Table of Content

31 January 2006, Volume 24 Issue 1

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Articles

A Family of Full Transmit Diversity Space-Time Codes


LIU Chen;LI Yue-hong;WU Zhen-yang

2006, 24(1):  1-0001 . 

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A new family of space-time block codes is constructed, called diagonal block orthogonal algebraic space-time (DBOAST) block codes. It can transmit at a normalized rate of 1 symbol per channel use. It is proved that they can achieve the full transmit diversity with a larger coding gain than DAST block codes over quasi-static or fast fading channels. The capacity of an equivalent channel using the proposed code is analyzed. The performance merit of DBOAST block codes is confirmed by Monte Carlo simulations and compared with other space-time block codes.


A Decision-Feedback LSCM Beam-Forming Algorithm Based on Pre-despreading

FU Hong-liang;FENG Guang-zeng

2006, 24(1):  6-0006 . 

Asbtract ( 1986 )  

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A new Least Squares Constant Modulus beam-forming Algorithm based on decision-Feedback using the pre-Despreading signals (D-LSCMAFB) in DS-CDMA system is proposed in this paper. This algorithm is simulated and compared with SDCMA and DRLSCMA in additive white Gaussian channel and multipath fading channel environments. Simulation results show that the proposed D-LSCMAFB algorithm is superior to SDCMA and DRLSCMA.


Analysis and Improvement of the Backoff Mechanism Used in IEEE 802.11 DCF




CHEN Yu-Zhong

2006, 24(1):  10-0010 . 

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IEEE802.11 is the most popular WLAN standard based on CSMA/CA. The primary Medium Access Control (MAC) protocol of IEEE802.11 is the contention-based distributed coordination function (DCF) which adopts uniform distribution for backoff process. In this paper, a Markov model is introduced to analyze the impact of backoff time distribution on system performance of IEEE802.11 DCF.A simple and effective mechanism for backoff time distribution is the proposed. Simulation result proves that this mechanism can effectively improve saturation throughput .

Hierarchical Reduction Algorithm of Huge Information System




LIANG Hong-li;ZHANG Hua-guang;LI Ming;LIU Jin-hai FENG Jian

2006, 24(1):  15-0015 . 

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A hierarchical reduction algorithm is proposed to reduce a huge information system. Based on detailed studies on the certain increment operator, a series of theorems are derived, which form a theoretic basis for the hierarchical reduction algorithm. The hierarchical reduction algorithms are then presented for both the information system with and without core attributes. Validity of the algorithms is shown with an example.


Adaptive Echo Cancellation Based on Decorrelation NLMS Algorithm




WANG Zhen-li;ZhANG Xiong-wei;YANG Ji-bin;HAN Yan－ming

2006, 24(1):  21-0021 . 

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Based on NLMS, this paper proposes a decorrelation NLMS algorithm (DC-NLMS) by employing auto-correlation of the input speech signal. The proposed algorithm has fast convergence speed, but small stability maladjustment with the same computational complexity as NLMS, therefore overcomes the drawback of APA. Simulation results indicate that the DC-NLMS algorithm is optimal in adaptive echo cancellation as compared with NLMS, APA, and a previously developed algorithm in the literature.


A New Smooth Handoff Mechanism with Tunnel for Wireless Local Area Network


LI Wei-zheng;HU Ai-qun

2006, 24(1):  25-0025 . 

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Based upon post-registration handoff mechanism in low latency mobile IPv4 and mobile agent buffer technology, a smooth handoff mechanism with bi-directional edge tunnel is presented for IEEE 802.11 wireless LAN. Combined with the proposed methods for reducing handoff latency at link layer and network layer, this mechanism reduces link layer triggers. This is not feasible in 802.11 wireless LAN. By realizing smooth handoff, handoff latency is reduced, and seamless handoff is more closely approached. Simulation experiments indicate that the mechanism not only reduces the possibility of packet loss in the process of handoff, but also lowers handoff latency by more than 500ms in average. The throughput of TCP is increased approximately by 70%. Therefore the handoff performance of wireless LAN is considerably improved.


Modeling Optimal Clustering Based on Continuous Hopfield Neural Network


WANG Mao-zhi;GUO Ke;XU Wen-xi;FAN An-dong

2006, 24(1):  31-0031 . 

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Clustering is a combinational optimal calculation based on its mathematical description. A model combined with continuous Hopfield neural network and used to solve optimal clustering is designed and constructed based on Hopfield’s optimal ability. Details of network mapping, energy function construction and nerve state changing equation are described. Their simplified formation is presented according to the winner-tale-all competitive mechanism. Convergence of the model is proved. Effectiveness and rationality of the model is verified in an application to image compression coding.


Traffic Pattern Based Scalability Analysis of Hybrid Routing Protocol in Mobile Ad Hoc Network



YANG Pan-Long;TIAN Chang;ZHANG Lei

2006, 24(1):  36-0036 . 

