Due to the limited frequency stability and poor accuracy of GNSS receiver's internal quartz oscillators, a receiver clock error has to be estimated in addition to the coordinates. This leads to two major drawbacks especially in kinematic applications: (i) the up-coordinate is determined two to three times less precise than the horizontal coordinates, (ii) high correlations between the clock estimates and the up-coordinates. This situation can be improved distinctly when connecting an atomic clock to a GNSS receiver, and modeling its behavior in a physically meaningful way. This approach is called receiver clock modeling. Recent developments in miniaturizing atomic clocks resulted in so called chip scale atomic clocks, and open up the possibility of using a stable atomic clock in GNSS applications. We present a deterministic method of receiver clock modeling in a sequential least-squares adjustment for the application of an atomic clock in code-based GNSS navigation. The benefits of clock modeling in such a case are assessed as follows: decrease of the noise of the upcoordinates by up to 58%, and enhancement of internal and external reliability. Hence, a more robust position is obtained. Additionally, artificial partial satellite outages are generated to show our method's capability of computing position solutions with only three satellites in view. Finally, we investigate the benefits of an atomic clock in spoofing detection, and show preliminary results. Especially in the early stages of a spoofing attack, such a stable clock helps to identify the same and warn the user.
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