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.

翻译：开放无线接入网络（RAN）利用解耦且可编程的RAN功能与开放接口，实现了闭环、数据驱动的无线资源管理。这一过程通过部署在RAN智能控制器上的定制化智能应用完成，优化了RAN策略调度、网络切片、用户会话管理及介质访问控制等功能。在此背景下，我们提出将dApps作为O-RAN架构向实时域与用户平面域扩展的关键组成部分。dApps直接部署于RAN节点，可访问因隐私或时序限制而无法被RIC获取的数据，从而在更短时间间隔内执行控制操作。本文首次提出了dApps的参考架构，定义了其从服务管理与编排部署到与宿主RAN节点进行实时控制循环交互的全生命周期。我们引入了新型dApp接口E3及其配套应用协议，该协议支持结构化消息交换与可扩展通信，适用于多种服务模型。通过将E3与现有O-RAN E2接口对接，我们实现了dApps、xApps及rApps的共存与协同。这些应用可协作处理复杂用例，并采用分层控制机制解决共享资源冲突。最后，我们基于OpenAirInterface开发并开源了dApp框架，在5G下一代基站场景下的频谱共享与定位两个实时控制用例中进行了性能基准测试。实验结果表明，通过dApps实现标准化实时控制循环具备可行性，平均控制延迟低于450微秒，并能实现共享频谱资源的最优利用。