orientations are 62.6dB and 64.3dB, respectively. The measured results are in agreement with the simulation results.

Evolutionary spectral approach to finding communities in dynamic networks

FU Lidong;MA Xiaoke;NIE Jingjing

Journal of Xidian University. 2018, 45(2):  43-47+53.  doi:10.3969/j.issn.1001-2400.2018.02.008

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To effectively detect community structure in dynamic complex networks, modularity and modularity density functions are optimized under the evolutionary framework. By optimizing these two functions, we prove that optimizing these two functions can be reformulated as an evolutionary spectral optimization problem, and novel evolutionary spectral clustering algorithms are proposed. Compared to state-of-the-art approaches, the proposed algorithms are more accurate for both the simulated networks and real world dynamic networks.

Mechanical-thermal matching design for the rope-wire mesh composite structure

LI Tuanjie;YANG Li;LI Yang;MA Xiaofei

Journal of Xidian University. 2018, 45(2):  48-53.  doi:10.3969/j.issn.1001-2400.2018.02.009

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The reflector of the mesh deployable antenna is made of a flexible rope sewn with a wire mesh. Due to the mechanical-thermal differences between two materials, the deformation of the wire mesh is uncoordinated with fiber ropes, which affects the pre-stress distribution and surface accuracy and degrades the electric performance of the reflector. Therefore, it is of great significance to study the mechanical-thermal matching design for the rope-wire mesh composite structure. In this paper, the rope is modeled as a two-point bar which only bears tension, and the wire mesh is modeled as a membrane. Then the mechanical model of the rope-wire mesh composite structure is established to analyze the influence of thermal deformation, and optimizes the design of cross-section parameter of ropes. Finally, the circular truss mesh deployable antenna is used as a numerical example to demonstrate the feasibility of the mechanical-thermal matching design method. Simulation results indicate the thermostability of the reflector is improved under a variable temperature, and the surface accuracy of the reflector increases by 92％, using the proposed mechanical-thermal matching design method for rope-wire mesh composite structures.

Cable-membrane modeling and shape optimization of the space membrane antenna

CAO Peng;BAO Hong;DU Jingli;PENG Fujun

Journal of Xidian University. 2018, 45(2):  54-58+65.  doi:10.3969/j.issn.1001-2400.2018.02.010

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A method about boundary modeling and shape optimization of the cable-membrane structure in the space planar membrane antenna is proposed. First, based on the characteristics of sliding between the cable and the membrane when the structure is tensioned, a method of the nonlinear finite element modeling is proposed. Second, the boundary of the cable-membrane structure is modeled by B-spline curves, and the design variables are displacements of the control points of the curve for this optimization problem. The shape optimization of the membrane with an arbitrary initial boundary is realized by optimizing the deviation between the actual stress and the engineering reference stress. Finally, the effectiveness of the proposed methods are illustrated by numerical examples and experimental verification.

Analysis of mechanical properties of the warp knitted metal mesh of cable-mesh antennas

ZHU Risheng;ZHANG Yiqun;YANG Dongwu;YANG Guigeng

Journal of Xidian University. 2018, 45(2):  59-65.  doi:10.3969/j.issn.1001-2400.2018.02.011

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The warp knitted metal mesh is the key material for the preparation of metal cable-mesh antennas, and its mechanical properties directly affect the mechanical and electrical properties of the antenna. In order to study its mechanical properties, based on the geometric model of the loop, a three-dimensional geometric model of the metal mesh is established, and the finite element method is used to realize the static analysis of the metal mesh. First, data points of the loop geometry are defined according to the three-dimensional experience geometric model of the loop and geometric model of the loop, and minimum repetitive structures are obtained by the NURBS curve, so as to obtain the geometric model of the metal mesh. Second, based on the augmented Lagrange multiplier method, constraint equations for the bonded contact are substituted into the potential energy functional, and the incremental finite element equation that considers the contact problem is established, so as to realize the analysis of mechanical properties of the metal mesh. Finally, the data comparison of the bi-axial tension simulation and experiment show the validity of the analysis method.

