Design of an End-to-End and Open-Source 5G MBS SDR Validation Pilot

Design of an End-to-End and Open-Source 5G MBS SDR Validation Pilot Carlos Barjau Estevan Instituto de Telecomunicaciones y Aplicaciones Multimedia Universitat Politècnica de València Valencia, Spain ORCID: 0000-0002-4258-6113 David Gómez-Barquero Instituto de Telecomunicaciones y Aplicaciones Multimedia Universitat Politècnica de València Valencia, Spain ORCID: 0000-0003-2610-7765 Jaime Sanchéz Roldán Instituto de Telecomunicaciones y Aplicaciones Multimedia Universitat Politècnica de València Valencia, Spain ORCID: 0000-0002-3262-055X María del Mar Moreno Escaño Instituto de Tecnologías e Ingeniería del Software Universidad de Málaga Málaga, Spain Borja Iñesta Instituto de Telecomunicaciones y Aplicaciones Multimedia Universitat Politècnica de València Valencia, Spain ORCID: 0000-0002-1613-616X Abstract—Point-to-Multipoint (PtM) communications were identified by 3GPP as a requirement during the start of 5G. Despite this, it was not until Release 17 that the New Radio (NR) native PtM mode was standardized, named 5G Multicast Broadcast Systems (MBS). Most notably, it added new Network Functions in the 5G Core while fully reutilizing NR physical layer to ease adoption and uptake amongst manufacturers. In this context, the paper provides the design and goals of an MBS validation pilot, fully end-to-end (from 5G Core to Receiver) based on open-source implementation from the 5G-MAG Reference Tools repositories. Moreover, this experiment leverages the programmability of Software-Defined Radio equipment and experimentation framework provided by the European 6G-SANDBOX SNS project, the Trial Network Lifecycle Manager to orchestrate and log the measurements performed. Keywords—3GPP, Broadcast, Multicast, SDR, Open-Source, SNS, Rel-18 I. INTRODUCTION The ITU has published the requirements of the 6G technology, called IMT-2030, in June 2023 [1]. Accordingly, 3GPP will prepare a candidate technology to align with the ITU submission process, with initial 6G studies beginning in Release 20 [2]. However, this does not mean that 5G specification work will stop. The latest release version of 5G is known as 5G-Advanced, and it aims to refine all the promised functionalities from 5G while expanding the market opportunities. In this regard, Point-to-Multipoint (PtM) was not specified until Release 17, despite being one of the original requirements of the 5G System [3]. PtM is the ability and the function to send the data once to several users without replicating packets. Inside 3GPP, several PtM solutions already exist: LTE-based 5G Broadcast [4], completed in Rel-16, which is a Digital Terrestrial Television (DTT) capable solution. As it is an evolution of enhanced Multicast Broadcast Multimedia Services (eMBMS), it incorporates several new logic functions in the EPC and requires specific waveform in the eNB to function, alongside a synchronization protocol between eNBs to ensure the Single Frequency Network operation. On the other hand, PtM in the 5G System involves the use of multicast delivery to several gNodeBs at Core level, while in the RAN, the same New Radio (NR) services and signals to multiple users or user-groups. To do so, 3GPP defined in Rel17 the 5G Multicast Broadcast Service or MBS, adding components to the 5G Core and (optional) Service Layer while reusing the NR PHY layer. MBS supports both Broadcast (no uplink) and Multicast (HARQ retransmissions). More info of all the innovations of MBS can be found in [5]; and the 3GPP architectural enhancements is located at [6]. MBS benefits are two-fold: PtM as a service e.g. Digital Terrestrial Television and a network optimization for scalable media delivery. For verticals, Public Protection and Disaster Relief (PPDR) and Vehicular to Everything (V2X) already incorporate 5G multicast signals that are required for operation and 5G connectivity. Several other sectors can be expanded with the inclusion of MBS: 1) Media and Entertainment, as PtM is a mean to massively delivery content in a scalable way; 2) Public Warning Services (PWS) can leverage the wide reach capabilities and increased bandwidth of MBS to send multimedia rich alarms over deeply granular geographical areas; 3) Internet of Things (IoT), for massively firmware updates of wide area sensors; and 4) Non-Terrestrial Networks, while not a vertical, can also benefit from MBS, as it fully reuses 5G protocols and use the extra coverage. MBS has gathered academic interest: in [7], ATSC 3.0 and MBS are compared for handheld applications; in [8], the performance of MBS is evaluated system-wide; in [9], the authors explore