Extrapolation of geocentric orbit corrections during loss of communication link — Analysis of different methods

Precise GNSS positioning requires the knowledge of all error components with their corresponding accuracy for a variety of different applications. The real-time precise products: orbit corrections, clock corrections and code biases are provided by the real-time service (RTS) of the International GNSS Service (IGS). The international GNSS service provides the access to real-time orbit corrections but RTS availability is sometimes disturbed or communication link is interrupted. Unfortunately any correction outage, either due to corrupted ephemeris or loss of communication link, will degrade the precise satellite position. Because it happens that corrections are not available in 100 % or they are sent with a certain latency it is necessary to apply the solution that will extend the application period of corrections until the connection will recover. For this purpose one can extrapolate directly the geocentric corrections. The prediction of corrections can be performed using the polynomial function. In this article, the authors analyze polynomial function using a different polynomial degree when predicting sought quantities. The tests were performed using various degree of polynomial calculation. To analyze this problem the own software was used. The software gets streams with SSR correction from IGS service. The experiment was performed in a several scenarios with several streams for different GPS satellites. The prediction time, accuracy and the degree of polynomial were tested for the best result. The results obtained in various scenarios were compared in order to find the optimal method geocentric corrections prediction. The time and accuracy of the prediction were chosen as the main comparative criteria.