Abstract: In GPS(Global Positioning System)/INS(Inertial Navigation System) ultratight coupling system, the tracking performance of satellite signal depends directly on the bandwidth of carrier tracking loop. In order to improve the computation accuracy of optimal bandwidth, on the basis of analyzing the tracking characteristics of INSassisted PLL(Phase Locked Loop), the deduction of the assisting error of carrier Doppler shift and its rate of change was performed, and the loop tracking error model aided by INS was established. With the realtime estimation of tracking carriertonoise ratio, the discrete secondorder Newtonian iterative method was applied, and the optimal bandwidth was calculated and adjusted in real time. The simulation results show that the optimal bandwidth iterative method achieves 99.6% accuracy in 11 iterations. When the optimal bandwidth is used as the real time bandwidth of the loop, the tracking accuracy of the loop can be effectively improved under the condition of weak signal and low assisting information accuracy.

Key words: ultra tight integration system, GPS receiver, iterative solution, optimal bandwidth, signal tracking