Table of Content

31 December 2004, Volume 22 Issue 4

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Articles

The Adaptive Predictive Assignment Algorithms of Random Access Channel in WLAN/WPAN

XU Guo-jun, SHEN Lian-feng

2004, 22(4):  423-427. 

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This paper suggests a new adaptive predictive random access channel assignment algorithms utilizing in WLAN/WPAN and describes the assignment processing of the algorithms. As a concrete example, the paper simulates the algorithms in HIPERLAN/2. Compared with other methods, the result of simulation indicates that this new adaptive predictive method decreases the number of collision and increases access efficiency. The algorithms utilizes wireless resource effectively and improves the performance of the system.

A M-Ary Biorthogonal Code SS Multicarrier CDMA System

XU Xin, CAI Yue-ming, BAI Bin-feng, CHENG Yun-peng

2004, 22(4):  428-432. 

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In this paper, a M-ary biorthogonal code spread spectrum (SS) high data rate multicarrier code division multiple access (CDMA) system is proposed. The system uses quadrature BPSK modulation and biorthogonal SS code to take data bits. Channel estimation eliminates the ambiguities of the phase generated by channel fading, and avoids the identification problem of the single/dual SS code. We use a modified subspace tracking channel estimation algorithm and simulate the system BER performance under different channel estimation approaches and combining methods.

Hidden Markov Model Adaptation Algorithm Using Gaussian-Similarity-Analysis-Based Maximum a Posteriori Nonlinear Transform

LIU Hai-bin, WU Zhen-yang, ZHAO Li, ZENG Yu-min

2004, 22(4):  433-437. 

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The performance of speech recognition system will be significantly deteriorated because of the mismatches between training and testing conditions. This paper addresses the problem and proposes an environment adaptation algorithm to adapt the mean vectors of HMM. The algorithm can reduce the performance deterioration of the speech recognition system caused by the mismatches. Firstly, we build a binary tree by Gaussian similarity analysis (GSA) and then adaptively adjust the class number according to the data. In each class, we adapt the HMM using nonlinear transform approximated by piecewise linear regression. Rather than using maximum likelihood estimation (MLE) in estimating the transformation parameters, we propose using maximum a posteriori (MAP) as the estimation criterion. The proposed algorithm, called GAS-MAPNT, has been evaluated on a Chinese digit recognition experiment based on continuous density HMM. The test shows that the proposed algorithm is efficient and superior to other algorithms with Gaussian similarity analysis, such as maximum a posteriori linear regression (MAPLR) algorithm and maximum likelihood linear regression (MLLR) algorithm.

An Analytical Model for CDMA MAC Protocol

ZHANG Yuan, BI Guang-guo

2004, 22(4):  438-442. 

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This paper analyzes the performance of CDMA MAC protocol. Most CDMA MAC protocols are based on reservation mechanisms. However, performance curves of these protocols are generally obtained via simulation. We have established a complete Markov model and carried out performance analysis. Simulation results validate the correctness of the analysis method.

Design and Analysis of a Scheme for the Doppler Shift Estimation

HUA Jing-yu, MA Zhang-yong, MENG Qing-min, YOU Xiao-hu

2004, 22(4):  443-448. 

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The Doppler-shift of the time-varying multi-path channel can be estimated by calculating the level crossing rate (LCR) of the signal envelope of the channel coefficient estimates on the effective fingers. Also some parameters relating to the Doppler shift are analyzed, and an improved estimation method to get the high estimation accuracy in all kinds of velocity and signal-to-noise ratio is raised.

The Waiting-Time Evaluation for the Small-ScaleTraditional Telecom Service Access Internet

ZHANG Lei, SHEN Lian-feng

2004, 22(4):  449-452. 

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The development of IP telephony shows that providing traditional telecom service on the Internet is becoming a trend. This paper focuses on the maximum queuing delay for small-scale traditional telephony streams accessing Internet under certain conditions. It is proved that the result of the simulation is the same as that of the theoretical analysis. The conclusions in this paper can be used to evaluate the queuing delay for various fixed-rate services transported on Internet.

Subspace-Tracking Channel Estimation for Training-Sequence-Based OFDM Systems with Transmitter Diversity

XU Xin, CAI Yue-ming, XU You-yun

2004, 22(4):  453-458. 

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In training-sequence-based OFDM systems, a training sequence is inserted in the specific location of each slot in order to estimate the channel impulse response in the time-domain and carry out equalization in the frequency-domain. In this paper, we propose two training-sequence-based channel estimation approaches for OFDM systems with transmitter diversity by tracking the delay-subspace and the amplitudes of the CIR or its DFT. Combined with Wiener interpolation filtering technique simulations of an OFDM system with two-transmit-antennas-and-one-receive-antenna space-time block coding show the advantages of the approaches.

