Cooperative resynchronization to improve the reliability of colocated IEEE 802.15.4 -TSCH networks in dense deployments

With the large adoption of small and smart objects, the interest of researchers to define new protocols to meet Internet of Things (IoT) requirements is growing. In particular, the Industrial Internet of Things (IIoT) aims to provide high reliability and upper bounded end-to-end latency while interconnecting a large collection of sensors and actuators. The TimeSlotted Channel Hopping (TSCH) mode of IEEE 802.15.4 exploits a slow channel hopping approach to combat efficiently external interference (e.g. Wi-Fi, Bluetooth). We envision in the future very dense deployments and we investigate here the mutual influence among different colocated TSCH networks. We first study analytically with a simple model the performance of several TSCH networks, able or not to be synchronized with each other. We emphasize the multiplication of collisions, exacerbated by clock drifts when no cooperation is achieved. We also highlight experimentally that a mutual synchronization improves very significantly the reliability. We propose here a mechanism to re-synchronize distributively the border routers of different TSCH networks. Our thorough experimental evaluation illustrates the relevance of our approach, able to guarantee high-reliability, even in very dense topologies.