OSCAR: An Optimized Scheduling Cell Allocation Algorithm for Convergecast in IEEE 802.15.4e TSCH Networks

Today's wireless sensor networks expect to receive increasingly more data from different sources. The Time Slotted Channel Hopping (TSCH) protocol defined in the IEEE 802.15.4-2015 version of the IEEE 802.15.4 standard plays a crucial role in reducing latency and minimizing energy consumption. In the case of convergecast traffic, nodes close to the root have consistently heavy traffic and suffer from severe network congestion problems. In this paper, we propose OSCAR, an novel autonomous scheduling TSCH cell allocation algorithm based on Orchestra. This new design differs from Orchestra by allocating slots according to the location of the node relative to the root. The goal of this algorithm is to allocate slots to nodes according to their needs. This algorithm manages the number of timeslots allocated to each node using the value of the rank described by the RPL routing protocol. The goal is that the closer the node is to the root, the more slots it gets in order to maximize the transmission opportunities. To avoid overconsumption, OSCAR sets up a mechanism to adjust the radio duty cycle of each node by reducing the slots allocated to inactive nodes regardless of their position in the network. We implement OSCAR on Contiki-ng and evaluate its performance by both simulations and experimentation. The performance assessment of OSCAR shows that it outperforms Orchestra on the average latency and reliability, without significantly increasing the average duty cycle, especially when the traffic load is high.