an hybrid delivery system using MBS over NTN and unicast. However, there are no commercial deployments of the system, nor off-the-shelf devices that support this mode. In order to perform MBS testing and prototyping, it is required to being able to customize and extend both the 5G Core, RAN and UE. Several open-source 5G solutions exist nowadays, such as OpenAirInterface, srsRAN, free5GC and Open5GS. To fill the gap in the radio transmitting (gNB) and receiving part (UE/device), Software-Defined Radio equipment (SDR) has been chosen, due to its flexibility in prototyping and testing new wireless technologies without requiring technologylocked hardware specific solutions. In this paper, we describe an end-to-end and fully open-source MBS validation pilot based on srsRAN for the receiver and gNodeB, and Open5GS for the 5GC. The validation pilot will make use of the 6G-SANDBOX project Trial Network Lifecycle Manager (TNCLM) [10]. The paper is structured as follows: Section II describes the technology solutions used, while Section III outlines the functionalities of the platform. Section IV describes the experimentation plan. Section V closes with the conclusions and future work for the SDR pilot. II. TECHNOLOGY DESCRIPTION The experiment aims to verify an interoperable validation pilot for MBS fully based on open-source solutions. To do so, the validation pilot incorporates open-source components, such as the MB-UPF, MB-SMF, and SDR-enabled gNB and UEs, adapted for MBS functionalities. This development is fully integrated into the European SNS project 6GSANDBOX. The MBS validation pilot will expand the trial network portfolio with a broadcast-enabled one. It is built upon the 5G-MAG Reference Tools and seeks to evaluate the efficiency and scalability of MBS against traditional unicast methods. Subsequent subsections will detail the SDR equipment used, the open-source code details and the TNCLM for experiment orchestration. A. SDR Equipment The RAN and UE part of the Validation Pilot is enabled thanks to SDR equipment. SDR allows for agile prototyping of mobile communications systems, including 4G, 5G, and future 6G technologies. This infrastructure enables full digital implementation of radio systems, where radio layer functionalities such as modulation, coding, and interleaving are executed in software, quick adaptation or switch between standards. UPV laboratory hosts a total of ten SDR devices— seven with embedded processors and Ethernet connectivity, and three connected via USB 3.0—enabling a range of deployment scenarios. Synchronization across multiple devices is supported through a dedicated OctoClock CDA2990 reference signal generator, which is essential for precise MIMO or Single-Frequency Network (SFN) configurations. In terms of radio capabilities, the available SDR hardware includes three USRP B210 units, five USRP N310, and two USRP N321 devices, each with unique specifications in terms of frequency range, bandwidth, and output power, which can be seen in Table 1. Table 1: SDR equipment specifications at UPV SDR laboratory Model Channels Frequencies Bandwidth Output Power B210 2TX & 2RX 70 MHz – 6 GHz 20 MHz 20 dBm N310 4TX & 4RX 10 MHz – 6 GHz 100 MHz -15 dBm N321 2TX & 2RX 3 MHz – 6 GHz 200 MHz -15 dBm The testbed’s high-speed switching fabric, comprised of a Layer 2 and 3 Ethernet switch with SFP+/QSFP+ interfaces, provides 10/40 Gbps connectivity, facilitating remote access and high-throughput data exchange. These specifications enable the laboratory to serve not just as a development platform but as a full experimentation facility, supporting dynamic allocation of SDR devices and network reconfiguration in real time. The SDR platform integrates seamlessly with open-source software environments such as srsRAN and OpenAirInterface, both of which provide 4G and 5G stack implementations. B. 5G-MAG Reference Tools The 5GC and the NG-RAN utilized for the MBS validation pilot are software-based and open source, leveraging the 5GMAG Reference Tools. In detail, an Open5GS fork enhanced to support MBS features forms the 5GC and the required and modified Network Functions; while the RAN and UE are provided by a modified srsRAN platform. The code implements MBS-capable Network Functions such as the Multicast-Broadcast Session Management Function (MBSMF) and Multicast-Broadcast User Plane Function (MBUPF) by extending the existing unicast SMF and UPF modules. Additionally, the Access and Mobility Management Function (AMF) and Network Repository Function (NRF) are modified to handle multicast contexts and APIs based on 3GPP TS 29.532, TS 29.518, and TS 29.244 specifications. The