The Open Radio Access Network (O-RAN) Alliance proposes an open architecture that disaggregates the RAN and supports executing custom control logic in near-real time from third-party applications, the xApps. Despite O-RAN's efforts, the creation of xApps remains a complex and time-consuming endeavor, aggravated by the sometimes fragmented, outdated, or deprecated documentation from the O-RAN Software Community (OSC). These challenges hinder academia and industry from developing and validating solutions and algorithms on O-RAN networks. This tutorial addresses this gap by providing the first comprehensive guide for developing xApps to manage the O-RAN ecosystem from theory to practice. We provide a thorough theoretical foundation of the O-RAN architecture and detail the functionality offered by Near Real-Time RAN Intelligent Controller (Near-RT RIC) components. We examine the xApp design and configuration. We explore the xApp lifecycle and demonstrate how to deploy and manage xApps on a Near-RT RIC. We address the xApps' interfaces and capabilities, accompanied by practical examples. We provide comprehensive details on how xApps can control the RAN. We discuss debugging strategies and good practices to aid the xApp developers in testing their xApps. Finally, we review the current landscape and open challenges for creating xApps.

翻译：开放无线接入网（O-RAN）联盟提出了一种开放式架构，该架构解耦了无线接入网（RAN）功能，并支持通过第三方应用程序（即xApp）以近实时方式执行定制控制逻辑。尽管O-RAN联盟已付出诸多努力，xApp的开发仍然是一项复杂且耗时的工作，而O-RAN软件社区（OSC）文档存在的碎片化、过时或已弃用等问题进一步加剧了开发难度。这些挑战阻碍了学术界和工业界在O-RAN网络上开发与验证解决方案及算法的进程。本教程通过提供首份涵盖从理论到实践的xApp开发完整指南，以弥补这一空白。我们系统阐述了O-RAN架构的理论基础，详细解析了近实时无线接入网智能控制器（Near-RT RIC）组件的功能特性，深入探讨了xApp的设计与配置方法。通过剖析xApp的生命周期，我们演示了在Near-RT RIC上部署与管理xApp的具体流程，并结合实际案例说明了xApp的接口规范与功能实现。我们全面阐述了xApp控制无线接入网的技术细节，讨论了调试策略与最佳实践以协助开发者测试xApp。最后，我们对当前xApp开发领域的现状与开放挑战进行了总结与展望。