GPS/Galileo 單頻即時動態定位效能分析
Today, real-time kinematic (RTK) positioning is the most widely used GNSS technique in surveying engineering. Compared with dual-frequency RTK, even though single-frequency receivers have the cost advantage, single-frequency RTK lacks enough measurements for quick and reliable carrier phase ambiguity resolution. This situation is about to change. The European Galileo constellation is scheduled to be completed by 2013 and it will be interoperable with the existing GPS system. This combined system (GPS/Galileo) will provide twice as many satellites as today’s GPS (30), and thus it should substantially promote the application of single-frequency RTK. The model designed for single-frequency RTK based on Kalman filter and using LAMBDA method to resolve integer carrier phase ambiguities. To decrease the impact of system biases, the Virtual Reference Station (VRS) technique would be applied by Taiwan e-GPS system. The performance of integer phase ambiguity resolution was assessed with 24-h actual GPS data and simulated GPS/Galileo data in three different scenarios: (1) single-frequency GPS (GPS L1), (2) dual-frequency GPS (GPS L1/L2), and (3) single-frequency GPS/Galileo (GPS L1/Galileo E1). Comparison results show that, among the three scenarios, the best ambiguity resolution and positioning accuracy performance are achieved with single-frequency GPS/Galileo, as a result of its much improved geometry strength. This indicates that the future dual-system RTK can be practically built with low-cost single-frequency receivers. And it should have a great impact on many engineering applications.