Performance Analysis of Software Based GPS Receiver Using a Generic Ionospheric Scintillation Model

L. Dyrud, N. Bhatia, S. Ganguly, A. Jovancevi

Abstract:	Scintillations in trans-ionospheric radio signals arise as the signal propagates through naturally occurring plasma irregularities. If the receiver, satellite, or ionospheric irregularities are in motion, a time series of signal fading and phase fluctuations will occur at the receiver. It is well known that diffraction of the radio phase front produces amplitude and phase fluctuations even at GPS frequencies. The statistical characterization of the degree of amplitude fluctuation is known as S4 while the Gaussian width of phase fluctuations is known as óö. Yet, these statistical characterizations are insufficient for properly understanding the time series of scintillated signals at all scales. Adequate understanding of the effects of scintillations on GPS signals is essential to making a GPS receiver immune to the degradation of scintillation effects under a full range of conditions, and to understanding the remote sensing capabilities of GPS measurements of ionospheric scintillations. The software based receiver developed by the Center for Remote Sensing, Inc. gives the user the flexibility to easily monitor these effects and facilitates advanced development of receivers under different conditions. In this paper we present the results of an analysis of GPS signals under varied simulated scintillation conditions. In order to produce a time series scintillation signal that takes into account actual motions of receiver, satellite and irregularity drift, we constructed realistic models of GPS satellite motion. Further, the model allows for realistic motion of a scintillation phase screen that represents ionospheric drift and irregularity evolution. These models are then used to produce realistic simulated time series of scintillated GPS signals. These synthesized signals are then fed to our software receiver, which allows us to characterize the amplitude fading and phase fluctuation effects caused by scintillation on the tracking loop performance for both L1 and L2 frequencies. Producing realistic, as opposed to statistical, time series of scintillated signals is critical to precisely understanding the conditions under which scintillations cause the receiver to lose lock, and other important effects. An example of such is if the ionospheric drift has similar motion to the apparent motion of the satellite, which could produce extend periods of deep fading or vice versa. Such situations produce non statistical results and can only be examined with a time series model. In this paper, we also suggest some improvements that could be introduced in the receiver algorithms in order to mitigate the scintillation effects. Finally, spaced GPS receivershave been used by a number of researchers to study ionospheric drifts. This realistic time series method demonstrates important results that allow for optimizing the use of GPS scintillation signals for remote sensing ionospheric drift in either high or low latitude regions.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	1402 - 1412
Cite this article:	Dyrud, L., Bhatia, N., Ganguly, S., Jovancevi, A., "Performance Analysis of Software Based GPS Receiver Using a Generic Ionospheric Scintillation Model," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 1402-1412.
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