Self-Organizing Networks in the 6G Era: State-of-the-Art, Opportunities, Challenges, and Future Trends

Self-organizing networks (SONs) need to be endowed with self-coordination capabilities to manage the complex relations between their internal components and to avoid their destructive interactions. Existing communication technologies commonly implement responsive self-coordination mechanisms that can be very slow in run-time situations. The sixth generation (6G) networks, being in their early stages of research and standardization activities, open new opportunities to opt for a design-driven approach when developing self-coordination capabilities. This can be achieved through the use of hybrid weakly coupled SON designs. In this article, we review the history of SONs including the inherent self-coordination feature. We then delve into the concept of hybrid SONs (H-SONs), and we summarize the challenges, opportunities, and future trends for H-SON development. We provide a comprehensive collection of standardization activities and recommendations, discussing the key contributions and potential work to continue the evolution and push for a wide adoption of the H-SON paradigm. More importantly, we propose that H-SONs must be weakly coupled networks, i.e., the various feedback loops must be almost isolated from each other to improve the stability and to avoid chaotic situations. We finally conclude the paper with the key hints about the future landscape and the key drivers of 6G H-SONs.