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With the development of GNSS technique, the application area of GNSS has been broadened widely. As a result, high sensitivity receiving and positioning technique attracts more and more attention. In those complex communication environment, like indoor, montains or streets, satellite signals become weak and unstable, which brings great trouble to GNSS positiong. This thesis aims to focus on several key techniques in high sensitivity positioning.According to the features and scenarios of GNSS weak signals, the thesis analyzes several key techniques of HS positioning, including UKF algorithm, Doppler-aided pseudorange smoothing algorithm, as well as information processing under short-time singal missing condition. The orgnization of this thesis is as follows:(1) Introduced traditional theories and algorithms of GNSS PVT resolution, including GNSS receiver measurements, iteration algorithm of local postion calculation, satellite orbit theory for satellite position calcalation and carrier phase smoothing pseudorange theory.(2) Presented processing procedure for GNSS PVT resolution, discussed two main methods of satellite position calculation, analyzed LS and EKF algorithm, in terms of precision accuracy and convergence performance, followed by a comparision of two filter algorithms.(3) Based on the feature of weak signals, applied UKF algorithm in GNSS PVT resolution, made a comparison with EKF and analyzed the influence of visible satellite numbers; proposed Doppler-aided psedorange smoothing technique, which greatly improved positioning accuracy when carrier phase got missing in weak signal environment; did research on information processing technique in the condition of short-time signal missing, and several feasible proposals were mentioned. (4) Introduced DOP theory to present positioning accuracy, and deduced its dicisive factors. Results showed measurement accuracy and satellite geometric distribution determined final positioning accuracy. Finally, introduced application and prospect of GNSS technique.
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