An Improved Algorithm for Terminal-Pair Reliability in Communication Networks with Unreliable Nodes

CHEN Yong, HU Ai-qun, ZHONG Zi-guo, WANG Xing-jian

2004, 22(4):  459-462. 

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By transforming the representation of network models, we propose an improved algorithm for terminal-pair reliability in communication networks with unreliable node. The proposed algorithm greatly reduces the complexity of the original one. Theoretical analysis and experimental results show the efficiency and validity of the proposed algorithm. The two errors in[5] are also pointed out.

DDFS in a SDR Portable Satellite-Earth Station

QI Zhuang-ping, LI Guo-tong, YANG Gen-qing

2004, 22(4):  463-466. 

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An ideal software radio needs efficient high speed digital down converters. The common approach for digital down conversion (DDC) is the so-called ROM table approach where the samples of the input signal are multiplied with amplitude values of the sine-and cosine-function stored in ROM. To achieve high resolution, this technique requires a large look-up table which means large chip area, high power consumption, lower speed, and increased costs.In this paper, a CORDIC-based direct digital frequency synthesizer is described. It is able to reduce the size of the look-up table considerably.

A Portable TT & C Station for Satellite Based on SDR

SHI Qing, LI Guo-tong, LIANG Xu-wen, YANG Gen-qing

2004, 22(4):  467-470. 

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The design and implementation of portable TT & C station for ChuangXin No.1 communication microsatellite based on SDR (software defined radio) are described. By the reconfiguration of the programmable devices, the portable TT & C station can receive the narrow band data for telemeter and the spread spectrum data for communication. It can also transmit three data stream(telecontrol, telemeter, communication).

The Stacked Fractal Microstrip Patch Antenna

WANG Wei, ZHONG Shun-Shi

2004, 22(4):  471-474. 

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This paper discusses a stacked fractal microstrip antenna in which both the fed patch and the parasitical patch are fractal with Minkowski islands. The effects of the fractal indentation width and the iterative generations on the antenna performance are analysized. A test fractal microstrip antenna is made and the measurement shows good agreement between the numerical calculations and the experimental results. The new design is much smaller in size than a convention rectangular patch antenna. Moreover, it has a medium bandwidth and 2D symmetry, suitable for dual-polarized antenna applications.

An 8-bit Successive Approximation ADC Based on a Design for the Testability of the Bluetooth RF Circuit

CHEN Jian, HONG Zhi-liang

2004, 22(4):  475-478. 

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This paper describes an 8-bit successive approximation ADC based on a design for the testability of the Bluetooth RF circuit. The ADC core is composed of a comparator with a rail-to-rail input range and a DAC with a R-2R structure. The main advantages of the ADC are that it is compact and simple in structure, low in power and small in the area, in this way it can meet the need of design for testability. Furthermore, a test method suitable for Bluetooth RF circuit based on the ADC is also presented. With this method, the function and performance of the Bluetooth RF circuit can be easily tested. The prototype was fabricated using 0.35 μm CMOS technology of TSMC. Its die area is only 0.15 mm~2. The measured results have shown that the circuit has more than 7 bit static resolution under 3.3 V supply voltage and good anti-interference performance in the high frequency has been achieved.

The Numerical Treatments of RCS Calculation for Partially Coated Conducting Objects and the Rapid Evaluation Using the AWE Technique

LIU Xue-guan, GUO Hui-ping, YIN Hong-cheng, ZHANG Xiang-yang, HUANG Pei-kang

2004, 22(4):  479-482. 

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With the electric field integral equations as the basis, a moment method formula is derived for calculating the RCS of arbitrarily partially coated conducting objects by using triangle-roof-top function as the basic function. Some special numerical treatments have been proposed for improving the calculation accuracy. The asymptotic waveform evaluation(AWE) technique combined with the method of moments, is applied to evaluate the RCS of arbitrarily partially coated conducting objects in a wide band. The numerical results show that the special treatments proposed here can improve the accuracy and the AWE can increase the computational efficiency.

The Selection of Morphological Structural Elements for Removing Noise in Infrared Images

YOU An-qing, CHENG Yi-min, ZHAO Ping, GUO Cong-liang

2004, 22(4):  483-486. 

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Noises in infrared images can be removed by using a filter operator of morphology. Scales of different signals are obtained by means of the constitute quad tree. The scale histogram is established and the best scale of structural elements in filter operation determined. An objective method is thus developed for selecting structural element in infrared image processing based on morphology.

A Method Using Skin-Color and Template Gradients for Face Detection

HE Liang-hua, ZOU Cai-rong, ZHAO Li

2004, 22(4):  487-492. 

