  Standalone Global Navigation Satellite Systems (GNSS) are known to provide
positioning accuracy of a few meters in open sky conditions. This accuracy can
drop significantly when the line-of-sight (LOS) paths to some GNSS satellites
are obstructed, e.g., in urban canyons or underground tunnels. To overcome this
issue, the general approach is usually to augment GNSS systems with other
dedicated subsystems to help cover the gaps arising from obscured LOS.
Positioning in 5G has attracted some attention lately, mainly due to the
possibility to provide cm-level accuracy using 5G signals and infrastructure,
effectively imposing no additional cost. In this paper, we study the
hybridization of GNSS and 5G positioning in terms of achievable position and
velocity error bounds. We focus on scenarios where satellite visibility is
constrained by the environment geometry, and where the GNSS and 5G positioning
systems fail to perform individually or provide a prohibitively large error.
