Massive connectivity is a key to the success of the Internet of Things. While mmWave backscatter has great potential, substantial signal attenuation and overwhelming ambient reflections impose significant challenges. We present OmniScatter, a practical mmWave backscatter with an extreme sensitivity of -115 dBm. The performance is theoretically comparable to the popular commodity RFID EPC Gen2 (900 MHz), and is empirically validated via evaluations under various practical settings with abundant ambient reflections and blockages - e.g., In an office where a tag is locked in a wooden closet 6m away, as well in libraries and retail stores where a tag is placed across two rows of metal shelves. At the heart of OmniScatter is the new High Definition FMCW (HD-FMCW), which interplays with the tag (FSK) signal to disentangle the ambient reflections from the tag signal in the frequency domain, essentially offering immunity to ambient reflections. To further support practical deployment, OmniScatter offers coordination-free Frequency Division Multiple Access (FDMA) that effortlessly scales to thousands of concurrent tags. The readers were built on commodity radars and the tags were prototyped on PCB. The trace-driven evaluation demonstrates concurrent communication of 1100 tags with the BER < 1.5%, paving a pathway towards practical mmWave backscatter for everyday and anywhere use.

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.