The adaptive combined receiver tracking filter design for high dynamic situations

Although the carrier Doppler and the code Doppler are generated by the same relative movement between the satellite and the user, often, the each tracking loop are designed separately and independently. For better GPS signal tracking performance, we need to design the PLL/FLL/DLL altogether optimally. So this paper uses a combined receiver tracking filter, which is the extended Kalman filter to track the C/A code and the carrier frequency together. However this combined receiver tracking filter shows a degraded performance under high dynamic situations because the Doppler frequency changes faster with time. To solve this problem, this paper proposes an adaptive combined receiver tracking filter using an adaptive two-stage extended Kalman filter, which can adapt to an incomplete model and a quickly changed bias. An adaptive combined receiver tracking filter gives a solution for the nonlinear system with the unknown random bias on the assumption that the stochastic information of the random bias is incomplete. The proposed adaptive combined receiver tracking filter has a strong tracking ability to the suddenly changing bias and has acceptable computational complexity. The performance of an adaptive combined receiver tracking filter is verified by simulation.