Performance Evaluation of a Tracking Algorithm for Galileo E1 Signals

摘要

Global Navigation Satellite System (GNSS) receivers are currently the standard equipment for precision positioning, navigation and timing, but their use in challenging environments, such as urban and natural canyons, is made difficult due to reduced Line of Sight visibility, multipath propagation conditions or RF interference from nearby sources. In the next years, given the announced plans of GNSS operators, the number of satellites will increase to more than 120 - with even more signals and frequencies. Today there are more than 70 operational GNSS satellites in orbit from several GNSS systems, transmitting a variety of signals on multiple frequencies. A multi-constellation receiver could benefit from the large envisioned number of visible satellites, especially in urban canyons and industrial areas with very tall obstacles, where only satellites at high elevations are in line of sight with the receiver, but this assumption is valid only if the receiver can actually acquire and track the respective satellite signals. This is hard to attain in difficult signal conditions with single-constellation receivers: if one or more signals are lost because of obstacles or interferences, the receiver might not be able to determine the position, in case less than four valid pseudoranges are available. This paper describes a tracking algorithm implemented in Mathworks Matlab for Galileo El Open Service. After an overview of the state of the art, the work evaluates the performance obtained through Matlab simulations, such as the variation of the correlator replicas and of the local carrier frequency. Conclusion are drawn about the capability of the loop to track the Galileo El signal at different SNR values that may be encountered in real-life situations.