Ionospheric Scintillation Effects on GPS Receivers during Solar Minimum and Maximum

The ionosphere has practical importance in GPS (Global Positioning System) applications because it influences transionospheric radio wave propagation. Among various phenomena in the ionosphere, ionospheric scintillation is characterized by rapid fluctuation and fading of the received signal intensity due to electron density irregularity inside the ionosphere. Deep signal fading caused by scintillation can lead to loss of lock of the carrier tracking loop in GPS receivers. The aircraft navigation system based on GPS and WAAS (Wide Area Augmentation System) uses code and carrier phase data to create the position estimate. If a significant number of carrier tracking channels lose lock simultaneously, the system cannot provide service until reacquiring a sufficient number of channels. Although scintillation is not frequent in the mid-latitude region, it is a potential hazard in terms of availability and continuity of the service in the equatorial region [1]. This paper investigates scintillation effects on GPS receivers during solar minimum in the equatorial region. Among four different receivers used for data collection in Brazil, this paper primarily focuses on the scintillation effects on a certified WAAS receiver because it is currently used for aircraft navigation. A maximum of two simultaneous loss of phase locks was observed in 0.05% of epochs. With the given satellite geometry, two satellites loss in a small fraction of time was not a critical problem for navigation. This paper also analyzes solar maximum data collected at Ascension Island during the previous solar maximum period. More satellite channels were affected by scintillation compared to solar minimum, but the maximum number of simultaneous loss of lock in a software receiver was the same as the solar minimum case. One of the most important results of this paper is that instances of simultaneous loss of satellite data can be reduced by minimizing reacquisition time of GPS receivers. Although 20 seconds reacquisition time is allowed by WAAS MOPS (Minimum Operational Performance Standards) [2], this number should be reduced to guarantee enough availability during strong scintillation.