A novel tight GPS/INS coupling concept was developed using adaptive higher-order GPS carrier tracking loops, enabled by the INS, which provide increased jamming immunity and robust tracking during high vehicle dynamics. Figure 1 shows a simulated missile flight in a typical jamming environment. In a GPS receiver, the carrier tracking phase-lock loop (PLL) is by far the most critical element in determining the performance and maintaining fidelity of GPS position measurements. Wide loop bandwidths are needed in the PLL to track the carrier signal for high vehicle dynamics, while narrow loop bandwidths are needed to suppress interfering jamming noise. Utilizing Inertial Measurement Units (IMU) or full Inertial Navigation System (INS) with GPS has shown some promise in improving the ability of a GPS receiver to maintain lock with GPS carrier signals during high flight dynamics without the need to increase the PLL bandwidth. However, many current techniques for combining GPS and INS information suffer from an excessive sensitivity to the noise and drift of the inertial sensors. The adaptive tight GPS/INS coupling architecture developed under this research increases the order of the carrier PLL based on INS inputs such that the loop can properly track the carrier dynamics. To reduce the dependence on the inertial sensor noise, the INS is not allowed to force the loop to change frequency as in traditional tight coupling algorithms unless, of course, the PLL loses phase lock completely. The two key features of the adaptive ultra-tight concept include INS enabling of the higher-order loop coefficients and calibration of the INS sensors during locked conditions
Figure.1: Example scenario for GPS navigation in the presence of RF jamming
Research Assistants:
- Christof Hamm
- Warren Flenniken
Sponsors:
- PhaseIV Systems Inc. (through a Phase I MDA STTR)
Publications: