What is RU?
The RU (Radio Unit) is the component of a disaggregated 5G base station that handles the lower physical layer processing and RF functions — converting digital signals to and from radio waves at the antenna site. The RU is the evolution of the RRH (Remote Radio Head) concept, with potentially more PHY processing moved into the radio unit compared to traditional CPRI-based RRH architectures. In O-RAN, the O-RU connects to the O-DU via the open fronthaul interface specified by the O-RAN Alliance.
How Does RU Work?
The RU performs RF transmission and reception (including power amplification, filtering, up/down-conversion, ADC/DAC) and lower PHY processing such as FFT/IFFT, cyclic prefix addition/removal, digital beamforming, and PRACH extraction. The split between RU and DU (known as the lower-layer split or LLS) defines how much PHY processing is in the RU versus the DU. The O-RAN Alliance defines Split 7-2x as the baseline, where the RU handles up to the FFT/beamforming and sends frequency-domain IQ data to the DU via eCPRI over Ethernet. This reduces fronthaul bandwidth compared to full IQ transport (CPRI) while keeping the RU relatively simple. The RU may be integrated with the antenna panel (Active Antenna Unit) or connected via RF cables.
Use Cases
5G NR cell site radio deployment, O-RAN open fronthaul architecture, massive MIMO active antenna systems, indoor small cell radio units, and multi-band multi-technology radio consolidation.
3GPP / Standards Reference
O-RAN Alliance WG4 (Open fronthaul interface), 3GPP TS 38.104 (NR BS radio parameters), CPRI/eCPRI specifications
Related Terms
RRH | O-RU / O-DU / O-CU | BBU | Fronthaul | CPRI
Learn More
This glossary entry is part of the 5GWorldPro Complete 5G Glossary. To go deeper into 5G architecture and technology, explore our 5G Training courses.
