C-RAN sometimes referred to as Centralized-RAN or Cloud-RAN or Collaborative-RAN is a proposed architecture for future cellular networks mainly driven by the following main operators requirements:
- Cost savings
- Lower power consumption
- Reduced vendors dependency
- Network update agility
- Better interference management
- More effective traffic management
The traffic of each Base Station (BTS) fluctuates (called ‘tide effect‘); the average utilization rate of an individual BTS is pretty low and the processing resources cannot be shared with any other BTS. All BTS are designed to handle maximum traffic as opposed to average traffic, resulting in a waste of processing resources and power at idle times.
Moreover, traditional 1G and 2G cellular network consists of many stand-alone base stations (BTS) with its own cooling, back-haul transportation, backup battery, monitoring system, and so on that offer no cost savings.
For 3G, a distributed base station architecture was introduced with the radio function unit, also known as the remote radio head (RRH), installed on the top of tower close to the antenna and separated from the digital baseband unit (BBU) by fiber link. The digital baseband signals are carried over fiber, using the OBSAI or CPRI standard allowing more flexibility in network planning and deployment as they can be placed a few hundred meters or a few kilometers away.
The centralized-RAN has been proposed as an evolution of the distributed architecture exploiting optical technology improvements for the transmission of baseband signal over long distances.
C-RAN allows large scale centralized base station deployment exploiting:
- Latest CPRI standard, low cost CWDM/DWDM technology and mmWave to allow transmission of baseband signals over long distances.
- Latest Data Center Network technology to allow a low cost, high reliability, low latency and high bandwidth interconnect network in the BBU pool
- Latest open platforms and eventually real-time virtualization technology to achieve dynamic shared resource allocation and support of multi-vendor and multi-technology environments.
C-RAN BBU pool is built with very high bandwidth and low latency interconnection among BBUs. Centralization of the RAN insures that the resources in the pool can be allocated dynamically to different base station software stacks according to network load. This is one major difference from BBU Hotelling where BBUs are simply stacked together and have no direct link among them to allow physical layer co-ordination.
The centralization approach is not only a means for performance improvement with feature like Coordinated Multi-Point (CoMP) but also a major driver for operational cost reduction. About two thirds of a network’s cost of ownership is in operational costs including site rental, energy, and support and maintenance expenses.
Centralization of the RAN will eventually result into its virtualization, aiming at reducing capital expenditure by applying network function virtualization (NFV) to the radio access network. Using commercial servers for base station hardware allows operators to leverage the economies of scale of the IT industry, additionally reducing by as much as 75% the baseband processing based on real-time needs and not on per site peak capacity.
Real-time virtualization capability is changing the way base station are built, based on proprietary hardware, where the software and hardware are closed-sources and provided by one single vendor.
Azcom Technology is strongly supporting the C-RAN evolutionary path with its HW and SW solutions. The latest Azcom C-BBU product and RRH CPRI based represent the basis for initial headway in BBU centralization and virtualization. The front haul and virtualization challenges are coupled in a manner such that a solution to both can be arrived at by judiciously choosing the functional split between centralized and distributed functions. Azcom Technology is actively building proof of concept solutions in this area that will eventually be the network architecture for 4.5G and 5G networks.