Open RAN telecom networks need testing for each disaggregated component, but that’s not enough. End-to-end testing is also necessary.

In How do Open RAN interfaces work?, we covered how Open RAN redefines traditional RAN architecture by disaggregating it into three primary components: the radio unit (RU), distributed unit (DU), and centralized unit (CU). This paradigm provides mobile network operators (MNOs) with a versatile, vendor-neutral software-defined network (SDN) supporting commercial off-the-shelf (COTS) components. Ensuring seamless interoperability, however, requires MNOs to thoroughly test Open RAN platforms at multiple stages. This article outlines the fundamental methodologies in Open RAN testing, covering pre-installation assessments, field trials, validation processes, and verification procedures.

Ensuring interoperability: Pre-deployment and in-field

During initial testing, MNOs conduct comprehensive Open RAN interoperability assessments across all components and systems. This involves an extensive analysis of the RAN intelligent controller (RIC), including simulated stress tests to evaluate resource optimization, adaptability, and resilience. MNOs also check conformance with the following specifications, protocols, and interfaces (Figure 1):

• 3GPP Long Term Evolution (LTE): ensures RAN components smoothly transition to LTE in areas with limited 5G availability.
• New Radio (NR): assesses the compatibility of RAN components with 5G technologies and functionalities.
• O-RAN Fronthaul Interface: formulated by the O-RAN Alliance, this interface validates communication and data synchronization between the radio and distributed units in the fronthaul segment of the network.
• O-RAN E2 Application Protocol (E2AP): verifies the RIC’s ability to manage and optimize RAN functions.
• O-RAN Open Fronthaul M-Plane: checks the management plane’s capabilities in network configuration, fault management, and performance monitoring.
• O-RAN SMO Security Specification: confirms robust security in the service management and orchestration (SMO) framework with features such as authentication, encryption, and access control to protect RAN components and data.

Subsequent field trials typically focus on critical RIC functionalities and the three primary Open RAN components: RU, DU, and CU. These evaluations assess network throughput and latency, confirming network resilience and quality of service (QoS) with additional scalability and stress tests.

Validating Open RAN installations

As Open RAN rewrites network-testing rules explain, MNOs use vendor-neutral platforms to validate Open RAN installations. Simulating real-world conditions, these emulation platforms analyze performance, scalability, and interoperability in diverse scenarios. Ensuring DU and fronthaul interface interoperability is particularly crucial, as disaggregated components from multiple vendors can potentially impact node interaction. Figure 2 shows an example of Open RAN testing.

Validating user equipment (UE) with a thorough assessment of QoS parameters, such as network latency and round-trip times, is essential for 5G new radio (NR) ultra-reliable low-latency communications (URLLC) applications, including intelligent edge devices and industry 4.0 automation. UE validation confirms compliance with sub-millisecond latency standards critical for Time-Sensitive Networking (TSN), Precision Time Protocol (PTP), and Generalized Precision Time Protocol (gPTP).

Open RAN validation also includes extensive RU testing. This process covers the real-time generation of control, user, synchronization, and management plane messages for in-phase and quadrature (IQ) data streams. These data streams encode amplitude and phase information of wireless signals, with the “in-phase” component aligning with a reference signal and the “quadrature” component being 90° out of phase. Effective processing of IQ data streams is crucial for the accurate modulation and demodulation of Open RAN radio signals.

Additionally, radio resource management and signal processing are thoroughly assessed, ensuring network efficiency and optimal QoS. This includes evaluating how effectively the radio spectrum is used and managed, an important factor in minimizing interference and maximizing data throughput in densely populated areas.

Lastly, MNOs evaluate RU compatibility with different DUs and Open RAN profiles to streamline multi-vendor management. This ensures seamless integration and functionality across diverse hardware and software configurations, reflecting the core Open RAN principle of an innovative and interoperable ecosystem. Figure 3 shows an RU tester that performs protocol, timing, and interoperability tests between the RU and DU.

