Table of Content

20 March 2007, Volume 25 Issue 2

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Articles

Joint Estimation of Sampling Clock and Residual Frequency Offset of OFDM System Based on Discrete Preamble

WEI Li;XU You yun;CAI Yue ming;WANG Deng lin

2007, 25(2):  111-111 . 

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Estimation and compensation of sampling clock and residual frequency offset in OFDM systems are an important issue. Using discrete preamble, we derive near optimal and sub optimal estimation based on the maximum likelihood (ML) estimation theory, and then analyze the estimation performance and discuss the design of discrete preamble to achieve best estimation performance. We also give a closed loop scheme for accurate and fast sampling clock tracking. Validity of the proposed method is verified in simulation.

Detection of Weak Signal Based on Instantaneous Polarization

LIU Tao;WANG Xue song;LI Yong zhen;XU Zhen hai;XIAO Shun ping

2007, 25(2):  117-117 . 

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We study the detection of weak signal using narrowband dual polarization radar. Description of Instantaneous Stokes sub Vector Sequences (ISVS) of radar target signal and noise are presented. The statistics of ISVS and probability density functions of different signals are given, and a novel detection algorithm proposed through polarization and power accumulation in time. We also derive an analytical expression of false alarm probability and show that the constant false alarm rate (CFAR) of the new receiver can be made bounded. Simulation results show that the radar detection performance is improved. It is useful in applications such as anti radar stealthy, early warning and space detection.

A Fast Optimal Configuration Algorithm for WDM Networks with PathProtecting pCycles

GE Chen hui;SUN Xiao han;ZHANG Ming de

2007, 25(2):  124-124 . 

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A new algorithm is proposed to quickly optimize WDM networks with path protecting p cycles. A heuristic method is considered to search the Mutually Disjoint Path Group (MDPG) set for each candidate p cycle. An Integer Linear Programming (ILP) model is introduced to design WDM networks with MDPG. Numerical studies show that the optimal results obtained with the MDPG ILP algorithm are all very close to the solutions of pure ILP method but with greatly reduced computational time for different network topologies. The optimization procedure tends to choose p cycles protecting connections that are completely straddling p cycles.

Multiuser Detection Algorithm Based on Diversity Combining and MMSE for FastMFSK/FHMA Communication System

LIU Chuan qing;HU Xiu lin;ZHANG Yun yu

2007, 25(2):  129-129 . 

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An optimization method has recently been presented by Brink to design the degree distribution of irregular LDPC codes using EXIT chart. Brink’s method is easier to visualize and program compared to density evolution, but it is unable to choose degree distribution automatically. An improved optimization algorithm based on EXIT curve fitting, DE EXIT, is proposed in this paper to overcome the drawback. The proposed algorithm can automatically choose an optimization degree distribution and obtain a corresponding ensemble threshold. Simulation results show that DE EXIT has a good performance and can be applied under different conditions to achieve optimal code structures.

Improved Optimization Algorithm Based on EXIT Chart for LDPC Codes

XU Hua;XU Cheng qi

2007, 25(2):  134-134 . 

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An optimization method has recently been presented by Brink to design the degree distribution of irregular LDPC codes using EXIT chart. Brink’s method is easier to visualize and program compared to density evolution, but it is unable to choose degree distribution automatically. An improved optimization algorithm based on EXIT curve fitting, DE EXIT, is proposed in this paper to overcome the drawback. The proposed algorithm can automatically choose an optimization degree distribution and obtain a corresponding ensemble threshold. Simulation results show that DE EXIT has a good performance and can be applied under different conditions to achieve optimal code structures.

A Fast and Precise Multimedia Inverse Quantization Algorithm

DAI Lin;YANG Jun;FAN Zhi xiang

2007, 25(2):  141-141 . 

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Nonlinear functions are essential in multimedia systems, but they are difficult to be implemented in fixed point SOC. In this paper, a method combining a lookup table and Taylor series is proposed to approximate nonlinear functions by considering the ability of fixed point SOC and the limitation of memory. In addition, a fast convergent method is presented to improve precision by only taking sixth order Taylor series. Experiments show that the proposed method needs less memory compared with the full lookup table method, and can greatly improve precision compared to the method proposed by Tsung Han Tsai [1]

Determining Word Length of FixedPoint Accelerator in SOC Based on FloatPoint to FixedPoint Conversion

ZHOU Fan;SHI Long xing;YANG Jun;ZHANG Yu;GAO Gu gang

2007, 25(2):  145-145 . 

