VMware RIC enables third parties to easily insert novel or advanced functions into the RAN; one among many benefits is a dramatic increase in spectrum efficiency
A few days ago, Vodafone announced in a press release that VMware and partners have “increased the capacity of a 5G cell site by two-fold using a…RAN Intelligent Controller (RIC)” and highlighted that the RIC is “fundamental in creating an open framework designed to further improve the cost-effectiveness of Open RAN, as well as expanding supply chain diversity, and promoting innovation.” In this blog, we aim to deconstruct this announcement for our readers, and help them understand why Communication Service Providers (CSPs) like Vodafone are looking at the VMware RIC as a fundamental piece of their open RAN strategy.
Let’s start with a quick RAN primer.
What and Why of RAN Transformation
Traditionally, the radio access network (RAN) has been closed and proprietary. The RAN baseband software is tightly integrated with the hardware on which it runs as well as with the RAN radio unit. Further, the control and management planes of the RAN baseband software, which contain all the RAN intelligence, are tightly integrated with the data plane of the software. As a result, CSPs must rely on a single RAN vendor1 to provide all the pieces that make up the RAN.
CSPs are moving to an Open RAN model which transforms the monolithic single-vendor traditional RAN into a disaggregated multi-vendor RAN.
- The RAN baseband software is disaggregated from the hardware and the radio unit, which enables the RAN baseband software to become virtual, cloud native and able to run on COTS hardware.
- The control and management planes of the RAN baseband software are decoupled from the RAN data-plane software, to enable the RAN data plane software to be programmed by third parties.
O-RAN Alliance, O-RAN, is an industry consortium that is specifying the modular components in an open RAN architecture and standardizing the open interfaces between them (See Figure 1). The key O-RAN defined elements that enable the transformation to a programmable and software-defined RAN are the Near-Real-Time and the Non-Real-Time RAN Intelligent Controllers (RIC) along with the E2, O1 and A1 interfaces.
The Importance of the RIC
Logically, the RIC is a RAN data-plane abstraction layer. As shown in Figure 1, O-RAN specifies two flavors of the RIC:
- Near-Real-Time (Near-RT) RIC for the near-real-time2 control plane
- Non-Real-Time (Non-RT) RIC for the management plane
Each of the RICs consists of a “platform” and a set of applications (called “xApps” for Near-RT RIC and “rApps” for Non-RT RIC) that run on the platform.
The VMware Near-RT RIC and Non-RT RIC Platforms are implementations of the O-RAN Near-RT RIC and Non-RT RIC Platforms respectively. The VMware RICs are RAN vendor neutral and are designed to support a multi-vendor RAN ecosystem on the south and a multi-vendor xApp/rApp ecosystem on the north. In essence, the VMware RICs are the enabler for a truly open and multi-vendor RAN. For CSPs, they help significantly diversify their supply chain to promote innovation and decrease costs, increase service agility, and improves the quality of service to help improve customer experience. It is therefore natural that CSPs like Vodafone are looking at the VMware RICs as a fundamental piece of their open RAN strategy.
There is one other concept we need to understand before we get to the announcement.
The Role of Multi-User MIMO
Multi-User MIMO (MU-MIMO) is a technology to boost the capacity or spectrum efficiency of a cell by enabling it to communicate with multiple users simultaneously in the same time and frequency slot. By enabling simultaneous use, a cell can push more bits per time and frequency, and thus improve the efficiency of the most valuable resource in the RAN – the spectrum.
MU-MIMO is extremely hard to implement in practice as it requires high intelligence in the controller. Without intelligent user pairing and precoding, using MU-MIMO can lead to worse performance than not using MU-MIMO at all. Till date, these “control plane” problems have not been generally and satisfactorily solved even by the Tier-1 RAN vendors, therefore even though the “data plane” for MU-MIMO has been standardized by 3GPP for many years, this technology is rarely used in practice.
Now to the announcement.
Clarity on the Vodafone Announcement and its Importance
In its press release, Vodafone announced that it had trialed an open multi-vendor RAN solution with MU-MIMO support – a solution where the MU-MIMO control plane was implemented as an xApp on a Near-RT RIC, and it significantly improved, almost doubled, the cell capacity and its spectrum efficiency.
Figure 2 shows a logical architecture of the solution that was trialed. It includes:
- O-Cloud and O-Cloud Manager from VMware
- Near-RT RIC Platform from VMware
- MU-MIMO scheduler xApp from Cohere
- RAN Layer-1 baseband software from Intel (part of DU)
- RAN Layer-2 (part of DU) and Layer-3 (CU) baseband software from Capgemini Engineering
The RAN baseband software from Intel and Capgemini Engineering supported the MU-MIMO data plane and exposed a pre-standard service model towards the Near-RT RIC, and Cohere’s xApp used the open APIs provided by the VMware Near-RT RIC to interact with this service model and optimize MU-MIMO scheduling, including MU-MIMO user pairing and precoding. The xApp, in essence, works in tandem with the local Layer-2 scheduler in the DU to make MU-MIMO scheduling intelligent. The solution also used standard 5GC (5G core network), RU (radio unit), UEs (user equipment, i.e., mobile devices) and COTS hardware for end-to-end testing.
This trial is a significant milestone in the industry’s open RAN journey for several reasons.
- It is the first demonstration and evaluation of an end-to-end multi-vendor open RAN where the Layer 1 software, Layers 2 & 3 software, RIC, xApp and RU were all provided by different vendors and integrated using open interfaces.
- It is the first demonstration of 5G MU-MIMO control using Near-RT RIC/xApp – where the MU-MIMO control-plane algorithms for user pairing and precoding were delivered by a 3rd party as an xApp.
- The Near-RT RIC concept was validated for its ability to decouple such complex RAN control-plane features as MU-MIMO pairing and precoding.
The Result? “When the technique is commercially deployed in a low-band (e.g. 700MHz) network, users will benefit from up to 2x the capacity achieved using traditional MIMO. This software can be extended to Massive MIMO in mid-band (e.g. 3.5GHz) networks in order to push capacity gains towards 4-5x.”