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Mobile network operators hope RAN disaggregation will speed innovation, meet performance expectations, and reduce costs. Some are moving forward now while others are waiting to see if early adopters find success.
Operators deploying Open RAN (O-RAN) are counting on its standardized open interfaces to create an ecosystem of vendor solutions that run virtualized software on vendor-neutral hardware.
In particular, early eyes are on the distributed unit (O-DU), one of O-RAN’s most complex, real-time components. Can it keep up with demands in an open, software, and cloud-based environment?
Getting to the answer requires comprehensive testing under real-world conditions.
What is the Open DU?
The O-DU performs real-time scheduling and baseband processing for multiple radio units (Open RUs), and interfaces with centralized units (Open CUs) that process higher layers of the protocol stack for multiple DUs.
It is a logical node that hosts the lower layers (RLC, MAC, and high physical) of the protocol stack. It can be virtualized and deployed in the cloud on commodity hardware.
O-DU is in the “hot seat,” managing the baseband processing necessary to deliver high-quality customer quality of experience (QoE). The O-DU manages real-time subscriber events, such as providing continuous coverage on a moving train, optimizing the signal in low-coverage areas, supporting the download of high-definition video, and, in general, meeting a diverse set of demands across multiple users. The O-DU provides the capabilities needed to deliver low latency and seamless mobility—the hallmarks of 5G.
An O-DU test playbook
Because the O-DU operates in real-time, it must be tested thoroughly under real-world channel conditions and applications to ensure it is ready to be deployed in the live network.
Standard conformance testing only validates the basic functionality of the O-DU and is not sufficient to assess O-DU ability to be field-ready and meet the demands of the real-world conditions. As such, Open DU tests should be assessed comprehensively for multi-vendor inter-operability and real-world performance:
Conformance under a variety of traffic mixes
Real-time scheduling and resource allocation capabilities
End-user applications and quality of service (QoS)
Real-world channel conditions like cell-edge, fading, and doppler effects
Performance, capacity, and throughput
The testing environment should include automation and control functions that connect UE, RF channel, O-RU, O-CU, and 5G Core emulation nodes which wrap around the DU under test.
A best-practice plan for testing real-time Open DU functions should focus on emulating adjacent node network functions, including RUs and user equipment, core network, neighboring CUs, and RAN intelligent controllers.
The Open DU under test should be subjected to realistic channel conditions to determine whether it handles them effectively and whether its baseband signal chain (Coding, Modulation, Forward Error Correction, etc.), and the relevant optimization algorithms are working as expected. This is crucial to ensure the impacts of these real-world propagation impairments are handled gracefully, and subscriber QoE is not negatively impacted.
The Open DU under test should also be subjected to realistic traffic mixes and network slices to determine whether the scheduling function in the O-DU handles them efficiently, as well as unexpected traffic to ensure the unit recovers properly.
Test solutions should have the flexibility to address factors such as:
Varying channel conditions that can stress the DU
A range of throughput and line rates between the DU and CU, and between the DU and RU
Mobility options, such as various inter and intra DU handovers
Application (such as video) QoS
Ability to handle thousands of UEs and sessions, and tens or hundreds of connected RUs
The wraparound test environment should be automated and software-centric, with a single user interface to control all test components. Powerful traffic modeling capabilities should allow users to shape and scale traffic as needed to replicate live network traffic conditions.
A test plan like the one described above is essential for service providers to determine whether the disaggregated DU can perform as well as an integrated traditional RAN.
Finding a comprehensive O-RAN test approach
This testing strategy represents the approach Spirent developed for its comprehensive Open RAN test solution.
The solution provides confidence that an O-DU is ready to be deployed in the live network. At the same time, built-in automation speeds time-to-market and reduces the cost of holistic testing.
Learn more about Spirent’s Open DU test solution and full suite of integrated Open RAN test solutions.
