CRAN Cloud RAN, cloud-based RAN Centralized RAN of Network of mobile communication based on clouds

Terminology

The existing terms Cloud RAN and Centralized RAN (both have an abbreviation of CRAN) often use one instead of another.

RAN (Radio Access Network) is the radio access network for mobile communication consisting of a set of base stations (masts, transceiving antennas with a radio part of RRH (Remote Radio Head), BBU mainframes (Base Ban Unit).

Cloud RAN, or cloud-based RAN - a radio access network on the basis of a cloud is the virtualized radio access network which coordinates work of many base stations in which BBU mainframes are virtualized in a cloud. At the same time, BBU mainframes are located in the nearest data centers of an edge network (Edge), in the form of the virtualized network VNF functions (Virtual Network Function). Though in such determination some centralization of management of base stations is meant, it differs from the concept Centralized RAN.

Centralized RAN is the centralized radio access network in which placement of BBU also in data centers, but using traditional co-location technology, but not virtualization of the network NFV functions (Network Function Virtualization) is provided. Such approach is used, for example, at a radio covering of stadiums, business centers of class "A" and other places with high traffic.

In terms of economy, a radio access network of RAN – the most expensive part of a mobile network of communication. According to the experts, costs for RAN make up to 80% capital and up to 60% of operating expenses of mobile operator. Both Cloud RAN, and Centralized RAN are good means of reducing costs of a radio network.

In this article Cloud RAN is considered. It is more profitable to the operator at deployment of a radio access network. Initial costs for Cloud RAN, perhaps, will be slightly higher, than for Centralized RAN because of need of transition to NFV. However, many operators already keep projects of digital transformation of the reference networks based on NFV therefore virtualization of a radio network of Cloud RAN it will be good "keep within" a bed of the general project of digital transformation based on technologies of virtualization.

Other name Cloud RAN of a radio access network of the telecom operator – MEC (Mobile Edge Computing).

Principle

Cloud RAN is architecture of a mobile network which well is suitable for solution of the problem of growth of expenses on an access network that still is one of the main problems in business of the telecom operator. Functions of call processing in BBU mainframes in Cloud RAN can flexibly be redistributed between the virtual devices BBU. The pool of resources (BBU Pool) which is located in data centers of a boundary cloud is for this purpose created. Flexible redistributions of resources between base stations of an access network allows to adapt to time and seasonal changes of traffic better.

For example, in the afternoon most of subscribers are at work in business centers, the different organizations and at the enterprises is closer to the downtown. In working hours traffic in this area increases, and more BBU resources are required there. In residential zones in working hours traffic is low. On the contrary, in evening, night and morning time, concentration of traffic of users in residential zones is more, than in the downtown.

At traditional creation of an access network, each zone will require quantity of the BBU resources at the rate on the maximum traffic in certain hours and days of the week. In other time the BBU resources are underloaded. It leads to growth of cost of ownership of a radio access network as the number of BBU is calculated from the maximum values.

In Cloud RAN network, costs for an access network manage to be reduced at the expense of two pacing factors:

• Virtualization of the network BBU functions when they are hardwired not, in the selected devices, and programmatically, in the form of VNF on virtual machines. It allows to increase loading of processors of the normal computing equipment of COTS (Commercial Off The Shelf) at which they work^[1].
• Migration of virtual machines on which VNF, between the distributed data centers of an edge network work that allows to organize more optimal loading of the BBU resources in time.

Figure 1. Stages of transition to Cloud RAN.

As the cost of resources for virtual BBU is lower in comparison with traditional architecture, and less BBU in quantitative expression are necessary, the solution Cloud RAN can lower construction costs and service of a radio access network considerably.

Advantages

Main advantages of the solution Cloud RAN:

1. Более rational use of the BBU resources due to their work on virtual machines;
2. Снижение operating expenses due to automation of service of virtual infrastructure of BBU, rapid implementation of new services in the program way;
3. Гибкость redistributions of the BBU resources due to migration of virtual machines on the distributed structure of data centers. Thus, becomes possible to move virtual BBU to places with the maximum loading of traffic;
4. Сеть a radio access it is possible to expand quickly, installing only inexpensive antennas with RRH radio units. At this BBU it is possible to create quickly in the form of VNF in data centers on network edge;
5. Виртуальная network infrastructure of NFV in the form of the distributed data centers can be shared by several operators, and their BBU resources will be logically separated. It reaches still big efficiency of use of BBU.

