Table of Content

25 September 2009, Volume 27 Issue 5

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Communication Engineering

Reliability Evaluation Based on Multipath Routing in WMN

HE Ming, QIU Hang-ping, BAO Guang-yu, XIAO Deng-hai

2009, 27(5):  441-445. 

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In order to evaluate reliability of wireless mesh networks (WMN), a new method for evaluating network
reliability based on multipath routing (MP-NRE) is proposed. High mobility and ratio of link failure are studied.
Incidental multipath attenuation has influence on the network reliability. Experimental results show that network
reliability is higher with disjoint path than with multipath routing in WMN, and link lifetimes may be relatively
short compared to traffic flows. This is significant for WMN to improve network reliability and reduce end-to-end
delay.

Efficient Probabilistic Coverage Protocol for Near Static Clustering in Large Scale Wireless Sensor Networks

DENG Shu-guang, SHEN Lian-feng, ZHU Xiao-rong, YANG Bing

2009, 27(5):  446-452. 

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In order to achieve good network performance, an efficient probabilistic coverage protocol using near static clustering (EPCSC) is proposed for large-scale wireless sensor networks (LWSN). This protocol employs a near
static clustering to economize network resource and insure the network connectivity. It selects minimum number of active sensors to achieve expected quality of service (QoS), implements cluster heads (CH) rotation mechanism, and computes transmitting path by using approximate Prim minimum spanning tree algorithm to prolong the network lifetime. Simulation results show that the EPCSC protocol can effectively reduce control overheads and prolong network lifetime, and provide desired QoS in LWSN.

Analytical Throughput Model of IEEE 802.11 DCF under Unsaturated Conditions

GUAN Jun-ming, LU Yang, XIE Kai, YANG Fei

2009, 27(5):  453-458. 

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Currently, a two dimensional Markov chain is generally used in mathematical modeling to evaluate the performance of IEEE 802.11 DCF under unsaturated conditions. Based on the notion that DCF shows fairness for all contending nodes in the network, this paper derives an average transmission cycle period of a node in unsaturated traffic environments and a mathematical representation of the throughput. Compared with existing works, the proposed approach is simple and can reflect the actual mechanism of DCF. There is a close match between the theoretical derivations and simulation results, indicating effectiveness of the proposed model.

Parameter Estimation for Simplified Class B Noise Model

ZHANG Shu-xia;JIANG Yu-zhong

2009, 27(5):  459-462. 

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The amplitude probability distribution (APD) of impulse noise can be changed when input single of communication receiver is filtered using a narrow-band filter. It is verified that the Middleton’s Class B model can be made to fit the APD of narrow bandwidth non-Gaussian noise. In this paper, the efficient estimation of the Class B model parameters based on characteristic function with least square gradient method is derived. The considered estimator has fast convergence and low computational complexity, with performance approaching theoretical up-limit for large data samples. Derivation of the estimator for the noise model parameters, and simulation results using this estimator with three unknown parameters are presented.

Wavelet Joint Detector in Cooperative CDMA System

PENG Zhang-you, LIN Jie, LIU Yan-yan

2009, 27(5):  463-467. 

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This paper proposes a wavelet multi-user detector to reduce the influence of multiple access interference
(MAI) in CDMA systems. Based on the cooperative time-division duplex CDMA (TDD-CDMA) model combined
with a wavelet multi-resolution analysis, we establish a wavelet multi-user detector model for cooperative CDMA
systems. According to the requirement of MMSE multi-user detector, we propose a joint MMSE multi-user detector (MUD) which can reduce the cost function. By theoretical analysis, a closed-from expression of bit error rateperformance is derived. Simulation results show that the proposed wavelet multi-user detector can effectively suppressMAI and increase system capacity, especially at low SNR.

Equalization for Cooperative Communication System Based on STBC-OFDM with Carrier Frequency Offsets

ZHANG Qing-chuan, SHU Feng, WANG Dong-ming, SUN Jin-tao

2009, 27(5):  468-474. 

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In cooperative communication systems based on space-time block coded orthogonal frequency division
multiplexing (STBC-OFDM), inter-channel interference (ICI) and co-channel interference (CCI) arise from multiple
carrier frequency offsets (CFO) among different user nodes. Practical equalization methods are studied to combat these two interferences. When difference of normalized CFOs (DCFOs) is small, a low-complexity iterative approach named IAZF is proposed, which achieves zero forcing (ZF) equalization. In case of large DCFOs, a joint equalization algorithm (JEA) is given, which combines successive minimum mean square error (MMSE) inter-block interference cancellation with parallel interference cancellation. Furthermore, by exploiting the approximate banded structure of channel matrix, we implement recursive calculation of matrix inversion of JEA to reduce the computation burden. Simulation results show that, in a quite large range of DCFOs, JEA is robust with significant improvement over the existing methods, especially when DCFOs is larger than 0.25. The performance of IAZF approaches those of other methods when DCFOs is less than 0.15, and requires low computation load.