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Many multimedia and communication applications require dedicated hardware accelerator to achieve acceptable performance and cost in SoC. The word length of the computation unit or memory in hardware accelerator is important to the chip area and power consumption. This paper proposes a novel method for the design of word length of fixed point hardware accelerator based on float point to fixed point conversion from statistical perspective. The proposed approaches take into account the hardware architecture design and the software conversion together, solving the problem on a mathematical layer. In any case, the method can greatly reduce computation load, and implement multimedia calculations of high computational complexity without using a DSP chip.

Methane Conversion to Acetylene via Microwave Plasmas

SUN Yong zhi;YANG Hong sheng;SUN De kun;SHEN Chang sheng

2007, 25(2):  152-152 . 

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A Novel AGC Scheme Based on Control of Equalizer Error

DENG Qing;ZHENG Wei shan;WU Jian hui

2007, 25(2):  157-157 . 

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Traditional approaches of AGC acquire error control signals by estimating the average value over a long period of time. It results in complicated circuitry and is susceptible to intersymbol interference. In this paper, we present an equalizer based AGC approach that uses the equalizer’s error to adaptively compensate for the input signal and effectively reduces the complication of the hardware. Simulation results demonstrate good acquisition and tracking performances under circumstances of degraded signal. |Keywords： automatic gain control (AGC); equalizer; intersymbol interference

WebOLAP System Based on Object Pool and Data Caching

XIE Qiang;YU Ya li;DING Qiu lin

2007, 25(2):  161-161 . 

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By analyzing the existing problems of traditional OLAP systematic in a web environment, a system structure of OLAP system based on object pool and data caching is proposed. The definition of data pool is given, and a processing user request algorithm is proposed. The definition of data cache and data cache processing algorithm are given. Object pool holds certain quantity of objects. An object is a function unit capable of providing decision support, which visits data in the data cache. If the data does not exist, it turns to the OLAP server so that the system performance can be greatly enhanced, and the OLAP server’s burden is lessened. Finally, system implementation and application results are discussed.

Extensible Storage Structure Based on Multidimensional Hierarchical Cube

ZHAO Qing jian;CHEN Sen fa;HU Kong fa

2007, 25(2):  166-166 . 

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As a multidimensional index structure, the multidimensional hierarchical B + tree is introduced, on which an expandable multidimensional hierarchical cube (MH-cube) is set up. With the hierarchical semantics, MH-cube may perform quick query, data updates and schema update with high efficiency. A theoretical analysis shows that the MH-cube is superior to other kinds of cubes.

Layered Software Reliability Model of Component Based Software…

LIU Jian hao;LIU Xiao ming;YAO Yi;HUANG Song

2007, 25(2):  171-171 . 

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Reliability is an important characteristic in quality architecture. For a component based software system, based on path analysis and testing from operational profile, a system reliability model is built using characteristics of the component development process and the system development process that are mutually unrelated. According to the layers of path information and the particular degree of component information, the model can be used at the appropriate granularity. An actual model is shown by statistical testing data, and methods for improving accuracy of reliability estimation is proposed.

An Integrated Solution to Automate Treatment Procedure for WholeBody Gamma Knife

ZHOU Zheng dong;LUO Li min;SHU Hua zhong

2007, 25(2):  177-177 . 

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In order to automatically determine the treatment procedure of whole body gamma knife and improve treatment results, a novel method based on the geometric optimization of shots and optimization of treatment path is proposed. A geometric optimization model based on boundary box is designed to arrange the shots. Coverage percentages of tumor and normal tissues are taken into consideration in the objective function. The optimization problem is solved by genetic algorithm. Based on the shot optimization arrangement, genetic algorithm is applied to find the best treatment path. In case a large number of shots are needed, a layer by layer treatment path optimization scheme is used to reduce computational time. This way, treatment can be carried out regularly according to the optimized shot locations and treatment path. Application of the method to simulated data shows that the treatment procedure is more convenient and faster.

Combined Algorithm for Damping Attitude of Inertial Attitude and Head Reference System Based on Fault Detection

ZHU Yan hua;LIU Jian ye;ZENG Qing hua

2007, 25(2):  183-183 . 

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In a platform inertial navigation system, damping network is applied to damp the gyro’s drift. For strap down inertial attitude and heading reference system (SIAHRS), gyro’s drift error can also be suppressed by the information from accelerometers. This paper proposes the idea of calculating vehicle attitude by both gyros and accelerometers, and designs a damping Kalman filter to integrate this information. However, only when the vehicle was moving without acceleration can one use the output of accelerometers to calculate its attitude. For this reason, the residual chi square test is employed in the Kalman filter to detect vehicle movement in real time. Besides, effects of outliers from measuring sensors are also considered in order to enhance system’s fault tolerant ability and sensitivity. Results of static and dynamic experiments are carried out.

Heave Motion Control for Submini Underwater Vehicle

ZHAI Yu yi;CHEN Yong;GONG Zhen bang;TANG Hai bin;MA Jin ming

2007, 25(2):  189-189 . 

