Sep 2007, Volume 2 Issue 3

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  • WANG Xin, ZHAO Yang, GU Wanyi
    The Gigabit-capable passive optical network (GPON) technology is being considered as a promising solution for the next-generation broadband access network. Since the network topology of the GPON is point-to-multipoint, a media access control called dynamic bandwidth allocation (DBA) algorithm is an important factor for determining the performance of the GPON. In this paper, we propose a new DBA algorithm to effectively and fairly allocate bandwidths among end users. This DBA algorithm supports differentiated services—a crucial requirement for a converged broadband access network with heterogeneous traffic. In this article we first reviewed the signaling and configuration of the DBA, and then proposed a new DBA scheme that implemented QoS-based priority for this need to maximally satisfy the requirements of all optical network units (ONUs) and provide differentiated services. Analyses and simulation results show that the new algorithm can improve the bandwidth utilization and realize the fairness for both different ONUs and services.
  • GUO Yang, QU Yugui, BAI Ronggang, ZHAO Baohua
    Mobile ad-hoc networks (MANETs) provide highly robust and self-configuring network capacity required in many critical applications, such as battlefields, disaster relief, and wild life tracking. In this paper, we focus on efficient message forwarding in sparse MANETs, which suffers from frequent and long-duration partitions. Asynchronous contacts become the basic way of communication in such kind of network instead of data links in traditional ad-hoc networks. Current approaches are primarily based on estimation with pure probability calculation. Stochastic forwarding decisions from statistic results can lead to disastrous routing performance when wrong choices are made. This paper introduces a new routing protocol, based on contact modeling and contact prediction, to address the problem. Our contact model focuses on the periodic contact pattern of nodes with actual inter-contact time involved, in order to get an accurate realization of network cooperation and connectivity status. The corresponding contact prediction algorithm makes use of both statistic and time sequence information of contacts and allows choosing the relay that has the earliest contact to the destination, which results in low average latency. Simulation is used to compare the routing performance of our algorithm with three other categories of forwarding algorithm proposed already. The results demonstrate that our scheme is more efficient in both data delivery and energy consumption than previously proposed schemes.
  • ZHU Qingbao, WANG Lingling
    The ant colony optimization algorithm has been widely studied and many important results have been obtained. Though this algorithm has been applied to many fields, the analysis about its convergence is much less, which will influence the improvement of this algorithm. Therefore, the convergence of this algorithm applied to the traveling salesman problem (TSP) was analyzed in detail. The conclusion that this algorithm will definitely converge to the optimal solution under the condition of 0⟨q0⟨1 was proved true. In addition, the influence on its convergence caused by the properties of the closed path, heuristic functions, the pheromone and q0 was analyzed. Based on the above-mentioned, some conclusions about how to improve the speed of its convergence are obtained.
  • ZHAO Baohua, JIANG Zhenhai
    Traditional solutions have encountered some bottleneck in improving the efficiency of protocol testing. A novel method that records the test sequence dynamically is proposed. Three dynamically reordering algorithms are brought forward in line with different fault conditions. The impact of the new method of testing efficiency is also presented. Simulation results demonstrate that the proposed solution is better than the traditional ones in terms of testing efficiency.
  • WU Ligang, WANG Changhong
    By using the exponential reaching law technology, a sliding mode controller was designed for Lorenz chaotic system subject to an unknown external disturbance. On this basis, considering the unknown disturbance, an adaptive law was introduced to adaptively estimate the parameters of the disturbance bounds. Furthermore, to eliminate the chattering resulting from the discontinuous switch controller and to guarantee system transient performance, a new adaptive fuzzy sliding mode controller was designed. The results of the simulation show the effectiveness of the proposed control scheme.
  • LIU Yusheng, LI Xingyuan
    The ideas of adaptive nonlinear damping and changing supply functions were used to counteract the effects of parameter and nonlinear uncertainties, unmodeled dynamics and unknown bounded disturbances. The high-gain observer was used to estimate the state of the system. A robust adaptive output feedback control scheme was proposed for nonlinearly parameterized systems represented by input-output models. The scheme does not need to estimate the unknown parameters nor add a dynamical signal to dominate the effects of unmodeled dynamics. It is proven that the proposed control scheme guarantees that all the variables in the closed-loop system are bounded and the mean-square tracking error can be made arbitrarily small by choosing some design parameters appropriately. Simulation results have illustrated the effectiveness of the proposed robust adaptive control scheme.