Reconstruction of the hidden 3D shape for transient imaging simulation

LI Hairui;WU Xin;ZHANG Jianqi

Journal of Xidian University. 2018, 45(2):  66-70.  doi:10.3969/j.issn.1001-2400.2018.02.012

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With the development of ultrafast imaging devices, transient imaging can record the movement of light on the femtosecond scale. One of its applications is the reconstruction of hidden 3D shapes, which is to reconstruct the three-dimensional structure of objects hidden outside the camera field. Due to the complex structure, the high price and difficult performance-evaluation of the transient imaging hardware system, this paper presents a new reverse reconstruction algorithm and establishes a transient imaging process using software simulation. Beginning with a simplified heatmap function according to the scene, this reverse algorithm introduces the detecting probability to obtain the sampled data of the object in the scene; after that, it computes the global detecting probability of the object using ray-tracing methods and gets a 3D point cloud by thresholding results; finally, the point cloud is visualized in the 3D space. The result shows that the simulation method presented in this paper is able to describe the transient imaging process of a hidden object in a 3D scene, and that the reverse reconstruction algorithm can improve the reconstruction of hidden objects.

Probe selection algorithm for faulty links localization in all-optical networks

QI Xiaogang;WANG Xiaolin;LIU Lifang

Journal of Xidian University. 2018, 45(2):  71-76+115.  doi:10.3969/j.issn.1001-2400.2018.02.013

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This paper studies the probe selection problem in all-optical networks for achieving unambiguous faulty links localization. The existing random walk algorithm can find feasible solutions for localizing the faulty link unambiguously, but it consumes a large number of probes and wavelengths in large-size networks. First, monitoring paths are set up for failure detection. Second, the probing signals are sent out through all monitoring paths, and then the failure localization is performed on every faulty path. The proposed scheme proves that the problem of the minimal monitoring path set is NP-complete and can be solved by the heuristic monitoring path selection algorithm. It is also proved that a network must be k+1 edge connectivity for localizing k faulty links with one monitoring node. Compared with random walk, the probe selection algorithm greatly shortens the number of probes and consumed wavelengths per link.

Multi-metric cross layer routing protocol for cognitive radio ad hoc networks

CAO Jing;WU Junsheng;YANG Wenchao;WANG Shuochen

Journal of Xidian University. 2018, 45(2):  77-83.  doi:10.3969/j.issn.1001-2400.2018.02.014

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With the aggravation of spectrum scarcity and the rapid increase of wireless service, the cognitive radio ad hoc network has become a hot research topic recently, and efficient routing protocol design is important in application. Owing to the dynamic feature of spectrum opportunity, the route protocol in the cognitive ad hoc network is complex and should be combined with power control and spectrum allocation. This paper proposes a multi-metric cognitive routing protocol MM-CAODV from the cross-layer prospect. They define routing metrics according to Quality of Service requirements, and provide multi-metrics solutions to secondary users considering spectrum opportunity. This paper points out the multi-path problem through the network topology model, analyzes different routing metrics of delay, transmit rate and stability, and then proposes the multi-metric optimization model. Simulation results show that the routing protocol in this paper has better network performance in three parameters: end-to-end delay, throughput, and packet delivery ratio.

Resource allocation based on opportunistic capacity for cognitive radio networks with heterogeneous services

HUANG Jie;ZENG Xiaoping;JIAN Xin;DU Derong;ZHU Bin;TIAN Mi

Journal of Xidian University. 2018, 45(2):  84-89+96.  doi:10.3969/j.issn.1001-2400.2018.02.015

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The spectrum resource is time-varied in cognitive radio networks (CRNs) with dynamic spectrum environment, which makes the traditional static chunk-based allocation be of poor performance. To solve this issue, this paper derives an opportunistic capacity model for chunks with time-varied spectrum resources and presents an opportunistic capacity based chunk allocation model for heterogeneous services for CRNs under the time-varied spectrum environment. Simulation results illustrate that the proposed scheme can guarantee the Quality of Service (QoS) requirements of heterogeneous services in the situation with time-varied spectrum resources.

Two-level frame aggregation retransmission scheme design in 802.11n/ac/ad

QIAN Xu;WU Bin;YE Tianchun

Journal of Xidian University. 2018, 45(2):  90-96.  doi:10.3969/j.issn.1001-2400.2018.02.016

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The IEEE802.11n/ac/ad support multiple aggregation schemes, which can improve the efficiency of the MAC layer by aggregating MAC protocol data units and thus reducing the overhead of the MAC and PHY layer. However, in error-prone environments, the aggregation level of retransmitted aggregation frames severely fluctuates, incurring the instability of system throughput. In this paper, we propose a novel two-level retransmission aggregation scheme in erroneous environments. This scheme first introduces the aggregation sliding window in the MAC layer to increase the aggregation level; second, through theoretical analysis, the second level aggregation level and the first level A-MSDU frame length are optimized and adjusted dynamically according to the subframe size, the maximum aggregation level (MAL) allowed by the current two-level frame aggregation and the real-time channel bit-error-rate (BER). Simulation by using NS-3 shows that this scheme outperforms other schemes for different subframe sizes and aggregation levels.

