5G OAI End-to-End Reference Architecture with USRP

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Application Note Number and Authors

AN-598

Authors

Bharat Agarwal and Neel Pandeya

Executive Summary

This Application Note presents a comprehensive reference design for deploying end-to-end (E2E) 5G NR Stand-Alone (SA) systems using the Eurecom OpenAirInterface (OAI) software stack on the USRP N300, N310, N320, N321, and X410 radios. The USRP B200, B210, B200mini, B206mini, X300, X310 radios can also be used, but with limitations, and are also discussed in this document The reference design encompasses the base station (gNB), the user equipment (UE), and the Core Network (CN) components of the network, enabling researchers and engineers to build and evaluate full end-to-end deployments.

The reference design offers flexibility in the Core Network deployment. The CN can be installed on the same machine as the gNB, suitable for compact and portable set-ups. Alternatively, the CN can be hosted on a separate machine, allowing for a distributed architecture to facilitate system testing and high-performance operation.

The reference design supports three types of UE.

  • The UE implemented using a USRP radio and the OAI UE software stack.
  • The UE implemented using a wireless modem module, such as from Quectel or Sierra Wireless.
  • The UE implemented using a commercial off-the-shelf (COTS) handset, such as the Google Pixel 9.

The reference design supports operation in Frequency Range 1 (FR1), and a discussion of operation in FR2 (20 to 44 GHz) and FR3 (6 to 20 GHz) will be added at a future date.

This document provides detailed instructions on hardware and software installation, configuration, and execution, alongside expected results, benchmarking methods, performance monitoring, and troubleshooting guidance.

The solution brochure for the OAI Reference Architecture for 5G and 6G Research with the USRP can be downloaded here.

An overview of using OAI Software for 5G and 6G research at this webpage here.

You can learn more about other solutions for 5G and 6G Wireless Research and Prototyping at the webpage here.

Overview of the USRP Hardware

The Universal Software Radio Peripheral (USRP) devices from NI (an Emerson company) are software-defined radios which are widely used for wireless research, prototyping, and education. The hardware specifications for the various USRP devices are listed elsewhere on this Knowledge Base (KB).

The ideal USRP radios for deploying end-to-end (E2E) 5G systems are the USRP N300, N310, N320, N321, and X410. These radios natively support all the 5G sampling rates used in the 3GPP specifications, and they support all the FR1 channel bandwidths from 5 to 100 MHz. The 5G systems use standardized sampling rates based on the channel bandwidth and sub-carrier spacing (SCS) (the numerology) to ensure interoperability and efficient signal processing.

For the USRP N300, N320, N321, there should be two 10 Gbps SFP+ Ethernet connections to the host computer, along with one 1 Gbps Ethernet link for the Management Port. On the host computer, a dual-port 10 Gbps Ethernet network card is used to connect to the USRP.

The USRP X410 has two QSFP28 100 Gbps Ethernet ports. There are two options for connectivity to the host computer, depending on what the IQ data rate is (how much bandwidth is needed). The first option is to use a QSFP28-to-4xSFP28 breakout cable on one of the QSFP28 ports. This will provide four 25 Gbps SFP28 Ethernet links. On the host computer, a dual-port SFP28/SFP+ Ethernet network card should be used. The second option is to use one of the two QSFP28 ports directly, with a QSFP28-to-QSFP28 cable, and with a 100 Gbps QSFP28 Ethernet network card on the host computer.

The USRP B200, B210, B200mini, B206mini radios can also be used as the gNB or UE, but with some limitations. The primary limitation is that you will only be able to operate with a maximum channel bandwidth of 40 MHz.  And even this channel bandwidth may not be possible, depending on what sampling rate is used, and whether the host computer has sufficient resources to support that sampling rate.  The host computer should ideally be able to support the maximum 61.44 Msps, but the sampling rate may be limited to 30.72 Msps, or other non-standard sampling rates such as 42.08 Msps may have to be used as a compromise, and this may correspondingly reduce the channel bandwidth and may cause quirks or problems in the physical layer processing. In addition, the USB interface is not as robust, and incurs more CPU overhead, than an Ethernet interface.

