Study On Carrier Loop Tracking Algorithm Of IMU-assisted GPS Receiver

Navigation and positioning technology develops as people’s demands increasing, especially the Global Navigation Satellite System is wildly used in human society. As national defense industry and aerospace field requiring satellite navigation to content more difficult application, facing the high dynamic situation and low SRN circumstance, the conventional GPS receiver technology shows it’s bottle-neck. In order to expand the application of satellite navigation, developing ultra-tight integration technology becomes an effective method to break through the bottle-neck. In the process of ultra-tight integration technology research, the algorithm of INS-assisted carrier tracking loop is an important part. Aiming at the needs of high dynamic situation and low SRN circumstance, this paper mainly researches on utilizing the velocity and accelerate of IMU to assist the GPS receiver’s carrier tracking loop with tracking GPS signal. This paper’s main contributions are embodied in the following aspects:1. In the process of GPS receiver tracking with IMU’s velocity aiding under high dynamic circumstance, because of the discretization of IMU’s velocity output, the rapidly changing control quantity for NCO makes the loop tracking unstable or even lose lock. This paper simulates the process of losing lock when the loop tracks specific signals with MATLAB, and a method, which is tracking loop with IMU’s acceleration and velocity information aiding based on self-adaptive control, is proposed. Theoretical analysis and simulated result of experiment indicates that this method, comparing with the traditional velocity aiding method, reduces GPS receiver’s dynamic stress error effectively and makes the loop hard to lose lock. Redesign the carrier tracking loop’s parameters, the loop’s bandwidth is reduced from 20 Hz to 5Hz. The new loop is analyzed and simulated result shows that it still has satisfactory dynamic performance.2. Build the system’s physical platform. Design the entire structure of the system, an integrate scheme of GPS receiver and IMU based on DSP/FPGA is designed. The IMU module with it’s data acquisition circuit is built, the performance of GPS receiver module used in this paper is analyzed and so as it’s radio frequency unit, the above-mentioned activities establish the foundation of two subsystems’ integration. The FPGA program including IMU data acquisition, bus communication with DSP and the UART module is designed with Quartus II, the DSP program including system initialization, IMU navigation solution, data fusion of subsystems and the tracking algorithm of FLL+PLL carrier tracking loop assisted with IMU’s velocity and accelerate is designed with CCS.3. Experiments of high dynamic semi-physical simulation and low SRN circumstance are carried out. High dynamic semi-physical simulation experiment simulate the IMU-assisted carrier tracking loop’s performance under the high dynamic environment of 58.3g linear acceleration, 3.813 m s jerk, the results indicate that the receiver can track the satellites’ signal well and won’t lose lock. Low SRN experiment of 5Hz bandwidth loop with IMU aid shows that the minimum SRN of normally tracking and recapture is 28.3 d B, which promotes about 8d B noise performance compared with 20 Hz bandwidth loop without IMU aid, whose minimum SRN is 36.5d B.