Table of Content

30 September 2006, Volume 24 Issue 5

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Articles

Effect of Channel Estimation Error on the Throughput of Downlink Multiuser System with Zero-Forcing Beamforming

HUANG Sen-hua, QIU Ling, ZHU Jin-kang

2006, 24(5):  441-446. 

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Impact of channel estimation error on the throughput of zero-forcing beam forming (ZFBF) is studied in this paper.By computer simulation, relations between the incurred throughput loss due to channel estimation error and the system parameters such as number of users, SNR, number of transmitting antennas and the order of data sub-stream are investigated.Simulation results demonstrate that, when the user number is moderate, a ZFBF system demonstrates its advantage over random beamforming (RBF) in terms of the linear increase of throughput with the number of transmitting antennas even under imperfect channel estimation at the transmitter.Also, in this paper, a referenced rate factor is given to meet the specific outage requirement of system.The results provide a reference for the design of practical downlink multi-antenna multi-user systems.

New Dual-Channel MAC Protocol for Ad Hoc Networks and Its Performance

GU Yan, SHEN Lian-feng, QIU Xiao-hua

2006, 24(5):  447-452. 

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This paper presents a new medium access control (MAC) protocol called DCMAC (dual-channel MAC) for multi-hop ad hoc networks.Dual-channel and improved handshakes as well as channel reservation are employed to avoid collision in data transmission.The hidden terminal and the exposed terminal problems during data transmission are resolved and the channel utilization is increased.Based on receiving control packets, nodes use 3 different network allocation vectors (NAV) in control channel or data channel.In the period of data transmission, the hidden terminal can receive data simultaneously and the exposed terminal can also transmit data.The throughput performance of the protocol is analyzed and evaluated in heavy traffic networks.A comparison with a RTS/CTS based protocol is given.The results show that the DCMAC protocol can improve the throughput in a multi-hop ad hoc network.

Design of Broadband Couplers with Non-uniform Coupled Transmission Lines

FENG Xi-yao, XIAO Gao-biao, MAO Jun-fa

2006, 24(5):  453-457. 

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For conventional uniform transmission-line directional couplers and interdigital couplers, it is difficult to realize fractional bandwidth greater than 50%.By using the S-parameter characteristics of even and odd modes of nonuniformly coupled transmission lines, this paper presents a new approach for designing 3dB couplers with high directivity and broadband.Cascaded ABCD matrixes are employed to calculate the S-parameters of the couplers.Simulation results show that coupled non-uniform transmission lines are suitable for designing broadband directional coupler.

Fast Analysis of Wideband Antenna Characteristics

ZHANG Yun-feng, CAO Wei

2006, 24(5):  458-462. 

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A method for analyzing wideband antennas is introduced.Characteristic modes and singular value decomposition are used at a small number of frequencies, and a set of frequency independent basis functions is constructed over the entire frequency range.The antenna characteristics can be determined rapidly by the frequency independent basis functions.A bowtie antenna and a slotted antenna are analyzed using the proposed method.The results agree with those obtained by direct method of moments, indicating correctness and effectiveness of the method.

Design of Space-Frequency Trellis Codes Based on Trace Criterion

GENG Jia, CAO Xiu-ying, BI Guang-guo

2006, 24(5):  463-468. 

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By analyzing the relation between space-frequency trellis codes (SFTC) and space-time trellis codes (STTC), it is demonstrated that the trace criterion can be used in the design of SFTCs although this criterion is originally proposed for STTCs.Simulation results show that the codes designed by the trace criterion outperform other known SFTCs.In addition, the code performance can be further improved by enhancement of the trace criterion.Effects of path delay, interleaving and encoder states on the code performance are analyzed.

Enhanced Soft-Input Soft-Output Multiuser Detection Algorithm

MEI Zhong-hui, YIN Wei-wei, WU Le-nan

2006, 24(5):  469-473. 

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The iterative multiuser detector is made up by a soft-input soft-output (SISO) multiuser detector concatenated with a SISO channel decoder.The computational complexity of the optimal SISO algorithm grows exponentially with the number of users, so it can not be well applied to the system with large number of active users.The probabilistic data association (PDA) algorithm is a novel SISO multiuser detection algorithm, which has a good performance approximating to that of the optimal algorithm and low computational complexity of order O(K³).In this paper, we make an improvement for the PDA algorithm to further reduce the computational complexity of the PDA algorithm with just a small lo ss in performance.

Skin Symptom Fuzzy Inferential System Based on Semantic Network

LIU Jing, HU Yue-li, CAO Jia-lin

2006, 24(5):  474-478. 

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Aiming at knowledge representation problem of intelligent diagnostic system for skin microscopic images, semantic network knowledge representation is discussed.A skin symptom fuzzy inferential system based on semantic network is proposed by introducing the fuzzy inference to recognition and classification of skin microscopic images.A kind of skin symptom semantic network and the fuzzy inference recognition arithmetic are discussed.Experimental results show that the system is suited to identification of different skin symptoms with a high correct rates.

