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Table of Content

    30 July 2009, Volume 27 Issue 4
    Communication Engineering
    Low Complexity User Selection for Multi-user MIMO Downlink Systems
    ZHANG Cai-hua, XU Wei, CHEN Ming
    2009, 27(4):  331-336. 
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    This paper deals with the user selection problem for multi-user MIMO downlink systems with minimum mean square error (MMSE) pre-coding. A low complexity user selection algorithm is proposed, which sequentially selects users with minimum MMSE using the principle of greedy search. Simulation results show that the proposed algorithm can approach the sum rate of exhaustive search. It provides a gain in the sum rate over conventional user selection algorithms for systems with zero forcing (ZF) pre-coding.

    UWB Autocorrelation Receiver Based on Decision Feedback Average
    WANG Feng1, XU Cheng-qi1, ZHANG Xiao-you2
    2009, 27(4):  337-342. 
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    This paper utilizes the decided symbols and their corresponding received signals to devise a reference signal for demodulation, and presents a structure of UWB autocorrelation receiver based on the decision feedback average (DFA). Theoretical performance of DFA autocorrelation receiver is analyzed in a resolvable multipath channel. Its upper bound is given for low bit error rate (BER). Simulation results verify that the performance of DFA autocorrelation receiver is superior to autocorrelation receivers with conventional transmitted reference, differential transmitted reference, and average transmitted reference. The DFA autocorrelation receiver can be improved by increasing the number of feedback symbols.

    Signal Detection in Broadband Reconnaissance Receiver Based on Morphological Filter
    WANG Yong-ming1, ZHANG Er-yang1, ZHAO Jin-li2
    2009, 27(4):  343-347. 
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    As large instantaneous-bandwidth reconnaissance receiver may miss weak signals when intercepting signals corrupted by non-ideal noise, a novel method of signal detection based on morphological filter is proposed to process the received spectrum as one-dimensional gray-scale image. Noise floor is estimated with a morphological filter to correct the Welch spectrum. A detection threshold is obtained from the corrected spectrum using the constant false alarm rate processing, and signals are detected by comparing the corrected spectrum with the threshold. Simulation results show that the noise floor can be estimated and weak signals reliably detected in a given non-flat noise environment. The proposed method is suitable for hardware implementation due to the low computational complexity.

    Twice Virtual Array Transformation for Overcoming Direction-of-Arrival Estimation Ambiguity
    LI An1;2, WANG Shu1
    2009, 27(4):  348-352. 
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    A new approach is proposed for resolving the direction ambiguity by using twice virtual array transformation, which makes use of the nonuniform time delay to generate virtual transformation matrix. Due to the random variation in time interval of nonuniform time delay, the transformation based on nonuniform time delay matrix is equivalent to altering the relative distance between sensors. This means that the plane wave impinges a virtual uniform linear array with a time-varying array element interval. Therefore, a larger array aperture is available without anglular ambiguity, which enhances resolution and accuracy of the direction-of-arrival (DOA) estimation. Simulation results show that the proposed algorithm is effective for DOA estimation, and capable of improving estimation performance
    at low SNR.

    Reduction of Blocking Artifacts and Analysis of Edge Map Contribution
    ZHU Fang, SHI Long-xing
    2009, 27(4):  353-358. 
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    Blocking artifacts are a major problem in discrete cosine transform (DCT)-based image compression algorithms, which degrades the image’s visual quality. In this paper, a new method of blocking artifact reduction is proposed. Contribution of edge maps in the deblocking filtering is analyzed. A criterion used to classify block types is introduced according to the distribution of DCT coefficients both in half-block-shifted image blocks and in the original source image blocks. Using such classification, an adaptive combination method is used to reduce blocking effects. Since all computation is performed in the DCT domain, compressibility of the original image is not affected. By comparing with some existing methods, the experiment results verified effectiveness and robustness of the proposed method.

    Multi-sensor Data Fusion for Satellite Based on Federate Adaptive Unscented Kalman Filter
    LI Dan1, LIU Jian-ye2, XIONG Zhi2, YU Feng2
    2009, 27(4):  359-364. 
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    Generally speaking, in a satellite autonomous navigation system, it is not easy to build a state model of the practical system, which requires the information fusion algorithm having some self-adaptive capability. However, due to nonlinearity in the system measurement model, the information fusion algorithm must maintain high accuracy and robustness in a strongly nonlinear circumstance. To this end, an advanced federal adaptive unscented Kalman filter(UKF) method is proposed based on star sensor, infrared horizon sensor, agnetometer, radar altimeter and ultraviolet sensor. This method combines information from multiple navigation sensors in the federated filter, and uses an adaptive UKF algorithm to build the local filter. With this method, information coming from navigation sensors can be effectively organized and fully utilized, and the system model possesses adaptability. Numerical simulation using the proposed method is compared to that only using a conventional federated Kalman filter. The results show that the proposed method is more suitable for systems that are highly nonlinear or have inaccurat parameters, and can make navigation more accurate.

