Intelligent IoT for the Digital World

6Clock Synchronization for Wide‐area Applications¹

6.1 Introduction

IoT devices have been widely deployed for sensing, computing, communication, and actuation capabilities. Data timestamping and clock synchronization are two basic system services for constructing IoT applications. Accurate timestamps are crucial for interpreting data and associating data from different sensors; synchronized clocks enable punctual and well coordinated operations among the nodes. On the other hand, wrong timestamps and malfunctioning clock desynchronization may lead to system chaos and failures.

Atomic clocks, GPS, clock synchronization, and calibration protocols represent principal means to achieve data timestamping and clock synchronization. For massive deployments, chip‐scale atomic clocks are still too expensive (e.g., $1500 per unit BusinessWire (2017)). Although GPS receivers can provide global time with s accuracy, they generally do not work in indoor environments. Existing clock synchronization and calibration approaches can be classified broadly into two categories. The first category consists of clock synchronization protocols (e.g., NTP Foundation (2017a), PTP IEEE (2008), RBS Elson et al. (2002), TPSN Ganeriwal et al. (2003), and FTSP Maróti et al. (2004)) that exchange network or radio messages among nodes to estimate and remove their clock offsets. As these approaches generally involve ...