Jun 2009, Volume 4 Issue 2

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    Huaxiang WANG, Li HU, Jing WANG, Lu LI

    Using a CT scan of the pulmonary tissue, a human pulmonary model is established combined with the structure property of the human lung tissue using the software COMSOL. Combined with the conductivity contribution information of the human tissue and organ, an image reconstruction method of electrical impedance tomography based on pulmonary prior information is proposed using the conjugate gradient method. Simulation results show that the uniformity index of sensitivity distribution of the pulmonary model is 15.568, which is significantly reduced compared with 34.218 based on the round field. The proposed algorithm improves the uniformity of the sensing field, the image resolution of the conductivity distribution of pulmonary tissue and the quality of the reconstruction image based on pulmonary prior information.

    Yi LIANG, Mengdao XING, Zheng BAO, Long ZHANG

    The frequency modulated continuous wave (FMCW) radar has the characteristics of low probability of interception, good hidden property and the ability to counter anti-radiation missiles. This paper proposes a new method for high-speed ground moving target detection (GMTD) using triangular modulation FMCW. According to the characteristic of the opposite range shift induced by the upslope and downslope modulation FMCW, the upslope and downslope are imaged, respectively. After compensation of continuous motion of the platform and time difference between upslope and downslope signals for imaging, the moving target can be detected through displaced phase center antenna (DPCA) technology. When the moving target is detected, the moving target image is extracted, and correlation processing is used to obtain the range shift, which can be used to estimate the target radial velocity, and further to find the real position of the target. The effectiveness of this method is verified by the result of computer simulation.

    Bo JIU, Hongwei LIU, Liya LI, Shunjun WU

    A novel method called the general water-filling, which is suitable when clutter is not negligible, is proposed to solve the waveform design problem of broadband radar for the recognition of multiple extended targets. The uncertainty of the target’s radar signatures is decreased via maximizing the mutual information between a random extended target and the received signal. Then, the general water-filling method is employed to the waveform design problem for multiple extended targets identification to increase the separability of multiple targets. Experimental results evaluated the efficiency of the proposed method. Compared to chirp signal and water-filling signal, our method improves the classification rates and even performs better at low signal-to-interference-plus-noise ratio (SINR).

    Nigang SUN, Lei HU

    A new family of GMW sequences over an arbitrary Galois ring was defined by using the trace functions and permutations. This generalizes the concept of GMW sequences over finite fields. Utilizing the Fourier representation, we derived an estimate of the linear complexities of this family of GMW sequences. And the result shows that such sequences have large linear complexities.

    Fei YU, Luxi YANG

    The joint optimization of cooperative relays in a multiple-input multiple-output (MIMO) multiple relay aided communication system is discussed in this article. A simple linear optimization solution is designed and a multi-user scheduling algorithm is proposed. The new algorithm chooses users with larger cooperation diversity gains from the waiting list to serve; it can reduce inter-user interference and maintain space diversity caused by parallel transmission of multiple relays, and achieve higher system throughput.

    Wei DONG, Jiandong LI, Zhuo LU, Linjing ZHAO

    The frequency offset and channel gain estimation problem for multiple-input multiple-output (MIMO) systems in the case of flat-fading channels is addressed. Based on the multiple signal classification (MUSIC) and the maximum likelihood (ML) methods, a new joint estimation algorithm of frequency offsets and channel gains is proposed. The new algorithm has three steps. A subset of frequency offsets is first estimated with the MUSIC algorithm. All frequency offsets in the subset are then identified with the ML method. Finally, channel gains are calculated with the ML estimator. The algorithm is a one-dimensional search scheme and therefore greatly decreases the complexity of joint ML estimation, which is essentially a multi-dimensional search scheme.

    Yong ZENG, Jianfeng MA

    Designing reliability differentiated services for missions with different reliability requirements has become a hot topic in wireless sensor networks. Combined with a location-based routing mechanism, a quantified model without full network topology is proposed to evaluate reliability. By introducing a virtual reference point, the data transfer is limited in a specified area. The reliability function of the area is given. A detailed analysis shows that the function increases quadratically with the distance between the source node and the reference node. A reliability differentiated service mechanism is then proposed. The simulation results show the efficiency of the proposed mechanism.

    Yong XU, Yinghua LV, Biao YANG, Hongxin ZHANG

    High-speed broadband power line communication (BPL) is a novel and practicable technique for Net-atHome or home area local area networking (LAN). Because of the characteristics of BPL, the electromagnetic wave emitted from the BPL transmission media will influence the indoor electromagnetic environment, which would also affect the performance of other wireless communications. Based on the analysis of the communication channel characteristic, network impedance and attenuation characteristic of the BPL, this paper proposes a novel model for calculating the BPL radiation and the computer simulation model, which are proved by the coherence of the simulation and the test data. The interferences from the high-speed BPL to indoor wireless communications are analyzed to stipulate the standards of high-speed BPL in the future.

