Table of Content

30 September 2005, Volume 23 Issue 5

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Articles

Adaptive Frequency Offset Synchronization Algorithm for OFDM in Rayleigh Fading Channels

LI Peng-huai, XU Pei-xia

2005, 23(5):  441-445. 

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Carrier frequency offset (CFO) has severe influences on the performance of OFDM systems.To alleviate this effect, a new expression for the difference between estimated and actual values of CFO is proposed and upon which an adaptive frequency offset tracking algorithm established.Simulation is carried out to study tracking performance of the proposed algorithm for several types of time-varying frequency offsets in a Rayleigh fading channel.The tracking curve and MSE are presented.Theoretical analysis and simulation results confirm that the algorithm has low complexity, fast convergence and good tracking performance. Demodulation performance of OFDM systems can be improved after CFO is compensated.

A New Scheme for Differential Space-Time Modulation Using Multilevel Code

RUI Hua, XU Da-zhuan

2005, 23(5):  446-450. 

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To combine multilevel code (MLC) with differential space-time modulation (DSTM), a new scheme based on an multilevel low-density parity-check (LDPC) code with iterative decoding is proposed.This scheme has lower decoding complexity compared to conventional MLC schemes using more than one channel coders.To avoid excessive error feedback that may cause decoding failure, both outer and inner iterations are used.The scheme uses LDPC codes as a criterion to terminate both iterations so as to further reduce the average decoding complexity.Simulation results for a quasi-stationary fading MIMO channel show that the proposed scheme is effective.

An Auto Rate Selection Mechanism Based on Channel Prediction for Wireless LAN

CHEN Li-quan, HU Ai-qun, LI Wei-zheng

2005, 23(5):  451-456. 

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A linear auto regressive (AR) model channel prediction technique is proposed to enhance the performance of auto rate selection mechanism in IEEE 802.11, and eliminate the delay effect between measurement of received signal strength (RSS) values and rate selection for the immediate frame transmission. The best rate is selected based on the data payload length, frame retry count and the RSS value estimated from recorded values.The estimation step-size is analyzed and the proposed mechanism is simulated in TwoRayGround and Ricean channel models in the NS2 environment.Simulation results show that the proposed mechanism enhances mean throughput performance of IEEE 802.11 system compared with that presented in the literature.In saturation, the enhancement reaches 7%, and under a finite load condition, the enhancement reaches 30%.

Joint Source-Channel Decoding Based on Iterative Structure and MS Estimation

ZHOU Lin, WU Zhen-yang

2005, 23(5):  457-460. 

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Using the non-uniform distribution and time domain correlation of source-encoded parameter and the soft-value provided by SISO channel decoder, a recursive joint source-channel decoding algorithm is proposed. The algorithm is composed of soft-bit source decoding based on MS estimation and Viterbi decoder based on iterative structure.Compared with separate source channel decoding, the joint algorithm has a gain in the parameter SNR of about 10 dB for colored Gaussian source and AWGN channel.

High-Rate Frequency Hopping with Multi-link Parallel Transmission

QIU Xiao-hua, SHEN Lian-feng, SONG Tie-cheng, SHEN Ke-qin

2005, 23(5):  461-466. 

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This paper describes a high-rate frequency hopping system with multi-link parallel transmission, implemented using Bluetooth.The system model and device diagram are first presented.In order to show feasibility of the scheme, throughput analysis of the system based on Bluetooth is then given.Finally implementation examples and experiment results are provided.The analysis and experiment results show that data rate of the designed system is greatly improved.The proposed method has good prospect in practical applications.

Spectral Efficiency Performance of an Optimum Bit and Power Allocation Method for MIMO Systems

TAN Guo-ping, CHENG Shi-xin, CHEN Ming

2005, 23(5):  467-472. 

