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Chapter 3: C-Ran

Centralized Radio Access Networks


As you’ve learned, Distributed Radio Access Networks have issues with cost, wasted capacity, and inefficient use of radio frequencies. As a result, telecoms companies are looking for good alternatives that will meet future consumer needs. One of the most promising and powerful technologies is the Centralized Radio Access Network, or C-RAN.


Differences Between C-RAN and D-RAN


The main difference between C-RAN and D-RAN installations is in how the baseband units (BBUs) are configured. In D_RAN technology, the BBUs are each located at the base station and act independently – in C-RAN, the BBUs are stored in one central location.


Moving the BBUs like this creates a “Fronthaul Architecture” and increases the distance between the BBU on one end (in the centralized location) and the antennas, remote radio heads, and fiber feeder on the other (in the base station).

Figure 1: D-RAN vs C-RAN

Although this is a simple idea, the configuration of C-RAN can vary. There are three main types of C-RAN implementations.

The simplest configuration centralizes the BBUs together in one location and dedicates each BBU to its own base station – it is a one to one relationship. This is very similar to a typical D-RAN installation, and lacks efficiency.

BBUS are congregated and protected in the Central Station. However, BBUs work independently and individual connections between BBUs and Towers are maintained.

A more advanced configuration connects the centralized BBUs together into a “BBU pool.” This pool can serve many cell towers at the same time. This is a many-to-many relationship.

BBUS are congregated and protected in the Central Station. The BBUs work together and proccess the data of multiple BTSs.

An even more sophisticated configuration is currently being researched. It involves the processing role of the BBU becoming software-based. This is known as Virtualized RAN (V-RAN) and lets telecoms businesses dynamically manage the processing power of their networks very easily.

BBUs are virtualized and software defined.

Figure 2: Types of C-RAN

The Advantages of C-RAN


C-RAN has several big advantages over D-RAN.


C-RAN is More Efficient

Centralized and interconnected BBUs are much more efficient than isolated ones. In D-RAN the BBUs are locked into serving only one base station, C-RAN allows a BBU pool to jointly process data for multiple base stations. This makes network processing power much more dynamic, allowing more data to be processed by less equipment.


For example, in a sports stadium, a full stadium would receive complete allocation from the BBU pool to meet demand (figure 1). Once the event is finished and demand drops, the processing power of these BBUs can easily be allocated to other areas (figure 2). The ability to redirect processing power allows the C-RAN to follow the users wherever they go. This creates much more efficient bandwidth usage and higher connectivity, speed, and availability.

Figure 3

C-RAN is less expensive to install, expand, maintain, and operate


C-RAN needs less equipment to manage the same amount of data as D-RAN. This significantly reduces capital and operational costs, as less equipment is needed, and energy costs are lowered.


Consolidating the BBUs in a central area shrinks the footprint of the base stations. This lowers rental and lease costs for base stations and reduces expenses to protect base stations from the weather. Maintenance and support costs are also lower due to much of the equipment being centralized.


C-RAN is Easier to Upgrade


Upgrading the capabilities, functionality, or capacity of centralized equipment makes those improvements available to the whole network.


C-RAN has Better Administration and Security


Centralization makes it easier to supervise and secure BBUs, increasing network safety and lowering the risk of malicious interference in the system. Coordination is also much easier. While in D-RAN Towers compete for frequencies, in C-RAN base stations can cooperate, increasing coverage.

Figure 4: D-RAN: Towers competing for frequency
Figure 5: Cloud-RAN: Towers sharing the same Frequency

C-RAN can significantly reduce installation and operational costs while improving efficiency, bandwidth, security, support, maintenance, and upgradability. Despite all these advantages, there are still important challenges that must be met when moving centralizing the BBUs of a network.


The next section will explore the challenges C-RAN faces including distance limitations and protocol requirements.


October 29, 2019


Mobile Fronthaul