GPS/INS/Pseudolite Integration: Concepts, Simulation and Testing

Traditionally, Inertial Navigation Systems (INS) provide positioning and attitude information for the guidance (and perhaps control) of a wide range of moving platforms in the air, at sea, or on the ground. However, the timedependent growth of systematic errors is a major concern in INS applications. Precise satellite measurements are ideally suited for the calibration of INS systematic errors. Therefore, integrated INS and GPS (and/or Glonass) systems have been developed, which can provide highrate precise positioning and attitude information. The major drawback of existing systems is that their performance decreases under difficult operational conditions, for example when satellite signals are obstructed for extended periods of time. In the worst situations, such as underground and inside buildings, the satellite signals may be completely lost. In circumstances where satellite signals are unavailable, it may be possible to maintain availability of range measurements for use in calibrating the INS systematic errors by placing 'pseudosatellites' (pseudolites) at appropriate locations. Thus, an augmentation of existing systems with ranging signals from ground-based pseudolites would result in a new design that could address the problems of signal availability. In fact, integrated GPS/INS/Pseudolite systems are, in principle, an ideal option for seamless indoor-outdoor positioning and attitude determination. This paper discusses the concept of GPS/INS/Pseudolite integration in detail. Both system performance simulation and experimental results are presented to demonstrate the feasibility of such an integrated system.