H procedures and have an established control channel (bearer). These connected users may or may not have actual data available for transmission. Connected user count can be 1000 seconds. Active users are the subset of connected users that have actual data available for transmission and as such should be considered for scheduling air resources to. Note that active user selection can include air interface-specific limitations such as Discontinuous Reception (DRX) operation where a mobile phone is spending time in power saving mode and hence cannot be scheduled, even if there is traffic available for transmission. Active user count can be 100 seconds. Eligible users are the subset of active users that are considered for actual scheduling based on exhibiting "schedulability" metrics even though they may not actually end up being selected for scheduling. This is an optional stage implemented to reduce compute complexity by reducing the active user count (100 seconds) to a smaller user count of 10 seconds of users that are considered further. Scheduled users are the subset of eligible users that are scheduled in the specific time instance under consideration. Scheduled user count typically is in the order of 10. Connected users Active users Eligible users Scheduled users FIGURE 7-7 User database reduction for scheduler user selection. 250 Open Radio Access Network (O-RAN) Systems Architecture and Design Practical implementations breakdowns consider the following: Static and regular scheduling-allocate resources to prescheduled (statically scheduled) users, hybrid-ARQ (HARQ), broadcast, and other channels that are not subject to dynamic scheduling. Active user selection-filter - out the users that are potential targets for scheduling to reduce computational load on remainder stages. Primary user selection-based on proportional fair (PF) scheduling to balance the competing interests of maximizing the network throughput while ensuring a minimum QoS is met. This stage is also known as "time-domain scheduling." Frequency re