Ionospheric Scintillation Fading Coefficients for the GPS L1, L2, and L5 Frequencies

Abstract

The terrestrial ionosphere over low‐latitude regions presents the unique phenomena of the equatorial ionization anomaly (characterized by global maximum in plasma concentration) and plasma‐depleted regions known as equatorial plasma bubbles and associated smaller‐scale plasma irregularities. Transionospheric radio signals such as those from Global Navigation Satellite Systems constellations, traveling across this ambient, may suffer severe scintillation in amplitude and phase due to these plasma structures. Presently, three civilian signals available for GPS users, at L1 (1575.42 MHz), L2C (1227.60 MHz), and L5 (1176.45 MHz) are used to investigate the propagation effects due to these irregularities. The purpose of the present work is to evaluate statistically the distribution of severe fade events for each of these carrier frequencies based on the nonlinear ionospheric propagation effects as represented by the fading coefficients of α‐μ distribution. The results from the analyses of data sets recorded by stations at different geomagnetic latitude locations in Brazil show that regions closer to the equatorial ionization anomaly crest present higher probability of severe fade events. Additionally, the L5 signals, dedicated for safety‐of‐life applications, revealed more unfavorable results when compared to the L1 and L2C frequencies. The results further showed that for 0.8 ≤ S4 ≤ 1.0 the probabilities of fades deeper than −10 dB were between 8.0% and 6.5% depending on the station position. Considering the case of fades deeper than −20 dB, the results reach values near 1%, which is quite concerning. These results show empirically the fading environment that users of the new civilian signals may experience in low‐latitude region. Additionally, the fading coefficients may help in the comprehension of the distribution of amplitude scintillation and its relation with the frequency used, aiding in the future the development of signal processing algorithms capable to mitigate errors for navigation users.

Performance analysis of κ-μ distribution for Global Positioning System (GPS) L1 frequency-related ionospheric fading channels

“…These results presented in Table 3 are consistent with Moraes et al (2018b) where the E[a] values are presented for the same location besides three others in Brazilian territory and the average value for S 4 ! 0.7 is~E[a] = 2 but with significant concentration of occurrences in the region where a < 2.…”

“…Figure 5 plots various shapes of a-l probability density function for different values of S 4 . It worth observe that for the same S 4 value, as a increases the tail of the distribution rises, which means that the received signal will present more fading events as discussed in Moraes et al (2014Moraes et al ( , 2018aMoraes et al ( , 2018b.…”

Regional Ionospheric Delay Mapping for Low‐Latitude Environments

“…On the other hand, Fortaleza, on the northeast coast of Brazil, detected scintillation activity until approximately 3:30 UT, which is also consistent with the map, because to the northeast at 4:00 UT there are no bubbles that could interfere with IPPs from GPS signals. Additionally, Presidente Prudente has more strength in the scintillation activity (higher values of S 4 ) than Fortaleza, which is in accordance with the analysis of Moraes, Muella, et al (2018) and Moraes, Vani, et al (2018).…”

Interfrequency Performance Characterizations of GPS During Signal Outages From an Anomaly Crest Location

“…Even though the values of depth of fading vary from 2-30 dB at L1 C/A, C/N O value of a signal during the events of loss of lock were never found below 25 dB-Hz, which is the tracking range of the receiver in analysis. Moraes, Vani, et al (2018) have presented results where GPS L1 signal, have lower probabilities of being affected by moderate to strong scintillations compared to GPS L2C and L5 signal, which are in accordance with the inverse dependence of ionospheric scintillation intensity and carrier frequency. A fading model used by the above workers has verified the degraded performance of new L2C and L5 signals with respect to L1 signal.…”