Why O-RAN’s Success Depends on the RU’s Ability to Perform High-Performance Real-Time Signal Processing

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There are significant challenges that must be addressed while building out O-RAN and ensuring it performs as planned. Fortunately there's a light at the end of the tunnel when it comes to O-RU testing challenges.

The benefits of Open RAN (O-RAN) are clear, including lower costs and an innovation boost fueling new monetization opportunities for service providers. Yet O-RAN faces multiple challenges, including ensuring performance, robustness, interoperability, and security, further complicated by the shift of responsibility from RAN vendors to carriers.

As 5G rollouts ramp up across the globe, O-RAN will offer standardized open and interoperable interfaces, allowing key functions to run as virtualized software functions on vendor-neutral hardware. This can result in an environment where networks can be deployed with a more modular design.

Under O-RAN architecture, traditional RAN is split into the centralized unit (CU), distributed unit (DU) and radio unit (RU). This helps avoid dependence on a single company, which lowers costs partly because more vendors means increased competition, driving prices down. At the same time, virtualizing RAN components allows carriers to utilize commercial off-the-shelf hardware, further cutting costs. It also gives carriers options to pick the best solution for each component in the market.

Given O-RAN’s benefits, it’s unsurprising that there’s an increasing push for its momentum. But implementing O-RAN is not a simple task.

Building a new O-RAN from the ground up and ensuring it performs as planned is a massive undertaking—especially when coupled with the move to 5G, which is already pushing technical boundaries.

The RU challenge

One of the biggest challenges relates to components, of which the RU is deemed to be the most pressing. This is because the RU needs to perform high-performance real-time signal processing as it converts digital signals from the DU to radio signals to the devices.

The RU needs to communicate with the DU via 7-2x protocol over the enhanced common public radio interface (eCPRI) and fully synchronize to a nanosecond level. At the same time, the RU needs to have good radio frequency quality to maximize the benefits from different advanced technologies, such as MIMO and beamforming.

Sensitivity and dynamic range of the RU are other key radio frequency metrics that provide broader high-quality cell coverage to the carriers. Adding to this, since the RU is the only component that cannot be virtualized and the quantity needed in a network is huge, the majority of deployment costs for carriers, over 70%, is tied to the RU.

In a recent poll, Spirent asked providers to outline the biggest challenges for O-RAN in the near term. Providers expressed concerns about multi-vendor interoperability, especially given that standards are not 100% complete.

Providers were also concerned about the performance and robustness of O-RAN in live deployments. They need O-RAN to have parity with traditional RAN but fear losing synchronization, as the RAN is disaggregated, moved to different locations, and becomes comprised of disparate vendors.

This disaggregation, alongside the introduction of multiple vendors, also expands the attack surface, raising security concerns that will require appropriate safeguards. So much so that many stakeholders fear the added security overhead will offset O-RAN’s potential cost savings.

The need for rigorous testing

For O-RAN to achieve its potential and address the many stakeholder requirements and challenges, especially those concerning the RU, a comprehensive testing and assurance strategy is key. After all, to achieve accelerated O-RAN adoption, stakeholder confidence is critical.

Every player in the O-RAN ecosystem must perform rigorous testing to ensure compliance with standards, interoperability, performance, and scalability. In addition, members of the O-RAN ecosystem have a range of targeted test requirements.

For example, service providers must test to ensure every component of their O-RAN environment performs as planned across the lifecycle, from development to operations. Network vendors must ensure their components meet 4G/5G and O-RAN specifications, that these components interoperate with another vendor’s, and—once installed—they continue to operate as planned.

Realizing O-RAN success

Taking all this into account, one thing is certain: O-RAN is coming, and comprehensive testing is the key to its proliferation. To realize success, the automated testing strategy must address performance across RU, DU, CU, and the core, while also accounting for factors such as security, conformance, interoperability, and synchronization.

So far, service providers have focused on compliance rather than performance testing, simply because the right platform wasn’t available. But thanks to Spirent, a new generation of state-of-the-art test and assurance technologies for O-RAN are emerging. These go beyond just compliance. Performance testing is key to ensuring O-RAN is evaluated under all conditions. By including a channel emulator in the O-RU solution, service providers can correctly evaluate advanced features (e.g., mMIMO) and also recreate the most complex situations of live deployments, such as fast fading at the cell edge or high-speed train scenarios, which normally may cause call drops and degradation to the quality of service.

With RF channel emulation, the test solution can emulate signals under fast fading, frequency drifting due to fast motion (e.g., high speed train, multipath, or different correlation between antennas or antenna elements.

In fact, Spirent is the only company offering the ability to perform advanced testing of the RU, emulating the stack end-to-end. Spirent’s Open RAN end-to-end test portfolio includes a fully automated, O-RAN O-RU test solution offering real emulation, with performance and functional testing. It offers real-time live network emulation for the DU, CU, core, and end user device and supports testing all applications in the system, including VoNR, video conference, FTP, media streaming, and gaming. Spirent’s solution aligns with O-RAN Alliance TIFG End-to-End Test Specification Section 5 performance testing and utilizes a user-friendly performance metric (i.e., data rate) to evaluate and compare RU performance, instead of decibels (dB) used for compliance testing, which is not easily translated into lost cell capacity. More importantly, due to emulation of the end-to-end full protocol stack, any real commercial devices can be used in Spirent’s O-RAN O-RU test solution. Other solutions use a UE emulator where only one type of call flow and timing can be verified. Spirent’s solution allows testing with different commercial devices with varying chipsets to verify all possible device behaviors and performance that may occur in the field. Additionally, Spirent’s O-RU solution can show realistic user experience results with scenarios that can only be tested with real devices, e.g., fast fading with high-speed train environments.

While there are challenges to overcome, the key to O-RAN’s success is within reach. By using Spirent’s unique-in-the-market testing solutions, service providers can ensure they are best placed to deal with and mitigate performance issues and allow O-RAN to progress.

Learn more about Spirent’s O-RAN O-RU test solution右矢印アイコン




William Chan

Senior Product Manager

William Chan is a senior product manager for Spirent Communications focused on cellular-assisted positioning solutions for automated device testing. William is actively involved in the 3GPP, CTIA, PTCRB, and GCF organizations where he is a key contributor to test specifications, test plans and validation processes for location testing, covering both GNSS and cellular location technologies such as OTDOA, E-CID, etc. He has concentrated on location technologies for over 18 years, from E-OTD in the GSM era to recent 5G NSA/SA location testing. He frequently works alongside subject matter experts at major US carriers to help define test specifications and plans to satisfy evolving FCC E911 requirements.