Prospects of 6G Technology Framework: A Big-Lite Multi-RATs Concept

The sixth generation mobile information network (6G) is expected to upgrade traditional communication functionalities and meanwhile introduce new capabilities such as sensing and artificial intelligence (AI), which reflects the trend of "more than communication." As the key performance indicators (KPIs) of 6G are currently being discussed by International Telecommunication Union (ITU), the study of technology framework is crucial to guide 6G air interface design. Notably, with a single framework that satisfies all the 6G KPIs, the protocol stack will inevitably become complex. On the other hand, if the 6G framework is divided into multiple sub-systems, multiple independent standards have to be developed. To address this issue, we introduce a concept called Big-Lite Multi-RATs, which suggests that 6G air interface consists of one big radio access technology (Big-RAT) and multiple lite radio access technologies (Lite-RATs). The common KPIs can be satisfied by the Big-RAT while some extreme KPIs can be served by the individual Lite-RATs. We demonstrate how this proposed multi-RAT approach can effectively serve the various use cases of 6G, and then briefly introduce the potential protocol stacks of the proposed framework. Additionally, we present our viewpoints on the potential development direction of the Big-RAT, including both qualitative and quantitative discussions. Finally, we outline critical technical directions for the Lite-RATs, accompanied by some detailed analysis. The proposed Big-Lite Multi-RATs concept is an innovative framework design for 6G that introduces entirely new RATs and coordinates the multiple RATs to organically serve various 6G use cases. Additionally, the protocol stack and air interface designs within this framework have the potential to significantly enhance 6G system performance.