Search

The satellite signals are always blocked by obstructions in urban canyons, therefore multi-constellation global navigation satellite system (GNSS) performs poor. Quantitative comparison of the performance of different satellite navigation systems can provide a basis to analyze their advantages and disadvantages. This paper proposes a fuzzy comprehensive evaluation (FCE) theory to quantitatively evaluate the performance of GNSS, and systematically puts forward how to quantitatively analyze precision, availability, continuity and integrity. A simulation was conducted to emulate the environment of urban canyons. Evaluation results show the performance of BDS is neck and neck with GPS, and much better than GLONASS. A multisystem has better performance than a single system. GPS+GLONASS+BDS has the best performance and gets a high FCE result of 0.3268, while the FCE result of GPS, BDS and GLONASS are 0.1722, 0.1570 and 0.0970 respectively.

To solve the problem of the least squares estimation does not have the ability to resist the gross errors in global navigation satellite system (GNSS), the theory of robust least squares estimation is introduced, three methods (Huber, IGG, IGGIII) to construct the equivalent weight are expounded and the determination of initial parameter of the equivalent weight is discussed. The results of simulation based on GPS/BDS multi-constellation show that the robust least squares estimation can ensure the accuracy of navigation and positioning effectively, the estimator with IGGIII equivalent weight method presents optimal solutions, furthermore the performance of the robust estimation method based on median parameter estimate is better than the individual robust estimation.

Urbanization is one of the most concerned trends in the world. But until now, the impacts of urbanization on the spatial patterns of alien plants remain little known. In this paper, the impacts of urbanization on the spatial patterns of alien plants in Yunnan were investigated. The results indicated that urban population, transportation mileage and their density all significantly correlated with spatial pattern of species diversity of alien plants. There were significant correlations between proportions of alien plants among all plant species and transportation density, urban population density. Step-wised regression analysis showed that transportation density played stronger roles in the spreading of alien species. Urbanization may not only shape the spatial patterns of alien plant diversity but also that of local plant composition. With the explosive development of urbanization in the study area, we should premeditate the potential of spreading or invasion of alien plants.

The dynamic characteristics of missile vary substantially with flight conditions such as flight Mach number, altitude and angle of attack. Therefore, in order to achieve adequate levels of robustness and performance, a controller that also varies during operation has to be designed in missile control. This paper is concerned with the application of advanced mixed linear parameter-varying (LPV)/\mu techniques to global control of a missile. The techniques can produce an H \infty based LPV controller, which is automatically "gain scheduled" with respect to the flight conditions and adapts to the variation of the missil'se dynamic characteristics. The power and effectiveness of the resulting controller are demonstrated by nonlinear simulations.

A mixed linear parameter-varying (LPV)/μ technique is applied to global control of an air defense missile. The technique is a direct extension of μ-synthesis that additionally incorporates the gain-scheduling task and makes the time-varying nature of the plant be explicitly taken into account. By use of the technique, an LPV controller is designed based on a model matching control structure. The controller is automatically "gain scheduled" with respect to the flight Mach number and altitude and therefore adapts to the variation of the missile's dynamic characteristics. The power and effectiveness of the resulting controller to handle the global robustness and performance of the missile over its entire operation range are verified by nonlinear simulations. The research results appear to be sufficiently promising to warrant further study of this approach for applications to missile control.