Investigating the Impact of Ionospheric Scintillation using a GPS Software Receiver

Ionospheric scintillations cause RF signal amplitude fading and phase variations as GPS satellite signals pass through the ionosphere. This is a particular concern for GPS operations in high latitude regions, such as Canada, where scintillations are associated with strong aurora – effects which persist even during solar minimum. In general, scintillations can cause degraded receiver tracking performance and, in extreme cases, loss of navigation capabilities entirely. Such effects are an issue for reliable GPS operations in the northern United States and Canada. The University of Calgary currently operates the Canadian GPS Network for Ionosphere Monitoring (CANGIM), which makes scintillations observations at various latitudes in the auroral and sub-auroral regions. These measurements are used to characterize high-latitude scintillation effects, and develop models for assessing GPS receiver performance in the presence of such effects. The focus of this paper is a study of the effects of ionospheric scintillation on GPS signals, based on a GPS software receiver developed at University of Calgary. This study consists of several components: simulating ionospheric scintillation effects on L1 using an intermediate frequency (IF) GPS software signal simulator, investigating phase lock loop (PLL) performance under scintillation conditions using a software receiver, and developing improved tracking loop models to minimize phase errors and loss of signal lock during scintillation events. Results indicate that PLL performance is degraded for moderate to severe scintillations, with loss of lock occurring for narrow bandwidths. By employing a fast adaptive bandwidth approach, reliable signal tracking can be achieved.