5G srsRAN End-to-End Reference Architecture with USRP
Contents
Application Note Number and Authors
AN-599
Authors
Bharat Agarwal and Neel Pandeya
Executive Summary
This Application Note presents a comprehensive reference design for deploying 5G NR Standalone (SA) systems using a hybrid open-source software stack: the srsRAN radio access network components and the OpenAirInterface (OAI) Core Network. This setup runs on NI/Ettus USRP radios, including the B210, enabling practical, low-cost, end-to-end 5G experimentation.
This configuration supports full 5G SA mode and enables complete end-to-end evaluation of the entire protocol stack, from the physical layer up to the core network.
Core Network Deployment Options
The OAI Core Network can be deployed in two modes:
- Single-machine deployment: CN and gNB run on the same machine — ideal for compact or portable test setups.
- Multi-machine deployment: CN is hosted on a separate machine — ideal for performance scaling or distributed 5G architecture evaluation.
UE Configuration Options
This reference architecture supports the following UE configurations:
- A software-defined UE implemented using srsUE with a USRP B210.
- A modem-based UE, such as Quectel or Sierra Wireless modules.
- A COTS 5G handset (e.g., Google Pixel 9) for interoperability and benchmarking.
Overview of the OpenAirInterface (OAI) Software Stack
The OAI) software provides a fully open-source and standards-compliant implementation of the 3GPP 5G New Radio (NR) 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) — a non-profit organization that promotes open wireless innovation and collaborative research.
OAI enables complete 5G system prototyping and research with implementations of:
- The gNB (next-generation base station)
- The UE (user equipment)
- The 5G Core Network (5GCN)
The OAI 5G NR stack is designed to:
- Operate in real time with USRP radios
- Support interoperability with commercial 5G NR handsets (e.g., COTS devices)
- Enable academic, experimental, and pre-commercial deployments
The OAI software stack is organized into multiple Git repositories, allowing modularity and collaborative development:
- OAI 5G Radio Access Network (RAN) Project:
gitlab.eurecom.fr/oai/openairinterface5g
- OAI 5G Core Network (OAI-CN):
gitlab.eurecom.fr/oai/cn5g
OAI source code is freely available for non-commercial and academic research use. Licensing details and additional documentation are available on the OpenAirInterface website.
Overview of srsRAN
srsRAN (Software Radio Systems Radio Access Network) is an open-source 4G and 5G software suite developed by Software Radio Systems Ltd. (SRS). It enables researchers, developers, and network engineers to deploy and experiment with end-to-end wireless communication systems. The suite provides modular components for building complete Radio Access Networks (RANs) and supports both 4G LTE and 5G NR (New Radio).
Key Components of srsRAN 5G
The srsRAN 5G stack is composed of several main components:
- srsRAN gNB: Implements the 5G NR base station (gNodeB), including PHY, MAC, RLC, PDCP, and NGAP layers. Supports standalone (SA) mode and connects to a 5G Core Network via NG interfaces.
- srsUE: A 4G LTE software user equipment used primarily for legacy LTE research. The 5G UE is under active development and partially supported.
- srsEPC (for LTE): The Evolved Packet Core for 4G LTE deployments. In 5G, this is replaced by external 5G Core Network solutions such as OAI-CN5G or commercial alternatives.
- srsGUI and nrscope: Tools for real-time visualization and debugging of signal and protocol layer performance.
Supported Features
- 5G NR Standalone (SA) mode operation (Release 15+)
- Configurable numerology, bandwidth, and frame structure
- Support for USRP hardware (e.g., B210, N3xx, X410)
- Dynamic scheduling, HARQ, and experimental beamforming
- Compatibility with open-source 5G Core solutions (e.g., OAI-CN5G)
Use Cases
srsRAN is widely used for:
- Academic research and prototyping
- 5G network testing and benchmarking
- Private network deployments
- SDR-based teaching and training environments
Licensing and Community
srsRAN is released under the AGPLv3 license, making it freely available for modification and redistribution under open-source terms. The project is actively maintained and supported by a growing developer community on platforms such as GitHub and GitLab.