Sparse Recursive Cholesky Factorization Preconditioning Technique for Acceleration of Iterative Solution to PO-MoM Problems

NIU Zhen-yi, XU Jin-ping

2006, 24(5):  479-484. 

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A novel sparse recursive Cholesky factorization preconditioning technique is proposed for accelerating analyses of radiation problems of wire antennas mounted on large complex platforms with a hybrid method of physical optics and moments (PO-MoM).Based on the physical meanings of the electric field integral equation (EFIE) kernel and neglecting coupling between MoM and PO regions, an approximate sparse matrix of the coefficient matrix derived from the PO-MoM hybrid method is obtained.Inverse of the sparse matrix is then factorized recursively with Cholesky factorization. Thereafter, a preconditioner in a form of successive multiplication is constructed.It is used in a preconditioned generalized minimal residual (GMRES) method to iteratively solve the systems of linear equations.The proposed preconditioning technique is applied to solve radiation problems of antennas mounted on a satellite model and a ship model in electrically large size.Numerical results demonstrate that the new preconditioning technique is efficient in reducing the number of iterations in solving the linear systems derived from PO-MoM.

Safety of Variant Camellia against Square Attack

LI Qing-ling, LI Chao

2006, 24(5):  485-490. 

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By changing round functions of Camellia into round function with an S-P-S structure, a variant Camellia is obtained, denoted Camellia1.This paper discusses safety of Camellia against square attack and analyzes the influence of FL/FL^-1 functions on the safety of Camellia and Camellia1 against square attacks.The results show that Camellia1 is safer than Camellia.The bit-rotation of FL/ FL^-1 functions does not noticeably affect the safety of Camellia and Camellia1, while the layer of FL/FL^-1 functions clearly affects the safety.

Test Framework of Object-Oriented Software Based on UML Statecharts

ZHAN Xue-de, MIAO Huai-kou

2006, 24(5):  491-497. 

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It is difficult to generate test cases of class directly from the UML statechart diagrams that contain a hierarchical and concurrent structure.This paper presents a test framework based on UML statecharts.The UML state chart diagram is first drawn using UML tools.The specification of the UML statechart is exported in XMI (XML metadata interchange).According to the formal semantics of UML statecharts, the UML statecharts are transformed into flattened regular expression (FREE) model diagrams.The hierarchical and concurrent structure of states is flattened in the FREE state model.The XML document of UML statechart diagram specification is converted into the specification of FREE model.Finally, test case sets of classes are generated separately based on different test coverage criteria from the specification of the FREE model.In addition, an algorithm generating transition sequence based on full ZOT path coverage criteria from a FREE model is presented.The test framework is implemented.

Online Detection of Data Stream Changes Based on Maximum Frequent Itemset Entropy

LIU Xue-jun, XU Hong-bing, DONG Yi-sheng, QIAN Jiang-bo, WANG Yong-li

2006, 24(5):  498-502. 

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Online detection of data stream changes is a new topic in data stream studies, which provides a salient feature compared to other types of data mining.In this paper, a novel method for detection and estimation of data stream changes is proposed.The main concerns include:1) adoption of a novel discrepancy measure for data streams, 2) a new algorithm which can effectively explore and store all maximum frequent itemsets for data streams, and 3) a method for detection of changes based on maximum frequent itemsets information entropy.No previous work has been reported to the authors' best knowledge using maximum frequent itemsets entropy model in detecting data stream changes.Experiments were carried out to study temporal and spatial efficiency of the algorithm.

Distributed Anycast Group Management Scheme

LI Ling-zhi, ZHENG Hong-yuan, WU Xiao-fan, DING Qiu-lin

2006, 24(5):  503-508. 

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A secure distributed solution is proposed in this paper according to the characteristics of anycast group management.Operations of group member such as joining and exiting are first authenticated by other members of the group.These members send relevant orders to every anycast router to complete the corresponding operations.By dividing members into smaller groups, monitoring between group members is performed.Cipher text is used when datagrams among members and the update message from members to anycast routers are transmitted.The analysis indicates that this scheme can satisfy the delay requirements of anycast group management, and is secure, robust and scalable.

Online Update of Materialized WebView

ZHANG Bai-li, SUN Zhi-hui, YANG Yi-dong, ZHOU Xiao-yun

2006, 24(5):  509-513. 

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WebView materialization is an important method to improve the query response performance of a web server. As opposed to data warehouse in which updates are usually performed off-line, updates of materialized WebView need to be done online.However, there is little research on the issue.This paper gives a review and proposes an asynchronous and deferring update approach (ADUA), which is composed of synchronous inspection of materialized WebView update (SUIMW), deferring update of materialized WebView (DUMV) and asynchronous update of materialized WebView (AUMW).The approach combines asynchronous update and deferring updating to realize the freshness of materialized WebView efficiently, and can significantly accelerate response to queries.

