# An IoT-Based System for Monitoring the Health of Guyed Towers in Overhead Power Lines
## 3 System Architecture  
Currently, many LPWAN technologies exist, including NB-IoT, LoRa, Sigfox, and WiSUN, among others. When choosing a particular technology, the systems integrator should know about the unique features of the technology as well as the specific application needs and demands. In this particular case, the choice for using the Wi-SUN network is due to several reasons. First, Wi-SUN networks are usually meshed networks. This topology allows multiple, redundant connection paths for a network with communicating tower sites, unlike star-based networks. As mesh networks scale, their reliability and performance improve because the possible communication paths multiply. Second, Wi-SUN provides high data rates that are consistent throughout the network and present the lowest latency [27]. Additionally, it uses less power for listening, enabling devices to listen frequently and still endure the long-term operation [28]. Finally, Wi-SUN is an open standard, and no company exclusively owns the technology. Thus, implementing private solutions will not require black box chips or licenses with potential vendor lock-in. The standard was established in 2011 and leveraged IEEE 802.15.4g [29] and IPv6 [30] protocols to drive innovative wireless Smart Utility and Smart City applications.  
The framework proposed in this research work considers the use of Low-Power and Lossy Networks (LLNs). Figure 2 illustrates an implementation of the proposed framework for monitoring the health of power line guyed towers. It consists of a set of sensors in a tower site where the information propagates through the LLN. The data hop site-to-site until the border node. The data coming from the border node can be stored in a local server or transmitted to a remote central server connected to the internet.  
The overall structural design includes leaf/router nodes and a border node. Router and leaf nodes are restricted to the tower site area and include a set of standard embedded sensors (i.e., accelerometer, gyroscope, thermometer, humidity, and barometer), while specific sensors can be connected on-demand (i.e., tensiometers, weather station). Figure 3 illustrates the position of leaf, router nodes, and tension sensors in one tower site. While leaf nodes and tension sensors are on the cables, a single router node is at the top of the tower. The tension sensor connects to its respective leaf node.  
The current devices operate as LLN routers, which typically run with constraints on processing power, memory, and energy (battery power). Supported traffic flows include point-to-point (between devices inside the LLN), point-to-multipoint (from a central control point to a subset of devices inside the LLN), and multipoint-to-point (from devices inside the LLN toward a central control point). On its stack proposal, IETF standardizes the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) as the routing protocol for LLNs. RPL is a tree-based proactive routing protocol that creates acyclic graphs among the nodes to allow data exchange. The most convenient method for the current framework is the Destination-Oriented Directed Acyclic Graphs (DODAGs), one of the techniques of multipath routing over conventional single-path routing methods for implementing  
Figure 2: The proposed solution framework.  
networks in a distributed way. The typical network arrangement to tackle the current problem is the directed acyclic graph with exactly one root node with no outgoing edges. Figure 4 illustrates a topology of the proposed solution where each tower site has four leaf nodes and one router node. The order of communication is, first, leaf nodes communicating to the router node. Next, the router node communicates to the router node of the following guyed tower site until the border node.