In recent years, the Open Radio Access Network (O-RAN) architecture has emerged as a major driving force for programmability in cellular networks and is recognized as a key enabler for network slicing within 5G and beyond. While O-RAN harbors the potential to revolutionize cellular access networks, the absence of an open platform for use case prototyping has served as an impediment to its widespread adoption. The situation is further compounded by the fact that O-RAN's flagship use case, network slicing, presents a rigid dichotomy. On the one hand, systems research in the slicing domain is largely centered around LTE, while, on the other hand, 3GPP slicing specifications exclusively cater to 5G Standalone (SA). From a practical standpoint, most commercial networks today use a mix of 4G, 5G NSA (Non-standalone), and 5G SA, necessitating the need for solutions across all radio access technologies (RATs). With a view to addressing these challenges, this paper introduces HexRAN, a first of its kind purpose-built multi-RAT O-RAN compliant access network. Key highlights of HexRAN include support for LTE, 5G NSA, and 5G SA with full disaggregation, a novel Programmable Protocol-level API repository, a multi-RAT RAN slicing framework, a modular and extensible E2 Agent, and a new O-RAN service model in support of slicing. Furthermore, the paper also includes a comprehensive system evaluation addressing the key themes of scalability and disaggregation, the slicing framework's impact, and system performance. The results thus obtained showcase that not only is HexRAN the most feature-complete RAN platform to date, it also offers a significant performance advantage over the prior art.

翻译：近年来，开放无线接入网（O-RAN）架构已成为蜂窝网络可编程性的主要驱动力，并被公认为5G及未来网络切片的关键使能技术。尽管O-RAN具有革新蜂窝接入网络的潜力，但缺乏用于用例原型开发的开放平台阻碍了其广泛采用。此外，O-RAN的旗舰用例——网络切片——呈现出严格的两极化问题：一方面，切片领域的系统研究主要围绕LTE展开；另一方面，3GPP切片规范仅针对5G独立组网（SA）。从实际角度来看，当前大多数商用网络混合使用4G、5G非独立组网（NSA）和5G SA，这要求解决方案能够兼容所有无线接入技术（RAT）。为应对这些挑战，本文首次提出HexRAN——一种专为多RAT设计的O-RAN兼容接入网络平台。HexRAN的核心特性包括：支持LTE、5G NSA与5G SA的完全解耦，新型可编程协议级API库，多RAT RAN切片框架，模块化可扩展的E2智能体，以及支持切片的新型O-RAN服务模型。此外，本文还通过系统级评估深入探讨了可扩展性与解耦性、切片框架的影响及系统性能等关键议题。实验结果表明，HexRAN不仅是当前功能最完备的RAN平台，其性能也显著优于现有技术方案。