    Image Segmentation Based on Chan-Vese Model Using Composite Multiphase Level Set
    WENG Xiao-guang, ZHENG Gang
    2009, 27(4):  365-369. 
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    The Chan-Vese model is used to partition an image into two regions. However it has limitation for multi-region segmentation. To deal with the problem, two models can be used: parallel multiphase algorithm using multiple level sets simultaneously, and serial multiphase algorithm using level sets hierarchically. In this paper, a composite multiphase level sets algorithm for image segmentation based on the C-V model is proposed. The two kinds of multiphase algorithms are combined, allowing detection of more regions with a serial structure and having high efficiency for segmentation with a parallel structure. Experimental results show that the proposed algorithm can partition a given image into multiple regions and detect sub-objects with weak boundaries.

    Space-Time Adaptive Processing for Detection of Moving Radar Target in Heterogeneous Environments
    GONG Qing-yong, ZHU Zhao-da
    2009, 27(4):  370-374. 
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    A moving ground target detection method based on space-time adaptive processing (STAP) is studied in a heterogeneous environment. By extending the amplitude and phase estimation of a sinusoid (APES) method from the space domain to the space-time processing in the direct data domain, this approach improves the accuracy of target amplitude estimation and the output signal-to-clutter-and-noise ratio (SCNR), and overcomes shortcomings of traditional methods such as insensitivity to weak targets and high false alarm probability. Simulation results demonstrate validity of this improved method.

    Simulation of Point Based Rendering for Three Dimensional Lithography Development
    CUI Bin, WAN Wang-gen, WU Yong-liang, JIN Long-cun, YANG Xiao-dong
    2009, 27(4):  375-380. 
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    Simulation results are presented with vertices and polygons which did not adequately support display of complex scenes of point-cloud data when using traditional methods. Thus we use a hierarchical point-based representation algorithm for rendering, and introduce a mesh-interpolation algorithm to fill the gaps in the advance of the surface. Meanwhile, a model for lithography development based on the Dill algorithm, the Kim model and the ray algorithm is established. Experimental results show that the hierarchical point-based rendering algorithm is effective for the real-time realization of large-scale 3D visualization.

    Synthesis of Radiation Pattern Using Genetic Algorithm for Antenna Array near Electrically Large Platform
    ZHANG Kai, CHEN Chen, GUO Chen-jiang, XU Jia-dong
    2009, 27(4):  381-386. 
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    A hybrid technique that combines the moment methods (MoM) with the uniform geometrical theory of diffraction (UTD) is presented. The method can accurately and efficiently compute the radiation pattern of an antenna array located near an electrically large platform. An optimization process based on the genetic algorithm(GA) is used to produce a desired radiation pattern. Usefulness of the proposed technique is shown by an example of a ten-element half-wavelength dipole array placed close to a finite-length PEC circular cylinder. Amplitude and phase of the element excited voltage are optimized using the method. Compared to other methods, the optimization technique based on GA and MoM-UTD is effective and accurate, and has high performance.

    Optimization of Constrained Multi-layer Routing Algorithm
    CHENG Xin, XIE Guang-jun, YANG Yi-zhong
    2009, 27(4):  387-391. 
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    The constrained via minimization (CVM) is a problem of determining which layers can be used for routing wire segments in interconnections of nets such that the number of vias is minimized. Based on a segment-crossing graph, a constrained via minimization algorithm for multi-layer routing is proposed. The algorithm uses tournament selection, selects individuals according to their penalty until feasible solutions are found, and searches for the best solution among feasible solutions. In addition, steady state reproduction and elitist model further improve efficiency of the algorithm. Experimental results show that the proposed algorithm is efficient and provides satisfactory solutions.

    Conductivity and Excitation of Surface Wave Plasma Column
    WANG Shi-qing1;2, XIANG Qian1, LIU Jian1;2, WEI Chao-lei1, SUN Nai-feng1
    2009, 27(4):  392-396. 
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    When using surface wave plasma column in stealth plasma antennas, it is difficult to improve conductivity of the surface wave plasma column for low-frequency excitation. This paper studies the relationship between conductivity and the excitation power/frequency of the monopole surface wave excitation weakly ionized plasma
    column. This is done by analyzing the equilibrium relationship between the plasma density and power. A  scheme for stabilizing the excitation power and frequency is proposed, using the direct digital frequency synthesis and power gain automatic control techniques to improve the plasma column conductivity. Experiments are carried out to study relationship between the physical properties of the plasma column conductivity and the plasma column density and length. Compared with the original excitation system without using the proposed method, this scheme can improve plasma column conductivity and the overall performance of the system.

     

     

    Novel Strategy of Intrusion Detection for Peer-to-Peer Networks
    HU Hai-jiang, GU Rui-fei, HOU Wen-mei, ZHANG Feng-deng
    2009, 27(4):  397-402. 
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    Intrusion detection is a critical technique in information security for peer-to-peer networks. This paper proposes a new strategy of intrusion detection that can meet the requirements of peer-to-peer networks with various topologies by discriminating multi-parameters after calculating reputation using an improved CRC algorithm. Effectiveness of the strategy is verified in intrusion tests and performance evaluations as it has shown low computational complexity and strong capability of intruder discrimination.

