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531.
Chengeng Su Shuren GuoHongwei Zhou 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
CPM (continuous phase modulation) has been widely used in the field of satellite communication, which has high spectrum efficiency and constant envelope. This paper explores the applicability of CPM to satellite navigation. A SS-CPM (Spread-Spectrum CPM) modulation is investigated. The SS-CPM with tuned parameters can resemble the spectrum of Binary Offset Carrier (BOC) modulation and yields comparable performance in terms of tracking accuracy, multipath mitigation, anti-jamming, and compatibility. The BOC-like SS-CPM signal maintains the constant envelope at transmission and less out-band emission in radio determination satellite service (RDSS) band, which provides a reference modulation for COMPASS satellite navigation signal. 相似文献
532.
Ali Mahmoud Samy Elbialy Biswajeet Pradhan Manfred Buchroithner 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The present study aims to evaluate the field-based approach for the classification of landcover using high-resolution SAR data. TerraSAR-X (TSX) strip mode imagery, coupled with digital ortho-photos (DOPs) with 20 cm spatial resolution was used for landcover classification and parcel mapping respectively. Different filtering and analysis techniques were applied to extract textural information from the TSX image in order to assess the enhancement of the classification accuracy. Several attributes of parcels were derived from the available TSX images in order to define the most suitable parameters discriminating between different landcover types. Then, these attributes were further statistically analysed in order to define separability and thresholds between different landcover types. The results showed that textural analysis resulted in high classification accuracy. Hence, this paper confirms that integrated landcover classification using the textural information of TerraSAR-X has a high potential for landcover mapping. 相似文献
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Interval-valued data and incomplete data are two key problems for failure analysis of thruster experimental data and have been basically solved by the proposed methods in this paper. Firstly, information data acquired from the simulation and evaluation system formed as intervalvalued information system (IIS) is classified by the interval similarity relation. Then, as an improvement of the classical rough set, a new kind of generalized information entropy called "H'-information entropy" is suggested for the measurement of uncertainty and the classification ability of IIS. There is an innovative information filling technique using the properties of H'-information entropy to replace missing data by some smaller estimation intervals. Finally, an improved method of failure analysis synthesized by the above achievements is presented to classify the thruster experimental data, complete the information, and extract the failure rules. The feasibility and advantage of this method is testified by an actual application of failure analysis, whose performance is evaluated by the quantification of E-condition entropy. 相似文献
535.
在电机高速弱磁或过载要求高的情况下,需要通过脉冲宽度调制(PWM)的过调制运行提高直流母线电压利用率。基于磁链观测的无传感器永磁同步电机矢量控制(磁场导向控制,FOC)技术具有算法简单、易实现等优点,但在过调制的情况下电压限幅环节会引起磁链观测及转子位置角估算误差。为提高PWM过调制情况下系统的控制性能,对传统的FOC控制框图进行了改进,省去了电压限幅环节并利用由占空比计算的实际电压对定子磁链进行估算。MATLAB仿真验证了改进方法的有效性。研究结果表明:该方法充分利用PWM调制自有的限幅特性,既能简化控制算法又能提高磁链观测精度,具有较好的技术经济性能。 相似文献
536.
探索了一种基于对应分析的限寿件锻造关键工艺参数的分级方法。以涡轴发动机钛合金压气机轮盘坯料锻造关键工艺参数为研究对象,以可能存在的内含缺陷三维尺寸数据为目标,通过加工过程数值仿真与对应分析法结合,辨识关键工艺参数并分级。结果表明:该分级方法下,温度对缺陷三维尺寸的影响随着其变化程度的增加先增加后减少,应变率、变形率对缺陷三维尺寸的影响随着其变化程度的增加而单调递增,摩擦系数的影响可以忽略。 相似文献
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永磁同步曳引机是典型的非线性多变量强耦合系统,在同步旋转坐标系下dq轴电流存在耦合,传统的PI控制器无法实现解耦,提出一种基于内模控制原理和空间矢量算法相结合的高性能永磁同步曳引机解耦控制方法,用内模控制策略控制理想电机模型,对定子电流交叉耦合电势动态解耦,提高系统的动态响应性能,同时在整个电流闭环过程中对参数摄动和外扰动具有良好的鲁棒性,这种方法不需要额外的电机参数和检测硬件,试验结果验证了这种方法有效可行。 相似文献