# An Investigation of CTP Use for Wireless Structural Health Monitoring of Infrastructure
## 1 Introduction
Moreover, high-speed train systems have been proposed using 802.15.4 and Zigbee in practical scenarios [20]. Moreover, another example is the monitoring of bridges [21] and highways [22], with energy-efficient devices that require multi-hop transmission for the data to reach the base station. The network of devices needs to remain operational for a large period of time; hence power management is of paramount importance and using low power consumption parts is essential, as well as being able to perform time-triggered and event-triggered sampling tasks. IEEE 802.15.4 devices are usually resource-constrained and with low-power listening; hence, they can be encapsulated to applications where range is not a big issue in a single hop. Furthermore, TCP/IP can be substituted with IEEE 802.15.4 to use these energy-constrained devices which operate with dedicated software which is more lightweight, such as the Contiki [23]. Moreover, the devices need to be accurately synchronised, in order to be able to perform correct correlation analyses of the measurements. Since this paper attempts to address monitoring of large infrastructures, the devices may need to communicate between them to forward the data to a dedicated server, potentially using wireless technologies. Wireless communications have made an impact in the SHM, whereas the data are transmitted and forwarded to the terminal computer. The network of devices communicate with each other or with a basestation/gateway directly depending on the technology used. Moreover, the type of communication is highly correlated with the application of the infrastructure. For instance, using a wireless sensor networks (WSN) on a bridge or a building may utilise low-range wireless technologies as opposed to distant or larger infrastructure. Specifically, WSNs [24, 25, 26] and their children, namely the Internet of Things (IoT) [27, 28] have been playing a pivotal role to the next generation of SHM. There is a plethora of communication methods that can be applied to infrastructure as it can be seen in [29]. Specifically, wireless technologies, such as IEEE 802.15.4 [30],Wi-Fi [31], and telecommunications [32], perform a metamorphosis of SHM into a wireless network procedure, where enhanced autonomicity is achieved. Other works include the implementation of an Edge-SHM framework through low-power, long-range, wireless, low-cost, and off-the-shelf components [33] to promote energy-efficiency, as well as the development of a new node, which provides powerful hardware and a robust software framework to enable edge computing that can deliver actionable information [34]. The vast number of devices led to specific problems that include the escalation in interference and wireless medium collisions that act negatively towards prolonging the lifetime of a wireless network, due to its limited resources. As such mechanisms that would mitigate interference and maximise successful packet transmissions and throughput are essential. The CTP is a protocol, which is a state-of-the-art in terms of Quality of Service (QoS), since it offers high throughput. The protocol may be used to promote energy efficiency if the transmission power is reduced. In particular, the IEEE 802.15.4 networking technology can be used to successfully monitor infrastructure. The reader can see a typical wireless node architecture based on IEEE 802.15.4 in Figure 1a. IEEE 802.15.4 has been used in monitoring applications in infrastructure as the reader can see in [35] and references therein. IEEE 802.15.4 is a low-range technology and it operates in a multi-hop function, meaning that in order to reach the terminal computer a packet from a source needs to be forwarded by other nodes. The CTP initially originated for IEEE 802.15.4-constrained devices. This definitely raises issues such as the QoS, whereby the nodes are required to transmit their data successfully, in order to prevent packets with defect values to be lost.