Evaluation of Data/Pilot Tracking Algorithms for GPS L2C Signals Using Software Receiver

Abstract

The current GPS constellation is being modernized to overcome the limitations of legacy GPS signals. L2C is the civilian signal added to L2 band as a part of modernization efforts. The major change in L2C signal structure is the inclusion of the pilot channel along with the data channel. In the context of tracking, the pilot channel carries the same information about frequency, phase and code errors. This information could be used along with that of the data channel for better tracking performance. This paper investigates the performance of Data/Pilot combined carrier-frequency tracking. A detailed analysis of existing methods to combine the frequency discriminators on data and pilot channel is done. Hybrid discriminators that make use of the data and pilot channel’s coherent integration output directly are proposed. Consequently, the performance of different possible combinations of the discriminators to form estimates of frequency error is analysed. They are evaluated under various ܥ/ ଴ levels. The advantages of using different discriminator combinations are demonstrated based on ܥ/ ଴.