XRAN spec to herald new disruption

RAN disruption is coming for established vendors... some of whom seem to welcome it.

The first XRAN specifications for a fully specified open interface between radio and central units  will break down the three vendor “stranglehold” on the RAN, according to one would-be rival vendor.

John Baker of Mavenir said that with all signalling between the Remote Radio and Baseband Unit now fully defined  – “unlike previous specs” – the road was now open for mavenir and others to break the stranglehold that the major NEPs have had on the radio market.

“Our goal is to disrupt the current ecosystem and allow operators make money, versus getting sucked into large license fees. You will see us attack things on an end-to-end basis,” Baker said.

However that shift will be an evolution over time, he said, as operators move to specify open interfaces in their RFPs, enabling them to mix and match RRH-BBU vendors if they want to. “Over time those networks will change to open interfaces in hardware and software and change the cost plan of the network,” Baker said.

In time the XRAN spec could circle back into 3GPP specs, Baker said. “Hopefully it will be adopted back into 3GPP. One of the challenges within 3GPP today is [vendor contributors] trying to block having open interfaces like that because the major OEMs are in control of the standards process. That’s why we are seeing open source programme start up, because 3GPP has become fairly slow and was not living up to the  requirements of the carriers in certain places any more. So it will be interesting to see if this circles back and does change 3GPP as well.”

Nokia’s commitment to XRAN and the open RAN interface.

The open-proprietary debate is not a binary new entrant/ established NEP one, however. Samsung and Nokia are both XRAN members. Speaking at the Brooklyn 5G Summit on Wednesday 25th, head of Networks at Nokia, Marc Rouanne, said that the company is committing to opening up across its portfolio.

In the radio interfaces, which has been closed for many years, why wouldn’t we open? There is no reason – so open radio is a given,” Rouanne said. 

XRAN Specification

The XRAN spec depends on a lower level architectural split known as Option 7 – with the current specification effort targeted to support physical layer channels as defined in 3GPP Release 15 for LTE and NR.

Option 7 is known as an Intra-PHY split as it splits the PHY layer between the Central Unit and a Radio Unit. The Central Unit has the base station functions, often known as the BBU, managing real time functions of the Radio Unit either over a fronthaul interface known in the X-RAN spec LLS-M, or over a management system. The specification and scope of this management plane is not included in this release, but is being considered to support configuration and performance management of the Radio Unit, using NetConf/Yang. That OAM spec should be available in June.

The xRAN Fronthaul Specification addresses several operator-defined requirements, including:
• BBU – RU interoperability based on well specified control, user and management plane interfaces.
• Efficient bandwidth scaling as a function of user throughput and spatial layers to address
increasing bandwidth needs and Massive MIMO deployments.
• Support for LTE, NR, associated features, 2T – 8T RU products and Massive MIMO beamforming
antenna systems.
• Advanced receivers and co-ordination functions.
• Ethernet based transport layer solutions.
• Extensible data models for management functions to simplify integration.

XRAN architecture

Improved fronthaul bandwidth efficiency is one of the key intended benefits of Option 7 split.

In the DownLink, iFFT (inverse Fast Fourier Transform), CP addition, and digital beamforming functions reside in the Radio Unit. The rest of the PHY functions including resource element mapping, precoding, layer mapping, modulation, scrambling, rate matching and coding reside in the Central Unit. Beamforming specific processing (expansion from layers/beams to digital transceivers) resides within the radio Unit.

In the UL, FFT, CP removal and digital beamforming functions reside in the Radio Unit. The rest of the PHY functions including resource element de-mapping, equalization, de-modulation, de-scrambling, rate de-matching and de-coding reside in the Central Unit. Beamforming specific processing (combining inputs from multiple digital transceivers to a set of 23 beams/layers) resides within the RU.

Opening up on the Open RAN
Mavenir hopes to benefit from open RAN trend