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According to the routing protocol scalability evaluation standard proposed by MANET research group, the acalability evaluation of routing protocol based on real network traffic pattern is analytically performed. With the mathematic modeling procedure, the analytical results of hybrid routing mechanism of FSR and DSR show that hybrid routing is a fast convergent, routing message stable and adaptive protocol. It is suitable for applications in complicated network scenarios with varying network parameter.


Indirect Adaptive Fuzzy Tracking Control for MIMO Nonlinear Systems



DU Zhen-bin;HU Shou-song

2006, 24(1):  41-0041 . 

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Combining the adaptive fuzzy control with the adaptive fuzzy identification, this paper presents an indirect adaptive fuzzy control scheme for MIMO nonlinear systems. By using the tracking error and the identification error, the parameter adjusting laws are derived. Both errors improve the performance of the system by regulating the parameters. Extended fuzzy logic systems are used to estimate the multidimensional unknown functions, and the compensator eliminates fuzzy approximation errors and external disturbances. The control scheme guarantees the system stability and attains tracking. Simulation results demonstrate that the control scheme is effective.


Queuing Network Based Model for Bus Buffer Estimation



WU Xu-fan;YANG Jun

2006, 24(1):  45-0045 . 

Asbtract ( 1945 )  

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A method based on a priority-ranked queuing network model for bus buffer estimation is proposed from the characteristics of the embedded microprocessor structure. By summarizing the system, a queuing network model of bus buffer is built. Detailed step of estimating is then presented. Results are analyzed, and an example constructed based on a real application. Comparing the results with high-level model simulation, validity of the method is proved.


Design of an Improved Current Summing Reference




ZHANG Yao-zhong;WU Jian-hui;DING Jia-ping;LONG Shan-li

2006, 24(1):  50-0050 . 

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A CMOS band-gap current summing reference is designed, which is self-biasd with a cascode structure. Hspice simulation with a Chart CMOS 0.35μm and 5V power supply shows that, within ?40?C ~ +85?C, the temperature coefficient is 15.2ppm/?C, and the power supply restrain ratio is ?51.8dB.


Vision Terrain Evaluation Function for Virtual Cockpit


TAN Hao;SONG Yan-yan;WANG Jin-yan;SHEN Chun-lin

2006, 24(1):  50-0050 . 

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Methods for analyzing dynamic multi-resolution terrain models for virtual cockpit systems are discussed. A new model based on the human vision characteristics is presented in order to make better display for terrain rendering, taking into consideration the models of retina gaze and eye motion. It is focused to simplify the 3D engine to avoid complex bio-characteristic of human eyes. The final vision terrain evaluation functions are quite simply with little additional computation cost. Experimental results show the effectiveness of the proposed algorithm.


Discovery of High Dimensional Outliers Based on Association Analysis


LU Jie-ping;NI Wei-wei;SUN Zhi-hui

2006, 24(1):  60-0060 . 

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Discovery of outliers is to extract a few data objects with abnormal behavior patterns, which are more interesting than common patterns in some cases, from a large amount of data. It is of practical significance in IDS, credit fraud detection, etc. Data in these domains are usually high dimensional, particularly featured by their sparseness and decline properties. An algorithm that can obtain the outliers with high efficiency is proposed based on association analysis. Effectiveness of the algorithm is shown by theory analysis and experiment results.


Algorithm for Mining Constrained Maximum Frequent Itemsets Based on Frequent Pattern Tree



CHEN Geng;ZHU Yu-Quan;SONG Yu-Qing;LU Jie-Ping;SUN Zhi-Hui

2006, 24(1):  64-0064 . 

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Most algorithms of frequent itemsets (or maximum frequent itemsets) do not consider any domain knowledge. As a result they generate many irrelevant patterns. Therefore, finding constrained maximum frequent itemsets is a key in important data mining application such as discovery of constrained association rules, constrained strong rules, etc. Little work has been done on this problem. This paper presents an effective algorithm for mining constrained maximum frequent itemsets and its update, UCMFIA, based on a novel frequent pattern tree (FP-tree) structure that is an extended prefix-tree structure for storing compressed and crucial information about frequent patterns. Experiments show that the algorithm is effective.


Statistical Analysis of Linear Mixed Model for Longitudinal Data



SUN Yan;CHAI Gen-xiang

2006, 24(1):  70-0070 . 

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The linear mixed model for longitudinal data proposed by Laird and Ware is studied.Estimators of the random effects, regression coeddicients and error variance are established without assuming any distributions of random effects and random errors.Strong consistency and ssymptotic normality are discussed under the general conditions of design points and moments.


Identities and Recursive Algorithm of Function-Valued Padé-Type Approximation for Solution to Integral Equations



Pan Baozheng

2006, 24(1):  74-0074 . 

