Exploring the Capabilities of xApps in O-RAN: From Conceptualization to Practical Implementation

Abstract

This paper serves as a foundation for researchers and practitioners to explore the key concepts, primary applications, and potential impacts of xApps in the open radio access network (O-RAN) architecture. We provide background information and examples related to xApps and discuss several fundamental concepts to familiarize readers with the key notions presented throughout the paper. In addition, we propose an architectural framework for the development and deployment of xApps within the near-real-time RAN intelligent controller (Near-RT RIC), offering a concise examination of its features, components, and interactions through internal and external open interfaces. Moreover, we explore three major aspects of the Near-RT RIC: the Near-RT RIC platform, the Near-RT RIC-related application programming interfaces (APIs), and the E2 service model (E2SM). Our primary objective is to provide a broader perspective on the theoretical foundation and practical implementation of xApps. Specifically, a) we examine the Near-RT RIC platform to understand how its functionalities facilitate the deployment and monitoring of xApps, b) investigate the APIs to comprehend the interconnections and data exchanges between xApps, the Near-RT RIC platform, and other components within O-RAN, and c) analyze the E2SM, which governs the interactions and actions of xApps with E2 Nodes. Furthermore, we shed light on the management and orchestration of a collection of xApps within the Near-RT RIC, as well as present the lifecycle management of an individual xApp, detailing the phases from design to termination. Subsequently, we demonstrate the practical implementation of an open-source xApp (the key performance indicator [KPI] Monitoring xApp) in our O-RAN testbed. To accomplish this, we offer a detailed overview of the xApp, discuss the setup and architecture of our testbed (including the hardware and software components used), and provide a step-by-step guide to implementing this xApp in the testbed. Following that, we explain xApp-related conflict mitigation, addressing a range of topics, with a particular focus on the types of xApp-level conflicts and corresponding mitigation strategies. We then present several lessons learned from our research on xApps and their practical deployment. Finally, we identify several research and engineering challenges that need further effort to develop novel xApps and ensure their seamless deployment in O-RAN.