Performance Evaluation of Kalman Filter Based Tracking for the New GPS L5 Signal

The performances of several GPS L5 tracking implementations are evaluated using IF samples obtained with a hardware simulator. The aim of this study is to determine the loop structure and parameters that are most suited to accommodate the various design innovations, such as the data/pilot implementation or spreading sequence definition, inherent to the GPS L5 signal. In particular, the Kalman filter based strategy is compared to the constant loop bandwidth approach for both code and carrier tracking. The analysis is conducted in the presence of various tracking error sources including noise, receiver clock jitter and dynamics. Tracking performances are assessed in the tracking, measurement and position domains with particular attention on carrier tracking and carrier phase measurement accuracy for potential highaccuracy applications. Results show that, despite the improvements brought by the GPS L5 structure regarding the constant bandwidth approach, the Kalman filter based strategy remains very beneficial in terms of frequency tracking and carrier phase measurement accuracy. INTRODUCTION Over the years, the use of GPS during ionospheric storms or in adverse environments has shown the limitations of the GPS C/A signal in terms of tracking sensitivity, accuracy and reliability. To overcome these limitations, and enable GPS signal acquisition and tracking in environments where previously impossible, high sensitivity technologies have been developed. Amongst them, the use of Kalman filter based tracking (and acquisition) have been shown to result in significant sensitivity gain over various constant loop bandwidth implementations (Psiaki & Jung 2002, Humphreys et al. 2005, Yu et al. 2006). While originally introduced for its high sensitivity capabilities, later research demonstrated the ability of Kalman filter based tracking to produce high quality carrier phase measurements (Petovello & Lachapelle 2006), and therefore, its interest for highaccuracy applications In the high-accuracy context, several efforts have been made by the U.S. government to provide civilian users with improved position and location services. These efforts encompass the introduction of two new civil signals (namely GPS L2C and GPS L5) and the upgrade of the ground segment. The L5 signal, designed to support safety-of-life applications, is expected to provide the best performance of all GPS civil signals, and is the main focus of this research. In particular, GPS L5 code and carrier tracking performances are expected to be greatly enhanced by the use of a higher chipper rate and the presence of a pilot channel respectively (Hegarty 1999).