: Reprinted from Liu et al. 2016 [18] under the terms of the ACM author copyright licence. Increasing distance From NOA Queue of users From NO Overall serving order Light load Effective QUR = 1:1 -sufficient RBs Heavy load 00000000 Effective QUR = 2:1 -insufficient RBs These two users are not qualified as there are insufficient resources Figure 8.6 Illustration of variability in implicit sharing. Source: Reprinted from Liu et al. 2016 [18] under the terms of the ACM author copyright licence. users, leading to the case where a user of NO A cannot be served, but a following user of NO has better channel conditions and can be served. However, sharing spectrum in this way is not a precise share as the ratio of the numbers of users served between the operators will vary depending on the user distribution and channel conditions, as illustrated in the very simple example of Figure 8.6. 8 Network Slicing with Spectrum Sharing In this example, with such a small number of users in the diagram, the variability is exag- gerated, but it does illustrate the reasons behind that variability. In the example there is an equal number of users from both operators, but the intention is to allocate twice as much spectrum to NOA as NO SO the serving order is user 1, user A2, user1, user a3, user 4, user2, The effective qualified user ratio (QUR) in this case gives the ratio of users achieving the required QoS between the two operators. More Complex Forms of Sharing While explicit spectrum sharing allocates spectrum between operators, it takes no account of the impact of that sharing on the number of qualified users, and with uneven distribu- tions this may lead to very unequal QURs. On the other hand, implicit spectrum sharing, while concentrating on user priorities, does not consider the actual spectrum sharing at all. To balance fairness between spectrum allocation and users served, more complex forms of sharing are required. An example of this was given in Liu et al. [18] where an explicit shar- ing ratio was used, but the allocatio