Chronos: Scalable and Cost-Effective Cloud-based RAN Emulation System

Abstract

The trend towards softwarized and AI driven radio access network (RAN) in 5G and beyond has created a need for RAN emulators to test and enhance cellular network performance prior to real-world deployment. However, large-scale RAN emulation remains challenging due to the complexity of the RAN protocol stack and the high cost of hardware-based solutions. Software alternatives are more affordable but current solutions sacrifice scalability or fidelity. This paper presents Chronos, a cloud-based RAN emulation system that overcomes these challenges by abstracting the compute-intensive PHY layer, virtualizing emulation time, introducing RAN slot level synchronization, and scalable middlebox based traffic forwarding. Chronos operates at the FAPI boundary: it models PHY outcomes that affect higher-layer behavior, while deliberately excluding complex physical layer signal processing. Experiments using OpenAirInterface based prototype on cloud infrastructure demonstrate Chronos's ability to emulate a RAN with 10,000 mobile devices and 10,000 base stations on 130 cloud instances (with 6400 CPU cores), two orders of magnitude larger scale than existing solutions, reflecting its potential for enabling scalable RAN emulation in an affordable manner, all while maintaining fidelity.