Stabilized Multi-Hop Route Construction Using a Modified Link Metric for Wi-SUN FAN Systems

Wireless Smart Utility Network Field Area Network (Wi-SUN FAN) is a technical specification of Wi-SUN that introduces multi-hop machine-to-machine transmission for advanced smart city infrastructure. Wi-SUN FAN uses the Internet Protocol Version 6 (IPv6) Routing Protocol for Low-Power and Lossy Network (RPL) as the routing protocol and expected transmission count (ETX) as the routing metric to build multi-hop networks. ETX is used to convert number of communications into a link metric, which measures the quality of communication between nodes. This metric measures the relative distance to the root node via adjacent nodes to determine the parent node. However, this method of determining link metrics may cause nodes to frequently change their parents. If a node selects a parent with poor link quality, the communication reliability deteriorates; therefore, each node must appropriately select a candidate parent node. This article presents the transmission characteristics of Wi-SUN FANs and highlights the problems of conventional link metrics. Based on this, a novel method is proposed for calculating the link metric. The performed computer simulations verified the superiority of the proposed metric when the packet generation rate remained unaffected by the generation of control frames that switched the parent nodes. Furthermore, the transmission success rate of the media access control (MAC) frame was experimentally measured in an office building using Wi-SUN FAN communication modules based on the proposed method. The evaluation confirmed that the proposed link metric improved the minimum MAC frame transmission success rate by 24.2% and the average success rate by 10.4%.