# A Co-Design-Based Reliable Low-Latency and Energy-Efficient Transmission Protocol for UWSNs
## 5 Design of Data Transmission Protocol
### Dynamic Routing Strategy
We will quantify the competitiveness of the set of competitors for each node according to the degree of overlap of their neighbors. An example for node \(n\) and its forwarding set \(F_{n}=\{A,B,C,D,E,F\}\) is shown in Figure 5. Nodes \(A-F\) are distributed in the layer \(L-1\), and node \(n\) is distributed in the layer \(L\) and will choose several nodes from \(A-F\) as its next-hop. The dotted lines between \(A-F\) indicate whether they are within communication range of each other, which expresses the neighbor relationships of \(F_{n}\). The competitor set brought by forwarders \(A-F\) is shown in Table 1. Nodes \(N_{1}-N_{8}\) are deployed in the same layer as node \(n\) (in order to prevent confusion, this is not marked in Figure 5). In order to facilitate the explanation of the attributes of competitors on node \(n\), we first choose \(\{A,B,E\}\) as the selection strategy that satisfies Equation (2). According to Table 1, if nodes \(N_{1}\) and \(n\) are sending a data packet at the same time, a conflict will occur at node \(A\), but will not affect nodes \(B\) and \(E\). Let Figure 6 denote the relationship between the competitors \(\{N_{1},N_{2},N_{5},N_{6}\}\) and chosen forwarders \(\{A,B,E\}\). Nodes \(\{N_{1},N_{2}\}\), \(\{N_{2},N_{5}\}\) and \(\{N_{5},N_{6}\}\) are brought by \(A\), \(B\) and \(E\) separately. Nodes \(N_{2}\) and \(N_{5}\) are at different intersections of two nodes, which coexist in the competitor sets of two nodes. Briefly speaking, if \(N_{2}\) and \(n\) send a data packet simultaneously, \(A\) and \(B\) will not receive the packet successfully because of a conflict. However, \(E\) can detect node \(n\) in this circumstance. Considering a worst-case scenario, if nodes \(N_{2}\), \(N_{5}\) and \(n\) send a package simultaneously, none of the nodes in \(\{A,B,E\}\) can receive the packet, which will cause the selection strategy to fail. After calculation, at least two competitors can cover all chosen forwarders. In other \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**A** & **B** & **C** & **D** & **E** & **F** \\ \hline \(N_{1}\),\(N_{2}\) & \(N_{2}\),\(N_{5}\) & \(N_{6}\),\(N_{7}\) & \(N_{3}\),\(N_{4}\) & \(N_{5}\),\(N_{6}\) & \(N_{6}\),\(N_{7}\),\(N_{8}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The competitor set of n.  
Figure 5: Node n and its forwarding set. words, less than two arbitrary competitors and \(n\) can send packets simultaneously this will not cause strategy \(\{A,B,E\}\) to become invalid. After the analysis of the example above, we define a _Conflict Competitors Set:_ under the selection strategy \(S_{n}\), the competitors who will cause a forwarding failure (all nodes in \(S_{n}\) influenced by competitors) when they send packets simultaneously with \(n\), which is a part of the permutation and combination of \(\{N_{1},N_{2},N_{5},N_{8}\}\) in the above example. The set with the smallest number of elements among all conflict competitor sets will be considered as the minimum conflict competitors set. In the above example, the minimum conflict competitors set is \(\{N_{2},N_{5}\}\). Let \(MC_{S_{n}}\) denote the the minimum conflict competitors set calculated from \(S_{n}\). The better selection strategy is supposed to have a larger size of \(MC_{S_{n}}\). The reason is that a larger size of \(MC_{S_{n}}\) can tolerate more nodes sending data packets at the same time. According to the above definition, we can also calculate that the size of the minimum conflict competitors set in selection strategy \(\{A,D,E\}\) is \(3(\{N_{1},N_{3},N_{5}\})\). Obviously, three nodes without the intersection of competitors will perform better. Above all, the attributes of competitors can be quantified by the size of the minimum conflict competitors set.