  • LIU Wei, SONG Aiguo, LI Huijun
    Virtual reality is an effective method to eliminate the influence of time delay. However, it depends on the precision of the virtual model. In this paper, we introduce a method that corrects the virtual model on-line to establish a more precise model. The geometric errors of the virtual model were corrected on-line by overlapping the graphics over the images and also by syncretizing the position and force information from the remote. Then the sliding average least squares (SALS) method was adopted to determine the mass, damp, and stiffness of the remote environment and use this information to amend the dynamic model of the environment. Experimental results demonstrate that the on-line correction method we proposed can effectively reduce the impact caused by time delay, and improve the operational performance of the teleoperation system.
  • LU Xiaoxu, ZHONG Liyun, ZHANG Yimo
    Phase-shifting measurement and its error estimation method were studied according to the holographic principle. A function of synchronous superposition of object complex amplitude reconstructed from N-step phase-shifting through one integral period (N-step phase-shifting function for short) was proposed. In N-step phase-shifting measurement, the interferograms are seen as a series of in-line holograms and the reference beam is an ideal parallel-plane wave. So the N-step phase-shifting function can be obtained by multiplying the interferogram by the original reference wave. In ideal conditions, the proposed method is a kind of synchronous superposition algorithm in which the complex amplitude is separated, measured and superposed. When error exists in measurement, the result of the N-step phase-shifting function is the optimal expected value of the least-squares fitting method. In the above method, the N+1-step phase-shifting function can be obtained from the N-step phase-shifting function. It shows that the N-step phase-shifting function can be separated into two parts: the ideal N-step phase-shifting function and its errors. The phase-shifting errors in N-steps phase-shifting phase measurement can be treated the same as the relative errors of amplitude and intensity under the understanding of the N+1-step phase-shifting function. The difficulties of the error estimation in phase-shifting phase measurement were restricted by this error estimation method. Meanwhile, the maximum error estimation method of phase-shifting phase measurement and its formula were proposed.
  • MA Lun, LIAO Guisheng
    A novel autofocus algorithm for synthetic aperture radar (SAR) based on total variation is presented in this paper. The method, which starts with a complex phase-degraded SAR image, after the phase errors model is introduced into the range-compressed phase-history domain, carries out phase errors correction by changing the focus till the total variation of the azimuth profile is maximized. Compared with the minimum entropy autofocus algorithm, the autofocus algorithm has less computational complexity and is easier to implement. The simulation and the processing results of the measured data show the validity of the proposed method.
  • YU Mingcheng, XU Jia, PENG Yingning
    An algorithm was developed to accurately estimate the Doppler centroid, which is needed for high-quality synthetic aperture radar (SAR) image formation by resolving the SAR pulse repetition frequency (PRF) ambiguity. The algorithm uses the SAR range migration to resolve the PRF-ambiguity by searching for a PRF-ambiguity number that minimizes the intensity contrast in the range-Doppler domain. Experimental results show that the approach, compared with traditional methods for resolving the SAR PRF ambiguity, is more suitable for both high contrast scenes such as urban areas and low contrast scenes such as mountains. Moreover, the approach is more computationally efficient for there are no time-consuming correlations or fast Fourier transform (FFT) operations needed in the range-Doppler domain and only part of the range cells are used in the calculation.
  • LIAO Xuewen, ZHU Shihua, ZENG Erlin
    A new auto-reference (AR) transmit-receive scheme and a corresponding group decision algorithm on the generalized likelihood ratio testing (GLRT) principle is proposed in this paper to overcome the drawbacks of the power inefficiency and the high noise vulnerability in transmitted-reference (TR) ultra-wideband (UWB) systems. A partly overlapped detection window structure is introduced in which the decided data frames are regarded as the reference signal so that energy and time resources in the reference frame are saved and full-rate data transmission is achieved. Differential coding was utilized to solve the error propagation problem introduced by the overlapped detection windows. The group decision algorithm on the GLRT principle was utilized to estimate the correlation template through all data frames in detection windows and could offer better noise suppression. Simulation results reveal that the AR scheme with its decision algorithm outperforms the conventional and other modified TR schemes in generalized signal-to-noise ratio (SNR).
