High-Sensitivity GNSS Doppler and Velocity Estimation for Indoor Navigation.

摘要

Doppler measurements in global navigation satellite system (GNSS) receivers are useful for various purposes since they not only convey velocity and attitude information, but also directly relate with carrier phase measurements. When it comes to poor signal conditions, conventional high sensitivity GNSS receivers usually extend integration time in order to maintain track of weak GNSS signals. However, due to low signal-to-noise ratio (SNR) and multipath effects, the navigation accuracy is still degraded in this case. Thus maintaining track of Doppler frequency with acceptable accuracy in challenged indoor environments is important and will be beneficial for both standalone and integrated solutions. This thesis investigates how to obtain more reliable and robust Doppler frequency and velocity estimates with GNSS signals for indoor navigation.;Doppler errors due to indoor multipath and user dynamics are first investigated. Experimental results show that these errors are further affected by some multipath statistics such as averaged multipath angle of arrivals (AOAs). A directional signal/multipath model is thus developed to characterize such errors.;To mitigate the adverse effects brought by multipath signals, a direct vector receiver with GLONASS capability is therefore proposed and developed. It is shown that when the user has partial visibility of line-of-sight (LOS) satellite signals, both the velocity and Doppler estimation accuracy is improved as compared to conventional high sensitivity receivers. Geometry dependent factors are defined and used to quantify such improvements.;Finally, the benefits of using such Doppler measurements for consistent navigation are evaluated in two real indoor environments. Doppler measurements from both direct vector receiver and conventional high sensitivity receiver are tightly integrated with a PDR algorithm. Results show that in large open space indoor environments, the former integration strategy significantly improves the navigation accuracy. For office like indoor environments, improvements of the former integration strategy are not very apparent, but still outperform the conventional integration strategy. All these indicate that the quality of Doppler estimated by direct vector receiver is as good as or better than the conventional one for the indoor environments considered herein.