architecture adopts 5GC Shared MBS traffic delivery over a Layer 2 multicast-enabled network using IGMP/MLD protocols. This choice facilitates efficient multicast data forwarding and serves as the basis for subsequent scalability evaluations. These components are containerized via Docker Compose and Kubernetes Helm Charts, simplifying deployment and reproducibility across different platforms. C. Trial Network Lifecycle Manager The Trial Network Lifecycle Manager (TNLCM) is an opensource core orchestration, execution and measurement gathering component, being used and validate within 6GSANDBOX project. It began as the Extended Lifecycle Manager (ELCM) in the 5GENESIS European project [11], enabling automated and resource-aware management of Figure 1: The SDR rack with the N310, N321, from the back (left) and front (middle). The B210 connected to an Intel 11 NUC (right). experiments across 5G platforms. Architecturally, it is divided into a Scheduler, Composer, and Execution Engine, each handling distinct stages of an experiment—ranging from resource feasibility checks and platform-specific configuration generation to stage-based task execution. The ELCM ensures parallel experiment execution through threaded executors, coordinated by a heartbeat mechanism that handles stage transitions. Additional components such as the Platform Registry, Experiment Registry, and an integrated Flask-based administration interface support configuration management, execution monitoring, and log inspection. Integration with external systems like the Katana Slice Manager for network service deployment and Grafana for dashboard visualization ensures a comprehensive and interactive experimental environment. Building on this foundation, the TNCLM emerges as the evolutionary step, designed to manage not just experiments but entire Trial Networks concept from 6G-SANDBOX [10]; with increased modularity and extensibility. Following the ELCM’s modularized approach, TNLCM adopts a componentized architecture to ensure that individual modules—such as workflow logic or interface layers—can be replaced or extended independently. At the core of TNLCM lies a RESTful API-driven Core component responsible for lifecycle management, integration with orchestration systems like Jenkins, and status reporting. The Front-End leverages these APIs to provide platform owners and potentially experimenters with a web-based control interface, while enabling the development of alternative clients using the same API layer. Complementing the core and front-end, TNLCM introduces Schedulers that automate interaction with Trial Networks, dynamically modifying their configurations or triggering transitions. The Playbook and Library components encapsulate the domain logic and interface with the 6GLibrary [12], respectively, enabling robust handling of workflows for the creation, update, and teardown of Trial Network entities. These components abstract the complexity of managing versioned infrastructure templates stored in Git repositories, offering reproducibility and isolation from upstream changes. TNCLM is implemented in Python 3.11 and organized as container-ready modular services using Docker and GitHub for versioning. III. PILOT DESIGN In order to create an MBS validation pilot, the implementation is focused on developing a Minimum Viable Product (MVP) using existing open-source tools that integrates MBS functionalities into a 5G architecture to test end-to-end connectivity between an origin server and several SDR UEs. The MVP prioritizes a reduced feature set for ease of implementation while preserving compliance with 3GPP Release 17. This includes supporting Broadcast only mode, and omitting support for mobility, policy and charging control, and QoS enforcement, given their limited support in the current Open5GS codebase. These repositories are available at 5G-MAG RefTools. The development of 5GC functionalities focuses on adapting the Open5GS software to support 3GPP TS 23.247-defined multicast-broadcast procedures. The project implements essential network functions such as the Multicast-Broadcast Session Management Function (MB-SMF) and MulticastBroadcast User Plane Function (MB-UPF) by extending the existing SMF and UPF modules. Additionally, the Access and Mobility Management Function (AMF) and Network Repository Function (NRF) are modified to handle multicast contexts and APIs based on 3GPP TS 29.532, TS 29.518, and TS 29.244 specifications. The architecture adopts 5GC Shared MBS traffic delivery over a Layer 2 multicast-enabled network using IGMP/MLD protocols. This choice facilitates efficient multicast data forwarding and serves