Timestamping of IEEE 802.15.4 CSS by CORDIC-based Chirp interpolation

Accurate timestamps of wireless frames are the basis for clock synchronization of distributed measurement devices as well as for time-based wireless localization. Wireless sensor networks (WSNs) benefit from both synchronization and localization as it enables the sensor node to fuse measurement data with temporal and spatial information. The lower communication layers of WSNs are often based on the IEEE 802.15.4 standard, whereas only for Ultra-wideband (UWB) timestamping and ranging abilities are specified. The Chirp Spread Spectrum (CSS) physical layer, recently introduced into IEEE 802.15.4-2011, is another promising modulation scheme for highly accurate timestamping. This paper presents a timestamping receiver architecture for 802.15.4 CSS based on a Delay-Locked Loop and subsample interpolation (chirp generation) using the CORDIC algorithm. This architecture generates arbitrary subsample- and frequency-shifted chirp templates on the fly and therefore does not require large correlation filters. Simulations of the timestamp performance show that the proposed architecture offers equal performance as post-correlation delay estimators, yet with a significantly reduced amount of multipliers. This facilitates the implementation of precision clock synchronization and localization into low-power wireless sensor nodes.