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Table of Content

    01 April 2009, Volume 27 Issue 2
    Communication Engineering
    Detection of Chaotic Direct Sequence Spread Spectrum Signal Based on the Largest Lyapunov Exponent
    XU Wei, GUO Jing-bo
    2009, 27(2):  111-116. 
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    Chaotic DS signal is a kind of spread spectrum signal that has the merits of both chaotic and directsequence spread spectrum (DSSS) signals. In order to realize blind detection of chaotic DSSS signal, both conventional
    DSSS signal methods and chaotic signal detection methods are investigated. A novel method is introduced in
    which the C-C method is used to determine key parameters. The largest Lyapunov exponent of time series is then calculated using small data sets. Simulation results verify feasibility of this method under different conditions such as Gaussian noise and multi-path channel.

    Design of LDPC Coder-Decoder Based on Cyclic Shift Matrices
    GUAN Wu, DONG Ming-ke, XIANG Hai-ge
    2009, 27(2):  117-123. 
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    In this paper, the LDPC codes used in DVB-S2 and WiMAX are analyzed. A universal structure based on cyclic shift matrices is presented for these codes. A partially parallel decoder is designed with a universal storage
    resource reusing architecture and serial operation processors. This decoder has been implemented on an Altera EP2S60 platform, and can work for 8 064 bit code length at rates 7/8, 6/8, 5/8, 4/8 and 3/8. Test results show that its code throughput can approach 80 Mbit/s.

    Peer-to-Peer Traffic Identification Using Bayesian Networks
    LI Jun1;2, ZHANG Shun-yi1, WANG Hao-yun1, LI Cui-lian2
    2009, 27(2):  124-130. 
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    Accurate traffic classification is vital to numerous network activities, such as security monitoring, quality of service provisioning and network planning. However, current P2P applications, which generate a substantial volume of Internet traffic, use dynamic port numbers, HTTP masquerading and payload encryption to avoid detection. In this paper, we present an accurate P2P identification method using Bayesian networks. Based on the abstracted attributes of flow statistics, the optimal attribute subset is selected using genetic algorithms and P2P traffic is identified using Bayesian networks. We evaluate the algorithms and compare them to the previously used Naive Bayesian model and BP perceptron. Experimental results show that the proposed algorithms achieve better overall accuracy up to 95% with less cost. Further, our result indicates that the approaches are capable of identifying unknown P2P traffic and applicable to the real-time applications.

    Orthogonal Constrained PARAFAC Blind Receiver for DS-CDMA Systems
    LIU Xu, HU Zong-Ze
    2009, 27(2):  131-136. 
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    A blind detection algorithm for multi-user DS-CDMA systems is presented based on the parallel factor (PARAFAC) model. A novel orthogonal constrained PARAFAC-based blind receiver is proposed, which utilizes
    orthogonality or semi-orthogonality of spreading code in DS-CDMA system. The Cramer-Rao bound (CRB) of the
    orthogonal constrained trilinear decomposition is analyzed. Simulation results show that the orthogonal constrained trilinear alternating least square (OCTALS) algorithm has a lower CRB than traditional trilinear alternating least square (TALS) algorithm in processing DS-CDMA received signals. Compared with the traditional PARAFAC receiver, the OC-PARAFAC receiver has a better BER performance and faster convergence.

    Identification of Digital Modulation Signals Based on Cyclic Spectral Density and Statistical Parameters
    ZHU Lei1, CHENG Han-wen1;2, WU Le-nan1
    2009, 27(2):  137-143. 
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     A novel method using decision-making theory is proposed to identify digital modulation signals. The method is based on the cyclic spectrum of received signals and the statistical parameters. Using the frequency domain smoothing periodogram to estimate the cyclic spectrum, the characteristic spectral density of digital modulation
    signals is analyzed on the cyclic frequency axis. Statistical parameters of digital modulation signals are then
    extracted. Finally, using the decision-making theory, we present a flow chart and a determination threshold for
    signal recognition by computer simulation. At 5 dB SNR, identification probability of 90% for 2ASK, 4ASK, 2FSK,
    4FSK, 4PSK and 8PSK can be achieved. The results show effectiveness of the method even when signals are buried in strong noise.

    Roaming Subnet Supported Mobile IP Protocol (MIP-RS)
    QIAN Hong-yan, CHEN Bing, QIN Xiao-lin
    2009, 27(2):  144-149. 
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    To support a subnet moving in the IPv4 environment, a roaming subnet supported mobile IP protocol (MIP-RS) is proposed by avoiding shortcomings of the mobile IP. In MIP-RS, STA/AP works as a gateway instead of as a MAC device. It is implemented by cooperation between the home agent, the foreign agent, and the intra-domain routing agent. Distance of the node in a mobile subnet from the HA-FA tunnel’s exit can be multi-hops, while it is only one-hop in the mobile IP. A demo system including the special STA/AP was developed to verify MIP-RS. Test results show that MIP-RS can provide high speed data transmission during the subnet moving at the vehicle speed.

