dApps: Enabling Real-Time AI-Based Open RAN Control

TL;DR

This work addresses the limitation of traditional O-RAN xApps/rApps in accessing user-plane data and delivering control at sub-$10\,\mathrm{ms}$ timescales. It proposes dApps, a reference architecture with an E3 interface and the E2SM-DAPP service model, and an open-source dApp framework to run near the RAN CU/DU. The authors demonstrate real-time control loops with average latency around $400\,\mathrm{\mu s}$ on Colosseum and Arena testbeds, and validate two use cases: spectrum sharing and sensing/positioning. This framework enables secure, low-latency interaction between dApps, xApps, and the RAN stack, facilitating tighter, data-driven resource management and enhanced sensing capabilities in Open RAN.

Abstract

Open Radio Access Networks (RANs) leverage disaggregated and programmable RAN functions and open interfaces to enable closed-loop, data-driven radio resource management. This is performed through custom intelligent applications on the RAN Intelligent Controllers (RICs), optimizing RAN policy scheduling, network slicing, user session management, and medium access control, among others. In this context, we have proposed dApps as a key extension of the O-RAN architecture into the real-time and user-plane domains. Deployed directly on RAN nodes, dApps access data otherwise unavailable to RICs due to privacy or timing constraints, enabling the execution of control actions within shorter time intervals. In this paper, we propose for the first time a reference architecture for dApps, defining their life cycle from deployment by the Service Management and Orchestration (SMO) to real-time control loop interactions with the RAN nodes where they are hosted. We introduce a new dApp interface, E3, along with an Application Protocol (AP) that supports structured message exchanges and extensible communication for various service models. By bridging E3 with the existing O-RAN E2 interface, we enable dApps, xApps, and rApps to coexist and coordinate. These applications can then collaborate on complex use cases and employ hierarchical control to resolve shared resource conflicts. Finally, we present and open-source a dApp framework based on OpenAirInterface (OAI). We benchmark its performance in two real-time control use cases, i.e., spectrum sharing and positioning in a 5th generation (5G) Next Generation Node Base (gNB) scenario. Our experimental results show that standardized real-time control loops via dApps are feasible, achieving average control latency below 450 microseconds and allowing optimal use of shared spectral resources.

Figures (12)

• Figure 1: Comparison between RT RIC and dApp architectures. From dappsOranReport.
• Figure 2: O-RAN control loops, limitations, and extensions to the real-time and user-plane domains. Adapted from polese2023understanding.
• Figure 3: O-RAN Near-RT integration with dApps and a generic node.
• Figure 4: Message exchanges for a real time control loop between a dApp and the node through the E3 interface.
• Figure 5: Interactions between a dApp, the E2 node, and an xApp through the E3 interface and the E2SM-DAPP custom Service Model.