The next generation of Radio Access Network (RAN) architecture is referred to as Cloud RAN or Centralised RAN, where Baseband Units (BBUs) are centralized in a single location, typically referred to as a BBU hotel or server. This centralization of BBUs involves moving them from cell sites to a central location, where they can be virtualized and managed more efficiently through network virtualization. This architecture offers improved network performance, reduced latency, more flexible and scalable network management, and lower costs compared to traditional RAN architectures.

A RAN cell site consists of a combination of a Remote Radio Head (RRH) and a Baseband Unit (BBU). The RRH is responsible for connecting mobile devices to the network and performing functions related to Radio Frequency (RF), such as transmitting, receiving, filtering, and amplification. All traffic and calls are then forwarded to the Mobile Switching Center (MSC). The RRH acts as an intermediary, facilitating communication between mobile devices and the central network.

The rise in mobile phone usage led to the creation of the Radio Access Network (RAN) to meet the increased demand for a larger network. With a growing number of mobile phone users, network operators have deployed a larger RAN to accommodate the need. To improve the efficiency of the network, the Baseband Unit (BBU) hotel has been centralized in a single location rather than being located at individual cell sites. This has several advantages over the traditional approach, including reduced space requirements and cooling solutions at cell sites, improved network performance, faster deployment, and easier testing access. Furthermore, the centralization of the BBU hotel allows for network virtualization and the implementation of advanced technologies and dynamic resource allocation, making C-RAN a more efficient and versatile solution.

BBU Hotel

The BBU hotel is the central location where the baseband units of a distributed Radio Access Network are housed. These units can be located up to 20 km away from the Remote Radio Head (RRH) and connected via fibre using CPRI (Common Public Radio Interface) protocols. By centralizing the BBUs, they can be replaced by a server, which enables the implementation of Software-Defined Networking (SDN) and Network Function Virtualization (NFV). This centralization provides a more flexible and efficient solution for managing the network.

Benefits of Network Virtualization include.

Centralized Baseband Units (BBUs) in a Cloud RAN or Centralised Radio Access Network (C-RAN) architecture result in cost savings, as well as faster and easier maintenance and troubleshooting. Additionally, this architecture enables dynamic resource allocation based on network requirements, allowing for faster network deployment.

C-RAN  system Structure:

This system is catagorized 3 types 

Fully centralized: 

The Cloud RAN or Centralised Radio Access Network (C-RAN) architecture is categorized into three types. In a fully centralized structure, the Media Access Control (MAC) and network layers are housed within the Baseband Units (BBUs), and the functions such as messaging and processing resources are handled by the BBUs. This setup requires physical centralization of the BBUs.

Partially centralized: 

The Cloud RAN or Centralised Radio Access Network (C-RAN) architecture has a partially centralized layer, where the Media Access Control (MAC) layer is performed at the Remote Radio Unit (RRU) while the physical layer functions are carried out at the Baseband Unit (BBU). In this setup, the overhead of the RRU-BBU communication is reduced, and the physical layer takes on a larger computational burden.

Hybrid centralized:

In the Centralised Radio Access Network (C-RAN) architecture, the physical layer functions are performed at the Remote Radio Unit (RRU), while the other functions are carried out at the Baseband Unit (BBU) layer. The RRU is primarily responsible for signal processing and takes on most of the user-related tasks in this centralized system.