# An Investigation of CTP Use for Wireless Structural Health Monitoring of Infrastructure
## 2 Attempting to Make CTP Cooperative for the Infrastructure Shm
### Cooperation Example in the SHM Application  
A WSN is considered, which is formed by a number of randomly distributed nodes functionally equivalent with respect to means of communication, signal processing, as well as battery demand. The function from [36] is suggested, which essentially proposes a game-theoretic formulation [50] towards link quality enhancement. We denote the \(ETX\) value that a source node \(j\) requires to transmit a packet directly to an upstream node \(k\) by \(ETX_{jk}\), as it can be seen in Figure 2 between nodes A and C. Additionally, denote the link quality demand of link quality required for a buyer node to transmit a packet to a seller node by \(ETX_{inter}\), shown in Figure 2 between nodes A and B. Furthermore, denote the link quality value of the \(i\)th seller to his own offer to the link quality saving of the cooperative coalition by \(c_{i}\) and the value of the \(j\)th buyer to the cooperation of the \(i\)th  
Figure 2: CTP Example. seller by \(ETX_{ij}\). We denote the value required by the intermediate node to reach the target upstream node as \(ETX_{frrad}\) (between nodes B and C in Figure 2). At this point, we assume that \(c_{i}=ETX_{frrad}\), since a seller node has \(ETX_{frrad}\) amount of link quality, favouring its corresponding source node. Note that the sellers' satisfaction will not be fulfilled unless its link quality is compensated. On the contrary, the cooperation between a buyer and a seller and the link quality that will be saved is the requirement of each buyer to form a coalition with a seller. Therefore, we calculate \(ETX_{ij}\) as  
\[ETX_{ij}=ETX_{jk}-ETX_{inter} \tag{5}\]  
if \(ETX_{inter}>c_{i}\), then a value exists that both the sellers and buyers prefer. It should be mentioned that when we refer to link quality saving, this corresponds to selecting the most efficient link quality to transmit each packet. A game-theoretic solution for this cooperative communication can be found in [36]. The objective is to attempt to show that there is a connection of a cooperative scheme with the nature of CTP forwarding. The CTP already performs such a procedure, by utilising the smallest ETX value of node, to which a node forwards the data. A potential application of the cooperative CTP may originate from the geographic routing paradigm [51]. Here, the nodes are suggested to be part of a bridge monitoring system, whereby they are placed in a geographic manner and wish to transmit their data to a specific direction using the CTP protocol. The geographic routing can be taken care of by CTP since, it operates in a parent-child hierarchical manner. In Figure 3, the reader can see an example of geographic routing, whereby the yellow circles denote the specific nodes which will communicate in a geographic manner. The yellow lines show the link of geographic communication. Moreover, the blue circles are the neighbouring nodes and the blue lines the links of communication. In this example, QoS metrics are not considered and the communication takes place in purely geographic manners. Specifically, there might be routes that are more efficient than the current ones. The CTP however, with its mechanism of selecting the best parent, may select a different route to forward the packet. The arguments is that such a mechanism can be enforced in CTP with the packet arriving at its geographically set device in a cooperative fashion. Even though this mechanism may resemble intuitive in the CTP operation, it is worth researching to further strengthen the CTP operation. The way the cooperative mechanism can be implemented at the testbed, is by adding a cooperative field in the struct of the packet. In this way, the seller node will be able to transmit the ETX values  
Figure 3: Geographic routing example. of forwarding the packet to the destination node. The nodes will geographically transmit the data to a destination node; however, they will essentially obtain an alternative with this cooperative packet field.