QuickCal: Assisted Calibration for Crystal-Free Micro-Motes

• Published in: IEEE internet of things journal 2021-02
• Main Authors: Chang, Tengfei, Watteyne, Thomas, Maksimovic, Filip, Wheeler, Brad, Burnett, David, Yuan, Titan, Vilajosana, Xavier, Pister, Kris
• Format: Article
• Language: English
• Subjects: Computer Science; Embedded Systems; Networking and Internet Architecture
• ISSN: 2372-2541; 2327-4662
• DOI: 10.1109/JIOT.2020.3015725

The Single Chip Micro Mote (SCµM) is a crystal-free single-chip mote that brings us one step closer to the Smart Dust vision, in particular as it can communicate with off-the-shelf IEEE802.15.4 and Bluetooth Low Energy devices. However, before it can be part of such networks, the crystal-free SCµM chip needs to be able to accurately tune its communication frequency to synchronize to the network. This is a challenge since its on-board RC and LC-based resonating circuits have a drift rate that can be 3 orders of magnitude worse than crystal-based oscillators typically used in today's radios. This article introduces QuickCal, a solution that allows a SCµM chip to self-calibrate against off-the-shelf devices dedicated to assisting with its calibration. We show that a SCµM chip can self-calibrate against this QuickCal Box in fewer than 3 min. We further validate that, once it has self-calibrated, a SCµM chip can reliably communicate with off-the-shelf IEEE802.15.4 devices. Finally, we demonstrate a heterogeneous network-composed of a SCµM chip and an OpenMote device-implementing a full 6TiSCH Industrial IoT protocol stack, which uses time synchronization and channel hopping. This is the first time that a crystal-free radio is participating in a channel-hopping enabled TSCH network.