Model Analysis on the Performance for an Inertial Aided FLL-Assisted-PLL Carrier-Tracking Loop in the Presence of Ionospheric Scintillation

Ionospheric scintillation has a significant impact on the availability of Global Positioning System (GPS) and Wide Area Augmentation System (WAAS), especially when the GPS/WAAS receiver is dynamically stressed. An example of such a scenario would be an aircraft using WAAS to make an approach and landing. This study investigated the tolerable wideband interference level given various conditions of ionospheric scintillation. Two important criteria are used to determine the tolerable wideband interference level: the tracking threshold and the word error rate (WER) of the navigation data demodulation. An inertial aided FLL-assisted-PLL carrier-tracking loop is considered to be effective for increasing the receiver robustness to interference. This paper quantitatively gives the improvement using the inertial aided FLL-assisted-PLL and compares it to the generic PLL as well as inertial aided PLL carrier-tracking loops. Theoretical model analysis was performed for the above three tracking-loop configurations considering all possible error sources which can potentially degrade carrier-tracking loop performance. These errors include satellite/receiver clock dynamics, platform dynamics, platform vibrations, sensitivity of the receiver clock to acceleration, wideband interference, and ionospheric scintillation. The results showed that there is a 10 dB improvement in the minimum C / N-0 by using a FLL as a backup tracking loop when compared to the receiver with PLL used as the primary tracking loop only. However, satisfying the requirements of the WER limits the performance of this technique.