  Smart and unobtrusive mobile sensor nodes that accurately track their own
position have the potential to augment data collection with location-based
functions. To attain this vision of unobtrusiveness, the sensor nodes must have
a compact form factor and operate over long periods without battery recharging
or replacement. This paper presents a self-sustaining and accurate
ultra-wideband-based indoor location system with conservative infrastructure
overhead. An event-driven sensing approach allows for balancing the limited
energy harvested in indoor conditions with the power consumption of
ultra-wideband transceivers. The presented tag-centralized concept, which
combines heterogeneous system design with embedded processing, minimizes idle
consumption without sacrificing functionality. Despite modest infrastructure
requirements, high localization accuracy is achieved with error-correcting
double-sided two-way ranging and embedded optimal multilateration. Experimental
results demonstrate the benefits of the proposed system: the node achieves a
quiescent current of $47~nA$ and operates at $1.2~\mu A$ while performing
energy harvesting and motion detection. The energy consumption for position
updates, with an accuracy of $40~cm$ (2D) in realistic non-line-of-sight
conditions, is $10.84~mJ$. In an asset tracking case study within a $200~m^2$
multi-room office space, the achieved accuracy level allows for identifying 36
different desk and storage locations with an accuracy of over $95~{\%}$. The
system`s long-time self-sustainability has been analyzed over $700~days$ in
multiple indoor lighting situations.
