## 4 AODV-EM Routing Protocol Design  
### Frame Structure Design  
The traditional AODV protocol only takes \"minimum hops\" as the unique routing criterion in the process of route selection, because the defined RREQ and RREP data frame formats only contain the Hop Count field as the criterion for route selection. Although this structure design can simplify the routing process and reduce computational complexity, it leads to several issues for AODV protocol in unmanned cluster networks, such as uneven energy consumption among network nodes and unstable routing paths. Therefore, the AODV protocol has certain limitations in the application of unmanned cluster networks. In order to improve the above problems, the AODV-EM protocol proposed in this paper modifies the data frame formats of RREQ and RRQP in the original AODV protocol and introduces two routing metrics proposed in Section 3 on the basis of the original data frame structure. In this way, the energy consumption level and relative mobility of the next hop node can be considered comprehensively in the process of route selection, so as to achieve a more balanced route selection. Figures 3 and 4 show the RREQ and RREP data frame formats of the AODV-EM protocol, respectively. The green part in the figure represents the new information based on the original AODV frame format. It can be seen that the RREQ and RREP data frames of the AODV-EM protocol add node energy loss, \(x\)-axis speed of node, \(y\)-axis speed of node, and route cost on the basis of the original data frame, so the frame lengths increase by 12 bytes each. RREQ data frames are mainly responsible for route discovery, while RREP data frames are mainly used for route reply. By adding this information to the data frames, nodes can obtain the movement speed information of the previous hop node when receiving RREQ or RREP data frames. By evaluating both the energy consumption of a node and the relative mobility with its previous hop node, the routing cost for communication between two nodes can be calculated as follows:  
\[RC_{i,j} =\alpha\times\overline{C_{j}}+\beta\times r_{i,j} \tag{9}\] \[=\alpha\times\overline{C_{j}}+(1-\alpha)\times r_{i,j}\]  
where \(RC_{i,j}\) represents the routing cost from node \(i\) to node \(j\), \(\overline{C_{j}}\) denotes the energy consumption value of node j based on node degree balance, \(r_{i,j}\) indicates the relative mobility between node \(i\) and node \(j\), and \(\alpha\) and \(\beta\) are the weight coefficients for the metrics of node energy consumption based on node degree balance and relative mobility between nodes, respectively. The sum of \(\alpha\) and \(\beta\) is always equal to 1, and their specific values can be dynamically adjusted based on the network conditions. If nodes in the network exhibit slower mobility, indicating that relative mobility has a smaller impact on routing cost, then \(\alpha\) is set to a higher value and \(\beta\) to a lower value. Conversely, if nodes exhibit faster mobility, \(\alpha\) is decreased and \(\beta\) is increased. During the process of routing from the source node to the destination node, multiple intermediate nodes are passed through. By calculating the routing cost between each pair of nodes and summing these costs, the total routing cost for the link between the source node and the destination node can be determined as follows:  
\[RC_{total}=\sum_{i=1}^{N-1}RC_{i,j}=\sum_{i=1}^{N-1}\alpha\times\overline{C_{j }}+(1-\alpha)\times r_{i,j},\ j=i+1 \tag{10}\]  
Figure 4: RREP data frame format in AODV-EM protocol. Figure 3: RREQ data frame format in AODV-EM protocol. where \(RC_{total}\) represents the total routing cost between the source node and the destination node, \(N\) is the number of all nodes on the link between the source node and the destination node, \(RC_{i,j}\) denotes the routing cost of the link between node \(i\) and node \(j\), and node \(j\) is always the next hop of node \(i\).