as the basis for subsequent scalability evaluations. On the RAN side, the implementation targets the broadcast subset of MBS due to its relative simplicity and unidirectional downlink nature. The RAN development uses srsRAN_Project for the gNB and srsRAN_4G for the UE. The support for different frame patterns and ModulationCoding Schemes (MCS) is enabled, since the existing NR unicast features are reused. The MVP also integrates support for key MBS channels such as Multicast Control Channel (MCCH), Multicast Transport Channel (MTCH), and Multicast Channel (MCH), all mapped to existing physical downlink shared channels (PDSCH). The system transmits control information using system information blocks SIB20 and SIB21, which inform UEs of the configuration parameters needed to decode 5MBS broadcast transmissions. Figure 2: 5G System used for the MBS validation pilot, with the modified logical functions to support MBS The SDR RAN libraries include a Graphical User Interface where the received data metrics are displayed in real-time, such as the received constellation, decoded service data (MCS, TMGIs…), synchronization and acquisition errors. It can be seen in the figure below. Figure 3: MBS SDR GUI at UE side for signal monitoring. The TNCLM is utilized to orchestrate the experiments and provide a compatible framework to migrate the setup in any testbed that also deploys the 6G-Library framework from 6GSANDBOX. Moreover, TNCLM incorporates a logging feature where measured KPIs can be stored for real-time display (e.g. via Grafana) or post-processing. IV. EXPERIMENTATION PLAN The experimentation plan goal is to, first, validate the functionalities implemented in the open-source solution, and second, compare the performance of using Multicast/Broadcast versus unicast delivery. In this stage, the paper focuses on the validation of MBS functionalities. The transmission details are covered in the table below: Table 2: Planned parametrization of the experiments Band Freq Bandwidth MIMO Scheme Antenna Gain Frame Pattern MCS N40 23702390 MHz 20 MHz 2x2 3 dBi (Omni) TX/RX 7D1S2U 9 22 With the parametrization chosen, using MCS 9 would provide a theoretical maximum of 31.270 Mbps, while choosing MCS 22 provides a total throughput of 92.014 Mbps. These capacities exceed what is usual for broadcast TV channels, but prepare for future immersive services such as eXtended Reality (XR) or Volumetric Video. For the experiments, the SDR N310 will act as a fixed gNB, radiating at -15 dBm; while 3 SDR B210 distributed across the laboratory will receive and decode the Broadcast signal. A tentative disposition of the laboratory and the receivers is shown in Figure 4. The experiment will be performed using two different types of file delivery: a test where the devices have to download a large file being delivered over Broadcast, measuring metrics such as total time for download, throughput variance, signal to interference plus ratio (SINR). The other test is a real-time delivery of video content, where each device will measure the throughput variance and SINR, and it will be evaluated subjectively if the video degrades (e.g. pixelation) while being received. A different batch of tests is also planned, where the TNCLM will be tested to automatically schedule experiments with the Table 2 parametrization. In these tests, different metrics will be measured such as the total time to experimentation setup, including the shutdown of the relevant processes. Figure 4: SDR distribution plan across the UPV indoor laboratory. V. CONCLUSIONS & FUTURE WORK This paper introduces the validation plan for an opensource MBS solution based on SDR equipment. The goal of the plan is two-fold: validate MBS functionalities as they get implemented and compare its performance against NR unicast in several scenarios. Moreover, orchestration tool TNCLM is used to prepare, automate and gather experiment metrics. In the future, the experiments will be carried out in UPV premises to evaluate MBS functionalities and then onboarded into the Universidad de Málaga testbed, as part of the 6G-SANDBOX Open Call project. ACKNOWLEDGMENT This work is funded from the 6G-SANDBOX 3rd Open Call , which has received funding from the Smart Networks and Services Joint Undertaking (SNS JU) under the European Union’s Horizon Europe research and innovation programme under Grant Agreement No 101096328. REFERENCES [1] International Telecommunication Union, “IMT towards 2030 and beyond (IMT2030),” June 2023. [Online]. Available: https://www.itu.int/en/ITU-R/study-groups/rsg5/rwp5d/imt2030/Pages/default.aspx. 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