# Beacon-Based Hybrid Routing Protocol for Large-Scale Unmanned Vehicle Ad Hoc Network
## 1 Introduction  
A modern battlefield considers large-scale unmanned vehicle network (LUVN) operations, with a single unmanned vehicle (UV) as the basic task unit. That is, the individual low intelligence is coupled into swarm intelligence, which could execute wide area target searches, target continuous mission coverage, and perform other complex tasks that could not be achieved with traditional vehicles [1]. An unmanned vehicle network (UVN) is a cluster network composed of multiple UV communication systems in which the vehicle is capable of information sharing and dynamic allocation. In large-scale specific application scenarios, the network could stably and reliably execute information interaction [2, 3]. Instructions for UVs and information exchange among them mainly rely on wireless networks. Considering LUVN communication in future military applications, it is particularly important to design a network routing protocol that can satisfy the requirements of a large-scale network of 100 or more nodes while maintaining good network performance with the topology of the network changing rapidly. Figure 1 illustrates the scheme diagram of LUVN. Currently, according to the network routing discovery policy, there are active routes, on-demand routes, and hybrid routes [4]. In the active routing protocol, all nodes maintain network topology information. Whether or not the network topology changes, its updated information will be transmitted throughout the entire network. In addition, the active routing protocol would generate a large amount of control overhead in the network, which consumes more bandwidth resources in the data transmission process. The nodes of an on-demand routing protocol trigger the path search process only when there is demand for service data. Route maintenance is executed on demand in the process of data transmission, that is, once the demand of service data stops, route maintenance will also be terminated, and the control cost can be reduced to some extent [5]. With the application of traditional protocols such as destination sequence distance vector (DSDV) and ad hoc on-demand distance vector (AODV) routing protocols in more scenarios, more obvious problems are exposed, mainly in the network overhead of active routing protocols and the long end-to-end transmission delay of data packets of on-demand routing protocols [6]. These problems are not suitable for LUVN scenarios. In network routing protocols, literature [7] comprehensively analyzed and simulated typical AODV, DSDV, and OLSR protocols, but has not proposed a routing protocol with higher efficiency according to the differences obtained by simulation. Literature [8] introduced a clustering algorithm into the DSDV protocol and modified the criterion of link quality in the protocol so as to improve the network throughput. However, this method still used the method of flooding in the process of maintenance and path discovery, and the problems of transmission delay were not solved. Another study [9] adopted the frequency-based policy to maintain routing to improve the AODV protocol, which effectively reduced the transmission delay of the protocol. Literature [10] used ant colony algorithm to discover paths, which solved the single path problem in AODV protocol and improved the network stability. Literature [11] modified the AODV routing protocols to reduce the number of route request (RREQ) and route reply (RREP) messages by adding direction parameters and two-step filtering. The two-step filtering process reduced the number of RREQ and RREP packets, reduced the packet overhead, and helped select the stable route. Literature [12] improved the MPR algorithm of the OLSR protocol and selected the MPR path to the left or right of the source node according to the destination node location, so as to reduce the network overhead and improve the network throughput.