Research On Tracking Loop Of High Dynamic Satellite Navigation Receiver

The acquisition and tracking of satellite signals are two important links of navigation receiver.The key to correctly calculating satellite navigation information is the accurate tracking of satellite signals.The paper will complete the design of tracking loop of satellite navigation receiver with the help of B1 frequency point of Beidou system.Firstly,the structure of satellite navigation system,the structural characteristics of satellite signals and the influence of high dynamic on the tracking loop are analyzed.Secondly,the working principle and filter characteristics of 1-3 order loop filters commonly used in carrier tracking loops are analyzed.In order to cope with the high dynamic environment,the fourth-order loop filter,which is one order higher than the third-order loop,is mainly studied,and on the basis of which the third-order frequency locked loop(FLL)auxiliary fourth-order phase locked loop(PLL)filter is built.The second-order loop filter is used in the code tracking loop filter,which is assisted by carrier loop.Finally,the tracking errors of the two loops are analyzed.The code loop can eliminate most of the dynamic effects with the assistance of the carrier loop,so the carrier loop is particularly important for highly dynamic receivers.The carrier tracking loop is improved in two ways: first,the optimal bandwidth of the loop is solved according to the dynamic tracking error of the loop,and the optimal bandwidth of the loop is dynamically adjusted by judging the set phase decision factor.Second,the principle of four-phase frequency discriminator is analyzed,and the switching between the four-phase frequency discriminator and the optimal bandwidth adjusted carrier tracking loop is realized by setting and judging the frequency decision factor.Simulation results show that,in a high dynamic environment,compared with a fixed bandwidth tracking loop,the carrier tracking loop based on the optimal bandwidth adjustment has higher accuracy and more stability,the phase locking time is improved by2/3,and it has more advantages under low carrier-to-noise ratio.When the carrier-to-noise ratio is low,the dynamic environment is unstable or the initial Doppler frequency entering the loop is large,the bandwidth adjustment carrier tracking loop assisted by frequency discriminator has more advantages than the traditional carrier tracking loop.Finally,the tracking loop is designed on the ZYNQ platform.The feasibility of the whole loop is verified,and the final experimental results show that the algorithm is feasible.