  • HAN Jing, HUANG Jianguo, SHEN Xiaohong, WANG Yu
    In underwater acoustic communication, because the available bandwidth of the channel is severely limited, the direct-sequence spread-spectrum scheme can only be realized at low bit rates. To improve the transmission speed, a multicode spread-spectrum scheme is considered. However, in this case, due to the rapid time-variability of the underwater channel, and the influence of inter-symbol interference (ISI) and inter-channel interference (ICI), the conventional rake receiver may fail to function. The hypothesis-feedback equalization algorithm has been proposed for the direct-sequence spread-spectrum system [1]. By updating coefficients at chip rate and feeding back hypothesized chips, it can track time-variability and combat ISI effectively. However, for a multicode system, its performance will be degraded by ICI. An improved algorithm is proposed in this paper, which combines parallel interference cancellation (PIC) with hypothesis-feedback equalization (HFE), with the capabilities of tracking the time-varying channel and suppressing the ISI and ICI at the same time. Simulation results prove that the proposed algorithm can significantly improve the performance of a multicode system.
  • OU Xiaojuan, ZHOU Wei
    Global positioning system (GPS) common-view observation data were processed by using the multi-scale Kalman algorithm based on a correlative structure of the discrete wavelet coefficients. Suppose that the GPS common-view observation data has the 1/ƒ fractal characteristic, the algorithm of wavelet transform was used to estimate the Hurst parameter H of GPS clock difference data. When 0<H<1, the 1/&fonf; fractal characteristic of the GPS clock difference data is a Gaussian zero-mean and non-stationary stochastic process. Thus, the discrete wavelet coefficients can be discussed in the process of estimating multi-scale Kalman coefficients. Furthermore, the discrete clock difference can be estimated. The single-channel and multi-channel common-view observation data were processed respectively. Comparisons were made between the results obtained and the Circular T data. Simulation results show that the algorithm discussed in this paper is both feasible and effective.
  • JIA Dagong, WANG Guanghui, ZHANG Yimo, ZHANG Yinxin, JING Wencai, ZHOU Ge
    An efficient dynamic interconnection model using wireless infrared technology and the theory of optical interconnections was constructed to design a dual-channelinterconnection component. There were three conditions between the rotating optical field and the stationary optical field: end separation, angle misalignment and lateral misalignment. The calculation formulas were given for these three conditions. A dual-channel optical interconnection component was designed based on the dynamic interconnection model and the data transmission rate of the component was measured. The experimental result showed that the dual-channel optical interconnection component could transmit optical signals across the rotating interface. The maximum transmission rate can reach 2.14 Mb/s.
  • SUN Lijuan, GUO Jian, LU Kai, WANG Ruchuan
    Nowadays, two trends appear in the application of sensor networks in which both multi-service and quality of service (QoS) are supported. In terms of the goal of low energy consumption and high connectivity, the control on topology is crucial. The algorithm of topology control based on quantum genetic algorithm in sensor networks is proposed. An advantage of the quantum genetic algorithm over the conventional genetic algorithm is demonstrated in simulation experiments. The goals of high connectivity and low consumption of energy are reached.
  • GUO Qiang, ZHANG Xingzhou, LI Zheng
    In this paper, a new feature extraction method for radar pulse sequences is presented based on structure function and empirical mode decomposition. In this method, 2-D feature information was constituted by using radio frequency and time-of-arrival, which analyzed the feature of radar pulse sequences for the very first time by employing structure function and empirical mode decomposition. The experiment shows that the method can efficiently extract the frequency of a period-change radio frequency signal in a complex pulses environment and reveals a new feature for the signal sorting of interleaved radar pulse serial. This paper provides a novel way for extracting the new sorting feature of radar signals.
  • YANG Hong, ZHAO Jun
    A robustness control of uncertain switched fuzzy systems is presented. Using the switching technique and the Lyapunov function method, a continuous state feedback controller is built to ensure that for all allowable uncertainties the relevant closed-loop system is asymptotically stable. Furthermore, a switching strategy that achieves system global asymptotic stability of the uncertain switched fuzzy system is given. In this model, each subsystem of the switched system is an uncertain fuzzy system, and a common parallel distributed compensation controller is presented. The main condition is given in the form of convex combinations which are more solvable. This method transforms a certain switched system and has strong robustness for various system parameters. Simulations show the feasibility and the effectiveness of this method.
