Superframe Planning and Access Latency of Slotted MAC for Industrial WSN in IoT Environment

Industrial wireless sensor network (IWSN) is a key enabling technology for the Internet-of-things (IoT). IWSN acts as one of the fundamental elements of the IoT infrastructure to bridge the physical sensors and actuators in field and backbone systems in the Internet. For deterministic performances, all mainstream IWSN standards utilize the slotted media access control (MAC) where the communication is allocated based on the superframe that comprises a number of slots in either contention-based access or contention-free access modes. In this paper, the planning of the superframe structure of the slotted MAC is investigated by two means: 1) a mathematical model of the MAC access latency based on the queue theory; and 2) an easy-to-use software tool based on packet-level simulation. The mathematical model gives an overall estimation of the average MAC access latency of the whole network. The software tool gives the exact latency of each packet and then can derive the optimal superframe structure of the network. The two means are validated correspondingly. With the methods proposed in this paper, IWSN designers can minimize the MAC access latency while satisfying the requirements at different generating rates of packet, number of nodes in the network, and packet buffer length of each node.