Overall, srsRAN provides a robust and flexible platform for 4G/5G experimentation and serves as a valuable resource for researchers working in wireless communications.
Overview of the Reference Architecture
The OAI USRP Reference Architecture enables researchers, developers, and system integrators to build complete 5G NR systems using open-source software and commercial SDR 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 User Equipment (UE), including Quectel 5G modules, USRP-based UEs, and commercial handsets such as the Google Pixel 9 with an open SIM.
Deployment 1: OAI gNB and CN on the Same Machine
In this setup, both the OAI Core Network (CN) and the OAI NR gNB are hosted on the same physical machine. This configuration is typically used for:
- Lab-based research and teaching environments
- Portable demos and proof-of-concept systems
- Quick-start testbeds for 5G protocol stack development
Architecture Highlights:
- Compute Node: High-core-count x86 server (e.g., Intel Xeon w7-2495X, 24 cores)
- Operating System: Ubuntu 22.04
- Software Stack: OpenAirInterface gNB (monolithic) and 5G Core (AMF, SMF, UPF, NRF, etc.)
- UHD Version: 4.8
- RF Front-End: USRP X410 with SFP+ (10/100 Gbps) link
Advantages:
- Simple setup with fewer network dependencies
- Easy to debug and deploy
- Lower hardware requirements
Limitations:
- Less suitable for high-throughput traffic testing
- Shared CPU and I/O resources may limit performance
Deployment 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
- Scalable testbeds with high-throughput and isolated workloads
- Large MIMO, beamforming, or MEC-based deployments
Architecture Highlights:
- gNB Node: Intel Xeon w7-2495X, 24 cores, Ubuntu 22.04
- CN Node: Separate x86 server, also running Ubuntu 22.04
- Interconnect: High-speed Ethernet via managed switch
- RF Front-End: USRP X410 with dual SFP+ for IQ data
Advantages:
- Higher reliability and scalability
- Easier to simulate real-world latency, routing, and interface constraints
- Better performance profiling of CN and gNB independently
Considerations:
- Requires correct IP addressing, routing, and DNS setup
- More complex to configure and monitor
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 Setup
The diagram in Figure 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 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 (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 a safe operating range.
- Downstream RF Splitting: The combined RF signal is routed to a 2-way splitter (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+ (10/25 G) links for baseband data transfer and synchronization.
USRP-Based srsUE Cable Setup
Figure below illustrates the RF cabling setup used when both the srsRAN gNB and srsUE are implemented using separate USRP X410 and B210 devices. This setup enables full bidirectional communication in a lab environment without the need for over-the-air (OTA) transmission.
- Dual SFP+ Connection: Each USRP is connected to its respective host PC via dual SFP+ ports (Port 0 and Port 1) and USB 3.0, 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. Within operational range for the 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.
USRP-Based OAI-UE Cable Setup
A similar RF cabling setup applies when both the srsRAN gNB and OAI-UE are implemented using separate USRP B210 devices. This configuration also enables full bidirectional communication in a lab environment without OTA transmission.
- USB 3.0 Connection: Each USRP B210 is connected to its respective host PC via USB 3.0, 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: A fixed 40 dB attenuator is inserted before the splitter connecting to the UE-side USRP.
- Bidirectional Lab Setup: The cable-based signal path ensures controlled, interference-free bidirectional testing.
Commercial UE Setup: Google Pixel 9 Over-the-Air (OTA)
Figure below illustrates the setup for using a commercial 5G smartphone (Google Pixel 9) as the UE in conjunction with the srsRAN 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 processor (24 cores, 2.5 GHz) and interfaces with a USRP X410 via two SFP+ ports.
- OTA Link: The RF connection between the USRP and the Pixel 9 is established over the air, eliminating the need for RF splitters or coaxial cabling.
