Owing to the explosive expansion of wireless communication and networking technologies, cost-effective unmanned aerial vehicles (UAVs) have recently emerged and soon they will occupy the major part of our sky. UAVs can be exploited to efficiently accomplish complex missions when cooperatively organized as an ad hoc network, thus creating the well-known flying ad hoc networks (FANETs). The establishment of such networks is not feasible without deploying an efficient networking model allowing a reliable exchange of information between UAVs. FANET inherits common features and characteristics from mobile ad hoc networks (MANETs) and their sub-classes, such as vehicular ad hoc networks (VANETs) and wireless sensor networks (WSNs). Unfortunately, UAVs are often deployed in the sky adopting a mobility model dictated by the nature of missions that they are expected to handle, and therefore, differentiate themselves from any traditional networks. Moreover, several flying constraints and the highly dynamic topology of FANETs make the design of routing protocols a complicated task. In this paper, a comprehensive survey is presented covering the architecture, the constraints, the mobility models, the routing techniques, and the simulation tools dedicated to FANETs. A classification, descriptions, and comparative studies of an important number of existing routing protocols dedicated to FANETs are detailed. Furthermore, the paper depicts future challenge perspectives, helping scientific researchers to discover some themes that have been addressed only ostensibly in the literature and need more investigation. The novelty of this survey is its uniqueness to provide a complete analysis of the major FANET routing protocols and to critically compare them according to different constraints based on crucial parameters, thus better presenting the state of the art of this specific area of research.INDEX TERMS UAV, FANET, mobility, simulation, routing protocols. TABLE 2. FANET communication comparison.
C. FANET CHARACTERISTICSEach mission or application comes with different requirements in terms of the number of UAVs, the flight time, and the communication constraints. This diversifies the characteristics of FANETs and makes them unique, which differentiate them from other kinds of ad hoc networks. In this section, we provide a detailed description of the most crucial FANET characteristics that are considered during the deployment of such networks.
1) NODE SPEEDThe LAUs are considered as the most studied categories of UAVs. In this category, we distinguish two kinds of UAVs: (i) Rotary-Wing (RW) UAVs and (ii) Fixed-Wing (FW) UAVs [61]. In a general case, the mobility of both types of