BlueSync: Time Synchronization in Bluetooth Low Energy With Energy-Efficient Calculations

Abstract

Time synchronization is one of the important services in wireless sensor networks (WSN), and Bluetooth low energy (BLE) is one of the wireless protocols that has drawn a lot of attention recently, with applications in Internet of Things (IoT) and sensor fusion. Although, nonconnectable beacons are the most energy-efficient advertising mode of BLE, no synchronization service is defined for them in the BLE standard. Here, we present <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BlueSync</i> , a BLE compatible time synchronization protocol, which uses beacons for data transfer. As part of this study, we investigate the tradeoffs between energy efficiency, synchronization error, and speed by considering different drift-management methods and various synchronization packet configurations. Additionally, we propose a Discrete Adjustment technique that can improve energy efficiency in calculating timer ticks updates up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15\times $ </tex-math></inline-formula> without sacrificing accuracy. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BlueSync</i> is implemented on two commercial BLE system on chips and tested in 10-min long sessions without any resynchronization. Experimental results show that depending on the settings, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BlueSync</i> can achieve average synchronization errors as low as 320 ns per 60 s (single hop) and is the most accurate time synchronization reported on BLE to date.