  Ultra-wideband (UWB) ranging has emerged as a key radio technology for robot
positioning and relative localization in multi-robot systems. Multiple works
are now advancing towards more scalable systems, but challenges still remain.
This paper proposes a novel approach to relative localization in multi-robot
systems where the roles of the UWB nodes are dynamically allocated between
active nodes (using time-of-flight for ranging estimation to other active
nodes) and passive nodes (using time-difference-of-arrival for estimating range
differences with respect to pairs of active nodes). We adaptively update UWB
roles based on the location of the robots with respect to the convex envelope
defined by active nodes, and introducing constraints in the form of
localization frequency and accuracy requirements. We demonstrate the
applicability of the proposed approach and show that the localization errors
remain comparable to fixed-role systems. Then, we show how the navigation of an
autonomous drone is affected by the changes in the localization system,
obtaining significantly better trajectory tracking accuracy than when relying
in passive localization only. Our results pave the way for UWB-based
localization in large-scale multi-robot deployments, for either relative
positioning or for applications in GNSS-denied environments.

Robotics