## 2 Routing Protocols for UAV Communication
### Optimized Link State Routing (OLSR)  
The OLSR protocol is an improved version of the traditional link-state algorithm. It is one of the recognized routing protocols used in MANET, VANET, and also UANET. As per table-driven routing, OLSR regularly updates and maintains the routing table of the network nodes [31]. The most important part of the OLSR protocol is the multipoint relay (MPR). Instead of sending routing messages all over the network, the OLSR protocol only keeps updating information about the MRP node [32]. MPRs are nodes that are chosen to relay broadcast messages during the flooding process. When compared to the traditional flooding method, this strategy significantly minimizes message overhead (where every node retransmits each message received). A mobile host can minimize battery consumption in this manner. Only nodes designated as MPRs generate link-state information in OLSR. Only links between an MPR node and its MPR selectors can be reported by an MPR node. As a result, in contrast to the standard link-state technique, partial link state information is spread throughout the network. This information is then utilized to calculate the path. The OLSR provides the best paths (in terms of the number of hops). Since MPRs perform effectively in this setting, the protocol is especially well suited for broad and dense networks. The fundamental functionality of the OLSR protocol is accomplished through the use of three different sorts of messages: \"Hello\" messages, topology control (TC) messages, and multiple interface declaration (MID) messages. Enhanced Optimized Link State Routing (E-OLSR)  
Most of the literature focuses on improving OLSR by improving the MRP selection criteria [33] or willingness concept [34]. [PERSON] et al. [35] provides a brief survey of OLSR improvement based on MRP selection. Improving performance by tuning parameters is also an efficient method to enhance the protocol performance. The new protocol needs extensive examination and analysis before practical deployment. In this context, parameter tuning is faster and more reliable for deployment [36]. Using a tuning strategy, this research improves the performance of the OLSR. An extensive simulation has been performed based on the heuristic method to find the optimal value for the UAV network. Table 1 represents the values for standard OLSR routing protocol parameters [37], whereas Figure 1 demonstrates E-OLSR values. The E-OLSR considers willingness to be high (6) rather than the default value of (3). Willingness indicates the node's desire to forward traffic on behalf of other nodes. Batteries, power, and capacity are related to it. In UAVs, willingness is crucial, as many nodes do not want to send traffic due to preserving energy, which is called a \"selfish node\" [38]. A high willingness indicates that the node will actively perform data transmission and perform an MRP. It improves the possibility of better system performance. In the OLSR packet format, there are two types of holding time. Htime corresponds to the HELLO message, while Vtime refers to the data packet. Holding time holds five types of time in the message header: neighbor hold time, topology hold time, duplicate message hold time, message id hold time, and HNA message holding time. The link expiration time is specified by the neighboring hold time. If a HELLO message is not received on a link within this time frame, the link is declared lost. By reducing neighbor hold time (6 s for standard OLSR, reduced to 2 s in E-OLSR), the lost node is detected faster instead of waiting a long time. It improves UANET system throughput. The expiration time for topology table entries is defined by the topology hold time. TC messages refresh topology table entries based on their originator address and sequence number.The topology hold time in E-OLSR is reduced from 15 s to 6 s. The topology of the UANET changes frequently. If the topology changes, UAVs receive updated information more quickly in E-OLSR because of the short topology hold time.