Fading timescales associated with GPS signals and potential consequences

Abstract

Abstract. The effect of equatorial ionospheric scintillations on the operation of GPS receivers is investigated, with special attention given to the effect of scintillation timescales on the code division multiple access (CDMA) protocol used by GPS. We begin by examining the timescales of scintillation fades modeled as a horizontally drifting pattern whose timescales are determined by the Fresnel length and the drift speed. The model is tested by comparing the speed, determined by dividing the Fresnel length by the autocorrelation time (width), with the speed estimated using spaced receivers, and the two independent estimates of speed are shown to possess a linear relationship. Next we show that the scintillation pattern drift speed is given by the difference of the ionospheric drift and the speed of the GPS signal F region puncture point. When the ionosphere and GPS signal puncture point speeds match, the fade timescales lengthen. Additionally, if the fade depth is adequate, during periods of longer fade times the loss of receiver lock on GPS signals is more likely, as shown in several examples; that is, both larger fade depths and longer fade timescales are required to produce loss of tracking. We conclude by demonstrating that speed matching or resonance between the ionosphere and receiver is most likely when the receiver is moving from west to east at speeds of 40-100 m/s (144-360 km/h). This is in the range of typical aircraft speeds.

Variability of ionospheric scintillation near the equatorial anomaly crest of the Indian zone

“…For the design of receiving systems, important considerations should be the fade margin and adaptive capability of the receiver to maintain the lock condition during the period of scintillation. A study of variability in scintillation interval along with fade depth is important for deciding the adaptive capability of the receiving system as loss of tracking and acquisition time are mostly dependent on these factors (Kinter et al, 2001). A distribution of an average scintillation patch duration at three locations is depicted in Fig.…”

Study of spatial and temporal characteristics of L-band scintillations over the Indian low-latitude region and their possible effects on GPS navigation

“…The movement of the ionospheric irregularities relative to the signal path converts these spatial fluctuations, due to diffraction effects, into temporal fluctuations, which, due to the diffraction effects, are observed as scintillations in the GPS received signal (Wanninger, 1993). It was observed that during strong scintillation, deep amplitude fades or large phase fluctuations may cause signal disruptions in the receiver-satellite link (Skone et al, 2000;Kintner et al, 2001). Amplitude scintillations can be monitored by the time series of C/N 0 (signalto-noise ratio) provided by the GPS output, and phase scintillations result from sudden changes in ionospheric refraction or from diffraction effects.…”

Space Weather Quarterly Volume 10, Issue 2, 2013

“…Scintillation is characterized by rapid fluctuations in the amplitude and phase of transionospheric radio signals as they pass through small-scale plasma density irregularities in the ionosphere [Kintner et al, 2001, and references therein]. The occurrence of scintillation shows large day-to-day variability with local time, season, latitude, longitude, as well as solar and geomagnetic activity.…”