O-RU, O-DU & O-CU
O-RAN Radio Unit, Distributed Unit & Centralized Unit
The three physically disaggregated, multi-vendor-interoperable hardware/software elements that an O-RAN gNodeB is split into.
Technical Explanation
The O-RU (O-RAN Radio Unit) performs RF conversion, PHY-layer low functions (FFT/iFFT, CP handling), and beamforming weight application, connecting to the O-DU over the Open Fronthaul interface. The O-DU (O-RAN Distributed Unit) hosts the upper-PHY, MAC, and RLC layers for one or more cell sites, typically at a nearby edge site. The O-CU (O-RAN Centralized Unit), further split into O-CU-CP (control plane: RRC, PDCP-C) and O-CU-UP (user plane: SDAP, PDCP-U), sits centrally and can serve many O-DUs. Because each interface between these units (Open Fronthaul, F1-c/F1-u, E1) is openly specified, operators can mix radio, distributed-unit, and centralized-unit hardware from different vendors instead of buying a single-vendor integrated base station.
Key Functions
- O-RU: RF front-end, digital beamforming weight application, low-PHY (FFT/CP) processing
- O-DU: Real-time scheduling, upper-PHY, MAC, and RLC layer processing per cell site
- O-CU-CP / O-CU-UP: Centralized RRC/PDCP-C control signaling and SDAP/PDCP-U user data handling
- Open Fronthaul (7-2x) and F1/E1 interfaces enable multi-vendor interoperability across all three units