### Related Previous Works  
A wide range of topics is covered in the latest papers, including networking upgrades, applications and security for 6G communication. As technology progresses, UAV communication is moving toward 6G networks and research papers have risen to various degrees in the previous three years. Our research strategy allows us to obtain a bird's eye view of the existing literature on basic 6G UAV communication technologies, with a focus on the research topic we have chosen. Because of the broader scope of research, UAV communication offers potential in a variety of disciplines, including academia, industry and even the military. Since the existence of bitcoin, the globe has seen the great worth of such a decentralized system, that can be implemented in many fields [9]. Similarly, Ethereum blockchain utilizes the concept of smart contracts and is acknowledged as an extension of core blockchain idea [10]. The extension of key properties of blockchain is being realized by the introduction of a smart contract that goes beyond just recording ledger transactions in accounts, which permits the distributed implementation of code. To increase the strength of the blockchain system to not just act as a database, the smart contracts can be implemented in a customized manner to allow enforcement of contracts and storage. A conventional centralized system serves almost all Internet of Things (IoT) devices over legacy internet. The blockchain has brought up a new concept, in the way that these devices now can communicate with each other, known as a decentralized system. This concept makes the blockchain system even more robust and prevents a single point of failure and ensures immutable data transfer between nodes. The diverse nature of IoT devices presents few challenges to blockchain applications converse to the typical implementation of blockchain that necessitates clusters and powerful computing machines [11]. Moreover, the system can work in entire anonymity, causing increases in its security. An IoT device does not possess enough CPU power to solve cryptographic puzzles that are required to be solved in a blockchain system. For stated causes, it is unworkable to have an IoT apparatus (e.g., UAVs) executing the typical mining algorithms [12]. Additionally, these devices do not possess the ability for storage of bigger amounts of data due to less storage capacity. In order to allow blockchain to be implemented in relatively low capacity IoT systems, recent studies have suggested a few mechanisms. For example, they can be executed on the basis of partitioning a single blockchain network in sub-chains under the control of a root-chain [13]. The root-chain at the top contains powerful computers and IoT devices reside at the bottom of this hierarchical system of chains, which connect with each other. Another concept named Tangles that is based on mathematical structures has been proposed in recent studies to adapt a blockchain system by small devices [14]. Subsequently, this new transaction allows two transactions, directly and indirectly, consequently, to perform approval of all transactions that these two tip transactions point to. In this concept, there is no need for miners and no node is neglected as every node gives approval for the transactions, and each node publishes transactions since each new transaction to be linked to Tangle necessitates transaction approval. As stated above, there is no requirement for miners to eliminate the associated fees with every transaction and this permits micro payment economy. One of the pertinent features of the Tangle concept is its high scalability as the trust in a transaction grows around the number of transactions that approve that transaction directly and indirectly [15]. The growth rate of trustfulness in a specific transaction increases as the number of new transactions increases. Hence, the time period for approval of a transaction is less on a network with a high load compared to a low load network.