Stability of Clock Frequency Offset Measurements and Synchronization in UWB devices

UWB positioning combines time measurements from several devices to estimate the position of a target device. These measurements, however, are expressed in the device's own timescale that is derived from its free running clock source, generally a crystal oscillator. The timescales are inherently offset and with different and time-variant drift, both of which have to be compensated during the estimation. With the coherent IR-UWB chips it is possible to measure the drift either directly (Carrier Frequency Offset) or indirectly with timestamps. This work provides the stability analysis of such measurements as well as the characterization of the noise that affects them. From the results the usability of drift measurement methods for synchronization and positioning is inferred.

I. Introduction

Precise timekeeping and time measurements are a critical task of numerous radio localization or navigation systems, including Ultrawide band (UWB) systems. In this paper, we focus on the UWB impulse radio (IR-UWB) technology specified by IEEE 802.15.4 [1]. Thanks to the bandwidth of 500 MHz it may be possible to achieve sub-decimeter level accuracy, according to the Cramér-Rao Lower bound results in [2].