The USRP X300 and X310 radios can also be used as the gNB or UE, but with some limitations. Due to the 184.32 master clock rate (MCR), many of the 5G sampling rates cannot be achieved, or can only be achieved using odd decimations factors, which is undesirable because of the much-higher attenuation. It is likely that other non-standard sampling rates such as 42.08 Msps may have to be used as a compromise, and this may correspondingly reduce the channel bandwidth and may cause quirks or problems in the physical layer processing. The OAI software supports a three-quarter sampling rate for these cases using non-standard sampling rates, which is enabled with the "-E" command line option. This can be used, for example, to select a 46.08 Msps sampling rate instead of the ideal 61.44 Msps sampling rate.

Listed below are links to resources for the relevant USRP devices.

  • The KB Hardware Resource page for the USRP B200, B210, B200mini, B206mini can be found here.
  • The KB Hardware Resource page for the USRP X300 and X310 can be found here.
  • The KB Hardware Resource page for the USRP N300 and N310 can be found here.
  • The KB Hardware Resource page for the USRP N320 and N321 can be found here.
  • The KB Hardware Resource page for the USRP X410 can be found here.

If the UE is implemented using a USRP device, then it is recommended that the gNB USRP and the UE USRP be synchronized with the use of a 10 MHz reference signal and a 1 PPS signal, distributed from a common source. This can be provided by the OctoClock-G (see here and here for more information).

This document focuses on the use of the USRP X410. The usage of the USRP N300, N310, N320 is very similar to that of the X410. Specific discussion of the use of the USRP B200, B210, B200mini, B206mini, X300, X310 will be added in the near future.

Further details of the hardware configuration will be discussed later in this document.

Overview of the OAI Software Stack

The OpenAirInterface (OAI) software stack provides a fully open-source and standards-compliant implementation of the 3GPP 5G New Radio (NR) Stand-Alone (SA) protocol stack. It is designed to run in real-time on commodity x86 hardware and interoperate with USRP software-defined radios. Initially developed by Eurecom, a leading research institute in France, the project is now actively maintained by the OpenAirInterface Software Alliance (OSA), which is a non-profit organization that supports open wireless innovation and collaborative research. OAI enables complete 5G system prototyping and research with implementations of the base station (gNB), the user equipment (UE), and the core network (CN). The OAI stack also allows for the use of other third-party core network software, such as Free5GC and Open5GS. This document does not discuss integration with the Free5GC and Open5GS core network softwares. The OAI software stack is designed to operate in real-time with USRP radios, support interoperability with commercial 5G handsets (COTS handsets), and enable academic, experimental, and pre-commercial deployments. The OAI software stack is structured around multiple Git repositories, enabling modularity and collaborative development of the OAI 5G Radio Access Network (RAN) Project and the OAI 5G Core Network (OAI-CN). The OAI source code is made freely available for non-commercial and academic research use, and licensing details can be found on the OAI website.

Links to the relevant Git repositories are listed below.

Overview of the Reference Architecture

This OAI End-to-End Reference Architecture enables researchers, developers, and system integrators to build complete 5G NR SA systems using open-source software and commercial USRP hardware. This section outlines two typical deployment modes of the architecture:

  • A compact, single-host configuration for integrated lab setups.
  • A modular, distributed configuration for scalable experimentation.

Each mode supports connectivity to a diverse range of UE devices, including Quectel 5G modem modules, USRP-based UEs, and COTS handsets such as the Google Pixel 9.

Deployment Configuration 1: OAI gNB and CN on the Same Machine

In this configuration, both the OAI Core Network (CN) and the OAI gNB are hosted on the same physical machine. This is typically used in lab-based research and teaching environments, portable demos and proof-of-concept systems, and quick-start testbeds for 5G protocol stack development.

The configuration of the system architecture is listed below.

