# Survey on Q-Learning-Based Position-Aware Routing Protocols in Flying Ad Hoc Networks
### Related Studies  
In this subsection, we discuss recent survey papers related to FANET routing protocols and the limitations of existing FANET routing protocols. Additionally, we discuss the motivation for our research and the key contributions of this survey paper. According to previous studies [30; 31; 32], the routing protocols in FANETs are classified as topology- and position-based. Topology-based routing protocols can be further classified as proactive, reactive, and hybrid routing protocols. Proactive routing protocols produce a large overhead to maintain the updated routing table for a dynamic topology. Thus, they consume higher bandwidth and energy, which is not suitable for resource-constrained FANETs. Additionally, they exhibit a slow reaction to a highly dynamic topology, which causes delays, routing loops, and blind paths [23]. A loop-free property is essential for dynamic FANETs to prevent data packets from being continually routed through similar nodes or paths. Blind path challenges occur in FANETs when the neighboring UAVs leave the transmission range of the corresponding source UAV within the intermediate time of the topology update because of several reasons such as sudden changes in relative mobility, requirements for energy replenishment, and UAV failure [23]. Additionally, FANETs may encounter frequent link breakages if the selected relay UAV leaves the transmission range of the corresponding source UAV during data transmission. Both the blind path and link breakage phenomena produce high retransmissions, delays, and energy consumption in FANETs. In [33], the authors studied the optimized link-state routing protocol (OLSR), which encounters higher overheads and routing loops and has a slow reaction in highly dynamic networks. Similarly, in [34], the authors studied the destination sequenced distance vector (DSDV), which consumes a large portion of the network bandwidth and provides a very high overhead owing to periodic updates in FANETs. Reactive routing protocols result in higher latency and delays owing to the on-demand route-discovery process. Additionally, in large-scale FANETs, the network overhead increases for reactive routing owing to an increase in the header size of the routing table [35]. In [32], the authors reported that dynamic source routing (DSR) provides a comparatively lower overhead at the cost of delays in route discovery. However, for large-scale FANETs, DSR routing encounters an extremely high overhead owing to an increase in the routing discovery table header [35]. Similarly, ad hoc on-demand distance vector (AODV) routing encounters route failures, higher delays, and higher bandwidth consumption in large-scale FANETs [34]. Hybrid routing protocols encounter higher computational complexities and overhead owing to the complex clustering, cluster-head selection, and cluster maintenance processes [3]. Therefore, all these traditional topology-aware proactive, reactive, and hybrid routing protocols encounter several limitations in highly dynamic FANETs owing to the high control overhead and large delays in neighbor and path discovery [36]. Additionally,they do not support adaptability to the dynamic topology to discover the efficient routing path autonomously. In position-based routing, each UAV node utilizes the GPS for localization. In addition, UAVs can use range-free and range-based cooperative localization in a GPS-denied environment. Position-based routing protocols utilize local knowledge, often one- or two-hop information, to make routing decisions. UAVs make forwarding decisions based on their current position, the position of the destination, and the position of their neighbors. In [37; 38], the authors studied several position-based routing protocols in FANETs by classifying them into the two categories of single-path and multipath strategies. Under the single-path strategy, they reviewed deterministic progress-based, randomized progress-based, and hybrid position-based routing protocols.