  Ultra-wideband (UWB) communications have gained popularity in recent years
for being able to provide distance measurements and localization with high
accuracy, which can enhance the capabilities of devices in the Internet of
Things (IoT). Since energy efficiency is of utmost concern in such
applications, in this work we evaluate the power and energy consumption,
distance measurements, and localization performance of two types of UWB
physical interfaces (PHYs), which use either a low- or high-rate pulse
repetition (LRP and HRP, respectively). The evaluation is done through
measurements acquired in identical conditions, which is crucial in order to
have a fair comparison between the devices. The LRP devices that we tested have
the same ranging and localization performance, but ten times (10x) lower power
consumption, 6x lower energy consumption per distance measurement, and at least
8x higher coverage than the HRP devices. Therefore, UWB LRP devices can offer
high-accuracy ranging and localization even to ultra-low-power devices in the
IoT. We performed measurements in typical LOS and NLOS scenarios and propose
theoretical models for the distance errors obtained in these situations. The
models can be used to simulate realistic building deployments and we illustrate
such an example. This paper, therefore, provides a comprehensive overview of
the energy demands, ranging characteristics, and localization performance of
state-of-the-art UWB devices.
