# Position-Monitoring-Based Hybrid Routing Protocol for 3D UAV-Based Networks
###### Abstract
Since UAVs are responsible for data transfer from source to destination, this leads to a new network environment different from traditional MANETs/VANETs that require novel mobility models, 3D coverage areas, and other possible strategies. In this regard, UAVs create a 3D wireless network environment with a free space environment to move independently. The research community faces unique challenges while working with decentralized flying UAV-based networks, mainly the communication in a 3D environment due to the high mobility of UAVs [6]. To this end, packet routing is one of the open problems in the Inter-UAVs 3D environment [7]. The wireless routing protocol is an important aspect that directly affects multiple UAVs' communication efficiency. The topology-based routing protocols maintain routing tables to perform routing [8]. The UAV nodes forward data packets to the destination via the shortest path hop by hop. In this case, where the hops are the UAVs, efficient path optimization  
Figure 1: Mobility models taxonomy. is essential. Due to the fast movement of UAVs, topology-based routing requires extra overhead to reinitiate route discovery. Therefore, typical topology-based routing protocols are not suitable to support the 3D nature of the UAV network [9]. To address the 3D issue when utilizing topology-based routing protocols, geographical, positioning, or location optimization throughout the network is necessary for determining the next hop toward the target [10; 11]. Each UAV node forwards packets to the optimal neighboring UAV node that is within communication range and in the direction of the destination. Position-based routing protocols offer many advantages over topology-based routing by utilizing additional geographical information about mobile UAVs available through global positioning systems (GPS) or other position-tracking services. A source UAV node sends signals to the destination UAV using position-based information [12; 13]. Due to dynamic topological changes, UAVs often lose connection or are out of communication range. Hence, the UAV-based network requires position-based routing to maintain the network efficiently. However, position-based routing uses local information instead of the entire network information. Therefore, the chance of a high delay occurs when the source node does not find the proper coordination position of the destination node at one hop. Another reason is that nodes are not in the communication range because of the high mobility of UAVs; hence, packets cannot be forwarded, which decreases packet delivery of the whole network. Based on the above issues mentioned in this paper, we research the 3D UAV scenario, especially for routing information. We propose a new, state-of-the-art routing protocol based on a position-monitoring-based hybrid routing protocol (PMHRPs) in a 3D UAV network, aiming to establish more appropriate routing services during the high mobility of wireless UAV nodes for better routing performance. The PMHRP combines proactive topology-based routing and position-based routing and introduces the PHC, which is responsible for updating and coordinating the routing information of all responsible UAVs based on their geographic position. The topology-based routing property of PMHRP establishes the shortest paths among the network nodes. In this way, all nodes receive routing information as well as the geographic position of other UAVs before data forwarding. To the best of our knowledge, no one has used our proposed methods in any published work to select the PHC node in a UAV-based system. Moreover, PMHRP not only reduces the delay but also maintains the packet delivery ratio in the UAV-based network. We compare our results with existing position-based and topology-based routing protocols. Table 1 shows the abbreviations and notations, with descriptions, that are used in this study.