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Under the assumption that the channel state information (CSI) is known only to the receiver, a simplified optimum bit and power allocation method is proposed for multiple-input multiple-output (MIMO) systems that uses V-BLAST as a detection algorithm to maintain fixed target link quality.Due to different ordering in detection resulting in different equivalent gains, forward ordering, revere ordering and optimal ordering, respectively, are considered in the simulation.When M-ary QAM is used with a target symbol error ratio (SER) of 10^-5 in the proposed method, it is found that the spectral efficiency performance of the revere ordering is better than forward ordering, but worse than the singular value decomposition (SVD) based scheme.The reverse is true in case the transmit power constraint is high enough.

Performance Analysis and Enhancement of Multi-WPANs System

GU Jin-shan, SHEN Lian-feng

2005, 23(5):  473-477. 

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A new model for analyzing mutual interference for multi-WPANs coexistence system is presented. Using this model and taking adjacent and co-channel interference into account, impact of distributing density of WPANs, distance between transmitter and receiver, path loss exponent, and packet length on packet error probability are discussed.Forward data transmission rates with different length packets are then obtained. Based on these analysis, methods for improving data transmission rates in two representative applications of WPAN are proposed based on characteristics of these applications.

A CMOS Limiting Amplifier and Received Signal Strength Indicator for Bluetooth Receiver

WANG Jing-guang, MA De-qun, HONG Zhi-liang

2005, 23(5):  478-482. 

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A piece-wise linear logarithmic amplifier is presented.It can be used as limiting amplifier and received-signal-strength indicator (RSSI) in Bluetooth receivers.The circuit, as a part of Bluetooth RF chip, is implemented with the 0.35 μm CMOS technology.Measurements show that RSSI linear error is less than 0. 5 dB with a dynamic range of 40 dB.

PCF Dynamic Power Management Predictive Policy Based on AR Model

BU Ai-guo, LIU Hao, HU Chen, WANG Chao

2005, 23(5):  483-488. 

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Energy consumption is an important design criterion for embedded and portable systems.Dynamic power management (DPM) is aimed at reducing power consumption of electronic systems by selectively shutting down idle components.In this paper, a novel PCF DPM policy based on an AR model is presented, which can solve the problems as mentioned in some publications.Experimental results show that the PCF policy is stable and the average power consumption of system can be further reduced as compared to other predictive policies.

Application of Slotted ALOHA to Anti-collision of RFID System

HU Jian-yun, LI Qiang, MIN Hao

2005, 23(5):  489-492. 

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Slotted ALOHA is a commonly used protocol in anti-collision of RFID system.Having analyzed RFID system's identification process, Markov chain is introduced to model the slotted ALOHA.The model is used to analyze performance of the slotted ALOHA, and find the relationship between success probability and number of slots and tags in the RFID system, providing a guide for practical applications.

An Adaptive Domain Decomposition FDTD Method Using Boundary Detection

ZHANG Hua, HONG Wei, HAO Zhang-cheng, CUI Tei-jun

2005, 23(5):  493-496. 

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An extension of the classical FDTD, adaptive domain-decomposition FDTD (ADD-FDTD) using a boundary detection method, is proposed to solve multiple sub-region problems.In ADD-FDTD, the problem domain is divided into several independent FDTD sub-regions.A boundary condition is applied to boundaries between sub-regions with adaptive detection.In each sub-region, FDTD iteration is activated only if the propagated wave reaches its boundary, otherwise no calculation is performed.Simulation results show that ADD-FDTD is efficient in both computational complexity and computational time.

Small-World Architecture Based Kernel Auto-Associative Memory Model and Its Application to Face Recognition

CHEN Lei, ZHANG Dao-qiang, ZHOU Peng, CHEN Song-can

2005, 23(5):  497-501. 

