Conflict-Aware xApp Admission Control With Priority-Based Preemption in O-RAN

Abstract

This paper investigates xApp conflict management in O-RAN from an admission-control perspective. We consider a representative conflict between a conditional handover (CHO) xApp and an energy-saving xApp, where inconsistent control actions may target the same small cell. To protect service-critical CHO actions, we propose a conflict-aware xApp admission control framework with priority-based preemption in the Near-RT RIC. The controller determines whether an arriving action is admitted, blocked, or admitted by preempting a lower-priority action. For performance analysis, we develop a two-dimensional continuous-time Markov chain (CTMC) in which xApp conflicts are embedded into state-dependent transition rates. From the steady-state distribution, we derive blocking, conflict, preemption, and utilization metrics and validate the analytical results through event-driven simulation. The framework is further generalized to $K$ priority classes with class-dependent conflict and preemption rules. A three-class analytical/simulation evaluation demonstrates distinct class-specific blocking and pairwise preemption behavior, confirming that the proposed framework can support multiple ordered priority levels. The CTMC is also coupled with the radio layer through a target-specific xApp control-exposure probability and radio-resource occupancy. Using 3GPP-aligned heterogeneous-network parameters, we evaluate co-tier and cross-tier interference under different macro/small-cell spectrum-overlap conditions. The results show that cross-tier interference reduces absolute CHO link reliability, whereas priority-based preemption consistently improves high-priority admission reliability.