Internet of Things (IoT), which connects a large number of devices with wireless connectivity, has come into the spotlight. As the scope of IoT applications becomes wider, we observe a surge of missioncritical IoT services, e.g., industrial automation systems and medical IoT systems, requiring to satisfy stringent latency, reliability, and/or energy efficiency guarantees. For this purpose, a new MAC, called Time Slotted Channel Hopping (TSCH), has been standardized in IEEE 802.15.4e. However, it is challenging to design a distributed scheduling protocol that achieves the required QoS and energy efficiency at the same time due to complicated tradeoff (providing enough number of slots for QoS vs. minimizing scheduled slots for energy efficiency). In this paper, we propose a novel framework for providing QoS, called SSAP, which is designed to maximize network lifetime in a distributed fashion while satisfying given reliability and latency requirements. To this end, we decompose our goal into two crucial design components: (i) scheduling of slot and channel, and (ii) control of medium access period, each of which is performed by low-complexity and distributed mechanisms. To the best of our knowledge, this paper is the first work to comprehensively handle multiple QoSes for TSCH-based IoT networks. We implement SSAP in Contiki OS and perform extensive simulations and real experiments under various scenarios. Our evaluation results demonstrate that SSAP satisfies highly reliable communication and latency requirements while having the network lifetime that is 1.6 times longer compared to existing protocols for TSCH.

Energy efficiency is critical in many IoT applications with sensors that deliver data over wireless communications. Duty-cycling has been a major method for reducing energy consumption. One popular duty-cycling is MAC duty-cycling where an MCU commands the periodic or adaptive turning on and off of an RF chip. Recently, there has been an increase in the number of RF chips for IoT that are equipped with PHY duty-cycling, a new capability of autonomously switching on and off an RF chip without the use of an MCU. These two schemes working at different layers have different pros and cons in terms of operating time scale, the amount of energy saved when the RF chip is switched off, all of which depend on the characteristics of the MCU and the RF chip. In this paper, we propose a novel protocol named HD-MAC (Hierarchical Duty-cycling MAC) that hierarchically integrates duty-cycling in the MAC and physical layers. By smartly applying the new function of chip-level duty-cycling, HD-MAC is able to further reduce the amount of on-time in MAC duty-cycling; hence, energy efficiency can be improved. To optimize HD-MAC’s energy efficiency while achieving a given delay requirement, we formulate an optimization problem and solve it to obtain the optimal parameters in the cross-layer context. We implement HD-MAC on Contiki OS and perform extensive experiments using a real sensor mote Firefly with a CC1200 RF chip. We demonstrate that the energy efficiency of HD-MAC is up to 72% higher than that of existing protocols while still satisfying the delay requirement and sustaining similar reliability.