- SIM Card: The 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.
Bill of Materials
The full Bill of Materials (BoM) for the OAI Reference Architecture is provided 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 co-locate or distribute gNB and Core Network (CN) components and switch between different UE types depending on the research focus (PHY-level tuning, link testing, or full-stack validation).
Hardware Components
- Three or Two Desktop Computers:
Intel Core i9 CPU (10th–12th Gen) @ ≥4.0 GHz, with ≥10 physical cores and NVMe disk drives. (See the Hardware Requirements section for further details.)
- Two 10 Gbps Ethernet Network Cards:
* Recommended: Intel 810-XXVDA2 * Recommended: NVIDIA/Mellanox ConnectX-6 Lx (MCX631102A-ACAT)
- Two USRP Devices:
The gNB and UE each require one USRP. Supported devices include N300, N310, N320, N321, and X410. Mixed configurations are also supported (e.g., X410 for gNB and N310 for UE).
* USRP X410: High-performance, 4 TX/RX channels, suitable for advanced 5G/6G R&D.
Documentation | Product Page
* USRP N320 / N321: Wideband 2 TX/RX MIMO SDR with high dynamic range and onboard GPSDO (N321 only).
Documentation | N320 Product | N321 Product
* USRP N300 / N310: Compact 4-channel SDR supporting distributed systems.
Documentation | N300 Product | N310 Product
- One QSFP28-to-SFP28 Breakout Cable (required for X410):
* NVIDIA MCP7F00-A003R26N – 100 GbE to 4×25 GbE, 3 m, 26 AWG * NVIDIA MCP7F00-A003R30L – 100 GbE to 4×25 GbE, 3 m, 30 AWG
- One OctoClock-G:
Provides synchronization for gNB and UE USRPs. Must be the “-G” model (with GPSDO). * Ettus KB – OctoClock CDA-2990 * Product Page
- Four 10 Gbps Ethernet Cables with SFP+ terminations:
Required for N3xx and N32x devices; not needed for X410. * DAC Cable Listing * 1 m SFP+ DAC * 3 m SFP+ DAC
- Four VERT900 and/or VERT2450 Antennas:
* VERT900 (824–960 MHz) * VERT2450 (2.4–2.5 GHz / 4.9–5.9 GHz)
- One Quectel RM500Q-GL 5G Wireless Modem Module:
Used as a UE option in the reference architecture. * Quectel 5G Modules * RM520N Series
- One Google Pixel 9 5G Handset:
Used as a COTS UE; ensure it is unlocked. * GSMArena Specs * Amazon Listing
- Two 5G SIM Cards + One USB UICC/SIM Reader-Writer:
* Open Cells – SIM Cards
- One Mini-Circuits 4-way DC-Pass SMA Splitter (ZN4PD1-63HP-S+): 250–6000 MHz / 50 Ω
* Splitters Catalog * Product Page
- Two Mini-Circuits 2-way DC-Pass SMA Splitters (ZN2PD2-50-S+): 500–5000 MHz / 50 Ω
* Splitters Catalog * Product Page
- Four Mini-Circuits VAT-10+ Attenuators (10 dB, DC–6000 MHz, 50 Ω):
* Product Page
- Four Mini-Circuits VAT-20+ Attenuators (20 dB, DC–6000 MHz, 50 Ω):
* Product Page
- Four Mini-Circuits VAT-30+ Attenuators (30 dB, DC–6000 MHz, 50 Ω):
* Product Page
- Fourteen Mini-Circuits Hand-Flex SMA Coax Cables (086-36SM+, 36", 18 GHz):
* Product Page * Datasheet PDF
- One NETGEAR GS108 8-Port Gigabit Ethernet Switch:
* Product Page * Amazon Listing
- Three USB 3.0-to-1 Gbps Ethernet Adapters:
* USB-A Adapter * USB-C Adapter
