Inter-DU Load Balancing in an Experimental Over-the-Air 5G Open Radio Access Network

2025-09-02

AI Summary

Load imbalance among Open Distributed Units (O-DUs) in 5G O-RAN architectures degrades resource utilization and user QoS. Method: We design the first fully open-source, real-wireless-environment-enabled closed-loop inter-O-DU load balancing system. Leveraging the Near-Real-Time RAN Intelligent Controller (Near-RT RIC) and xApp framework, we extend the srsRAN protocol stack to support E2SM-RC Style 3 Action 1 and MAC-layer downlink buffer status reporting. The system integrates Open5GS core network, SDR hardware, and commercial 5G NR SA user equipment to enable real-time cross-band O-DU load sensing, decision-making, and handover control. Contribution/Results: This work presents the first end-to-end, O-RAN-compliant dynamic load balancing closed loop validated in a live 5G NR standalone deployment. Experiments demonstrate significant improvements in network resource efficiency and user QoS, establishing a reproducible, scalable, and open-source reference for O-RAN intelligent operations and maintenance.

Technology Category

• Planning, Routing, and Scheduling: Plan Execution and Monitoring
• Intelligent Robots: Learning & Optimization for ROB
• Search and Optimization: Distributed Search

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Responsible Web: Data and user privacy-enhancing technologies for the Web

Abstract

This paper presents the first ever fully open-source implementation of Load Balancing (LB) in an experimental Fifth Generation (5G) New Radio (NR) Standalone (SA) network using Open Radio Access Network (O-RAN) architecture. The deployment leverages the O-RAN Software Community (SC) Near Real-Time RAN Intelligent Controller (Near-RT RIC), srsRAN stack, Open5GS core, and Software-Defined Radios (SDRs), with Commercial Off-The-Shelf (COTS) User Equipments (UEs). The implementation extends the srsRAN stack to support E2 Service Model for RAN Control (E2SM-RC) Style 3 Action 1 to facilitate Handovers (HOs) and adds Medium Access Control (MAC) downlink (DL) buffer volume reporting to srsRAN's E2 Service Model for Key Performance Measurement (E2SM-KPM). The deployment demonstrates Near-RT RIC closed-loop control where our Mobility Load Balancing (MLB) xApp makes HO decisions based on network load metrics for LB between two Open Distributed Units (O-DUs) operating at different frequencies in the same band.

Problem

• Implementing load balancing in 5G O-RAN architecture
• Extending srsRAN stack for handover control functionality
• Demonstrating closed-loop load balancing between distributed units

Innovation

• Open-source O-RAN load balancing implementation
• Extended srsRAN with E2SM-RC and KPM enhancements
• Near-RT RIC closed-loop control for inter-DU handovers