that if we cannot meet the QoS of all UEs, we will reject some of 9.1 A Framework of User Access Control for RAN Slicing the UEs to give more resources to others, thus avoiding significant overall network perfor- mance degradation. Before studying this problem, we first give the following assumption and definition. Assumption 9.1 Network slice allocates the minimal required wireless bandwidth to UEs to satisfy the UEs' QoS requirements. According to Assumption 9.1, the original constraints (9.1-3)-(9.1-5) about the QoS of UEs become equality constraints, and the admissible UEs obtained under Assumption 9.1 are still admissible for the original problem. Moreover, as we use this assumption, the allo- cated bandwidth wik is not the optimal variable for AC design. We will optimize wik in Section 9.1.3.2 by solving P1 for those admissible UEs. Definition 9.1 Subset A is an admissible UE set (AUS) if problem P1 is feasible when V is replaced by A. Definition 9.1 describes the feasibility of a UE subset. Hence, for a specific AUS, the RAN slicing can simultaneously guarantee the QoS of all the UEs in this AUS. However, it is not a sufficient condition to achieve good overall network performance. For example, it is meaningless to choose an AUS that contains only one UE. Therefore, we need to design an approach to find a UE subset that is not only feasible for problem P1 but also achieves good overall network performance. We will thus develop two AC schemes under Assumption 9.1 to optimize the QoS and the number of admissible UEs respectively. 9.1.3.1 Optimal QoS AC Mechanism We first consider the AC scheme from the UE QoS perspective. As not all UEs could be admissible, there is a gap between the achieved QoS and the required QoS of UEs (we use QoS degradation to represent this gap). Our main idea is to serve the UEs whose QoS can be satisfied simultaneously while minimizing the overall QoS degradation. To this end, we formulate a new optimization problem based on P1, and then design an AC policy based on the solution to