## 3 Opportunistic Transmission Scheme for Integrated UAV-ICV Networks Enabled by Node Cooperation
### UAV-Assisted Information Transmission  
After the initial information flooding, the proposed opportunistic transmission scheme leads to a continuous decrease in the number of remaining message copies at communication nodes as the copies are forwarded. Generally, when a communication node has only one remaining message copy and fails to successfully transmit it to its destination node, the relay communication node can only encounter the destination node either by moving or waiting. However, this stage may introduce significant delays in information transmission. Therefore, the proposed opportunistic transmission scheme can be combined with the information forwarding probability in the Prophet routing protocol [9] and the UAV-assisted mechanism to transmit message copies. Specifically, in the proposed opportunistic transmission scheme, during the initial information flooding process, the encounter probability \(P_{i,d}\) between node \(i\) and the destination node \(d\), as well as the encounter probability \(P_{k,d}\) between the next-hop relay node \(k\) and the destination node \(d\), should be calculated. If \(P_{i,d}\leq P_{k,d}\) the information is transmitted. Otherwise, to prevent excessive message flooding, the transmission does not occur. However, under this scheme, there may still be cases where certain communication nodes have only one remaining message copy and fail to successfully transmit it to the destination node. In such cases, the message copy can be forwarded to a UAV. Compared to ICVs, UAVs have a wider communication range, greater cache size, and lack selfishness. Therefore, in integrated UAV-ICV networks, UAVs have more centrality. Strong node centrality means that, within the same time period, a UAV node can contact more communication nodes. According to the above analysis, UAV nodes are more suitable as relay nodes for message forwarding. The node centrality \(D_{\text{Centrality}}\) can be expressed as  
\[D_{\text{Centrality}}=\sum_{k=1,k\
eq i}^{N+R}\frac{x_{i,k}}{N+R-1}, \tag{14}\]  
where \(x_{i,k}\in\{0,\ 1\}\). If nodes \(i\) and \(k\) are within each other's communication range, \(x_{i,k}=1\), otherwise, \(x_{i,k}=0\). This paper defines the initial energy of UAVs as \(E_{\text{init\_UAV}}\) and its standby energy consumption as \(E_{\text{st\_UAV}}\). The initial energy of ICVs is defined as \(E_{\text{init\_veh}}\), with a standby energy consumption of \(E_{\text{st\_veh}}\). The energy refresh cycle for both types of communication nodes is \(T\). The energy consumed by the UAV and ICV for a single node detection is \(E_{\text{det\_UAV}}\) and \(E_{\text{det\_veh}}\), respectively. Moreover, the energy consumed by the UAV and ICV for a single information transmission is defined as \(E_{\text{tran\_UAV}}\) and \(E_{\text{tran\_veh}}\), respectively. Furthermore, during one refresh cycle, the UAV performs node detection and information transmission \(N_{\text{det\_UAV}}\) and \(N_{\text{tran\_UAV}}\) times, respectively. The ICV performs node detection and information transmission \(N_{\text{det\_veh}}\) and \(N_{\text{tran\_veh}}\) times, respectively. Based on the above analysis, for the \(l\)-th transmission, the remaining energy of the UAV and ICV, denoted as \(E_{\text{rest\_UAV}}\) and \(E_{\text{rest\_veh}}\), can be calculated by using (15) and (16), respectively. \[E_{\text{rest\_UAV}}(l) =E_{\text{rest\_UAV}}(l-1)-E_{\text{det\_UAV}}(l)\times N_{\text {det\_UAV}}(l) \tag{15}\] \[-E_{\text{tran\_UAV}}(l)\times N_{\text{tran\_UAV}}(l)-E_{\text{ st\_UAV}}(l),\]  
and  
\[E_{\text{rest\_veh}}(l) =E_{\text{rest\_veh}}(l-1)-E_{\text{det\_veh}}(l)\times N_{\text {det\_veh}}(l) \tag{16}\] \[-E_{\text{tran\_veh}}(l)\times N_{\text{tran\_veh}}(l)-E_{\text{ st\_veh}}(l),\]  
where \(E_{\text{rest\_UAV}}(0)=E_{\text{init\_UAV}}\) and \(E_{\text{rest\_veh}}(0)=E_{\text{init\_veh}}\). Meanwhile, when transmitting message copies to communication nodes with higher centrality, the remaining cache space of these nodes must also be considered.