What is RAN(Radio Access Network)? What is CRAN(Centralized-RAN) and DRAN(Distributed-RAN)?

CRAN_DRAN eyecatch 5G Tech
[Reference] unsplash, Richard Burlton https://unsplash.com/photos/_LBR2osPHKA

This section describes terms related to RAN (Radio Access Network), which is a mobile wireless access network. This blog post will explain the difference between CRAN (Centralized-RAN) and DRAN (Distributed-RAN). It also describes the BBU Pooling technology used in CRAN deployments.

What is RAN (Radio Access Network)?

5G and 4G mobile networks are broadly divided into radio access networks (RAN) domain and core networks (CN) domain. The figure below shows the 5G RAN and 5G core network (5GC).

Fig, 5G RAN (Radio Access Network) and Core Network
  • [Glossary]
  • RU: Remote Unit
  • DU: Distribution Unit
  • CU: Cauterized Unit
  • DN: Data Network
  • UE: User Equipment

RAN is Radio Access Network in 5G or 4G mobile network. RAN is a network for connecting terminals such as mobile phones (smartphones) to the core network through wireless connection. RAN is a network for controlling wireless connectivity between mobile phones (smartphones) and base station antennas.

Difference between CRAN and DRAN

Radio access networks have different deployment methods for DRAN and CRAN. The difference between DRAN and CRAN is depending on where the BBU (Base Band Unit) that performs baseband processing is placed.

What is DRAN (Distributed-RAN)?

In DRAN, the BBU that performs baseband processing is placed near the Radio Unit (RU). In 3G (3rd Generation Mobile Communication) and 4G (4th Generation Mobile Communication), there was only a deployment method for this DRAN. In 5G case, This DRAN deployment method is used in areas with a small population.

Fig, D-RAN deployment

What is CRAN (Centralized-RAN)?

In CRAN, BBUs that perform baseband processing are centrally located in the central site (regional edge site). CRAN is a relatively new technology and is a RAN deployment method used in populated areas.

In 5G, the difference between DRAN and CRAN is selected as the difference in the RAN deployment method, depending on the location where the 5G wireless area is deployed and the plan of the mobile network carrier.

Fig, C-RAN Deployment

Detail about CRAN(Centralized-RAN)

Benefits of CRAN

By installing the baseband processing unit (BBU) in the central station, CRAN can assign the baseband processing resources to the required RU according to the traffic situation. This method allows operator to flexibly use expensive wireless processing resources depending on the traffic situation.

In the DRAN deployment method, baseband processing resources that take into account the maximum traffic expected for each RU are fixedly installed for each RU. However, in CRAN, baseband processing resources are dynamically assigned to the RU as needed. Therefore, with CRAN, the waste of baseband processing resources is greatly reduced for RAN as a whole.

Fig, Advantage of C-RAN

What is BBU Pooling?

BBU Pooling is a technology that consolidates baseband processing resources into a central site and provides the necessary baseband processing resources only to the required RUs. BBU Pooling has been standardized by standards bodies such as the O-RAN alliance.

BBU Pooling is based on processing resources pooling technology in the cloud technology field. BBU Pooling applies this pooling technology to the baseband processing of wireless mobile networks.

Please refer to the following article for the standardization activities of O-RAN alliance.

Fig, BBU Pooling

A processing device that performs wireless connectivity control is called a baseband unit (BBU). The baseband unit (BBU) provides signal processing and protocol control. This wireless control processing is called baseband processing.

In 5G and 4G radio access networks (RANs), this baseband process is very heavy and requires a large amount of expensive equipment. BBU Pooing allows baseband processing resources to be used efficiently throughout the RAN.

In addition, this BBU Pooling can deal with unexpected problems and server malfunctions that performs RAN baseband processing. Since multiple general-purpose servers for baseband processing are prepared as BBU Pool, it will be possible to take measures such as automatically switching servers when a server problem occurs.

5G Base Band Processing and 5G Protocol Stack

In RAN, protocol processing is performed to control the wireless connection with terminals such as mobile phones (smartphones). Part of that protocol processing is baseband processing.

Baseband processing refers to the processing of Layer 1, Layer 2 (MAC and RLC), and Layer 3 above the Physical layer of signal processing performed by RAN. Baseband processing includes Layer 1 Physical processing, MAC, and RLC real-time sharing processing.

Fig, Functional Split Options for 5G, (by Teppei Nagumo)
  • [Glossary]
  • RRC: Radio Resource Control (Layer 3)
  • PDCP: Packet Data Convergence Control (Layer 3)
  • RLC: Radio Link Control (Layer 2)
  • MAC: Media Access Layer (Layer 2)
  • PHY: Physical Layer (Layer 1)

CRAN deployment as HetNet

The CRAN deployment method is often deployed as HetNet (Heterogeneous Network). HetNet refers to a network that links and deploys various types of base stations with different transmission power, such as small cell base stations, in addition to macro cells that cover a wide range.

In HetNet, cooperation between different frequencies is performed as CA (Carrier Aggregation). In addition, eICIC (enhanced Inter-Cell Interference Coordination), a technology that reduces radio wave interference at the same frequency, is also used.

Fig, C-RAN deployment and HetNet


This blog post described RAN (Radio Access Network), a mobile wireless network. In particular, we explained the difference between CRAN (Centralized-RAN) and DRAN (Distributed-RAN). We also explained the advantages of CRAN and the BBU Pooling technology used in CRAN.

Please refer to the following blog post for RAN virtualization and VRAN (Virtual-RAN) and ORAN (Open-RAN).