  Hybrid acoustic-RF systems offer excellent ranging accuracy, yet they
typically come at a power consumption that is too high to meet the energy
constraints of mobile IoT nodes. We combine pulse compression and synchronized
wake-ups to achieve a ranging solution that limits the active time of the nodes
to 1 ms. Hence, an ultra low-power consumption of 9.015 {\mu}W for a single
measurement is achieved. Measurements based on a proof-of-concept hardware
platform show median distance error values below 10 cm. Both simulations and
measurements demonstrate that the accuracy is reduced at low signal-to-noise
ratios and when reflections occur. We introduce three methods that enhance the
distance measurements at a low extra processing power cost. Hence, we validate
in realistic environments that the centimeter accuracy can be obtained within
the energy budget of mobile devices and IoT nodes. The proposed hybrid signal
ranging system can be extended to perform accurate, low-power indoor
positioning.
