# Research on Multi-Strategy Routing Protocol in Flying Ad Hoc Networks
## 2 Hybrid Location Service Strategy Design  
Although the flooding-based method is practical in some traditional location-based service methods, it needs a high consumption of network resources. It is difficult to apply the set-based method to high-dynamic networks because the nodes in the update set and search set will constantly change, so it is necessary to constantly adjust the node set at the intersection. However, the method based on attribution generally needs some fixed nodes or infrastructure as location servers, which is not conducive to the deployment and expansion of the network. Therefore, a hybrid location service strategy was used in the RGF protocol, which combined proactive and reactive mechanisms. In a certain range, the location information and motion information between nodes are exchanged in the way of active flooding. Outside the range, the target node's location information and motion information are obtained on demand by building a reactive path, which effectively controls the cost of flooding and ensures the scalability of this location-based service scheme. In the proactive location service, an active flooding strategy based on fisheye technology was adopted, as shown in Figure 2.  
Figure 1: RGF protocol overall design. Each node needs periodic flooding HELLO messages, and the remaining forwarding times field controls the size of the flooding area. Each time the intermediate node forwards a HELLO message, it is necessary to reduce the value of the remaining forwarding times by 1. When the value of the remaining forwarding times is 0, the HELLO message will not be forwarded. Therefore, the coverage area of HELLO messages can be controlled by setting the initial number of the remaining forwarding times, reducing the cost and ensuring the scalability of the proactive location service. The average update frequency in different areas will be different. The closer the node gets, the higher the average update frequency, and the more accurately the location and motion information can be maintained. In addition, considering the high mobility of UAVs, the faster the UAV moves, the more frequently the position changes. Therefore, to obtain the latest location information in time, the update cycle of the HELLO message should be short. The node in AODV is usually set to route outage when it does not receive HELLO messages from the next-hop node twice in a row. The HELLO message interval is usually set to 1 s. Therefore, if the next-hop node has moved out of the communication range of the current node, the current node will only know after 2 s, so the packets transmitted during this temporary blind period will be lost. Therefore, the update period of the HELLO message should be less than or equal to 0.5 s. Here, Equation (1) is used to adjust the HELLO message's update cycle dynamically. \[T_{HELLO}=T_{MIN}+\beta^{\alpha^{\left|\overrightarrow{v}\right|}}, \tag{1}\]  
In the formula, \(T_{HELLO}\) represents the current update cycle of the HELLO message, \(T_{MIN}\) is the minimum update cycle of the HELLO message, and \(\left|\overrightarrow{v}\right|\) represents the UAV's motion rate, \(0<\beta<1\), \(\alpha>1\). When the destination node is out of the fisheye range, it will not be able to obtain the HELLO message of the destination node regularly, and the source node will not be able to obtain the location information and motion information of the destination node. Therefore, we need to obtain the information of the destination node through the reactive location service. The reactive location service process is shown in Figure 3, which is realized through the route discovery process of the reactive mechanism. Figure 3: Reactive location service. Figure 2: Scope of fisheye. In reactive location service, the source node and the destination node use the reactive mechanism's RREQ message and RREP message for route discovery to build a reactive path.