Delay-aware and reliability-aware contention-free MF–TDMA protocol for automated RFID monitoring in industrial IoT

This paper presents a multi-frequency time division multiple access (MF–TDMA) protocol for Radio Frequency IDentification (RFID) monitoring system in industrial Internet of Things (IoT). Unlike critical industrial control system which requires 1–2 ms response in communication, the monitoring system in industries normally demands a guaranteed delay in hundred-millisecond level. Under the context of IoT, massive items are monitored, the requirements of the monitoring system thus further include reliable communication, low-power low-cost flexible hardware structure, scalable system infrastructure, and quality of service (QoS) on demand. To fulfill these, we employ a flexible hardware infrastructure which uses a centralized coordinator and a set of readers to support multiple frequency channels or technologies to maximize the system capacity. The proposed MF–TDMA protocol provides a scheduled communication both in time and frequency with an optional automatic repeat request (ARQ), independent/uniform synchronization and control mechanism, and an optimization of time slot allocation to increase the transmission reliability while decreasing the latency to a guaranteed bound. The performance evaluation indicates that based on the proposed MF–TDMA protocol, the system can promise more than 95% of the tags to enjoy than 50 ms waiting time. And a delay bound of 100 ms is achieved when a 16-byte packet is transmitted at 256 kbps. Moreover, 100% packet transmission ratio can always be obtained thanks to the schedule and optimization mechanism.