The O-RAN Alliance, a global community advancing the open radio access network (O-RAN) ecosystem, has published a technical report evaluating several spectrum aggregation approaches.
Led and initiated by Mavenir, the report examines the technical challenges and solutions for interconnecting Open Distributed Units (O-DUs) to enable carrier aggregation across multi-vendor deployments.
A primary conclusion is the need for a dedicated interface between O-DUs to support efficient spectrum aggregation. Carrier aggregation lets operators combine different frequency bands to deliver higher data rates and broader coverage, a critical capability as operators acquire new spectrum over time and seek to integrate it with existing assets.
Supporting multi-vendor spectrum aggregation
The proposed “Inter O-DU” solution requires a new signalling protocol and management framework to handle tasks such as connection setup, resource allocation, and synchronization across geographically distributed units.
“A new interface connecting multiple O-DUs needs to be defined for supporting spectrum aggregation. This requires defining a management interface for tasks such as to establish and maintain O-DU relations, and SCell associations,” the report explains.
The report highlights the complexity of this work and stresses careful evaluation of bandwidth needs, latency constraints, and potential operational impacts:
“The bandwidth and latency requirements and their impact on performance of carrier aggregation also needs to be evaluated in detail at WI phase,” the report states.
Today, there is no standardized open interface for carrier aggregation across vendors, which can create vendor lock-in when operators expand spectrum. While proprietary aggregation interfaces have been used since LTE and are well understood in specific implementations, efforts to standardize an open interface in bodies such as 3GPP have so far met resistance from incumbent vendors.
Benefits and mitigating risks
Enabling interoperable O-DUs for carrier aggregation can deliver several tangible benefits for operators:
- Enhanced performance: Aggregating spectrum increases spectral efficiency and can translate into faster user data speeds and a smoother experience.
- Increased capacity: Combining multiple bands allows networks to serve more users simultaneously, addressing rising traffic demand.
- Expanded coverage: Inter O-DU carrier aggregation can leverage lower-frequency bands—particularly for uplink traffic—to extend the effective range of high-frequency carriers and improve coverage in hard-to-reach areas.
- Vendor independence: An open interface reduces operator reliance on single vendors, strengthening bargaining positions and giving operators greater control over network evolution.
- Future-proofing: A standardized, open specification could enable new low-latency features and services—important for advanced 5G capabilities and a pathway toward 6G—by supporting real-time communication between DUs.
The report also stresses that risks must be carefully managed. It recommends minimising disruption to the existing O-RAN architecture, avoiding the imposition of new requirements on current 3GPP specifications, and embedding robust security considerations throughout the design process.
“If new interface(s) are defined, the security and integrity of data transfer over the interface are to be protected as specified by O-RAN WG11. The impact of the security requirements on the equipment and the underlying transport needs to be assessed,” the report notes.
Dr Sridhar Rajagopal, Senior Vice President of Access Technologies at Mavenir and rapporteur for the technical report, commented: “This report from the O-RAN Alliance, with its welcome set of recommendations on multi-vendor carrier aggregation, could not come at a more pivotal time for Open RAN as spectrum discussions continue for expanding 5G deployments and with 6G on the horizon.
“Standardising the interface between DUs for multi-vendor carrier aggregation will remove single vendor stickiness and will be a game changer for Open RAN.”
The proposed standardisation effort represents another step toward reducing vendor lock-in and fostering a more open, competitive telecommunications ecosystem.
A full copy of the report is available from the O-RAN Alliance (PDF).
See also: NEC and Cisco launch enterprise private 5G solution
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