Signal and Information Processing

Comparison and Analysis for Image Clustering Methods of Camouflage Design

YU Jun, CHU Miao, TIAN Shao-hui, HU Zhi-yi

2009, 27(5):  475-479. 

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In the process of camouflage design, information of background images is classified, and background
spots acquired using image segmentation. Camouflage patterns corresponding to luminance and natural textures of the background are designed. The common method of mean clustering uses the gray information for image segmentation, resulting in fuzzy details of textures. This paper proposes a new method based on self organizing feature map (SOFM) neural-networks for clustering segmentation. The method uses the entire image as input to the neural-networks, and colors after segmentation as output. Calculation is done iteratively using its special functions in the learning process of self-organizing feature map neural-networks until the learning stops. Experiments show that the SOFM method can preserve more texture details than the mean-clustering method and provide good results.

Distortion Correction of Medical Endoscopic Images Using BP Neural Network

WANG Mu-yun, YAN Zhuang-zhi, GE Jun-jie

2009, 27(5):  480-484. 

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Traditional distortion correction methods for medical endoscopic images have problems such as complication
of distortion modeling, high computation complexity, and susceptibility to errors. The proposed method uses a correction template. Sample coordinates are extracted from the template, and the distorted template image
acquired by the endoscope. These two kinds of extracted coordinates serve respectively as inputs and targets for
training to give the distortion model. Based on the distortion model, a one-to-one correspondence between pixels on the ideal and distorted images is set up. Image correction can then be accomplished by using interpolation. The experimental results show that the proposed method is simple, effective and accurate.

Simulation of X-Ray Imaging Using Monte Carlo Method

SHEN Ao-dong, LI Bing, LUO Li-min

2009, 27(5):  485-490. 

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A novel method for simulating X-ray imaging is presented to describe scattering of photons. The initial projection is generated by a fast ray tracing technique. Properties of the object are recorded and traversed by the rays simultaneously. The scattering points are then picked along the ray direction based on probability of scattering,
neglecting the invalid photons. This is followed by Monte Carlo simulation for photon scattering. Experimental
results demonstrate that the presented method provides results within several minutes similar to that obtained with the conventional Monte Carlo algorithms.

Blind Detection and Separation for Permuted Signals

FANG Yong, WANG Wei, WANG Rui

2009, 27(5):  491-497. 

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For permuted signals, the blind detection and separation problems are considered from the perspective of
blind source separation. A mathematical mode is given to describe the permuted signals, and a blind detection and separation method presented according to the signal characteristics. By using the spectrum and partial correlation characteristics, blind detection and separation of the permuted sinusoidal signals and the permuted images are proposed. Simulation results show the effectiveness of the proposed method.

Seafloor Sediments Classification of Side-Scan Sonar Imagery in Fast Discrete Curvelet Transform Domain

SHI Dan, LI Qing-wu, FAN Xin-nan, HUO Guan-ying

2009, 27(5):  498-501. 

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Fast discrete curvelet transform is performed on the seabed sonar image to obtain low frequency subband coefficients and various directional subband coefficients. Standard deviation is used to describe the image’s global unevenness in the low frequency subband. The texture energy measure (TEM) is used to process coefficients at each scale in the directional subbands, which describes directivity and roughness of texture. The extracted texture feature vectors are used in the classification of side-scan sonar seafloor images with support vector machines (SVM). The side-scan sonar images of sand, mud and rock seafloors are classified using the method described in this paper, and other methods. Comparison results show that the presented seafloor classification method has better performance.

Macroblock Layer Rate Control in Multi-view Video Coding

LI Zhen-gang, AN Ping, YAN Tao, LU Feng, ZHANG Zhao-yang

2009, 27(5):  502-507. 

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Joint video team (JVT) proposed joint multi-view video model (JMVM) for multi-view video coding (MVC). However, the model does not provide an efficient rate control scheme. In this paper, a new rate control algorithm for multi-view video coding is proposed, which consists of four levels for more accurate bits rate control. In a GOP level, it implements reasonable bit allocation among views based on correlation function. In the frame level, it performs bit allocation based on the hierarchical B-picture bit allocation method. In the MB level, rate control is activated to provide more accurate rate control based on the Laplacian rate-distortion model. Compared to JMVC 1.0 with a fixed quantization parameter, the proposed algorithm achieves better accurate rate control and higher image quality.

Identification and Selection of Persistent Scatterer Pixels from SAR Images

TAO Qiu-xiang, LIU Guo-lin, SUN Cui-yu

2009, 27(5):  508-513. 

