INS-Assisted High Sensitivity GPS Receivers for Degraded Signal Navigation

This paper proposes a novel architecture for ultra-tight integration of a High Sensitivity Global Positioning System (HSGPS) receiver with an Inertial Navigation System (INS), to address the issue of GPS tracking and positioning in degraded signal environments. By enhancing signal tracking loops in receivers through the use of optimal controllers/estimators and aiding from external source such as INS, the capabilities of the GPS receiver can be enhanced to provide the positioning in indoor and urban canyon environments. The proposed approach is distinct from the commonly used ultra-tightly coupled GPS/INS approaches, and absorbs different tracking enhancement technologies used in typical HSGPS receivers, multi-channel co-operated GPS receivers and the current ultra-tightly coupled GPS/INS methods. The method consists of three loops in signal tracking: sophisticated conventional Delay Lock Loops (DLL) and Phase Lock Loops (PLL) in all individual signal tracking channels, external INS aiding loop and multi-channel cooperated tracking loop, namely CO-OP loop. The signal tracking strategy is described, with specific focus on the discussion of the role of CO-OP loop in the developed ultra-tightly coupled GPS/INS. Furthermore, the effect of inertial measurement unit (IMU) quality and the effect of receiver oscillator noise and coherent integration time on weak signal tracking are also analyzed in this paper. To perform ultra-tight integration, an INS simulator is developed, and static and dynamic field tests were simulated to analyze the system performance. The test results show that, the designed INS-aided GPS receiver can track the incoming weak GPS signals down to 15 dBHz without carrier phase locked, or 25 dB-Hz with carrier phase locked. When there are multiple strong GPS signals in view, the other weak signals can be tracked down to 15 dB-Hz with carrier phase locked.