What is BBU?
A BBU (Baseband Unit) is the main processing component of a base station responsible for handling all baseband signal processing functions including channel coding, modulation/demodulation, scheduling, and protocol stack processing. In traditional RAN architectures, the BBU is co-located with the radio unit at the cell site. In C-RAN (Centralized RAN) architectures, BBUs are pooled in a centralized data centre and connected to Remote Radio Heads (RRH) via fronthaul links. The BBU concept has evolved in 5G into the split DU/CU architecture defined by 3GPP.
How Does BBU Work?
The BBU receives user data and control signalling from the core network, processes it through the Layer 2 (MAC, RLC, PDCP) and Layer 3 (RRC) protocol stacks, then performs Layer 1 (PHY) baseband processing including channel coding (LDPC/Polar codes in 5G NR), OFDM modulation, MIMO precoding, and resource scheduling. The processed digital baseband signals are sent to the radio unit (RU/RRH) via CPRI or eCPRI interfaces for conversion to RF and transmission. In 5G O-RAN, the traditional BBU functions are split between the O-DU (Distributed Unit) and O-CU (Centralised Unit).
Use Cases
Centralized RAN deployments for cost-efficient baseband pooling, traditional macro cell sites, C-RAN virtualisation with vBBU for cloud-native RAN, Open RAN architectures where BBU functions map to O-DU and O-CU, and mobile edge computing co-location scenarios.
3GPP / Standards Reference
3GPP TS 38.401 (NG-RAN architecture description), O-RAN Alliance specifications (WG1-WG6)
Related Terms
C-RAN | RRH | CPRI | O-RU / O-DU / O-CU | Fronthaul
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.