    Signal and Information Processing
    Time-Frequency-Space Domain Processing for Radar Detection of Aircraft Wake Vortices
    LI Jun, WANG Xue-song, LIU Yi, WANG Tao
    2009, 27(2):  150-155. 
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    In this paper, a signal model representing the time-frequency-space domain characteristics of aircraft wake vortices is established for coherent Doppler radar. The optimal likelihood ratio detector for detection of aircraft
    wake vortices and its quasi-optimal form for large number of pulses and low signal-to-noise ratio (SNR) are derived. The quasi-optimal form is shown to possess the structure of time-frequency-space domain processing and constant false alarm rate (CFAR) property independent of the signal power. Analytical expressions and their approximations for probabilities of detection and false alarm are derived for the quasi-optimal detector. The results indicate that the radar performance of detecting aircraft wake vortices can be effectively improved by using time-frequency-space domain processing.

    Crater Detection from Gray Image of the Moon Surface
    DING Meng1, CAO Yun-feng1;2, WU Qing-xian1
    2009, 27(2):  156-160. 
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    A method for autonomous detection of crater from gray images is proposed. The original image blocks are census-transformed. The obtained histograms are used as feature vectors. Principal component analysis is performed to compress the feature space. Pattern classification is done with support vector machine. Craters of different sizes are detected by reducing and magnifying the crater candidate area. The results show that the proposed method can effectively detect craters of size greater than 20*20.

    Initialization Algorithm for Blind Image Separation Based on Curvelet Sparse Representation
    WANG Jun-hua1, FANG Yong1;2
    2009, 27(2):  161-166. 
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    A new initialization algorithm for blind separation of images is proposed based on curvelet sparse representation. A mixed matrix can be estimated by estimating the center of received signals. This method can
    improve convergence and effectively avoid falling into local minima. Simulation results show that the proposed
    algorithm can achieve better performance for blind source separation of images.

    Accelerating GPU-Based Volume Rendering in Conjunction with Surface Rendering
    GE Jun, SHU Hua-zhong, BAO Xu-dong, LUO Li-min
    2009, 27(2):  167-171. 
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    An improved GPU-based volume rendering method is presented for interactive visualization of image datasets. The closed 3D surface that warps the user-interested datapart is created using a 2D contour-based surface
    rendering algorithm. The 3D surface is then used as proxy geometry for GPU-based ray-casting to achieve fast
    volume rendering. With the rendering of proxy geometry, the number and sampling length of rays are reduced, and the ray-casting time saved. We implement the method on medical and industrial datasets, showing improvement of efficiency without any loss of interested dataparts.

    Novel Sensor System for Measuring Tri-axial Pressure on Foot-Ground Interface
    ZHU Xiang-ming1, YAN Zhuang-zhi1;2, LIU Shu-peng1;2, SI Wen1
    2009, 27(2):  172-176. 
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     This paper presents a new sensor system for measuring the pedaling strength of human foot and the sustenance between the athlete’s tread and the ground. The system consists of a tri-axial pressure sensor, circuits for data acquisition and signal filtering, and data storage and display modules. The sensor is designed and fabricated with a novel mechanical structure using a new piezoelectric material. Based on the nonlinear model of the dual systems of impact machine, a test-bed to simulate the impact on the foot-ground interface is developed to validate the system. The experimental results well agree with the theoretical curve obtained with the nonlinear model dual systems of impact.

    Vertical Tilt Correction for Vehicle License Plate Based on Minimizing Variance of Coordinates of Projection Points
    WU Yi-quan, DING Jian
    2009, 27(2):  177-181. 
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    In order to facilitate character segmentation and recognition in a license plate recognition system, the tilting license plates in the located images should be corrected in both the horizontal and vertical directions. A vertical
    tilt correction method by minimizing variance of coordinates of the projection points is proposed. Coarse character segmentation is performed after horizontal correction and upper and lower border delineation. The character points are projected along the vertical direction after shear transform. Two closed-form expressions of the shear angle are derived based on minimizing variance of coordinates of the projection points. Thus the vertical tilt angle is directly determined and the license plate images corrected using the vertical tilt angle. Experimental results show that, compared to the vertical tilt correction methods of the license plate based on rotation projection and line fitting, the proposed method has high accuracy, requires less computation, and is robust. The proposed method has been applied in practical engineering system.