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By introducing the kernel method into conventional auto-associative memory model (AM), a unified framework of kernel auto-associative memory model (KAM) is established, which extends the existing AM. Taking into account the complex full connectivity of KAM, and based on the small-world network described by Watts and Strogatz, this paper proposes a framework of small-world architecture based kernel auto-associative memory model (SWA-KAM), making VLSI implementation of AM easier.Simulation results on FERET face image database show that, SWA-KAM is more robust and has higher recognition rate than both PCA and (PC)²A algorithms in the presence of additive noise or partial occluding on face images.

A Map Query Implementation Based on Mobile Equipment

YU Li, XU Hong-bing, OU-yang Qian

2005, 23(5):  502-505. 

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This paper presents a map query algorithm and defines a query language based on mobile equipment, termed the embed geography SQL (EGSQL).The standard flow of EGSQL is explained with an implementation in an application of bus query used in the system of Southeast University Swift DB, providing an indication of its effectiveness and potential for general uses.

Mining Algorithm Based on User Query and Its Application in Intrusion Detection

ZHONG Yong, QIN Xiao-lin, BAO Lei

2005, 23(5):  506-512. 

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As traditional user identification and access control of database security mechanism have limitations such as inability of resisting illegal SQL injection and abuse of authorization, a transaction-level user query profiles mining algorithm is presented by using characteristics of structure stabilization of user queries and attributes.The method can be used for database intrusion detection to effectively prevent these illegal actions. Implementation, complexity and application of the algorithm are discussed, and influence of the algorithm on the database query analyzed.

Model Identification in Rough Factor Neural Network Based on Nearness Relationship

XIAO Di, HU Shou-song

2005, 23(5):  513-516. 

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In this paper, relation of nearness is proposed to replace that of indiscernibility for increased robustness of a decision system against noise.Preliminaries of nearness relationship rough sets are defined and the properties of nearness rough membership function are studied.An architecture of neural network based on nearness relationship rough sets and nearness rough membership functions is described.Neurons in such a network consist of conventional neurons and rough neurons, each neuron having a rough factor.Influence of noise on the network is reduced, and convergence is speeded.An example based on fault identification of an aircraft actuator is presented.Simulation results indicate effectiveness of the proposed method.

Extended AHP Method in Virtue of Rough Sets Theory Based on GA

NI Ming, XU Fu-yuan

2005, 23(5):  517-521. 

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AHP method can be used to solve problems in multi-criterion decision systems with its special advantages.However, some complicated problems cannot be easily solved with general methods after AHP analysis, because either the complicated tasks are unable to be solved by AHP as they do not satisfy the consistency condition or the estimated matrix is too intricate to solve so that AHP is invalidated.To deal with such problems, the AHP knowledge system is reduced with the aid of GA.The issue of AHP ordering is then solved with the RST method, or problems are reduced by RST still with classical AHP method.Thus, in addition to the four rules in changing an AHP system into an RST decision system, the comparison decision system of region informatization level is solved using this method, and the results solved are the same as that obtained by classical AHP, indicating that the method is simpler and more reliable.

Forward Kinematics Based on Improved Genetic Algorithms of 6-DOF Parallel Robot

HE Li-le, LIU Hong-zhao, WANG Peng, DUAN Zhi-shan

2005, 23(5):  522-525. 

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The problem of forward kinematics is treated as optimization of multi-variable nonlinear equation group in this paper.Improved genetic algorithms are used to obtain optimum values, and a new grouping method is presented based on gray relative analysis.Seven groups of real values of the 6-DOF Stewart parallel platform are provided as examples.It is proved that the proposed method is simple, effective and useful in solving forward kinematics problems for parallel robots.

Accuracy Synthesis Based on Chaos-Genetic Algorithms of Parallel Robot

HE Li-le, LIU Hong-zhao, PAN Fang-wei, DUAN Zhi-shan

2005, 23(5):  526-529. 

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Taking into account the influence of randomness of clearance error caused by the joints including spherical and rotational hinges, this paper proposes an actual error model of parallel robot.Based on error analysis, a mathematical model of optimization for accuracy synthesis for parallel robots is established by taking accuracy of connecting rods and joints as design variables and manufacturing cost of tolerances as a target function, and making position and volume errors within the design criterion.The accuracy synthesis is carried out using chaos-genetic algorithms.This method has many advantages such as legibility, ease of programming and high precision as demonstrated by the simulation results.

