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 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 firstly 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, open access protocols for flexible resource integration, security and privacy protection in the 6G era, as well as the digital twin concept. Finally, recent research efforts are analyzed with 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.