Table of Content

31 July 2008, Volume 26 Issue 4

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Articles

Diagonal Alternating Unitary Space-Time Codes at Low Signal-to-Noise Ratio



DU Zheng-feng;CHEN Jie;GAO Xi-qi;PAN Wen

2008, 26(4):  331-0331 . 

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Based on cyclic diagonal codes, an improved design of unitary space-time codes (USTC) at low SNR is proposed. What makes the new design different from cyclic diagonal codes is that the nonzero entries of unitary matrices in the signal constellations appear at the leading diagonal and the minor diagonal alternately. Theoretical analysis shows that the union bound (UB) on symbol error probability (SER) of the proposed USTC is smaller than that of cyclic diagonal codes. To further improve performance of the proposed design, its parameters are optimized to minimize UB on SER. Simulation results demonstrate superiority of the proposed method over cyclic diagonal codes in a wide range of SNR.


Probability Model Identification for Amplitude of Extremely Low Frequency Atmospheric Noise




ZHANG Shu-xia;XU Da-yong;JIANG Yu-zhong;BI Wen-bin

2008, 26(4):  336-0336 . 

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It is shown that the Middleton’s Class A model can be made to fit the amplitude probability distribution (APD) of the extremely low frequency (ELF) atmospheric noise measurement. For the accurate APD of ELF noise, the measured noise is processed with an FFT filter to suppress the 50 Hz interference. The non-Gaussian property of ELF noise is testified by Lilliefors hypothesis testing. By considering the APD and the Quantile-Quantile plot of real ELF atmospheric noise based on a parameter estimation of Class A noise model, excellent agreement between the measured data and the theoretical curves provided by the model can be obtained.


Rejection of Narrow-Band Interference Based on Improved RRLS Algorithm in DSSS Communication Systems


MEI Yang;ZHANG Er-yang

2008, 26(4):  342-0342 . 

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By investigating narrow-band interference suppression based on eigenanalysis in direct sequence spread spectrum (DSSS) communication systems, this paper simplifies the weight vector of eigencanceller. An improved algorithm, orthonormal robust recursive least square (ORRLS) algorithm is proposed to realize the eigencanceller. ORRLS algorithm can guarantee orthonormality of the weight matrix in iteration. Moreover, it can track the rank of interference subspace. Theoretic analysis and simulation indicate that the ORRLS algorithm can converge robustly when the interferences are very strong. It is suitable to reject narrow-band interferences in DSSS communication systems.


Bandwidth Estimation and Control of TCP Congestion on Wireless Networks


YAO Guo-liang;HU Chen

2008, 26(4):  348-0348 . 

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This paper analyzes in theory the factors affecting bandwidth estimation accuracy of TCP Westwood, and presents a method to average the ACK space time to eliminate measure error. By using this method, the bandwidth measurement accuracy can be improved. Further, congestion avoidance of TCP Westwood is divided into two phases according to the bottleneck length, making the sending process stay longer at a high level. Simulation results based on ns2 shows effectiveness of the modified TCP algorithm.


Correlated Uniform Random Variables Produced by a Diffusion Model



HU Luo-quan;XIE Hai-jun;LU Quan-rong;PAN Su

2008, 26(4):  354-0354 . 

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Correlated uniform random variables (URVs) play an important role in simulation of communication and radar systems. The stationary distribution of Markov diffusion model described by a stochastic differential equation (SDE) is used to obtain drift and diffusion coefficients. The approximate probability density function (pdf) model of URVs is used to generate URVs. The method can avoid the drawbacks when the drift coefficient becomes meaningless in taking logarithm of zero. Correlated URVs are obtained in simulation. Their characteristics are discussed in detail.



Improved Iterative Estimator of Carrier Phase for Modulated Signal at Low SNR


LI Ming;ZHENG Hui

2008, 26(4):  358-0358 . 

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An improved iterative expectation-maximization estimator of carrier phase at low SNR is proposed. A new method of parallel initialization is provided, which gives multi-initialization at possible phase space and selects the best result as the new initialization after the first EM iterative process. Thus the EM algorithm can avoid convergence at local maximum and solve the phase ambiguity problem without the aid of a pilot sequence. Simulation results show that the proposed technique performs better than some previous methods, and is convenient to implement with lower complexity and faster convergence.


Feature Extraction from Ultrasonic Image of Fatty Liver Using 2D Hybrid Transform




XIAO Yang;ZHANG Chao;HU Shao-hai

2008, 26(4):  362-0362 . 