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Face detection is a traditional subject. However with the development of computer science, it is attracting increasing attention. In this paper a combined method for face detection is proposed using skin-color detection and template gradient matching. First, skin-color regions which are considered as face candidate areas are detected using a color model. The principal component analysis is then carried out to produce a common face which is used as a matching face model. Finally, the second order gradient is employed as a decision criterion. Experimental results show that the proposed method can substantially increase detection speed and improve the detection rate.

A Generalized Fuzzy Controller with Self-tuning Scaling Factors

HU Hui-qin, LI Shao-yuan

2004, 22(4):  493-497. 

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In consideration of the model mismatch of real plants, a generalized fuzzy controller with delay compensation is designed. The design is based on the model obtained by a biased relay feedback test. The performance of the generalized controller is compared with traditional PID controller. Simulation results demonstrate the effectiveness of the proposed process.

An Unmanned Helicopter Decoupling Control Based on the Fuzzy PID Control Method

ZENG Li-lan, WANG Dao-bo, FAN Chun-xia

2004, 22(4):  498-502. 

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The unmanned helicopter is a strong nonlinear and multi-variable coupled system. Baseing on fuzzy PID control method, this paper proposes a decoupling control for the unmanned helicopter. The method can be applied to the unmanned helicopter's attitude decoupling. It can also search for the best control parameters by using the chaos-optimize theory. The simulation result shows that the proposed control strategy can attain high control performance and good robustness, and can be easily realized.

Boolean Algebra Based on the Two New Operations in the Rough Set Theory

ZHANG Hua-guang, LIANG Hong-li

2004, 22(4):  503-508. 

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In this paper, two new operators are defined and the algebra properties of the rough set based on these two operators are discussed. The operations of union, intersection and complement based on the two operators prove that the complement of the rough set under this definition is Boolean complement.

A Multiplex Forecasting Model Based onan Artificial Neural Network and Its Application

XUE Li-hua, HUANG Hong-zhong, SHI Zhang-ming

2004, 22(4):  509-512. 

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On the basis of our study of the industrial converting process as well as through comprehensive application of the BP neural networks and the experiential evaluation method, a multiplex forecast model is set up at the endpoint of copper blow period in a converting process. The fuzzy clustering anaysis method is also used to determine the number of hidden nodes in the neural networks. Experience shows that the forecast is highly dependable and capable of providing effective guidance to the production process.

Artificial Neural Network Based Drill Wear Monitoring Using the Wavelet Decomposition of a Power Spectrum

ZHENG Jian-ming, LI Yan, XIAO Ji-ming, HONG Wei

2004, 22(4):  513-517. 

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In the drilling process, the power spectrum of a drilling force is closely related to the drill wear. This relationship is widely applied in the monitoring of drill wear. But the problem of how to extract and identify the features of power spectrum have not been completely sloved. This paper achieves this through the multilayer decomposition of the power spectrum by using the wavelet transform and the extract of the low frequency decomposition coefficient as the envelope information of the power spectrum. Intelligent identification of the state of drill wear is achieved in the drilling process through fusing the wavelet decomposition coefficients of the power spectrum by using BP neural network. The experimental results show that the features of power spectrum can be extracted efficiently through this method, and the trained neural networks have high identification precision and the ability of extension.

A Study on the Modeling of a Design Process Based on the Design Structure Matrix

ZHANG Dong-min, LIAO Wen-he, LUO Yan-ling

2004, 22(4):  518-522. 

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By analyzing the relations between two designing activities, a matrix representation for a product design process is described in this paper. A method for constructing a design structure matrix based activity is presented; an algebra-analyzing method is proposed for identifying the sets of coupling activities; algorithms for activity-decomposing and activity-tearing are presented, and re-engineering for a design process is proposed; finally, a case, the crane telescopic boom design process modeled with design structure matrix, is presented.

The Simulation of the Forming of Microsegregaiton During Solidification Process in the Calculation of Coupling Phase Diagrams

LIU Yong-gang, CHEN Guang, SUN Yu, SUN Guo-xiong

2004, 22(4):  523-527. 

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Macro-and micro-models of microsegregation simulation are suggested and the primary numerical methods are discussed at the same time. As an example, microsegregation simulation of Al-4.5%Cu binary alloy in water-cooled Cu mould is also presented. The comparison of simulation results and experiments indicates that these two results were in complete agreement. This verifies the validity and the applicability of the models and the numerical methods.

Research on a Scanning Superconducting Quantum Interference Device Microscope for Room Temperature Samples

DING Hong-sheng, HE Yu-sheng, ZHANG Feng-Hui, HAN Shi-ji, DONG Shi-ying, CHEN Geng-hua, YU Hong-wei

2004, 22(4):  528-532. 

