Open Loop Algorithm Based on Circular Distributions for Robust Phase Tracking

GNSS positioning applications expect phase tracking loops to be more and more robust to ensure a user precise positioning in challenging environments such as urban canyons or under ionospheric scintillations. Classical GNSS phase tracking loops, generally based on closed architecture schemes, are not able to meet the expected robustness requirements. Phase tracking suffer from a lack of robustness due to the cycle slips phenomenon resulting from the ambiguous nature of the phase measurements. Closed loops are very sensible to cycle slips due to the presence of the estimation feedback step which propagates errors inside the loop. On the other hand, open loops can perform robust phase tracking in harsh environments because they don't propagate any errors during the recursive phase estimation. This article presents a new open loop architecture for robust phase tracking. By using circular models for phase measurements, the proposed open loop is able to deal with the ambiguous nature of the phase to be tracked. The performances of the proposed architecture had been assessed under low C/N-0 conditions and under ionospheric scintillations. Compared to performances of classical DPLLs, the proposed loop offers a better robustness in terms of loss of lock probability even if results showed that some additional studies are necessary to improve the cycle slips rate.