Verifying Open RAN deployments

MNOs identify interoperability issues between DUs and RUs with verification platforms that include advanced packet capture and filtering capabilities. A critical element of this verification process is the stateful management plane (M-plane), which facilitates the DU’s execution of standard M-plane procedures to establish connectivity with the RU. The DU emulator’s control/user-plane (C/U-plane) engine subsequently generates enhanced common public radio interface (eCPRI) packets, with MNOs analyzing downlink signals at the RU’s transceiver ports through the Open Fronthaul interface.

MNOs rely on radio-performance tools to assess multipath interference in complex scenarios, verifying key parameters such as beamforming, conformance, transmit power, and downlink modulation quality. Used for targeted drive and walk testing, spectrum analyzers, signal generators, and network scanners help identify and address various performance issues under real-world field conditions.

Additionally, verification includes a thorough evaluation of the near real-time (near-RT) RIC and multi-vendor xApps. These xApps, functioning within the near-RT RIC environment, dynamically optimize network resources, automating key processes such as load balancing, interference management, and power management. This evaluation confirms the effective enforcement of operator policies across various subscribers, services, and network slices.

Exploring post-deployment monitoring tools

Open RAN’s disaggregated architecture increases the risk of transport network issues in the backhaul and midhaul segments, potentially leading to latency, packet loss, or even complete fiber link disruptions. Multi-vendor complexity also heightens the probability of performance degradation in both disaggregated RAN and core network functions.

Similarly, Open RAN 5G networks supporting multiple applications may face resource allocation issues for specific subscriber demands, risking radio resource congestion and reduced network accessibility. Moreover, new service mixes (combinations of different network services) and mobility profiles (patterns of user movement and connectivity requirements) in 5G networks could potentially cause edge failure cases and impact performance.

To effectively manage these challenges, MNOs rely on post-deployment monitoring tools that identify issues across RF, RAN, xHaul transport, and core network components. For example, advanced spectrum analyzers are used for detailed signal analysis, while network health monitoring systems with AI capabilities track real-time performance and detect anomalies. These tools continuously scan the network’s RF spectrum, analyzing signal quality, bandwidth utilization, and error rates.

Advanced machine learning (ML) algorithms also play a key role in detecting anomalies, predicting potential network failures, and initiating automated responses to mitigate risks. These algorithms correlate data from various network layers, providing holistic snapshots of network health and performance.

Adapting to emerging challenges

As Open RAN architecture evolves, MNOs will face new challenges ensuring interoperability across an increasingly diverse landscape of components, vendors, and devices. Testing must ensure Open RAN deployments effectively manage the massive influx of low-latency IoT and smart edge devices, while addressing the network’s needs for high density and scalability. Another notable challenge for Open RAN installations is network slicing, which requires each slice to meet its unique performance requirements without spectrum or radio interference.

Automated testing environments are poised to play an important role in bolstering the efficiency of Open RAN testing, with scripts and tools quickly adapting test parameters and scenarios. Employing AI, these automated environments will more proactively predict potential issues by rapidly analyzing vast amounts of data and effectively learning from network behaviors. These capabilities are essential for managing the complexities of future Open RAN deployments and delivering optimal network performance across components and devices.

Summary

Open RAN disaggregates traditional RAN into three fundamental components, creating a modular SDN-based architecture that runs virtualized network functions on COTS hardware. While encouraging innovation and competition, the multi-vendor RAN paradigm introduces potential interoperability and performance challenges. To maintain QoS, MNOs must comprehensively test Open RAN installations before, during, and after deployment. As Open RAN continues to evolve, MNOs will adapt their testing strategies to meet emerging challenges.

References
How to Test an Open RAN Installation, The Fast Mode
Why 5G O-RANs Need Compliance and Interoperability Testing, 5G Technology World
How Do Open RAN Interfaces Work?, 5G Technology World
Open RAN Rewrites Network-Testing Rules, 5G Technology World
Open RAN Update, 5G Americas
How to Set a Winning Open RAN Testing Strategy, Spirent Communications
Open RAN Standardization Developments: What’s Done and What’s in Progress, ABI Research