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A hybrid 2D transform, discrete Fourier transform-discrete wavelet transform (2D DFT-DWT), is applied to remove speckle noise mixed in the liver scatters so that liver scatters can be extracted. The proposed feature extraction algorithm uses DFT to filter the ultrasound image along the horizontal direction, and DWT along the vertical direction in order to extract the size feature of fatty liver scatters. The definitions and algorithms of partial DFT and partial DWT are given. Realistic processing of fatty liver ultrasound images are performed to show application of the proposed algorithm, and comparisons with classical 2D DFT and 2D DWT are made.


Coronary Centerline Extraction in Multi-slice CT Data Sets


Yang Guan-yu;Toumoulin Christine;Shu Hua-zhong;Luo Li-min;

2008, 26(4):  370-0370 . 

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Cardiac multi-slice computer tomography (MSCT) as a widely used non-invasive imaging modality for cardiovascular diseases diagnosis can image anatomical structures of the heart including cavities and coronary tree. In this paper, we present a new centerline extraction algorithm of coronary arteries in MSCT data sets. Based on a local vessel model, the algorithm uses the 3D geometrical moment operator, multi-scale Hessian matrix analysis and vessel filter to estimate the centroid coordinates, diameter and direction of the local vessel with the optimal scale. A tracing-based strategy is adopted to improve the algorithm’s efficiency. Beginning with interactively initialized seed points, the extraction follows the local estimated direction to search the points of centerline consecutively. A bifurcation detection operator can locate the potential bifurcations and extract seed points of subordinate branches of a single centerline. Promising experimental results are presented finally by illustrating a hierarchical coronary centerline model combined with estimated local diameters. The extraction process can be achieved in few minutes for one volume on a standard PC platform.


High Quality Voice Morphing System


Xu Ning;Yang Zhen

2008, 26(4):  378-0378 . 

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This paper introduces a novel predictable voice morphing system. It is superior due first to the use of the STRAIGHT model that allows flexible manipulation of speech parameters such as pitch, vocal tract length, and speaking rate while maintaining high reproduction quality. The advantage of the system is also attributed to the introduction of the predictable spectrogram, resolving the problems of over smoothing of GMM mapping, and discontinuities between consecutive frames caused by traditional LPC model. Subjective evaluation and objective measurement indicate that the proposed method outperforms the traditional method both in synthesized quality and precision of mapping target characteristics.


On-line Screening for Datecting Product Damages Based on Image Processing


LI Yun;CHEN Guo;GAO Xu-wei

2008, 26(4):  384-0384 . 

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For online damage detection for product packages, this paper proposes two methods based on coordinate transformation. We first select an image region to be analyzed, and obtain binary images using global threshold segmentation. Then, according to the image features, we rotate the coordinate system, and establish two damage recognition criteria, variance criterion and peak number criterion, based on the degree of separation and the probability distribution of projection values of the object pixels in the image. Finally, an image online detection system is set up. The package images are captured to verify the two criteria. The results show that both methods are effective and robust. The proposed technique can be used to similar online detection applications.


Expansion of Wavelet Basis Functions for Parameters Identification of Linear Time Varying System



CHEN En-wei;LIU Zheng-shi;WANG Yong;LU Yi-min

2008, 26(4):  392-0392 . 

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By applying basis-functions expansion that uses wavelet decomposition and reconstruction filters and is rich in local time-frequency features, we introduce a novel algorithm identifying time varying parameters in TVAR model. A periodical extension method for processing two terminals of signals is implemented. Some high frequency coefficients in the wavelet decomposition are neglected to overcome the restriction in solving linear equations by layer number of wavelet reconstruction and the relationship between the model order and the minimal layer number of wavelet reconstruction. Research shows that the algorithm is effective in identifying the trend and frequency features of time-varying parameters. Increasing the sampling rate can reduce the effect of the neglected high frequency component, which is helpful to the identification the high frequency features of fast and instantaneous change signal.


Improved Probability Weighted Dynamic Stochastic Simulation Algorithm



ZHOU Wen;LIU Huan;WANG Yi-fei

2008, 26(4):  397-0397 . 

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This paper presents an improved probability-weighted stochastic simulation algorithm(IPWSSA) which adaptively determines the weighted factor. The method can simulate chemical reaction systems, which have widely varying rate constants, more efficiently and applicably. We apply a probability-weighted and improved probability-weighted stochastic simulation algorithm to a chemical reaction system. Numerical results show that the improved method can significantly reduce the simulation time and increase precision.


