Analyzing the Impact of Integrating Pseudolite Observables into a GPS/INS System

Abstract

This paper deals with the issue of incorporating pseudolite measurements into an integrated Global Positioning System/Inertial Navigation System (GPS/INS) positioning and attitude system with a view to improving signal availability, solution reliability, and accuracy in a localized area. Existing GPS/INS systems can overcome inherent shortcomings of each of the navigation technologies (line-of-sight signal requirement for GPS and INS errors that grow with time); therefore, such systems are now used for a wide variety of land, sea, and airborne applications where accurate positioning and/or attitude information is required with high output rate. However, their performance can still be degraded under certain conditions, such as when the duration of satellite signal blockage exceeds a certain time period (related to the quality of the INS), resulting in large accumulated INS errors. Such a scenario is a common occurrence for many kinematic applications. In an integrated GPS/Pseudolite/INS scheme, in order to gain the maximum benefit from additional pseudolite measurements, it is necessary to investigate how pseudolites can best be deployed to complement an existing GPS/INS system. A series of simulations, as well as field experiments with a GPS/Pseudolite/INS system comprising a NovAtel Millennium GPS receiver, an IntegriNautics IN200 pseudolite, and a MIGITS strapdown INS, were carried out, and the impact on performance of integrating pseudolite(s) has been assessed for a variety of operational conditions and different system configurations. The results indicate that the overall performance of the system can indeed be significantly improved using additional pseudolite measurements.