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We have constructed a scanning high-Tc superconducting quantum interference device (SQUID) microscope for room temperature samples, in which YBCO DC SQUID is mounted on the lower end of a copper rod and cooled to liquid nitrogen temperature. There is a 75 μm thick sapphire window under the SQUID. The microscope has a magnetic field sensitivity of 46pT/Hz^1/2 in a magnetically unshielded environment and the spatial resolution is better than 500 μm. We have used this scanning SQUID microscope to measure various room temperature samples, especially for non-destructive evaluation.

The Effect of Multi-irreversibilities on Thermoeconomic Performance of a Heat Transformer

WU Su-zhi, PAN Yu-zhuo, LIN Bi-hong, LIN Guo-xing, CHEN Jin-can

2004, 22(4):  533-537. 

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The heating load per unit cost is taken as the thermoeconomic objective function with the cycle model of a class of irreversible three-heat-source heat transformers as the basis. The objective function is used to optimize the performance of the cycle. The effect of internal irreversibility, heat leak and economic parameter on the performance of the cycle is analyzed. The maximum thermoeconomic function and the corresponding performance parameters are obtained by using numerical calculation. The results obtained here provide some valuable guidance for the optimal design and operation of practical systems.

M-Consecutive-k-out-of-n:F Systems with Exchangeable Lifetimes

TANG Sheng-dao, WANG Feng-quan

2004, 22(4):  538-541. 

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This paper firstly proposes a m-consecutive-k-out-of-n:F system model in order to calculate the reliabilities of some special systems. It also gives a formula to figure out the reliability of the system by aid of the combinatorial method. Further, the model is applied to a system with loads-sharing.

Computer Aided Optimization on the Parameters of a PID Controller

ZHANG Fu-bo, LI Jian-ping, ZHANG Dian-hua, LIU Xiang-hua, WANG Guo-dong

2004, 22(4):  542-544. 

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By applying the graphical user interface (GUI) and the optimal toolbox under the MATLAB environment, a practical and convenient software has been developed to meet the purpose of optimizing the parameters of a PID controller. With the parameters obtained from Ziegler-Nichols tuning as the initial value, a set of excellent PID parameters was gained by means of finding the minimum of an object function known as ITAE rule. Testing results indicate that the control system's dynamic characteristics can be improved observably after being optimized with the above method.

Guaranteed Cost H^∞ Control for a Class of Uncertain Discrete Time-Delay Systems

LIANG Zheng

2004, 22(4):  545-548. 

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This paper deals with the problem of guaranteed cost and H^∞ disturbance attenuation during the robust asymptotic stabilization period of a class of uncertain discrete time-delay systems. Based on Lyapunov stability theory and the linear matrix inequalities (LMI) approach, a sufficient condition is presented for the existence of guaranteed cost H^∞ state feedback controllers. By solving a certain linear matrix inequality, the guaranteed cost H^∞ control laws are obtained. A numeric example is given to demonstrate the effectiveness and superiority of the designing method.

A Parallel Primal-Dual Interior Point Algorithm Based on the QR Decomposition

CHEN Zheng-hong, YU Song-nian

2004, 22(4):  549-552. 

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This paper first describes the steps involved in primal-dual interior point algorithm and explains which step in it can be parallelized. Next the theory of the QR decomposition is also detailed. It also points out how to use the QR decomposition to solve the linear simultaneous equations parallelly. In conclusion, it proposes a parallel primal-dual interior point algorithm based on the QR decomposition and lists some test results.

SwiftDB:A Mobile Database System for Application in Various Industries

XU Li-zhen, ZHANG Jie, YUN Yi-qun, ZHAO Yang, WU Wen-ming, DONG Yi-sheng

2004, 22(4):  553-556. 

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SwiftDB is an embedded mobile database management system for application in various industries. Its physical file format supports SwiftDB's.sdb file format and Microsoft's Pocket Access.cdb file format simultaneously; Through the strong synchronizing servers, the mobile terminal's sharing and synchronizing with the contral database of an enterprise is made possible, and the heterogeneity of the contral database is shielded at the same time; By introducing the concept of connector agent layer, the mobility of computing terminal is also shielded, and a complete scheme of implementing database transaction management in mobile computing environment is thus brought forward from a new point of view; The dynamic report generating tool, embedded GIS/GPS application platform, and the programming API are also provided, which made the SwiftDB a complete platform for the development of mobile applications; The object-oriented technology was used so that the system could be customized very flexibly and finely according to the demand of actual application. The probation suggests that the design of SwiftDB is simple, effective and it can fill the bill of mobile computing in various industries.