  • Host Computer: Intel or AMD CPU, with minimum 20 physical cores, such as the Intel Xeon W7-2495X, and with minimum 16 GB memory, and with 10 or 100 Gbps Ethernet card.
  • Operating System: Ubuntu 22.04.5, running on-the-metal (no virtual machine (VM))
  • Software Stack: OpenAirInterface gNB (monolithic) and 5G Core Network (AMF, SMF, UPF, NRF, etc.)
  • UHD Version: 4.8
  • USRP X410

Advantages:

  • Easy to debug and deploy.
  • Lower hardware requirements.
  • Simple setup with fewer network dependencies.

Disadvantages:

  • Shared CPU and I/O resources may limit performance.
  • Less suitable and less scalable for high-throughput traffic testing and when using high sampling rates.
Single-machine deployment with both OAI Core Network and gNB on the same host. USRP X410 provides RF connectivity to various UE types, including Quectel module, USRP UE, and Google Pixel 9.

Deployment Configuration 2: OAI gNB and CN on Separate Machines

This configuration separates the OAI gNB and CN onto two dedicated physical systems connected via an Ethernet switch. It is ideal for research involving modular network slicing, edge cloud integration, or realistic RAN-Core interface behavior, or for scalable testbeds with high-throughput and isolated workloads, or for large MIMO, beamforming or MEC-based deployments.

The configuration of the system architecture is listed below.

  • gNB Host Computer: Intel or AMD CPU, with minimum 20 physical cores, such as the Intel Xeon W7-2495X, and with minimum 16 GB memory, and with 10 or 100 Gbps Ethernet card.

• CN Host Computer: Intel i9 CPU or Xeon CPU, with minimum 8 physical performance cores

  • Operating System: Both hosts running Ubuntu 22.04.5, running on-the-metal (no virtual machine (VM))
  • Software Stack: OpenAirInterface gNB (monolithic) and 5G Core Network (AMF, SMF, UPF, NRF, etc.)
  • UHD Version: 4.8 (gNB only)
  • USRP X410 (gNB only)

Advantages:

  • Higher reliability and scalability.
  • Easier to simulate real-world latency, routing, and interface constraints.
  • Better performance profiling of CN and gNB independently.

Disadvantages:

  • More complicated IP addressing, routing, and DNS configuration.
  • More complicated to configure and monitor in real-time.
Multi-machine deployment with OAI Core Network and gNB on separate hosts. The setup uses a high-speed Ethernet switch and supports flexible UE integration over coaxial and OTA interfaces.

Cable and Connectivity Setup

This section describes the physical connectivity between the USRP hardware and various types of UE. The cabling requirements are independent of whether the gNB and CN are deployed on the same machine or on separate systems.

Quectel Wireless Module UE Cable Configuration

The diagram in the figure listed below illustrates the cabling and RF signal routing between the UE system running a Quectel RM520N wireless module and the USRP X410 connected to the OAI gNB. This setup enables direct RF loopback in a controlled lab environment using coaxial cable connections.

  • USB Connection: The Quectel RM520N is connected to the UE system via a USB 3.0 interface. The host PC runs Windows and interacts with the module through Qualcomm QMI or MBIM drivers.
  • RF Antennas: The module has 4 RF ports (ANT 0–3) which are routed to a 4-way power splitter (Mini-Circuits ZN4PD1-63HP-S+) to combine the signals.
  • Attenuation: A fixed 40 dB attenuator is inserted after the splitter to protect the downstream USRP RF front end and ensure signal levels remain within safe operating range.
  • Downstream RF Splitting: The combined RF signal is routed to a 2-way splitter (Mini-Circuits ZN2PD2-50-S+) which separates it into TX/RX and RX-only paths.
  • USRP Connection: These RF paths are connected to the USRP X410, which is linked to the OAI gNB system over dual SFP+ (10/25G) links for baseband data transfer and synchronization.
Cable and RF splitter and attenuator setup for Quectel Wireless Module UE with USRP X410 and OAI gNB

USRP-Based UE Cable Configuration

The figure listed below illustrates the RF cabling setup used when both the OAI gNB and OAI UE are implemented using separate USRP X410 devices. This setup enables full bidirectional communication in a lab environment without the need for OTA transmission.