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Based on the mathematical model used in a self designed underwater vehicle, a simulation model is induced. Reasonable simplification has been made in model. Having analyzed the overall performance, correction to the system using the PID algorithm is proposed. The PID parameters are calibrated, and its effects on the digital PID controllers are analyzed. Simulation has been performed with Simulink providing some useful results.

Experimental Study and Fractal Analysis of Ice Crystal Structure at Initial Period of Frost Formation

HOU Pu xiu;CAI Liang;YU Wei ping

2007, 25(2):  193-193 . 

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Using a system of image magnification and acquisition, we observed and collected pictures of ice crystal in various shapes under different growth conditions. The original pictures were converted into binary images, and fractal analysis was performed with the box counting dimension. The results show that the dentritic ice crystal has a fractal structure, and the fractal dimension can be obtained. However ice crystals that are not fully developed do not have a fractal structure. The meaning of fractal dimension is discussed. This study provides a basis for a frost growth model that is close to reality.

Gray SelfMemory Prediction of Inflow to Hydropower Station Reservoir

LI Li;SHEN Bing;LI Rong feng;ZHAO Chang sen

2007, 25(2):  198-198 . 

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Combining the theory of gray system with self memory principle, a new model for predicting time series of reservoir inflow is proposed. The model has been used to predict the annual and flood period inflow to reservoir of Caohe Hydropower Station on the Jin River. The case study indicates that the model can deal with non stationary time series and provide the inflow trend and extreme values with improved accuracy.

Adaptive Robust Stabilization for a Class of Nonlinear Systems with TimeVarying Delayed Disturbance

XU Jian qiang;CHEN Shu zhong

2007, 25(2):  202-202 . 

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The problem of adaptive stabilization for a class of nonlinear systems including matching time varying delayed disturbance is discussed. The bound of the time varying delayed state disturbances are unknown, and are assumed to satisfy the linear growth conditions. By using the Lyapunov stability theory and Lyapunov Krosovskii functional, we propose a robust adaptive state feedback controller, which can guarantee that the closed loop system is globally stable in the sense of uniform ultimate boundedness, and the state trajectories uniformly asymptotically tend to zero. An illustrative example is given to demonstrate validity of the results.

Fuzzy Adaptive Control for a Class of Nonlinear Systems

QU Zi fang

2007, 25(2):  207-207 . 

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Combining both kinds of fuzzy logic forms including fuzzy T S model and adaptive fuzzy logic systems, this paper presents an adaptive control scheme for a class of nonlinear systems. The fuzzy T S model is used to approximate the nonlinear systems, and the fuzzy control law of the fuzzy model is derived from the linear matrix inequality. The adaptive fuzzy logic systems are then constructed, and the modeling errors eliminated with a compensator based on the adaptive fuzzy logic systems. It is proved that the closed loop system satisfies the anticipated H∞ performance. Simulation results demonstrate that the control scheme is effective.

TimeFrequency Domain Interference Suppression Algorithm for Linear Frequency Modulation

ZHANG Xiao;SHI Zhao wu;WU Qi hui;ZHANG Yu heng

2007, 25(2):  210-210 . 

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By analyzing sub band decomposition of linear frequency modulation (LFM) signals, a subband signal processing based time frequency cell delete (SSP TFCD) algorithm for LFM interference suppression is proposed. Because the algorithm makes good use of the time frequency localization feature of the subband decomposition, signal distortion is minimized when interference is deleted. Simulation results show that the proposed algorithm is superior to the SSP based subband deletion algorithm.

Complicated Property of Runoff Time Series Studied with R/S Method

YAN Ai ling;HUANG Qiang;LIU Zhao;WANG Yi min

2007, 25(2):  214-214 . 

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Rescaled range (R/S) analysis is a useful method in representing fractal structures. To study the complex stochastic and undulatory property of the runoff time series, an R/S method is used. Through the time varying Hurst index, complicated properties of runoff time series are investigated from a new angle. The results indicate that runoff time series in the upstream of the Yellow River follow a fractal distribution, showing a strong persistence and a certain non periodic cycle. This provides a new idea and method for the rational exploitation and utilization of the water resources.

Modification of Curves with Rational Cubic Bezier Splines

XIE Wei song;XIONG Yan

2007, 25(2):  216-216 . 

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A new method for modification of curves is described in this paper. To modify an initial G 2 rational cubic Bezier curve, we give constrained boundaries, replace the curve segment intersecting the boundaries with one of its curve family, which is either tangent to the boundaries or passes their vertexes, and restore G 2 continuity according to the curvature. The modified curve does not intersect the boundaries and keeps geometric continuity. Numerical examples are given, showing that the method is simple, fast and efficient.