| Summary: | 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 <italic>within</italic> a TSCH slot, and find room for performance improvement even when multiple links unfortunately share a slot. To this end, we propose <italic>DualBlock</italic> 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 <italic>within</italic> 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. <italic>DualBlock</italic> operates in a distributed manner for scalability. Extensive experiments demonstrate that TSCH networks achieve significant performance improvement in many aspects when <italic>DualBlock</italic> is combined with a scheduler (i.e., Orchestra), up to 3.6 times higher packet delivery ratio and 75% less radio duty cycle.
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