Imaging system of fluorescence molecular tomography with spiral excitation

HOU Yuqing;WEI Hongna;YI Huangjian;ZHANG Xu;HE Xiaowei

Journal of Xidian University. 2018, 45(2):  97-102.  doi:10.3969/j.issn.1001-2400.2018.02.017

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An imaging system of fluorescence molecular tomography based on spiral excitation is proposed. In the case of unknown specific locations of the fluorescent target, it can ensure that the fluorescent target is fully excited, which guarantees the accuracy of measured data. Heterogeneous phantom experiments have tested the feasibility and effectiveness of this system.

Minimum rate optimization with joint power allocation for full-duplex MIMO relay

SUN Yanjing;LIU Wen;CAO Qi;WANG Xiaolin;ZHOU Shu;LI Song

Journal of Xidian University. 2018, 45(2):  103-109.  doi:10.3969/j.issn.1001-2400.2018.02.018

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This paper aims at maximizing the end-to-end rate of the full-duplex Multiple-Input Multiple-Output (MIMO) relay system suffering from channel estimation errors and the limited dynamic range (LDR) of electronic components in the RF chain. The problem of rate maximization is formulated as a weighted sum-rate optimization problem and we propose a joint power allocation (JPA) algorithm to solve it. Allowing the system to allocate power based on the channel state information (CSI), JPA is able to jointly optimize the pre-coding matrices of the source node and the relay node. Simulation results reveal that the JPA algorithm outperforms the traditional algorithms associated with individual power constraints.

Memory efficient architecture for 2-D DWT

GAO Jiaming;LIANG Yu;ZHANG Wei;LIU Yanyan

Journal of Xidian University. 2018, 45(2):  110-115.  doi:10.3969/j.issn.1001-2400.2018.02.019

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Two-dimensional (2-D) Discrete Wavelet Transform (DWT) is a commonly used method in digital signal processing, image analysis and image compression. Due to its large amounts of computation, it is often implemented in a hardware circuit. In general, the hardware architectures have a large input RAM and large hardware resources, which restrict the improvement of system hardware efficiency. Therefore, a memory efficient 2-D DWT architecture based on the lifting scheme is proposed in this paper. The order of input data is adjusted, horizontal parallel scanning and data dislocation 3-input method are introduced in this work for reducing hardware resources and eliminating the off-chip RAM. For an image size of N×N, the total ram requirement of the proposed architecture is reduced to 9N bytes. The estimated hardware requirement shows that at least 8％ less transistor count-delay-product (TDP) can be saved compared with the existing architectures.

Novel and miniaturized hendeca-band antenna for mobile phones

YANG Ming;SUN Yufa

Journal of Xidian University. 2018, 45(2):  116-121.  doi:10.3969/j.issn.1001-2400.2018.02.020

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The traditional mobile phone antenna has many disadvantages, such as complicated structure, high profile, large size. In order to reduce the size of a mobile phone antenna, a novel miniaturized mobile phone antenna with a hendeca-band is presented in this paper by studying the method of frequency band broadening of the miniaturized low profile dual layer microstrip antenna. The size of the presented antenna is only 37.0mm×7.2mm. First, by using the monopole and the ground strip coupling technologies to excite the resonant mode, the high-frequency bandwidth of the antenna is broadened. Then, the low-frequency bandwidth of the antenna is also broadened by using the loading inductance method to shift low-frequency resonance. The measured results have demonstrated that eight LTE/WWAN bands can be covered and that the S₁₁ of the proposed antenna is lower than -10dB in the range of GPS, WiFi and Bluetooth bands. Compared with traditional microstrip antennas, the proposed antenna has good radiation gain and efficiency as well as the small size, simple structure and wide frequency band.

Multi-authority attribute-based encryption scheme with policy semi-hidden and dynamic updating

YAN Xixi;LIU Yuan;LI Zichen;TANG Yongli

Journal of Xidian University. 2018, 45(2):  122-128+147.  doi:10.3969/j.issn.1001-2400.2018.02.021

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Attribute-Based Encryption (ABE) is a new cryptographic technique which guarantees fine-grained access control of outsourced encrypted data in the cloud. However, privacy revealing and policy updating are the key limitations. Thus, a Multi-Authority attribute-based encryption scheme with policy partially hidden and dynamic updating is proposed. In the scheme, the users' attribute is divided into two parts: the attribute name and the attribute value. The values of the user's attributes are hidden to prevent from revealing to any third parties. In addition, the Linear Secret-Sharing Scheme(LSSS) access structure and policy updating algorithms can support any type of policy updating, and it proves secure against the chosen plaintext attack in the standard model. Compared to the existing related schemes, the size of both users' secret key and ciphertext is reduced, and the lower computing cost makes it more effective in protecting users' attributes and support policy updates.

