Open RAN: Clearing Up the Confusion About Greenfield & Brownfield References

Open RAN is considered one of the technological trends with more potential to reshape the telecom industry and has received worldwide interest from telcos. There are several mobile network operators, both greenfield and brownfield, around the globe considering the adoption of Open RAN solutions or already deploying this technology. Key examples are Rakuten, which operates the world’s largest Open RAN in Japan, and Vodafone, which has been conducting multiple trials over the past few years in its European and African OpCos.

The terms “greenfield” and “brownfield” are being used to competitively differentiate the virtual distributed unit (vDU) software performance and capability of a vendor- and operator-deployed Open vRAN solution. “Greenfield” refers to a low-capacity network and “Brownfield” refers to a high-capacity network. Contrary to the narrative, the vDU’s available today support high-capacity features of 4G/5G, such as Carrier Aggregation, CoMP, and interference coordination, for both greenfield and brownfield deployment.

A look back at history

Since the birth of GSM back in the 90s, all generations (2G, 3G, 4G and 5G) of mobile networks’ RAN (Radio Access Network) infrastructure interfaces have remained proprietary to the providing vendor. Apart from solutions being provided with “Open RAN” interfaces, this statement remains true today. 3GPP has specified the X2/Xn interface to allow gNB to gNB connectivity, but instead, legacy vendors used this interface as a commercial obstacle, prohibiting the mixing of vendor RAN solutions.

As a result, today you cannot overbuild or mix and match proprietary vendor RAN solutions. Regrettably, all the above-mentioned features, such as Carrier Aggregation and COMP, are proprietary solutions and are vendor-specific. Because of the specific nature of these features, interworking between different vendors Open RAN and proprietary RAN solutions is currently not possible.

Advanced vDU Features

Advanced vDU features, such as carrier aggregation, CoMP and Interference coordination, are possible and available today on vDU offerings. Sadly, these are still vendor-specific solutions because 3GPP allowed propriety implementations. These features need focus by the O-RAN Alliance to schedule open specifications of these parameters.

Today, vDU solutions are being tested under load for capacity and performance. System test, performance, and stability are also being tested. As part of these tests:

  • Call model scenarios are run to stress systems with a number of users and for a long duration
  • Number of users is loaded based on the scenario and customer configuration. The typical common configuration used in lab tests are:
    • 100 Active users, 200 connected users per cell
    • 200 active users and 320 connected users per cell
    • The duration of the test varies. We aim to achieve 24hr+ stability with loaded scenarios at least.
  • At the end of each long execution, KPIs are monitored and compared for performance assessments
  • Open vRAN performance is shown to be equal to and in some cases, exceed that of existing incumbent


Open vRAN Networks will Support Advanced Features

Open vRAN is a disaggregated RAN functionality that offers flexibility and a variety of options, which is its strength. The architecture adapts to the assets and the requirements of the carrier as opposed to providing a black box solution, where the carrier must adapt. This is one of the leading value propositions; Open vRAN adapts to carrier requirements, not the other way around.

The Open RAN industry will add advanced features, and vendors will compete on differentiated vDU solutions. We can expect the O-RAN Alliance and other organizations to standardize interfaces that enable more advanced features in an open environment, and companies like Intel, Mavenir and others are doing great work to implement advanced vDU features on standard server hardware. Operators will be able to upgrade software and processor technology for more capacity and features as they add customers …. like a Tesla customer boosting the performance of their car with a software upgrade.

Vodafone, Intel and Cohere have also demonstrated advanced features that are not available from proprietary RAN providers improving spectral efficiency.

Necessary Interfaces for Open RAN Integration into Existing Networks

To allow integration into existing networks traditional vendors should be requested to add the following 3GPP specified interface support in their existing deployments to facilitate the integration of new spectrum in current brownfield deployments with new vendors:

(1) Integration on X2 / Xn interface to make it work with another vendor.

(2) To share the spectrum or aggregate the spectrum with an existing vendor, specification design is needed to support features on existing CPRI/eCPRI interfaces

(3) Network optimization currently uses proprietary SON interfaces which make integration with new spectrum support and optimization with new vendors difficult

(4) Other features that are more forward-looking, which will require integration with incumbents

  1. Network slicing (when slices are developed by different vendors), 
  2. IAB (when nodes are developed by different vendors), 
  3. mmWave and unlicensed band anchored on licensed low-band (when band-specific systems are developed by different vendors)


 (5)  Multi-vendor EMS integration

The use of “greenfield” and “brownfield” is being used for marketing purposes, adding confusion to the marketplace. vDUs will continue to support improved capacity and spectrum optimization features. Further specification work from the O-RAN Alliance and 3GPP needs to continue to specify common RF optimization and high-capacity features listed above.

  • This article has been contributed by John Baker, Senior Vice President, Business Development at Mavenir.