State Feedback Tracking Control for Nonlinear Time-Delay Systems

CHEN Wei-sheng, LI Jun-min

2006, 24(5):  514-518. 

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A design approach to state feedback tracking controller is proposed for a class of strict feedback nonlinear time-delay systems by means of backstepping technique.Domination method is used to deal with nonlinear time-delay functions.Under the assumption that the nonlinear time-delay functions of systems satisfy Lipschitz condition, globally asymptotical tracking of the given reference signal is achieved and the bound of all signals of the resulted closed-loop sy stem is also guaranteed.By constructing a Lyapunov-Krasoviskii functional, stability of the closed-loop system is proved.Feasibility of the proposed approach is shown in a simulation example.

Fault Diagnosis of Nonlinear Time-Delay System with Unmeasurable States Using Nueral Network

LIU Chun-sheng, HU Shou-song

2006, 24(5):  519-524. 

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A novel fault diagnosis architecture for a class of nonlinear time-delay systems is studied.As the input to neural networks, the estimated states and time-delay states are used to approximate the faults.A state observer is proposed, and unmeasured states estimated on-line using the output of system based on nonlinear approximate ability of neural networks.The estimated states are input to the fault estimator whose outputs are an estimated fault model.Based on the Lyapunov theory, the system stability and convergence of the parameters are analyzed.The condition of solution to ensure existence of algorithm is given.Simulation results show effectiveness of the proposed approach.

New Obstacle Avoidance Method for Mobile Robot

DUAN Hua, ZHAO Dong-biao

2006, 24(5):  525-528. 

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A novel and effective obstacle avoiding method for mobile robot is developed.First, a maximal encasing box and relative velocity between obstacles and the robot are used to analyze the orientation of collision.The principles of le ast changes and optimal changes of velocity are used to realize the robot's obstacle avoidance capability.Simulation results show that this method can help the robot safely reach a target in a dynamic environment where both stationary and moving obstacles exist.

Stress-Strength Interference Reliability Analysis Considering Cyclic Stochastic Stress and Strength Aging Degradation

ZHAO Jian-yin, SUN Quan, ZHOU Jing-lun

2006, 24(5):  529-532. 

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A stress-strength interference (SSI) reliability model taking into consideration stochastic stress and strength aging degradation and point estimation of unknown parameters in the model are presented.Dependence of strength aging degradation on stochastic stress level is included into the models.An example is given to show the effectiveness of the method.

Optimal Group Preventive Maintenance Model for Complex Systems

CAI Jing, ZUO Hong-fu, LIU Ming, GENG Duan-yan

2006, 24(5):  533-537. 

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Maintenance of complex systems is different from maintenance of individual units, because there are economic and failure dependence between units in the system.The optimal maintenance intervals of the units are not necessarily optimal in view of the entire system.For this reason, group preventive maintenance is presented for complex systems. First, maintenance cost and availability are analyzed.The optimal group preventive maintenance model is then proposed for complex systems.Subject to hazard, the model minimizes maintenance cost and maximizes availability.Finally, an air conditioning system is presented as an example in the case study, and the result shows effectiveness of the model.

COP Comparison of Refrigeration Cycles with Two-Stage Evaporating Temperatures

LIU Jing-hui, CHEN Jiang-ping, CHEN Zhi-jiu

2006, 24(5):  538-542. 

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This paper presents a mathematical model for theoretical analysis of refrigeration cycles with two -stage evaporating temperatures, and makes a COP comparison between conventional refrigeration cycle with evaporating pressure adjustment valve and 3 cycles with ejectors.The results show that compression/ejection refrigeration cycles can reduce energy loss and improve COP of refrigeration systems.The more the cooling capacity of the high temperature evaporator, the higher the COP can be improved.

Research Notes

New Fourier Expansion Differential Method for Analyzing Waveguide with Arbitrary Cross-Section

CAO Bin-zhao, XU Fu-yong

2006, 24(5):  543-546. 

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A new Fourier's expansion-differential method for analyzing waveguides with arbitrary cross-section is presented, and a new type of truncated-circular waveguide is analyzed.The mode distribution is obtained.The method has advantages of direct-viewing expansion, simplicity and easy computation, therefore it is applicable to analyzing and calculating waveguide characteristics in microwave engineering.

Dynamic Load Identification in Multi-freedom Structure Based on Precise Integration

CAO Yuan, WANG Feng-quan

2006, 24(5):  547-550. 

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Load identification research is vital to dynamic analysis and applications.In this paper, load identification is studied in the time domain by combining the coupling method and the precise time integration method.The described algorithm is concise, clear and simple.Computer simulation shows that the method is effective and practical.