Xu Liu, Tsinghua University and Beijing Satellite Navigation Center, China; Zheng Yao, Tengfei Wang, Mingquan Lu, Department of Electronic Engineering, Tsinghua University, & Beijing National Research Center for Information Science and Technology, China

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Abstract:

Pseudolites Positioning System (PLPS) is an alternative regional positioning system suitable for GNSS-denied environments due to its advantages of layout flexibility, strong signal power, and high positioning accuracy. However, PLPSs suffer severely from the near-far problem that the non-ideal orthogonality of pseudo-random codes is amplified by the large power difference of received signals. Acquisitions for weak signals can easily fail since the autocorrelation peaks of weak signals are overwhelmed by cross-correlations of strong signals when conventional acquisition algorithms are independently applied to each channel of receivers. The dependencies among synchronization parameters consisting of time delay and Doppler shift of each channel are ignored. Considering the above drawback and exploiting the dependencies that synchronization parameters of all pseudolite signals are related to each other through the same spatiotemporal parameters consisting of the user’s position, velocity and time (PVT), we propose a direct acquisition method in the PVT domain to alleviate the near-far problem. This method combines the energy of all received pseudolite signals by adding up their cross-ambiguity functions (CAFs) to ensure that all signals are used to reduce the uncertainty of PVT and indirectly eliminate interference from strong signals. Finally, acquisitions for synchronization parameters are indirectly achieved by the estimation of PVT. Numerical results have verified the effectiveness of this method and show that the proposed method can achieve successful acquisitions of each signal’s synchronization parameters with required accuracy under the condition that the severe near-far problem fails the existing algorithms. Meanwhile, the maximum likelihood estimation of PVT can be applied to low-precision services or to provide good auxiliary information for tracking loops, ambiguity resolution, and initialization of position determination.