A Survey on Architectural Approaches for 6G Networks: Implementation Challenges, Current Trends, and Future Directions

As the discussions on sixth-generation (6G) wireless networks progress at a rapid pace, various approaches have emerged over the last few years regarding new architectural concepts that can support the 6G vision. Therefore, the goal of this work is to highlight the most important technological efforts in relation to the definition of a 6G architectural concept. To this end, the primary challenges are first described, which can be viewed as the driving forces for the 6G architectural standardization. Afterwards, novel technological approaches are discussed to support the 6G concept, such as the introduction of artificial intelligence and machine learning for resource optimization and threat mitigation, cell-free deployments, and novel physical layer techniques to leverage high data rates. In the same context, open-access protocols for flexible resource integration, security, and privacy protection in the 6G era, as well as the digital twin concept, are discussed as well. Finally, recent research efforts are analyzed, with an emphasis on the combination of the aforementioned aspects towards a unified 6G architectural approach. To this end, limitations and open issues are highlighted as well.