# Research on Multi-Strategy Routing Protocol in Flying Ad Hoc Networks
## 4 Forwarding Strategy Design
### Reactive Mechanism Design Based on Joint Measurement Optimization
Source node or minimum local node sends RREQ, where the minimum link expiration time field is set to a negative value, indicating infinity. 2. After receiving an RREQ, the intermediate node first adds 1 to the hop value of the RREQ, then calculates the link expiration time with the previous hop node, and finally compares it with the value in the minimum link expiration time field in the RREQ. If it is less than the minimum link expiration time in the RREQ, then the intermediate node alternates the values. Otherwise, it does nothing. 3. The intermediate node calculates the joint metrics of the new and old paths and updates the routing table's request node entries according to the routing table's update conditions. For RREQs that have been forwarded, if the recorded path is better, it is allowed to forward the RREQ repeatedly. 4. After receiving the first RREQ, the destination node starts a timer, during which the joint measurement value of the corresponding path is calculated for each received RREQ. 5. After the timer expires, the destination node selects the path with the largest joint metric value and sends an RREP for activation. The minimum link expiration time field is also set to a negative value. 6. After receiving the RREP, the intermediate node also judges whether it is necessary to update the minimum link expiration time field of the RREP. At the same time, it updates the destination node entry of the routing table according to the update conditions of the routing table and then looks up the request node entry to forward the RREP to the previous hop node. 7. When the source node or the minimum local node receives the RREP of the destination node, it transmits the packet with the activated reactive path. ### Greedy Forwarding Strategy Design Based on Multi-Objective Joint Optimization

RGF encapsulates the destination node's location and motion information in the packet header, so it can switch to a greedy forwarding strategy when the reactive path is interrupted. The greedy forwarding of the RGF protocol adopts the greedy geographical forwarding method, and the forwarding node needs to forward the packets to the neighbor node closer to the destination node than itself. In order to ensure the stability of packet transmission, when the RGF protocol performs greedy forwarding, the forwarding node also needs to calculate the corresponding link expiration time for each neighbor node closer to the destination node according to Equations (2) and (3), to select the next hop with a stable link. In addition, if the sending queue of the next-hop node is long, the packet will be sent to the node, which will obviously increase its load. At the same time, if the remaining energy of the next-hop node is low, the packets will be forwarded to the node, which will cause the node to die faster, and the packets that the node has not yet sent will also be lost. Therefore, considering load balancing and energy saving, each node's HELLO message also encapsulates the sending queue length and remaining energy of the node. The forwarding node will finally calculate a transmission cost for each neighbor node closer to the destination node according to Equation (6) and select the node with the lowest cost as the next hop. \[cost=\rho_{1}\frac{D}{D_{f}}+\rho_{2}L+\frac{\rho_{3}}{LET}+\frac{\rho_{4}}{E}, \tag{6}\]

In the formula, \(cost\) represents the transmission cost, \(D\) represents the distance from the neighbor node to the destination node, \(D_{f}\) represents the distance from the current node to the destination node, \(L\) represents the normalized transmission queue length of the neighbor node, \(LET\) represents the link expiration time between the current node and the neighbor node, \(E\) represents the remaining energy of the neighbor node, and \(\rho_{1}\rho_{2}\rho_{3}\rho_{4}\) is the corresponding weight and meets the requirements of \(0<\rho_{1},\rho_{2},\rho_{3},\rho_{4}<1\) and \(\rho_{1}+\rho_{2}+\rho_{3}+\rho_{4}=1\).