Demo: Chronos - A Cloud-based RAN Emulation System

Abstract

We demonstrate Chronos, a cloud-based RAN emulator that allows running unmodified 4G/5G protocol stack software at large scale over commodity cloud VMs, using OpenAirInterface as the representative vRAN software. Chronos replaces compute-intensive PHY processing at the FAPI boundary, while employing time dilation and slot-level synchronization to preserve RAN timing semantics despite variable number/type of cloud resources. The demo presents four capabilities. First, fidelity is demonstrated by comparing a Chronos UE with a Commercial-Off-The-Shelf (COTS) UE using attach packet captures, gNodeB (gNB) logs, latency under two gNB configurations, and traffic responses to the same CQI trace. Second, scalability is demonstrated by scaling from one to hundreds of gNBs and UEs on a fixed compute pool while monitoring attach success, throughput, latency, and time dilation. Third, a closed-loop O-RAN control is demonstrated with a custom xApp that changes the OLLA target BLER through E2SM-RC and tracks the resulting link-adaptation response. Finally, a mobility controller triggers handovers from overloaded cells to underutilized neighbors while maintaining active UE traffic. Together, these scenarios show that Chronos supports faithful, scalable, and closed-loop RAN experimentation entirely in the cloud.