A cloud RAN replaces purpose-built RAN hardware used in distributed unit (DU) and central unit (CU) functions with generic compute platforms based on COTS hardware. Heavy Reading survey research shows that — like centralized RAN (C-RAN) architectures — cloud RAN architectures are gaining momentum globally. Beneath the virtualization layer, the transport network plays a crucial role.

In November 2021, Heavy Reading conducted the third iteration of the Operator Strategies for 5G Transport Market Leadership Survey with project partners Ericsson, Fujitsu, Infinera and Nokia. The 2021 survey attracted 81 qualified network operator responses from around the world who shared their views on transport deployment issues and timelines, fronthaul networks and RAN centralization, routing and synchronization and 5G edge connectivity.

This blog is the final installment in the four-part series highlighting the key findings from the study. It focuses on cloud RAN adoption expectations and the pros and cons of different approaches to handling CPRI traffic.

The path to cloud RAN architectures

As noted in the previous blog, cloud RAN and C-RAN can be related, but they are not the same and can be implemented independently of one another. 57% of operators surveyed in the study report they expect to implement cloud RANs in the network by 2025 — with North American operators reporting more aggressive timelines compared to their Rest of World counterparts.

There has been minimal adoption of cloud RAN to date, but communications service providers (CSPs) have ambitious growth plans over the next five years based on survey results. Just over two-thirds of respondents (67%) expect 20% or less of 5G RAN sites to have virtualization by year-end 2022. However, more than three-quarters of those surveyed (78%) expect greater than 20% of 5G RAN sites will have virtualization by the end of 2025. At 43%, a plurality anticipates cloud RAN adoption will range from 21% to 40% of 5G RAN cell sites by the end of 2025. For those operators interested in cloud RAN, adoption timelines are ambitious. But readers should also keep in mind that 43% of the survey group reported no plans for cloud RAN.

Figure 1: What percentage of your organization's 5G RAN sites will implement a cloud RAN (i.e., with virtualization) by year-end 2022? By 2025? n=46
(Source: Heavy Reading)

The CPRI Consortium's eCPRI specification is an important technology for reducing capacity demands in the fronthaul portion of the xHaul network. Packet fronthaul transport based on eCPRI can reduce fronthaul capacity requirements by 10x — thus addressing the top challenge identified by CSPs in moving to cloud RAN.

However, even as they deploy eCPRI in new builds, CSPs will continue to have massive amounts of legacy CPRI streams. 5G and previous mobile generations (particularly 4G) will coexist in networks for many years. Handling legacy CPRI traffic as 5G emerges is essential.

Service providers have multiple means at their disposal to handle legacy CPRI, and Heavy Reading survey data shows that they intend to make use of all of them. Selected by 64% of the survey group, legacy overlay using dark fiber or WDM is the top choice for legacy CPRI transport, followed by transport via eCPRI with CPRI-to-eCPRI conversion (selected by 52%). Trailing individually are structure-agnostic Radio over Ethernet (RoE; selected by 43%) and structure-aware RoE (selected by 29%).

Figure 2: Which technologies will your organization use to transport legacy CPRI radio traffic? (Select all that apply) n=69
(Source: Heavy Reading)

Each CPRI approach has its pros and cons. Fiber-rich networks will make use of dedicated direct fiber transport, which is easy to install and traffic-independent. However, fiber transport is not bandwidth efficient (and thus can be costly) and must also be a bookended solution. RoE — in its structure-aware and structure-agnostic forms – is popular among survey respondents, but it also comes with limitations. First, it offers limited bandwidth reduction compared to native CPRI and has limited ability to aggregate and automate traffic flows. RoE bandwidth can be an issue because fronthaul capacity is a primary CSP concern in both centralized and cloud RAN architectures. Lastly, like fiber/WDM, RoE must be bookended.

CPRI-to-eCPRI conversion is also highly popular among CSPs based on survey results, and Heavy Reading expects that its advantages will make it more popular over time. Top eCPRI conversion advantages compared to RoE alternatives are high bandwidth savings (selected by 55% of respondents), longer distances in the fronthaul network (selected by 49%) and the ability to allow traffic differentiation and redirection (selected by 48%).

Figure 3: What are the biggest advantages of CPRI-to-eCPRI conversion compared to RoE? n=69
(Source: Heavy Reading, 2021)

As a final point, eCPRI conversion is necessary to support cloud RAN infrastructure when legacy CPRI radios are present. The question is whether this conversion occurs at the cell site (as with eCPRI) or deeper in the network. At 28%, a minority of respondents see cloud RAN as an important driver for eCPRI conversion today, but as cloud RAN matures, this advantage will become more significant.

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