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.