Expedited antenna multi-objective optimization method based on gradient-enhanced kriging surrogate model

WANG Danqing;LI Ping

Journal of Xidian University. 2018, 45(2):  129-134+165.  doi:10.3969/j.issn.1001-2400.2018.02.022

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Based on classical optimization algorithms and electromagnetic simulations, traditional antenna optimization method is inefficient, especially when it is used to solve the complex antenna multi-objective optimization problem. With the introduction of the genetic operator, the paper proposes an efficient global optimization algorithm named the Multi-Gradient Descent Algorithm Hybrid with the Genetic Operator to alleviate the problem above. For the merits of quick establishment and reduced samples scale, the Gradient-Enhanced Kriging(GEK) model is invoked by the proposed algorithm as the surrogate of antenna electromagnetic analysis. A Novel broadband UHF monopole antenna enabled by anisotropic Ⅰ-shaped periodic structure cladding and a dual-band UHF antenna together with its anti-jamming array antenna reserved for the private airborne communication system are designed with the proposed optimization method. The necessary electromagnetic simulation time of the proposed method is 10.30％ and that of the traditional optimization method is 18.96％, which verifies the merit of high efficiency.

Analysis of the K users BC network with nullspace intersection and multicast

WANG Yue;LIU Feng;ZENG Liansun

Journal of Xidian University. 2018, 45(2):  135-140.  doi:10.3969/j.issn.1001-2400.2018.02.023

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This paper proposes a new method for the multi-user BC multicast network model and forcing-zero with nullspace intersection interference message. The model uses the "circular mode" to distribute the desired message to the receiving end to form a multicast network. The zero-forcing method first obtains the interference message from the receiver corresponding to the zero space, then takes a number of zero-space intersection spaces, and finally if a number of interference messages are simultaneously placed in the corresponding cross-space, you can achieve multi-zero-forcing interference messages at the same time at each receiving terminal. For the multi-user system, the paper obtains the optimal antenna configuration scheme and the generalized result for system degrees of freedom. Based on the system using Matlab simulation analysis, the theoretical value of the degree of freedom and the simulation results are in agreement.

Gravity optimized particle filter algorithm

LIU Runbang;ZHU Zhiyu

Journal of Xidian University. 2018, 45(2):  141-147.  doi:10.3969/j.issn.1001-2400.2018.02.024

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As the traditional particle filter has problems of particle degeneracy and particle diversity loss and filter accuracy depends heavily on the particle number, a gravity optimized particle filter algorithm is proposed.The particle swarm is optimized by the gravity algorithm in the particle filter to improve the filtering accuracy. Each particle is regarded as a mass point and the mass is proportional to the particle weight.The gravity attracts particles moving toward the high likelihood region which optimizes the particle swarm.Then elite particle strategy is introduced to accelerate the particle convergence rate and avoid the local optimum in the gravity algorithm. The perceptual model is used to prevent particles from crowding or overlapping due to excessive convergence. Simulation results show that the proposed algorithm has a better filtering accuracy and speed in the case of few particles compared with the classical particle filter algorithm and particle swarm optimization particle filter algorithm.

Novel two-step method of bandwidth synthesis for SF-MIMO-SAR

JING Guobin;SUN Guangcai;XING Mengdao;GUO Rui;BAO Zheng

Journal of Xidian University. 2018, 45(2):  148-153+159.  doi:10.3969/j.issn.1001-2400.2018.02.025

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For stepped frequency multiple-input and multiple-output synthetic aperture radar (SF-MIMO-SAR), the result of bandwidth synthesis in range is affected by channel phase mismatch. In order to solve this problem, this paper proposes a two-step error estimation method based on echo data. First, aiming to optimize the focus sub-band image, phase adjustment by contrast enhancement algorithm is modified to estimate high-order phase errors in range. Then, the sub-band signal is up-sampled, shifted, and the model of balanced side-lobe is proposed to calculate and compensate the constant phase error. After the above compensation, we will obtain the synthesized SAR image with the resolution of 0.06 meter in range, and experimental data demonstrate the effectiveness of the proposed method.

