O-DU Low Project Introduction

The O-DU low project focus on the baseband PHY Reference Design, which uses Xeon® series Processor with Intel Architecture. This 5GNR Reference PHY consists of a L1 binary and three kinds of interfaces which are validated on a Intel® Xeon® SkyLake / CascadeLake platforms and demonstrates the capabilities of the software running different 5GNR L1 features. It implements the relevant functions described in [3GPP TS 38.211, 212, 213, 214 and 215].

The L1 has three interfaces to communicate with other network functions as described below:

  • Interface between L1 and Front Haul, it adopts the WG4 specification for the CUS plane communication.
  • Interface between O-DU Low and O-DU High, it adopts the FAPI interface according to the WG8 AAL specification.
  • Interface between O-DU Low and accelerator, DPDK BBDev was adopted as original contribution, it will follow the WG6 definition after the WG6 specification is finalized.

The following figure shows the ORAN O-CU, O-DU and O-RU blocks for a gNB implemetation. The O-DU Low projects implements the FAPI interface by a 5G FAPI TM module, the OFH-U and OFH-C by means of the FHI Library and the functionality of the High-PHY and a test MAC are available through github in the form of a binary blob for the current release. For the details refer to the Running L1 and Testmac section of this document

Figure1.Oran OCU ODU and ORU Block Diagram


In this O-DU Low document, the details on how the build the modules supporting each interface, how to run the L1 and associated components, the architecture for each interface implementation and the release notes that describe each component release details are provided.

Intended Audience

The intended audience for this document are software engineers and system architects who design and develop
5G systems using the O-RAN Specifications.


Table 1. Terminology

Term Description
5G NR Fifth Generation New Radio
BOM Bill of Materials
CP Cyclic Prefix
DPDK Data Plane Development Kit
gNB Next-generation NodeB also named as Base Station
HARQ Hybrid Automatic Repeat Request
HW Hardware
IOT Inter-Operability Testing
IQ In-band and Quadrature
NIC Network Interface Controller
O-DU O-RAN Distributed Unit: a logical node hosting RLC/MAC/High-PHY layers based on a lower layer functional split.
O-RU O-RAN Radio Unit: a logical node hosting Low-PHY layer and RF processing based on a lower layer functional split. This is similar to 3GPP’s “TRP” or “RRH” but more specific in including the Low-PHY layer (FFT/IFFT, PRACH extraction).
PDCCH Physical Downlink Control Channel
PDSCH Physical Downlink Shared Channel
PRACH Physical Random Access Channel
PUCCH Physical Uplink Control Channel
PUSCH Physical Uplink Shared Channel
PTP Precision Time Protocol
RA Random Access
RAN Radio Access Network
RB Resource Block
RE Resource Element
RU Radio Unit
SR-IOV Single Root Input/Output Virtualization
SW Software
ToS Top of the Second
UE User Equipment
UL Uplink
VIM Virtual Infrastructure Manager
VLAN Virtual Local Area Network
xRAN Extensible Radio Access Network

Reference Documents

Table 2. Reference Documents

Document or Reference Document No./ Location
3GPP* specification series http://www.3gpp.org/DynaReport/38-series.htm
Wolf Pass Server Documentation https://ark.intel.com/products/codename/80739/Wolf-Pass
Intel® C++ Compiler system Studio XE https://software.intel.com/en-us/system-studio/choose-download
DPDK documentation http://dpdk.org/doc/guides/
O-RAN Fronthaul Working Group Control, User and Synchronization Plane Specification (ORAN-WG4.CUS.0-v02.00) https://www.o-ran.org/specifications