A scintillation signal model and a Global Positioning System (GPS)--Wide Area Augmentation System (WAAS) receiver model are developed. The scintillation signal model is based on a Nakagami-m distribution for intensity and a Gaussian distribution with zero mean for phase. The GPS receiver model includes Link 1 (L1) GPS and WAAS carrier- and C/A-code-tracking loops, as well as semicodeless Link 2 (L2) carrier and Y-code tracking capabilities. The results show that noncoherent delay locked loops (DLLs) typically used for code tracking are very robust to both amplitude and phase scintillation. Carrier-phase-tracking loops are much more susceptible to scintillation, and the signal-to-noise threshold for reliable carrier tracking is very dependent on the scintillation strength. Fortunately, it appears that the worst case scintillation encountered at midlatitudes, including the United States, does not significantly impact L1 carrier-tracking performance. Semicodeless tracking of the L2 carrier is shown to be very fragile. Even weak scintillation can cause loss of L2 carrier lock for low-elevation satellites. ¿ 2001 American Geophysical Union