Vibration Characteristics of Multi-body System in NC Lathe

WU Nan-xing , SUN Qing-hong, YU Dong-ling

2005, 23(5):  530-534. 

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Based on the theory of multi-body system, the mainshaft system of high-speed high-precision NC la the is investigated.It is treated as a coupled rigid-flexible multi-body system made of rigid and elastic bodies linked together in a specific manner.A dynamic model is established.Computation of vibration characteristics is carried out, and the computation results obtained using the multi-body system theory and the traditional lu mped mass method are compared.Results show that the developed mainshaft system of NC lathe is always within a stable and reliable operating area.Theoretical bases for application of the method to other multi-body systems are shown.

Development of Cermet Cutter by Nano-TiN Powder Dispersion

XIE Feng, SHEN Wei-lei, YANG Hai-dong, LIU Ning

2005, 23(5):  535-538. 

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Dispersion of nano-TiN powder is a key technique in the development of nano-modified Ti(C,N)-based cermet.Suitable dispersion method and medium for spreading nano-TiN grains are studied experimentally.Optimized dispersion parameters for nano-TiN modified TiC-based cermets are determined.The results are useful in obtaining high performance cermet cutters.

Desalination Techniques of Carbon Nanotube Electrodes by Electric Adsorption

DAI Kai, SHI Li-yi, FANG Jian-hui, ZHANG Deng-song, YU Bing-kun

2005, 23(5):  539-544. 

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This paper discusses desalination techniques of carbon nanotube electrodes by electric adsorption. Pre-treatment of carbon nanotubes, carbonization of carbon nanotube electrodes and aperture of carbon nanotubes are studied.Measurement and analysis under different conditions of voltage, initial salt intensity, water current, and number of electrodes suggest that desalination performance is improved after pre-treament, carbonization can strengthen intensity of electrodes, the best aperture of carbon nanotubes to desalt the brackish water is 2~10 nm, and the best work condition is 2.0 V in voltage and 10 ml/min in water current. This new kind of desalinator, under the best work condition, offers a new way to desalt high salt water for higher salt concentration, higher ratio of desalination, more pieces of carbon nanotube electrodes, and better efficiency of desalination.Test of circle life indicates that the described desalinator not only has effective desalination but also a long cycle period.

Research Notes

Analysis of Fault Pattern Based on Data Mining

HE Yue-shun, DING Qiu-lin

2005, 23(5):  545-547. 

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A new approach to trouble pattern analysis is proposed for after service of products based on data mining.Dimensionality of the fault information is collected, and the fault is cleaned up.The dimensionality table of association rules is made up of technical parameters and the causes of fault.The fault information is analyzed by a set of frequent items with the apriori algorithm based on the dimensionality tables of fault information and association rules.Causes of fault are found and the primary solution is chosen by fault matching, candidate generation and candidate screening.

Wavelet Based Fusion Model of Feature Information in Remote Sensing Images

FU Wei, XING Guang-zhong, HOU Lan-tian, WANG Wen-jun

2005, 23(5):  548-550. 

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Fusion of feature information in remote sensing (RS) images is generally based upon spectral and texture features in object images.This paper presents a feature fusion approach to RS images after enhancement of edges in the remote sensing image with multi-resolution wavelet analysis.The image resolution is improved. Instead of the conventional HIS-wavelet fusion, fusion processes of the low frequent components of the RGB channels and the high frequency components, both obtained with wavelet decomposition, are performed separately, and a new fusion image is composed of the new RGB channels.In this way, not only resolution of the multi-spectral image is improved, but also color features, which are important for multi-spectral fusion, are retained.Effectiveness of the proposed method is verified with experimental results.