Why is it necessary to change the RAN architecture?

First, we need to know why we need to evolve from the traditional RAN architecture to a more flexible RAN architecture?

The answer is: the rapid growth of data

Each new generation of mobile technology provides higher data rates for mobile devices. And users' data usage habits continue to shift from fixed devices to smartphones, tablets and other mobile devices. Therefore, operators must find ways to increase bandwidth for cellular base stations and mobile users while reducing transmission costs.

The most common RAN architecture at present is a distributed RAN architecture, that is, both RRH and BBU RAN functions are located at the cell site and are backhauled to the central switching center. This architecture is effective on 3G, but cannot provide the required greater bandwidth capabilities for 4G or its higher versions at a lower cost.

In the 5G era, device data rates will reach 1 Gbit/s, so many mobile operators have concluded that a distributed RAN architecture will become unfeasible.

From D-RAN to C-RAN

The "C" here stands for "Centralized", "Collaborative", "Cloud
(Cloud)" and "Clean (Green)" - it is a green wireless access network architecture based on centralized processing, collaborative radio and cloud computing architecture (Clean
The centralized C-RAN architecture places only the RRH on the cellular base station and moves the BBU function to a centralized BBU pool.

Centralized BBU can bring many benefits to telecom operators.

(1) High efficiency and utilization

In traditional RAN architectures, each base station requires its own dedicated BBU, along with associated power, cooling, and routing. Centralizing the BBUs in one location allows a pool of BBUs to share the same data center/central office physical space, batteries, generators, and cooling sources.

Additionally, a pool of BBUs can be served by one large router, rather than the separate smaller routers required for each cell site. In short, physical pooling ensures that all data center infrastructure and routing resources are used most efficiently, leaving minimal idle and wasted capacity.

(2) Simplify base station maintenance and reduce operating costs

Centralized BBU can further save equipment and site operating costs. With centralized RAN, the workload of sending technicians to each base station to troubleshoot and perform routine maintenance of BBU is reduced.

(3) Better inter-cell coordination to improve system performance

Economies of scale and reduced maintenance are the most significant benefits of physical centralization. Even without any virtualization, centralization can lead to performance improvements.

Differences between D-RAN and C-RAN

The C-RAN architecture mainly consists of three parts: baseband unit pool (BBU), remote radio head (RRH) and the fronthaul network connecting RRH and BBU.

In distributed RAN, RRH and BBU are usually separated in the base station, with RRH at the top of the tower and BBU in the equipment room at the bottom. They are connected via a standardized CPRI (Common Public Radio Interface Protocol) interface.

As we can see from the figure above, in D-RAN, the capacity of each site is not fully utilized most of the time. But in C-RAN, we can see that the utilization rate is significantly increased, and fewer resources are needed to expand the RAN capacity, which means smaller capital expenditure.