Abstract
Weak-signal and high-dynamics are of two primary concerns of space navigation using GNSS (Global Navigation Satellite System) in the space service volume (SSV). The paper firstly defines a reference assumption third-order phase-locked loop (PLL) as the baseline of an onboard GNSS receiver, and proves the incompetence of this conventional architecture. Then an adaptive four-state Kalman filter (KF)-based algorithm is introduced to realize the optimization of loop noise bandwidth, which can adaptively regulate its filter gain according to the received signal power and line-of-sight (LOS) dynamics. To overcome the matter of losing lock in weak-signal and high-dynamic environments, an open loop tracking strategy aided by an inertial navigation system (INS) is recommended, and the traditional maximum likelihood estimation (MLE) method is modified in a non-coherent way by reconstructing the likelihood cost function. Furthermore, a typical mission with combined orbital maneuvering and non-maneuvering arcs is taken as a destination object to test the two proposed strategies. Finally, the experiment based on computer simulation identifies the effectiveness of an adaptive four-state KF-based strategy under non-maneuvering conditions and the virtue of INS-assisted methods under maneuvering conditions.
Highlights
The demand for reducing the burden of ground TT&C (Tracking, Telemetry and Command) stations and surveying vessels stimulates the development of precise orbit and attitude determination using GNSS
phase-locked loop (PLL) structure as the baseline of state-of-art; in Section 3, a four-state Kalman filter (KF)-based signal tracking method is presented which can adjust the equivalent loop noise bandwidth (LNBW) adaptively; Section 4 depicts the architecture of the inertial navigation system (INS)-assisted open loop design, and further proposes the non-coherent maximum likelihood estimation (MLE) algorithm applied in the architecture
To improve the loop performance in weak-signal and high-dynamic environments, we introduce the state of code phase error and extend the three-state to four-state
Summary
The demand for reducing the burden of ground TT&C (Tracking, Telemetry and Command) stations and surveying vessels stimulates the development of precise orbit and attitude determination using GNSS. The loop of SSV RRAM is likely to lose its lock in harsh environments, for instance, when the C/N0 is lower than 30 dB-Hz and the jerk is over 4 m/s3 at the same time Owing to this reason, an adaptive four-state Kalman filter (KF)-based algorithm is presented with the intention of maximizing the signal processing performance of closed loop (CL) form. An INS-assisted open loop tracking strategy is another effective method to find the true signals with high dynamics and high noise level [11] All of these methods are derived on the basis of some assumption that disregarding the coupling effect between the carrier phase and Doppler frequency. PLL structure as the baseline of state-of-art; in Section 3, a four-state KF-based signal tracking method is presented which can adjust the equivalent LNBW adaptively; Section 4 depicts the architecture of the INS-assisted open loop design, and further proposes the non-coherent MLE algorithm applied in the architecture.
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