An Overview of Flexible Spectrum Management Approaches for 6G

6G networks will operate on a wider range of frequencies and channel sizes compared to previous generations of cellular networks. Using multiple frequency bands to ensure seamless connectivity, increased capacity, and improved spectral efficiency requires innovation in spectrum management, as most of the considered bands are already used by other radio technologies and services. The main challenge for spectrum management is to manage the very fragmented spectrum bands, and, at the same, time co-exist with the earlier cellular network generations, non-terrestrial networks and unlicensed technologies. At higher frequencies, sub-THz bands exhibit propagation characteristics that lead to narrow-beam alignment inefficiencies, severe attenuation, and susceptibility to blockage, complicating low-latency channel access. This paper addresses all these critical challenges and proposes solutions such as inter-technology handshaking protocol to mitigate interference and improve performance whenever possible. System-level evaluations demonstrate the effectiveness of multi-radio spectrum sharing (MRSS) between 5G and 6G networks. A multi-pronged approach is proposed to mitigate mutual interference between terrestrial and non-terrestrial networks. A non-standalone, booster-based radio access approach is proposed to provide low-latency access to sub-THz communications, while a risk-informed random access method is proposed to dynamically balance interference risks in loosely coupled, uncoordinated radio systems. The findings highlight the importance of dynamic and flexible spectrum frameworks, cooperative spectrum-sharing policies, and intelligent interference management strategies to ensure a smooth transition from 5G to 6G.