  • XIE Chenbo, ZHOU Jun, YUE Guming, QI Fudi, FAN Aiyuan
    The content of water vapor in atmosphere is very little and the ratio of volume of moisture to air is about 0.1%–3%, but water vapor is the most active molecule in atmosphere. There are many absorption bands in infrared (IR) wavelength for water vapor, and water vapor is also an important factor in cloud formation and precipitation, therefore it takes a significant position in the global radiation budget and climatic changes. Because of the advantages of the high resolution, wide range, and highly automatic operation, the Raman lidar has become a new-style and useful tool to measure water vapor. In this paper, first, the new mobile Raman lidar’s structure and specifications were introduced. Second, the process method of lidar data was described. Finally, the practical and comparative experiments were made over Hefei City in China. The results of measurement show that this lidar has the ability to gain profiles of ratio of water vapor mixing ratio from surface to a height of about 8 km at night. Meanwhile, the measurement of water vapor in daytime has been taken, and the profiles of water vapor mixing ratio at ground level have been detected.
  • WU Jiangang, YUE Ruifeng, ZENG Xuefeng, LIU Litian
    A droplet-based actuating chip by using the method of electrowetting-on-dielectric (EWOD) was developed to manipulate the microfluidics. Here, the actuation mechanism of the sandwiched-configuration EWOD chips was carefully studied, and the movement of droplets was numerically analyzed by using the computational fluidic software, CFD-ACE+. The fabrication of the chip, including a heavily phosphorus-doped poly-silicon micro-electrode array and a thermally grown SiO2 dielectric layer, was exploited to improve the chip stability and decrease the actuation voltage. In experiments, the transportation of a deionized droplet of about 0.5 μL is successfully achieved in air by applying the low voltage of 45 V.
  • GONG Zhuqian, GUO Jianyan, XIAO Boxun, ZHU Guoqiang
    The combined moment method (MoM)-physical optics (PO) approach proposed by Bilow fails in some cases. Based on the theory of diffraction and the fundamental theory of electromagnetism, Bilow’s diffracted current basis function was modified both within and outside the transition regions. The improved MoM-PO technique is validated by comparison with exact solutions for a right-angled perfectly conducting wedge at normal incidence.
  • ZHANG Hanlei, ZHOU Jiemin, LI Gang
    Eccentricity is one of the frequent faults of induction motors, and it may cause rub between the rotor and the stator. Early detection of significant rub from pure eccentricity can prolong the lifespan of induction motors. This paper is devoted to such mixed-fault diagnosis: eccentricity plus rub fault. The continuous wavelet transform (CWT) is employed to analyze vibration signals obtained from the motor body. An improved continuous wavelet transform was proposed to alleviate the frequency aliasing. Experimental results show that the proposed method can effectively distinguish two types of faults, single-fault of eccentricity and mixed-fault of eccentricity plus rub.
  • LIU Qihui, HE Yikang, ZHAO Rende
    This paper analyzed the operating principles and power and torque characteristics of the wind turbine and the direct current motor (DC motor), and investigated the operating characteristics of the wind turbine compared to that of the DC motor. The torque imitation scheme, which has good performance and high feasibility, together with the whole wind turbine imitation system, was provided. The wind turbine imitation system includes not only a hardware platform composed of PC, data-collection board and thyristor-based velocity-regulator, but also monitor software of wind turbine imitation. The experimental results of different occasions verify the correctness and feasibility of the wind turbine imitation scheme proposed in this paper, which provided a valid idea for wind turbine imitation and investigation of wind power generation techniques in the laboratory.
  • YU Yixin, YAN Xuefei, ZHANG Yongwu
    Aimed at solving the problem of optimal planning for high voltage distribution substations, an efficient method is put forward. The method divides the problem into two sub-problems: source locating and combina tional optimization. The algorithm of allocating and locating alternatively (ALA) is widely used to deal with the source lo cating problem, but it is dependent on the initial location to a large degree. Thus, some modifications were made to the ALA algorithm, which could greatly improve the quality of solutions. In addition, considering the non-convex and non-concave nature of the sub-problem of combinational optimization, the branch-and-bound technique was adopted to obtain or approximate a global optimal solution. To improve the efficiency of the branch-and-bound technique, some heuristic principles were proposed to cut those branches that may generate a global optimization solution with low probability. Examples show that the proposed algorithm meets the requirement of engineering and it is an effective approach to rapidly solve the problem of optimal planning for high voltage distribution substations.