A Method for Monitoring GNSS Signal Power Changes Using Carrier-to-Noise Ratio

Signal power level of GNSS satellites is key parameter for service performance. The relationship between navigation signal power and carrier-to-noise ratio (CNR) of GNSS receiver is described. The time variation characteristics of CNR for one station and satellite pair during 10 days and also characteristics between different stations is analyzed. Results show that the relationship between CNR and elevation angle is consistent and repeatable for a specified signal of one station and satellite pair during that 10 days. Then a model related CNR with elevation angle is established based on global observation data. Using the model, CNR changing trend could be predicted, and so its anomaly could be monitored. For more efficient monitoring, we use a mapping method to transform the CNR at different elevation angles to its corresponding value of 90-degree elevation angle. Finally, data from global tracking network are used to validate the feasibility and reliability of this approach. The results show that there are signal power changes for GPS satellites occurred during April 13th 2018 UTC.