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- Performance of an adaptive partitioned vector tracking algorithm with real scintillation dataPublication . Marçal, José M. S. V.; Nunes, Fernando; Sousa, FernandoVector tracking algorithms have been used in both frequency and code tracking of GNSS signals in the last years with success. Vector phase tracking algorithms still present a challenge due to the order of magnitude of the errors when compared to the wavelength of the carrier wave, especially in situations where strong disturbances are present in one or more satellites. Partitioned vector tracking for carrier phase signals has been used in simulation scenarios with good results. In this work the performance with real scintillation data is shown. Furthermore, an adaptive method with dynamic optimization of the weights in the partitioned vector tracking is included, in order to adjust the tracking structure to the variation of environmental parameters.
- State-space estimation of ionospheric scintillation processes with a static GNSS receiverPublication . Sousa, Fernando; Nunes, FernandoThe determination of the ionospheric scintillation processes that affect the reception of Global Navigation Satellite System (GNSS) signals is an important issue as it permits to monitor the ionosphere for practical and scientific applications and optimize the receiver performance in scintillation-prone scenarios using, for instance, a differential GNSS configuration. We propose an hybrid architecture for the receiver being constituted by a vector tracking block that estimates the receiver's clock drift coupled with an ensemble of extended Kalman filters driven by the prompt correlators that estimate the amplitude and phase of the fading processes. Those processes include as an important case the ionospheric scintillation.
- Generalized gamma fading simulation of scintillation disturbed GNSS signalsPublication . Nunes, Fernando; Sousa, FernandoThe generalized gamma distribution includes as particular cases different well-known distributions, such as the Nakagami-m. We propose a computationally efficient technique to generate correlated time-series with generalized gamma distribution. This method is useful in the simulation of GNSS signals disturbed by ionospheric scintillation. The technique requires only knowledge of two parameters, besides the definition of a model for the amplitude power spectrum.
- Statistical characterization of ionospheric scintillation using a phase-screen modelPublication . Nunes, Fernando; Sousa, Fernando; Marçal, José M. V.A fast technique to simulate the effect of equatorial ionospheric scintillation on GNSS signals was proposed by the authors in a previous work. The algorithm uses a single-layer phase-screen model of the ionosphere and the scintillation is expressed by the Huygens-Fresnel (HF) integral which can be determined analytically. Herein, we characterize statistically the amplitude and phase obtained with the HF integral for different values of the scintillation index S4. A phase unwrapper is also developed to determine the phase from the modulo two-pi version provided by the argument of the HF integral.