Three carrier approaches for future global, regional and local GNSS positioning services: Concepts and performance perspectives

The next generation Global Navigation Satellite Systems (GNSS), such as the modernized GPS and Galileo, will transmit three or more carrier signals for civilian use. The paper outlines a geometry-free, distance-independent TCAR approaches, and explores ambiguity resolution and possible positioning performance at local, regional and global scales. The proposed TCAR approach comprises three steps: (1) resolving the integer ambiguities of the extra-widelane and widelane signals using smoothed code measurements; (2) estimating the first-order differential ionospheric bias with the two ambiguity-fixed widelane phases, which may be smoothed for centimetre accuracy over a short period; and (3) using the refined ionospheric correction and widelane signal to estimate the integer ambiguity of the third phase measurement chosen to be independent of the first two. The performance of the proposed method is distance-independent, although averaging or smoothing over multiple epochs, or a certain period of observation, is necessary for reliable ambiguity solutions. Depending on whether two or three combined ambiguities are resolved successfully, real-time kinematic positioning is achieved at two scales: at the regional-to-global scale with decimetre accuracy, and at the local scale with centimetre accuracy. Numerical results indicate the dependency of the positioning accuracy on the level of phase noise and residual tropospheric effects. The most notable result is the smoothing time for achieving decimetre-level RTK solutions over long distances can be reduced significantly - tens of seconds to a few minutes with three frequencies instead of the hundreds of seconds to tens of minutes in the case of two frequencies. This technological advance is remarkable, promising much wider regional and global scale applications than existing GPS technologies.