Seamless roaming and guaranteed communication using a synchronized single-hop multi-gateway 802.15.4e TSCH network

Abstract

Industrial wireless sensor and actuator networks (WSANs) are being used to improve the efficiency, productivity and safety of industrial processes. One open standard that is commonly used in such cases is IEEE 802.15.4e. Its Time-Slotted Channel Hopping (TSCH) mode employs a time synchronized based medium access control (MAC) scheme together with channel hopping to alleviate the impact of channel fading and interference. Until now, most of the industrial WSANs have been designed to only support static nodes and are not able to deal with mobility. In this paper, we show how a single-hop, multi-gateway IEEE 802.15.4e TSCH network architecture can tackle the mobility problem. We introduce the Virtual Grand Master (VGM) concept that moves the synchronization point from separated Backbone Border Routers (BBRs) towards the backbone network. With time synchronization of all BBRs, mobile nodes can roam from one BBR to another without time desynchronization. In addition to time synchronization, we introduce a mechanism to synchronize the schedules between BBRs to support fast handover of mobile nodes. We show that with the proposed network architecture handovers happen instantly without any packet losses, while the handover time can be up to tens of seconds without any time synchronization between BBRs. The solution is evaluated in a testbed setting as well as in a real industrial environment.