DCS: Dilution-based Convergecast Scheduling in a TSCH network

Abstract

We describe Dilution-based Convergecast Scheduling (DCS), an algorithm to compute a convergecast tree and a corresponding schedule to Timeslotted Channel Hopping (TSCH) networks. DCS works by dividing the plane into a grid and computing local trees inside each grid box. DCS uses the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) to assign specific labels to nodes (called ranks) and to connect the local trees into a single convergecast tree spanning the whole network. DCS creates schedules that are collision-free. Additionally, differently from existing related approaches, apart from the use of RPL, DCS is itself a collision-free algorithm, i.e., the convergecast tree and the schedules are computed without collision during message transmissions. DCS adapts and implements over contiki-ng and the Cooja simulator a previous scheduling algorithm designed for the Signal-to-Interference-plus-Noise Ratio (SINR) model. contiki-ng is an operating system for embedded devices that offers a reference implementation of TSCH. In this paper we describe how DCS builds and structures TSCH schedules over a real communication stack. In particular, beyond being collision-free, DCS can generate short schedules when compared to the number of nodes in the network. In DCS schedule sizes do not depend directly on the number of nodes. We present simulation results where DCS outperforms related approaches in terms of slotframe sizes, packet delivery ratio and end-to-end delays.