Thor: Fine-grained Per-UE Baseband Routing in vRAN

Abstract

Today's virtualized and disaggregated RAN (vRAN) architectures bind all User Equipments (UEs) in a cell to a single PHY layer (L1) implementation, leaving operators with no ability to run multiple L1s concurrently and select different L1 processing for different UEs. As such, this precludes the possibility of incremental L1 updates, A/B testing of new L1s, and prevents any form of service differentiation at the L1. In this paper, we present Thor, a practical system that introduces a new primitive for vRANs: fine-grained per-UE baseband routing. Thor enables operators to route each UE to its designated L1 instance by interposing lightweight, standards-compliant middleboxes at the FAPI and O-RAN fronthaul interfaces. These middleboxes safely split and merge control, data, and IQ samples across multiple concurrently running L1 implementations while preserving cell-wide shared context and meeting strict slot-level deadlines. We prototype Thor on a standard-compliant 5G testbed and show that it is robust and incurs negligible overhead. Finally, we demonstrate Thor's per-UE baseband routing primitive using incremental L1 updates as an example case study.