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To solve Fredholm integral equations of the second kind, a generalized linear functional was introduced and then function-valued Padé-type approximation was defined. Some useful identities are established by means of error formulas for function-valued Padé-type approximation. A recursive algorithm is also constructed. An example is given to show effectiveness of this method.


Effect of System Parameters on Dynamic Stability of DWX Single Hydraulic Prop


WANG Zhong-min;CHEN Shi-qi;LI Bing-wen

2006, 24(1):  78-0078 . 

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A dynamic model of DWX single hydraulic prop is established. Differential equations of motion for each part of the hydraulic prop are derived based on the Hamilton principle. Using the finite difference method and by discretization of spatial variables, differential equations with only time variable are obtained. By introducing state vector, the first order state equations with periodic coefficients is solved by the implicit second class fourth order Runge-Kutta method. Based on the Floquet theory, the principal dynamic instability regions and dynamic stability regions for the hydraulic prop are determined. As an example of DWX35 single hydraulic prop with a cylinder of 100mm diameter, effects of the system parameters on dynamic stability of the hydraulic prop are discussed.


Adaptive Nonlinear Design of Autopilot for Ship Course Tracking


DU Jia-lu;GUO Chen;YANG Cheng-en

2006, 24(1):  83-0083 . 

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An adaptive nonlinear control algorithm combined with an adaptive backstepping algorithm using the Nussbaum gain technique is proposed for ship course tracking steering, which takes into account rudder characteristics and parameter uncertainty. With the proposed algorithm, a ship course-tracking autopilot is designed without any a priori knowledge about virtual control coefficient. Based on the Lyapunov function, it is proved in theory that the controller makes all signals in the nonlinear system of unmacthed uncertain ship motion uniformly bounded, and the desired reference course is asymptotically tracked by the ship’s actual heading. Performance is demonstrated in a series of simulation studied.


Decision-Making for Air Combat Dogfight



LUO De-lin;SHEN Chun-lin;WU Wen-hai;WU Shun-xiang

2006, 24(1):  89-0089 . 

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Considering a scenario of air combat involving two opposing fighter aircrafts, a decision-making model for the pilot in air combat is established. The model is based on a situation of continually updated threat. An influence diagram analysis method is employed to describe the pilot decision-making process. Evaluation of air combat threat and the decision-making behavior are easy to describe and modify, if necessary, according to the experience and preference of the individual pilot. Simulation results show that the proposed model is effective to guide the fighter aircraft during air combat dogfight, and its decision-making process conforms to the concept of air combat dogfight.


Principle and Parameter Design of Hybrid Magnetic Axial Bearings



JIA Hong-yun;ZHU Huang-qiu

2006, 24(1):  94-0094 . 

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Based on configuration and operation of hybrid magnetic bearings used in an axial direction, the principle of suspension force generation is studied. The flux path is calculated by using an equivalent magnetic circuit. The equation of attraction is derived. Mathematic expressions of force/displacement coefficient, force/current coefficient and the maximum bearing capacity are obtained. A set of design and calculation methods are given, such as those for gap magnetic induction intension, pole area, gas length, electromagnet iron parameters, and permanent magnet parameters, providing reference to applications.


Analysis of Repeatedly Available Thermal Energy in Engines


ZI Kun;LAN Xu-guang YANG Xiu-qi

2006, 24(1):  99-0099 . 

Asbtract ( 1863 )  

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To further improve thermal efficiency of internal combustion engine, analysis of energy utilization in engine dynamical cycles is needed. Analysis of available energy can estimate the energy utilization in dynamical cycles of engine in terms of quality. Based on a model of finite time thermodynamics in the engine operation, loss of the available energy is analyzed. The results obtained are in good agreement with that in the actual engine operation.


A Novel Cooling System for Direct Methanol Fuel Cell Stacks


WANG Jiang;SHI Ming-heng;CHEN Zhi

2006, 24(1):  103-0103 . 

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A theoretical analysis is carried out for the effective heat management of a direct methanol fuel cell. Based on the requirement of heat management, a novel cooling system with fractal network channels is designed for the direct methanol fuel cell stacks. Optimum structural parameters of the fractal network channels are calculated, and the effect of flux of cooling water and heat load on the temperature distribution in the stacks quantitatively analyzed. The results can be applied to determine the optimal flux of cooling water and to optimize the stack design.


Application of Wavelet Transformation to Dynamic Measurement of Men-Board System


WANG Jun WANG Feng－quan;Li Zhi－jun;ZHOU Xing－de

2006, 24(1):  108-0108 . 

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In order to acquire the starting condition of a springboard diver from the response curve, discrete wavelet transform is used to decompose the signal. A correlation algorithm based on time-frequency analysis is improved to estimate only the low frequency relative coefficients of similar signals which contains most energy. The moment of take-off can be caught, and the jumping acceleration and velocity are obtained. Moreover, shock spectrum of the board is figured out to obtain optimum pressing condition. Experimental results indicate that the method can be used to evaluate the jumping skill, which is useful in the training.