By: Ganesh Shenbagaraman
In my first blog in this new Who Disaggregated My RAN? series, “How it All Falls in Place,” I provided the background that led to the industry’s push for the adoption of an open and disaggregated RAN.
Based on my engagements with the entire ecosystem of Open RAN technology providers in these forums and through our customer base on behalf of Radisys, I can share that there is an exciting whole new landscape of Open RAN technology. Let’s take a look!
COTS hardware for RAN - really?
The traditional RAN was a monolithic base station with all of the functionality integrated. It had multiple components – a baseband processing unit, cabling and connectors, the Radio processing unit and the antenna – provided as a single RAN package by the original equipment manufacturers (OEMs). As it was a monolithically designed architecture, mobile operators were left with little to no say on how the RAN was built and could not choose best-of-breed components.
A disaggregated RAN architecture, however, allows the base station to be split into three distinct parts – a centralized unit (CU), a distributed unit (DU), and a radio unit (RU). This opens up a new realm of possibilities, allowing operators to choose different hardware based on the needs of the particular node. The CU and the DU can be provided by different hardware vendors, and operators can choose the amount of processing power and additional functionalities that they require.
Initially hardware was specialized, perhaps using X86 based or ARM based processors, and customized for the traditional RAN vendors. Today the RAN can run on general-purpose hardware “white boxes” like in a data center with the software functionality completely decoupled from the underlying hardware. While this separation is taken for granted in enterprise data centers, it is just now gaining traction in the mobile network.
The O-RAN Alliance has a working group focused on developing reference designs for white box hardware for various RAN deployment scenarios. The Telecom Infra Project (TIP) continues to be a vibrant community of Open RAN hardware and software providers. The Open Compute Project is working to standardize white-box hardware for use in data centers and telecom networks. These open hardware designs are available to any vendor. As a result, multiple vendors are now offering RAN solutions that run on general-purpose hardware.
Figure 1 shows how a combination of COTS hardware and open interfaces from the standards forums enable truly Open RAN solutions for deployments with a variety of hardware and software options to choose from.
Figure 1: A truly white box view of an O-RAN based radio network
Figure 2: 5G Small Cell Solution – Hardware and software components
In the case of small cells, typically reference SoC platforms with PHY and radio functions are available with option 6 split advocated by the Small Cell Forum. The Small Cell Forum ensures open interfaces through FAPI and nFAPI interfaces which are available as standards that any vendor can implement as shown in Figure 2. This has led to a thriving ecosystem of small cell technology providers.
Meeting the Acceleration Challenge
All this being said, the RAN still needs some specialized hardware and processing in the RAN base station functionality, especially certain functions in the PHY layer, fronthaul, and security and compression algorithms.
PHY layer acceleration: Some of the PHY layer functional blocks including channel coding are compute intensive. These can be hardware accelerated using COTS components like FPGA, ASIC or GPUs. Such options are incorporated in base station and radio implementations.
Fronthaul acceleration: In case of O-RAN fronthaul (split 7.2x) the benefits of compressions can be availed with hardware accelerating this compute intensive algorithm. Hardware acceleration can be achieved by FPGAs, ASICs or SmartNICs.
Security and compression algorithms: Signaling messages are encrypted in the call flows and the processing can be offloaded to specialized hardware. And in the case of user data, IP header compression is another candidate for acceleration. Most often these are achieved by add-on pluggable cards on COTS servers.
As the market for a decomposed base station using general purpose processors has grown, the vendors of ASICs, FPGAs and GPUs have recognized the growing opportunity to provide customizable acceleration functions. Because the accelerator market is already well developed, any company designing an open RAN solution can implement one of these hardware accelerators. Radisys’ Open RAN 5G Software Suite supports hardware offload to the FPGA and can be uploaded to a hardware component where needed.
Finally, open RAN vendors are able to leverage designs from the processors embedded in the servers. These chassis are readily available from multiple RAN vendors and allow operators to choose the performance, power requirements, and cooling requirements that they need. These white-box solutions enable operators to configure a wide number of base stations that meet their needs while reducing TCO.
Cloudification of RAN functions
With all this decoupling of software and hardware in the RAN nodes, it is now easier for most of the RAN functions to be cloudified. As shown in Figure 1, these nodes on a cloud infrastructure are in the form of VMs or containers. There are some design challenges in cloudifying a DU in 5G against all the timing constraints with the various numerologies of 5G.
Currently operators must deal with rather high operational costs due to proprietary network management systems and personnel required for RAN operations. In the traditional model, vendors provided operators with proprietary Element Management Systems (EMS) and Network Management Systems (NMS) management software of their own.
The O-RAN Alliance, in its efforts to standardize all infrastructure and management aspects, has multiple working groups addressing operations and management, cloudification and hardware abstraction aspects. With standardization on the management aspects too and with RAN becoming cloud native, orchestration vendors are able to introduce a standard software lifecycle management, scaling up and down network functions, all of which was previously impossible. Service Management Orchestrators (SMOs) bring in a whole new level of sophistication in the operation of RAN along with efficiency improvement and OpEx benefits.
Future Ecosystem Growth and New Vendor Categories
A new area of growth for the Open RAN ecosystem comes from outside the base station that provides operators with an increased layer of intelligence. The RAN Intelligent Controller (RIC) is a part of the O RAN Alliance specification focusing on delivering radio resource management, higher layer procedure optimization, and policy optimization in the RAN. The O-RAN Alliance recently published standards for RIC and this will usher in a whole new variety of vendors specializing in AI/ML, Big data and highly specialized apps and algorithms to solve RAN specific problems and optimizations. I will cover this topic in detail in this blog very soon.
Vendors of test solutions in the RAN space are also racing against time to deliver new products and capabilities to test the new interfaces and nodes of Open RAN. This ensures conformance against emerging standards and interoperability among vendors. The O-RAN Alliance is also ensuring this by publishing conformance and interoperability test specifications and conducting Plugfest (Interop) events regularly.
The Road Ahead
I have tried to present an across the spectrum view of the new Open RAN ecosystem so far. While promising freedom of choice to operators, the new vendors are providing cost optimized and innovative solutions.
This ecosystem being built up around the open disaggregated RAN will continue to evolve. The newer players are already disrupting and creating irreversible change like the rest of the computing industry has gone through, bringing with it a new ecosystem and new opportunities. This momentum is undeniably felt in one category that I deliberately did not cover.
In my next blog in this series, I will take a deep look at this important category - the last mile in Open RAN - the fronthaul and the radio.