ABSTRACT PROBLEMS AND FEATURES OF 5G AND 6G NETWORKS: A SUBJECT FIELD REVIEW

6G and beyond will fulfill the requirements of a fully connected world and provide ubiquitous wireless connectivity for all. Transformative solutions are expected to drive the surge for accommodating a rapidly growing number of intelligent devices and services. Major technological breakthroughs to achieve connectivity goals within 6G include: line-of-sight blocking, energy efficiency, micromobility, antenna equipment, spreading loss, path losses and cell-free massive MIMO communication networks. The searches were conducted in Scopus electronic database from September 2006 to December 2021. A total of 2,178 papers were identified, 80 articles were selected based on the predetermined eligibility criteria and included in this review with a total of 28564 participants combined. The majority of studies focused on energy efficiency and line-of-sight blocking. In this roadmap paper, use cases for these enabling techniques as well as recent advancements on related topics are highlighted, and open problems with possible solutions are discussed, followed by a development timeline outlining the worldwide efforts in the realization of 6G. Going beyond 6G, promising early-stage technologies such as the Internet of NanoThings, the Internet of BioNanoThings, and quantum communications, which are expected to have a far-reaching impact on wireless communications, have also been discussed at length in this paper. The results of this subject field review can be used by the professionals interested in the topic.