# Two-Tier Cooperation Based High-Reliable and Lightweight Forwarding Strategy in Heterogeneous WBAN
## 3 Two-Tier Collaboration Based High-Reliable and Lightweight Forwarding (TTCF) Mechanism for WBAN
### Forwarding Model Based on Multi Factor Dynamic Fusion in TTCF
While striving to improve the successful delivery rate of WBAN data, taking into account system energy saving, the paper will comprehensively consider energy consumption based on the distance between nodes and the nodal forwarding capacity measured by the importance factor of sampling frequency, the influence factor of residual energy and the importance factor of network status to build the forwarding decision utility. Set \(\xi\) as the target node. If sensor \(i\) holds forwarding data at this time, when \(i\) transfers the data to \(\xi\), \(i\) may be have a communication connection with multiple other sensor nodes (such as \(j\)) at this time due to the change of the network environment caused by the dynamic behavior of monitoring objects. Then, the selection condition of the next hop node, that is, the forwarding decision function, is as follows. \[D_{j}=\alpha E_{j}+\frac{\beta}{FA_{j}} \tag{15}\]  
where \(\alpha\) and \(\beta\) are weight coefficients, which meet the requirements of \(0\leq\alpha\), \(\beta\leq 1\) and \(\alpha+\beta=1\). The paper considers that it is equally important to measure the nodal energy consumption and forwarding capacity, namely, \(\alpha=\beta=0.5\). Obviously, the smaller the \(D_{j}\) value, the stronger the nodal forwarding capability and the lower the system energy consumption is. Forwarding Rule and Algorithm  
WBAN is a wireless sensor network with a small number of nodes, and the star network topology is a simple topology, which is more suitable to be the first choice of WBAN network structure. However, in the star network topology, each node is independent of each other. When a node dies, there are still nodes with a large amount of residual energy, which leads to the excessive waste of network energy. Dijkstra algorithm can make good use of the relay function of the forwarding nodes to realize multi-hop transmission between remote nodes, greatly reduce network energy consumption and reasonably allocate network energy resources. It is very suitable for data transmission in WBAN. The idea of the original Dijkstra algorithm includes four steps. First, when calculating the shortest path in graph \(G\) = (\(V\),\(E\)) through Dijkstra, it is necessary to specify the starting node. Secondly, the node set \(V\) in \(G\) is divided into two sets \(V_{i}\) and \(V-V_{i}\). \(V_{i}\) is to record the nodes that have been obtained in the shortest path and the corresponding shortest path length, while \(V-V_{i}\) is to record the nodes that have not been obtained in the shortest path and the distance from the nodes to the starting node. Third, at the beginning, there is only the starting node \(i\) in \(V_{i}\). In \(V-V_{i}\), there are vertices other than \(i\), and the path of vertexes in \(V-V_{i}\) is \"the path from the starting node \(i\) to these nodes\". Then, find the node with the shortest path from \(V-V_{i}\) and add it to \(V_{i}\), and next, update the nodes in \(V-V_{i}\) and the paths corresponding to the nodes. Fourth, repeat the above operation until all nodes are traversed. Therefore, to prolong the lifetime of WBAN, the paper improves the Dijkstra algorithm in TTCF according to the actual needs, mainly changing the path parameters in Dijkstra into the comprehensive measurement of communication energy consumption between human sensor nodes and the forwarding ability of encounter nodes. The main pseudo codes executed by the improved Dijkstra algorithm at a certain time are as follows. Obviously, Algorithm 1 can calculate the shortest path with the least energy consumption and the highest data transmission efficiency between the source and destination nodes according to the characteristics of the nodes and energy consumption between nodes. It can realize the reliable and lightweight forwarding of heterogeneous medical data by combining the SITCSE model, and the main pseudo code is shown in Algorithm 2.