Current GNSS (Global Navigation Satellite System) receivers include an internal quartz oscillator, such as TCXO (Temperature Compensated Crystal Oscillator) or similar, limited by its frequency stability and a poor accuracy, being one of the main sources of uncertainty in the navigation solution (also multipath and ionosphere effects are an important error sources.) Replacing the internal TCXO clock of GNSS receivers by a higher frequency stability clock such a CSAC (Chip Scale Atomic Clock) can improve the navigation solution in terms of availability, positioning accuracy, tracking recovery, multipath and jamming mitigation and spoofing attacks detection. For achieving these benefits, the deterministic errors from the CSAC need to be modelled, by determining and predicting the clock frequency stability in the positioning estimation process. The procedure of calculating a position without the need of estimating continually the clock error parameter is also known as clock coasting. The presented research shows the potential of the clock coasting method in order to be able to obtain position with only three satellites, improve the vertical positioning accuracy and increase the navigation solution availability.