    Wavelet De-noising with Double-Threshold Based on Particle Swarm Optimization
    ZHOU Xian-guo, LI Kai-yu
    2009, 27(2):  182-186. 
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    To improve the de-noising performance of filters, we present a new method to optimize the two thresholds based on particle swarm optimization (PSO) in the wavelet domain. Having analyzed the widely used soft threshold and hard threshold de-noising methods, we select the Donoho threshold as the upper threshold, and minimax threshold as the lower threshold. The PSO algorithm is used to optimize the double-threshold for the best threshold for de-noising. Simulation results show that the proposed method can overcome the psuedo-Gibbs phenomenon of the hard-thresholding method and excessive smoothness of the signal caused by soft-thresholding. It enhances SNR and reduces RMSE, providing better performance than the traditional methods.

    Electronic Engineering
    Ultra-wideband Antenna Design Using Genetic Algorithms
    DING Xiao 1, DING Xuan-hao 2
    2009, 27(2):  187-191. 
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    An ultra-wideband microstrip log-periodic antenna (UWB-MLPA) is studied by using genetic algorithms (GA). A multi-object function with low VSWR and high gain is used in the program. The results of GA optimization are compared with traditional methods. An antenna is designed and fabricated, and outdoor measurements carried
    out with good results. The antenna can operate in the L/S band with good electrical and radiation characteristics.
    It is shown that GA is an effective method for this type of UWB antennas.

    Direct Data Domain Approach of Real Weights with Multiple Constraints for Uniform Circular Array
    ZHAO Jun, ZHU Zhao-da
    2009, 27(2):  192-197. 
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    In this paper, an improved direct data domain method is studied for airborne radar with uniform circular array antennas in STAP. Based on a single snapshot, this algorithm can effectively restrain jamming and clutter while keeping the signal of interest. By implementing multiple space-time constraints, the system gain is maintained
    when the signal of interest deviates slightly. Experimental results show effectiveness of the method.

    Computer Science and Applications
    Judgement and Mechanism of Handling on Aperiodic Real-Time Task Overload
    WU Yue, TANG Li-san, YANG Hong-bin
    2009, 27(2):  198-202. 
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    A real-time aperiodic task overload handling mechanism based on value of task is presented in this paper. A method of verifying task overload is first presented. A mathematical model termed dynamic constraint knapsack model is established by combining two parameters, deadline and value of task. An enhanced dynamic greed algorithm (EDGA) is then presented to handle the model. By determining parameters and the value function of tasks, performance of EDGA is analyzed in terms of hit value ratio. Experimental results show that EDGA can
    achieve higher hit value ratio compared to the earliest deadline first (EDF), highest value first (HVF) and robust
    highest value first (RHVF) algorithms under all workload conditions.

    Control and System
    Parallel Signal Processing for GPS Software Receiver
    MIAO Jian-feng1, SUN Yong-rong1, CHEN Wu2, LIU Jian-ye1, HU Cong-wei3
    2009, 27(2):  203-209. 
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    In view of the inability of real time processing in conventional GPS software receivers, a GPS signal parallel processing algorithm is proposed based on dual core processors. Algorithmic modules in GPS software receivers including signal acquisition, tracking loop and pseudo-range position are analyzed. A parallel processing acquisition algorithm which includes a parallel processing and real-time optimization is studied. In the tracking loop, a separate carrier and CA code phase tracking loop are designed. An optimized bandwidth algorithm is described based on a mathematical analysis, which leads to better dynamic performance and less noise vulnerability of the receiver. The GPS software receiver is validated in computer simulation. Comparison with real testing data shows that the proposed method can improve processing ability at least by 30%, satisfying the requirements of the single point pseudo-range positioning approach.

    Steering Pose Error of the Forklift Robot
    MA Bin-liang1;2, HUANG Yu-mei1, ZHU Cong-min1, YANG Xing-fang1
    2009, 27(2):  210-215. 
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    The manipulator’s acceleration and load quality have influence on steering pose of the forklift robot in its operation. Change of acceleration and load quality of the manipulator is transformed into jump of working centroid of the forklift robot. The steering pose error model of the forklift robot is established based on sideslip motion by the coordinate transformation. The effect of acceleration and load quality of the manipulator on steering pose of the forklift robot is analyzed based on the steering pose error model. Analysis shows that change of acceleration and load quality of the manipulator can result in various degrees of understeer and oversteer of the forklift robot.

    Autonomous Constellation Positioning and Timing by Dual-frequency Inter-satellite Measurement
    CAO Hui, XIONG Zhi, YU Feng
    2009, 27(2):  216-220. 
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    Traditional autonomous constellation mainly concerns about inter-satellite position measurement. It lacks effective means to overcome the overall constellation rotation. This paper uses a module of inter-satellite measurement with additional parameters including velocity, delay error and clock error, and describes the dispelling ionosphere scattering technique and the method of achieving time and position decoupling. By using GPS, accuracy of LEO satellites in constellation is improved considerably, which offers the entire constellation a fixed time basis simultaneously. Simulation results show that the module with additional parameters has higher accuracy than the traditional module measurement of the entire constellation. Meanwhile, GPS can suppress positioning and clock errors caused by the location error of satellite.