    System Behavior Modeling for Scenario-Based Specifications
    CHEN Zhong-yu, MIAO Huai-kou
    2009, 27(4):  403-408. 
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    We propose to adopt semi-formal graphic language-message sequence charts to describe scenarios, regard events sequence of message transferring between use cases as an explicit scenario, and give its semantic. The main idea of this approach is to construct a prefix tree with positive scenario samples, which is a deterministic finite state automaton (DFA) accepting these positive scenario samples. A state combination algorithm that can get quotient automation is given.

    Online Incremental Learning Algorithm and Application to Functional Networks
    ZHOU Yong-quan1, LUO Qi-fang1, L?U Yong-mei1, ZHAO Bin2
    2009, 27(4):  409-413. 
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    A mathematical model of functional networks is proposed. The property of its topology structure and learning process is analyzed. Online incremental learning algorithms based on the block matrix and the property of functions matrix are designed. The learning algorithms make fully use of the training history, and have functions of learning, modification and emergency adaptation. Simulation on a Hénon time series shows effectiveness of the proposed algorithms.

     

    Simulation of Basketball Shooting in Virtual Reality
    XU Hong-wei, WAN Wang-gen, CUI Bin, LIN Ji-cheng, ZHANG Kai-yi
    2009, 27(4):  414-418. 
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    A set of construction of virtual basketball shooting system is designed. A virtual reality scene is established including a basketball court, athletes and a basketball. It provides models for the movement and elastic deformation of the basketball. The entire process of the basketball movement, from shooting to stopping, is simulated by describing the ball’s moving traces, and the elastic deformation in its collision with ground. Experimental results show that the proposed algorithm is efficient in simulating the virtual shooting process and is applicable to improve the athletes training efficiency.

    Adaptive Sliding-Mode Control for Uncertain Flight System with Actuator Dynamics
    LIU Chun-sheng, JIANG Bin
    2009, 27(4):  419-424. 
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    Dynamics of high-performance aircraft are highly nonlinear, time-varying and strongly coupled. Conventional control designs are based on the assumption that the system works at a specific operating point and described by linear perturbation equations. In addition, the longitudinal motion is assumed to be independent of lateral motion. Therefore the equations can be decoupled and treated independently. The objective of this work is to develop a new sliding mode control (SMC) designs for the nonlinear flight model with actuator dynamics. The key feature of the scheme is that prior knowledge of uncertainties of both the upper bound and matched condition is not required. The controller consists of a nominal controller and an adaptive sliding controller. The proposed SMC technique is applied to a nonlinear 6-DOF flight dynamics model. Simulations demonstrate robustness and accurate tracking in the presence of system uncertainties.

    Transfer Alignment of Inertial Navigation System Using Specific Force Integration
    ZHAO Bin, LIU Jian-ye, ZENG Qing-hua, QIAN Wei-xing
    2009, 27(4):  425-429. 
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    Transfer alignment of some airborne equipment is executed during takeoff of the aircraft. With traditional matching schemes, the transfer alignment accuracy is affected due to the limited speed of aircraft. To solve this problem, a specific force integration matching scheme is proposed to adapt to the aircraft’s low speed. Observation of Kalman filtering is the integration of specific force difference between master inertial navigation system (MINS) and slave inertial navigation system (SINS), and gyro error is not imported. Since SINS only performs calculation of the specific force integral, computation complexity is reduced. Taking into account error angle in installation and the flexural distortion angle, a system error model is established. Simulation results indicate that the proposed method can improve transfer alignment accuracy at low aircraft speed. It is potentially useful in medium- and low-precision strap-down inertial navigation systems.

    Mathematical Model of Double Parallel-Joint Coordinate Measuring Machine
    CHENG Wen-tao, YU Lian-dong, FEI Ye-tai, WANG Chen-chen, DING Yang
    2009, 27(4):  430-434. 
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    Double parallel-joint coordinate measuring machine (CMM) is a new type of coordinate measuring devices. An improved four-parameter DH model is used to deduce the double parallel-joint CMM measurement model. Error model of the double parallel-joint CMM is discussed based on the measurement model. Compared with the ideal model, correctness of the measurement model is verified by the error model. This forms a theoretical basis for designing and error distribution of double parallel-joint CMM.

    Construction of Augmented Proportion Navigation Law with Tracking Differentiator
    PENG Jian-liang, SUN Xiu-xia, DONG Wen-han, ZHOU Xin-li
    2009, 27(4):  435-440. 
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    A new approach of constructing augmented proportion navigation (APN) is investigated. Light of sight (LOS) angle velocity and acceleration are estimated using a tracking differentiator (TD) with filtering function. A coupler is constructed with a delay section and command softening sector to eliminate the bad effects of TD’s transient process on guidance performance. Some typical applications of TDs are given. A new terse fast TD without chattering is designed based on the merits and drawbacks of typical TDs. Simulation results show that APN with
    TD has good guidance performance, and is simple to implement.