Rates of Cycle Slips and Outages for GPS L1/L2C/L5 due to Ionospheric Scintillation

Abstract

Irregularities in the ionosphere modulate the amplitude and phase of trans-ionospheric satellite signals, causing signal fluctuations known as scintillation. The scintillation of global navigation satellite system (GNSS) satellite signals can impact tracking loop performance and degrade positioning accuracy. Cycle slips and outages are manifestations of tracking loop impacts which are known to correlate with the scintillation index S4 and other statistical measures of the fluctuating ionospheric channel. The purpose of our study is to compare and validate theoretical models of cycle slip and outage rates using high-rate scintillation measurements at low latitudes. We detrended the high rate amplitude and phase measurements ourselves, and counted cycle slips and data gaps. We calculated the S4 index and intensity decorrelation time directly. We used the maximum likelihood (ML) technique to fit the ?-µ model to the distribution of signal fades. This procedure was performed using data from two different receiver models and for each of the three GPS carrier signals L1/L2C/L5. We compared the measured rates of cycle slips and data gaps with three theoretical models, namely the Rician model proposed by Humphreys [1], the Nakagamim model, and the ?-µ model proposed by Moraes et al. [2]. We found that both the Humphreys and ?-µ models yielded accurate predictions of the mean rates of cycle slips and outages. Notably, we observed experimentally the behavior that was predicted theoretically by Moraes et al. [2], namely that for a given S4 value the rate of cycle slips and outages increases with increasing ?. This corroborates the interpretation of ? as a measure of scintillation “severity” for a given S4.