# UAV-Enabled Mobile Edge-Computing for IoT Based on AI: A Comprehensive Review
## 2 UAV System Model
### UAV-Enabled and -Assisted MEC Architecture  
Centralized networks are easy to maintain because they have just one point of failure. However, due to the instability of the system categories, this design is insufficient to respond to ubiquitous applications. A single issue affecting the core server might destroy the entire system. Unlike centralized networks, distributed networks are deemed more stable due to their decentralized architecture, since the entirety of the information system is dispersed among a vast number of nodes that maintain similar conditions. This feature improves distributed system security by making it challenging to target many users. Furthermore, blockchain is a peer-to-peer (P2P) distributed ledger that provides a secure, immutable, transparent, and trustless environment due to its distributed architecture. Integrating this approach with UAVs allows them to record their data in the chain of blocks as a transaction, ensuring their trustworthiness [74]. The essential foundations of blockchain technology are intelligent contracts and consensus mechanisms. This method eliminates the requirement for a trusted third-party system to protect data privacy since consensus techniques maintain data integrity. The use of cryptographic methods guarantees that data on blockchains are secure. These exciting blockchain characteristics increase the applicability of UAVs in a variety of civil and mission-critical applications that use UAV-enabled MEC architecture. Moreover, distributed systems outperform centralized systems in terms of network speed, since the information is not stored in a central location, and the number of users attempting to access a server is more significant than the server can support, causing long waiting times and slowing down the system for decentralized architecture. Moving all computing activities to the cloud has proven an effective mechanism to process data since the cloud offers greater processing capacity than network edge devices. However, data-processing speeds have risen rapidly due to the size of communicated data and the networks' bandwidth. Therefore, CC suffers from bottlenecks due to the massive volume of data generated in real time. Cameras in UAVs capture a tremendous amount of video data, which the system should process in real-time to enable good decision-making. Sending data from UAVs to the cloud server would mostly result in longer delays. Deploying a large number of IoT devices, such as UAVs, would restrict bandwidth, reliability and security. Therefore, processing data at the network edge would yield shorter response times, more efficient processing, and less pressure on the network. MEC is widely acknowledged as a vital technology to implement many methods for next-generation IoT applications. Due to their versatility and ease of deployment, UAVs can play various roles in delivering edge computing services. UAV-enabled MEC designs can be classified and dedicated to a specific application scenario. A UAV can be considered as a mobile EC server, an IoT node, or a relay. Firstly, UAVs can participate in the system as mobile devices when they offload their computing to an MEC server. Secondly, the UAV can act as the MEC responsible for monitoring a group of mobile end nodes. Thirdly, the UAV can serve as a relay or gateway between mobile end nodes and an MEC server. The UAV may be regarded as a specific user that could offload those computing tasks exceeding its memory and processing capacity to a MEC server, as shown in Figure 4a. UAVs typically have limited battery capacity and insufficient memory and computing power to execute complex computational tasks. As a result, offloading their processing to the ground MEC server for computation may increase its battery life. In another situation, as shown in Figure 4b, the UAV may keep the MEC server on board and fly to assist the ground-based users with the task of computing once the ground-based users offload their computation responsibilities to the latter.