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This paper presents a new method for identification and selection of persistent scatterer (PS) pixels in SAR images based on wavelet phase analysis. The wavelet filtering theory is introduced into the PS pixel identification and selection. The differential phase interferograms are filtered using the interferogram filtering method based on the wavelet phase analysis. Noise phase and its indicator, and probability of candidate PS pixels are then estimated. Taking into account stability of the amplitude and phase of the candidate PS pixels, the PS pixels are effectively identified and selected from the SAR image. Theoretical analysis and experimental results show that the PS pixels identified and selected using the proposed method are effective and reliable.

Time-Scale Modification of Audio Signal Using Improved WSOLA Algorithm

XU Xue-qiong, YU Xiao-qing, LI Chang-lian, WAN Wang-gen

2009, 27(5):  514-519. 

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To improve efficiency of the waveform similarity overlap-and-add (WSOLA) algorithm in audio signal processing at high sampling rate, this paper proposes a matching method that is progressively performed from the short time mean envelop to the signal waveform. We compute a rough matching envelop based on short time mean envelop, and then perform an exact waveform matching for time-scale modification of the audio signal. The
algorithm reduces computation complexity, and improves efficiency with good outcome. In addition, the length of
analysis windows is dynamically adjusted based on the modified low energy ratio parameter. Experiments show that it significantly improves processing results of mixed audio.

Electronic Engineering

Fast Multiple Grid Algorithm Based on Higher Order Hierarchical Vector Basis Functions

LI Qing-bo, ZHOU Ping, CHEN Ru-shan

2009, 27(5):  520-524. 

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According to Andersen’s high order curl vector basis function, a set of higher order hierarchical basis functions is proposed for electrical field integral equations solved with the method of moments. Combined with the multilevel fast multipole method (MLFMM) the basis function is used to accelerate matrix vector product in
analyzing electromagnetic scattering and radiation of electrical targets. A hierarchical grid iterative algorithm based on the generalized minimal residual (GMRES) algorithm is proposed to improve computation efficiency. Numerical results show that this method is effective in dealing with electromagnetic scattering.

Control and System

Hœ Control for Consensus of Discrete-Time Networked Swarm Agents

LI Xiang-shun, FANG Hua-jing

2009, 27(5):  525-531. 

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Aimed at consensus of discrete-time swarm agents, the existence conditions of state feedback Hœ controller are proposed. Criteria for H1 controllers are obtained by variable decomposition based on the robust control theory and the linear matrix inequality theory. With the designed Hœ control law, the system states achieve
consensus, and the non-consensus part is Lyapunov stable, meeting the H1 performance disturbance attenuation. Simulation results show validity and effectiveness of the method.

Localization of Mobile Robot Based on Clustering

XU Yu-hua, ZHANG Chong-wei, WAN Ting-ting

2009, 27(5):  532-537. 

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In this paper, a new localization method for mobile robot is developed based on a laser range finder. The scanned data points in each frame are first divided into clusters. The current and previous scans are matched
according to the clusters to obtain two types of match clusters, holonomic matches and nonholonomic. For a pair
of holonomically matched clusters, both pairs of endpoints and centroids are considered as match points, while
for nonholonomically matched clusters, only endpoints are considered as match points. Random sample consensus (RANSAC) algorithm is then used to remove outliers, and nonlinear least squares method is adopted to estimate the motion parameters of the mobile robot. Experimental results demonstrate that the approach has satisfactory performance in both static and dynamic indoor environments.

Tracking Control of Underactuated Ship Systems

CAO Ke-cai

2009, 27(5):  538-544. 

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This paper studies the tracking control problem of underactuated ship. With a time-varying coordinate transformation based on dilation and the method for dealing with non-autonomous cascaded systems, the tracking control problem of a complex system is simplified by splitting it into two stabilization problems of simple subsystems. When the reference target converges to zero exponentially, globally K-exponential tracking controllers are constructed which is also effective when the reference trajectory is a line or a circle. Effectiveness of the presented controllers is validated in numerical simulation.

Fuzzy Sliding Mode Variable Structure Control of Digital Cabin Pressure Regulating System

ZHU Lei, FU Yong-ling, ZHAO Jing-quan, PENG Chao-qin

2009, 27(5):  545-550. 

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Based on the nonlinear and time varying parameter of the cabin pressure regulating system characteristics,
a control strategy of fuzzy sliding mode variable structure control is proposed. The fuzzy sliding mode variable structure controller keeps advantages of unreliable system mode of fuzzy controllers, and has the additional
advantages of strong robustness to parameter variation and disturbance, elimination or avoidance of chattering phenomena of sliding mode controllers by using softening control signals. Experiment results show that the proposed method can improve the system’s dynamic response and reduce steady-state errors, and is invariant to disturbances compared to PID controllers.