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Cloud Radio Access Network (Cloud-RAN)

(Salem, Massachusetts - Harvard Taiwan ROC Student Club)


5G, C-RAN, and the Required Technology Breakthrough


A mobile network divides a region into cells (as shown above), with each cell covered by a radio base station. These base stations are typically mounted on towers (or tall buildings), with the sites owned by tower companies and the equipment owned by telecoms in most developed countries. Mobile devices (smartphones, tablets etc.) within each cell communicate with the nearest base stations via radio for voice and data communication, where the signal is then transmitted to the core network either via cables or high-frequency radio links to a terminal (edge router) 

A radio base station can be functionally separated into:

  • BBU (baseband unit, or a digital unit), which generates and processes a digitized baseband RF signal
  • RRH (remote radio head, aka RRU, remote radio unit), which creates the analog transmit RF signal from the baseband signal and sources it to the antenna respectively, digitizes the RF receive signal

In brief, BBU possesses the “digital” function, RRH possesses the analog.

5G will require a tremendous increase in the number of base stations since 5G would be using much-higher-frequency spectrum. In the traditional RAN (radio access network) architecture, each cell site requires its own dedicated BBU and RHH, along with the associated power, cooling and routing functionality. The tremendous increase in base stations will cause major capital expenditure and operating expense concerns, which would significantly limit the number (and locations too) of base stations could be deployed. Without a rapid and massive deployment, the sparse high-frequency 5G base stations will be incapable to accommodate.

In brief, BBU possesses the “digital” function, RRH possesses the analog.


A Simplified Mobile Network

(Simplified Overview of a Mobile Network - Medium Technology)



Nowadays, with the increasing number of mobile Internet technology, operators like AT&T are faced with huge pressure on the increasing number of operating expenses with much less growth in their income. Such growth would require more and more base stations to support user needs which would be really expensive to deploy and manage. Cloud Radio Access Network (C-RAN) is an innovative new architecture that tries to meet such needs by centralizing the base stations and providing a cooperative solution between multiple operators. Such technology comes with minimal cost, high energy efficiency, and centralized network architecture that attracted a lot of attention in both academia and industry. 


- Radio Access Network (RAN)

A radio access network (RAN) is part of a mobile telecommunication system. It implements a radio access technology. Conceptually, it resides between a device such as a mobile phone, a computer, or any remotely controlled machine and provides connection with its core network (CN). Depending on the standard, mobile phones and other wireless connected devices are varyingly known as user equipment (UE), terminal equipment, mobile station (MS), etc. RAN functionality is typically provided by a silicon chip residing in both the core network as well as the user equipment.

The radio access network (RAN) has been in use since the beginning of cellular technology and has evolved through the generations of mobile communications (1G through 5G). Components of the RAN include a base station and antennas that cover a given region depending on their capacity.

Two types of RANs are Generic Radio Access Network (GRAN), which uses base transmission stations and controllers to manage radio links for circuit-switched and packet-switched core networks; and GSM Edge Radio Access Network (GERAN), which supports real-time packet data. Two other types of RANs are UMTS Terrestrial Radio Access Network (UTRAN), which supports both circuit-switched and packet-switched services; and Evolved Universal Terrestrial Radio Access Network (E-UTRAN), which focuses only on packet-switched services. E-UTRAN also provides high data rates and low latency.


- Edge Router

An edge router is a specialized router located at a network boundary that enables a campus network to connect to external networks. They are primarily used at two demarcation points: the wide area network (WAN) and the internet.

[More to come ...]






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