Service Service layer Slice 1 Slice Slice 3 Slice 4 Slice layer Spectrum allocated Figure 8.7 Concept of network slicing. 8 Network Slicing with Spectrum Sharing In [25] the authors state that RAN sharing will become more common as studies have shown [30] that resources belonging to an operator are often underutilized. They define a slice in Kokku et al. [25] as "a group of user flows that belongs to a single entity and requires a chosen fraction of spectrum resources to be allocated for satisfying the service level agree- ments (SLAs)." They do not specify that it is a contiguous block of spectrum in each cell. In [26], the authors note that it is possible to dynamically allocate the RBs across mutually interfering cells in a multi-cell arrangement, and thus to dynamically assign RBs to slices in a coordinated manner. This is reinforced by the authors in [31] who agree that "a better method is to allow all operators access to the whole bandwidth but apply a mechanism to manage the fraction of resources each operator consumes on average." Allowing such fully dynamic access to all of the spectrum was shown in Yang et al. [32] to not only give higher efficiency but also better fairness between slices. While this fully dynamic sharing seems at first sight to violate the principles of slicing, logically it provides exactly the same independence for each slice: instead of the slice having a fixed resource allocation, the slice specifies the requirements under an SLA and the RAN is managed to deliver those SLAs. Moreover, fixed slicing is not really sharing of spectrum; it is just allocating different blocks of spectrum to different slices. This arrangement does not allow for changing demand, and ICI means that there can be intra-slice interference. However, another aspect that needs considering with dynamic RAN slicing is the need to provide isolation between slices [23, 33]: what happens in one slice should not affect users in other slices. In the multi-cell RAN scenario, interference reduces isolation because a new 