Prediction of Protein-Protein Interaction Sites Using Support Vector Machine


MENG Wei;WANG Fei-fei;PENG Xin-jun;SHEN Chen-yi;WANG Yi-fei

2008, 26(4):  403-0403 . 

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Identification of protein-protein interaction sites is essential for the mutant design and prediction of protein-protein networks. This paper proposes a method for predicting protein-protein interaction sites by combining support vector machine (SVM) and the sequence profiles, the accessible surface area (ASA) and the evolution rate of a residue. The dataset is trained and tested using 10-fold cross-validation. Accuracy of the proposed method is 72.91%, 5.71% higher than that of the method only using the sequence profiles and the evolution rate of a residue.


Anisotropic Dual-Tree Complex Wavelet Packet Transform


SHI Fei

2008, 26(4):  409-0409 . 

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A new type of complex wavelet packet transform based on the dual-tree complex wavelet transform is proposed. By introducing anisotropic decomposition into the transform, the associated wavelet bases may have different sizes in different dimensions, and better directivity. The transform can be used on 2D or 3D data. Experiments of denoising of image and video show that PSNR are 0.1~1dB higher than those based on isotropic complex wavelet transform. Visual quality of the denoised images is improved. This indicates advantages of the proposed decomposition method.


Chaotic Time Series Prediction Using Variational Bayesian Regressive Model



WANG Jin-ju;XU Xiao-hong;ZHU Gong-qin;HUANG Guo-lin

2008, 26(4):  413-0413 . 

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We present a linearly regressive prediction model for noisy chaotic time series phase space based on variational Bayesian and phase space reconstructive theory. Time series phase space is constructed. The variational Bayesian method estimates the linear regressive coefficient. We use the model to predict the Mackey-Glass chaotic time series with additive Gaussian noise. The results show that the model is robust to noise and can effectively control over-fitting. The prediction effect is not sensitive to the change of embedding dimension and time delay.


Detection of Defects in Welding Line from X-Ray Film Using SVM



SUN Lin;YANG Shi-yuan;WU De-hui

2008, 26(4):  418-0418 . 

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It is important to detect defects of welding lines on an X-ray film for improving welding techniques and the product quality. This paper proposes a detection method based on support vector machine based on analysis and comparison with several other methods. In the proposed method, the film is first converted into digital format, and characteristics of the defect are extracted. A “one against one” SVM clustering structure is constructed according to the characteristics, and recognition is made. Experiments show high accuracy and processing speed, and easy implementation of the method. The method is suitable for detection and recognition of defects of welding lines from X-ray films.


Discrete Dynamic Model of FOG Temperature Drift



ZHOU Hai-bo;LIU Jian-ye;LAI Ji-zhou;XIONG Zhi

2008, 26(4):  425-0425 . 

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Temperature of FOG drift can be described either with a static model or a dynamic model. Having obtained experimental data by controlling the temperature changing rate around FOG, the two kinds of models were established to study the affects of temperature, temperature changing rate and temperature gradients of FOG drift. The results show that effects of temperature rate and its gradients are not invisible. The compensation accuracy by dynamic model considering both temperature and temperature changing rate or temperature gradients is better than static model by 50 percent. The latter only considers temperature. Therefore the dynamic temperature model should be used for better compensation.


Laser Aided Lateral Visual Lineup Landing System for Carrier Aircraft



ZHENG Feng-ying;YANG Yi-dong;HU En-yong

2008, 26(4):  430-0430 . 

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Carrier aircrafts now use drop light guidance when performing visual approach landing. In order to improve security and accuracy of the lateral aided landing system, a laser visual lineup system is developed. Based on the working principle, long, middle, and close-range flight trajectory geometry and system structural allocation are presented. The pilot handling model and the kinematics of system are developed. A simulation system is constructed to evaluate the performance. The results provide useful information to the theoretical and practical aspects for improved lateral landing system.


Nonlinear Error Compensation of Gyroscope Using Algebra Algorithm of Neural Networks


MA Bin-liang;HUANG Yu-mei;LIU Shu-yang;CHEN Liang

2008, 26(4):  436-0436 . 

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To improve measurement precision of gyroscope, a novel nonlinear error compensation model is proposed using an algebra algorithm of neural networks. The model has advantages of real-time processing and precision mapping in the sample space because the algorithm transforms the complicated nonlinear optimization problem into linear algebraic equations. Compared to polynomial fitting, the proposed model has better precision. Experiments show that the model can reduce error to 0.1o/s and meet practical control needs.