Operators have tended to use the “layer-cake” analogy when describing their spectrum needs. This typically involves low-band spectrum below 1 GHz that provides significant propagation characteristics for coverage; a mid-band of spectrum between 1.5 GHz and 15 GHz that is a mix of capacity and modest coverage; and then high-band, millimeter-wave (mmWave) spectrum above 20 GHz that typically has a lot of capacity but struggles with coverage.
The challenge for 6G is that there is little new low-band spectrum that can be directed toward the mobile communications space. Some of those bands have already been allocated to mobile operators and will need to be re-farmed to support 6G, though there could be opportunities to free up resources that are currently held by television broadcasters.