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  • Study of Precise Positioning for stratospheric Airship-based GPS Augmentation System

    Paper number



    Dr. Long Yang, China



    Abstract: Recently some countries have begun conducting feasibility studies and R&D projects on stratospheric airship technology. There have been successful prototype experiments reported. For the airship fly at the altitude of about 20-30km, the construction and maintenance technology is relative low, and its covering scope is much larger compared to ground stations. It can function as a stratospheric platform for applications such as environmental monitoring, communications and broadcasting. If pseudolites (PL) were mounted on the airships, their GPS-like signals would be stable augmentations that would improve the accuracy, availability, and integrity of GPS-based positioning systems because the airship network would cover all of special area. Tsujii and Won have made some researches in the DOP analysis, precise positioning method and tropospheric delay model of the airship-based augmentation system. The accuracy of the pseudolite positions would be a limiting factor for such a service since the PL 'ephemeris error' is more serious than GPS due to the lower height of the airship. In the former studies, the GPS based positioning and inverted GPS positioning methods are proposed and studied. But these two can’t solve the precise positioning problem entirely. When the GPS signal is not available or the satellite number is less than 4, the airship will fail to work for it can’t determine the position of itself. The inverted GPS positioning method is designed to track kinematic platform flying in the sky or the space orbit with a set of receivers on the ground. There are several limit factors for stratospheric airship positioning with inverted GPS. The first one is that a reference station is needed and the line of sight between reference station and all receivers can’t be block by anything. The second is there should be communication network between center control station and all ground receivers. The third, how to ensure all the computed position results are sent by control station is a difficulty problem. Another method that the airship receives the signal transmitted by the ground station network has also been proposed. But the ground stations need to be time synchronized seriously. This is very difficulty and costly for stratospheric airship system.
    The transceiver positioning system is studied in this paper. A network consisted of several ground located transceivers and one transceiver mounted on the airship is used. The ground stations not only receive signal from the airship and make range measurements like inverted GPS but also transmit radio signal to the airship fly in the near space. The airship can also make a range measurement and get the ground stations’ measurements by tracking and demodulating the radio signal. The position computation is done on the airship independently. It become unnecessary for the ground transceiver stations to be synchronized seriously and no reference station is needed. The requirement for construction and implementation of this positioning system is simple. A theoretical analysis is made and involved factors are discussed in detail. A preliminary simulation of the transceiver based positioning method has been conducted in both static and kinematic mode, and a high positioning accuracy in both modes has been demonstrated. In order to simplify the ground station network the inter range measurements between the airships is also used. Simulation results shows that when inter range measurements are available only one ground station below is needed for some special located airships.
    Abstract document


    Manuscript document