# An Investigation of CTP Use for Wireless Structural Health Monitoring of Infrastructure
## 1 Introduction  
Structural Health Monitoring (SHM) constitutes major industrial research areas, with applications in the civil infrastructure domain [1]. SHM in a civil infrastructure could be considered as a network of devices. SHM can be used in many forms by using acousto-ultrasions [2, 3], Acoustic Emissions (AE) [4, 5, 6, 7], and accelerometers [8], among others. SHM has been successfully applied to infrastructure including bridge monitoring [9] with satellite data, fibre-optic sensor SHM of infrastructure as it can be seen in [10] and references therein, buildings assessment [11], as well as tunnels [12]. In [13], the authors recommended and tested a WSN consisting of 45 nodes with IEEE 802.15.4 technology for suspension bridge monitoring. The short-range communication occurred using IEEE 802.15.4 and Code Division Multiple Access (CDMA) for communication with a longer distance basestation. The aim was to exhibit the ability to encapsulate a WSN for bridge monitoring. However, the requirement of interference of multi-hop communication needs to be explicitly mentioned. [PERSON] et al. [14], suggest the Compressive Sensing (CS) method to tackle lossy links and data loss in WSNs. In particular, they indicate that this method is suitable for data reconstruction and can be compared with reliable communication protocols. This method is implemented in the imote2 platform and this paper targets to provide accurate compensation for stationary and compressible acceleration signals which are retrieved from structural health monitoring (SHM) systems with data loss ratio below 20%. Even though this is a goodtechnique to be utilised, a reliable protocol, such as the Collection Tree Protocol (CTP) [15] can be utilised to tackle the data loss quite effectively. [PERSON] et al. [16] is the closest research to the work presented in this paper. The authors utilise the CTP in SHM; however, they highlight the effect of distance on RSSI and throughput. This is somewhat problematic due to the fact that the distance is difficult to be computed in wireless communications due to reflections and refractions, as well as obstacles in front of the devices. Moreover, devices may not be within Line-Of-Sight, which creates an extra problem with this referencing. The main difference between this work and the work presented here is that we aim to enhance CTP with a cooperative field on the programming struct, in order to perform cooperative transmission when the communication conditions are difficult. Even though the CTP is quite robust and intuitively performs the best parent selection, our approach will ensure that the packet will be forwarded to a specific node in a geographic position via a cooperative link if the upstream node is not the best parent. This will give that opportunity for sensing comparison at a node level, before reaching the basestation. [PERSON] et al. [17] suggested the monitoring of concrete infrastructures using passive radio frequency identification (RFID)-based sensors. The RFID-based sensors can last for long term and they are protected from harsh environments. The energy supply, as well as the transfer of the data, are being done by the RFID. The authors show monitoring of specific parameters from a large period of time. However, the RFID is not multi-hop meaning that they need to transfer their data locally. In [18], the authors suggest the implementation of a WSN, which serves as a bridge SHM system. The system comprises the use of IEEE 802.15.4 and 3G for short-range and long-range communication, respectively. The system is tested and debugged and it finally meets the design requirements. The data loss needs to be further investigated, in various conditions such as with high interference. There is a number of examples a that the CTP with IEEE 802.5.4 transmission can operate to. These examples require that the communication range is not large and multi-hop transmission is promoted. One of these examples is building SHM monitoring with accelerometers and gyroscopes [19].