This paper presents a survey of the state of the art in research related to handovers employing software defined networking (SDN) enabled architectures, serving multiple coexisting radio access technologies. As the industrial roll-out of cellular services continues to evolve, it brings with it the coexistence of various IP based networks such as 5G NR, LTE, WiFi, Satellite, and IoT networks. This coexistence of different radio access technologies presents researchers with the opportunity to use these technologies interchangeably to address the longstanding challenges associated with network and traffic management. Advances in software defined technologies including SDN enables handover and interoperability schemes that utilize the principles of SDN to improve the handover performance and achieve interconnection between these heterogeneous networks. This paper explores such advanced SDN enabled architectures for radio access networks, offloading techniques, and implementation approaches. Finally, the challenges and shortcomings of the SDN based handover optimization approaches are discussed, and a few future research paths are laid out.

翻译：本文对采用软件定义网络架构、服务于多种共存无线电接入技术的切换相关研究现状进行了综述。随着蜂窝服务的产业部署持续演进，5G NR、LTE、WiFi、卫星及物联网网络等各类基于IP的网络共存态势日益凸显。不同无线电接入技术的并存为研究人员提供了交替运用这些技术以应对网络与流量管理长期挑战的契机。软件定义技术的进步催生了基于SDN原理的切换与互操作方案，可改善切换性能并实现异构网络间的互联。本文深入探究了此类先进SDN架构在无线接入网络中的应用、卸载技术及实现方法，最后讨论了基于SDN的切换优化方法面临的挑战与不足，并提出了未来若干研究方向。