# From 5G to 6G--Challenges, Technologies, and Applications
## 4 Current Research
### Numerical Discussion
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Paper** & \multicolumn{1}{c}{**Main Contribution**} \\ \hline
[144] & Presented a comprehensive overview of the challenges faced by the main 6G technologies, such as distributed massive multiple-input, multiple-output (MIMO), and terahertz communications. & Gave an in-depth study of antenna types and their operational frequency, and phased array designs. \\ \hline
[145] & Gave an overview of the timeline of wireless communication generations and a comprehensive look at 6G networks in great depth, in addition to different ongoing global 6G projects and standards. & Compared different surveys of 6G networks from depth point of view and 6G technology-related work. \\ \hline
[146] & Focused on the discussion of 6G technologies and their architecture in 6G and the associated challenges with different deployment scenarios and the global research groups’ work on 6G. & Laid out 6G’s technical requirements and a detailed description of virtualized network slicing. \\ \hline
[147] & Concentrated on presenting a comprehensive study of 6G radio access network techniques and 6G- enabling technologies and requirements, as well the roles of AI and energy harvesting in 6G. & Described the architecture of cloud, edge AI, and network slicing in 6G networks. \\ \hline
[148] & Gave an in-depth overview of 6G’s usage scenarios, architecture, requirements, key technologies, challenges, timelines, and activities globally. & Gave a summary of the state-of-the-art works on 6G from the literature and KPIs as 6G enablers. \\ \hline
[149] & In addition to reviewing 6G’s requirements and key enablers, this work focused on presenting in-depth discussions of and architectures for security in 6G technologies and their challenges. & Detailed many security threats and the global teams working on 6G projects related to security. \\ \hline
[150] & Discussed key 6G technologies to enable UAV networks and presented the 6G space-air-ground integrated networks (SAGINs) architecture and compared different airspace management techniques and designs. & Presented and studied full designs for each network layer (ground, air, and space). \\ \hline
[151] & Presented a comprehensive study of 6G networks including the challenges, requirements, key drivers, future trends, architecture, and global research on 6G by various countries. & Detailed 6G’s KPIs with values and use cases and surveyed works on 6G and its technologies. \\ \hline
[152] & Gave a vision of 6G networks and focused on massive IoT and SAGIN architectures in 6G and the framework for the main 6G technologies including AI, blockchain, automation, and distribution. & Focused on the roles of ML and surveyed the literature related to ML in the IoT framework. \\ \hline
[153] & Besides drawing 6G’s vision and requirements, it discussed the architecture of IoT networks in 6G and their use cases and showed how radio-over-fiber (RoF) systems will operate in 6G. & Surveyed the literature on 6G and IoT integration solutions, RoF applications, and IoT-RoF integration. \\ \hline
[154] & Described 6G’s requirements and technologies and focused on the role of transfer learning (TL) in 6G by displaying possible scenarios and integration techniques and challenges. & Presented an in-depth classification and description of TL methods and works on this in the literature. \\ \hline
[155] & Presented a comprehensive study of 6G including its vision, requirements, and enablers and discussed network design principles, new PLS techniques, propagation characteristics, and RF transceiver design. & Exploited ultra-massive MIMO systems and IRSs for 6G and terahertz signal propagation and attenuation. \\ \hline
[156] & Presented a comprehensive view of 6G networks and focused on energy and spectral efficiency techniques, SAGINs, coverage, privacy, AI, and ultra-reliable and lowlatency communication (URLLC) in 6G. & Surveyed the literature on 6G papers and focused on green communication and the smart Internet. \\ \hline \hline \end{tabular}
\end{table}