Temperature-Resilient Time Synchronization for the Internet of Things

Abstract

Abstract-Networks deployed in real-world conditions have to cope with dynamic, unpredictable environmental temperature changes. These changes affect the clock rate on network nodes, and can cause faster clock de-synchronization compared to situations where devices are operating under stable temperature conditions. Wireless network protocols such as Time-Slotted Channel Hopping (TSCH) from the IEEE 802.15.4-2015 standard are affected by this problem, since they require tight clock synchronization among all nodes for the network to remain operational. This paper proposes a method for autonomously compensating temperature-dependent clock rate changes. After a calibration stage, nodes continuously perform temperature measurements to compensate for clock drifts at run-time. The method is implemented on low-power IoT nodes and evaluated through experiments in a temperature chamber, indoor and outdoor environments, as well as with numerical simulations. The results show that applying the method reduces the maximum synchronization error more than 10 times. In this way, the method allows reduce the total energy spent for time synchronization, which is practically relevant concern for low data rate, low energy budget TSCH networks, especially those exposed to environments with changing temperature.

Multipoint Synchronization for Fog-Controlled Internet of Things

“…Synchronized clocks are used to achieve synchronization in the systems by making each node have a common notion of time. Time synchronization schemes [3], [27] have been developed for IoT to allow devices have a common notion of time. In [3], a visible light produced by light emitting diodes (LEDs) are used by devices within that vicinity to synchronize.…”

“…Synchronization is achieved by allowing a number of LEDs to send out binary signals at the same time and at predefined intervals, and devices synchronize when there is a phase transition. In [27], a time synchronization protocol was proposed to mitigate the effect of temperature change on hardware clocks in IoT networks using time-slotted channel hopping.…”

“…This work extends beyond time synchronization [3], [27] in that nodes need not only have the same notion of time, but there is a need for the right availability of nodes before executing a synchronous task. Tasks are not bundled to be scheduled together on the same processor in our scheme as in [30], rather, the same set of tasks are run across all participating nodes.…”

Wireless Sensor Network Synchronization for Precision Agriculture Applications

“…Furthermore, time-keeping devices are known to drift apart, especially when subjected to harsh environmental conditions [78], which showcases the need for effective communication-based synchronization [79]. For reference, under normal conditions, the resonator of an Arduino Uno or Mega, operating at 16 MHz, lose 10s of seconds per day, a performance that is fairly poor [80] for time-critical applications.…”

Lightweight Synchronization Algorithm with Self-Calibration for Industrial LORA Sensor Networks

“…This solution permits an average drift correction but the variable effects such as temperature changes, power supply variations or ageing are still present. To compensate for temperature variations a lookup table or a mathematical relation can be used to relate changes to clock calibration correction [4]. This method alone does not solve the problems due to ageing or power supply changes.…”