DualBlock: Adaptive Intra-Slot CSMA/CA for TSCH

Abstract

IEEE 802.15.4 Time-Slotted Channel Hopping (TSCH) has drawn significant attention as a low-power network solution for the Internet of Things (IoT). To make the TSCH scalable and robust, slot scheduling is an important issue that needs to be addressed. The research community has made significant strides with various autonomous or decentralized technologies in recent years. While these techniques try to provide non-overlapped slots for each link, they take collision for granted when multiple links utilize the same slot. In this paper, we challenge the perspective, investigate what happens within a TSCH slot, and find room for performance improvement even when multiple links unfortunately share a slot. To this end, we propose DualBlock that provides another chance for collision avoidance when multiple links try to utilize a slot at the same time by enabling clear channel assessment (CCA) and random backoff within the congested slot. In addition, given that the intra-slot backoff consumes more energy, a control mechanism is added that adjusts maximum backoff by monitoring network congestion level. DualBlock operates in a distributed manner for scalability. Extensive experiments demonstrate that TSCH networks achieve significant performance improvement in many aspects when DualBlock is combined with a scheduler (i.e., Orchestra), up to 3.6 times higher packet delivery ratio and 75% less radio duty cycle.