    Fang HE, Zhengyu ZHAO

    A two-dimensional Ohm heating theoretic model in the magnetizing ionosphere and a ray-tracing model in a discrete ionosphere background are used to analyze quantitatively the characteristics (mainly the Doppler shift and the phase shift) of the over-the-horizon radar (OTHR) wave, which propagates through the ionospheric region heated by high frequency radio wave. The simulation results about the Doppler and the phase shift are obtained within two minutes after the heater is on. Preliminary conclusions are given by comparing the numerical results with experimental data.

    Ming YAN, Gang LEI, Xiwei HU, Keran SHAO

    In this article, a novel and normalized Z-transform finite-difference time-domain (ZTFDTD) method is presented. This method uses a more general form of Maxwell’s equations using the BoldItalic, BoldItalic, BoldItalic fields. The iterative model of BoldItalic-BoldItalic-BoldItalic-BoldItalic can be obtained by using the Z-transform resulted frequency-dependent formula between BoldItalic and BoldItalic. The advantages of the ZTFDTD consist in that the discrete equations are simple, the results are precise, easy to program and capable of dealing with the key technologies of finite-difference time-domain (FDTD), such as absorbing boundary conditions (uniaxial anisotropic perfectly matched layer, UPML) and near-to-far-field transformation. The ZTFDTD method is then used to simulate the interaction of electromagnetic wave with plasma. Using a simplified two-dimensional model, the stealth effect of inhomogeneous, unmagnetized plasma is studied both in different electron densities of plasma, different electromagnetic wave frequencies and different plasma collision frequencies. The numerical results indicate that plasma stealth is effective in theory and a reasonable selection with the plasma parameters that can greatly enhance the effectiveness of plasma stealth.

    Gang WU, Huiling WANG, Jiangbo XIE, Yan ZHAO, Yuejin TANG, Jindong LI

    China’s first 35 kJ high temperature superconducting magnetic energy storage (SMES) system with an experiment equipment was depicted. The dynamic heat analysis of the magnet of the SMES was conducted through the current load test on the directly cooled conduction magnet. The research results were as follows: when the converter charges and discharges the magnet for energy storage, the hysteresis loss is the main part of power loss, and contributes significantly to temperature rise; reducing the current frequency at the side of direct current is conducive to restraining temperature rise. The optimizing factors of the cool-guide structure were analyzed based on the heat stability theory, and it was found that the heat transfer of its key part (at the top of the magnet) must be strengthened to reduce the axial temperature difference of the magnet.

    Shouxiang WANG, Zhijie ZHENG, Chengshan WANG

    The Taylor model arithmetic is introduced to deal with uncertainty. The uncertainty of model parameters is described by Taylor models and each variable in functions is replaced with the Taylor model (TM). Thus, time domain simulation under uncertainty is transformed to the integration of TM-based differential equations. In this paper, the Taylor series method is employed to compute differential equations; moreover, power system time domain simulation under uncertainty based on Taylor model method is presented. This method allows a rigorous estimation of the influence of either form of uncertainty and only needs one simulation. It is computationally fast compared with the Monte Carlo method, which is another technique for uncertainty analysis. The proposed method has been tested on the 39-bus New England system. The test results illustrate the effectiveness and practical value of the approach by comparing with the results of Monte Carlo simulation and traditional time domain simulation.

    Huaisheng WANG, Mingxiang WANG, Zhenyu YANG

    The temperature distribution of typical n-type polycrystalline silicon thin film transistors under self-heating (SH) stress is studied by finite element analysis. From both steady-state and transient thermal simulation, the influence of device power density, substrate material, and channel width on device temperature distribution is analyzed. This study is helpful to understand the mechanism of SH degradation, and to effectively alleviate the SH effect in device operation.

    Weilian GUO, Shilin ZHANG, Xin YU

    In this paper, using a δ-doping dual-channel structure and GaAs substrate, a real space transfer transistor (RSTT) is designed and fabricated successfully. It has the standard Λ-shaped negative resistance I-V characteristics as well as a level and smooth valley region that the conventional RSTT has. The negative resistance parameters can be varied by changing gate voltage (VGS). For example, the PVCR varies from 2.1 to 10.6 while VGS changes from 0.6 V to 1.0 V. The transconductance for IP (ΔIP/ΔVGS) is 0.3 mS. The parameters of VP, VV and threshold gate voltage (VT) for negative resistance characteristics arising are all smaller than the value reported in the literature. Therefore, this device is suitable for low dissipation power application.

    Yichao MA, Heming CHEN

    This article designs a novel type of non-bravais lattice photonic crystal fiber. To form the nesting complex-period with positive and negative refractive index materials respectively, a cylinder with the same radius and negative refractive index is introduced into the center of each lattice unit cell in the traditional square lattice air-holes photonic crystal fiber. The photonic band-gap of the photonic crystal fiber is calculated numerically by the plane wave expansion method. The result shows that compared with the traditional square photonic band-gap fiber (PBGF), when R/Λ is 0.35, the refractive index of the substrate, air-hole, and medium-column are 1.30, 1.0, and -1.0, respectively. This new PBGF can transmit signal by the photonic band-gap effect. When the lattice constant Λ varies from 1.5 μm to 3.0 μm, the range of the wavelength ranges from 880 nm to 2300 nm.