Open RAN architecture gives operators options, challenges

Open RAN architecture could give telecom operators more flexibility as they deliver enterprise-grade 5G services. But making the RAN a virtual function takes careful planning.

Telecoms use network functions virtualization to make their core networks more flexible, innovative and cost-effective. The radio access network, or RAN, which enables high-speed 5G access, is the next piece of the network to be disrupted by NFV.

RAN provides the wireless connectivity between an end device and the core of a wireless network. Implemented in network equipment form factors, the RAN typically consists of a base station -- including radios -- at the remote cell site and base station controllers. Virtual RANs alter the traditional RAN architecture by splitting and centralizing control of wireless functions to optimize performance and cost.

Virtual, or cloud RAN architecture, has three main components:

  1. a centralized baseband unit (BBU) containing compute resources;
  2. remote radio units (RRUs); and
  3. a transport network that connects the multiple RRUs to the BBU, typically via fiber.

Open RAN deployment status

Full adoption of 5G will take years. This gives wireless operators the opportunity to explore the benefits of disaggregated, or Open RAN, deployments.

Open RAN breaks wireless access into components -- for example, radio, fronthaul and backhaul, compute and radio control -- which can be sourced from a variety of suppliers.

Open RAN deployment is in its early stages, with the exception of a few greenfield operators, such as Rakuten. It confronts the same challenges early NFV deployments faced, including a lack of mature standards, poor interoperability between vendors and limited integration resources.

Open RAN may, in fact, provide wireless operations with too many deployment architecture choices. Multiple options exist for server hardware (with or without acceleration cards), radios, radio control, xHaul, etc. Operators deploying systems from multiple vendors will need sophisticated integration to ensure their networks not only operate at gigabit speeds, but meet 99.999% uptime requirements.

Open RAN, like NFV, provides the ability to host different virtualized applications on common hardware platforms.

Where the Open RAN model will take root

Doyle Research expects Open RAN architecture to encompass about 10% of the RAN market by 2026. The leading adopters are greenfield deployments, rural, private 5G and small cell. Open RAN architecture differs substantially by geography and use case, with compute platforms, radios, control software and integration partners varying widely.

Proponents of virtualized RAN promise a wide range of benefits to operators, among them improved performance, reduced Capex and lower latency. Open RAN, like NFV, provides the ability to host different virtualized applications on common hardware platforms. Additionally, Open RAN enables intelligent traffic steering between distributed cell sites, supports the use of locally cached data to reduce latency and offers higher reliability.

5G architectures require many more cell sites of different sizes than comparable 4G architectures to deliver the promised performance improvements. To that end, Open RAN is critical for controlling and operating new 5G base stations.

Challenges to Open RAN deployment

Virtualization of RAN functions requires low latency and high-bandwidth connections between the cell site and a centralized or distributed control point, which likely means fiber optic networks. A number of competing standards organizations are currently developing Open RAN standards, including the O-RAN Alliance and the Telecom Infra Project. RAN is a critical aspect of the mobile network, and integration of virtual elements from different suppliers remains especially challenging.

The touted Capex benefits of NFV may be offset, at least initially, by the increased operational costs of deploying virtual RANs with equipment sourced from multiple suppliers. Many operators will turn to a single vendor -- large or medium-sized -- to deliver a comprehensive Open RAN platform for reliable and efficient operations.

Status of virtual RAN deployments

Virtual RAN is still a novelty for most 5G networks, although many operators with large deployments are currently testing the concept. Still, a number of large communications service providers have said they will commit a significant percentage of their wireless budgets to Open RAN by 2025, although these targets could be flexible. In the meantime, COVID-19-related business restrictions have delayed some testing and deployment.

Open RAN platforms

As with NFV, virtual RAN will drive significant deployment of x86-based servers from HPE, Dell Technologies and other server vendors. Operators and integrators have a number of server options, including the following:

  • Intel-only, with the newest processor;
  • Intel plus a smart network interface card;
  • customized box, with x86 and field-programmable gate array; and
  • other chip vendors, such as Arm, Broadcom, Marvell, Nvidia and Qualcomm.

Open RAN software runs on containers with software supplied by Red Hat, VMware and Wind River.

Mobile operators have many Open RAN suppliers to select from, including large vendors, such as Ciena, Cisco, Ericsson, Huawei, NEC, Nokia, Samsung and ZTE. Smaller suppliers include Altiostar, Celona Inc., IP Infusion Inc., JMA Wireless, Mavenir, Parallel Wireless Inc. and Volta Networks.

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