Zeynep G. Elmas

On determining spectral parameters, tracking jitter, and GPS positioning improvement by scintillation mitigation

A method of determining spectral parameters p (slope of the phase PSD) andT (phase PSD at 1 Hz) and hence tracking error variance in a GPS receiver PLL fromjust amplitude and phase scintillation indices and an estimated value of the Fresnelfrequency has been previously presented. Here this method is validated using 50 HzGPS phase and amplitude data from high latitude receivers in northern Norway andSvalbard. This has been done both using (1) a Fresnel frequency estimated usingthe amplitude PSD (in order to check the accuracy of the method) and (2) a constantassumed value of Fresnel frequency for the data set, convenient for the situation whencontemporaneous phase PSDs are not available. Both of the spectral parameters(p, T) calculated using this method are in quite good agreement with those obtainedby direct measurements of the phase spectrum as are tracking jitter variances determinedfor GPS receiver PLLs using these values. For the Svalbard data set, a significantdifference in the scintillation level observed on the paths from different satellitesreceived simultaneously was noted. Then, it is shown that the accuracy of relative GPSpositioning can be improved by use of the tracking jitter variance in weighting themeasurements from each satellite used in the positioning estimation. This has significantadvantages for scintillation mitigation, particularly since the method can be accomplishedutilizing only time domain measurements thus obviating the need for the phase PSDsin order to extract the spectral parameters required for tracking jitter determination.

The impact of ionospheric scintillation on the GNSS receiver signal tracking performance and measurement accuracy

The GNSS modernization provides new signal frequencies and satellites which can allow for more accurate methods of monitoring, modeling and mitigating the ionospheric effects on the GNSS applications. In this work, part of the Innovative Navigation using new GNSS SIGnals with Hybridized Technologies (iNsight) project funded by the UK Engineering and Physical Sciences Research Council (EPSRC), the ionospheric scintillation effects (abrupt power fades and phase variations in the received signals) are investigated regarding the GNSS modernization. Analysis of the scintillation effects is done through a simulation-based approach using the Spirent GSS8000 GNSS signal simulator where the signals are perturbed using the Cornell Scintillation Model (CSM). The receiver signal tracking performance is evaluated based on the variance of the code and carrier tracking loop errors using the scintillation-sensitive tracking models [1, 2]. Preliminary results on the User Equivalent Range Error (UERE) on particular receiver-satellite links are investigated to understand the effect of scintillation on the (code-based) range measurements