  • Dual SFP+ Connection: Each USRP X410 is connected to its respective host computer via dual SFP+ ports (Port 0 and Port 1), providing high-throughput data and synchronization channels.
  • SMA Cabling and RF Splitting: RF ports from the USRP gNB are connected via SMA cables to a 2:1 power splitter, enabling simultaneous TX/RX operation.
  • 40 dB Attenuator: To ensure RF power levels are safe and within operational range for lab setup, a fixed 40 dB attenuator is inserted before the splitter connecting to the UE-side USRP.
  • Bidirectional Lab Setup: This configuration mimics over-the-air conditions by enabling a fully enclosed cable-based signal path between the USRP radios representing the gNB and UE, ensuring interference-free testing.
Cable setup between OAI gNB and OAI NR UE using two USRP X410 devices and RF splitters

Commercial UE Configuration with COTS Handset Over-the-Air (OTA)

The figure listed below illustrates the setup for using a COTS 5G smartphone (Google Pixel 9) as the UE, in conjunction with the OAI NR gNB running on a USRP X410.

  • gNB Host System: The gNB stack (OAI NR Monolithic) runs on an Ubuntu 22.04 server equipped with an Intel Xeon W7-2495X CPU, and interfaces with a USRP X410 via two SFP+ ports.
  • OTA Link: The RF connection between the USRP and the Google Pixel 9 is established over the air, eliminating the need for RF splitters or coaxial cabling. The Pixel 9 receives the signal wirelessly from the gNB.
  • SIM Card: The Google Pixel 9 uses a programmable Open Cell SIM card provisioned with the correct PLMN and network parameters to allow registration with the OAI core network.
  • Use Case: This setup is ideal for validating interoperability with COTS 5G devices and ensuring compatibility with commercially available UEs under real-world radio conditions.
OTA-based connectivity with Google Pixel 9 and Open Cell SIM

Bill of Materials

The full Bill of Materials (BoM) for the OAI Reference Architecture is listed below. This comprehensive list includes all necessary hardware components required to support a variety of deployment configurations for 5G and 6G research. The design supports multiple flexible system architectures, where the gNB (base station) and UE can each be implemented using any combination of the following USRP Software Defined Radios: N300, N310, N320, N321, or X410.

This BoM covers all shared components (host machines, network interfaces, RF cabling, timing/sync equipment, antennas, attenuators, and splitters) required for various testbed configurations. The system design is modular and scalable—users can choose to co-locate or distribute gNB and Core Network (CN) components, and can switch between different UE types depending on the research focus, such as PHY-level tuning, link testing, or full-stack validation with 3GPP-compliant UEs.

  • Two or three desktop computers, with Intel i9 and/or Xeon CPU, of 12th, 13th, or 14th Generation, with clock speed of minimum 4.0 GHz, with minimum 8 (for i9 CPU) or 20 (for Xeon CPU) physical cores, and also with only NVMe disk drives. See further details about this item in the Hardware Requirements section.
  • Two 10 Gbps Ethernet networks cards. We recommend the Intel 810-XXVDA2 and the Nvidia/Mellanox ConnectX-6 Lx (MCX631102A-ACAT) network cards. See further details about this item in the Hardware Requirements section.
  • The USRP may be any of USRP N300, N310, N320, N321, X410. There will be one USRP for the gNB, and one USRP for the UE. The USRP devices can be mixed (i.e., the gNB could run with a USRP X410, while the UE runs with a USRP N310).
  • One QSFP28-to-SFP28 breakout cable. This is only required when using the USRP X410.
  • One OctoClock-G. This is needed to synchronize the gNB USRP and the UE USRP. Ensure that device used is the "-G" model, which contains an internal GPSDO module. This is only needed when the UE is implemented on a USRP device.
  • Four 10 Gbps Ethernet cables with SFP+ terminations: Required when using USRP N300, N310, N320, or N321. Not needed for USRP X410. Available in multiple lengths:
  • Four VERT900 and/or VERT2450 antennas: Select based on the frequency bands in use. Third-party antennas are also compatible if they have a 50-ohm impedance and SMA connectors.
  • One Quectel RM520-GL 5G wireless modem module: Used as a UE option in the reference architecture. See the Hardware Requirements section for integration and compatibility details.
  • One Google Pixel 9 5G handset (phone). Used as a commercial off-the-shelf (COTS) UE in the test setup. Ensure that the handset is unlocked for compatibility with test SIM cards.
  • Two 5G SIM cards and one USB UICC/SIM card reader/writer.
  • One Mini-Circuits 4-way DC-Pass SMA Power Splitter (ZN4PD1-63HP-S+), 250 to 6000 MHz, 50 ohms.
  • Two Mini-Circuits 2-way DC-Pass SMA Power Splitters (ZN2PD2-50-S+), 500 to 5000 MHz, 50 ohms.
  • Four Mini-Circuits VAT-10+ Attenuators (10 dB, DC to 6000 MHz, 50 ohms, with SMA connectors.
  • Four Mini-Circuits VAT-20+ Attenuators (20 dB, DC to 6000 MHz, 50 ohms, with SMA connectors.
  • Four Mini-Circuits VAT-30+ Attenuators (30 dB, DC to 6000 MHz, 50~$\Omega$, with SMA connectors.
  • Fourteen Mini-Circuits Hand-Flex SMA Coax Cables (086-36SM+, 36-inch, 18 GHz.
  • One NETGEAR GS108 8-Port Gigabit Ethernet Unmanaged Switch.
  • Three USB 3.0 to 1 Gbps Ethernet Adapters (USB-A or USB-C depending on host ports).

