In a cellular wireless system, power thresholds used for determining whether to add or drop servers held in a set of servers, such as an active set, for serving a user equipment (UE) are determined based on the motion of the respective UE. A lower threshold may be used with respect to the adding or dropping of a given server to or from a set of servers for serving a fast moving UE than would be used for the same server with respect to adding or dropping to or from a set of servers for serving a slow moving UE, while maintaining a given quality of service. As a result, the average number of servers held in sets is reduced in a typical network that comprises a plurality of UEs moving at different speeds, compared to a situation in which the threshold is set irrespective of the motion of a UE.