Enhancing the reliability of GNSS carrier phase measurements for precise positioning applications

Licentiate thesis, 2024

Global Navigation Satellite System’s (GNSS) position, navigation and time
(PNT) is used worldwide for numerous applications. With the advent of
sophisticated techniques such as real time kinematic (RTK), precise point
positioning (PPP) and the combination RTK-PPP, GNSS positioning using
carrier phase data can now achieve centimetre to millimeter levels of accuracy in
real time both in static or kinematic mode on land and decimeter to centimeter
levels of positioning accuracy on the sea. In a post processing mode this
accuracy can go down to sub-millimeter. However, the different error sources
of GNSS continue to pose a hindrance to this. Even in a differential mode of
operation, while error sources such as clocks and troposphere may cancel out
for short baselines, rapid variations in ionosphere can cause loss of lock of the
GNSS receiver, leading to cycle slips resulting in degraded position estimation.
Also, local unmodelled error sources such as diffraction and multipath cannot
be handled automatically by standard post processing software since they are
dependent on the receiver environment. These error sources lead to large range
errors which in turn impacts the position estimation accuracy. This work is a
compilation of different studies on GNSS error sources and aims at enhancing
the reliability of GNSS carrier phase measurements from a precise positioning
perspective.