## 1 Introduction  
The applications of unmanned aerial vehicles (UAVs) are increasing in different fields. They can be utilized for emergency services, life-saving missions and information-gathering systems. In order to ensure the reliability of a specific mission, a robust wireless communication channel is required. A number of technical committees have defined the basic standards for UAV radio communication links. Similarly, a regulatory body named the Radio Technical Commission for Aeronautics (RTCA) has standardized the minimum set of parameters for stable UAV operation [1]. Moreover, for the safe induction of UAVs in the airspace, another technical committee has developed the standards [2]. Generally, the UAVs are divided into three categories, such as rotary-wing, fixed-wing and vertical-takeoff ones. However, each type has its advantages and disadvantages in terms of hovering capabilities, take-off and landing, endurance length, loading capacity and operating radius. Specifically, in emergency response scenarios, the UAV relaying communications, emergency lighting and other rescue support can be used to collect on-site data and enable communication relay, night illumination and other support [3]. In the case of UAV swarms, a collection or group of UAVs carry out activities in a self-organized and self-adaptive manner to accomplish a task, which is the current trend in the developments of UAV technology. The self-organized part indicates that through local interactions, the UAV swarm spontaneously creates a totally decentralized or hybrid mode [4]. In the literature, numerous networking techniques and routing protocols have been developed and examined to improve networking performance. In order to guarantee the stability and dependability of UAVs, many researchers have already made significant progress in task allocation and cooperative execution. The idea of an avionics cloud based on a UAV swarm was proposed by [5], wherein the cloud model for avionics system integration was discussed. Regarding the communication mechanism of an intelligent UAV swarm, UAVs are highly mobile communication nodes that may function as transmitters or relays simultaneously. However, in the presence of interference, UAV swarms require multi-channel access and networking, and the omnidirectional antenna often employed for inter-UAV coordination may degrade spectrum efficiency [6]. Additionally, the cognitive-radio, broad-spectrum sensing capacity set up the learning process for reinforcement learning and produced better policy sets than conventional Q-Learning [7]. A real-time reinforcement learning system based on Q-Learning that utilized broadband spectrum sensing and greedy policy to improve real-time policy was presented by [8]. Additionally, multiple machine-learning types, their utilization and specific algorithms are provided in the alluvial map in Figure 1.  
A detailed review paper related to swarm intelligence algorithms was published, where a number of optimization techniques are discussed [9]. The reallocation in emergent scenarios has been reported by [10]. In order to solve the problem of reallocation, [PERSON] et al. utilized the clustering of UAVs based on fuzzy C-means (FCM), along with ant colony optimization (ACO). The clustering head of a UAV swarm has been discussed by [11], wherein effective communication management has been addressed. Additionally, a multistage cluster of remotely located UAV swarm has also been addressed by [PERSON] et al. [12]. The UAV swarm coordination protocol for supporting the assigned mission was reported by [13]. The problem of edge intelligence for UAV swarms has been discussed in [14]. Similarly, an adaptive weighted clustering algorithm is presented by [15]. [PERSON] summarized the trends and application areas of UAV swarms; he also discussed the layer-based control of swarms [16]. Another paper was found related to UAVs' collision avoidance, wherein, the author has discussed new approaches [17]. In addition, the uses of UAV swarms for modern applications are reported in [18].