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8 June 2021

Vodafone and Cohere claim to double cell capacity using MU-MIMO and RIC

Amidst all the excitement surrounding Open RAN, one element is attracting more vendor attention than anything else – the RAN Intelligent Controller (RIC). This is the most novel element of the O-RAN Alliance’s particular set of specifications for an open, multivendor RAN, and it aims to become, in effect, the operating system for the 5G mobile network.

However, there is a great deal of testing, development and confidence-building that needs to go on before it achieves that goal. The RIC is an ambitious initiative, which abstracts a wide range of network control functions and runs them as xApps on a common platform. It has non-real time functions, which relate to management and orchestration, and the more challenging near-real time apps, which take functions that were previously embedded in the radio, or at most, implemented in SON (self-optimizing network) systems.

The aim is to disaggregate RAN control from RAN equipment and enable multiple vendors, including those with no RAN portfolio, to provide xApps. While that would allow operators to tap into a broad base of innovation, the real prize for vendors would be to shape the platform itself, providing services and integration to enable real world RIC deployments. Many suppliers see the RIC platform as their opportunity to enter the previously closed world of the RAN, from Cisco and Juniper to Amdocs and Oracle; while Nokia, in particular, has contributed a great deal of code to the O-RAN RIC in a bid to keep its hand firmly on the RAN steering wheel.

None of this will matter in a few years’ time if operators are not convinced that the RIC can deliver the same functionality, performance and reliability as a conventional RAN with embedded control, while also adding a new layer of intelligence and openness. Vodafone has taken a step towards providing some early proof points, in a major 5G Open RAN/RIC test conducted with Telecom Infra Project (TIP) and four vendors (Cohere Technologies, VMware, Capgemini and Intel).

It said this was the first demonstration of 5G Multiuser MIMO (MU-MIMO) running on a RIC platform in an Open RAN test site. MU-MIMO apportions bandwidth to individual users connected to the same mobile site and is one of the core techniques for increasing cell capacity in next generation 5G networks.

But making Open RAN and RIC work optimally with various sizes of MIMO antenna arrays is a key challenge for the ecosystem. MIMO, especially massive arrays or those with multiuser capabilities, require very intensive Layer 1 baseband processing, which some companies believe cannot be carried out efficiently on cloud infrastructure, rather than embedded functions running on ASICs.

Vodafone, one of the most active of the large operators in driving Open RAN, challenged such claims with the results of this test, saying the MU-MIMO/RIC combination delivered twice the cell site capacity of a traditional MIMO solution.

The lab test involved running different network functions from different vendors on Intel cloud compute platform and FlexRAN reference design. The RIC, supplied by VMware, was used to control and orchestrate baseband and MIMO functions and particularly to manage the MU-MIMO tasks in order to maximize capacity available to users in the 700 MHz band. Capgemini Engineering provided baseband software to support the MU-MIMO.

The main technique to boost the capacity of the MU-MIMO, however, was not directly related to O-RAN – it came from Cohere’s MU-MIMO Spectrum Multiplier scheduling application, which was launched in February this year.

“MU-MIMO apportions ample bandwidth to individual users connected to the same mobile site and is considered the pivotal technique to boost cell capacity in future 5G networks,” said Vodafone in its statement. If used in midband spectrum such as 3.5 GHz, with Massive MIMO antenna arrays, Vodafone believes capacity would be boosted by 4-5 times.

Cohere’s software is also central to a trial that another Open RAN leader, Deutsche Telekom, has been running, which also involves Intel and VMware, plus Mavenir. The German telco is exploring one way to address the higher costs of general purpose processors (GPP), compared to dedicated ASIC chips, in a high performance RAN. While the ability to run RAN functions as software on COTS hardware is central to the vision of a fully open, virtualized network, it does run up against the high cost of the chips – processors and accelerators – needed to support the very demanding tasks involved in running a RAN, especially those related to low latency and constant updating.

While acknowledging the issue, Alex Choi, SVP of strategy and technology innovation at DT, believes one solution is to offset the high cost of the processors by using the hardware far more efficiently. This is the focus of the project, and the resulting system, based on Intel’s FlexRAN stack, completely separates the radio resource management (RRM) from the underlying hardware and runs it as a discrete application on top of the VMware virtualization platform.

The efficiencies were increased by implementing an advanced RRM algorithm from Cohere. The result, said Choi, was that “in total the overall cost can be lower than in the case of using a traditional platform” because of the improvement in radio performance. Choi said throughput doubled on the test network, leading to a reduction in total costs.

Its next step is to open up the platform and invite others to develop RRM software so that this approach can become more mainstream and competitive.

Both the Cohere tests are likely to add to the store of knowledge that the ‘Gang of Five’ European operators – Vodafone and DT plus Orange, TIM and Telefónica – are amassing to support their initiative to stimulate Open RAN trials, adoption and ecosystem in Europe.

“This initiative validates the role that this powerful new platform plays in defining Open RAN as the future of networking,” noted Francisco ‘Paco’ Martín, head of Open RAN at Vodafone. “It boosts capacity for customers when they need it most, reduces the need for expensive hardware by a third and cuts down on energy consumption. These time and cost savings will ultimately encourage the introduction of new, innovative services.”

Cohere’s CEO, Ray Dolan, commented that the trial “shows how the functionalities held remotely can provide mobile network providers with the flexibility to keep network intelligence localized at the tower, or hosted at the edge data center, while improving spectrum assets.”

The test builds on TIP’s RAN Intelligence and Automation (RIA) project, which aims to “aggregate mobile network operator use cases for RIC platforms and to develop, test and deploy specific solutions for these use cases,” as chief engineer Dave Hutton put it. “Taking a use case from the requirements phase to a working, value enhancing solution that is fulfilled by multiple parties working together is the guiding principle upon which TIP RIA was founded.”