Sparse feature extraction technique and its applications to machinery fault diagnosis

HE Wangpeng;SUN Wei;SU Bo;YANG Yunyi;GUO Baolong

Journal of Xidian University. 2018, 45(2):  154-159.  doi:10.3969/j.issn.1001-2400.2018.02.026

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To address the problem of extracting periodic-group-sparse features for the purpose of detecting machinery faults, the periodic overlapping group sparsity (POGS) method is thoroughly investigated. The POGS method formulates a convex optimization problem to extract periodic sparse features based on the prior knowledge of machinery fault diagnosis. The non-convex penalty functions are employed to further enhance the sparsity of useful fault features. Moreover, the convexity condition of the POGS optimization problem is provided. A fast iterative algorithm is given for its optimal solution based on the majorization-minimization approach. A simulated signal is formulated to verify the performance of the POGS method for periodic feature extraction. Finally, the POGS method is applied to process experimental data for detecting bearing faults. The estimated results demonstrate that the POGS method can effectively extract the periodic-group-sparse fault features.

Diagnosis method for defective array elements based on compressive sensing

LI Wei;DENG Weibo;YANG Qiang;YSUO Ying;MIGLIORE Marco Donald

Journal of Xidian University. 2018, 45(2):  160-165.  doi:10.3969/j.issn.1001-2400.2018.02.027

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As the number of elements of the array increases, huge sampling data, long measurement time and high computation costs are several features of existing array fault diagnosis methods. Therefore, a diagnosis approach based on Compressive Sensing is investigated in this paper. The proposed method utilizes the sparsity of the number of failed elements and the sparse signal derives from difference incentives of reference array and the array under test. The criterion for grid division of the measurement matrix is designed according to the target direction in the spatial domain and a small number of measurement data are then obtained in the far field radiation pattern via a random under-sampling strategy. The Parallel Coordinate Decent Algorithm is used to implement fault diagnosis by reconstructing this sparse signal. Theoretical analysis as well as simulation results indicate that the proposed method not only reduces the amount of spatial sampling data, truncates the diagnosis time and abates the computational complexity significantly , but also improves the accuracy of recovered information on defective elements.

New method for designing the two-channel orthogonal graph filter bank

JIANG Junzheng;CAO Xiang;OUYANG Shan

Journal of Xidian University. 2018, 45(2):  166-170.  doi:10.3969/j.issn.1001-2400.2018.02.028

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An iterative algorithm based on second-order approximation of Taylor's series is proposed to overcome the problem that the two channel orthogonal graph filter bank possesses poor frequency characteristic.First, the design problem is formulated into a constrained optimization problem, whose objective function is the reconstruction error of the two channel orthogonal graph filter bank, and the constraint function is the stopband attenuation.Then, by means of the Taylor approximation, the highly nonlinear nonconvex objective function is approximately transformed into a convex quadratic function with respect to increments. Thus, the nonconvex optimization problem is approximated to a convex optimization problem.Finally, an iterative technique is used to solve the optimization problem.Simulation results show that the reconstruction error of the two channel orthogonal graph filter bank obtained by the new method is approximately one order of magnitude lower than that by the Bernstein polynomial approximation algorithm and that the improvement on the reconstruction error is about 8dB.

Efficient closed-form estimator for TDOA-FDOA-AOA localization

DENG Bing;SUN Zhengbo;YANG Le

Journal of Xidian University. 2018, 45(2):  171-175+180.  doi:10.3969/j.issn.1001-2400.2018.02.029

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This paper proposes a simple and efficient closed-form solution for a moving source localization using the time difference of arrival(TDOA), frequency difference of arrival(FDOA) and angle of arrival(AOA) measurements obtained at spatially distributed moving receivers. The developed method first converts nonlinear TDOA, FDOA and AOA equations into linear ones by the localization geometry relation, and then obtains the final source status estimate using the weighted least squares(WLS) technique. Theoretical analysis and simulations verify the approximate efficiency of the developed positioning technique and its improved performance over the benchmark iterative method.

Interference alignment for MIMO downlink heterogeneous networks

LI Chuan

Journal of Xidian University. 2018, 45(2):  176-180.  doi:10.3969/j.issn.1001-2400.2018.02.030

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We propose a null space based interference alignment (IA) scheme for the downlink of a heterogeneous network. By jointly designing the transmit beamforming matrix at pico base stations and the receive beamforming matrix at macro users, the proposed null space based IA scheme can effectively cancel the interference from pico base stations to macro users. Furthermore, the proposed scheme supports an arbitrary number of macro users and provides one closed form solution. Moreover, the proposed null space based IA scheme is valid for the region where the traditional IA schemes are infeasible. Finally, simulation results are provided to demonstrate the achievable degrees of freedom (DoF) by the proposed null space based IA scheme.