GPS/Pseudolite/SDINS Integration Approach for Kinematic Applications

This paper discusses the introduction of pseudolites (ground-based GPS-like signal transmitters) in existing integrated GPS/INS systems in order to provide higher availability, integrity and accuracy in a local area. Even though integrated GPS/INS systems can overcome inherent drawbacks of each component system (line-ofsight requirement for GPS, and INS errors that grow with time), performance is nevertheless degraded under adverse operational circumstances. Some typical examples are when the duration of satellite signal blockage exceeds an INS bridging level, resulting in large accumulated INS errors that are not able to be calibrated by GPS. Such a scenario is unfortunately a common occurrence for certain kinematic applications. To address such shortcomings, both pseudolite/INS and GPS/pseudolite/INS integration schemes are proposed here. Typically the former is applicable for indoor positioning where the GPS signal is unavailable for use. The latter would be appropriate for system augmentation when the number and geometry of visible satellites is not sufficient for accurate positioning or attitude determination. This paper describes some technical issues concerned with implementing these two integration schemes, including the measurement model, and the appropriate Kalman filter for GPS and pseudolite carrier phase measurements. In addition, geometric analyses and the results from the processing of simulated measurements, as well as field experiments, are presented in order to characterize the system performance. It has been established that the GPS/PL/INS and PL/INS integration schemes would make it possible to ensure centimeter level positioning accuracy even if the number of GPS signals is insufficient, or completely unavailable.