Adaptive GNSS Carrier Tracking Under Ionospheric Scintillation: Estimation vs. Mitigation

Jordi Vila-Valls,Jose A Lopez-Salcedo,Gonzalo Seco-Granados,Pau Closas,Carles Fernandez-Prades

doi:10.1109/lcomm.2015.2415789

Abstract

This letter deals with carrier synchronization in Global Navigation Satellite Systems. The main goals are to design robust methods and to obtain accurate phase estimates under ionospheric scintillation conditions, being of paramount importance in safety critical applications and advanced receivers. Within this framework, the estimation versus mitigation paradigm is discussed together with a new adaptive Kalman filter-based carrier phase synchronization architecture that copes with signals corrupted by ionospheric scintillation. A key point is to model the time-varying correlated scintillation phase as an AR(p) process, which can be embedded into the filter formulation, avoiding possible loss of lock due to scintillation. Simulation results are provided to show the enhanced robustness and improved accuracy with respect to state-of-the-art techniques.

Highlights

T HE vast deployment of Global Navigation Satellite Systems (GNSS) receivers in personal electronic devices and new scientific/industrial applications are pushing the limits of traditional receiver architectures, which were initially designed to operate in clear sky, benign propagation conditions
Conventional carrier synchronization architectures rely on traditional well established phase-locked loops (PLLs), which have been shown to deliver poor performances or even fail under severe propagation conditions [2] because of the noise reduction versus dynamic trade-off
Simulation results are provided to support the discussion and to show the improved accuracy. Note that this contribution generalizes the results presented in [8], [9], where a standard Kalman filter (KF) and an AR(1) model was used considering an almost static user scenario and fully known KF characterization, being of limited applicability for the advanced GNSS receivers of interest here

Summary

INTRODUCTION

T HE vast deployment of Global Navigation Satellite Systems (GNSS) receivers in personal electronic devices and new scientific/industrial applications are pushing the limits of traditional receiver architectures, which were initially designed to operate in clear sky, benign propagation conditions. Where k stands for the discrete time tk = kTs, Ak is the signal amplitude at the output of the correlators after accumulation over Ts, the amplitude αk may include the scintillation amplitude effects, αk = Akρs,k; the carrier phase includes both the phase variations due to the receiver’s dynamics, θd,k, and the scintillation phase variation, θs,k, θk = θd,k + θs,k; and the Gaussian measurement noise is nk ∼ N (0, σn2,k) Notice that both phase contributions, θd,k and θs,k, are independent, which allows to build the following state-space model. Modern mass-market receivers implement a 3rd order PLL, which implicitly assume a 3rd order Taylor approximation of the phase evolution, to obtain a fair comparison this is the case considered to construct the KF state-space model, θk = θ0 + 2π fd,k kTs. where θ0 (rad) is a random constant phase value, fd,k (Hz) the carrier Doppler frequency shift and fr,k (Hz/s) the Doppler frequency rate (i.e., the Doppler dynamics).

COMPUTER SIMULATIONS AND DISCUSSION

CONCLUSION