A Floating Vertical TEC Ionosphere Delay Correction Algorithm for Single Frequency GPS Receivers

This paper presents an innovative method to mitigate ionosphere delay error for single frequency receivers. Traditional approach to ionosphere delay correction is carried out through modeling the total electron content (TEC) along each satellite signal path. Because of the large deviation of the TEC during different times of the day, season, and solar cycle from any mean measurements, the ionosphere delay error has always been the dominant error factor in signal frequency receivers. In our method, we allow a reference vertical TEC to “float” or to remain as an unknown in the range equation. The TEC along each satellite signal path is modeled as having its own vertical TEC whose major component is the reference vertical TEC with additional contributions from the TEC spatial derivatives. The TEC spatial derivatives can be modeled using existing ionosphere models, services that provide ionosphere measurements, or even better, the ionosphere correction algorithm (ICA) coefficients which are part of the navigation message. By having the reference vertical TEC as an additional unknown in the range equations, a minimum of five satellites is required to obtain the receiver position. As a byproduct of the range equation solution, we also solve for the reference vertical TEC which can be a convenient and inexpensive way to provide information on the ionosphere. The paper describes the detailed algorithm and simulation studies that demonstrate order of magnitude improvement in ionosphere error correction using this method over the conventional method.