ration, management, and optimization. References 1. Shuangfeng Han, Tian Xie, Chih-Lin I, Li Chai, Zhiming Liu, Yifei Yuan, Chunfeng Cui, "Artificial-Intelligence-Enabled Air Interface for 6G: Solutions, Challenges, and Standardization Impacts", vol. 58, no. 10, pp. 73-79, IEEE Communications Magazine, October 2020. 2. Mohammad A. Matin, Mohammad S. Sharawi, Sotirios K. Goudos, Jiang Zhu "Antenna Systems for 5G and Beyond" IEEE Communications Magazine, Jan. Dhaka, Bangladesh Mohammad Abdul Matin Acknowledgments In the first place, I am grateful to my Lord Almighty ALLAH who helped and guided me throughout my life. I would like to acknowledge the effort and time invested by all contributors for their excellent work in completing this book, also thanks to the authors whose manuscripts were not included due to rigorous review process. I am indebted to numerous reviewers for valuable suggestions and comments during the review process. The authors were SO cooperative during different stages of book development. I am also beholden to the Springer team, in particular Mary James for her cordial assistance throughout this project. I wish to include here a word of appreciation to them including Mr. Arun Siva Shanmugam for smoothly and efficiently handling the project from the beginning until the final stage of production and keeping it in line with the publisher's policies. I would also like to thank my wife Momtaz Begum and my children Zabeer Ahmed and Zawad Ahmed for their constant encouragement, patience, and understanding throughout the project. My special thanks to Mrs. Sufia Khaton (dearest mother) for the motivation that has encouraged me to keep going. North South University, Bangladesh Mohammad Abdul Matin Contents A Comprehensive Study on 5G: RAN Architecture, Enabling Technologies, Challenges, and Deployment Mohammed Alfaqawi, Martine Gateau, Patrick Huard, Pascal Reungoat, Marie-Christine Le Mercier, Stéphane Davai, and Mouna Ben Mabrouk Information Flows at the Deep Physical Layer Level Marco Donald Migliore F