Hardware Requirements

This section discusses details about each of the hardware components in the system.

Host Computers

Two or three host computers are needed, one for the gNB, one for the UE, and optionally one for the Core Network (CN). While the CN host has lower performance requirements, it is recommended that all machines meet the same baseline specifications. Each system should be dedicated to a single role (gNB, UE, or CN). A single host should not run multiple components simultaneously.

Example Host Systems:

CPU

  • Recommended: Intel Core i9 or Intel Xeon (12th to 14th Generation)
    • Minimum clock speed: 4.0 GHz
    • Minimum 8 physical cores (for CN) or 20 physical cores (for gNB and UE)
    • At least 24 PCIe lanes (for network card, more if GPU is also needed)
    • PCIe Gen 4 support

Example Processors:

Disk

RAID configurations with multiple NVMe drives are optional and should not be required.

Memory

  • Minimum: 16 GB
  • Dual-channel or quad-channel DDR4 or DDR5 memory
  • Higher memory is optional unless running virtualized workloads.

GPU

  • The GPU is not required for UHD or OAI operation.
  • Include one only if performing AI/ML workloads.
  • The OAI 5G stack currently does not utilize GPU acceleration.

10 Gbps Ethernet Network Card

  • The gNB and UE each require a dual-port 10/25 GbE NIC.
  • The CN does not interface directly with USRPs and can use standard 1 Gbps Ethernet.
  • Ensure adequate cooling and PCIe slot space.

Recommended network cards:

QSFP28-to-SFP28 Breakout Cable for USRP X410

The USRP X410 has two QSFP28 (100 GbE) ports. To connect the USRP X410 to the 10 GbE network card on a host computer, use a QSFP28-to-4xSFP28 breakout cable.

Recommended cables:

The USRP X410 can also use its QSFP28 100 Gbps Ethernet Connection. This requires that the host computer have a 100 Gbps QSFP28 Ethernet card.

Recommended network cards:

This reference architecture does not require full 100 GbE links. Dual 10 Gbps SFP+ links are sufficient for 1x1 and 2x2 MIMO operation in FR1.

USRP Devices

Two USRP devices are required — one for the gNB and one for the UE. They can be any of the following models:

Interchangeability: You can mix devices (e.g., X410 for gNB and N310 for UE).

Supported Bandwidths:

  • FR1 (Sub-6 GHz): All models support up to 100 MHz.
  • FR2 (mmWave):
    • USRP N320: 50 / 100 / 200 MHz
    • USRP X410: 50 / 100 / 200 / 400 MHz

OctoClock-G

An OctoClock-G is required to synchronize the gNB and UE USRP radios (only necessary when both ends use USRPs).

  • Ensure you are using the “-G” version, which includes an internal GPSDO (GPS-Disciplined Oscillator).

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