Figure 2. Flexibility of use of the distributed BBU resources in Cloud RAN.

Network cutting (Network Slicing)

The virtualized network of the operator built on SDN/NFV technologies gives the chance to use Network Slicing technology ("cutting of network"). It means that the operator does not need to build more separate network infrastructure for different services and applications. Resources of the virtualized network will be automatically selected at the request of resources from different applications (orchestration).

It will also allow to redistribute flexibly distributed computing infrastructure of the central core of reference network between different technology radio access networks of RAT (Radio Access Technology).

For example, in 5G network simultaneous operation of different RAT on different network layers (slice), unlike networks of the previous generations is possible. For example:

• LTE network for services of telephony of VoLTE for use on smartphones and other personal devices;
• Network of control of unmanned vehicles and the systems of the help to the driver (ADAS) and also a communication network between devices at traffic of D2D;
• Network of Internet of Things (LPWA, NB IoT, other IoT technologies) and others.

Figure 3. Network cutting of Network Slicing.

And for all slices uniform computing and transport infrastructure of reference network of the operator, as shown in the drawing is used.

It is very expensive and irrational create different networks RAT with separate network infrastructure of reference network of the operator. However, advantage of NFV technology is the possibility of creation of uniform computing infrastructure of a core of reference network of the operator with implementation of NFV for different technologies of a radio access of RAT. It allows to cut down considerably expenses upon transition to 5G network which basis just and is uniform computing infrastructure of a core of network and edge networks on the basis of NFV.

Cloud RAN equipment

What data centers are used in Cloud RAN? At a word "data center" in imagination arises approximately such picture (see the drawing below).

Figure 4. One of data centers of Google.

However, the concept of the configured data center of SDDC (Software-defined Distributed Data Center) distributed program is more and more used now. SDDC represents logical data center which is distributed geographically, and its components can represent small-size container and modular data centers.

Figure 5. Small-size container and modular data centers as a part of SDDC.

Through such data centers which gather previously on the plant and can be unrolled quickly on location, it is possible to create quickly infrastructure for Cloud RAN. It is a part of the virtualized infrastructure of the operator based on the normal computing equipment of COTS on which network functions of the operator programmatically are implemented.

The concept of CORD (Central Office Rearchitectured as Data-Center), "architecture of automatic telephone exchange in the form of data center", was developed by the American operator AT&T. Now it is the recognized leader of digital transformation and already virtualized about 70% of the network using the data centers similar to shown in fig. 5.

Economy

The Red Hat company carried out the economic analysis of deployment of RAN for the standard mobile operator. For calculation the number of subscribers in 10 million SIM cards which service 12 thousand base stations 4G (LTE) was accepted. For calculation of operating costs the work period was accepted five years. The analysis showed that deployment by the virtualized Cloud RAN (vRAN) gives double economy regarding capital costs (CAPEX).

Such gap happens because of a difference in the cost of the specialized selected equipment of BBU of traditional network RAN and cost of the standard COTS servers which are used for virtualization of network^[2] of the BBU functions in Cloud RAN. Besides, also concentration gives economy: BBU needs to be placed not on 12 thousand base stations, and in much smaller number of the distributed data centers.

Operating costs in vRAN are also much lower, than in traditional RAN. It occurs because for the last on platforms of base stations it is necessary to place more equipment. Besides, each BBU on 12 thousand base stations requires exit service by qualified specialists. On the contrary, virtual BBU can be serviced from the central management console in the administrative center of the operator.

Figure 7. Comparison of TSO for traditional RAN and Cloud RAN (a source: Rad Hat).

You See Also

• 5G (Fifth generation of mobile communication)
• Software-defined networks (Software-Defined Network, SDN) and software-defined DPCs (Software-Defined Data Center, SDDC)
• NFV Network Functions Virtualization Virtualization of network functions

Notes